In Vivo Engineering of Organs: the Bone Bioreactor

Molly M. Stevens, Robert P. Marin, Dirk Schaefer, Joshua Aronson, Robert Langer, and V. Prasad Shastri

It has long been the goal of tissue engineers to successfully utilize cells to create new tissues and organs so that they may be transplanted into patients in need. Over the years, some level of success has been achieved in simpler human tissues such as blood vessels and skin. It has proved to be harder to engineer organs and tissues with greater complexity, namely tissues with blood vessels running through them, such as bone tissue. Even if the tissue is cultured, the tissue needs to be successfully transplanted into the patient. At this point issues such as immune rejection and mechanically mismatched tissues need to be considered. To avoid such issues in culturing/transplanting bone tissue, this experiment focuses on exploring the regenerative properties of the bone’s periosteum cells to create an in-vivo bone bioreactor.

Periosteum cells are cells lining our bones that divide and differentiate upon wounding and fracture. It is hypothesized that the same healing response can be used to generate new tissue. To test this hypothesis, a saline solution was injected between the tibia and periosteum of rabbits. This was done to create a cavity that serves as a bioreactor for bone cells to grow. Alginate, a calcium-rich gel (which promotes bone cell formation), is then injected into this cavity to prevent it from collapsing when the saline solution is absorbed back into the body. Under these conditions, bone cells are allowed to grow and proliferate in this cavity over a period of a few weeks. The content (percentage of gel, percentage of saline, percentage of bone matrix) of the cavity is measured every week and data is compiled.

As predicted, within a few weeks, the cavities were filled with bone. The concentration of alginate gel and saline decreased over time as bone cells proliferated and filled up the cavities. By four weeks, more than 90% of the cavity was filled with new bone. This bone tissue was then removed and transplanted into damaged bone cites (defect was created in the rabbit’s bone) in the rabbit and the wounds healed seamlessly. As the transplantation was autologus, no immune rejection was observed. This result demonstrates not only the successful culturing of bone cells, but also the successful transplantation of bone tissue into a host with damaged bone. In conclusion, by utilizing this method of in-vivo bone regeneration, one can achieve desired periosteum differentiation and successful transplantation of new bone cells to other damaged bone cites within the same animal. Further research may allow for this method to benefit human patients with bone / spinal damage.


Not only was the hypothesis proven in this experiment, the methods utilized are clear and reproducible. The next step would be to conduct this experiment on human subjects. If this is successful, clinical applications would include fusing vertebrae in spinal fusions, bone repair for fractures/breakages, and cartilage replacement for arthritis. In addition, this process is much better than the current method of harvesting bone from a patient’s hip, which is very painful. Further research must be conducted to achieve this goal for humans, but the successful culturing/transplantation in rabbits has made this endeavor optimistic.

Fabrication of Pulsatile Cardiac Tissue Grafts Using a Novel 3-dimensional Cell Sheet Manipulation Technique and Temperature-Responsive Cell Culture S

Fabrication of Pulsatile Cardiac Tissue Grafts Using a Novel 3-dimensional Cell Sheet Manipulation Technique and Temperature-Responsive Cell Culture Surfaces

Tatsuya Shimizu, Masayuki Yamato, Yuki Isoi, Takumitsu Akutsu, Takeshi Setomaru, Kazuhiko Abe, Akihiko Kikuchi, Mitsuo Umezu, Teruo Okano

This article documents research regarding the use of a special type of polymer for a successful tissue culture and subsequent transplantation. What is special about this polymer is it is temperature responsive. The surface undergoes a change from being hydrophobic, cell adhesive, at 37 deg C to hydrophilic, non cell-adhesive, below 32 deg C. It is thought to produce a more viable transplant tissue culture, one could culture a sheet of cells on this sheet, easily detach them, and then transplant the cell sheet into a patient. What is advantageous about this polymer is that one more easily culture and transplant cell sheets. The change in cell adhesiveness of the polymer allows the detachment of cell sheets while preserving the ECM of the culture versus more traditional methods which involves enzymatic digestion i.e. trypsinization. It is then thought that a 3d-tissue culture could be constructed by layering cell sheets that have been cultured with this polymer.

The polymer was effective in the way that the researchers intended it to work. Myoblasts were successfully cultured as a sheet. The resulting sheet of cardiac tissue would uniformly pulse when growing on the sheet and when detached from from the sheet. A 3D culture was created by growing multiple sheets and then layering them on top of one another through a scaffold structure of collagen membrane. What is interesting to note is that the cell sheet would shrink and thicken significantly once detached from the sheet due to cytoskeletal reorganization. In addition, depending on the thickness of the sheet, it was take some time before the sheet would be able to pulse synchronously. Transplant efficacy was tested by transplanting sheets of various thickness of cultured cardiac tissue into the heart area of rats. The transplantation effectiveness was compared to injection of myoblasts, muscle stem cells, directly into the heart area.

While the research team did demonstrate the efficacy of the use of the polymer to culture cell sheets, there are some trade offs in their approach. The researchers do not construct true vascularized 3d-cell culture. As a result their culturing methods is still limited by mass-transport. In addition, in testing the efficacy of their treatment, they did not compared transplantation of their 3d culture to other methods of 3d culture the transplantation of cells cultured in a biodegradable polymer. So while they do demonstrate the efficacy of their method, we only know this relative to the worst case scenario.

In Vivo Engineering of Organs: The Bone Bioreactor

Molly M. Stevens, Robert P. Marini, Dirk Schaefer, Joshua Aronson, Robert Langer, and V. Prasad Shastri

Proc Natl Acad Sci USA 2005 August 9; 102(32): 11450-11455.

Although bone continues to remodel throughout lifetime, people with different conditions will have different bone regeneration capacity. For example, the bone regeneration capacity of older people tends to be slower than younger people. So it is very important to have effective treatment for large bone defects. Since in vitro engineering of bone tissue is very challenging and it encounters many problems. The most common treatment nowadays for large bone defects is by harvesting new bones in the crest of the iliac. Not only is autologous bone very good at integrating with the host bone, it also does not contain any immune-related problems. But there are many downsides of this method such as limited supply of autologous bone, long-term pain from the crest of the iliac and bone morbidity. This research paper is about a study of bone formation/growth in a bone bioreactor in vivo.

The hypothesis of the experiment is that functional bone tissue can be harvest by creating a space between the surface of a long bone and periosteum (a membrane that's rich in pluripotent cells) because all necessary cells and biomolecular signals for bone formation are delivered locally to the bioreactor and they greatly enhance the bone formation. This hypothesis is investigated by using New Zealand White rabbits. First, the experimenter creates a bone bioreactor in the tibia of the rabbit by injecting biocompatible calcium-alginate gel that's crosslinked. Then after 6 weeks of the creation of bioreactor, autologous bone tissues are transplated into the bioreactor and harvest for many weeks. Then the bone is transplanted to the defects. At the end, the experimenter also testes how good the bone samples function by using Merlin Materials Testing Software.

The result of this experiment proves its hypothesis. After creating a bioreactor between the surface of long bone and periosteum, cells quickly proliferate inside periosteum and the bioreactor space is filled with periosteal cells and capillaries. Then woven bone is formed after 2 weeks and it turns into compact bones later in time. This kind of bone formation process is quite different from the usual process which involves the formation of fibroblasts scar tissue. Beside testing the effectiveness of bone formation in bioreactor, the experimenter also study the functionality of newly formed bone. The result is that the newly formed bone is the same as other bones and it has the same functions. In this paper, the experimenter also discuss results of bone regeneration from different modified bioreactor. These discussions are very useful to understand more about the bone regeneration in bioreactor such as the necessary conditions etc.

The reason why I chose this paper is because I am very interested in bone regeneration. Since I and some of my friends have minor bone fracture for quite a long while already, but still the fracture has not recover and so I am very interested in the treatment of bone defects. After reading this paper, I found this method of bone regeneration in vivo bioreactor very useful. Not only it is effective, also it is less painful if we compare it to the harvesting in the crest of iliac. I think we should definitely study more about it and maybe carry out clinical trials to see if it really works or not.

Development of quantitative PCR methods to analyse neural progenitor cell culture state

Elsa Abranches, Analeah O’Neill, Matthew J. Robertson, David V. Schaffer, and Joaquim M. S. Cabral

Biotechnol. Appl. Biochem. (2006) 44, 1-8

Stem cells have great potential for use in tissue engineering since they are able to differentiate into various specialized types of cells. But in order for them to be helpful we must be able to grow them up immature (undifferentiated) and then control their differentiation into the specific cell lineage needed for the application of interest. Being able to quantify the cell differentiation in a cell culture is therefore very important.

There are a few existing methods for quantifying cell differentiation. One of these is immunostaining in which slides of cells are stained and the number of cells of each phenotype is counted manually. This technique is very laborious and time consuming and cannot be readily automated because of complex images due to elaborate cell morphologies and surface markers. Accurate quantification is also difficult using this method especially if the cells are very dense or have extensive cellular processes. In this paper a quantitative reverse transcription polymerase chain reaction (qRT-PCR) method is developed to improve quantification of cell differentiation. This faster method accurately quantifies mRNA to monitor expression of markers that are specific to different cell types. The paper also discusses how this method was applied to a study on how conditions of cell culture effect the cell differentiation.

So what is qRT-PCR? Let’s start with RT-PCR…

Reverse transcription polymerase chain reaction (RT-PCR) is a very useful technique for measuring gene expression. It works by amplifying a specific sequence of RNA even if it has a low copy number. This allows the investigator to see what is going on in the cell. For example, if you insert a plasmid encoding a protein into a strain of bacteria and you want to find out if the bacteria are actually producing the protein then you can use RT-PCR to see if the mRNA for your protein is present in the cell.

So how does RT-PCR work? Your mRNA is first copied to cDNA via reverse transcriptase. The temperature is then raised so that the two strands of the cDNA separate. Then the temperature is lowered to allow specific primers to anneal to the single stranded DNA. Again the temperature is raised (though not as high as before) and Taq DNA polymerase extends the DNA from the primers. Then the temperature is further increased to separate the DNA. At this point there are four strands of cDNA (from the two we started with). And the process continues to repeat itself a number of times (30-40 cycles) increasing the number of strands of DNA each time. The products can then be analyzed using gel electrophoresis.

RT-PCR is useful for detecting the presence of a specific RNA molecule but it is not good for quantifying the abundance of the molecule. There is a newer method that allows for quantification in addition to amplification which is called quantitative RT-PCR or qRT-PCR (also known as real time PCR). As we saw above, in each cycle the amount of DNA doubles, but at some point during the 30-40 cycles a plateau is reached where the amount of DNA is no longer doubling with each cycle. With RT-PCR you don’t know when this plateau was reached so you don’t know when the DNA stopped doubling with each cycle and therefore don’t know how much of your RNA of interest was in your original sample.

In qRT-PCR a dye (in this case SYBR Green) is used that has very high fluorescence when it binds with double stranded DNA and low fluorescence with single stranded. This allows you to track the growth of the amount of DNA. Comparison of the amount of fluorescence of your sample at a certain cycle number to that of a control containing a known initial quantity of RNA allows you to quantify the amount of RNA in your original sample.

In this paper a method of qRT-PCR is developed for use in quantifying the cell differentiation of neural progenitor cells. Under the proper conditions, neural stem cells are able to undergo extended proliferation while remaining undifferentiated or they may be differentiated into the three major neural lineages becoming astrocytes, oligodendrocytes, or neurons. It is believed that there are also shorter-term neural precursor cells called neural progenitor cells present in the central nervous system in addition to the neural stem cells. In this paper cell differentiation of neural progenitor cells from the hippocampus of adult female rats is investigated under proliferation and differentiation conditions.

Neural progenitors were cultured for 2 weeks in serum with retinoic acid which promotes neuronal differentiation (differentiation conditions). The cultures had markers for astrocytes, oligodendrocytes, and neurons. Over the 2 weeks the total RNA was isolated from samples of the cell cultures. qRT-PCR was used to measure the levels of gene expression markers in these samples. On day 0 (proliferation conditions) and day 8 immunostaining was also used to quantify differentiation. Immunostaining was not done at the conclusion of the 2 weeks because the cell density was too great.

What was found is that the level of nestin (associated with undifferentiated cells) increased for the first 4 days while the cell population increased and then after that the level decreased as the cells differentiated. The expression of the astroctye marker steadily increased through the 2 weeks showing that the fraction of cells differentiating into astrocytes increases with time. Neuron expression also increased whereas oligodendrocytes initially increased until overtaken by the growing populations of astrocytes and neurons. The qRT-PCR measurements were consistent with those obtained via immunostaining.

The other study that was done using this qRT-PCR method was to monitor the effect of cell culture feeding schedule on cell differentiation. Undifferentiated cells were cultured for 4 days with one culture being fed on day 2 and the other remaining unfed. It was found that the unfed cells started differentiating and the fed cells did not. Therefore it was determined that fresh medium is required to keep cells in the undifferentiated state.

From being exposed to immunostaining in class it is easy to see how laborious it would be to use this method to quantify cell differentiation in a culture, especially one containing cells that differentiate into more than one type of specialized cell. I think this paper is important because it shows how the qRT-PCR results were consistent with those from immunostaining, which is the standard method used for studying cell phenotype. Also, I chose this paper because it provides a couple examples for applications of qRT-PCR.

Effects of the mechanical properties of collagen gel on the in vitro formation of microvessel networks by endothelial cells

Nahoko Yamamura, M.S., Ryo Sudo, Ph.D., Mariko Ikeda, Ph.D., and Kazuo Tanishita, Ph.D.

Overview:

In this experiment, the effects of the mechanical properties of collagen gel on the formation of 3D capillary networks were studied. Bovine pulmonary microvascular ECs (BPMECs) were cultured in collagen gels along with an angiogenic factor (added 24 hours after seeding) to promote growth of the networks. The gel stiffness was varied by using several different pHs of the collagen polymerization solution, keeping the collagen concentration constant. Within pH values between 5 and 8, the relaxation moduli of collagen gel increases linearly with pH (i.e. “flexible gels” polymerized at pH 5; “rigis gels” polymerized at pH 9). Microscope imaging showed that the formation of 3D microvessel networks differed based on the stiffness or flexibility of the gel in which the tissue was cultured. Also, vinculin expression varied along with the gel’s mechanical properties, indicating that microvessel network morphogenesis involves a vinculin-mediated interaction between the ECs and ECM substrate.

Methods:

In order to study network growth, the cultures were photographed under a phase-contrast microscope every 10 minutes for 2 days. To study network configuration, the cells were fluorescently labeled with CellTracker Green BODIPY (after 7 days of culturing) and observed using confocal laser scanning microscopy. Imaging software was used to calculate the area, length, and density of the EC networks. To examine thin vertical sections of the network, they were stained and transmission electron microscopy was used. And finally, to study actin and vinculin expression, the cells were incubated overnight with mouse anti-human vinculin antibody, anti-mouse IgG antibody, and phalloidin, and then observed using a confocal laser scanning microscope. Successive vertical section images were reconstructed to form a 3D image.

Results:

ECs in the flexible gel grew by elongating into thin vessels and interlinking with other networks. Cells invaded the gel individually and formed few clumps, creating thin and dense netrworks. In the rigid gel, however, ECs formed aggregates, which grew while filamentous cytoplasmic processes extended out and formed branched networks. Thicker, more sparsely distributed clumps formed in the rigid gel (in addition to forming deeper networks). In general, network area decreased with depth in all gels, but networks at lower depths seemed to grow best in the rigid gel. Also, intracellular vacuoles were observed in networks in the flexible gel, while luminal structures were observed in the rigid gel. In the flexible gel, faint expression of vinculin was observed, whereas intensive actin filaments and numerous clumps of vinculin were observed in the rigid gel.

In conclusion, the formation, configuration, and distribution of microvessel networks depend on the gel’s mechanical properties, which has an effect on EC morphogenesis by regulating the proliferation, migration, and differentiation of ECs.

Importance:

This experiment is important because while 2D tissues (such as skin) can be reconstructed, 3D tissues (such as liver tissue) are still hard to grow and manipulate. 3D tissue organoids can be grown in vitro, but they must be vascularized. In order to do this, the interaction between endothelial cells (ECs) and extra cellular matrix (ECM) must be better understood. This experiment gives us further insight into the relationship between ECM mechanical properties and EC proliferation, migration, and differentiation.

It is also important because it shows that the mechanical properties of the adhesion substrate must be considered, as they have an effect on microvessel network configuration. Focal adhesion proteins can be used as mechanosensors, because they respond differently to different gel stiffnesses.

Stimulation of fetal rat lung cell proliferation in vitro by mechanical stretch

It has been suggested in animal experiments that normal utero development of the lung requires normal fetal breathing movements. Abnormal growth of the fetal lung can be the result of restriction of normal intrathoracic volume by lesions or other thoracic abnormalities. The physical forces involved in the developmental pathways of the fetal lung have yet to be modeled. This group has developed a model which addresses the question of whether mechanical stretch or distortion directly stimulates in vitro fetal lung cell proliferation. By establishing organotypic fetal lung cell cultures subjected to controlled stretches, they have observed that the forces resulted in enhanced fetal lung cell growth and DNA synthesis.

Cells from fetal lungs of rats were obtained at 19 days gestation period and incubated and grown in culture. These cultures were then applied to gelatin sponges for mechanical testing using a mechanical stretch device. The device can be varied in amplitude, frequency, and periodicity. These cells were stretched for a 48-h period starting 48 h after cell inoculation. Cell growth was assessed by both using a cell counter and incorporation of thymidine into DNA synthesis. Stretch-induced cell damage was evaluated by the measurement of release of adenine.

A significant response to stretch was observed with a specific seeding density and concentration of fetal bovine serum (1-2% FBS). In addition, with a continuous cycle of cell stretch, cell proliferation was stimulated at frequencies of 6/min and 30/min, but cytotoxicity was evident at rate of 60/min. In preliminary studies, continuous thymidine incorporation took 48 h to demonstrate stretch-mediated enhancement. For the minimal duration of stretch, the group stretched intermittently at 6, 12, 24, and 48 h of 60 cycles/min. A stretch period of 6 h did not result in increased synthesis rate, but others exhibited rates of increase by 60-80% of the control.

The group did find significant results that mechanical forces are directly on lung cells stimulate cell proliferation in vitro and the response to stretch is dependent on amplitude, frequency, periodicity, and duration. This paper is significant because it shows that the in vitro experiments of cell cultures from live tissue cannot all account for the mechanical forces that exist in live bodies. I do not think, personally, there is any way to mimic the effects of mechanical forces in vitro while conducting an experiment. The cell cultures we used of course were prepared cell-lines that do not resemble any live tissue. However for future in vitro experiments using cells from live tissue, we need to keep these considerations in mind.

Stem cells in tissue engineering

insight
Nature 414, 118-121 (1 November 2001) | doi:10.1038/35102181

Stem cells in tissue engineering
Paolo Bianco1 and Pamela Gehron Robey2

In this “Stem Cells in Tissue Engineering” paper, the authors describe the diverse range of tissue that can now be engineered via stem cells, including epithelial surfaces (skin, cornea, and mucosal membranes) to skeletal tissues. The two most important factors when reconstructing tissues using stem cells include their inherently different rates of self-renewal as well as physical structures. This paper examines two specific applications of stem cells to tissue engineering—the regeneration of skin involving the structural formation of two-dimensional sheets as well as a more complex formation of bone, which involves the reconstruction of three-dimensional shapes and scaffolding.
In engineering the skin and other surfaces, permanent restoration of tissues that are characterized by high and continuous self-renewal require stem cells that are self-renewing. In most recent studies, a small but pure population of holoclone-generating cells is what is needed to generate epidermal grafts; the identification of a keratinocyte stem cell markers may provide a new tool for this approach with respect to epidermis. Success for these procedures have varied—usually with graft failure after a promising initial engraftment. In clinical trials, skin autografts are produced by culturing keratinocytes to generate an epidermal sheet, and then transplanting this sheet along with a suitable skin-like substrate. The long-term success of a skin graft depends on appropriate replenishment of stem cells in the graft. To engineer the skeleton, skeletal stem cells are needed, and can be found in bone-marrow stromal stem cells, which are able to undergo extensive replication in culture. The stem cells obtained in culture must be then combined with appropriate carriers before transplantation, which provide a three-dimensional scaffold in which a vascular bed can be established so that transplanted progenitor cells can differentiate and form a bone/marrow organ. Suitable materials that have been used include synthetic hydroxyapatite/tricalcium phosphates and polyglycolic and polylactic acids. Studies have yet to show their compatibility with long-term maintenance of stem cell properties, or the fate of bone-biomaterial composites being generated at the site of transplantation. One procedure for bone reconstruction includes loading the skeletal stem cells into appropriate carriers and transplanting it into a non skeletal site surrounding an artery and vein. It is here that they generate a vascularized segment of bone, the size and shape of which are dictated by the carrier geometry.
This paper is particularly important because it details the potential of tissue-engineering—both in its approach as well as with its usage. Specifically, researchers hope to utilize stem cell’s ability of restoration to develop continuously self-renewing tissues such as skin. The list of tissues with the potential to be engineered is growing steadily—the most important contributing factor being that there has been recent progress in stem cell biology and recognition of the unique biological properties of stem cells. Tissue engineering is not simple reconstruction of tissue, but engineering of tissue function.

Survival, migration and differentiation of retinal progenitor cells

Survival, migration and differentiation of retinal progenitor cells
transplanted on micro-machined poly(methyl methacrylate) scaffolds to the
subretinal space

Sarah Tao, Conan Young, Stephen Redenti, Yiqin Zhang, Henry Klassen, Tejal Desai and
Michael J. Young

Age related macular degeneration or AMD is the degeneration of the macula, a highly specialized region of the ocular retina. It leads to the loss of central vision and in severe cases it leads to bleeding in the retina and eventually blindness. It is one of the leading causes of blindness in the elderly and current therapies only slow down the progression of the disease but do not restore the lost vision.

Possible treatment therapies include transplantation of retinal progenitor cells (RPC) to the sub retinal space which would eventually differentiate into some of the lost photoreceptor cells of the retina. However there are many obstacles in delivering RPCs to the sub retinal space which is less than 100µm in width. Injection of RPCs to the sub retinal space is not effective as it leads to cell death and reflux of large amount of injected cells. Introduction of cells using scaffolds is more effective than standard bolus injection as it provides greater control over the microenvironment of the cell but due to the physical constraints provided by the ocular structure of the eye it is critical to develop a scaffold thin enough to be accommodated in the sub retinal space which would not induce any trauma. Not only should the scaffold be small enough it should have an optimum surface chemistry and topographic cues to induce differentiation.

This study looks into the survival, migration and differentiation of RPCs in the sub retinal space delivered via an ultra thin PMMA poly (methyl methacrylate) scaffold. The study also looks at the porosity of the scaffold and how it influences the adherence of RPCs to the scaffold and later differentiation. The PMMA scaffolds were fabricated using a two step photolithographic technique and ion etching process; they measured 6µm in width and contained pores 11µm in diameter, 63µm apart. PMMA has been used extensively in contact and intraocular lenses and is biocompatible. The scaffolds were coated with lysine and laminin after which RPCS were cultured on both porous and non-porous scaffolds for 7 days. The scaffolds with adherent RPCs were than surgically transplanted into the sub retinal space of mice. After 4 weeks the mice were sacrificed and retinal tissue sections were prepared for immunohistochemical characterization and microscopy.

Characterization of the sectioned tissue revealed that RPCs cultured on porous scaffolds had significantly greater morphological integration – migration and process extension with the host retinal layer. In four out of five transplant recipients that received RPCs from porous scaffolds had developed cell processes as compared to non porous scaffolds where only one out of five had such processes. Moreover RPCs from porous scaffolds revealed morphologic differentiation features consistent with retinal neurons and some even spanned the radial extent of the retina similar to meuller cells. They also expressed cell surface markers specific for retinal cells – recoverin, glial cell marker (GFAP) and neural marker – NF 200. RPCs cultured on non-porous scaffolds either died or failed to express the differentiation factors observed in the RPCs cultured on the porous counterparts.

In conclusion, the use of porous PMMA scaffolds not only increases the survival of cells during the delivery of RPCs to the sub retinal space in comparison to bolus injection but it also provides favorable micro environment for cell migration and differentiation into the retinal layer. I chose this paper as this has a major therapeutic application and is an elegant example of how a scaffold with specific properties can be used to reengineer a tissue.

Interactive effects of surface topography and pulsatile electrical field stimulation on orientation and elongation of fibroblasts and cardiomyocytes

Hoi Ting H. Au, Irene Cheng, Mohammad F. Chowdhury and Milica Radisic

To engineer cardiac tissue, proper structural organization of cardiomyocytes and fibroblasts must be attained. Since functionality of these cells is depended on cellular orientation, it is important to understand what cues govern this. Previous studies have focused on topgraphical, adhesive or electrical cues alone, but this study focuses on the interactive effects of topography and electrical fields on the orientation and elongation of fibroblasts and cardiomyocytes. The authors hypothesized that the same molecular pathways were involved in responding to both cues, and did a pharmacological study to analyze the effects of the actin polymerization and p13k pathways on cell orientation and elongation. To test topographical effects, microabraded coverslips were used with a variation of grain sizes, with half of the coverslip abraded perpendicular to the other half. 3T3 fibroblasts and cardiomyocytes from neotanal rats were used.

The abraded surfaces improved elongation of both fibroblasts and cardiomyocytes, The most significant improvement in comparison to the nonabraded occurred in the surfaces worn with greatest grain size. Electrical field simulation yielded more elongated fibroblasts on abraded surfaces at low voltage, while at higher voltage, the nonabraded surfaces showed a greatly increased elongation, meaning there was no significant difference in elongation between surfaces. The cardiomyocytes showed similar results, with the cells aligning perpendicular to the field lines when the abrasions were also perpendicular. The improved orientation from electrical field stimulation was observed using ImageJ. These results indicated that topographical cues were a stronger determinant of orientation than electrical fields, and also that the same pathways could be involved in responding to both cues. The pharmacological study showed that blocking actin polymerization inhibited the ability of cardiomyocytes to respond to topographical and electrical cues, while the P13K pathway showed reduced alignment and elongation.

I chose this paper because it involved techniques we had done in lab (culture of 3T3s in T75s, live/dead assays, ImageJ, etc) but took them a step further and applied them to a real problem. Effectively engineering cardiac tissue is becoming an increasingly important area of research, and the authors are able to offer suggestions for future improvements, and provide information about the never before studied interaction of various cues on cell orientation.

Dynamics of the Self-Assembly of Complex Cellular aggregates on Micromolded Nonadhesive Hydrogels

Dynamics of the Self-Assembly of Complex Cellular aggregates on Micromolded Nonadhesive Hydrogels
Napolitano, A., Chai, P., Dean, D., and Morgan, J.
http://www.liebertonline.com/doi/pdf/10.1089/ten.2006.0190


Cell aggregation to form three-dimensional spherical shapes combined with self-segregating properties that allow the formation of multilayered, tissue-esque, three-dimensional shapes are important to the development of living tissues. Spheroid tissue shapes serve to increase gene expression; they also generate appropriate cell-cell interactions. Since previous studies involving embryonic tissues and adult cells have shown such self-aggregating properties, Napolitano, et al. sought to create nonadhesive hydrogels to study size, shape, dynamics, and composition involved with the normal human fibroblast (NHF) and the human umbilical vein endothelial cell (HUVEC) self-assembly process. The micromolded hydrogels enabled the group to study the dynamics of cell assembly given various geometric forms, including a toroid shape.

The group designed arrays of 800micron tall pegs that served as molds for seeding wells. Using different diameter wells and different morphological shapes, the team evaluated recess shape in cell aggregation and found that aggregation was controlled by recesses in hemispherical, large, flat bottoms more so than by irregularly shaped recesses. Hemispherical wells generated better cell regularity than did flat-bottom wells. The researchers used time-lapse (brightfield) microscopy to assess parameters such as circumferential contraction, re-segregation potential*, spheroid viability, and aggregate geometry for the cells. They analyzed the ells via a live/dad and calcein staining. When HUVECs and NHFs were co-seeded, a multi-layered spherical structure formed wherein the HUVECs formed a multilayer surrounding a NHF core. They also noted that given HUVEC spheroids combined with a NHF cell suspension, the NHFs reorganized to form a core surrounded by a HUVEC layer. They thus showed that spheroids retain the ability o reassemble and that cells can assemble to form complex shapes.

I chose this paper since the group used various techniques used in class to study methods of enhancing cell morphology. Some techniques we’ve studied include: live-dead determination/calcein staining, brightfield microscopy, cell passaging, cell counting, etc. Overall, though, this paper is important since the group utilizes non-adhesive hydrogels that minimize cell-substrate interactions and maximize cell-cell interactions. Also, since three-dimensional spheroid shapes are important in increasing gene expression, this study is an intriguing look on ways to improve culture techniques.

* by this, I mean the ability for mature spheroids to re-segregate into multilayered elementary tissue structures

Microfluidic Environment for High Density Hepatocyte Culture

by: M. Zhang, P. Lee, P. Hung, T. Johnson, L. Lee, M. Mofrad

When hepatocytes are isolated from tissue and grown in monolayer culture, they experience rapid loss of liver-specific function. Current methods used to improve in vitro hepatocyte culture include the growth of hepatocytes on extracellular matrix treated surfaces or the formation of spheroid hepatocyte aggregates. Although these hepatocyte aggregates maintain long term hepatocyte functions in vitro more effectively than monolayer counterparts, recent microfluidic technologies offer many advantageous features that allow better control of cell culture microenvironments and in turn hepatocyte behavior. This paper describes a bioreactor with a microfluidic environment that mimics physiological liver mass transport to allow hepatocytes to be cultured in high-density arrays and maintained in a tissue-like microarchitecture of extensive cell-cell contact in close contact with nutrient circulation. The microfluidic environment also enables hepatocytes to be cultured at a high density without nutrient limitation for over one week by maintaining a continuous flow of medium that diffuses to the cells across a porous barrier. The microfluidic cell culture array device consists of a cell culture area and a nutrient flow channel separated by a microfluidic perfusion barrier that localizes and concentrates cell within the cell culture area while allowing diffusion of nutrients from the nutrient flow channel to the cells. The cells used in the device were human hepatoma HepG2/C3A cells, which have a protein synthesis profile that closely resembles that of native liver cells and have improved albumin production compared to the HepG2 cell line.

Continuous flow of nutrients such as glucose in the bioreactor was modeled using finite element analysis software and validated by the survival and proliferation of the cells in culture. Using Trypan Blue and Live/Dead fluorescence assay, 80% viability of hepatocytes cultured in the microfluidic device was observed after 1 week of incubation. By day 8, cells exhibited liver tissue morphology of dense packing, cuboidal geometry, and indistinguishable fused membranes. In comparison, cells grown under control conditions in standard tissue culture 12-well plates appeared strongly attached to the surface and more spread with distinct instead of fused cell membranes. Cells grown in the device maintained a cell density that was 3 times higher than that of monolayer culture and results from quantitative dot-blot assays to assess hepatocyte function via albumin secretion revealed that after 4 days of culture HepG2/C3A cells were producing 3 times more albumin per cell compared with cell grown in the 12-well plates. Thus, a microfluidic environment with mass transport conditions that is physiologically similar to that experienced by hepatocytes in vivo can affect cell behavior by inducing hepatocytes to grow in a natural liver configuration with a high density of hepatocytes and maintain liver tissue specific function.

I came across this paper while searching for recent papers involving PDMS and hepatocytes in an attempt to do some background research on my group’s research idea and found the idea of microscale bioreactors to be very interesting. This technology overcomes the limitation of loss of function observed in hepatocytes grown in monolayer culture and allows a more precise control of the microenvironment experienced by the cells in the culture. This opens up many possibilities in research to determine which physiological conditions are most important to maintain differentiation and function of hepatocytes and many other cell types as well. This technology can also be applied in drug metabolism screening in a more efficient manner at the microscale level so would be very useful for testing of many pharmaceutical products.

Induction of Pluripotent Stem Cells from Mouse Embryonic and Adult Fibroblast Cultures by Defined Factors

Kazutoshi Takahashi and Shinya Yamanaka
Department of Stem Cell Biology, Institute for Frontier Medical Sciences, Kyoto University, Kyoto 606-8507, Japan
CREST, Japan Science and Technology Agency, Kawaguchi 332-0012, Japan

This research is about reprogramming the nuclear content of fibroblast cells to pluripotent stem cells. Since we all know the importance of pluripotent stem cells, they can growth and differentiate to all the three germs layers of tissues. However, collecting contamination-free pluripotent stem cells in a significant amount that are suitable for therapeutic use is problematic. This paper provided a possible solution about the source of pluripotent stem cells. As all cells in a single human body share the same DNA sequence, the only difference between cell types is that some genes are inhibited and some of them are enhanced. In this research, the Japanese scientists reprogrammed the nuclear content of the fibroblast cell by introducing four factors Oct3/4, Sox2, c-Myc, and Klf4; at the end they found that the modified fibroblast cells expressed some similar characteristics as pluripotent stem cell.

At first they started with 24 candidate genes, they modified the 24 genes of the fibroblasts and compared their morphology and resistance to G418 with pluripotent stem cells. Afterward, they narrowed to 10 genes and created colonies of modified cells with the combination of the 10 genes. They sorted out the colonies by their similarity with ES cell on G418-resistant, morphology, proliferation properties and RT-PCR analysis of ES cell markers; at last, the combination of Oct3/4, Sox2, c-Myc, and Klf4 is reported to have the closest characteristic with pluripotent stem cell. This “winning” combination of cells is called induced pluripotent stem (iPS).

Furthermore, additional tests were preformed on the iPS. They studied the iPS’s global gene-expression by DNA microarrays with pluripotent stem cell and found that their gene expression is similar, but not identical. Since they are not identical, this also confirmed that the result is not due to contamination of the modified fibroblasts cell colony by the pluripotent stem cell. At last, they transplanted the modified fibroblasts cells to a living mouse and caused a teratoma which contains all three germ layers as same as the pluripotent stem cell.

Link

Chitosan-based hyaluronan hybrid polymer fibre scaffold for ligament and tendon tissue engineering.

T Majima, T Irie, N Sawaguchi, T Funakoshi, N Iwasaki, K Harada, A Minami, S-I Nishimura

In the event of a tendon injury, the preferred method of treatment is an autograft. But this requires additional surgery and healing at the donor site. The authors of my selected paper have been working on a method to grow tendon tissue on a three-dimensional scaffold. The scaffold acts as a temporary template for the cells and provides the biomechanical characteristics that they would be exposed to in vivo. The difficulty is in finding a biomaterial that possesses those characteristics. Collagen can cause immunogenic reactions and polyglycolic acid does not possess the proper mechanical properties, making them poor candidates. It was known to the authors that glycoaminoglycans, specifically their main component hyaluronan (HA), improved tissue healing. Chitosan was also an excellent biomaterial for tissue repair. The authors decided to create hybrid polymer-fibers using the two and a hyaluronan-like material, alginate. They developed a chitosan-based hyaluronan hybrid and an alginate-based chitosan hybrid. The polymer-fibers were made using wetspinning using the base material and adding either 0, .05 percent, or 0.1 percent of the other material. The selected control was polyglactin, a material used for wound closure.

The authors tested various properties of the polymer-fibers in-vitro. A tensile strength test showed that adding HA to chitosan fibers increased tensile strength while adding chitosan to alginate did not. A cell adhesion test showed that adding HA to chitosan fibers and adding chitosan to alginate fibers decreased cell adhesion, with the addition of HA to chitosan fibers causing a more significant difference. From these tests, the authors decided to continue their study using chitosan-based 0.1 percent HA material. The fibers were incubated for 0, 2 hours, 14 days, or 28 days and tested for tensile strength again and it was discovered that tensile strength drops before 2 hours but is maintained between 2 hours and 28 days. In a test of cell proliferation, fibroblasts were loaded into scaffolds and it was found that chitosan-based 0.1 percent HA material had significantly greater amounts of DNA content that 0.05 percent or 0 percent. After 14 days, they were observed producing ECM.
The authors then began testing the chitosan-based 0.1 percent HA hybrid polymer-fibers in-vivo. First, they tested biodegradability by implanting the scaffolds into rats and measuring failure load at 0, 2, 4, 6, 12, and 16 weeks. After two weeks, maximum failure load had significantly dropped but gradually increased afterwards. To test the feasibility of repairing tendons with the scaffold, defects in a rabbit's rotator cuff tendon model were created and covered with a fibroblast-seeded scaffold. After 4 and 12 weeks, the engineered tendons were tested. In the fibroblast-seeded scaffolds, collagen I was detected and tensile strength was increased compared to a non-cell-seeded scaffold. To test the feasibility of repairing ligaments with the scaffold, the medial collateral ligament was injured, removed, and reconstructed using the engineered scaffold. After 12 weeks, the engineered ligaments were tested. Two of the engineered ligaments actually did not break in the ligament but where it was bound to bone. The other three engineered ligaments and all ligaments repaired with scar tissue broke in the ligament. This means that the engineered ligaments are an improvement over normal healing with scar tissue.

I chose this paper because ligament injuries, especially of the knee, are a fairly common sports injury and an injury that can result from normal wear-and-tear as life expectancy increases. In addition, ligament injuries are relatively difficult to heal because of the low number of active cells present in a ligament with most of it consisting of ECM but also because ligaments are constantly in tension which prevent the damaged ends of a torn ligament from ever meeting. The current treatment of autograft can be extremely painful because of the secondary surgery to remove ligament from the donor site, which also increases the healing time. If ligament tissue could be successfully grown on a scaffold, such treatments would not be needed anymore thus improving the recovery process and increasing quality of life for those who suffer from ligament injuries.

I should mention, the link to the paper I reviewed is in the title of my last post. It's easy to miss.

Also, this blog seems to have changed the formatting of my post, so when I say "left" or "right," I really mean "above."

Vitreous cryopreservation maintains the function of vascular grafts

Although successful human cryopreservation and revival likely won’t be available in the near future, it’s amazing to think that nowadays, living cells can be frozen for over a year before being thawed and re-cultured. As engineered vascular grafts increase in demand, a method is needed to store tissue constructs for indefinite periods of time, they will be of limited practical use. This need is the basis for work on cryopreservation.

Cryopreservation so far has mainly involved simply placing cells and solvent in low-temperature freezers in vials, cryoprotectant optional. Ice crystals formed through this method, however, cause damage to the tissue, and blood vessels do not maintain the same mechanical properties as when they are first obtained. To avoid this problem, scientists have developed an alternative technique for cryopreservation called vitrification. Rather than relying on the slow freezer, this process involves an extremely fast temperature decrease (e.g. plunging the sample into liquid nitrogen). This reduces the formation of ice crystals and instead causes the solution to become increasingly viscous and glass-like.

In this paper’s study, researchers tested the effects of freezing on the mechanical properties of rabbit blood vessels. Blood vessels were placed into one of three categories: fresh (control), slow-frozen (the original method for cryopreservation), or vitrification. After being cut into cross-sectional vein rings and undergoing their respective procedures, the vessels were treated with various drugs such as histamine or acetylcholine. Contractile tensions were measured to indicate response to these drugs.

The results show that slow-frozen blood vessels show a marked decrease in contractile response to the drugs compared to fresh tissue, while vitrified vessels mostly maintain this contractile response.

The graphs to the left show the differences in contractile response to various drugs among control (C), slow-frozen (F), and vitrified (V) vessels.

Microscope images of these tissues also reveal the extensive damage in slow-frozen tissue due to ice crystal formations, a feature largely absent in vitrified blood vessels.

Microscope images of slow-frozen (A) and vitrified (B-D) tissues are shown on the right. Slow-frozen tissue shows extensive ice crystal formation, while vitrified tissue remains mostly free of this damage.

The ultimate goal for cryopreservation is, as previously mentioned, storage and revival of complete organisms. The possibilities of such a technique are so varied that I won’t attempt to go into the details, lest I lose sight of the line dividing the real world with science fiction (Is cryopreservation of astronauts as in the movie 2001: A Space Odyssey possible?). Even nowadays, cryopreservation is used in such areas as sperm banks, where sperm can be frozen for long periods of time until someone wants them. There is a large need for effective storage of tissue for future use, and I predict that cryopreservation will become increasingly important in the medical and in the bioengineering fields.

Reconstruction of Functional Tissues with Cell Sheet Engineering

Joseph Yang, Masayuki Yamato, Tatsuya Shimizu, Hidekazu Sekine, Kazuo Ohashi, Masato Kanzaki, Takeshi Ohki, Kohji Nishida and Teruo Okano

The approach of seeding cells into biodegradable scaffolds has become a hallmark of modern tissue engineering. Rather than using biomaterials as scaffolding materials for tissue reconstruction, the investigators have created an alternative approach using polymer-coated culture surfaces to facilitate the non-invasive harvest of cultured cells as intact tissue sheets. The culture surface is grafted with poly(N-isoproplyacrylamide) (PIPAAm), a temperature responsive polymer that allows controlled attachment and detachment of living cells via temperature changes.

With this new method, cell types that secrete significant amounts of extracellular matrix (ECM) proteins, are cultured for prolonged periods to create sheet-like structures for tissue reconstruction. By covalently immobilizing PIPAAm onto conventional culture surfaces, changes in the surface properties can be controlled by varying the incubation temperature. At temperatures above 32 °C (lower critical solution temperature), culture surfaces are slightly hydrophobic and enables various cell types to attach, spread and proliferate as if on normal tissue culture polystyrene. When the temperature is below 32 °C, the PIPAAm-grafted surfaces spontaneously become hydrophilic. A hydration layer forms between the culture surface and the attached cells, allowing the harvest of confluent cells as intact sheets. Since the grafted surfaces facilitate spontaneous cell detachment, scientists can avoid using proteolytic enzymes such as typsin and collagenase. With non-invasive cell harvest, cell-to-cell junction and ECM proteins can be maintained. Cell sheet engineering had been used to create functional tissue sheets to treat a wide range of diseases including corneal dysfunction, esophageal cancer, tracheal resection, and cardiac failure. The researchers have also developed methods to create thick vascular tissues as well as, organ-like systems for the heart and liver by generating 3D tissues of cultured cells and deposited ECM proteins with the cell sheets. The article goes in more detail about each of these applications.

Using cell sheet engineering, numerous cell types have shown the maintenance of differentiated functions after low-temperature cell sheet harvest due to the preservation of cell surface proteins, such as growth factor receptors, ion channels, and cell-to-cell junction proteins. In addition, cell sheets can be easily transferred and attached to other surfaces (culture dishes, host tissues). A disadvantage is that engineered tissues created using this cell sheet method contain relatively little ECM. Thus, the method may not be ideal for the creation of cell-sparse tissues like bone and cartilage. Regardless, cell sheet engineering seems to be able to provide new possibilities in regenerative medicine and tissue engineering.

I chose this article because cell sheet engineering seemed interesting and it could be useful for future projects. This method is like an extension of the basic cell culture techniques taught in class - some day, I would like to try it out and see the results. Cell sheet engineering is a method that could be implemented with regeneration of specific tissues without the risks of using traditional scaffold-based methods. In addition, cell sheet engineering is novel alternative for research projects that require the re-creation of functional tissue structures.

Designing synthetic materials to control stem cell phenotype

This review discusses how stem cell behavior is manipulated using synthetic materials. Ligands have been designed to emulate the natural extracellular matrix, cell-cell contacts, and growth factors. Fate determination of the stem cells is regulated by material architecture and mechanical properties. Synthetic material systems are specifically designed to interact with cells on different length scales (e.g. macro vs cellular). Thus, they replicate the elements of natural stem cell niches (micro-environment needed to sustain self-renewal and control differentiation). However, synthetic materials differ from natural because they have the potential for improved control, repeatability, safety and scalability. Several classes of synthetic materials have been created to control stem cell phenotype: natural polymers (like mammalian ECM), synthetic polymers (like polyacrylamides), inorganic materials, and self-assembling peptides. Whichever class is used, the material must be processed and functionalized for specific clinical applications. Important material properties include ligand identity, presentation (conformity/orientation), and density. Optimizing these parameters creates materials that resemble the natural environment of the stem cells and allows for controlled mechanical properties.

Self-renewal and differentiation mechanisms are sensitive to many ligands/combinations of ligands: adhesion ligands from ECM, ligands from neighboring cells, and immobilized growth factors. Once a set of ligands is selected, it must be conjugated to the material for proper orientation. The way a material is organized and structured on the nanoscale (aka material architecture) is known to control cell signaling and organization. The geometry of the cellular interface with the material is a major factor in determining ligand engagement, molecular diffusion, and force transmission. Material architecture also determines bulk mechanical properties at larger scales. Both 2D and 3D architectures have been used for stem cell cultures. For 3D scaffolds, there are 3 predominant types: porous solids, hydrogels, and nanofibers. Material mechanics is largely determined by material's composition, water content, and structure. These affect intermolecular forces and stress distributions. Common techniques to change mechanical properties include altering molecular composition/connectivity, thermal processing, and creating porous composites. Mechanical properties affect cell migration and proliferation. Tensional homeostasis with the micro-environment (via integrins) causes cytoskeletal rearrangements and changes gene regulation pathways. The elastic modulus of culture material can alter or maintain human stem cell phenotype. Viscoelasticity is another mechanical property that may affect stem cell phenotype, but its effect is not fully known yet.

I chose this paper because I believe that studying how to manipulate stem cells is crucial, particularly if we want to successfully utilize stem cells in therapeutic applications. This paper discusses several properties that play significant roles in directing stem cell phenotype, but concludes that much work needs to be done in the future to realize the full clinical potential of stem cells.

-Rustin

Collective migration of an epithelial monolayer in response to a model wound

M. Poujade*, E. Grasland-Mongrain*, A. Hertzog†, J. Jouanneau†, P. Chavrier†, B. Ladoux‡, A. Buguin*, and P. Silberzan*§

The study of cell migration is important in wound healing. Usual methods of observing migratory behaviors of cells in vitro is the classical “wound healing” scratch assay, in which a razor blade or pipette tip is used to mechanically remove some cells in a confluent epithelium monolayer. However, researchers have been trying to develop new ways in proving how cells acquire their motility. In the scratch assay, the removed cells release intracellular content into the medium, sending chemical signals to neighboring cells to trigger migration. Another theory in why cells migrate is something called a “free surface” in which a removal of a barrier, which initially inhibits the growth of the epithelium, causes the cell to migrate. However, previous studies have been inconclusive and remain to be controversial.

As a result, the authors of this article orchestrated a very simple but elegant design to study the response of the monolayer as a result of a free surface. The experiment involved culturing a monolayer of cells constrained within a microstencil, which is fabricated from polydimethylsiloxane (PDMS) that precisely defined the geometrical conditions of the monolayer. The stencil was removed and the cells were free to migrate as shown in Figure 1. There are some advantages with this assay in observing cell migration. First, it eliminates the need to “scratch” the monolayer, which might depend on the user and the tool used to scratch the surface. Next, the wounds are well defined and perfectly controlled, allowing the authors to observe the cells progress from its initial position. The authors concluded that their injury-free wound healing assay on MDCK epithelial cells showed that the free surface was sufficient in inducing cell migration. Moreover, they note that the cells migrate in a leader-follower pattern which a certain cell will take “lead” in migration.

I chose this paper because of the simplicity of the experiment. For my project, I plan to use a similar design in determining cell migratory patterns within various defined regions.

UTILITY AND CONTROL OF PROTEOGLYCANS IN TISSUE ENGINEERING

Proteoglycans (PGs) and their glycosaminoglycan (GAG) have been used commonly in tissue engineering (TE) to produce scaffolds. However, their specific biophysical and biological functions in TE have not been fully studied. Proteinglycan is an important part of the extracellular matrix (ECM). PG molecule consists of a core protein and the GAG chains. The core protein doesn’t have serine residues. GAG chains are attached to core protein by tetrasaccharide link. The variety of PGs are the result of the variety of GAG chains attach to core protein. GAGs are long chains of disaccharide units that are sulfated differently. PGs in the native tissues have roles in tissue remodeling, intracellular signaling, cell migration, cell compressibility and transparency, and other functions. PGs in the extracellular space are the following: basement membrane PGs, hyalectines, and small leucine-rich PGs (SLRPs). In this paper, we will discuss the functions of perlycan in the TE scaffold. Another category of PGs is the cell surgace PGs, which include syndecans, glypicans. Thrombomodulin, and CD44. The more we learn about functions of specific PG and its GAGs, the closer we are to reconstruct native environment of tissues.
This paper review two kinds of PGs and GAGs grafted in scaffolds. The first one is collagen-GAG scaffold. The collagen-GAG suspension is solidified, which results in the co-precipitation of collagen-GAG and the growing ice crystals. The GAG chains are then grafted to the scaffold through exposure to high temperature. This process also sterilizes the scaffold. Studies have proved that the present of GAGs in scaffold improve tissue growth and regeneration over the use of collagen alone. This type of scaffold help inducing cells to retain more PG aggregates in scaffold and retain more newly synthesized PGs within the cell layers. Collagen-GAG scaffolds recently have been used in nerve regeneration, artificial skin, osteogenic and chondrogenic tissue development. Studies have suggested that osteoblasts seeded in collagen-GAG scaffolds show greater adhesion, proliferation and make more markers. Silicone tube-collagen-GAG combination has shown more success in inducing greater number of axons per nerve. There are also many applications of this type of scaffold discussed in this paper.
Matrigel scaffolds have also been studied for TE applications. Matrigel is a soluble extract of Engelbreth-Holm-Swarm tumor cells’ basement membrane. Its components include laminin, fibril, nidogen, entactin, collagen IV, perlecan, and growth factors. This scaffold has been used to study tumor cell migration and invasion of the basement membrane. HSPG perlycan is one of the major component of matrigel which has not been studied widely. It is suggested to play key roles in blood vessel growth. The C-terminus of perlycan has been reported to inhibit endothelial cell migration, collagen-induced endothelial tube formation, and blood vessel growth in vivo. Therefore, it is suggested to contribute in the control of tumor cell growth.
There are still many type of PGs and GAG that are commonly used in TE. Scientists have done many studies on the total amount of PGs synthesized in engineered tissues. However, not many studies have been done to fully explore the potentials of PGs in creating the native environment of tissues.

Cells on chips

Info. of Article
Jamil El-Ali, Peter K. Sorger & Klavs F. Jensen, "Cells on chips", Nature, v. 442, 2006, pp. 403~411.
Full text: http://www.nature.com/nature/journal/v442/n7101/pdf/nature05063.pdf

Main idea of article
In the first section, the authors explain why the "cells on chip" is important to us. ("cells on chip" means to do cell-related biological research or analysis on chips. Some people also call them "lab-on-a-chip" or "micro-total-analysis-system"(uTAS)). The authors believe the significance of "cells on chip" will be similar to the role that miniaturization has played for microelectronics. Our intuition thought would be that "cells on chip" simply represent miniaturized versions of conventional laboratory techniques, but the authors tell you it is far beyond that. In micro world, there are many wonderful advantages that are not true in macro scale. For example, you can easily have favorable scaling of electrical fields due to small length and well-controlled laminar flows due to the low Reynolds numbers in microchannels. Moreover, instead of fabricating individual small-scale equipments piece by piece, the researchers have been making the microsystems incorporating several steps of an assay into a single system. By doing this, you can do experiments on a single chip quickly and effectively. You name the benefits: small sample request, far less labour intensive (just think about what people expect typical biology-majored students often do in their labs), and avoiding of potential error-prone laboratory manipulations. With developed micromaching technology, it is also easy to batch produce such devices cheaply. In a word, “cells on chip” will be a wonderful breakthrough, no matter you consider from the perspective of pure research, cost, or effectiveness.

After the introduction, the authors go into the details, extensively but logically introducing up-to-date progress in each step of a cell experiment ranging from cell culture, selection, lysis, separation to final analysis. The article is well organized. Roughly speaking, in each step, the authors will tell you the major biological mechanisms in this step, then how they can be realized in micro scale, and finish it with some vivid practical examples and beautiful pictures. I would like to introduce as detail as above, however, the topics of this article are so wide that you bet my summary would be far less attractive than those used by the authors. Since you know what they are going to talk about, why don't you explore it by your self?

Why it is worth your reading?

——Chosen from a possibly different view
Slightly different from most of you, I am a graduate student spending years in Electrical and Mechanical Engineering but having never learnt any biology (BioE115 is my first-ever bio-related class in college.) So my choice may be more from an engineer view rather than a biologist view. Read it to see whether your view is different from mine.

——Read it like watching movies
Instead of focusing on a specific phenomenon or application, this article is like an excellent scientific documentary. You won't have to face any never-heard-of nomenclatures or massive arguments and calculations.

——Open yourself to a new world
By using a short period of time (if you exclude pictures and references, this article has only about 5 pages of text content.), you may quite probably open yourself to an unknown world which is actually not far away from you. No matter how well you are familiar with biology or engineerings, you will find something new and worthy. Trust me on this.

——Be an early bird
With the well-known example of IC technology, device miniaturization is a long-term tendency in many fields. You had better know a little about it from now on.

——Trustable and strong
It is a REVIEW in NATURE written by several MIT professors. You can imagine how often you could see such a combination.

You are welcome to raise any questions. With spending years in microfabrication cleaning room, I believe I may be helpful in practical issues such as device design and fabrication (but weak in those too theorital and too biological).

Now, welcome to micro world, a both familiar and unknown world!

Titin expression in human articular cartilage and cultured chondrocytes: A novel component in articular cartilage biomechanical sensing?

(Antibody Recognition and RT-PCR applications...)

The objective of this experiment was to test for the presence of titin on human articular cartilage tissue (e.g. joints). This large protein has previously been detected on heart and skeletal muscle tissue, where a biomechanical strain-bearing role has been attributed to it. "...Titin accounts for most of the passive elastic response retention that prevents over stretching... acts as an adjustable spring element..." Being this the case, it might be reasonable to look for the expression of this protein on other stress/strain-bearing tissues where elasticity is also required (e.g. joints).
Cartilage samples were taken from three groups of donors: Adults with osteoarthritis (OA), adults without OA, and infants (disgusting sampling). Immunolabelling was done with specific antibodies for "four" different domains of Titin; the N-terminal Z1-Z2 domain, the Novex III exon, the PEVK region, and N2A region (Fig.1). [I have to point out that even when only "three"antibodies were mentioned in the abstract, the paper showed results for "four" antibodies. Even section 2.3 (immunohystochemistry) doesn't make it clear (maybe it is me... I'm open to suggestions)].
However, it seems interesting to see positive results for titin presence in cartilage tissue (previously detected on muscle only). More than just existing on cartilage tissue, titin differences between Osteoarthritis and normal tissues were not detectable (Fig. 2,3). This suggests a crucial structural role of titin in cartilage.
Another result that called my attention was the detection of titin in extracellular matrix (ECM), when it was claimed to be intracellular (Fig. 2-4). This has two possible explanations:1) "a cross-reaction with other member of the Ig-domain gene superfamily, to which titin belongs" (detection of something else that has a domain in common with titin), and 2) titin has both intra- and extracellular strain-bearing functions.
Third interesting outcome: Some of the infant samples showed negative results for N2A region of titin (table 1, fourth column). This was associated to possible expression of a different titin isoform during maturation of the cartilage. This changes can be related to skeletal growth or mechanical load needs. This is a good point in favor of the specificity of antibody recognition (optimum trial and error, huh?). There were also discrepancies on the OA patients results (table 1, columns 2 & 3). This was similar to findings of aberrant forms of titin on patients with OA or Charcot Marie Tooth disease (Banes et. al. 2004). This is open to argument, though. Banes' aberrations where on the N2A region while aberrations here might be on Z1-Z2 (X112 113 X) and PEVK (9D10 ) regions.
Presence of titin was also shown by RT-PCR done from cells cultured from the samples. However, some domain fragments could not be amplified (see table2, Fig. 5). Again, might be related to the titin isoforms during cartilage maturation. Howeer, PEVK region was detected in all tissues by antibody recognition but not by RT-PCR. This case remains not clear. Further research will be required to clarify this.













Secondary Reference Sites:
1- http://www.ks.uiuc.edu/~ericlee/Telethonin/
2- http://www.psc.edu/science/2000/schulten/rude_mechanicals.html

Tissue Engineering of Skeletal Muscle

http://www.liebertonline.com/doi/abs/10.1089/ten.2006.0408

Tissue Engineering

Tissue Engineering of Skeletal Muscle.

Wentao Yan, Sheela George, Upinder Fotadar, Natalia Tyhovych, Angela Kamer, Michael J. Yost, Robert L. Price, Charles R. Haggart, Jeffrey W. Holmes, Louis Terracio. Tissue Engineering. ahead of print. doi:10.1089/ten.2006.0408.

Although a considerable amount of research has been done in skeletal muscle tissue engineering, there has yet to be a method for replacing lost tissue. In their study, Yan et al. have suggested the possibility of reconstruction through an in vitro construction of skeletal muscle with satellite cells to be reconstituted in vivo. Their 3D skeletal construct, engineered by seeding satellite cells on an aligned matrix of type I collagen fibrils, has been shown to closely resemble adult skeletal muscle function and structure and brings us only one step closer to a striated muscle implant in the future.

Experimental results prove the validity of their construct. Immunohistochemical staining of actin filaments and MyoD, the regulatory protein in muscle differentiation, revealed the differentiation of the satellite cells to myotubes and the parallel orientation of the multilayer muscle cells that are characteristic of skeletal muscle. Real-time RT-PCR tracked the muscle cell maturation process by assessing gene expression for various proteins. mRNA expressions for embryonic and adult myosin heavy chain, dystrophin, and alpha- and beta-enolases were consistent with patterns of in vivo mRNA expression reported in previous studies. Cell viability, measured using Trypan blue, was determined to filter out the possibility of death with aberrations in gene expression. Twitch and titanic stresses were implemented on the cells to test for their function. Measurements of the construct showed that the amount of developed force increases with the amount of stretching until the force plateaus. This force-length relationship observed parallels with that of known skeletal muscle. It is clear from their analyses that their construct mimics the basic phenotypes of adult skeletal muscle; however, their research is still incomplete. Further examinations on thickening the culture, contributions of extracellular matrix components, and hypertrophy of muscle stretching are needed until we can perform the first muscle transplant.

As the paper indicates, muscle loss has no answer, so I believe this study has a lot of potential in solving the problem. What I found most interesting is how simple the muscle construct was—a plate painted with stripes of collagen, seeded with isolated satellite cells. This comes to show that a project as a complex as skeletal muscle tissue engineering need not necessarily be carried out with an intricate protocol, but rather one that is well thoroughly thought-out. In addition, I realized how universal and widely-applicable the techniques we learned in class are. In fact, most of the techniques Yan et al. used to characterize their construct were introduced to us in class—immunochemistry, RT-PCR, Trypan blue counting. For my project, I hope to research on a topic related to skeletal muscle engineering, and I feel that this paper will serve as a good guideline.

Bioreactor-based bone tissue engineering: The influence of dynamic flow on osteoblast phenotypic expression and matrix mineralization

Currently, osteoblast cells have been successfully seeded and cultured into 3D ceramic and biodegradable polymer scaffolds for bone substitute replacement, but the cells’ ingrowth into the scaffolds have been limited, possibly due to limited nutrient diffusion (200-800μm in PLAGA foam) in static culture conditions. Some have tried bypassing this diffusion limitation by utilizing a rotating bioreactor, which has low shear, is 3D, and most importantly, has a high mass transfer rate, imparting dynamic culture conditions. However, the densities of conventional scaffolds are generally greater than the density of the surrounding medium, causing the scaffold to collide with the bioreactor walls due to centrifugal force, inducing cell damage and disrupting cell growth and mineral deposition.

To address these issues, the investigators developed a system that utilized 3D degradable microcarrier scaffolds and a rotating bioreactor. The 3D scaffolds were composed of different mixtures of heavier-than-water (HTW) and lighter-than-water (LTW) PLAGA microspheres that were sintered together. These scaffolds, because of their varying densities, were proposed to have different interactions with the bioreactor walls than conventional scaffolds. The scaffolds were seeded with rat calvarial osteoblastic cells, which had been isolated from 2-day-old Sprague Dawley rats via the enzymatic digestive method at a density of 2E4 cells/ mL.

The cell cultures were characterized for cell proliferation, differentiation, mineralized matrix synthesis, bone marker protein expression, and morphological analysis. After 7 days of culture, cells were shown to grow mainly on the surface of the static control scaffolds unlike the scaffolds cultured in the rotating bioreactor, where the cells seemed to proliferate preferentially on the interior, as seen by SEM (scanning electron microscopy) and MTT assays. The osteoblasts also retained their characteristics and activity, as determined by alkaline phosphatase activity, osteocalcin, osteopontin, mineralized matrix formation, and calcium quantification. These results, in conjunction with video visualization, demonstrate that the mixed scaffold does indeed decrease the amount of collisions with the reactor walls, allowing the cells to proliferate and grow normally. Furthermore, by controlling the level of fluid flow, enhanced differentiation and mineral deposition could be achieved.

I chose this paper because bioreactor tissue culture has both economical and research implications: not only does it allow for better cell growth penetration into a scaffold, but the method also allows for faster and possibly more affordable methods of producing tissue engineered replacements for not only bone, but other tissues as well.