Tissue engineered autologous bladders for patients needing cystoplasty
http://www.thelancet.com/journals/lancet/article/PIIS0140-6736(06)68438-9/fulltext
Anthony Atala, Stuart B. Bauer, Shay Soker, James J. Yoo, and Alan B. Retik
The Lancet, Volume 367, Issue 9518, Pages 1241 - 1246, 15 April 2006
Introduction and Background
Cystoplasty is a medical procedure used to surgically repair aspects of the bladder. It is commonly needed when medication is not enough to maintain organ function. Patients with myelomeningocele often require cystoplasty, as they experience frequent urination as often as every half hour. Traditionally, repair has been achieved by using two sources. Synthetic sources such as polyvinyl sponge, Teflon, collagen matrices, and, and biological sources such as the skin, omentum, placenta, and small intestines have been tested for use in cystoplasty. However, tissue grafts have often failed due to mechanical, structural, functional, and biocompatibility issues. Atala and his group have been working on a new system of reconstructing bladder tissue using the patient’s own cells. Their technique involves seeding scaffold with urothelial (bladder) and smooth muscle cells, incubating the construct in vitro, and implanting the organ into the patient.
Materials and Methods
The study and surgical technique was performed on 7 patients (range 4-19 years old) with severe bladder complications due to myelomeningocele. For each patient, urothelial and muscle cell samples were taken and cultured in vitro using standard techniques. Two types of scaffolds were made, one comprised of a decellularized bladder submucosa and the other consisting of a collagen-PGA composite. The bladder scaffolds were custom-made to match the sizes of the patient’s original organs, all with thickness at around 2 mm. The scaffolds were seeded with about 700 x 106 cells of each type. The exterior was seeded first with muscle cells, incubated for 1 hour, and submerged in media that was changed every 12 hours. Next, the interior was seeded with urothelial cells, and the entire construct was incubated in media for 3-4 days when the surgery began.
During the procedure, the patients’ bladders were cut open, and the scaffold was oriented and attached in its place with fibrin glue and polyglycolic sutures. Some patients also had an omental wrap surrounding the construct. Urinary catheters were inserted during the surgery to allow for urine drainage during post-operative recovery. After a three week period, the bladder was conditioned by a cyclic process of clamping and draining through the catheters. Post-operative tests were done that included histological staining of the bladder, serum analyses, ultrasounds, leak point pressures, cystograms, and other urodymanic tests.
Results and Discussion
All the patients tolerated the procedure with no significant complications. Overall, bladder compliance and maximum leak-point pressures (indicating storage capacity) increased, showing a significant improvement with the engineered bladders. Histological tests confirmed proper growth of urothelial and muscle cells. The group found that the optimal technique was the use of a collagen-PGA construct that was inserted with an omental covering.
Critique
This study shows great promise in tissue engineering. The group has been testing tissue regeneration from autologous sources for quite a while, and the success of the group’s technique on human patients yields major implications for the future of tissue engineering. The relatively simple structure of the bladder even allowed them to tackle the challenge at an organ-level, but dealing with other organs will surely be more challenging.
The paper introduced many variables that were monitored, like the use of decellularized bladder submucosa versus a collagen-PGA scaffold, the effect of an omental wrap on bladder function, and the time intervals for cyclic conditioning of the engineered bladder. Performed with only 7 patients, there should be more replicates to fully determine which combination of techniques is optimal for bladder reconstruction. Also, although it showed an improvement in compliance and leak-point pressures, it fails to reference the ideal values that are typical for fully functional bladders. Moreover, the paper did not strongly address long-term factors related to the procedure. For example, it failed to mention the degradation behavior of the collagen-PGA scaffold, nor does it analyze the appropriate vascularization of the system. Thus, I believe more tests can be done to fully analyze the technique of autologous bladder reconstruction.
12 comments:
What an interesting paper! The results are really impressive and applicable to so many different conditions that result in bladder deterioration.
I would be interested to see what particular variables were tested in each of the seven individuals who received implants. Most noticeably, I saw that the scaffold used varied and was wondering if factors other than bladder size were used to determine if a synthetic scaffold versus native one was used for a particular patient. I also think it would be fascinating to see how long these implants were viable and how they impacted each patient's quality of life.
I would also be interested to see how exactly they set up their bioreactor to get the muscle cells to align properly. I understand that the people who carried out the protocol were intentional in their placement of cells, but was the scaffold really enough to guide them to populate the correct local regions? It would also be neat to see why the authors seeded as many cells as they did and where the cells came from. A sense of time frame would play into this as self cells would take longer to acquire and populate the scaffold than cells taken from a donor and seeded on a scaffold to form a bladder that was just waiting for implantation. To investigate these questions and other variables I agree that more trials are needed.
Also, some pictures would have been nice.
I found this paper to be very interesting as it shows the future potential that tissue engineering can have on patients with significant complications. I thought the design idea was straightforward and easy to understand, with the authors comparing the performance of two different scaffolds with and without an omental wrap. Looking over the results, however, it seems that there was a significant variation in the improvements for each patient. Furthermore, the capacity of the bladder decreases over time after the operation has been completed. It would be interesting to research the causes for the changes in capacity, leak point pressure, and compliance over time. I think it would also be helpful for the authors to survey the patients and correlate their subjective bladder function with the results they obtained in the paper. As the authors mentioned, there needs to be longer studies of these tissue-engineered bladders in order to ensure safety and consistency.
This paper was interesting to read and it made me think of a few things. First, the paper mentioned that they seeded the scaffold with urothelial cells and smooth muscle cells by using a particular concentration, but I was wondering how many cells actually get seeded onto the scaffold. Also, what would be the relative ratio of the smooth muscle cells to the urothelial cells and could changing the ratio affect results? In addition, perhaps playing around with the stiffness of the scaffold might help improve the mechanical properties of the engineered bladder. I think these questions might be interesting to explore in future work.
I was impressed by the consideration of the author's part to be able to scaffold both bladder urothelial and muscle cells. However, the article did not seem to explicitly address the function of the muscle cells included in the bladder scaffold. The smooth muscle layer evidently lends strength to the urothelial layer, allowing for a stronger bladder. What I'm wondering is whether the researchers intend to /are capable of possibly reattaching the muscle layer to preexisting surrounding nerves, and possibly restore a greater degree of function to the bladder. It seems the scaffolding procedure is not yet complex enough to allow for this.
Thanks for posting an interesting paper. It was summarized well. It made me think more about the possible future of tissue engineering. In reading the paper, I had a few considerations from past papers I have read. As this study was applied at the organ level, I wonder if there are any possible uses for other organs with "simple" geometries currently, maybe like the vasculature. Also, how did they determine which type of scaffold was used in the study, or they both used together to form the final tissue product? And lastly, how did they determine the orientation at which the graft would be attached?
This paper seems quite interesting and very applicable to the medical field. However, I wasn't able to open the link to the actual paper and have a few questions that may or may not have been addressed. How exactly were the scaffolds fabricated, and how were they customized to fit into the bladders of each individual patients? Did they use any quantitative methods to evaluate the extent of bladder function recovery? As mentioned in previous posts, I would like to see the results from continued monitoring of the patients beyond the timeframe of the experiments to determine any changes in behavior or properties of the scaffold
Great summary James! Your ability to hash out the main concepts without taking away from the original paper is commendable. I find the results of this study to be the stepping stones for relevant, future tissue engineering applications regarding organ regeneration and repair. Because the study only uses young patients, I wonder if this design can be applied to the elderly population, when bladder muscles become weakened. Also, I agree with the previous posts that a larger sample size can illuminate which scaffolding technique is optimal (or perhaps it really depends on the existing conditions of the patient.) I believe a future application for this study would be to investigate the long-term consequences of engineered bladders.
As previously mentioned by my peers, this article is one of the more interesting ones. I am surprised some of the materials you mentioned that they have previously used for the cystoplasty procedure include Teflon – a material I have only associated with cooking utensils and not as a biomaterial.
I noticed you specifically mention patients with myelomeningocele requiring this procedure, but myelomeningocele is a rare birth defect while I would assume the new technique of seeding scaffold with bladder and smooth muscle cells has a larger impact. Is there a reason myelomeningocele is specifically mentioned – maybe this procedure is specific only to those with that condition?
This is a really interesting paper to read and it point out a good artificial bladder apporach. The use of the decellularized bladder submucosa and collagen-PGA composite scaffold for seeding urothelial and muscle cell avoids the side effects caused by the use of small intestine tissue in the tranditional method. However in the result only the leak point pressure was presented. I am just wondering what is the degradation rate of the scaffold and what is the cell distribution, especially for the muscle in the artificial bladder.
I think this is an interesting paper and it is promising that the patients showed no complications. However, the very small sample size (N=7) means that a larger-scale study must be performed to accurately access the viability of this approach. Additionally, the procedure was performed on patients ranging from 4-19 years old. I wonder if the properties of urothelial and muscle cells change with aid and if the scientists addressed or are planning to address this by varying their approach? Just something they might consider in the future, but so far the results appear promising.
The authors did not address the nature of muscle cell seeding and growth; from previous studies I have seen, there have been efforts to make bioreactors that cyclic-ly strain muscle-seeded scaffolds to condition the cells for proper growth. In this case, the authors may have addressed muscle-cell conditioning post-operatively: they used a technique for cycling the bladder by opening and closing catheters periodically to allow the bladder to expand/contract.
I think changing the relative ratio of muscle cells / urothelial cells would be something good to look at. However, it would be better to look into animal models, unlike the human trials in this paper. Atala's group (Yoo et al., 1998) has initially used beagle dogs in their studies before moving on to human tests.
The bladders were fabricated from standard techniques for synthesizing a layer of collagen-PGA, and the layer was woven into a ball-shape with sutures. The size of the bladder constructs were matched with CT scans of the patients bladders.
The researchers quantified values like bladder compliance and leak-point pressure (the pressure at which the bladder releases fluid), as a means for characterizing bladder performance in vivo.
It's interesting how they specifically targeted myelomeningocele. I'm sure that the procedure could have been done on other similar conditions, but maybe testing only on these types of patients allowed for sufficient comparisons among the results. It seems that this study was extremely specific to a rare defect, but it lays the foundation for future organ-level work, especially since it is the first study of its kind to complete human trials.
On a final note: the results that the paper presents seem very promising with little to no negative comments; would it be possible for even normal people with over-active bladders to get the procedure done? Personally, I would love to have a large bladder with high leak-point pressure, compliance, and capacity. Growing whole organs might be something we see in the near future...
I liked this paper, especially because the result was very positive with various supportive evidences. However, I want to know more about the mechanics to build the structure. Was there a bladder-shaped structure made of collagen, and the patient's tissues were put onto the structure for better suturing? What was the scaffold made of?
Just an FYI: The images cannot be enlarged, and the first link was not accessible. I couldn't figure out how to look at the original article through the second link. (I could still see the summary though)
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