Cell Adhesion Strength to Bioceramics and Morphology
Cell Adhesion Strength to Bioceramics and Morphology
Tetsuya TATEISHI, Takashi USHIDA
Biomechanics Division, Mechanical Engineering Laboratory, Agency of Industrial
Science & Technology, Namiki 1-2, Tsukuba, Ibaraki 305, Japan
The authors of this paper set out to find and improve the characteristics of cell/biomaterial interfacing. To do this they setup a control of fibroblast cells on a standard alumina cell culturing plate, and compared the adhesion properties to an alumnia cell culture plate coated with fibronectin. the two cultures were tested under conditions of vertical stress in hopes that the results will yield information as to better adhere cells to biomaterials.
The specimens were put under vertical load by attaching the culture upside down and attaching to a centrifuge to produce a vertical acceleration. The cultures were then imaged to see the number of lost cells and area. The results found that the fibronectin coated plates had a larger adhesion area( 1200 microns squared vs 500 microns squared). This is thought to correlate with higher strength because cells adhere to material surfaces with adhesion plaques where fibronectin receptors interact with fibronectin of the surfaces. So if adhesion area correlates to number of plaques this would mean a stronger bond. The results of the experiment supported this theory. The mesured rate of cell peeling was higher on the alumina plate( 80% as apposed to 50% of fibronectin coated).
A mathematical model was used to predict cell peeling by characterizing the rupture process of fibronecting receptor bonds. The results of the model gave a distribution that was very close to the results shown in the non coated cell plate.
Significance:
Many applications of bioengineering involve in vitro implementation of devices. The common problem with these devices is their incompatibility with the cells around them. An ability to vary the inter-material properties would be valuable in implants such as an artificial hip joint. In a hip joint the stem that is implanted into the bone needs to be a place of high friction so the implant doesn’t slip. On the other end, the surface needs to have a minute friction coefficient so that there is no rubbing between the prosthesis and the pelvis. To be able to vary the friction on cell/material interfaces would allow for a more viable and longer lasting prognosis.
7 comments:
I have three questions regarding this research:
1. First, you mentioned the importance of this research in applications such as implants, noting the impact of friction on an effective and safe articial hip joint. My concern is that in these settings, the stress typically experienced by cells at the interface is typically a combination of normal and shear stress (and indeed, friction typically results in shear stress) whereas the article only covered the effects of normal ("vertical") stress. What impact do you think shear stress might have on cells?
2. The paper noted that 6 hours after seeding each plate with cells, the cells of the fibronectin plate had an average adhesion surface 3 times greater than the alumina plate. Combined with the fact that cells of the fibronectin plate also were less likely to be pulled off by centrifugation, I am wondering what the exact function the fibronectin might be? The authors mentioned the significance of the fibronectin-receptor bonds in cell peeling, but did they also account for the increased adhesion area? In other words, do you think fibronectin primarily served as a signal to increase adhesion area or do you think it also served as a structural element to resist peeling?
3. Clearly, there are many more cell types and many more surfaces than presented here. Do you think this finding (and specifically, the mathematical model) could be easily modified to explain this type of cell behavior in general?
In your paper, you said that "the specimens were put under vertical load by attaching the culture upside down and attaching to a centrifuge to produce a vertical acceleration. The cultures were then imaged to see the number of lost cells and area." Did the researcher have any other control or employ any other research results to make sure that the lost of cells were totally due to the load and acceleration? Also how did they know if the cells detached becuase of the applied load or they were killed by the load?
You mention that a viable application is that of implants, especially that of 'slipping.' The tests performed on the sample cells were primarily vertical loads, which correspond to compressive forces (normal forces) instead of slipping/frictional forces (shear forces). If the fibronectin-coated cells are believed to have stronger bonds due to greater cell adhesion, do you think this also applies to shear stresses?
I'm also a little confused by the described mathematical model. From the way its worded, it seems the cell peeling distribution was very similar for the non-coated and the coated plates. This is counter-intuitive to the experimental results of fibronectin-coated cells having greater adhesion properties. Could you explain this?
answers to comments as of dec 7 2008
spectator
1. in this experiment the test for vertical stress was used to estimate the amount of connectivity formed between the cells and the material. the estimation was based on a mathamatical model and found that there was higher connectivity. i assumed this conectivity will result allow higher stresses in the x z and theta directions. though it would be interesting further work to see if the connectivity is only related to vertical stress.
2
because there was a larger adhesion area and a larger resistance to peeling i think fibronectin has a role in both. the cells have better communication between fibronectin than they do with alumina. this allows for more rapid connectivity with the material. faster connectivity could result in larger area and more connective plates. the greater number of plates would result in a larger resistance to peeling.
3
the mathematical model is an applied model from defect stress growth. this could be applied to any cell type as long as it can be assumed that there are bonding units that provide the connective integrity.
ye Qiu
it is possible that peeling could have been due to outside factors other than the load. the only control mentioned in the paper is the alumnia control. the assumption being that (since both cultures were treated equally) the only difference in the cell peeling would be the fibroconnectin. this doesnt account for other phenomena that might be happening. you bring up a good point, it might be possible that fibroconnectin creates greater resistance to death-by-load.
shyam
for questions regardign shear see spectator 1
the mathematical model is a model of defect stress prorogation. the difference between the fibroconnectin and the alumina is represented in the model by a variance of the initial defect function (c). for fibroconnectin the c value was set to zero changing the solution to the model and resulting in a lower rate of pealing (beta).
Could you explain or go into more detail about the experimental set-up. If the cultures were put upside-down, were they completely without media? Can you account for the cells that might have "let go" because of the lack of media present? Did their controls take these into account?
Did you feel that their mathematical model was accurate? Was it completely based off of theory and had a lot of assumptions, or was it a computer simulation? Is this model applicable to engineers would like to create that implant?
You mentioned bioincompatibility in implants and a huge drawback of alumina is that the body recognize it as a foreign material (as oppose to, say, titanium), and coats it with problematic non-fibrous tissues.
Having said that, do you think fibronectin-coating will be just as effective on more bio-inert materials like metals or other ceramics, like dental porcelain?
My question concerns the value of vertical stresses on cells. Do the connections vary in strength between direct stress and shear stress?
Also, many/most biological devices adsorb proteins naturally and the composition of the adsorbed surface changes with time and the proteins present in the extracellular matrix/fluid. Are there any similar experiments with other proteins like vitronectin, thrombin etc? Also is the model of fibronectin attachment predicated on integrin attachement or something else?
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