Effect of microgravity, temperature, and concentration on fibrin and collagen assembly.

In purified form collagen and fibrin can be processed into gel-like matrices of interconnecting fibers. The microscopic structure of materials produced from these macromolecules is critical to their utility as biomaterials. Varying the conditions of the assembly environment allows for the production of a wide range of morphologies. In this study, changes in gravity, temperature, and concentration were examined. Contrary to protein crystal growth studies which indicate substantial increases in organization and size in microgravity, the gravitational environment had no repeatable effect on collagen and fibrin fiber diameters and matrix porosity. However, fibrin gels formed in microgravity appeared more homogeneous than ground samples. Changes in temperature and concentration of both protein and buffer had substantial effects on fiber diameters and material porosity for both collagen and fibrin. Temperature experiments were performed over the range 23.8 to 39 degrees C for fibrin and 22 to 33 degrees C for collagen. Thrombin concentration was varied from 0.02 to 0.10 units/ml for fibrin experiments and buffer concentration was varied by means of a dialysis membrane for collagen experiments. Consequently, the temperature and concentration controls developed for flight experiments are being considered for their potential in developing fibrin and collagen based materials with well-defined microscopic structures. The increased homogeneity of fibrin gels produced in microgravity suggests the possibility of using this environment for the production of optimal biomaterials.

Effect of gravity and diffusion interface proximity on the morphology of collagen gels.

Collagen solutions (0.25% w/v) were polymerized in microgravity (STS-77, 10 days) along with simultaneous ground controls. Assembly conditions were achieved by the passage of buffer ions across a dialysis membrane into a reaction chamber containing the dissolved collagen. The gels were analyzed macroscopically and microscopically to assess the influence of gravity and the oriented diffusion of buffer ions on the resulting product. Double-blind rankings based on visual observation of the gels established that all of the flight gels (n = 8) were more uniform in appearance than all of the ground gels (n = 6). Photography using side illumination of the gels revealed the more granular appearance of the ground gels relative to the highly uniform appearance of the flight gels. Scanning electron microscopy established this difference at the microscopic level. Proximity to the dialysis interface and the presence or absence of gravity were both found to control the porosity and uniformity of the matrix.

Collagenase digestion of bone fragments in microgravity.

The effect of a quiescent microgravity fluid environment on the activity of collagenase directed at demineralized bone fragments was investigated over a period of 10 days. Enzyme treatment resulted in greater mass loss in microgravity, with nearly three times the loss of mass during Space Shuttle mission STS-62 compared to the stationary ground control. Clinorotation enhanced the loss of mass relative to a stationary control, but this increase was still significantly less than the increase with exposure to microgravity. This suggests the detrimental influence of turbulence on the enzyme function and the benefit of using microgravity to provide both low turbulence and uniformity of unequally dense materials within the reaction chamber. The results are considered for their general applicability to a variety of bioprocessing applications that may be enhanced in microgravity.