Collagen shrinkage

Various phenomena may be suggested as giving rise to confusion as to the nature of fibers observed in connective tissue from pathological sources, or isolated tissue that has been treated chemically or with enzymes. The dramatic shrinkage that takes place when collagen fibers are denatured is... 

The collagen gelatin transformation in solution has been recognized as a reversible first-order phase transition, subject to the same physical laws which govern the crystalline amorphous phase transitions observed in systems of linear polymers. The direct relationship between the transition in solution and the well-known thermal shrinkage phenomenon exhibited by collagen fibers has also been established. 

The shrinkage temperature of collagen is very much affected by interaction with various small molecules, including electrolytes and nonelectrolytes, acids and bases, tanning agents, etc., and much interesting ex-... 

Relation between Imino Acid Content and Shrinkage and Denaturation Temperatures for Various Collagens... 

In particular, acetylation experiments seemed to lend strong support. Gustavson (1954) found that complete iV-acetylation of bovine collagen does not affect the thermal shrinkage temperature of the fibers. On the other hand, combined iV- and 0-acetylation (blocking both amino and hydroxy groups) lowered T, by approximately 20°C. 

To investigate this idea, Esipova (1957) and Doty and Nishihara (1958) examined the temperature at which solutions of various types of collagen were transformed to gelatin, and compared these measurements of T with thermal shrinkage temperatures obtained by Gustavson and others. 

The extensive and presumably closely related studies on the effects of various electrolytes, urea, and pH on the thermal shrinkage of collagen in the solid state have been comprehensively reviewed by Gustavson (1956). 

Flory (1956a,b) considered the shrinkage of collagen in terms of statistical mechanics and concluded that thermal shrinkage is a phase transition similar to melting. The elevation of the melting temperature with increasing cross-link density was treated theoretically. 

Gustavson (1962), recalling that the shrinkage temperature of collagen is unaltered by complete acetylation or deamination, points out that the cross-links in collagen cannot involve the e-amino groups of lysine and hydroxylysine. 

Shrinkage temperatures were determined as an indicator of the de-naturation temperature of the films. In all cases, crosslinking greatly increased shrinkage temperatures for each preparation. Thus, crosslinking stabilizes collagen molecules and retards denaturation (Table II). 

---