Cross-linking of human amniotic membrane by glutaraldehyde.

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Abstract

The transplantation of cryopreserved human amniotic membrane has been introduced recently for the reconstruction of the ocular surface. However, in some diseases the transplant usually dissolves rather quickly and early detachment may occur. Therefore, we tried to stabilize the amniotic transplant by applying glutaraldehyde for collagen cross-linking of the membrane.

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Influence of different crosslinking treatments on the physical properties of collagen membranes.

V Charulatha (2003)

The physical properties of collagen-based biomaterials are profoundly influenced by the method and extent of crosslinking. In this study, the influence of various crosslinking treatments on the physical properties of reconstituted collagen membranes was assessed. Five crosslinking agents viz., GTA, DMS, DTBP, a combination of DMS and GTA and acyl azide method were used to stabilize collagen matrices. Crosslinking density, swelling ratio, thermo-mechanical properties, stress-strain characteristics and resistance to collagenase digestion were determined to evaluate the physical properties of crosslinked matrices. GTA treatment induced the maximum number of crosslinks (13) while DMS treatment induced the minimum (7). Of the two diimidoesters (DMS and DTBP), DTBP was a more effective crosslinking agent due to the presence of disulphide bonds in the DTBP crosslinks. T(s) for DTBP and DMS crosslinked collagen were 80 degrees C and 70 degrees C, and their HIT values were 5.4 and 2.85MN/m(2), respectively. Low concentration of GTA (0.01%) increased the crosslinking density of an already crosslinked matrix (DMS treated matrix) from 7 to 12. Lowest fracture energy was observed for the acyl azide treated matrix (0.61MJ/m(3)) while the highest was observed for the GTA treated matrix (1.97MJ/m(3)). The tensile strength of GTA treated matrix was maximum (12.4MPa) and that of acyl azide treated matrix was minimum (7.2MPa). GTA, DTBP and acyl azide treated matrices were equally resistant to collagenase degradation with approximately 6% solubilization after 5h while the DMS treated was least stable with 52.4% solubilization after the same time period. The spatial orientation of amino acid side chain residues on collagen plays an important role in determining the crosslinking density and consequent physical properties of the collagen matrix.

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Effect of physical crosslinking methods on collagen-fiber durability in proteolytic solutions.

K S Weadock, E Miller, E L Keuffel … (1996)

We previously demonstrated that ultraviolet (UV) or dehydrothermal (DHT) crosslinking partially denatured fibers extruded from an insoluble type I collagen dispersion. In this study denaturation effects were evaluated by measuring collagen-fiber sensitivity to trypsin. Shrinkage-temperature measurements and sensitivity to collagenase served as indices of crosslinking. UV or DHT crosslinking increased the collagen-fiber shrinkage temperature, resistance to degradation in collagenase, and durability under load in collagenase. However, in trypsin solutions, solubility was significantly increased for UV (approximately 11%) or DHT (approximately 15%) crosslinked fibers compared with uncrosslinked fibers (approximately 4%). Size-exclusion chromatography indicated that no intact collagen alpha-chains were present in the soluble fraction of fibers exposed to trypsin (MW < 1 kD). Interestingly, UV-crosslinked collagen fibers remained intact an order of magnitude longer (4840 +/- 739 min) than DHT-crosslinked (473 +/- 39 min) or uncrosslinked (108 +/- 53 min) fibers when placed under load in trypsin solutions. These data indicate that mechanical loading during incubation in a trypsin solution measures denaturation effects not detected by the trypsin-solubility assay. Our results suggest that DHT-crosslinked collagen fibers should not be used as load-bearing implants. UV-crosslinked fibers may retain more native structure and should exhibit greater resistance to nonspecific proteases in vivo.