In vitro surface characterization of a biological patch fixed with a naturally occurring crosslinking agent

Biocompatibility of NDGA-polymerized collagen fibers. II. Attachment, proliferation, and migration of tendon fibroblasts in vitro

The material properties of collagen fibers polymerized with nordihydroguaiaretic acid (NDGA) are equivalent to native tendon, suggesting that NDGA crosslinking may provide a viable approach to stabilizing collagenous materials for use in repairing ruptured, lacerated, or surgically transected fibrous tissues, such as tendons and ligaments (Koob & Hernandez, Biomaterials, in press). The present study evaluated the biocompatibility of these fibers with cultured bovine tendon fibroblasts. Fibroblast attachment, migration, and proliferation on NDGA-crosslinked materials were compared to those on prepolymerized type I tendon collagen constructs as well as on tissue-culture-treated plastic. Fibroblast attachment on NDGA-crosslinked collagen fibrils was equivalent to attachment on plates coated with collagen alone. Over a period of 8 days in culture, attached fibroblasts proliferated on NDGA-crosslinked collagen at a rate identical to that of fibroblasts attached to native collagen. In order for the biomaterial effectively to bridge gaps in fibrous tissues, fibroblasts must be able to migrate and replicate on the bridging fiber. Control and crosslinked fibers were inserted in calf tendon explants, with a portion of the fiber extending out of the sectioned end of the tendon. Explants were cultured for 9 weeks, and the number of cells was measured at weekly intervals. Cells appeared on the fibers after 1 week of culture. By 2 weeks, cells had colonized the entire fiber. The number of cells continued to increase throughout the 9 weeks in culture, forming a layer several cells thick. Histologic analysis indicated that the fibroblasts populating the fibers appeared to originate in the epitenon. There was no difference in the rate of fibroblast migration and replication, nor in the ultimate number of colonizing cells, between control collagen fibers and NDGA-crosslinked fibers. NDGA-crosslinked fibers may provide a means of bridging gaps in ruptured, lacerated, or surgically transected tendons by providing a mechanically competent scaffold on which tendon fibroblasts can migrate, attach, and proliferate.

Effects of heparin immobilization on the surface characteristics of a biological tissue fixed with a naturally occurring crosslinking agent (genipin): an in vitro study

Heparinized biomaterials have been used to manufacture blood-contacting prostheses. The present study was intended to characterize the surface properties of a genipin-fixed biological tissue immobilized with heparin using the methods of ionic binding (the /h-i tissue) or covalent binding via multi-point attachment (the /h-m tissue) or end-point attachment (the /h-e tissue). The surface characteristics of test tissues evaluated were water contact angle, surface tension, protein adsorption, platelet adhesion, and cellular compatibility. Nonheparinized and the glutaraldehyde-fixed counterparts were used as controls. It was found that immobilization of heparin on the glutaraldehyde- and genipin-fixed tissues increased their hydrophilicity and surface tension and suppressed their mole ratio of adsorbed fibrinogen to adsorbed albumin and the amount of platelets adhered. Among the heparinized tissues, the /h-m tissue was more hydrophobic and had a higher mole ratio of adsorbed fibrinogen to adsorbed albumin and a greater amount of platelets adhered than the /h-i and /h-e tissues. In general, the surface characteristics of the /h-i tissue were comparable to the /h-e tissue. However, it is known that the ionically immobilized heparin may be displaced from the surface by an ion-exchange mechanism when exposed to blood. There were no significant differences in hydrophilicity, surface tension, the mole ratio of adsorbed fibrinogen to adsorbed albumin, and the amount of platelet adhesion between the glutaraldehyde- and genipin-fixed tissues in comparison with their respective counterparts. However, the cellular compatibility of the genipin-fixed tissues with or without heparinization was significantly superior to its glutaraldehyde-fixed counterparts.