Crosslinking of discrete self‐assembled collagen threads: Effects on mechanical strength and cell–matrix interactions

Abstract

Bundles of threads extruded from type I collagen have been researched extensively as scaffolds to promote the repair and regeneration of torn tendons and ligaments. The success of these scaffolds has been limited by insufficient tissue ingrowth from the wound margin, which may be inhibited by the chemical or physical crosslinking treatment used to increase the mechanical properties and decrease the degradation rate of these scaffolds. Recently, self-assembled collagen threads extruded from solutions of type I collagen molecules were shown to possess ultimate tensile strengths and structural properties comparable to native tendon fibers; however the tissue response to these threads has yet to be determined. The goal of this study was to investigate the effects of various crosslinking techniques on the mechanical properties as well as the in vitro rate of new tissue ingrowth on these threads. Our findings indicate that the physical crosslinking techniques, dehydrothermal (DHT) or ultraviolet light (UV), most significantly improve the mechanical strengths of the threads, but most significantly decrease the rate of cell migration. In contrast, carbodiimide (EDC) crosslinking achieved sub-optimal strength generation, but demonstrated improved cell migration rates. Future studies will investigate the design of threads with surface biochemistries that maximize tissue ingrowth while maintaining the mechanical stability of the scaffold.

Exogenous collagen cross‐linking recovers tendon functional integrity in an experimental model of partial tear

“…The present study tested these hypotheses using three cross-linking agents, genipin (GP), methylglyoxal (MG), and ultra-violet irradiation with photosensitizer riboflavin (UV). These agents were chosen due to their demonstrated potential to cross-link other collagenous tissues, [6][7][8]10,11 their potential to diffuse into tissue, 10 and their reported low toxicity. 9 Our experiments confirmed that GP, MG, and UV augment tissue mechanics on the fascicle level in a rat tail tendon model (RTTF).…”

“…For instance, collagen cross-linking induced by irradiation with ultra-violet (UV) light has been reported in augmenting biomechanical properties of self-assembled collagen threads. 6 A similar procedure involving UV stiffening of the sclera has been clinically applied in patients for treatment of keratokonus. 7 Genipin (GP), a naturally occurring cross-linker derived from the gardenia fruit used in traditional Chinese medicine has successfully been applied to improve intervertebral disc strength and functional integrity in experimental models of disc degeneration.…”

Combined Effects of Scaffold Stiffening and Mechanical Preconditioning Cycles on Construct Biomechanics, Gene Expression, and Tendon Repair Biomechanics

“…10 Under appropriate conditions, dehydrothermal (DHT) or ultraviolet light physical crosslinking can significantly improve scaffold strength without introducing cytotoxic chemicals as occurs with glutaraldehyde chemical crosslinking. 11,12 For example, Wang et al reported that exposing reconstituted collagen fibers to 5 days of DHT crosslinking at elevated temperatures increased tensile strength and modulus values. 13 Initial improvements in the structural and material properties of collagen fibers (e.g., by DHT crosslinking) will be critical to developing biodegradable materials that promote healing of orthopedic soft tissues.…”

“…[10][11][12][13][30][31][32] If not applied appropriately, DHT crosslinking is well known to change the chemical composition of collagen-based membranes.…”

“…31 DHT crosslinking has also been postulated to significantly decrease the rate of cell migration by masking the integrin binding sites that promote cellular attachment. 11,32 One or more of these crosslinking-induced phenomena could have adversely affected repair tissue, while at the same time improved the construct's in vitro properties compared to non-ADHT-crosslinked constructs.…”