Effect of genipin collagen crosslinking on porcine corneas

Using genipin-crosslinked acellular porcine corneal stroma for cosmetic corneal lens implants

Acellular porcine corneal stroma (APCS) has been proven to maintain the matrix microenvironment and is therefore an ideal biomaterial for the repair and reconstruction of corneal stroma. This study aims to develop a method to prepare cosmetic corneal lens implants for leukoma using genipin-crosslinked APCS (Gc-APCS). The Gc-APCS was prepared from APCS immersed in 1.0% genipin aqueous solution (pH 5.5) for 4 h at 37 °C, followed by lyophilization at -10 °C. The color of the Gc-APCS gradually deepened to dark-blue. The degree of crosslinking was 45.7 ± 4.6%, measured by the decrease of basic and hydroxy amino acids. The porous structure and ultrastructure of collagenous lamellae were maintained, and the porosity and BET SSA were 72.7 ± 4.6% and 23.01 ± 3.45 m(2)/g, respectively. The Gc-APCS rehydrated to the physiological water content within 5 min and was highly resistant to collagenase digestion. There were no significant differences in the areal modulus and curvature variation between Gc-APCS and nature porcine cornea. The dark-blue pigments were stable to pH, light and implantation in vivo. Gc-APCS extracts had no inhibitory effects on the proliferation of keratocytes. Corneal neovascularization, graft degradation and corneal rejection were not observed within 6 months.

Differential cross-linking and radio-protective effects of genipin on mature bovine and human patella tendons

Gamma irradiation is a proven sterilization method, but is not widely used on allografts for anterior cruciate ligament reconstruction (e.g., patella tendon) due to radiation-induced decreases in mechanical strength. Addressing this drawback would improve the safety and supply of allografts to meet current and future demand. It was hypothesized that genipin-induced collagen cross-linking would increase the tensile modulus of patella tendon tissue such that 5 MRad gamma irradiation would not reduce the tissue mechanical strength below the original untreated values. Optimized genipin treatment increased the tensile modulus of bovine tendons by ~2.4-fold. After irradiation, genipin treated tissue did not significantly differ from native tissue, proving the hypothesis. Optimized genipin treatment of human tendons increased the tensile modulus by ~1.3-fold. After irradiation, both control and genipin-treated tissues possessed ~50-60% of their native tendon modulus, disproving the hypothesis. These results highlight possible age- and species- dependent effects of genipin cross-linking on tendon tissue. Cross-linking of human allografts may be beneficial only in younger donor tissues. Future research is warranted to better understand the mechanisms and applications of collagen cross-linking for clinical use.

Biomechanical and angiogenic properties of tissue-engineered rat trachea using genipin cross-linked decellularized tissue

In this study, the obtainment and characterization of decellularized rat tracheal grafts are described. The detergent-enzymatic method, already used to develop bioengineered pig and human trachea scaffolds, has been applied to rat tracheae in order to obtain airway grafts suitable to be used to improve our knowledge on the process of tissue-engineered airway transplantation and regeneration. The results demonstrated that, after 9 detergent-enzymatic cycles, almost complete decellularized tracheae, retaining the hierarchical and mechanical properties of the native tissues with strong in vivo angiogenic characteristics, could be obtained. Moreover, to improve the mechanical properties of decellularized tracheae, genipin is here considered as a naturally derived cross-linking agent. The results demonstrated that the treatment increased mechanical properties, in term of secant modulus, without neither altering the pro-angiogenic properties of decellularized airway matrices or eliciting an in vivo inflammatory response.

Effect of genipin crosslinking on the optical spectral properties and structures of collagen hydrogels

Genipin, a natural cross-linking reagent extracted from the fruits of Gardenia jasminoides, can be effectively employed in tissue engineering applications due to its low cytotoxicity and high biocompatibility. The cross-linking of collagen hydrogels with genipin was followed with one-photon fluorescence spectroscopy, second harmonic generation, fluorescence and transmission electron microscopy. The incubation with genipin induced strong auto-fluorescence within the collagen hydrogels. The fluorescence emission maximum of the fluorescent adducts formed by genipin exhibit a strong dependence on the excitation wavelength. The emission maximum is at 630 nm when we excite the cross-linked samples with 590 nm light and shifts to 462 nm when we use 400 nm light instead. The fluorescence imaging studies show that genipin induces formation of long aggregated fluorescent strands throughout the depth of samples. The second harmonic generation (SHG) imaging studies suggest that genipin partially disaggregates 10 μm "fiberlike" collagen structures because of the formation of these fluorescent cross-links. Transmission electron microscopy (TEM) studies reveal that genipin largely eliminates collagen's characteristic native fibrillar striations. Our study is the first one to nondestructively follow and identify the structure within collagen hydrogels in situ and to sample structures formed on both micro- and nanoscales. Our findings suggest that genipin cross-linking of collagen follows a complex mechanism and this compound modifies the structure within the collagen hydrogels in both micro- and nanoscale.

Limitations in bonding to dentin and experimental strategies to prevent bond degradation

The limited durability of resin-dentin bonds severely compromises the lifetime of tooth-colored restorations. Bond degradation occurs via hydrolysis of suboptimally polymerized hydrophilic resin components and degradation of water-rich, resin-sparse collagen matrices by matrix metalloproteinases (MMPs) and cysteine cathepsins. This review examined data generated over the past three years on five experimental strategies developed by different research groups for extending the longevity of resin-dentin bonds. They include: (1) increasing the degree of conversion and esterase resistance of hydrophilic adhesives; (2) the use of broad-spectrum inhibitors of collagenolytic enzymes, including novel inhibitor functional groups grafted to methacrylate resins monomers to produce anti-MMP adhesives; (3) the use of cross-linking agents for silencing the activities of MMP and cathepsins that irreversibly alter the 3-D structures of their catalytic/allosteric domains; (4) ethanol wet-bonding with hydrophobic resins to completely replace water from the extrafibrillar and intrafibrillar collagen compartments and immobilize the collagenolytic enzymes; and (5) biomimetic remineralization of the water-filled collagen matrix using analogs of matrix proteins to progressively replace water with intrafibrillar and extrafibrillar apatites to exclude exogenous collagenolytic enzymes and fossilize endogenous collagenolytic enzymes. A combination of several of these strategies should result in overcoming the critical barriers to progress currently encountered in dentin bonding.