Bioengineered collagen composite materials as implantable artificial corneas
Creators: name: Rafat, Mehrdad
Publisher: name: Université d'Ottawa / University of Ottawa
Year: 2007
Subjects: subject: Engineering, Biomedical.
subject: Engineering, Chemical.

description: The clinical need for an alternative to donor corneal tissue has encouraged much interest in recent years. The development of a reconstructed human cornea is necessary in view of the world-wide shortage of donors, the increasing risk of transmissible diseases, the widespread use of corrective surgery, which renders corneas unsuitable for grafting, and the severe limitations of currently available synthetic polymer-based artificial corneas. The development of a reconstructed human cornea is vital and will represent a real breakthrough, allowing diseased or damaged corneas to be replaced by tissue-engineered corneal implants that resemble in all respects their natural counterparts. An artificial cornea whether it is a synthetic keratoprosthesis or bio-engineered must fulfill the key functions of the native cornea including transparency, strength, elasticity, biocompatibility, and non-immunogenic. A wide range of implants and biomedical devices have been developed in an attempt to correct corneal blindness. Limitation of existing biomaterials is evident when reviewing keratoprosthesis surgery complications, e.g., infection, intraocular inflammation, retro corneal membrane formation, insufficient interface seal thus epithelial cells down growth, and glaucoma, as well as issues involved with bio-engineered materials such as inadequate mechanical strength and elasticity for implantation, and rapid biodegradation. My main objective was to address these issues by reconstructing an implantable bio-engineered human cornea with proper bulk and surface properties. More specifically, one of the aims was to develop a well-defined slowly-degradable corneal material with sufficient mechanical elasticity and strength, high optical transparency, and good biocompatibility that allows regeneration of corneal epithelial, stromal, and nerve cells. Another aim was to engineer material's surfaces to inhibit endothelial cell attachment onto the posterior surface while enhancing epithelial cell attachment onto the anterior one using surface modification techniques such as radio frequency (RF) plasma. The originality of this study lies in the use of systematic multivariate experimental designs (MED) combined with a novel bio-inspired material development approach to construct hybrid polymer networks (HPN) for artificial cornea application. Material development was carried out by crosslinking of bio-functional natural polymers, e.g., collagen and chitosan with a hybrid amalgamation of synthetic bio-inert molecules, e.g., poly (ethylene glycol) dibutyraldehyde (PEG-DBA), 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC), and N-hydroxysuccinimide (NHS). HPNs were designed and fabricated with the aid of a 23 full factorial experimental design (FED) merged with a response surface design (RSD). The combined FED/RSD approach allowed us to efficiently evaluate the key experimental factors (e.g., molar ratios of the components), their interactions and their impacts on key responses (mechanical, optical, and biological properties), and to screen and develop optimum material formulations. This strategy resulted in a synergistic effect on physical and biological properties of the materials. It became possible to simultaneously enhance mechanical strength, and elasticity while retaining biological characteristics and optical clarity of the matrices. The select HPN materials were implanted into pig corneas for 12 months and demonstrated successful in vivo regeneration of the host corneal epithelium, stroma, and nerves with seamless host-graft integration. In addition to studies focused on bulk design of corneal materials, design principles for the engineering of surfaces that direct epithelial and endothelial cell adhesion to the corneal implants were investigated and developed. The designs contributed to the development of epithelial cell-adhering and endothelial cell-resistance surfaces. Attempts were made to augment attachment of epithelial cells to the surfaces of corneal materials that were crosslinked with glutaraldehyde (GA) and glutaraldehyde-polyethylene oxide dialdehyde (PEO-DA). Argon plasma treatment of corneal surfaces at a RF power of 100 Watts for 30 minutes enhanced the cell attachment, surface hydrophilicity, and roughness. Prevention of endothelial cell migration onto the posterior surface of HPN corneal implants was achieved using a NH3 plasma-assisted surface modification technique. Briefly, hydrogels were subjected to ammonia plasma functionalization followed by grafting of alginate macromolecules to the target surface. Treated hydrogel surfaces showed observable decreases in endothelial cell attachment. The decrease in cell adhesion was dependant upon the concentration of alginate and plasma radio frequency (RF) power. High concentrations of alginate of 5% (w/v) and high RF power of 100 W produced surfaces with minimal cell attachment. I demonstrated that alliance of MED with material and surface sciences played a significant role in development of novel materials that might lay a foundation for a new generation of implantable biomaterials that could be tailor-made into cornea or other tissue/organ transplants such as skin, crystalline lens, liver, and heart.