Research On Artificial Cornea Of N-HA/hydrogel Composite

Corneal blindness caused by herpetic disease, acid or alkali burns and various diseases such as rheumatoid arthritis, pemphigoid and Stevens Johnson's syndrome cannot be treated with corneal transplantation. However, the vision can be restored with a clear optic of artificial cornea. Unfortunately, the use of artificial cornea is associated with a significant rate of complications. Most artificial corneas failed because of poor interaction between the artificial implant and host cornea, and poor attachment of the transparent center to the rim. These problems have led to the search for more suitable materials for the supporting rim, which should be porous, long-term biocompatibility and hydrophilicity in the eye to encourage tissue growth and the penetration of body fluids. And that also had led to the search for how to improve the adhesive strength between the rim and the transparent center.HA is the main component of the bone and teeth. HA has long-term biocompatibility and favorable interaction with soft tissue and bone .Because porous HA is hydrophobilic, brittle and difficult to be prepared and sutured, the use of hybrid materials consisted of HA and polymer may be a good choice.The research is engaged in developing an improved artificial cornea consisting of a porous nano-hydroxyapatite / poly(vinyl alcohol) hydrogel (n-HA/PVA-H) skirt and a transparent center of poly(vinyl alcohol) hydrogel (PVA-H). PVA-H has high strength, elasticity and high water content. PVA-H has been employed in some biomedical applications, especially as the core of artificial cornea. Porous n-HA/PVA-H skirt is favorable to improve the biocompatibility, hydrophilicity and flexibility to avoid complications. The tight attachment of the skirt to the core was achieved through the inter-penetration between them. The research includes in the following aspects:1. PVA was added into n-HA crystal slurry with heating and stirring for 6-8 hrs to get the n-HA and PVA composite solution. The n-HA /PVA-H are prepared by exposing n-HA and PVA composite solutions to repeated cycles of freezing at -20 "C and thawing at room temperature for crystallization and cross-linking of PVA molecules. The obtained composite gel was milk white. The n-HA: PVA: H2O ratios (wt.%) of prepared composites can be changed. Fourier transform infrared absorption spectra (FT-IR), transmission electron microscopy(TEM), x-ray diffraction (XRD), thermogravimetric analysis (TG) and burning test were used to test the physical and chemical characteristics of the composite. Chemical binding between inorganic n-HA and organic PVA was investigated and discussed. The results showed that the composite had good thermal stability and homogeneity. The n-HA crystals were uniformly distributed in the polymer matrix.2. Porous n-HA/PVA hydrogels with different n-HA compositions were made by solution-blending and particulate-leaching method. The porous hydrogels were investigated by scanning electron microscopy (SEM), image analysis system, infrared absorption spectra and transmission electron microscopy. And the water contents of porous hydrogels were tested. The porous hydrogel exhibited open-cellular pore structures. Chemical binding between inorganic n-HA and polyvinyl alcohol was investigated and discussed. The results showed that the n-HA crystals were uniformly distributed in the polymer matrix and the water contents of porous hydrogels were about 80%. The novel porous hydrogel could be used as the skirt of artificial cornea.3.The biological evaluation of n-HA/PVA composite has been done in vivo and in vitro. The results indicate that the composite has not hemolysis, toxic, excite, heredity toxic, stimulation and hypersuscepte. And the composite has nonegative tissue responses after implanted intramuscularly for 180 days. The result demonstrates that the n-HA/PVA composite has good compatibility. The composite is suitable for the artificial cornea skirt.4.An artificial cornea consisting of a porous n-HA/PVA-H skirt and a transparent center PVA-H was prepared. The n-HA/PVA-H skirt was homogeneously porous and the pores were interconnected. Inter-penetrating network was observed along the interface between the core and the skirt. The artificial corneas were implanted in eyes of rabbit. The corneal tissues were evaluated histologically. The results showed that good biocompatibility and interlocking had happened between artificial cornea and host eye tissues. This novel cornea has good perspective for clinical applications.