Ultrapure poly(viny1 alcohol) hydrogels with mucoadhesive drug delivery characteristics

Poly(viny1 alcohol) (PVA) hydrogels were prepared by treating 15 or 20% aqueous PVA solutions to repeated cycles of freezing for 6 or 12 h at 20°C and thawing for 2 h at 25°C. The resulting gels did not contain any leachable toxic crosslinking agents or other residues. Their adhesive characteristics were examined using tensile experiments in contact with bovine submaxillary mucin. As the number of freezing/thawing cycles increased, the work of fracture (detachment) decreased due to the increase in the PVA degree of crystallinity. The PVA gels prepared from the 20 wt.% solution and exposed to two freezing/thawing cycles exhibited the largest work of adhesion. Surface contact angle measurements of the PVA gel in contact with water were used to evaluate their wettability. As the number of freezing/thawing cycles was increased and the degree of crystallinity increased, there was a decrease in the contact angle. The degree of crystallinity of PVA gels was determined by comparing the heat required to melt a PVA sample to the heat required to melt a 100% crystalline sample. The average degree of crystallinity of PVA samples prepared from 20 wt.% solutions was 19.3% on a dry basis. Oxprenolol and theophylline delivery studies were conducted using PVA samples prepared from a 20 wt.% solution and exposed to two, three or four cycles of freezing for 12 h followed by thawing for 2 h. Drug release was affected by the number of freezing/thawing cycles. Thus, the mucoadhesive characteristics and drug release could be optimized by controlling the freezing/thawing conditions.