Preparation And Properties Of Polyvinyl Alcohol/Sodium Alginate Hydrogels

Hydrogels were the first biomaterials designed for use in the human body because they are more biocompatible than any other class of biomaterials. Synthetic polymer hydrogels display controlled gelation process, structure and mechanical properties. While some natural polymers exhibit superior and rare properties. However, many hydrogel biomaterials prepared by single polymer lack the desired functional properties to interface with biological systems and have not been engineered for optimized performance. Therefore, blending synthetic polymers and natural polymers has been of special interest to develop new hydrogel materials to address the problem.In this study, polyvinyl alcohol (PVA)/sodium alginate (SA) hydrogels were prepared by freezing-thawing followed by Ca2+ crosslinking. Gel fraction, degree of swelling and equilibrium water content of the hydrogels were examined to discuss the relationship of processing conditions and properties. The texture morphology and thermal properties of the hydrogels were investigated with SEM and DTA-TGA respectively. The effects of SA content, the number of freezing and thawing cycles and Ca2+ concentration on the tension, unconfined compression, swelling, and controlled release properties of blend hydrogels were investigated in order to fabricate functional biomaterials with controlled properties. The physical and chemical changes of blend hydrogels in simulated body fluid were observed to provide some essential scientific date for clinical application.PVA / SA hydrogels with water content ranged 89.5% ~ 93.6% were prepared by freezing-thawing followed by Ca2+ crosslinking. The hydrogels containing different SA content showed various porous sponge structures when observed with SEM. The SEM photographs also indicated a good miscibility and blend homogeneity between PVA and SA networks. With the increase of freezing-thawing cycles, the crosslinking density of PVA network in the hydrogels increased, resulting in an increase of gel fraction and Tg, and a decrease of the degree of swelling, equilibrium moisture content and the thermal stability of SA. The crosslinking of sodium alginate were complete within 4h in CaCl2 solution. The treatment by using 1% CaCl2 solution may not be able to form a sufficiently crosslinked SA network in the hydrogel. And the equilibrium moisture content decreased with the increasing of the concentration of CaCl2 solution and immersion time.The mechanical properties of blend hydrogels not only related to the compositions, but also depended on the processing parameters. When the PVA content was high, the blend hydrogels were PVA dominant and showed good flexibility and high tensile strength. The number of freezing-thawing cycles correlated positively with tensile strength, Young's modulus and elongation at break. The elongation at break of the hydrogel treated with 1% CaCl2 solution was lowest due to insufficient crosslinking of SA network. The tensile strength and Young's modulus of the blend hydrogels increased with increasing of the concentration of CaCl2 aqueous solution. The stress-strain curve of unconfined compression suggesting a non-linear stress-strain response, which means the hydrogels was a viscoelastic material. And this can be affirmed when the compressive modulus increased with increasing of compression rate. The compressive modulus increased with increasing of SA proportion, freezing-thawing cycles and concentration of CaCl2 aqueous solution. The shape, mass and compressive modulus change slightly after several compression processes, suggesting the blend hydrogels have excellent compression resistance capability.The blend hydrogels were sensitive to ionic strength, temperature and pH value when immersed in solution with different ionic strength, temperature and pH value. The pH sensitivity of the blend hydrogels increased with the increase of SA content, but decreased with the increase of concentration of CaCl2 solution. While freezing-thawing cycles had little effect on the pH sensitivity of blend hydrogels.The water content and mass of blend hydrogels decreased as they were immersed in simulated body fluid. Meanwhile, the pH value of simulated body fluid decreased because of the disintegration of blend hydrogels, the decreasing amount of pH value increased with the increase of SA content. The morphology of hydrogel changed slightly owing to the disintegration in simulated body fluid. And hydroxyapatite was not found on the surface of hydrogels when the sample was analyzed with XRD.Drug loading, release rate and cumulative release amount of drug loaded PVA / SA hydrogels were decreased with the increase of SA content, freezing - thawing cycles and the concentration of CaCl2 solution. The hydrogel samples with different SA content have similar release tendency, the drug released quickly at first, then got slowly, and the release process lasted more than 6 h. The release rate and cumulative release amount of chloramphenicol-loaded hydrogel given orally in simulated intestinal fluid was higher than that in simulated gastric fluid.