Preparation And Characterization Of Freeze-dried Calcium Alginate And Calcium Alginate-Based IPN Membranes

Alginate is a naturally occurring linear polysaccharide found in all species of brown algae and some species of bacteria. It is hydrophilic, non-toxic, biocompatible, and relatively economical with desirable physical properties. In recent years, Alginate has been widely commercialized and explored for biomedical and pharmaceutical applications. The interpenetrating polymer networks (IPN) have extracted extensive research interests due to their unique properties.In the thesis, porous Calcium Alginate(CA) membranes were prepared using freeze-drying method and CA-based IPN membranes were prepared by stepwise IPN technique. The structure and the performances of those materials were studied.(1) Porous CA membranes were prepared by freeze-drying method, which displayed a highly porous, three-dimensional and well interconnected pore structure. Their morphology was highly dependent on the preliminary freeze temperature and initial concentration of Sodium Alginate (SA), investigated by infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). FTIR spectroscopy showed the formation of cross-linked bonds in the system. The optimum membranes were formed when 2% SA were preliminary frozen at-5℃.The pores were round or oval in shape and pore diameters were 100-300μm, which were beneficial to cells penetration, propagation and adhesion.(2) Two kinds of CA membranes were obtained by nature-drying and freeze-drying methods respectively. Typical morphologies and properties were evaluated, including water absorbency, retention ratio, swelling ratio and mechanical properties.The nature-dried membranes were dense membranes of colorless and transparent, while the freeze-dried membranes were white and porous sponges. The results showed that CA membranes were salt-sensitive. Comparatively, the water absorbency and water retention performance of freeze-dried membranes were better but the maximum force and tensile strength of nature-dried membranes were stronger.(3)Calcium Alginate-Poly(vinyl Alcohol)(CA-PVA) IPN and Calcium Alginate-Gelatin(CA-Gel) IPN membranes were cross-linked with glutaraldehyde and calcium chloride step by step using nature-drying and freeze-drying methods respectively. The results indicated that the CA-based IPN membranes were salt-sensitive, and possessed excellent water absorbency, water retention performance and mechanical properties, which were desirable for medical wound dressing and tissue-engineering scaffold material.The obtained membranes were characterized by FTIR, SEM, differential scanning calorimetry (DSC) and Transmission electron microscopy (TEM). The results revealed that the interpenetration between two networks increased the compatibility. The pores of freeze-dried CA-PVA IPN membranes were oval in shape and 10-150μm in sizes. The pores of freeze-dried CA-Gel IPN membranes were spherical and honeycombed, and pore sizes were 500-600μm.The results of contract angle revealed that the hydrophilicity of CA-Gel IPN membranes were better than that of CA-PVA IPN membranes. Comparatively, the water absorbency and water retention performance of CA-PVA IPN were better to nature-dried membranes but those of CA-Gel IPN were better to freeze-dried membranes. With the increasing of PVA and Gel, the water absorbency and water retention performance of the CA-based IPN membranes increased at first and then decrease.The mechanical test results showed that the maximum force and tensile strength of CA-based IPN membranes increased, while elongation at break decreased. Comparatively, the maximum force and tensile strength of CA-PVA IPN membranes were superior. The tensile strength of the CA-based IPN membranes increased with the increasing of PVA and Gel.