Study On The Preparation, Structure And Properties Of Starch Based Medical Sponge

In recent years, considerable research attention has been focused on absorbable medical sponges made from natural polymers due to their potential applications including wound dressing, drug delivery, cell culture, tissue engineering and so on. The medical sponges used for these purposes must be highly porous, biodegradable and biocompatible, easily processed and have adequate mechanical properties. Starch, one of the most abundant natural polymers, is a good candidate for the preparation of medical sponge because of its biocompatibility, biodegradation, non-toxicity and non-allergic reaction. There are several ways to prepare porous medical sponges. Among these, freeze-drying treatment is one of the most simple and useful methods because porous sponges can be fabricated without using any organic solvent.In this thesis, starch was modified by gelatinization and graft copolymerization reaction. Then gelatinized starch sponge and grafted starch sponge were prepared by freeze-drying method. The structure, morphology and property of the sponges were studied in detail. The influence of freezing condition on the formation of the sponges and pore architecture were also investigated. The main results obtained were as follows:(1) Medical sponges were prepared by freeze-drying method and main facts which affect structures and properties of sponges were studied. Results showed that in order to obtain porous medical sponges, the starch should be gelatinized at first. The gelatinized starch is a kind of gel containing water, in which the molecular chains of starch were entangled to form a three dimensional networks. During freeze-drying process, water in the gel was first frozen to form ice crystals, then ice crystals were sublimated under vacuum, porous structures were well fabricated and three dimensional networks structure was retained in gelatinized starch sponge. Gelatinized starch sponges exhibit fast absorption rate and good mechanical properties.(2) Effects of freezing condition on structures and morphology of sponges were investigated in detail. Results indicated that different cooling conditions may dramatically influence the pore architecture. With decreasing freezing temperature, pore size of sponge decreased. Furthermore, the pore architecture at different locations of sponge was characterized by means of scanning electron microscopy (SEM). It also has been found that pore size, orientation and uniformity of sponges are significantly affected by condition of heat transfer during freeze-drying process. Tailoring pore architecture of sponges is feasible by controlling heat transfer.(3) Gelatinized starch was further modified by graft copolymerization of hydrophilic acrylamide (AM) and acrylic acid (AA) onto cassava starch via a redox initiator system. The chemical structure of grafted starch was characterized by FTIR and NMR. Grafted starch sponges were prepared by freeze-drying method and effect of starch grafted composites on formation and property of sponges were studied. Results showed that grafted starch sponges have larger water absorption capacity and better mechanical properties compared with pure gelatinized starch sponges.(4) A preliminary study on starch/PNIPAAm composite sponge and starch membrane has been performed. SEM result showed that starch/PNIPAAm composite sponge consisted of pores that are highly interconnected, which enhanced water absorption capacity. Starch/PNIPAAm composite sponge also exhibited limited temperature-responsive due to the introduction of thermosensitive PNIPAAm. Moreover, different methods for preparing starch membrane were also discussed. It is found that starch membrane with high transparence and good flexibility could be prepared by slowly drying in the air.