Preparation And Characteristics Of Medical Hemostatic Carboxyl Methyl Starch Sponge

In recent years,considerable research attention has been focused on porous,absorbable medical sponges made from natural polymers due to their potential applications including scaffolds of cell,tissue transplantationg,wound dressing and so on.The medical sponges applied for these purposes should meet certain requirements.Firstly,high porosity is necessary in order to provide sufficient space and surface. Secondly,they should be completely degradable and eliminated from the body.There are several ways to prepare porous medical sponges.Among these,freeze-drying treatment is one of the most simple and useful methods.In this thesis,carboxyl methyl starch sponges(CMS),CMS/sodium alginatecomposite sponges(CMS/SA) and CMS /carboxyl methyl cellulosecomposite sponges(CMS/CMC) were prepared by freeze-drying method.The structure and morphology of the sponges were investigated in detail.In addition,the hemostatic and absorbable properties of the CMS sponge on the animal body were examined.The main results obtained are as follows:1.The CMS medical sponges were prepared by freeze-drying method and the main facts which affect the structures and properties of the sponges were studied.The SEM results show that starch granules were still existed in the CMS sponges,which is due to the fact that CMS hardly dissolve in the water and a homogeneous solution can not be formed.As the adhesive force between starch granules is not strong enough to form a three dimensional network,the prepared sponges exhibit poor mechanical properties.The CMS sponges have high water absorbability and the fast water absorbed rate as compared with the common medical sponges.2.CMS /SA and CMS/CMC composite sponges were prepared by freeze-drying method and their structure and properties were also studied. The results indicated that starch granules were conglutinated by SA or CMC molecular chains and three dimensional networks were formed in the composite sponge.The porous structures were well fabricated and their surfaces are smooth without any crack in the sponge.The composite sponges show fast water absorbed rate and the good mechanical properties.With increasing the contents of polymer,the compression modulus and the volume density of sponges are increased.3.The effects of freezing condition on the structures and morphology of the sponges were investigated in detail.The results indicated that the pore size of sponge was controled by the freezing temperature.With decreasing the freezing temperature,the pore size of sponge decreased. The fast freezing process in liquid nitrogen for 20 minutes produced sponges with smaller pores than those obtained through the slow freezing process in a freezer kept at -20℃for 24 hours.It is possible that a lower freezing temperature would cause a large number of crystal nucleus formed during the initial stage of the freeze-drying treatment.The growth rates of ice crystals at lower freezing temperature were much slower than those at higher freezing temperature,which led to a smaller size of ice crystals was formed.During the second stage of the freeze-drying treatment,the ice crystals were sublimated under vacuum and the spaces originally occupied by them became pores.Therefore,the pore size of the sponges can be controlled only by the size of ice crystals formed during the freezing process.4.The hemostatic and absorbable properties of the CMS sponge were examined.The results indicate that the CMS sponge can be degraded to glucose after 8 hours.The CMS sponge can increase the clot rate of the blood and shorten sonACT time,which indicated the CMS sponges have a function to improve the blood clot.The preliminary results of the hemostatic test on the liver and spleen of small pig indicated that the CMS sponges have good haemostatic and absorbable properties which have rapid hemostasis in 2 minutes and is basically absorbed in body of pig within 7 days.