Preparation Of Alginate Hydrogel With Tunable Structure And Properties

Sodium alginate,as a kind of natural polymer material with excellent biocompatibility,can form hydrogels by crosslinking with calcium ion due to the unique structure of the carboxyl group in its a-L-guluronic acid(G units).It has drawn lots of attention from academics and industry owning to its wide application in food,biomedical,tissue engineering,cosmetics and industrial fields.Aiming to explore the application of alginate hydrogels in biomedical adhesives,this paper focused on the tunning of gelation time of alginate hydrogels as well as their tissue adhesion properties.And to improve the biodegradation performance of alginate hydrogels,oxidized sodium alginates in different oxidation degree were prepared and their gelation properties were preliminarily studied.Moreover,a relatively easy process method with repeatable results for tissue adhesion in vivo test was established to evaluate the tissue adhesion property of hydrogels.Major findings in this study are summarized as follows.(1)Alginate hydrogels were prepared by using calcium carbonate(CaC03)and gluconolactone(GDL)as calcium ion slow-release system.Four typical kinds of CaCO3,micron-sized and nano-sized,precipitated and ground with different sediment volume were employed as caicium source,respectively.Their gelation time and mechanical property were studied by varying the molar ratio of caicium ion and carboxyl group(f),the molar ratio of GDL and caicium ion(n)and the concentration of sodium alginate solution(CSA).The results showed that the alginate hydrogels prepared by nano-sized and precipitated calcium carbonate expressed short gelation time as well as good mechanical properties.When the temperature was 37 ℃,f valued 0.792,n valued 1.404 and CSA valued 2.0 wt.%,the gelation time of the hydrogels prepared by nano-sized and precipitated CaC03 was 5 min and 2.5 min,respectively,and their compression strength was 0.16 MPa and 0.13 MPa.(2)Since the biological tissue is difficult to acquire and inconvenient to stock,and the test result is not repeatable,the feasibility by using gelatin and its composite films to replace biological tissue as adherent matrixes has been examined.The effects of the factors,for example,the moisture content of the gelatin films,on tissue adhesion properties were studied in detail.The results showed that adhesive strength could be varied from 1.9×102 Pa to 18.1×102 Pa by controlling the moisture the film and introducing polyethylene oxide(PEO)to the film,which could cover the adhesive strength of different biological tissues,for example,pork liver and stomach mucosa,on alginate hydrogels.Therefore,a realtively easy process method with repeatable results for tissue adhesion in vivo test was established by taking self-made instead of the biological tissue as adherent matrix.(3)Four typical water-soluble polymers with high adhesion properties,including polyvinylpyrrolidone(PVP),hydroxy propyl cellulose(HPC),sodium carboxymethylcellulose(CMCNa)and PEO,were employed to composite with sodium alginate,respectively,and their alginate composite hydrogels were successfully prepared,and their tissue adhesion properties,gelation time and mechanical properties were studied.The results showed that the tissue adhesion property of alginate hydrogel could be both enhanced by the introduction of CMCNa and PEO,respectively.However,CMCNa greatly weakened the mechanical properties of the hydrogels and PEO did not.The tissue adhesion strength of the alginate composite hydrogels prepared with the mass ratio of PEO and sodium alginate 1:1 were twice as that of the alginate hydrogels,indicating that PEO could be a better choice for the enhancement of tissue adhesion property of the alginate hydrogels.(4)To shorten the biological degradation period of sodium alginate and maintain its gelation ability,the oxidized sodium alginates with different oxidation degree by the introduction of aldehyde groups in C2 and C3 positions of a-L-guluronic acid(G units)in sodium alginate molecular chain structure were prepared by using sodium periodate as oxidant.And their hydrogels composited with PEO composite were prepared by using the previous calcium ion slow-release system.Preliminary research suggested that under a large degree of oxidation,the C-C bond in the G unit of sodium alginate molecule fractured and the egg-box structure of hydrogel could not be formed,and the oxidized alginate with less than 5%oxidation degree can form hydrogel.Compared with that of alginate hydrogels,the biodegradation rate of the oxidized alginate/PEO composite hydrogels in six days was increased from 9.0%to 92.1%,confirming that the biodegradation performance of the oxidized alginate/PEO composite hydrogels had been greatly improved.The oxidized alginate hydrogel has good potential application in biomedical adhesives and is worth further investigation.