| Sericin,a natural protein secreted by silkworm,Bombyx mori,is produced abundantly every year,but was not utilized thoroughly.It is born with several natural activities including hydrophilicity,anti-bacterial ability,anti-ultraviolet,anti-oxidant,anti-cancer,anti-frozen,tyrosinase-inhibiting activities and promoting cell adhesion and proliferation activities et al.It has been widely used in the fields like fiber modification,functional additives,medical treatment and biological materials and so on.There are various methods to extract sericin.In this paper,protein sericin was extracted from a fiber deficient kind of cocoon with a mild LiBr extraction method.The sericin hydrogel was prepared through sonication method and then a novel sericin hydrogel with good properties was achieved.1.Preparation of sericin hydrogelThe cocoons mainly composed of sericin were used in this experiment which were produced by a silk fibroin deficient kind of silkworm strain 140 Nd-s.Through a mild LiBr extraction method,we obtained a high quality,low-degradable silkworm sericin.It is the first time that the ultrasound method applied on the high quality and low degradable sericin protein to conduct a research on the preparation of sericin hydrogel.The relationship between sericin concentration,sonication amplitude,sonication time and the gelation time was investigated.Reaults show that the more concentrated the sericin is,or the the longer the ultrasonic time,the larger the ultrasonic amplitude,and the faster the sericin solution was converted to sericin hydrogel.Set the sericin concentration at 2.5%,sonication amplitude at 10% and sonicated the sericin for 20 s,it will take only 3 minutes to complete the sol-gel trasition which approaches the fast gelation speed.2.Structure analysis of sericin hydrogelThe hydrogel used for structure analysis was prepared by 2% sericin,10% amplitude and 20 s sonicated time.The samples were all freeze and dried before testing.Scanning electron microscope,Fourier Transform infrared spectroscopy and X-ray diffraction were carried out for the structure analysis.The results show that the pores of sericin hydrogel were intercommunicated with each other,and the pores sizes decreased while the frozen temperature decreased.When the frozen temperature was-20 ℃,the average pore size exceeded 100 μm.The porosity of sericin hydrogel researches the top 93% at a frozen temperature of-80 ℃.After gelation,the β-sheet content of sericin increased to about 40% compared with that before gelation,while the Random coil and α-helix were reduced,and the gel structure was more stable.3.Property characterization of sericin hydrogelThe swelling kinetics of sericin hydrogel was fine and the maximum swelling ratio approaches 20 folds of its initial weight.The swelling rate at pH 7.0 is the fastest while the swelling ratio was low under acidic and alkali environment.The degradation rate of sericin hydrogel under different pH conditions is different,as well.The degradation rate is slowest under low pH environment(pH 3.0).The degradation ratio could maintain at about 20%.While degradation rate is accelerated with the increase of pH value.The degradation ratio was as high as 80% in the alkaline environment after a 35d-degrade.The sericin hydrogel has good mechanical properties both in compression and in elasticity.It can withstand compressive pressure up to 150 kPa with the compression modulus 20 kPa and a stretching pressure about 1.5 kPa.The tensile modulus is about 38 kPa by curve analysis.When encapsulated the protein drug HRP,sericin hydrogel can sustain the release duration to more than 22 days.The sericin hydrogel is injectability and shape moldability,which is beneficial for the injection of the drug-loaded sericin hydrogel into the diseased site.Cell culture can be carried out on the sterilized hydrogel surface.The sericin hydrogel can support long term cell survival and proliferation due to its perfect cell adhesion ability.Through a comprehensive analysis of the properties of sericin hydrogel made from cocoons produced by a fibroin deficient silkworm species prepared by ultrasound treatment,it turns out that the hydrogel is a high optically transparent,high elastic and biocompatible material.Additionally,the degradation kinetics and drug release profile of this hydrogel are excellent either.It is a versatile material candidate for tissue engineering.It is expected that further research on its application in wound dressings,medical drug carriers and tissue engineering scaffolds would be carried out. |
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