壳聚糖三维材料的降解及其降解速率的调控
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摘要
本课题组采用原位沉析法,制得高强度的壳聚糖三维材料,有望用做可降解吸收骨折内固定材料。本论文对其在制备及使用过程中的降解情况进行了研究：如在其制备过程中不同温度下的热处理对其材料性能和降解速率的影响；在其使用过程中,辐射灭菌对材料性能和降解速率的影响；在初步探明其体外降解机理和降解速率的前提下,采用不同脱乙酰度的壳聚糖原料、不同的材料制备工艺、形成不同的材料结构以及复合载酶微球调控其降解速率,以期达到材料降解速率与骨修复速率相匹配,为壳聚糖骨折内固定材料在人体内的安全应用提供理论依据。
(1)在壳聚糖三维材料的制备过程中对其在80-400℃范围内热处理2 h。结果表明：材料在热处理过程中发生分子间交联。在热处理温度不高于200℃时,随着热处理温度的升高,壳聚糖三维材料热稳定性上升,弯曲强度在140℃时出现最大值,为161.3±4.9 MPa,与未经热处理的材料相比提高了33.1%。酶解实验结果发现热处理会降低材料的体外降解速率。
(2)采用60Co辐射源对壳聚糖三维材料和热处理壳聚糖三维材料进行辐射。对于前者,随辐射剂量的增加,分子量下降,在辐射剂量为20 kGy时出现最强结晶峰,同时出现最高弯曲强度132.8±1.6 MPa。结果表明20 kGy的60Co辐射不但可以增强壳聚糖三维材料,而且对其体外降解速率不会造成明显影响。
(3)壳聚糖三维材料在PBS和溶菌酶/PBS中的体外降解研究结果显示：其初始酶解速率较高,因为壳聚糖残基会阻碍溶菌酶对里层壳聚糖链的剪切,使得溶菌酶较难渗透入材料内部。在PBS和溶菌酶/PBS中降解24 w后,壳聚糖三维材料的失重率分别可达4.1%和7.9%。根据Burkersroda等提出的溶蚀模型计算,其在PBS和溶菌酶/PBS中都经历整体溶蚀。
(4)采用N-乙酰化工艺,制得一系列不同脱乙酰度的壳聚糖,然后将不同脱乙酰度的壳聚糖共混制备壳聚糖三维材料或以不同脱乙酰度的壳聚糖层层叠加制备壳聚糖三维材料,并进行体外降解实验。结果表明：不同脱乙酰度的壳聚糖,降解速率不同,可以通过调节壳聚糖的脱乙酰度在一定的范围内调控材料的降解速率,尤其当脱乙酰度为45.7%时,所制备的材料在5w内可以完全降解。
(5)初步探索了复合载酶微球调节壳聚糖三维材料降解速率的方法。结果表明：当溶菌酶和明胶微球的质量比为1：12时,包封率和载酶率综合来说较高,分别为75.9%,6.3%。在前14天,溶菌酶很快从明胶微球中释放出来,和外界溶菌酶共同作用、剪切壳聚糖,使壳聚糖三维材料的降解速率明显增大。
By an original in-situ precipitation method, our research group has successfully prepared three dimensional chitosan rod with a high bending strength, which has a potential application as biodegradable and bioabsorbable internal fixation nail. In this work, we investigated its degradations in preparation process and application process. For example, the influence of heat treatment at different temperatures in the preparation process on the properties and in-vitro degradation rate of chitosan rod was investigated; the influence of 60Co radiation as a sterilization method on the properties and in-vitro degradation rate of chitosan rod was studied; after the in-vitro degradation mechanism and in-vitro degradation rate of chitosan rod were clarified, in order to make the in-vitro degradation rate match the bone repair rate, several methods were adopted to adjust the in-vitro degradation rate of chitosan rod, including using chitosan raw materials with different deacetylation degrees and complexing chitosan rod with microspheres loaded with lysozyme. I hope the results of this research can provide theoretical basis to the safe applications of chitosan-based bone internal fixation materials in the human body.
(1) The chitosan rods were heated at 80～400℃for 2 h. During the heat treatment, the CH2OH group in C-6 of chitosan would be oxidized to aldehyde group, and then react with the free amino group of chitosan, forming an intermolecular crosslinking structure. With the increase of temperature (when the temperature was not higher than 200℃), for the chitosan rod, the solubility decreased, and the thermal stability increased. The bending strength reached maximum at 140℃and was 161.3±4.9 MPa. Compared with the bending strength of chitosan rod without heat treatment, the bending strength of CS-140 increased by 33.1%. Moreover, the heat treatment could decrease the in-vitro degradation rate of chitosan rod.
(2) Both the chitosan rods and heated chitosan rods were irradiated at doses from 10 kGy to 200 kGy by 60Co irradiation. In the degradation process induced by 60Co irradiation, the chain-scission reaction was dominant and deamination would also happen. With respect to chitosan rod with no heat treatment, when the irradiation dose increased, the molecular weight kept decreasing, and both the crystallization degree and the bending strength reached their maxima at the dose of 20 kGy. In the in-vitro degradation test, CS-20 kGy and CS-0 kGy displayed similar degradation rate. The results indicated that moderate 60Co irradiation not only could strengthen the chitosan rod, but also would not have obvious effect on the in-vitro degradation rate of chitosan rod.
(3) The in-vitro degradations of chitosan rod in PBS and lysozyme/PBS were studied. The enzymatic degradation rate at the first week was higher than that at other weeks. This was because the chitosan residues would hinder the penetration of lysozyme into interior chitosan rod. After degraded in PBS and lysozyme/PBS for 24 weeks, the weight losses of chitosan rods were 4.1% and 7.9% respectively. According to the erosion model proposed by Burkersroda et al., the chitosan rod would undergo bulk erosion both in PBS and lysozyme/PBS.
(4) Methods such as N-acetylation, blending and layered compositing were adopted to adjust the in-vitro degradation rate of chitosan rod. The results indicated that chitosan rod with different deacetylation degree had different in-vitro degradation rate. Therefore, by adjusting the deacetylation degree of chitosan, the in-vitro degradation rate of chitosan rod could be controlled. Especially when the deacetylation degree of chitosan was 45.7%, the chitosan rod could be fully degraded.
(5) A preliminary study was made on tuning the in-vitro degradation rate of chitosan rod by complexing chitosan rod with microspheres loaded with enzyme. In this paper, a hollow chitosan rod was prepared at first, and then the gelatin microspheres loaded with lysozyme were added in. When the mass ratio between lysozyme and gelatin microspheres was 1:12, the encapsulation ratio and loading ratio were the most suitable, and were 75.9% and 6.3% respectively. In the first 14 days of in-vitro degradation, the degradtion rate of the composite rod was much higher than the pure rod, because the lysozyme was released from the gelatin microspheres and degraded the chitosan jointly with lysozyme in the lysozyme/PBS solution.
(1)在壳聚糖三维材料的制备过程中对其在80-400℃范围内热处理2 h。结果表明：材料在热处理过程中发生分子间交联。在热处理温度不高于200℃时,随着热处理温度的升高,壳聚糖三维材料热稳定性上升,弯曲强度在140℃时出现最大值,为161.3±4.9 MPa,与未经热处理的材料相比提高了33.1%。酶解实验结果发现热处理会降低材料的体外降解速率。
(2)采用60Co辐射源对壳聚糖三维材料和热处理壳聚糖三维材料进行辐射。对于前者,随辐射剂量的增加,分子量下降,在辐射剂量为20 kGy时出现最强结晶峰,同时出现最高弯曲强度132.8±1.6 MPa。结果表明20 kGy的60Co辐射不但可以增强壳聚糖三维材料,而且对其体外降解速率不会造成明显影响。
(3)壳聚糖三维材料在PBS和溶菌酶/PBS中的体外降解研究结果显示：其初始酶解速率较高,因为壳聚糖残基会阻碍溶菌酶对里层壳聚糖链的剪切,使得溶菌酶较难渗透入材料内部。在PBS和溶菌酶/PBS中降解24 w后,壳聚糖三维材料的失重率分别可达4.1%和7.9%。根据Burkersroda等提出的溶蚀模型计算,其在PBS和溶菌酶/PBS中都经历整体溶蚀。
(4)采用N-乙酰化工艺,制得一系列不同脱乙酰度的壳聚糖,然后将不同脱乙酰度的壳聚糖共混制备壳聚糖三维材料或以不同脱乙酰度的壳聚糖层层叠加制备壳聚糖三维材料,并进行体外降解实验。结果表明：不同脱乙酰度的壳聚糖,降解速率不同,可以通过调节壳聚糖的脱乙酰度在一定的范围内调控材料的降解速率,尤其当脱乙酰度为45.7%时,所制备的材料在5w内可以完全降解。
(5)初步探索了复合载酶微球调节壳聚糖三维材料降解速率的方法。结果表明：当溶菌酶和明胶微球的质量比为1：12时,包封率和载酶率综合来说较高,分别为75.9%,6.3%。在前14天,溶菌酶很快从明胶微球中释放出来,和外界溶菌酶共同作用、剪切壳聚糖,使壳聚糖三维材料的降解速率明显增大。
By an original in-situ precipitation method, our research group has successfully prepared three dimensional chitosan rod with a high bending strength, which has a potential application as biodegradable and bioabsorbable internal fixation nail. In this work, we investigated its degradations in preparation process and application process. For example, the influence of heat treatment at different temperatures in the preparation process on the properties and in-vitro degradation rate of chitosan rod was investigated; the influence of 60Co radiation as a sterilization method on the properties and in-vitro degradation rate of chitosan rod was studied; after the in-vitro degradation mechanism and in-vitro degradation rate of chitosan rod were clarified, in order to make the in-vitro degradation rate match the bone repair rate, several methods were adopted to adjust the in-vitro degradation rate of chitosan rod, including using chitosan raw materials with different deacetylation degrees and complexing chitosan rod with microspheres loaded with lysozyme. I hope the results of this research can provide theoretical basis to the safe applications of chitosan-based bone internal fixation materials in the human body.
(1) The chitosan rods were heated at 80～400℃for 2 h. During the heat treatment, the CH2OH group in C-6 of chitosan would be oxidized to aldehyde group, and then react with the free amino group of chitosan, forming an intermolecular crosslinking structure. With the increase of temperature (when the temperature was not higher than 200℃), for the chitosan rod, the solubility decreased, and the thermal stability increased. The bending strength reached maximum at 140℃and was 161.3±4.9 MPa. Compared with the bending strength of chitosan rod without heat treatment, the bending strength of CS-140 increased by 33.1%. Moreover, the heat treatment could decrease the in-vitro degradation rate of chitosan rod.
(2) Both the chitosan rods and heated chitosan rods were irradiated at doses from 10 kGy to 200 kGy by 60Co irradiation. In the degradation process induced by 60Co irradiation, the chain-scission reaction was dominant and deamination would also happen. With respect to chitosan rod with no heat treatment, when the irradiation dose increased, the molecular weight kept decreasing, and both the crystallization degree and the bending strength reached their maxima at the dose of 20 kGy. In the in-vitro degradation test, CS-20 kGy and CS-0 kGy displayed similar degradation rate. The results indicated that moderate 60Co irradiation not only could strengthen the chitosan rod, but also would not have obvious effect on the in-vitro degradation rate of chitosan rod.
(3) The in-vitro degradations of chitosan rod in PBS and lysozyme/PBS were studied. The enzymatic degradation rate at the first week was higher than that at other weeks. This was because the chitosan residues would hinder the penetration of lysozyme into interior chitosan rod. After degraded in PBS and lysozyme/PBS for 24 weeks, the weight losses of chitosan rods were 4.1% and 7.9% respectively. According to the erosion model proposed by Burkersroda et al., the chitosan rod would undergo bulk erosion both in PBS and lysozyme/PBS.
(4) Methods such as N-acetylation, blending and layered compositing were adopted to adjust the in-vitro degradation rate of chitosan rod. The results indicated that chitosan rod with different deacetylation degree had different in-vitro degradation rate. Therefore, by adjusting the deacetylation degree of chitosan, the in-vitro degradation rate of chitosan rod could be controlled. Especially when the deacetylation degree of chitosan was 45.7%, the chitosan rod could be fully degraded.
(5) A preliminary study was made on tuning the in-vitro degradation rate of chitosan rod by complexing chitosan rod with microspheres loaded with enzyme. In this paper, a hollow chitosan rod was prepared at first, and then the gelatin microspheres loaded with lysozyme were added in. When the mass ratio between lysozyme and gelatin microspheres was 1:12, the encapsulation ratio and loading ratio were the most suitable, and were 75.9% and 6.3% respectively. In the first 14 days of in-vitro degradation, the degradtion rate of the composite rod was much higher than the pure rod, because the lysozyme was released from the gelatin microspheres and degraded the chitosan jointly with lysozyme in the lysozyme/PBS solution.
引文
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