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Degradation study of gelatin gel: A 5 ml solution (20% w/v) of gelatin in 0.05 M PBS, pH 7.4 was prepared. Then a 0.4 ml portion of 2.5% (v/v) glutaraldehyde solution was added to the gelatin solution and mixed well. A 0.6 ml aliquot of the gelatin solution was then poured into a glass tube (φ: 6 mm) to obtain a gel. The glass tube was soaked into a 10ml of 0.1 M calcium chloride solution for a day at room temperature and then soaked into water to remove excess salt such as sodium chloride, sodium phosphate and calcium chloride. The patterned gel in glass tube was soaked into 5mL of 0.1 M PBS (pH7.4) at 37℃ for 2 days to swell to equilibrium. Then 33 U of collagenase was added to the PBS and the glass tube containing patterned gel was weighed with time. The degradation property was evaluated based on the weight change. 3. Results and discussion Liesegang pattern phenomenon in gelatin gel is well known as its biocompatibility, low antigenicity and enzymatic degradability. Many researchers have been studied gelatin gel as the materials of tissue engineering scaffold and the drug release device. In this study, we used it as a biodegradable structural material for the fabrication of device and Liesegang pattern forming in the gel as a regulator of degradation, and then we tested this device to investigate the feasibility of achieving pulsatile DDS without imposing y stimulus. Pattern formation in gelatin gel Liesegang band or ring has been studied to understand non-equilibrium pattern formation, especially the mechanism of periodic pattern formation since its discovery. On the other hand our objective is to use this phenomenon for design of DDS device. Therefore, at first, the optimal conditions of pattern formation for DDS device were investigated. We studied the formation of calcium phosphate precipitate in chemically cross-linked gelatin gel. Calcium phosphates are classified as bioresorba e and biocompatible materials. Due to the physiological nature of calcium phosphate, they have been p posed as potential bone defect fillers, and sustained DDS devices. Experiment of Liesegang pattern formation was carried out in gelatin gel which was cured by general method using glutaraldehyde as cross-linker. When calcium chloride solution was poured onto gelatin gel containing phosphate salt, periodic precipitation bands were formed perpendicularly to the concentration gradients (Fig. 3). Their interval distance and band thickness varied regularly according to the distance from the gel/solution interface. The formation of a periodic pattern is basically understood by Ostwald supersaturation theory in which the cou ling between diffusion and the reaction with supersaturation is essential. The formed pattern in a gel was more clearly with increasing gelatin concentration from 5 to 20%. However, the remarkable differences in pattern shapes such as the interval distance and strip thickness were not observed. It indicated that the formed pattern shape was independent to the gelatin concentration in gel matrix. This result implies it is expectable that the gel matrix can be controlled to optimal condition for DDS device without changing th pattern shape formed in gel. 急用,谢谢大家了 |
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明胶凝胶的降解研究：用pH为7.4的0.05M磷酸盐缓冲液配成5ml明胶溶液（20％w/v），然后将0.4ml2.5％（v/v）的戊二醛溶液加入上述明胶溶液中并混合均匀。将0.6ml明胶溶液试样倒入玻璃管(直径:6mm)中获得明胶。在室温下，将玻璃管浸入10ml0.1M氯化钙溶液一天，然后再浸入水中以除去多余的盐如氯化钠、磷酸钠和氯化钙。将玻璃管中表面图案化的明胶于37℃浸入5ml0.1M磷酸盐缓冲溶液（pH7.4）两天，使溶涨达到平衡。然后将33U胶原蛋白酶加入缓冲溶液中并按时称量含明胶的玻璃管。用重量变化评价降解性能。 3. 结果及讨论 由于明胶的生物相容性、低抗原性和酶解性能，明胶的 Liesegang现象已经为公众所知。已经有很多针对明胶作为组织工程支架材料和释药装置材料的研究。在本研究中，我们将明胶作为释药装置制造中一种生物降解性支架材料，并将明胶产生的Liesegang现象作为降解的调控器，随之在不加刺激剂的情况下测定了该装置达到脉冲给药的可行性。 明胶的模式形成 已经有人对Liesegang带或环进行了研究以理解非平衡模式形成，特别是从其被发现以来针对周期性模式形成机理的研究。另一方面我们的目的是把这种现象用于药物传递系统装置的设计。因此，首先，考察了DDS装置模式形成的最佳条件。研究了化学交联明胶中磷酸钙沉淀的形成。磷酸钙为一种生物可吸收和生物降解性材料。由于磷酸钙的生理特性，它们被建议作为骨缺陷填充物及用于缓释给药系统装置。使用常规方法，以戊二醛为交联剂对明胶形成Liesegang现象进行了研究。 当将氯化钙溶液倾入含有磷酸盐的明胶凝胶时，沿与浓度梯度垂直的方向形成了周期性的沉淀带(Fig. 3)。沉淀带的间距和厚度随与明胶表面距离的变化而逐渐变化。周期性条代的形成基本上可以通过Ostwald过饱和理论加以解释，在该理论中，扩散与过饱和反应之间的耦合是最关键的。随着明胶浓度从5％升高到20％，明胶条带的形成也更加清晰。但没有观察到条带形状如间距和带宽之间的显著差别。这表示条带形状的形成是依赖于凝胶骨架中明胶浓度。上述结果表明可以在不改变明胶条带形状的情况下控制凝胶骨架以大道释药系统装置所需的最佳条件。 |
2楼2008-05-15 13:51:58
