[Preparation and roles of sliver-loaded viscous hydrogel in healing of full-thickness skin defect wounds with bacterial colonization in mice].

Objective: To prepare the modified hyaluronic acid viscous hydrogel loaded with sliver particles and to explore the roles and mechanism of the hydrogel in healing of full-thickness skin defect wounds with bacterial colonization in mice. Methods: The experimental research method was adopted. Dopamine modified hyaluronic acid (HA-DA) and phenylboric acid modified hyaluronic acid (HA-PBA) were prepared, and their characteristic peaks were detected by Fourier-transform infrared spectroscopy. Different mass of acrylamides was added to HA-DA and HA-PBA to prepare the viscous hydrogel with mass fraction of acrylamide in 10%, 15%, and 20%. The gelation of the viscous hydrogel with mass fraction of acrylamide in 20% was observed in the state of tilt and inversion at 37 ℃, and the storage modulus and loss modulus of the above 3 kinds of viscous hydrogels were detected by rotational rheometer. The sliver-loaded viscous hydrogel was prepared by adding nano silver ions to the viscous hydrogel with mass fraction of acrylamide in 20%. The concentration of silver ions released by sliver-loaded viscous hydrogel was measured by inductively coupled plasma mass spectrometer, and the cumulative release rate of silver ion was calculated (n=5). The mouse fibroblasts L929 were divided into phosphate buffered saline (PBS) group, viscous hydrogel group, and sliver-loaded viscous hydrogel group, which were dealt correspondingly, and the cell survival was detected by cell counting kit 8 method after 1, 2, and 3 d of culture (n=5). Twenty-four male C57BL/6 mice aged 6-8 weeks were selected, and forty-eight full-thickness skin defect wounds were inflicted and inoculated with the mixture of Escherichia coli and Staphylococcus aureus in the back of the mice, with two wounds in each mouse. The wounds were divided into normal saline group, viscous hydrogel group, and sliver-loaded viscous hydrogel group, which were dealt correspondingly, with 16 wounds in each group, and two wounds in each mouse were divided into different groups. On post injury day (PID) 3, 7, 10, and 14, the wound healing was observed and the wound healing rate was calculated. On PID 3, the colony forming units of Escherichia coli and Staphylococcus aureus in wounds were observed and counted. On PID 14, the epithelized epidermal thickness and the optical density of collagen fiber in wounds were observed and analyzed after hematoxylin eosin staining and Masson staining, respectively. On PID 3, 7, and 10, the expressions of tumor necrosis factor α (TNF-α), transforming growth factor β1 (TGF-β1), and vascular endothelial growth factor (VEGF) were detected by immunohistochemistry. The number of wounds in each index detecting at each time point was four. Data were statistically analyzed with analysis of variance for factorial design, one-way analysis of variance, and Bonferroni correction. Results: The characteristic peaks of HA-PBA were detected at the wave numbers of 1 369 and 1 425 cm-1, indicating that phenylboric acid had been successfully grafted on hyaluronic acid, and the characteristic peaks of HA-DA were detected at the wave numbers of 1 516 and 1 431 cm-1, indicating that dopamine had been successfully grafted on hyaluronic acid. The viscous hydrogel with mass fraction of acrylamide in 20% maintained the stable and no-flow condition of gelation in the state of tilt and inversion at 37 ℃. The storage modulus and loss modulus of the viscous hydrogel increased with the increase of acrylamide content, the storage modulus and loss modulus of the 3 kinds of viscous hydrogels had no obvious changes with the increase of the oscillation frequency or time, and the storage modulus of the 3 kinds of acrylamide hydrogels were greater than the loss modulus. The release of silver ion in the sliver-loaded viscous hydrogel lasted for 7 days, and the cumulative release rate of silver ion was up to 65%. After 1, 2, and 3 d of culture, the cell survival rates in sliver-loaded viscous hydrogel group were significantly lower than those in PBS group and viscous hydrogel group (P<0.05 or P<0.01), while after 1 d of culture, the cell survival rate in viscous hydrogel group was significantly lower than that in PBS group (P<0.01). With extension of time after injury, the wounds of mice in the 3 groups shrank gradually. On PID 3, 7, 10, and 14, the wound healing rates in sliver-loaded viscous hydrogel group were (53.0±3.6)%, (75.3±6.9)%, (93.3±1.2)%, and (96.7±0.8)%, which were significantly higher than (21.8±6.4)%, (53.9±8.2)%, (72.0±7.8)%, and (92.5±0.4)% in normal saline group (P<0.01). On PID 3 and 14, the wound healing rates in sliver-loaded viscous hydrogel group were significantly higher than (43.5±2.4)% and (94.1±1.5)% in viscous hydrogel group (P<0.05). On PID 3 and 10, the wound healing rates in viscous hydrogel group were significantly higher than those in normal saline group (P<0.01). On PID 3, the colony forming units of two bacteria in wound of sliver-loaded viscous hydrogel group were significantly less than those in normal saline group and viscous hydrogel group (P<0.01), while the colony forming units of two bacteria in wound of viscous hydrogel group were significantly less than those in normal saline group (P<0.05). On PID 14, the wounds were basically epithelialized and the epidermis was thicker, with collagen protein content being increased significantly and more orderly arranged collagen in sliver-loaded viscous hydrogel group compared with those in the other 2 groups. On PID 14, the epidermal thickness in wounds of sliver-loaded viscous hydrogel group was significantly increased compared with that in the other two groups (P<0.05), and the optical density of collagen fiber was significantly increased compared with those in normal saline group (P<0.05). On PID 3, the expressions of TGF-β1 and VEGF in wounds of sliver-loaded viscous hydrogel group were significantly higher than those in normal saline group (P<0.05 or P<0.01), while the expression of VEGF in wounds of viscous hydrogel group was significantly higher than that in normal saline group (P<0.01). On PID 7, the expression of TGF-β1 in wounds of sliver-loaded viscous hydrogel group was significantly higher than that in the other 2 groups (P<0.01), and the expression of VEGF was significantly higher than that in normal saline group (P<0.01). On PID 10, the expression of TNF-α in wounds of sliver-loaded viscous hydrogel group was significantly lower than that in normal saline group (P<0.05), the expressions of TGF-β1 and VEGF in wounds of sliver-loaded viscous hydrogel group were significantly higher than those in normal saline group (P<0.05 or P<0.01), and the expression of VEGF in wounds of sliver-loaded viscous hydrogel group was significantly higher than that in viscous hydrogel group (P<0.05). Conclusions: The sliver-loaded viscous hydrogel prepared in this study has good stability and elasticity, which can continuously release silver ions and help to accelerate the healing of full-thickness defect wounds with bacterial colonization in mice. Besides, the sliver-loaded viscous hydrogel has low biological toxicity and can promote re-epithelialization, collagen deposition as well as angiogenesis of wounds, which may be related to the infiltration and regression of inflammatory cells.目的： 制备负载银粒子的改性透明质酸黏性水凝胶，探讨其在小鼠细菌定植全层皮肤缺损创面愈合中的作用及可能的机制。 方法： 采用实验研究方法。制备多巴胺修饰的透明质酸（HA-DA）和苯硼酸修饰的透明质酸（HA-PBA），傅里叶变换红外光谱检测其特征峰。在HA-DA和HA-PBA中加入不同质量的丙烯酰胺，制备质量分数为10%、15%、20%丙烯酰胺的黏性水凝胶。观察含质量分数20%丙烯酰胺的黏性水凝胶在37 ℃下倾斜状态和倒立状态的成胶情况，旋转流变仪检测前述3种黏性水凝胶的储存模量和损耗模量。在含质量分数20%丙烯酰胺的黏性水凝胶中加入纳米银离子，制备含银黏性水凝胶，采用电感耦合等离子体质谱仪测量含银黏性水凝胶释放的银离子浓度，并计算累计银离子释放率（样本数为5）。取小鼠成纤维细胞L929，分为磷酸盐缓冲液（PBS）组、黏性水凝胶组及含银黏性水凝胶组并进行相应处理，采用细胞计数试剂盒8法检测培养1、2、3 d细胞存活情况（样本数为5）。取24只6~8周龄雄性C57BL/6小鼠，在其背部建立48个接种大肠埃希菌和金黄色葡萄球菌混合悬液的全层皮肤缺损创面模型，每只小鼠2个创面。将创面分成生理盐水组、黏性水凝胶组、含银黏性水凝胶组并进行相应处理，每组16个创面，且每只小鼠的2个创面纳入不同组。伤后3、7、10、14 d，观察创面愈合情况并计算创面愈合率；伤后3 d，观察并计数创面中大肠埃希菌及金黄色葡萄球菌菌落数；伤后14 d，行苏木精-伊红染色和Masson染色分别观察并分析创面上皮化的表皮厚度和胶原纤维的光密度；伤后3、7、10 d，采用免疫组织化学法检测创面中肿瘤坏死因子α（TNF-α）、转化生长因子β1（TGF-β1）及血管内皮生长因子（VEGF）的表达。各指标各时间点创面数均为4个。对数据进行析因设计方差分析、单因素方差分析及Bonferroni校正。 结果： HA-PBA在波数为1 369、1 425 cm-1处检测到特征峰，表明苯硼酸成功接枝到透明质酸上；HA-DA在波数为1 516、1 431 cm-1处检测到特征峰，表明多巴胺已成功接枝到透明质酸上。含质量分数20％丙烯酰胺的黏性水凝胶在37 ℃下，无论是倾斜还是倒立时都保持稳定不流动的凝胶状态。随着丙烯酰胺含量的增加，黏性水凝胶储存模量和损耗模量均有所增加，但3种不同丙烯酰胺含量黏性水凝胶的储存模量和损耗模量随振荡频率或时间的增加变化不明显且储存模量均大于损耗模量。含银黏性水凝胶中银离子释放长达7 d，累计银离子释放率最高达65%。培养1、2、3 d，含银黏性水凝胶组细胞存活率明显低于PBS组和黏性水凝胶组（P<0.05或P<0.01）；培养1 d，黏性水凝胶组细胞存活率明显低于PBS组（P<0.01）。随着伤后时间的延长，3组小鼠创面均不断缩小。伤后3、7、10、14 d，含银黏性水凝胶组创面愈合率分别为（53.0±3.6）%、（75.3±6.9）%、（93.3±1.2）%、（96.7±0.8）%，明显高于生理盐水组的（21.8±6.4）%、（53.9±8.2）%、（72.0±7.8）%、（92.5±0.4）%（P<0.01）。伤后3、14 d，含银黏性水凝胶组创面愈合率明显高于黏性水凝胶组的（43.5±2.4）%、（94.1±1.5）%（P<0.05）；伤后3、10 d，黏性水凝胶组创面愈合率明显高于生理盐水组（P<0.01）。伤后3 d，含银黏性水凝胶组创面中2种细菌菌落数明显少于生理盐水组及黏性水凝胶组（P<0.01），黏性水凝胶组创面中2种细菌菌落数明显少于生理盐水组（P<0.05）。伤后14 d，含银黏性水凝胶组创面基本上皮化且表皮厚度更厚，胶原蛋白含量较其他2组明显增多且胶原排列更加有序；含银黏性水凝胶组创面的表皮厚度较其余2组明显增加（P<0.05），胶原纤维光密度较生理盐水组明显增加（P<0.05）。伤后3 d，含银黏性水凝胶组创面TGF-β1和VEGF的表达明显高于生理盐水组（P<0.05或P<0.01），黏性水凝胶组创面VEGF的表达明显高于生理盐水组（P<0.01）。伤后7 d，含银黏性水凝胶组创面TGF-β1的表达明显高于其余2组（P<0.01），VEGF的表达明显高于生理盐水组（P<0.01）。伤后10 d，含银黏性水凝胶组创面TNF-α的表达明显低于生理盐水组（P<0.05），TGF-β1和VEGF的表达明显高于生理盐水组（P<0.05或P<0.01），且VEGF的表达明显高于黏性水凝胶组（P<0.05）。 结论： 本研究制备的含银黏性水凝胶具有良好的稳定性和弹性，可以持续释放银离子，有助于加速小鼠细菌定植全层皮肤缺损创面的愈合，生物毒性较低，可以促进创面再上皮化、胶原沉积和血管再生，可能涉及炎症细胞的浸润与消退。.