| Infection occurs more easily to a trauma patient as injured skin cannot provide good prevention against microorganism, which is sometimes life-threatening. Antibiotics may not meet the demand as the drug-resistance of bacteria is increasingly common, which indicates the need to develop alternatives.Nano silver has great advantages in preventing bacteria for its high specific area and surface activities. Its bacteriostasis is better than silver ion with the same concentration. Unlike traditional antibiotics, low content of nano silver can also prevent pathogenic bacteria effectively and persistently. However, nano silver may aggregate spontaneously,to prevent its aggregation and sediment, organic or inorganic materials are commonly used as stabilizers.Sodium alginate, a natural alkaline polysaccharide,consists of mannuronic acid(M block) and guluronic acid(G block)units. It can form hydrogel by binding with divalent cations. Due to its low price, low toxicity, great biocompatibility and biodegradability, sodium alginate is used widely. During the preparation of nano silver sol, sodium alginate can be served as reducing agent and stabilizer. There are many hydroxyl and carboxyl groups on alginate molecular chains. Hydroxyl groups can reduce the Ag+ to nano silver, meanwhile carboxyl groups can electrostatically interact with Ag+ to form a complex.Although nano silver can effectively prevent bacteria, Ag in excessive concentrations is toxic to humans.Generally, all living organisms need trace elements, such as calcium, phosphate and other ions.β- tricalcium phosphate(β-TCP), a common biomedical material, can be degraded into Ca2+ and PO43- by living organisms. In this study, β-TCP particles and nano silver were co-blended to prepare silver-tricalcium phosphate(Ag-TCP) nanoparticles, in which nano silver evenly distributed on the surface of β-TCP particles. Ag-TCP nanoparticles could stabilize nano silver and prevent aggregation. Also it could control the release of silver and reduce the dose of silver by utilizing features of bacteria degrading the β-TCP particles.Calcium alginate hydrogel can form freeze-dried membranes by lyophilization. Due to its three-dimensional porous structure, the freeze-dried membrane has strong absorption ability and keeps the environment of wound moist. Besides, it can release Ca2+ in the ion-exchange, helping blood clot. In spite of its advantages, the freeze-dried membrane lacks antimicrobial activities. Plenty of wound fluid will increase the risk of infection, which restricts its application. By adding silver-tricalcium phosphate nanoparticles into calcium alginate freeze-dried membrane,we obtained a highly absorbent and good antimicrobial wound dressing in this research.In this research, nano silver carried by sodium alginate was prepared by photochemical reducing method, which was analyzed in terms of bacteriostasis. Then silver- tricalcium phosphate nanoparticles were formulated by co-blending. Moreover, freeze-dried calcium alginate served as the base material, with which nanoparticles were combined to form silvertricalcium phosphate/calcium alginate membrane. Its physical properties and antibacterial activity were evaluated later. The main results were summarized as follows.Firstly, nano silver sol was prepared and its antibacterial activity was analyzed. Sodium alginate was used as reducing agent and stabilizer, and silver nitrate as precursor to produce nano silver sol under UV lighting. The physical properties of nano silver were determined with the instruments such as UV-vis, TEM, XRD, FTIR and DLS, and its bacteriostasis was evaluated by inhibition zone experiment. The results showed that by taking sodium alginate as reducing agent and stabilizer, stable silver nanoparticles were produced, of which the shape was ball-like or spherical, the particle size was between 1 and 5 nm, and showed excellent antibacterial activity against gram-negative bacteria E.coli and gram-positive bacteria S.aureus.Secondly, silver-tricalcium phosphate nanoparticles were prepared. Pure β-TCP particles were successfully prepared through high temperature calcination by chemical coprecipitation method. XRD results indicated that the precursor, calcium-deficient hydroxyapatite, became pure β-TCP after high temperature calcination, and there were not any other diffraction peaks appearing. FTIR analysis showed that after the calcination, existence of the absorption peak corresponding to phosphate indicated the product was β-TCP. As the absorption peak corresponding to the precursor HPO42- disappeared, there was no HPO42- after the reaction.Thirdly, silver-tricalcium phosphate/calcium alginate membrane was prepared and its properties were studied. Silver-tricalcium phosphate/calcium alginate membrane was produced by freeze drying technology. SEM was adopted to observe its interior structure. FTIR and XRD were used to evaluate changes of its groups and crystallinity. Also, its absorption and liquid-binding abilities were detected. Moreover, inhibition zone and plate colony-counting method were employed to evaluate its bacteriostasis. According to the results, with three-dimensional porous structure, the freeze-dried membrane had strong absorption ability, and the rate of its absorption of distilled water and normal saline respectively reached 20g/g and 21g/g; besides, it also had certain liquid-binding power, which enabled it to absorb plenty of wound fluid, maintained the moist environment of the wound, and promoted the wound healing. Mixed with silver- tricalcium phosphate nanoparticles, freeze-dried membrane had fine bacteriostasis, which ensured the effective bacteriostasis of the material, and meanwhile controlled the release of silver.TEM showed that β-TCP particles were bar-shaped, 200~300nm long, and appeared certain aggregation. β-TCP particles and nano silver/sodium alginate produced by photochemical reducing method were co-blended to prepare silver-tricalcium phosphate nanoparticles; XRD results indicated that composite particles contained nano silver of face-centered cubic configuration; and FTIR results showed that compared with β-TCP, although the intensity of the absorption peak corresponding to phosphate decreased, nano silver and β-TCP both maintained their structural stability; and TEM showed that the size of silver nanoparticle was between 2 and 5nm, and it evenly distributed on the surface of β-TCP particle.In general, nano silver/sodium alginate was successfully prepared in a simple and environment-friendly way. The nano silver prepared had strong stability and small particle size, and its antibacterial activity against gram-negative bacteria E.coli and gram-positive bacteria S.aureus was obvious, which provided references for the development of environmental bacteriostasis agent. Meanwhile, the silver-tricalcium phosphate nanoparticles were formulated by co-blending. Sodium alginate served as the base material, with which nanoparticles were combined to form silver-tricalcium phosphate/calcium alginate freeze-dried membrane. The freeze-dried membrane possessed three-dimensional porous structure, strong absorption and liquid-binding ability, and it could maintain moist environment of the wound. Besides, it had fine bacteriostasis, which was of potential application value in the anti-infection field. |
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