Construction, Characterization And Antibacterial Activity Study Of Silver Nanomaterials Coated Biomaterials

Material-centered infection has been a fatal problem in the application of biomaterials in medical area. The pathogenic bacteria always can find their way to attachment to the medical devices or biomaterials, because no patient can be totally isolated from the surroundings. The microorganisms are abundant in the environment, from biomaterials, surrounding tissues and devices to superficial infections and blood-borne contamination. What’s worse, the formation of biofilm deactivates many normal sterilizing methods. Once attached to a surface, the bacteria often show a developmental sequence involving cell-cell signaling and the production of polysaccharide surfactants that help to maintain free flowing water channels, protecting them from the outside negative environment. The bacteria can band together in pods, making they are difficult to wipe out. Infection of materials would trigger severe pains and extra costs to patients by longer revision surgeries that result from the removal of infectious implants. Therefore, drugs that prevent biofilms would make many infections easier to treat.One promising prevention strategy against implant infections is based on surface modifications and coatings. Silver has broad use in in biomedical applications, water and air purification, clothing, and numerous household products by its broad-spectrum antimicrobial properties. People has been using silver as containers to preserve food thousands years before. Even though scientists proved that the metallic silver can result to argyrism, new researches suggested that silver nanomaterials inherit the excellent antibacterial activity but avoid its toxicity to tissues. Therefore, silver releasing coatings are believed to exhibit many desirable advantages used as antibacterial agent. It acts against a wide range of bacteria and viruses and possesses longer release periods, lower toxicity to mammalian tissues, simple incorporation methods and no bacteria resistance. The release of silver ions can prevent the attachment of bacteria to materials and devices, as well as kill the bacteria in the surroundings, which help to solve the problem of infection.Based on the antibacterial property of silver nanomaterials, we try to solve the infection problem of several traditional and novel biomaterials. In this work, three kinds of biomaterial are modified with prophylactic silver nanomaterials:the stainless steel that is widely used as medical devices, the porcine acellular dermal matrix that are used as wound dressings and the chitosan-hydroxyapatite scaffold used in bone tissue engineering.The main work is as follows:1. In this work, we present a simple method to fabricate stainless steel-based antimicrobial composites by fixing silver nanoparticles onto the surface. Silver nanoparticles were covalently assembled on the surface of stainless steel by using3-aminopropyltriethoxysilane (APTES) as the coupling agent. First, APTES monolayer is fixed onto the surface of the steel by immersing stainless steel into a1%ethanol solution of APTES by a covalent bond Si-O-Cr through the dehydration between Si-OH and the-OH linked to chromiumoxide on the stainless steel surface. Then silver nanoparticles are coordinated with-NH2group in APTES. The crystal structure of the silver nanoparticles was examined by X-ray diffractometry (XRD) and the particle size distribution in the colloid was measured on a dynamic light scattering instrument. The ultraviolet-visible (UV-vis) spectrum of the silver colloidal solution was measured. Scanning electron microscopy (SEM) observations were carried out and the atomic absorption spectrometry measurements were performed to gauge the release rate of silver ions from the AgNPs-stainless steel surface. After24h immersion the release of silver ions amounts to a total of0.07ppm. The bactericidal rate of the composite on Escherichia coli (E. coli) is greater than99%, and the inhibition zone is about28mm in diameter. Combining the low cost and high effectiveness in inhibiting the growth of bacteria, such composites are expected to be useful as antimicrobial materials that may have great potential antimicrobial applications.2. We take advantage of the great amount of-NH2residue in the porcine acellular dermal matrix (PADM) network whose main composition is type Ⅰ collegan to bond silver nanoparticles on the surface of PADM by directly immersing PADM into silver nanoparticle suspension, and finally to form a wound dressing with antibacterial activity. Silver nanoparticle solution was examined by XRD and UV-vis. SEMobservations were carried out and the atomic absorption spectrometry measurements were performed to gauge the release rate of silver ions from the AgNPs-stainless steel surface. Silver nanoparticles can be coordinated with-NH2group in the PADM. Moreover, porous structure is not destroyed, because the amount and size of silver nanoparticles are very small. The mechanical property, water adsorption and water vapor permeability of PADM coated with silver (Ag-PADM) is as good as pure PADM. The bactericidal rate of the0.005Ag-PADM on E. coli is greater than99.8%, and the inhibition zone is about21mm in diameter. With the increase of the concentration of silver nanoarticles solution, the antibacterial rate of Ag-PADM increase. In vitro fibroblast3T3culture shows that PADM treated by low concentration of silver nanoparticles is cytocompatible, with slight influence of cell proliferation and morphology.3. In this study we proposed a practical ion-substitution method (ion substitution) to in situ synthesize silver phosphate on the surface of a two level three dimensional chitosan/nano-hydroxyapatite scaffold (CnHS). The chitosan/nano-hydroxyapatite scaffold was immersed into silver nitrate solution with different concentration. X-ray photoelectron spectroscopy (XPS) measurement, XRD and FTIR spectroscopy were carried out to analyze the composition of the CnHS that is undergone ion-substitution process. SEM was carried out to examine the topography of the scaffolds loaded with silver. Silver phosphate was in-situ formed on the surface of CnHS and did not change the porous structure of original scaffold, leaving the channels for cell proliferation, immigration and mass transportation. Release test of silver ions in a PBS solution suggests that silver ions were released gradually and continuously during the initial six days. Antibacterial property and cytocompatibility of the scaffolds treated with different concentrations of silver nitrate were assessed by in vitro assays with E. coli and MC3T3-E1, respectively. The bacteriostasis ability of the silver-containing scaffolds is confirmed by the large inhabitation zone (15mm) and high bactericidal rate (>99%). Cell proliferation, migration, morphology and ALP activity of MC3T3-E1cultured on the scaffold with low silver phosphate contents were comparable with those on control samples. High concentration of silver phosphate is toxic to MC3T3-E1.