A combined approach for the development of novel sutures with antibacterial and regenerative properties: the role of silver and silk sericin functionalization

Chronic wounds and related infections cause physical and psychological distress in patients, increased mortality, disability and high health care costs. The healing process can be delayed by several factors and in particular by the risk of infections, which can be further complicated by the increasing number of antibiotic-resistant microorganisms. New approaches in wounds management have been encouraged, aiming at preventing infections and improving wound healing. In this scenario, silver has emerged as an ideal antimicrobial agent due to its recognized efficacy against bacteria, viruses and fungi. Moreover, silk and in particular silk sericin from Bombyx mori has demonstrated excellent biological properties and can be considered a good candidate for skin tissue engineering. In this study absorbable PLGA sutures were functionalized with silk sericin and, then, they were treated with silver through an in situ photochemical deposition technology in order to develop an antibacterial and regenerative biomedical device. Morphological analysis was performed by Scanning Electron Microscopy and Energy Dispersive X-Ray Spectroscopy (SEM-EDX) in order to evaluate the presence and distribution of silver deposited on the sutures. The stability and durability of the sericin/silver coatings were tested and the results were related to both antibacterial properties and sample degradation. The biological analyses also aimed at studying the biocompatibility and wound healing properties of the device, evaluating the synergistic effect between sericin and silver.

Open image in new window

     

Synthesis of silver chloride nanocrystal on silk fibers

The synthesis of silver chloride nanocrystals on silk fiber is reported. The growth of the nanocrystal was achieved by sequential dipping of the silk fibers in alternating solution of either silver nitrate or sodium chloride followed by a rinse step. The negative charge present at the surface of the fibers can immobilize silver ions which react in the next sodium chloride bath to form an initiator seed of silver chloride. The repeated alternating dipping of the fiber in the different solutions leads to the growth of AgCl nanocrystals. After 20 alternating dipping steps, the formation of cubic AgCl nanocrystal was observed by SEM, which revealed the presence of 100 nm cubes on the silk fiber. The crystallographic nature of the AgCl crystals was confirmed by X-ray diffraction which confirmed the presence of characteristics diffraction peak of AgCl and a cell size of 5.549 Å. The resulting fiber coated with nano-AgCl crystals could be used as a photocatalyst in water splitting applications or as an antibacterial agent.     

Fabrication of novel biofibers by coating silk fibroin with chitosan impregnated with silver nanoparticles

Nanoparticle based agents often applied as coatings on biomaterials have shown promise in delivering the improved sterility against variety of microbes. In the present study, silk fibers (SF) were coated with chitosan impregnated with silver nanoparticles (Ag–C–SF). These Ag–C–SF fibers were characterized using scanning electron microscopy (SEM) with energy dispersive X-ray analysis, atomic force microscopy (AFM), Infra Red spectroscopy, Thermogravimetric Analysis and Microbiological assay techniques. AFM studies have confirmed the nano sized silver particles in chitosan solution; SEM pictures have exhibited the coating of chitosan along with silver nanoparticles on the silk fibroin. The modified fibers have also shown anti-microbial activity and improved thermal stability. The Ag–C–SF fibers may be explored as wound dressing and tendon reconstruction material in future.     

丝织物基纳米结构银膜形貌及抗菌性能研究

为了实现纺织材料表面抗菌功能化,采用低温磁控溅射技术在真丝织物表面沉积1~5nm厚的纳米结构银薄膜。采用振荡烧瓶法测试样品的抗菌性能;利用原子力显微镜(AFM)分析了纳米银薄膜的表面形态和粒径。结果表明:在实验范围内,1nm厚的银膜已具有优良的抗菌性能。从纳米银薄膜表面形态结构可以看出,纳米结构银薄膜由极其微小的均匀性较好的粒子组成,基本呈连续覆盖状态,随着溅射时间的延长,纳米银颗粒存在一定团聚现象,粒径呈增大趋势。X射线衍射(XRD)测试表明,沉积在丝织物表面的纳米银薄膜形成了一定结晶结构。     

In situ synthesis of silver nanoparticles on silk fabric with PNP for antibacterial finishing

This research presents a generic strategy to fabricate antibacterial textile through in situ synthesis of silver nanoparticles on the fabric with smart polymeric molecules. Silk fabric and polyamide network polymer (PNP) were chosen for this study. PNP which has numerous amino groups and three-dimensional structure was applied to entrap silver ions into silk fabric. The pretreated silk fabrics were heated by steam method to make silver nanoparticles synthesized in situ on them without any other reductant and linker to provide silk fabric with antibacterial properties. The results indicated that the treated silk fabrics had excellent antibacterial activity and laundering durability. The quantitative bacterial tests showed the bacterial reduction rates of Staphylococcus aureus and Escherichia coli were able to reach above 99 % with not more than 0.05 mmol/L of AgNO₃. The whiteness of silk fabric only changed from 90.47 to 86.49. The antibacterial activity of the treated silk fabric was maintained at 98.86 % reduction even after being exposed to 30 consecutive home laundering conditions. In addition, the results of scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy confirmed that silver nanoparticles had generated and dispersed well in Ag⁰ form on the surface of silk fibers. The understanding acquired from this work will allow one to work with the preparation of other silver nanoparticles functional textiles with excellent antibacterial activities and laundering durability through this facile, eco-friendly in situ synthesis method.     

Photoluminescence spectroscopy as a probe of silver doped zeolites as photocatalysts

Nanoclusters of silver ions, dicyanoaurate ions, and dicyanoargentate ions doped in zeolite hosts have been prepared. Luminescence, Raman, and FT-EXAFS spectroscopies along with extended Hückel calculations indicate the formation of silver and [M(CN)₂⁻]_m (M=Au and Ag) oligomers in the zeolite host. The silver and gold nanoclusters in zeolites enhance the photodecomposition rates of NO_x, malathion, and carbaryl when compared to the pollutant's behavior in the absence of silver doped zeolites with the observed rate increase attributed to excimer and exciplex formation.     

Elastic constants of silver as a function of temperature

The temperature dependence of the elastic constants of silver single crystals has been determined over the range 300–1173 K with the piezoelectric ultrasonic composite oscillator technique (PUCOT). From a comparison of the present results with those available from the literature, it is deduced that the PUCOT and hence other standing-wave techniques are adequate for measuring compliances, but these techniques may have complications for computations of stiffnesses.     

Bio-composite aspects of silk: the sericin sheath acting as a matrix

Industrial Bombyx mori silk yarns have been degummed and mechanically tested. The principal mechanical characteristics of these yarns have been obtained and compared, before and after degumming. It has been observed that the sericin sheath surrounding the silk fibres plays a bigger part in determining behaviour than had been expected. The initial gradients of the force/strain curves were reduced by 21% when the sericin were removed and this was associated with a 20% fall in the failure forces obtained. The force/strain curves up to failure of the yarns were completely modified with the removal of the sericin and showed a multi-level fracture surface rather than a net failure. This variation was not due to the treatment involved in removing the sericin. The role of the sericin sheath has been studied using scanning electron microscopy with in situ tensile testing. The sericin have been seen to act like a matrix, as in a fibre composite with the silk fibres as the reinforcements. As in a composite, the force transfer between the sericin sheath and the inner fibre is controlled by shear forces at the interface between the two and result in the modified fracture morphology and physical properties.     

Fast patterning of poly(methyl methacrylate) by a novel soft molding approach and its application to the fabrication of silver structures

A novel single-step approach for the fabrication of poly(methyl methacrylate) structures by soft molding of a 5 wt% solution in acetone is reported. The use of a low weight solution and of a solvent with high volatility ensures a very fast patterning, down to 10 s. In addition, the process is extremely simple and cost-effective, since just one elastomeric mold is needed, and areas as large as 1 cm² were patterned uniformly and defect-free. The process was applied to the fabrication of silver structures by silver deposition via electroless plating or evaporation followed by poly(methyl methacrylate) removal. Structures of various shapes and sizes, with dimensions in the micrometer and submicrometer range were successfully fabricated, showing the versatility of the process. This silver patterning process is particularly well suited for applications in microelectronics and optoelectronics, such as the fabrication of transparent electrodes for solar cells and displays, manufacturing of metal etching masks and wiring of printed circuits.     

A novel approach to a fine particle coating using porous spherical silica as core particles

The applicability of porous spherical silica (PSS) was evaluated as core particles for pharmaceutical products by comparing it with commercial core particles such as mannitol (NP-108), sucrose and microcrystalline cellulose spheres. We investigated the physical properties of core particles, such as particle size distribution, flow properties, crushing strength, plastic limit, drying rate, hygroscopic property and aggregation degree. It was found that PSS was a core particle of small particle size, low friability, high water adsorption capacity, rapid drying rate and lower occurrence of particle aggregation, although wettability is a factor to be carefully considered. The aggregation and taste-masking ability using PSS and NP-108 as core particles were evaluated at a fluidized-bed coating process. The functional coating under the excess spray rate shows different aggregation trends and dissolution profiles between PSS and NP-108; thereby, exhibiting the formation of uniform coating under the excess spray rate in the case of PSS. This expands the range of the acceptable spray feed rates to coat fine particles, and indicates the possibility of decreasing the coating time. The results obtained in this study suggested that the core particle, which has a property like that of PSS, was useful in overcoming such disadvantages as large particle size, which feels gritty in oral cavity; particle aggregation; and the long coating time of the particle coating process. These results will enable the practical fine particle coating method by increasing the range of optimum coating conditions and decreasing the coating time in fluidized bed technology.     

Electrodeposition of silver as a precursor matrix of magnetoresistive materials

The design of a bath able to electrodeposit silver at a relatively high negative potential was attained. The preparation of silver films at negative potentials in conditions at which dendritic growth is avoided, makes the process useful in silver-matrix magnetoresistive materials manufacture. Thiourea as a complexing agent was able to accomplish this purpose. Results indicate that thiourea bath produces homogeneous and fine-grained silver deposits with low sulfur content, avoiding hydrogen reaction in the potential range at which coherent deposits were obtained. Morphological and structural analysis were made as a function of temperature and the presence in the bath of other species.     

Development of a silk and collagen fiber scaffold for anterior cruciate ligament reconstruction

The objective of this study was to determine a silk-collagen fiber ratio for an anterior cruciate ligament (ACL) reconstruction composite scaffold device. Composite fiber scaffolds with silk volumes ≥14 % and collagen volume <86 % demonstrated comparable or greater initial ultimate tensile stress relative to the human ACL. Silk scaffolds implanted subcutaneously and intraarticularly in rabbits demonstrated an 84 and 92 % reduction in strength with a 26 and 22 % reduction in volume after 8 weeks, respectively. The mechanical degradation findings of this preliminary study suggest that a composite scaffold with an initial UTS value of at least 129 MPa, or roughly a 48:52 silk to collagen volume ratio meets the minimal mechanical requirements necessary to proceed to a functional ACL reconstruction study in vivo.     

仪表用高强度弹簧不锈钢丝(带)强化机制的研究

较详细化阐述了高强度不锈钢中各元素的作用和各种组织的强化机理,对指导生产和加工起到的一定的作用。     

Preparation and properties of a novel electrically conductive adhesive using a composite of silver nanorods, silver nanoparticles, and modified epoxy resin

A novel preparation method for a high-performance electrically conductive adhesive (ECA) which consisted of silver nanorods, silver nanoparticles and modified epoxy resin was developed. Silver nanorods (100 nm in diameter and 5 μm in length) were synthesized by reduction of silver nitrate with ethylene glycol in the presence of Pd seeds and poly (vinyl pyrrolidone) (PVP). Silver nanoparticles (50~60 nm) were synthesized using N, N′-Dimethylformanide as the reducing agent and PVP as the stabilizer. The nanorods and nanoparticles were dispersed well and no agglomerate in the matrix. The volume electrical resistivity tests showed the volume electrical resistivity of the ECA was closely related with the various sintering temperatures and time, and the ECA could achieve the volume electrical resistivity of (3–4) × 10⁻⁵ Ω cm after sintering at 160 °C for 20 min. Moreover, the results showed the as-prepared ECA was able to achieve low-temperature sintering and possessed excellent electrical, thermal, and mechanical properties.     

System performance evaluation of refractive surgical lasers: a mathematical approach

A study was conducted for the purpose of improving the designs of the next generation of refractive surgical laser systems. Two common refractive laser systems, variable-spot scanning (type A) and small-spot scanning (type B), are discussed by identifying sources of error that could adversely affect the capability of these lasers to accurately produce complex, customized wavefront guided ablations. A mathematical model was used to construct a laser simulator that models the two common laser systems in terms of the root-mean-square error. Error sources from ablation profile fitting, ablation registration, eye tracking, and the laser delivery system are compared, and the relative contribution of each to the overall system error is analyzed. This system-level analysis can be helpful to the improvement of both laser systems.     

A quicker degradation rate is yielded by a novel kind of transgenic silk fibroin consisting of shortened silk fibroin heavy chains fused with matrix metalloproteinase cleavage sites

Degradation performance of silk fibroin is an important property for its medical applications. Herein we constructed a shortened silk fibroin heavy chain protein fused with a matrix metalloproteinase cleavage site (SSFH-MMP) along with a glutathione S-transferase tag ahead. The digestion assay shows it can be cut by matrix metalloproteinase-2 (MMP-2) at its MMP cleavage site. Furthermore, we introduced the SSFH-MMP into silk fibroin by genetic modification of silkworms in order to increase the degradation rate of the silk fibroin. After acquisition of a race of transgenic silkworms with the coding sequence of the MMP cleavage site in their genomic DNA, we tested some properties of their silk fibroin designated TSF-MMP. The results show that the TSF-MMP has MMP cleavage sites and yields a quicker degradation rate during dilution in MMP-2 enzyme buffer or implantation into tumor tissues compared with that of normal silk fibroin. Moreover, the TSF-MMP is in vitro non-toxic to human bone marrow mesenchymal stem cells (hBM-MSCs) indicating that the TSF-MMP may become a biomaterial with a quicker degradation rate for its medical applications.