In vitro method to assess the antimicrobial activity and potential efficacy of novel types of wound dressings

AIMS: To develop a simple, reproducible in vitro static diffusion method using cellulose disks and defined species to test antimicrobial efficacy of wound dressings. METHODS AND RESULTS: Cellulose disks were inoculated by immersion in cell suspensions of target species Staphylococcus epidermidis, Candida albicans and Fusobacterium nucleatum. Test and control wound dressings were cut into equal sized squares (25 x 25 mm) and applied to the surface of 10-mm thick tryptone yeast extract agar on test beds. Following a 2-h equilibration period, inoculated cellulose disks were inserted (one per dressing) at the interface between dressing and agar surface and a small weight applied over each square. At various sampling times, disks were removed and surviving cells enumerated by viable counts. Disk to disk variation for microbial loading was assessed using S. epidermidis for both initial (n = 16) and standard treatment (n = 16) conditions. The coefficient of variation was low (<5%) indicating good reproducibility for cell loading and treatment position on the test bed. Replicate assays (n = 6) using S. epidermidis and oxyzyme gels produced similar kill rates with low scatter (R2 > 0.9) indicating good reproducibility between assays. Significant differences (P < 0.05) in kill rates were observed for different target species, types of dressing and test bed conditions (+/-blood and nutrients). CONCLUSIONS: The method is reproducible and useful in tracking the death kinetics of test species, enabling the comparison of different types of dressing. SIGNIFICANCE AND IMPACT OF THE STUDY: The reported method has significant advantages over established test procedures; it can be applied equally across a wide range of target species (including anaerobes and yeasts), a wide range of conditions, and different types of surface dressings, including those relying upon oxygen diffusion.     

一种可止血的富血小板血浆壳聚糖/丝素蛋白多孔伤口敷料的制备及性能表征

为了进一步提高伤口敷料的止血性能,文中在生物相容性良好的壳聚糖溶液中引入含有多种生长因子的人源性富血小板血浆(Humanplatelet-richplasma,hPRP),并加入不同体积比例(1∶1、1∶3、3∶1、1∶0)的丝素蛋白溶液以提高材料的多孔性与止血性,通过冷冻干燥法制备不同配比的hPRP-壳聚糖/丝素蛋白敷料,并将纯壳聚糖敷料作为对照组,研究hPRP和丝素蛋白对敷料的止血性能的影响以及丝素蛋白对PRP中生长因子控制释放的影响。结果表明,在壳聚糖敷料中引入hPRP对敷料的止血性有所提高,但对敷料的多孔结构及吸水率无明显改善,若在hPRP-壳聚糖溶液中按照体积比为1∶1的比例加入丝素蛋白溶液,会得到具有较为均匀的多孔结构的敷料,敷料的孔隙率与吸水率分别可达到86.83%±3.84%与1 474%±114%,且该比例的敷料在快速止血性能上表现优异。此外,加入丝素蛋白与壳聚糖比例为1∶1的PRP敷料能有效减少PRP中生长因子在初始阶段的爆裂释放。因此,含hPRP的壳聚糖/丝素蛋白复合敷料有望成为一种能快速止血且能促进伤口愈合的新型伤口敷料。     

静电纺丝用作难愈合伤口敷料的研究进展

静电纺丝伤口敷料作为一种新型功能性敷料,具有较大的比表面积、可调控的孔隙率和良好的生物性能,既有益于细胞呼吸,又 可抑制细菌感染伤口,并能促进细胞增殖和加速创面愈合,是未来伤口敷料研发领域发展的新方向。介绍静电纺丝纳米纤维的原理、特点, 重点阐述各类聚合物、生物活性物质在静电纺丝伤口敷料制备中的应用进展。     

基于"湿性愈合"理论的新型敷料在糖尿病足溃疡创面处理中的应用

目的:观察基于"湿性愈合"理论的新型敷料用于糖尿病足溃疡创面的处理的治疗效果。方法:首先评估糖尿病足溃疡创面,然后根据不同情况采用不同新型敷料,应用湿性伤口愈合理论对48例糖尿病足溃疡的患者进行临床研究,选取48例传统方法处理的同类患者作为对照。结果:结果显示湿性愈合组患者出院时的创面愈合率较对照组明显提高,治疗周期明显缩短(P<0.05),换药次数明显减少(P<0.05)。结论:基于"湿性愈合"理论的新型敷料在糖尿病足溃疡创面的处理中取得了良好效果,值得进一步研究与应用。     

Plasma treatments of dressings for wound healing: a review

This review covers the use of plasma technology relevant to the preparation of dressings for wound healing. The current state of knowledge of plasma treatments that have potential to provide enhanced functional surfaces for rapid and effective healing is summarized. Dressings that are specialized to the needs of individual cases of chronic wounds such as diabetic ulcers are a special focus. A summary of the biology of wound healing and a discussion of the various types of plasmas that are suitable for the customizing of wound dressings are given. Plasma treatment allows the surface energy and air permeability of the dressing to be controlled, to ensure optimum interaction with the wound. Plasmas also provide control over the surface chemistry and in cases where the plasma creates energetic ion bombardment, activation with long-lived radicals that can bind therapeutic molecules covalently to the surface of the dressing. Therapeutic innovations enabled by plasma treatment include the attachment of microRNA or antimicrobial peptides. Bioactive molecules that promote subsequent cell adhesion and proliferation can also be bound, leading to the recruitment of cells to the dressing that may be stem cells or patient-derived cells. The presence of a communicating cell population expressing factors promotes healing.     

Effect of a Synthetic Dressing Formed on a Burn Wound in Rats: a Comparison of Allografts, Collagen Sheets, and Polyhydroxyethylmethacrylate in the Control of Wound Infection

Allograft dressings to control Pseudomonas wound infections in rats were studied on surgical wounds and escharectomized burn wounds. The effects of allografts were compared with a collagen sheet (Aviderm) and a synthetic dressing, polyhydroxyethylmethacrylate (Hydron), formed on the wound by mixing the polymer and the solvent. The results indicated that infections in surgical wounds were more easily controlled by dressings than similar contaminations in burn wounds. A procedure was described for the formation of a synthetic dressing directly on the wound from a mixture of polymer and solvent. This type of preparation completely filled the wound area and sealed the edges, preventing further contamination, and gave excellent coverage of the wound. With 24 h of coverage of escharectomized burn wounds, allografts provided the best dressing for reduction of wound organisms. At 96 h of coverage, Hydron and Aviderm produce significant reductions in the Pseudomonas resident in the burn wound. The results support the thesis that suitable dressings promote local host defense processes which kill the contaminating bacteria.     

Swelling of hydrocolloid dressings

Wound healing is promoted by dressings that maintain a moist environment. Specifically, hydrocolloid dressings allow excess fluid to escape without permitting wound desiccation. However, the fluid handling capacity of hydrocolloid dressings depends on many factors such as the physicochemical properties of the gel formulation, and the design of the dressing. We measured the moisture uptake kinetics of different hydrocolloid dressings by placing the gel side of a sample in contact with water. The time evolution of the thickness was measured by means of a video camera linked to a computer. The theory of Tanaka and Fillmore 1979 was used to predict the kinetics of uniaxial swelling of a cylindrical gel sample. The model allows to associate to an experimental curve a total thickness increase h_f — h₀ (where h_f and h₀ are respectively the final and initial thickness) and a characteristic time τ. The model also relates h_f — h₀ and τ to the physicochemical composition of the dressing, and to the initial thickness h₀. The influence of h₀ is discussed by means of experiments performed on dressings with different initial thickness.     

Antimicrobial Activity of a Novel Vascular Access Film Dressing Containing Chlorhexidine Gluconate

Background

Covering insertion sites with chlorhexidine impregnated dressings has been proven to be clinically effective in reducing catheter related blood stream infections (CR-BSI). Two chlorhexidine gluconate (CHG)-impregnated dressings are commercially available, a polyurethane foam disk and a film dressing containing a chlorhexidine gluconate-impregnated gel pad. While both have demonstrated efficacy in clinical settings, the major drawback of high cost and impaired IV insertion site visibility limits their usage. A new, simple film dressing containing CHG within its adhesive layer is now available. The objective of this study was to test the in vitro antimicrobial efficacy of the new dressing in comparison to the CHG-impregnated gel dressing.

Methods

Quantitative aliquots of suspensions (concentration of 1.0x10⁶ to 5.0x10⁶ cfu/sample) of clinically relevant challenge organisms (Staphylococcus species, gram-negative bacilli, Candida albicans) were incubated in contact with the new CHG-containing film dressing, a placebo version of the same (negative control) and the commercially available CHG-impregnated gel dressing (positive control). Serial dilutions of the surviving organisms were quantified using the pour plate after 1, 3, 5, and 7 days of incubation in order to calculate an antimicrobial log₁₀ reduction for each organism/dressing combination at each point in time.

Results

The new CHG-containing film dressing delivered greater than 5.0 log₁₀ reduction throughout the 7 days on all aerobic gram-negative bacilli and Staphylococcus species tested. As of day 1 the CHG-containing film dressing provided greater than 5.0 log₁₀ reduction on Candida albicans. There were no statistically significant differences in the log₁₀ reduction between the two dressings tested.

Conclusion

The new CHG-containing film dressing was found to be as effective as the chlorhexidine gluconate-impregnated gel dressing on clinically relevant microbes.     

Preparation and characterization of antimicrobial wound dressings based on silver, gellan, PVA and borax

Silver-loaded dressings are designed to provide the same antimicrobial activity of topical silver, with the advantages of a sustained silver release and a reduced number of dressing changes. Moreover, such type of dressing must provide a moist environment, avoiding fiber shedding, dehydration and adherence to the wound site. Here we describe the preparation of a novel silver-loaded dressing based on a Gellan/Hyaff(?) (Ge-H) non woven, treated with a polyvinyl alcohol (PVA)/borax system capable to enhance the entrapment of silver in the dressing and to modulate its release. The new hydrophilic non woven dressings show enhanced water uptake capability and slow dehydration rates. A sustained silver release is also achieved. The antibacterial activity was confirmed on Staphylococcus aureus and Pseudomonas aeruginosa.     

A seed dressing combining fungal endophyte spores and fungicides improves seedling survival and early growth in barley and oat

The use of beneficial fungi as crop inoculants is constrained by the need for application of fungicides because the pathogen controlling fungicides often concurrently suppress the efficacy of the beneficial mycobiont. Root endophytic fungi have been shown to improve agronomic traits in spring barley and may be less sensitive to the regularly applied foliar fungicides. We hypothesised that a consortium of fungal endophyte species applied as a seed spore dressing may improve the germination and subsequent growth of barley and oat seedlings. We tested a range of seed dressings to evaluate the effects of the endophytes: untreated seed, regular fungicidal dressing (triticonazole and prochloraz), endophyte seed spore dressing and a combination of endophyte and fungicide. We found significant increases in mean barley seedling length induced by the endophytes after 28 days of seedling growth at time points of up to 6 months from seed dressing. The increases in mean seedling length were greatest for the combined fungal endophyte and fungicide treatment. For the oat cultivar, we found even more substantial endophyte associated increases in mean seedling length. These results indicate that the endophytes tested here are persistent in a seed dressing, enhance early seedling growth, are fungicide tolerant and are competent in two different genera of cereal crops.     

Clinical trials of amniotic membranes in burn wound care

Four test conditions of increasing complexity were used to evaluate the clinical efficacy of amniotic membranes as biologic dressings on donor sites and burn wounds in children. These were the clean-skin donor-site wound, the uncontaminated shallow partial-thickness burn wound, the bed of freshly excised full-thickness wounds, and the granulating surface of colonized burn wounds. The rate of epithelialization under amniotic membranes was the same as that under 5% scarlet red ointment or 0.5% silver nitrate solution dressings. Preservation of a healthy excised wound bed and maintenance of a low bacterial count in contaminated wounds paralleled the experience with human allograft dressings despite technical difficulties and the absence of vascularization of amniotic membrane and its fragile structure. Tentative conclusions are drawn as to the mechanisms by which biologic dressings exert their beneficial effects.     

Electrospun zwitterionic poly(sulfobetaine methacrylate) for nonadherent, superabsorbent, and antimicrobial wound dressing applications

Zwitterionic poly(sulfobetaine methacrylate) (PSBMA) has been well studied for its superhydrophilic and ultralow biofouling properties, making it a promising material for superabsorbent and nonadherent wound dressings. Electrospinning provides multiple desirable features for wound dressings, including high absorptivity due to high surface-area-to-volume ratio, high gas permeation, and conformability to contour of the wound bed. The goal of this work is to develop a fibrous membrane of PSBMA via electrospinning and evaluate its properties related to wound dressing applications. Being superhydrophilic, PSBMA fibers fabricated by a conventional electrospinning method would readily dissolve in water, whereas if cross-linker is added, the formation of hydrogel would prevent electrospinning. A three-step polymerization-electrospinning-photo-cross-linking process was developed in this work to fabricate the cross-linked electrospun PSBMA fibrous membrane. Such electrospun membrane was stable in water and exhibited high water absorption of 353% (w/w), whereas the PSBMA hydrogel only absorbed 81% water. The electrospun membrane showed strong resistance to protein adsorption and cell attachment. Bacterial adhesion studies using Gram negative P. aeruginosa and Gram positive S. epidermidis showed that the PSBMA electrospun membrane was also highly resistant to bacterial adhesion. The Ag(+)-impregnated electrospun PSBMA membrane was shown microbicidal, against both S. epidermidis and P. aeruginosa. Such electrospun PSBMA membrane is ideal for a novel type of nonadherent, superabsorbent, and antimicrobial wound dressing. The superior water absorption aids in fluid removal from highly exudating wounds while keeping the wound hydrated to support healing. Because of the resistance to protein, cell, and bacterial adhesion, the dressing removal will neither cause patients' pain nor disturb the newly formed tissues. The dressing also prevents the attachment of environmental bacteria and offers broad-spectrum antimicrobial activity. It is the first work to develop the water-stable electrospun PSBMA membrane, which has great potential for wound dressing and other applications.     

纳米银-活性炭纤维敷料的体外抗菌实验研究

目的：观察比较纳米银-活性炭纤维敷料、纳米银敷料、碳纤维敷料和普通敷料对大肠杆菌、金黄色葡萄球菌和绿脓杆菌的抑菌效果,为临床创面合理应用敷料提供理论依据。方法：1）、抑菌圈法将敷料剪成直径为10mm的圆片,灭菌后贴于接菌的培养皿上,置37℃电热恒温培养箱培养16～24小时,游标卡尺测量抑菌圈大小。2）、振荡烧瓶实验称取被剪成10mm×10mm大小的敷料样品0.75g,灭菌后加于含70mL PBS和5mL浓度为1×104cfu/mL菌悬液的250 mL烧瓶,封口固定于振荡器上以300r/h分别振荡2min和1h,各取20μL样液作为振荡前和振荡后,均匀涂于MH培养皿,37℃电热恒温培养箱孵育16～24小时后计数,测定抑菌率。结果：与其他三组敷料相比,纳米银-活性炭纤维敷料的抑菌圈和抑菌率最大（P〈0.05）。结论：纳米银-活性炭纤维敷料具有较强的广谱抗菌作用,是目前临床上较为理想的创面抗感染敷料。     

THE CONTROL OF WIREWORM BY GAMMA BENZENE HEXACHLORIDE: THE DEVELOPMENT OF A SEED DRESSING FOR CEREALS

Gamma benzene hexachloride has been used successfully as a seed dressing in field trials for wireworm control. For application to cereals at 2 oz./bushel, the optimum concentration of γ-isomer was 20–30 % in a dressing which advantageously included an organomercurial seed disinfectant.
Risks to germination and plant growth were thoroughly explored in the field. The 20 and 30 % dressings were safe; over-strength dressings containing 50 or 70 %γ-B.H.C. did not reduce grain yields significantly.
Seed dressed with 20 or 30 %γ-B.H.C. germinated normally after storage for 12 months. When seed was dressed at 4 oz./bushel with 35 %γ-B.H.C. and 1 % mercury as organomercurial, germination was delayed but total emergence was not affected.     

A new dressing for laser-treated areas

Contemporary studies and observations have left no doubt that occlusive dressings are superior to open treatment after laser resurfacing. The currently available occlusive dressings, however, are time-consuming to apply, often dislodge shortly after application, and most require reapplication. The authors report a cross-sectional observational study of patients who were treated with a new dual silicone-based dressing (DiamondSeal) after full-face laser resurfacing, with or without rhytidectomy. Patients who previously underwent similar surgeries and who were treated with a popular occlusive tape dressing (Flexzan) acted as historic controls. A combination of two silicones produced a gel-like silicone admixture that was spread evenly over the laser-treated areas. The silicone gel solidified into a flexible membrane and remained on the patient's face for 5 days. Questionnaires were sent to patients who were treated with the silicone dressing and those who were treated with a currently popular occlusive dressing. When the attributes of these dressings were compared, the superiority of the silicone dressing approached statistical significance ( = 0.08). The majority of patients treated with the silicone dressing (71 percent) had a positive experience with this dressing, stating they would repeat the experience if necessary. Only 54 percent of patients with a tape dressing were willing to repeat their experience ( = 0.18). The major advantages of this dressing, noted from the surgeon's perspective, were the speed with which the mask was applied; the ease of application, without the need for templates; the acceptable cure duration, allowing spontaneous contouring of the silicone along facial contours; the simple tailoring of the dressing; the reduced need for and minimal time for reapplication; and the paucity of complications.     

Cytotoxicity testing of wound-dressing materials

A method was developed for testing the cytotoxicity of various bandage-like wound dressings and gel wound dressings. In this method, the ability of human polymorphonuclear neutrophils (PMNs) to initiate a respiratory burst after exposure to the various wound dressings is used as a marker of cytotoxicity. Luminol-amplified chemiluminescence stimulated with opsonised zymosan or phorbol 12-myristate 13-acetate (PMA) is used to measure the degree of activation of the respiratory burst, i.e. the NADPH oxidase activity, after exposure to wound dressings. Opsonised zymosan (material from yeast cell walls) is a phagocytic stimulus that activates the NADPH oxidase by binding to FC-receptors and complement receptors, and functions as an artificial bacterium, whereas PMA activates the NADPH oxidase by direct activation of protein kinase C. NADPH oxidase activity was inhibited by several wound dressings. The down-regulation of the respiratory burst is detrimental to the bactericial effect of PMNs, and can be used as a marker for the cytotoxicity of wound dressing materials.     

Wound‐healing evaluation of entrapped active agents into protein microspheres over cellulosic gauzes

The use of active ingredients in wound management have evolved alongside the pharmaceutical agents and dressings used to deliver them. However, the development of gauzes, dressings with specific properties, still remains a challenge for several medical applications. A new methodology for the controlled release of active components for the healing of burn wounds is proposed herein. Cotton and non‐woven bandages have been cationised to promote the attachment of protein microspheres. The active agents, piroxicam and vegetable oil, were entrapped into the microspheres using ultrasound energy. Active agents were released from the microspheres by a change in pH. Wound healing was assessed through the use of standardised burn wounds induced by a cautery in human full‐thickness skin equivalents (EpidermFT). The best re‐epithelialisation and fastest wound closure was observed in wounds treated with proteinaceous microspheres attached to gauzes, after six days of healing, in comparison with commercial collagen dressing and other controls. Furthermore, the ability of these materials to reduce the inflammation process, together with healing improvement, makes these biomaterials suitable for wound‐dressing applications.     

Wound dressings for a proteolytic-rich environment

Wound dressings have experienced continuous and significant changes over the years based on the knowledge of the biochemical events associated with chronic wounds. The development goes from natural materials used to just cover and conceal the wound to interactive materials that can facilitate the healing process, addressing specific issues in non-healing wounds. These new types of dressings often relate with the proteolytic wound environment and the bacteria load to enhance the healing. Recently, the wound dressing research is focusing on the replacement of synthetic polymers by natural protein materials to delivery bioactive agents to the wounds. This article provides an overview on the novel protein-based wound dressings such as silk fibroin keratin and elastin. The improved properties of these dressings, like the release of antibiotics and growth factors, are discussed. The different types of wounds and the effective parameters of healing process will be reviewed.     

Use of Irradiated Amnion as a Biological Dressing in the Treatment of Radiation Induced Ulcers

The management of moist skin desquamation (ulceration) following radiation therapy has been a concern since the inception of this therapy. The treatment of skin reactions focuses on promoting healing, improving patient comfort preventing infection and decreasing trauma to the area. Various dressings like topical preparations, hydrocolloid and gentian violet 1 % dressing have been used for its treatment. We present our experience with the use of amnion as a biological dressing in patients with radiation induced ulceration following pelvic radiation using megavoltage beam. The preliminary experience with treatment in 14 patients proved to be cost effective due to a shorter duration of ulcer healing (median of 7 days), fewer dressing changes (median of 4 dressings) and diminished use of analgesics.     

Functional extracellular matrix hydrogel modified with MSC‐derived small extracellular vesicles for chronic wound healing

ObjectivesDiabetic wound healing remains a global challenge in the clinic and in research. However, the current medical dressings are difficult to meet the demands. The primary goal of this study was to fabricate a functional hydrogel wound dressing that can provide an appropriate microenvironment and supplementation with growth factors to promote skin regeneration and functional restoration in diabetic wounds.Materials and MethodsSmall extracellular vesicles (sEVs) were bound to the porcine small intestinal submucosa‐based hydrogel material through peptides (SC‐Ps‐sEVs) to increase the content and achieve a sustained release. NIH3T3 cell was used to evaluate the biocompatibility and the promoting proliferation, migration and adhesion abilities of the SC‐Ps‐sEVs. EA.hy926 cell was used to evaluate the stimulating angiogenesis of SC‐Ps‐sEVs. The diabetic wound model was used to investigate the function/role of SC‐Ps‐sEVs hydrogel in promoting wound healing.ResultsA functional hydrogel wound dressing with good mechanical properties, excellent biocompatibility and superior stimulating angiogenesis capacity was designed and facilely fabricated, which could effectively enable full‐thickness skin wounds healing in diabetic rat model.ConclusionsThis work led to the development of SIS, which shows an unprecedented combination of mechanical, biological and wound healing properties. This functional hydrogel wound dressing may find broad utility in the field of regenerative medicine and may be similarly useful in the treatment of wounds in epithelial tissues, such as the intestine, lung and liver.

Schematic illustration showing synthesis of the SC‐Ps scaffold dressing and nanoscale sEVs loaded SC‐Ps scaffold dressing and the potential application of the dressings in diabetic wound healing and skin reconstruction.