Bio-inspired crosslinking and matrix-drug interactions for advanced wound dressings with long-term antimicrobial activity

Core-shell chitosan/PVA-based nanofibrous scaffolds loaded with Satureja mutica or Oliveria decumbens essential oils as enhanced antimicrobial wound dressing

Wounds are prone to bacterial infections, which cause a delayed healing process. Regarding the emergence of bacterial resistance to common antibiotics, using natural antimicrobial agents can be beneficial. Chitosan is a biological polymer, which has shown partial antioxidant and antimicrobial activities. In this study, core-shell nanofibrous scaffolds composed of chitosan (CS)/polyvinyl alcohol (PVA) as the core and polyvinylpyrrolidone (PVP)/ maltodextrin (MD) as the shell were developed. Satureja mutica (S. mutica) or Oliveria decumbens (O. decumbens) essential oil (EO) was encapsulated into the core of the produced scaffolds. The broth microdilution analysis showed significant antimicrobial activity of the EOs. The SEM analysis indicated that the unloaded and loaded core-shell scaffolds with S. mutica or O. decumbens EO had a uniform, beadless structure with fiber mean diameters of 210 ± 50, 250 ± 45, and 225 ± 46 nm, respectively. The CS/PVA-PVP/MD and CS/PVA/EO-PVP/MD scaffolds indicated suitable mechanical properties. The addition of the studied EOs enhanced the antioxidant activity of the scaffolds. The antimicrobial test of produced scaffolds showed that loading of 10% S. mutica or O. decumbens EO could broaden the microbicidal activity of the CS/PVA-PVP/MD scaffolds. These results revealed that the CS/PVA/EO-PVP/MD nanofibrous scaffolds are promising candidates for wound dressing.

Multifunctional hydrogels for wound healing: Special focus on biomacromolecular based hydrogels

Hydrogels are widely used for wound healing applications due to their similarity to the native extracellular matrix (ECM) and ability to provide a moist environment. However, lack of multifunctionality and low mechanical properties of previously developed hydrogels may limit their ability to support skin tissue regeneration. Incorporating various biomaterials and nanostructures into the hydrogels is an emerging approach to develop multifunctional hydrogels with new functions that are beneficial for wound healing. These multifunctional hydrogels can be fabricated with a wide range of functions and properties, including antibacterial, antioxidant, bioadhesive, and appropriate mechanical properties. Two approaches can be used for development of multifunctional hydrogel-based dressings; taking the advantages of the chemical composition of biomaterials and addition of nanomaterials or nanostructures. A large number of synthetic and natural polymers, bioactive molecules, or nanomaterials have been used to obtain hydrogel-based dressings with multifunctionality for wound healing applications. In the present review paper, advances in the development of multifunctional hydrogel-based dressings for wound healing have been highlighted.

A rose bengal/graphene oxide/PVA hybrid hydrogel with enhanced mechanical properties and light-triggered antibacterial activity for wound treatment

The numerous advantages of hydrogel make it possible to apply as dressing. However, it is challenging in designing hydrogels with desired antibacterial activity and enhanced mechanical properties at the same time. Herein, a graphene oxide/rose bengal/polyvinyl alcohol hybrid hydrogel (β-GO/RB/PVA HD) is prepared by freezing and thawing a mixed polyvinyl alcohol (PVA) solution of rose bengal (RB) immobilized with chitosan microspheres (CM) and a modified graphene oxide network (β-GO). The mechanical properties and light-triggered antibacterial activity of hydrogel are systematically evaluated. The β-GO inorganic network interpenetrate into the PVA porous structure, which significantly improves the mechanical properties of hydrogel. The hyperthermia generated by β-GO under 808 nm light irradiation combined with reactive oxygen species (ROS) produced by RB under 550 nm light irradiation give rise to excellent antibacterial activity requiring irradiation for only 10 min as demonstrated by our experiments conducted in vitro and in vivo. Meanwhile, β-GO/RB/PVA HD exhibits outstanding biocompatibility and water-absorbing capacity. More importantly, the hybrid hydrogel can significantly accelerate bacteria-accompanied wound healing. The results demonstrated that the hybrid hydrogel could be a promising wound dressing for preventing bacterial infection.

Curcumin nanoparticles incorporated in PVA/collagen composite films promote wound healing

Skin repair remains a common problem in plastic surgery. Wound dressing plays an important role in promoting local skin healing and has been widely studied. This study aimed to manufacture a composite film (CPCF) containing curcumin nanoparticles, collagen, and polyvinyl alcohol (PVA) to effectively promote the healing of skin wounds. Sustained drug release from the composite film provides long-term protection and treatment for skin wounds. Both antibacterial property and good histocompatibility of the CPCF were examined by analyzing antibacterial activity and cytotoxicity to validate its applicability for wound management. Moreover, in vivo studies proved that the CPCF had a rapid healing rate of 98.03%±0.79% and mature epithelialization on day 15 after surgery. Obvious hair follicles and earlier re-epithelialization was also noticed in the CPCF group using H&E staining. The result of Masson’s trichrome staining confirmed that CPCF could promote the formation of collagen fibers. In summary, CPCF may be promising as a wound dressing agent in wound management owing to its rapid wound-healing effects.

Development and evaluation of a novel beneficent antimicrobial bioscaffold based on animal waste-fish swim bladder (FSB) doped with silver nanoparticles

Treated fish wastes have found many applications in industry and medicine. Besides, nowadays low-cost scaffold with antimicrobial activity which can accelerates the process of wound healing is very demanding. In this study fish swim bladder (FSB), taken from Rutilus frisii, which is a disposable waste was doped with silver nanoparticles (AgNPs) and evaluated as antimicrobial wound dressing. The scanning electron microscopy (SEM) micrographs showed the presence of AgNPs on the scaffold. Histological observation confirmed cells and muscle removal from FSB and collagen preservation. There was significant antibacterial activity even in 50 ppm AgNPs concentration against pathogenic bacteria, swelling ratio was rather low, and cytotoxic assay revealed that the AgNPs-FSB scaffold had no toxic effect on human foreskin fibroblast (HFF) cells. Interestingly, despite the porous structure, the AgNPs-FSB scaffold was found to be a suitable barrier to microbial penetration even after 72 h. Further study showed the gradual release of AgNPs during 24 h. In conclusion, biofabricated FSB prepared in this study have appropriate characteristics notably encompassing a high quantity of collagen and broad-spectrum antimicrobial activity. Also, its porous structure made it suitable as a 3-D structure for the growth of cells and adding other antimicrobial nano-sized materials.

An antibacterial and biocompatible multilayer biomedical coating capable of healing damages

Besides the excellent biocompatibility and high antibacterial property, multifunctional biomedical coatings with a long service time is highly desirable for extended applications, which is still an ongoing challenge. The self-healing property enables new directions for effectively prolonging their service life and significantly improving their reliability. Herein, an efficient and simple method is used to facilely prepare antibacterial, biocompatibile multilayer polyelectrolyte coatings, which are capable of healing damages. The synthetic strategy involves the alternate deposition of Chitosan (CS) and sodium carboxymethyl cellulose (CMC) via the layer-by-layer (LBL) self-assembly technique. The CS/CMC multilayer polyelectrolyte coating features high antibacterial property, fast and efficient self-healing property, and excellent biocompatibility. These features allow the CS/CMC polyelectrolyte coating to have extended lifespan and to be highly promising for novel functional stent coating applications.

A CS/CMC multilayer polyelectrolyte coating was developed, which features fast and efficient self-healing property, high antibacterial property, and excellent biocompatibility.

Smart Ti3C2Tx MXene Fabric with Fast Humidity Response and Joule Heating for Healthcare and Medical Therapy Applications

An increasing utilization of flexible healthcare electronics and biomedicine-related therapeutic materials urges the development of multifunctional wearable/flexible smart fabrics for personal therapy and health management. However, it is currently a challenge to fabricate multifunctional and on-body healthcare electronic devices with reliable mechanical flexibility, excellent breathability, and self-controllable joule heating effects. Here, we fabricate a multifunctional MXene-based smart fabric by depositing 2D Ti₃C₂T_x nanosheets onto cellulose fiber nonwoven fabric via special MXene-cellulose fiber interactions. Such multifunctional fabrics exhibit sensitive and reversible humidity response upon H₂O-induced swelling/contraction of channels between the MXene interlayers, enabling wearable respiration monitoring application. Besides, it can also serve as a low-voltage thermotherapy platform due to its fast and stable electro-thermal response. Interestingly, water molecular extraction induces electrical response upon heating, i.e., functioning as a temperature alarm, which allows for real-time temperature monitoring for thermotherapy platform without low-temperature burn risk. Furthermore, metal-like conductivity of MXene renders the fabric an excellent Joule heating effect, which can moderately kill bacteria surrounding the wound in bacteria-infected wound healing therapy. This work introduces a multifunctional smart flexible fabric suitable for next-generation wearable electronic devices for mobile healthcare and personal medical therapy.

Electrospun vancomycin-loaded nanofibers for management of methicillin-resistant Staphylococcus aureus-induced skin infections

Skin damage exposes the underlying layers to bacterial invasion, leading to skin and soft tissue infections. Several pathogens have developed resistance against conventional topical antimicrobial treatments and rendered them less effective. Recently, several nanomedical strategies have emerged as a potential approach to improve therapeutic outcomes of treating bacterial skin infections. In the current study, nanofibers were utilized for topical delivery of the antimicrobial drug vancomycin and evaluated as a promising tool for treatment of topical skin infections. Vancomycin-loaded nanofibers were prepared via electrospinning technique, and vancomycin-loaded nanofibers of the optimal composition exhibited nanosized uniform smooth fibers (ca. 200 nm diameter), high drug entrapment efficiency and sustained drug release patterns over 48 h. In vitro cytotoxicity assays, using several cell lines, revealed the biocompatibility of the drug-loaded nanofibers. In vitro antibacterial studies showed sustained antibacterial activity of the vancomycin-loaded nanofibers against methicillin-resistant Staphylococcus aureus (MRSA), in comparison to the free drug. The nanofibers were then tested in animal model of superficial MRSA skin infection and demonstrated a superior antibacterial efficiency, as compared to animals treated with the free vancomycin solution. Hence, nanofibers might provide an efficient nanodevice to overcome MRSA-induced skin infections and a promising topical delivery vehicle for antimicrobial drugs.

Visible light responsive CuS/ protonated g-C3N4 heterostructure for rapid sterilization

As the environment deterioration is becoming more serious, bacterial pollution is threatening the health of human beings. Hence, it is vital to develop rapid and safe sterilization strategy. Herein, CuS/protonated g-C₃N₄(CuS/PCN) composites were synthesized by simple hydrothermal method and electrostatic adsorption. This heterostructured system exhibited enhanced photocatalytic properties under visible light compared with CuS or g-C₃N₄ alone, ascribing to the rapid separation of photogenerated electron-hole pairs. Meanwhile, the obvious photothermal effects of CuS/PCN were achieved and the temperature increased with the increased amount of CuS in the composites due to the more light absorption. However, when the CuS content is more than 10 %, photocurrent density is decreased with increasing the amount of CuS, indicating the increased recombination of photogenerated electron-hole pairs. When the CuS content is 20 %, the composite can perform the optimized synergistic effects of both photothermal action and photocatalysis under light irradiation for 20 min. The corresponding bacteria-killing efficiency against Staphylococcus aureus and Escherichia coli is 98.23 % and 99.16 %, respectively. The underlying mechanism is that the bacterial membrane can be weakened by reactive oxygen species and bacterial activities are inhibited by hyperthermia. This CuS/PCN heterojunction is promising for environmental disinfection including water and public facilities sterilization.

Nanostructured Fibers Containing Natural or Synthetic Bioactive Compounds in Wound Dressing Applications

The interest in wound healing characteristics of bioactive constituents and therapeutic agents, especially natural compounds, is increasing because of their therapeutic properties, cost-effectiveness, and few adverse effects. Lately, nanocarriers as a drug delivery system have been actively investigated and applied in medical and therapeutic applications. In recent decades, researchers have investigated the incorporation of natural or synthetic substances into novel bioactive electrospun nanofibrous architectures produced by the electrospinning method for skin substitutes. Therefore, the development of nanotechnology in the area of dressings that could provide higher performance and a synergistic effect for wound healing is needed. Natural compounds with antimicrobial, antibacterial, and anti-inflammatory activity in combination with nanostructured fibers represent a future approach due to the increased wound healing process and regeneration of the lost tissue. This paper presents different approaches in producing electrospun nanofibers, highlighting the electrospinning process used in fabricating innovative wound dressings that are able to release natural and/or synthetic substances in a controlled way, thus enhancing the healing process.

In-situ sulfuration of Cu-based metal-organic framework for rapid near-infrared light sterilization

Some new kinds of antibiotics-free antibacterial agents are required to deal with bacterial infections due to the occurrence of drug-resistance. In this work, Cu-based metal-organic framework (HKUST-1) embedded with CuS NPs were fabricated via a simple in-situ sulfuration process. The synthesized MOFs exhibited an highly effective disinfection efficacy of 99.70 % and 99.80 % against Staphylococcus aureus and Escherichia coli within 20 min irradiation of near-infrared (NIR) light, respectively, which was ascribed to the cooperative effects of photodynamic and photothermal effects of the composites. A certain amount of Cu²⁺ ions of the MOFs were reacted to form CuS NPs, which endowed this composite with outstanding photocatalytic and photothermal performance during NIR light irradiation. Moreover, HKUST-1 that composed of low toxic organic ligand 1,3,5-benzenetricarboxylic acid (H₃BTC) coordinating copper ions could be a controllable carrier that imposed certain constraint on the NPs. Hence, these CuS@HKUST-1 would be a promising bioplatform for rapid bacteria-killing.

Mesenchymal stem cell-laden, personalized 3D scaffolds with controlled structure and fiber alignment promote diabetic wound healing

The management of diabetic wounds remains a major therapeutic challenge in clinics. Herein, we report a personalized treatment using 3D scaffolds consisting of radially or vertically aligned nanofibers in combination with bone marrow mesenchymal stem cells (BMSCs). The 3D scaffolds have customizable sizes, depths, and shapes, enabling them to fit a variety of type 2 diabetic wounds. In addition, the 3D scaffolds are shape-recoverable in atmosphere and water following compression. The BMSCs-laden 3D scaffolds are capable of enhancing the formation of granulation tissue, promoting angiogenesis, and facilitating collagen deposition. Further, such scaffolds inhibit the formation of M1-type macrophages and the expression of pro-inflammatory cytokines IL-6 and TNF-α and promote the formation of M2-type macrophages and the expression of anti-inflammatory cytokines IL-4 and IL-10. Taken together, BMSCs-laden, 3D nanofiber scaffolds with controlled structure and alignment hold great promise for the treatment of diabetic wounds. STATEMENT OF SIGNIFICANCE: In this study, we developed 3D radially and vertically aligned nanofiber scaffolds to transplant bone marrow mesenchymal stem cells (BMSCs). We personalized 3D scaffolds that could completely match the size, depth, and shape of diabetic wounds. Moreover, both the radially and vertically aligned nanofiber scaffolds could completely recover their shape and maintain structural integrity after repeated loads with compressive stresses. Furthermore, the BMSCs-laden 3D scaffolds are able to promote granulation tissue formation, angiogenesis, and collagen deposition, and switch the immune responses to the pro-regenerative direction. These 3D scaffolds consisting of radially or vertically aligned nanofibers in combination with BMSCs offer a robust, customizable platform potentially for a significant improvement of managing diabetic wounds.

Multifunctional Antimicrobial Nanofiber Dressings Containing ε-Polylysine for the Eradication of Bacterial Bioburden and Promotion of Wound Healing in Critically Colonized Wounds

Bacterial colonization of acute and chronic wounds is often associated with delayed wound healing and prolonged hospitalization. The rise of multi-drug resistant bacteria and the poor biocompatibility of topical antimicrobials warrant safe and effective antimicrobials. Antimicrobial agents that target microbial membranes without interfering with the mammalian cell proliferation and migration hold great promise in the treatment of traumatic wounds. This article reports the utility of superhydrophilic electrospun gelatin nanofiber dressings (NFDs) containing a broad-spectrum antimicrobial polymer, ε-polylysine (εPL), crosslinked by polydopamine (pDA) for treating second-degree burns. In a porcine model of partial thickness burns, NFDs promoted wound closure and reduced hypertrophic scarring compared to untreated burns. Analysis of NFDs in contact with the burns indicated that the dressings trap early colonizers and elicit bactericidal activity, thus creating a sterile wound bed for fibroblasts migration and re-epithelialization. In support of these observations, in porcine models of Pseudomonas aeruginosa and Staphylococcus aureus colonized partial thickness burns, NFDs decreased bacterial bioburden and promoted wound closure and re-epithelialization. NFDs displayed superior clinical outcome than standard-of-care silver dressings. The excellent biocompatibility and antimicrobial efficacy of the newly developed dressings in pre-clinical models demonstrate its potential for clinical use to manage infected wounds without compromising tissue regeneration.

Gelatin sponge functionalized with gold/silver clusters for antibacterial application

Pathogenic bacterial infection, especially in the wound, may threaten human health. Developing new antibacterial materials for wound healing is still urgent. Metal nanoclusters have been explored as a novel antibacterial agent. Herein, biomolecule gelatin was chosen as a substrate and functionalized with gold/silver clusters for bacterial killing. Through a simple amidation reaction, gold/silver clusters were successfully conjugated in a gelatin substrate to obtain a Au/Ag@gelatin sponge. The presence of gold/silver clusters modified the porous structure of the gelatin. Thus, the water absorption and water retention of the Au/Ag@gelatin sponge were enhanced. More importantly, the gold/silver clusters show aggregation-enhanced emission and strong reactive oxygen generation, that endow the Au/Ag@gelatin sponge with a good antibacterial property. The good physical performance and favorable bactericidal activity of the Au/Ag@gelatin sponge suggest its potential for application as a wound dressing.

Antibiotic Delivery Strategies to Treat Skin Infections When Innate Antimicrobial Defense Fails

The epidermal skin barrier protects the body from a host of daily challenges, providing protection against mechanical insults and the absorption of chemicals and xenobiotics. In addition to the physical barrier, the epidermis also presents an innate defense against microbial overgrowth. This is achieved through the presence of a diverse collection of microorganisms on the skin (the "microbiota") that maintain a delicate balance with the host and play a significant role in overall human health. When the skin is wounded, the local tissue with a compromised barrier can become colonized and ultimately infected if bacterial growth overcomes the host response. Wound infections present an immense burden in healthcare costs and decreased quality of life for patients, and treatment becomes increasingly important because of the negative impact that infection has on slowing the rate of wound healing. In this review, we discuss specific challenges of treating wound infections and the advances in drug delivery platforms and formulations that are under development to improve topical delivery of antimicrobial treatments.

Biodegradable nanocomposite fibrous scaffold mediated local delivery of vancomycin for the treatment of MRSA infected experimental osteomyelitis

The study shows the development of a biodegradable bi-functional composite scaffold that can reduce bacterial infection, while promotes bone regeneration in osteomyelitis, without the need for revision surgery.

Wound healing properties of magnesium mineralized antimicrobial nanofibre dressings containing chondroitin sulphate – a comparison between blend and core–shell nanofibres

Effect of chondroitin sulphate incorporated PCL/gelatin as blends or core–shell composite nanofibres are compared in terms of their biocompatibility for skin cells and wound healing in porcine model of partial thickness burns.

Bacterial Nanocellulose and Its Surface Modification by Glycidyl Methacrylate and Ethylene Glycol Dimethacrylate. Incorporation of Vancomycin and Ciprofloxacin

Among nanocelluloses, bacterial nanocellulose (BNC) has proven to be a promising candidate in a range of biomedical applications, from topical wound dressings to tissue-engineering scaffolds. Chemical modifications and incorporation of bioactive molecules have been obtained, further increasing the potential of BNC. This study describes the incorporation of vancomycin and ciprofloxacin in BNC and in modified BNC to afford bioactive BNCs suitable for topical wound dressings and tissue-engineering scaffolds. BNC was modified by grafting glycidylmethacrylate (GMA) and further cross-linking with ethylene glycol dimethacrylate (EGDMA) with the formation of stable C–C bonds through a radical Fenton-type process that involves generation of cellulose carbon centred radicals scavenged by methacrylate structures. The average molar substitution degree MS (MS = methacrylate residue per glucose unit, measured by Fourier transform infrared (FT–IR) analysis) can be modulated in a large range from 0.1 up to 3. BNC-GMA, BNC-EGDMA and BNC-GMA-EGDMA maintain the hydrogel status until MS reaches the value of 1. The mechanical stress resistance increase of BNC-GMA and BNC-GMA-EGDMA of MS around 0.8 with respect to BNC suggests that they can be preferred to BNC for tissue-engineering scaffolds in cases where the resistance plays a crucial role. BNC, BNC-GMA, BNC-EGDMA and BNC-GMA-EGDMA were loaded with vancomycin (VC) and ciprofloxacin (CP) and submitted to release experiments. BNC-GMA-EGDMA of high substitution degree (0.7–1) hold up to 50 percentage of the loaded vancomycin and ciprofloxacin amount, suggesting that they can be further investigated for long-term antimicrobial activity. Furthermore, they were not colonized by Staphylococcus aureus (S.A.) and Klebsiella pneumonia (K.P.). Grafting and cross-linking BNC modification emerges from our results as a good choice to improve the BNC potential in biomedical applications like topical wound dressings and tissue-engineering scaffolds.

High Efficiency Fabrication of Chitosan Composite Nanofibers with Uniform Morphology via Centrifugal Spinning

While electrospinning has been widely employed to spin nanofibers, its low production rate has limited its potential for industrial applications. Comparing with electrospinning, centrifugal spinning technology is a prospective method to fabricate nanofibers with high productivity. In the current study, key parameters of the centrifugal spinning system, including concentration, rotational speed, nozzle diameter and nozzle length, were studied to control fiber diameter. An empirical model was established to determine the final diameters of nanofibers via controlling various parameters of the centrifugal spinning process. The empirical model was validated via fabrication of carboxylated chitosan (CCS) and polyethylene oxide (PEO) composite nanofibers. DSC and TGA illustrated that the thermal properties of CCS/PEO nanofibers were stable, while FTIR-ATR indicated that the chemical structures of CCS and PEO were unchanged during composite fabrication. The empirical model could provide an insight into the fabrication of nanofibers with desired uniform diameters as potential biomedical materials. This study demonstrated that centrifugal spinning could be an alternative method for the fabrication of uniform nanofibers with high yield.

Tazarotene Released from Aligned Electrospun Membrane Facilitates Cutaneous Wound Healing by Promoting Angiogenesis

Wound treatment is a long-lasting clinical issue. Poor angiogenesis leading to delayed wound closure causes huge challenges for healing. Functional electrospun membranes have been established as an efficient strategy to promote wound recovery by protecting and improving vascular regeneration. Here, we aimed to investigate the effect of tazarotene, an active drug for angiogenesis, loaded in aligned electrospun nanofibrous barrier on a soft tissue wound. This aligned membrane was arranged in a single direction, and tazarotene could be released from its nanofibers sustainably. The in vitro study demonstrated that compared with the random drug-loaded or other control groups, the aligned tazarotene-loaded membranes [poly-caprolactone (PCL)/AT] could stimulate proliferation, migration, angiogenesis, and vascular endothelial growth factor secretion and its gene expression of human umbilical vein endothelial cells. Furthermore, the in vivo model showed that the prepared tazarotene-loaded aligned membrane significantly accelerated the speed of healing, improved the neovascularization and re-epithelialization, and inhibited the inflammatory reaction in the wound area. All these results above indicated that the PCL/AT nanofibrous dressing, which could promote angiogenesis because of both stimulation of structure and chemical signals, is a promising wound-caring material.

Synthesis of magnetite hybrid nanocomplexes to eliminate bacteria and enhance biofilm disruption

Bacteria can increase drug resistance by forming bacterial biofilms. Once the biofilm is formed, it becomes difficult to remove or kill the related bacteria completely by antibiotics and other antibacterial agents because these antibacterial agents cannot easily break through the biofilm matrix barrier and reach the internal bacteria. Therefore, we synthesized magnetite hybrid nanocomplexes that can penetrate and disrupt bacterial biofilms. The obtained nanocomposites are composed of multinucleated iron oxides and Ag seeds. The outer iron oxides can help the internal Ag nanoparticles penetrate the bacterial biofilms, hence killing the internal bacteria and disrupting the biofilms. We took advantage of E. coli and P. aeruginosa bacteria to test the antibacterial properties of the magnetite hybrid nanocomplexes. When planktonic E. coli and P. aeruginosa bacteria were incubated with 100 μg mL-1 magnetite hybrid nanocomplexes for 30 min, almost all the bacteria were killed. When the obtained biofilms of E. coli and P. aeruginosa were treated with magnetite hybrid nanocomplexes (10 μg mL-1 and 100 μg mL-1), the survival of E. coli and P. aeruginosa biofilms with a magnetic field showed a big decrease compared with that without a magnetic field. Therefore, the as-synthesized nanocomposites have promising potential as antimicrobial agents for killing bacteria and disrupting biofilms in the presence of a magnetic field, and thus should be further studied for a wide range of antibacterial applications.

Advanced drug delivery systems and artificial skin grafts for skin wound healing

Cutaneous injuries, especially chronic wounds, burns, and skin wound infection, require painstakingly long-term treatment with an immense financial burden to healthcare systems worldwide. However, clinical management of chronic wounds remains unsatisfactory in many cases. Various strategies including growth factor and gene delivery as well as cell therapy have been used to enhance the healing of non-healing wounds. Drug delivery systems across the nano, micro, and macroscales can extend half-life, improve bioavailability, optimize pharmacokinetics, and decrease dosing frequency of drugs and genes. Replacement of the damaged skin tissue with substitutes comprising cell-laden scaffold can also restore the barrier and regulatory functions of skin at the wound site. This review covers comprehensively the advanced treatment strategies to improve the quality of wound healing.

Recent advances in gelatin-based therapeutics

INTRODUCTION

Biomaterials have provided a wide range of exciting opportunities in tissue engineering and regenerative medicine. Gelatin, a collagen-derived natural biopolymer, has been extensively used in regenerative medicine applications over the years, due to its cell-responsive properties and the capacity to deliver a wide range of biomolecules.

AREAS COVERED

The most relevant properties of gelatin as biomaterial are presented together with its main therapeutic applications. The latter includes drug delivery systems, tissue engineering approaches, potential uses as ink for 3D/4D Bioprinting, and its relevance in organ-on-a-chip platforms.

EXPERT OPINION

Advances in polymer chemistry, mechanobiology, imaging technologies, and 3D biofabrication techniques have expanded the application of gelatin in multiple biomedical research applications ranging from bone and cartilage tissue engineering, to wound healing and anti-cancer therapy. Here, we highlight the latest advances in gelatin-based approaches within the fields of biomaterial-based drug delivery and tissue engineering together with some of the most relevant challenges and limitations.

Rapid and Superior Bacteria Killing of Carbon Quantum Dots/ZnO Decorated Injectable Folic Acid-Conjugated PDA Hydrogel through Dual-Light Triggered ROS and Membrane Permeability

One of the most difficult challenges in the biomedical field is bacterial infection, which causes tremendous harm to human health. In this work, an injectable hydrogel is synthesized through rapid assembly of dopamine (DA) and folic acid (FA) cross-linked by transition metal ions (TMIs, i.e., Zn²⁺ ), which was named as DFT-hydrogel. Both the two carboxyl groups in the FA molecule and catechol in polydopamine (PDA) easily chelates Zn²⁺ to form metal-ligand coordination, thereby allowing this injectable hydrogel to match the shapes of wounds. In addition, PDA in the hydrogel coated around carbon quantum dot-decorated ZnO (C/ZnO) nanoparticles (NPs) to rapidly generate reactive oxygen species (ROS) and heat under illumination with 660 and 808 nm light, endows this hybrid hydrogel with great antibacterial efficacy against Staphylococcus aureus (S. aureus, typical Gram-positive bacteria) and Escherichia coli (E. coli, typical Gram-negative bacteria). The antibacterial efficacy of the prepared DFT-C/ZnO-hydrogel against S. aureus and E. coli under dual-light irradiation is 99.9%. Importantly, the hydrogels release zinc ions over 12 days, resulting in a sustained antimicrobial effect and promoted fibroblast growth. Thus, this hybrid hydrogel exhibits great potential for the reconstruction of bacteria-infected tissues, especially exposed wounds.

Electrospinning and Electrospun Nanofibers: Methods, Materials, and Applications

Electrospinning is a versatile and viable technique for generating ultrathin fibers. Remarkable progress has been made with regard to the development of electrospinning methods and engineering of electrospun nanofibers to suit or enable various applications. We aim to provide a comprehensive overview of electrospinning, including the principle, methods, materials, and applications. We begin with a brief introduction to the early history of electrospinning, followed by discussion of its principle and typical apparatus. We then discuss its renaissance over the past two decades as a powerful technology for the production of nanofibers with diversified compositions, structures, and properties. Afterward, we discuss the applications of electrospun nanofibers, including their use as "smart" mats, filtration membranes, catalytic supports, energy harvesting/conversion/storage components, and photonic and electronic devices, as well as biomedical scaffolds. We highlight the most relevant and recent advances related to the applications of electrospun nanofibers by focusing on the most representative examples. We also offer perspectives on the challenges, opportunities, and new directions for future development. At the end, we discuss approaches to the scale-up production of electrospun nanofibers and briefly discuss various types of commercial products based on electrospun nanofibers that have found widespread use in our everyday life.

Poly-ε-Caprolactone/Gelatin Hybrid Electrospun Composite Nanofibrous Mats Containing Ultrasound Assisted Herbal Extract: Antimicrobial and Cell Proliferation Study

Electrospun fibers have emerged as promising materials in the field of biomedicine, due to their superior physical and cell supportive properties. In particular, electrospun mats are being developed for advanced wound dressing applications. Such applications require the firers to possess excellent antimicrobial properties in order to inhibit potential microbial colonization from resident and non-resident bacteria. In this study, we have developed Poly-ε-Caprolactone /gelatin hybrid composite mats loaded with natural herbal extract (Gymnema sylvestre) to prevent bacterial colonization. As-spun scaffolds exhibited good wettability and desirable mechanical properties retaining their fibrous structure after immersing them in phosphate buffered saline (pH 7.2) for up to 30 days. The initial burst release of Gymnema sylvestre prevented the colonization of bacteria as confirmed by the radial disc diffusion assay. Furthermore, the electrospun mats promoted cellular attachment, spreading and proliferation of human primary dermal fibroblasts and cultured keratinocytes, which are crucial parenchymal cell-types involved in the skin recovery process. Overall these results demonstrated the utility of Gymnema sylvestre impregnated electrospun PCL/Gelatin nanofibrous mats as an effective antimicrobial wound dressing.

A Bi-Layer PVA/CMC/PEG Hydrogel with Gradually Changing Pore Sizes for Wound Dressing

Wound dressings are vital for cutaneous wound healing. In this study, a bi-layer dressing composed of polyvinyl alcohol/carboxymethyl cellulose/polyethylene glycol (PVA/CMC/PEG) hydrogels is produced through a thawing-freezing method based on the study of the pore size of single-layer hydrogels. Then the physical properties and healing of full-thickness skin defects treated with hydrogels are inspected. The results show that the pore size of the single-layer PVA/CMC/PEG hyrogel can be controlled. The obtained non-adhesive bi-layer hydrogels show gradually increasing pore sizes from the upper to the lower layer and two layers are well bonded. In addition, bi-layer dressings with good mechanical properties can effectively prevent bacterial penetration and control the moisture loss of wounds to maintain a humid environment for wounds. A full-thickness skin defect test shows that bi-layer hydrogels can significantly accelerate wound closure. The experiment indicates that the bi-layer PVA/CMC/PEG hydrogels can be used as potential wound dressings.

Cobalt-mediated multi-functional dressings promote bacteria-infected wound healing

Wound dressings with multiple functions are required to meet the complexity of the wound healing process. The multifunctionality often leads to an increase in the complexity and difficulty in dressing preparation. To surmount this problem, we used a facile preparation and fabrication process to fabricate a multi-functional dressing by integrating four widely accessible materials: plain gauze, sodium alginate (SA), Ca²⁺ and Co²⁺. Firstly, mixed Ca²⁺/Co²⁺ ion solutions with different concentration were applied to gauzes. After drying, SA solution was added to ionized gauze and Co²⁺-Ca²⁺/Gauze/SA (Ion-GSA) composite dressings were formed easily. In vitro results showed that all Ion-GSA dressings exhibited strong mechanical properties, uniform dispersion and sustained release of Ca²⁺ and Co²⁺, and the ability to retain moisture and absorb wound exudate. Besides the above advantages, dressings prepared with 0.25 g/L Co²⁺ and 4 g/L Ca²⁺ (Co²⁺0.25-Ca²⁺4 GSA composite dressings) exhibited the best overall effect for inducing a hypoxia-like response, and favorable cytocompatibility, hemostatic property and antibacterial activity. In vivo wound healing assays revealed that Co²⁺0.25-Ca²⁺4 GSA composite dressings inhibited bacterial growth, increased local Hypoxia-inducible factor-1α (HIF-1α), vascular endothelial growth factor (VEGF), transforming growth factor-β1 (TGF-β1) protein expression, and accelerated full-thickness skin wound healing in mouse bacterial-infected wound model. The quick healing wounds had improved angiogenesis, macrophages regulation, re-epithelialization and dense collagen deposition. Collectively, our results indicated that Co²⁺0.25-Ca²⁺4 GSA composite dressings promote wound healing. STATEMENT OF SIGNIFICANCE: Wound dressings with integrated functionalities are required to meet complex clinical requirements. However, there is often a trade-off between reducing preparation complexity and increasing the multifunctionality of the dressing's properties. In this study, we prepared multifunctional composite dressings by a facile preparation process using widely accessible materials. The composite dressings possessed the mechanical strength of gauze, had the effective wound exudate absorption, moisture maintenance and hemostatic property capacity of calcium alginate hydrogels, and had the hypoxia-like induction and the antimicrobial effects of Co²⁺. These functions all together promote bacteria-infected wound healing. Thus, we believed that the composite dressings can be widely applied in skin wound repair duo to their facile preparation method and good therapeutic effect.

Remodeling of inherent antimicrobial nanofiber dressings with melamine-modified fibroin into neoskin

A melamine-modified fibroin was synthesized and fabricated into electrospun nanofiber films with broad-spectrum antimicrobial activity, sustained water retention, and fast reepithelialization and revascularization.

Biomimetic Elastomeric Polypeptide-Based Nanofibrous Matrix for Overcoming Multidrug-Resistant Bacteria and Enhancing Full-Thickness Wound Healing/Skin Regeneration

Overcoming the multidrug-resistant (MDR) bacterial infection is a challenge and urgently needed in wound healing. Few wound dressings possess the capacity to treat MDR bacterial infections and enhance wound healing. Herein, we develop an elastomeric, photoluminescent, and antibacterial hybrid polypeptide-based nanofibrous matrix as a multifunctional platform to inhibit the MDR bacteria and enhance wound healing. The hybrid nanofibrous matrix was composed of poly(citrate)-ε-poly lysine (PCE) and poly caprolactone (PCL). The PCL-PCE hybrid nanofibrous matrix showed a biomimetic elastomeric behavior, robust antibacterial activity including killing MDR bacteria capacity, and excellent biocompatibility. PCL-PCE nanofibrous system can efficiently prevent the MDR bacteria-derived wound infection and significantly enhance the complete skin-thickness wound healing and skin regeneration in a mouse model. PCL-PCE hybrid nanofibrous matrix might become a competitive multifunctional dressing for bacteria-infected wound healing and skin regeneration.

Effect of annealing temperature on mechanical and antibacterial properties of Cu-bearing titanium alloy and its preliminary study of antibacterial mechanism

Cu-bearing titanium alloys are designed and studied as a novel medical metal material with antibacterial function. However, the addition of Cu would affect the mechanical properties of titanium alloy more or less, especially the ductility, despite its excellent antibacterial property. Thus, the aim of this study was to optimize the heat treatment for Cu-bearing titanium alloys in order to achieve a balance of satisfactory mechanical, antibacterial and other properties. In this study, Ti6Al4V-5 wt% Cu alloy was fabricated, and then different annealing treatments with various heating temperatures (700-910 °C) were employed on the alloy. The effects of heating temperature on microstructure evolution, mechanical properties, corrosion resistance and antibacterial performance of Ti6Al4V-5Cu alloy were systematically studied. It was found that annealing at 740 °C for Ti6Al4V-5Cu alloy showed the best comprehensive properties of high strength, excellent ductility, corrosion resistance and antibacterial performance. The Ti₂Cu phases played an important role in the mechanical property and antibacterial performance for Ti6Al4V-5Cu alloy, and bacteria preferred to adhere on the α phase region, rather than the β or globule Ti₂Cu region.

Incorporation of antimicrobial peptides on electrospun nanofibres for biomedical applications

The aim of this work was to immobilize antimicrobial peptides onto a fibrous scaffold to create functional wound dressings. The scaffold was produced by electrospinning from a mixture of the water soluble polymers poly(acrylic acid) and poly(vinyl alcohol) and subsequently heat cured at 140 °C to produce a stable material with fibre diameter below micron size. The peptides were incorporated into the negatively charged scaffold by electrostatic interaction. The best results were obtained for lysozyme impregnated at pH 7, which rendered a loading of up to 3.0 × 10-4 mmol mg-1. The dressings were characterized using SEM, ATR-FTIR, elemental analysis, ζ-potential and confocal microscopy using fluorescamine as an amine-reactive probe. The dressings preserved their fibrous structure after impregnation and peptides were distributed homogeneously throughout the fibrous network. The antibacterial activity was assessed by solid agar diffusion tests and growth inhibition in liquid cultures using Staphylococcus aureus, a pathogenic strain generally found in infected wounds. The antibacterial activity caused clear halo inhibition zones for lysozyme-loaded dressings and a 4-fold decrease in S. aureus viable colonies after two weeks of contact of dressings with bacterial liquid cultures. The release profile in different media showed sustained release in acidic environments, and a rapid discharge at high pH values. The incorporation of lysozyme resulted in dressing surfaces essentially free of microbial growth after 14 days of contact with bacteria at pH 7.4 attributed to the peptide that remained attached to the dressing surface.

Advancements in Regenerative Strategies Through the Continuum of Burn Care

Burns are caused by several mechanisms including flame, scald, chemical, electrical, and ionizing and non-ionizing radiation. Approximately half a million burn cases are registered annually, of which 40 thousand patients are hospitalized and receive definitive treatment. Burn care is very resource intensive as the treatment regimens and length of hospitalization are substantial. Burn wounds are classified based on depth as superficial (first degree), partial-thickness (second degree), or full-thickness (third degree), which determines the treatment necessary for successful healing. The goal of burn wound care is to fully restore the barrier function of the tissue as quickly as possible while minimizing infection, scarring, and contracture. The aim of this review is to highlight how tissue engineering and regenerative medicine strategies are being used to address the unique challenges of burn wound healing and define the current gaps in care for both partial- and full-thickness burn injuries. This review will present the current standard of care (SOC) and provide information on various treatment options that have been tested pre-clinically or are currently in clinical trials. Due to the complexity of burn wound healing compared to other skin injuries, burn specific treatment regimens must be developed. Recently, tissue engineering and regenerative medicine strategies have been developed to improve skin regeneration that can restore normal skin physiology and limit adverse outcomes, such as infection, delayed re-epithelialization, and scarring. Our emphasis will be centered on how current clinical and pre-clinical research of pharmacological agents, biomaterials, and cellular-based therapies can be applied throughout the continuum of burn care by targeting the stages of wound healing: hemostasis, inflammation, cell proliferation, and matrix remodeling.

Biodegradable crosslinked polyesters derived from thiomalic acid and S-nitrosothiol analogues for nitric oxide release

Crosslinked polyesters with Young's moduli similar to that of certain soft biological tissues were prepared via bulk polycondensation of thiomalic acid and 1,8-octanediol alone, and with citric or maleic acid. The copolymers were converted to nitric oxide (NO)-releasing S-nitrosothiol (RSNO) analogues by reaction with tert-butyl nitrite. Additional conjugation steps were avoided by inclusion of the thiolated monomer during the polycondensation to permit thiol conversion to RSNOs. NO release at physiological pH and temperature (pH 7.4, 37 °C) was determined by chemiluminescence-based NO detection. The average total NO content for poly(thiomalic-co-maleic acid-co-1,8-octanediol), poly(thiomalic-co-citric acid-co-1,8-octanediol), and poly(thiomalic acid-co-1,8-octanediol) was 130 ± 39 μmol g-1, 200 ± 35 μmol g-1, and 130 ± 11 μmol g-1, respectively. The antibacterial properties of the S-nitrosated analogues were confirmed against Escherichia coli and Staphylococcus aureus. The hydrolytic degradation products were analyzed by time-of-flight mass spectrometry after a 10-week study to investigate their composition. Tensile mechanical tests were performed on the non-nitrosated polymers as well as their S-nitrosated derivatives and suggested that the materials have appropriate Young's moduli and elongation values for biomedical applications.

Fabrication and characterization of chicken feather keratin/polysaccharides blended polymer coated nonwoven dressing materials for wound healing applications

In this research work, three kinds of nonwoven wound dressings were developed from chicken feather keratin (CFK-NW), keratin‑sodium alginate (CFK-SA-NW) and keratin-chitosan (CFK-CS-NW) and characterized using FTIR and SEM. The physical characteristics such as air permeability, thickness and areal density test results revealed the suitability of fabricated materials for wound dressing applications. CFK-SA-NW and CFK-CS-NW indicated a positive antibacterial effect against Gram's positive Staphylococcus aureus and Gram's negative Klebsiella pneumoniae and Escherichia coli bacteria with the zone of inhibition enhanced over >2.0 cm. Moreover, the biomedical potentials of dressing materials has been investigated by cell viability and cytotoxicity tests. Further, the wound healing ability was demonstrated using in vivo model (Albino Wistar rat). The fabricated materials exhibited good support for cell viability and a strong cytocompatibility. Furthermore, the hundred percent wound healing ability of CFK-CS-NW, CFK-SA-NW, CFK-NW and untreated control rats was observed at 15, 17, 21 and 23 days, respectively, Moreover, the wound healing potential of CFK-CS-NW and CFK-SA-NW was found to be better than that of CFK-NW and control group of rats. The outcome of the present study discloses the prospective applications of the developed materials as wound dressing biomaterial.

Novel pH-responsive tobramycin-embedded micelles in nanostructured multilayer-coatings of chitosan/heparin with efficient and sustained antibacterial properties

To endow orthopaedic implants with satisfactory antibacterial properties, the design and development of antibiotic coating on the surface of implants is highly desired. In this work a novel and facile strategy was developed to form pH-responsive layer-by-layer (LbL) films implanted with polymeric micelles as nano-vehicles loaded with charge-weak antibiotic drugs, enabling high drug loading efficiency. Negatively charged tobramycin (Tob)-embeded heparin miscells (HET) and positively charged chitosan (CHT) were exploited as a pH-responsive LBL multilayer building block, respectively. The formation mechanism and pH-stimulated release behavior of the Tob-contained heparin micelles were studied. The characterization on the morphologies, chemical compositions and hydrophilicity of the modified surface confirmed the successuful deposition of the Tob-loaded CHT/HET multilayers coatings on the polydopamine-modified Ti surface. The drug release profiles displayed fast release at pH 7.4 and slow release after exposure to weakly acidic environments. Antibacterial tests indicated that the Tob-embed CHT/HET nanostructured multilayers not only strongly inhibited initial bacterial adhesion, but also disruptted biofilm formation. Particularly, this functional coatings showed "long-term antibacterial" pattern in acid condition. Meanwhile, MC3T3 cells showed acceptable adhesion, spread and proliferation on the multilayer coatings in cytocompatible studies. In a word, these multilayer coatings incorporated with a wide variety of antibiotics show promisiong applications in preventing postoperative infection and resolving unmet clinical need.

Antimicrobial gelatin-based elastomer nanocomposite membrane loaded with ciprofloxacin and polymyxin B sulfate in halloysite nanotubes for wound dressing

Bacterial infection is a major problem world-wide, especially in wound treatment where it can severely prolong the healing process. In this study, a double drug co-delivery elastic antibacterial nanocomposite was developed by combining ciprofloxacin (CPX) and polymyxin B sulfate-loaded halloysite clay nanotubes (HNTs-B) into a gelatin elastomer. CPX nanoparticles which act against both gram positive and gram-negative bacterium were dispersed directly in the matrix, and polymyxin B sulfate was loaded in HNTs and then distributed into the matrix. The effect of CPX and HNTs-B content on the physical properties, cytotoxicity, fibroblast adhesion and proliferation, in vitro drug release behavior and anti-bacterial properties were systematically investigated. The ciprofloxacin crystals and HNT-B were distributed in the matrix uniformly. The HNTs in the drug loading system not only enhanced the matrix' tensile strength but also slowed down the release rate of the high dissoluble polymyxin B sulfate. When the amount of HNT in the matrix increased, the thermal stability and tensile strength also increased but the polymyxin B sulfate release rate decreased because the HNTs prevented the drug release inside. All the nanocomposites exhibited antimicrobial activity against both gram-negative and gram-positive bacteria with the dual combination of drugs released from the nanocomposites. Furthermore, this kind of gelatin-based nanocomposites possesses higher water-absorbing quality, low cytotoxicity, adaptable biodegradability and good elasticity which can satisfy the requirements for an ideal biomaterial for use in wound healing applications.