Effect of Amino Acid Types on the Mechanical and Antimicrobial Properties of Amino Acid-Based Polyionic Liquid Hydrogels

Polyionic liquid hydrogels attract increasing attention due to their unique properties and potential applications. However, research on amino acid-based polyionic liquid hydrogels is still in its infancy stage. Moreover, the effect of amino acid types on the properties of hydrogels is rarely studied to date. In this work, amino acid-based polyionic liquid hydrogels (D/L-PCAA hydrogels) are synthesized by copolymerizing vinyl choline-amino acid ionic liquids and acrylic acids using Al3+ as a crosslinking agent and bacterial cellulose (BC) as a reinforcing agent. The effects of amino acid types on mechanical and antimicrobial properties are systematically investigated. D-arginine-based hydrogel (D-PCArg) shows the highest tensile strength (220.7 KPa), D-phenylalanine-based hydrogel (D-PCPhe) exhibits the highest elongation at break (1346%), and L-aspartic acid-based hydrogel (L-PCAsp) has the highest elastic modulus (206.9 KPa) and toughness (1.74 MJ m-3). D/L-PCAsp hydrogels demonstrate stronger antibacterial capacity against Escherichia coli and Staphylococcus aureus, and D/L-PCPhe hydrogels possess higher antifungal activity against Cryptococcus neoformans. Moreover, the resultant hydrogels exhibit prominent hemocompatibility and low toxicity, as well as excellent self-healing capabilities (86%) and conductivity (2.8 S m-1). These results indicate that D/L-PCAA hydrogel provides a promise for applications in wound dressings.

Conductive Biomaterials as Bioactive Wound Dressing for Wound Healing and Skin Tissue Engineering

Conductive biomaterials based on conductive polymers, carbon nanomaterials, or conductive inorganic nanomaterials demonstrate great potential in wound healing and skin tissue engineering, owing to the similar conductivity to human skin, good antioxidant and antibacterial activities, electrically controlled drug delivery, and photothermal effect. However, a review highlights the design and application of conductive biomaterials for wound healing and skin tissue engineering is lacking. In this review, the design and fabrication methods of conductive biomaterials with various structural forms including film, nanofiber, membrane, hydrogel, sponge, foam, and acellular dermal matrix for applications in wound healing and skin tissue engineering and the corresponding mechanism in promoting the healing process were summarized. The approaches that conductive biomaterials realize their great value in healing wounds via three main strategies (electrotherapy, wound dressing, and wound assessment) were reviewed. The application of conductive biomaterials as wound dressing when facing different wounds including acute wound and chronic wound (infected wound and diabetic wound) and for wound monitoring is discussed in detail. The challenges and perspectives in designing and developing multifunctional conductive biomaterials are proposed as well.

Harnessing Multifaceted Next-Generation Technologies for Improved Skin Wound Healing

Dysregulation of sequential and synchronized events of skin regeneration often results in the impairment of chronic wounds. Conventional wound dressings fail to trigger the normal healing mechanism owing to the pathophysiological conditions. Tissue engineering approaches that deal with the fabrication of dressings using various biomaterials, growth factors, and stem cells have shown accelerated healing outcomes. However, most of these technologies are associated with difficulties in scalability and cost-effectiveness of the products. In this review, we survey the latest developments in wound healing strategies that have recently emerged through the multidisciplinary approaches of bioengineering, nanotechnology, 3D bioprinting, and similar cutting-edge technologies to overcome the limitations of conventional therapies. We also focus on the potential of wearable technology that supports complete monitoring of the changes occurring in the wound microenvironment. In addition, we review the role of advanced devices that can precisely enable the delivery of nanotherapeutics, oligonucleotides, and external stimuli in a controlled manner. These technological advancements offer the opportunity to actively influence the regeneration process to benefit the treatment regime further. Finally, the clinical relevance, trajectory, and prospects of this field have been discussed in brief that highlights their potential in providing a beneficial wound care solution at an affordable cost.

Development and Characterization of Conducting-Polymer-Based Hydrogel Dressing for Wound Healing

Objectives

Normal and chronic wound healing is a global challenge. Electrotherapy has emerged as a novel and efficient technique for treating such wounds in recent decades. Hydrogel applied to the wound to uniformly distribute the electric current is an important component in wound healing electrotherapy. This study reports the development and wound healing efficacy testing of vitamin D entrapped polyaniline (PANI)-chitosan composite hydrogel for electrotherapy.

Materials and Methods

To determine the morphological and physicochemical properties, techniques like scanning electron microscopy (SEM); differential scanning calorimetry; X-ray diffraction; fourier-transform infrared spectroscopy were used. Moreover, pH, conductance, viscosity, and porosity were measured to optimize and characterize the vitamin D entrapped PANI-chitosan composite hydrogel. The biodegradation was studied using lysozyme, whereas the water uptake ability was studied using phosphate buffer. Ethanolic phosphate buffer was used to perform the vitamin D entrapment and release study. Cell adhesion, proliferation, and electrical stimulation experiments were conducted by seeding dental pulp stem cells (DPSC) into the scaffolds and performing (3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyl tetrazolium bromide) assay; SEM images were taken to corroborated the proliferation results. The wound healing efficacy of electrotherapy and the developed hydrogel were studied on excision wound healing model in rats, and the scarfree wound healing was further validated by histopathology analysis.

Results

The composition of the developed hydrogel was optimized to include 1% w/v PANI and 2% w/v of chitosan composite. This hydrogel showed 1455 μA conduction, 98.97% entrapment efficiency and 99.12% release of vitamin D in 48 hrs. The optimized hydrogel formulation showed neutral pH of 6.96 and had 2198 CP viscosity at 26°C. The hydrogel showed 652.4% swelling index and 100% degradation in 4 weeks. The in vitro cell culture studies performed on hydrogel scaffolds using DPSC and electric stimulation strongly suggested that electrical stimulation enhances the cell proliferation in a three-dimensional (3D) scaffold environment. The in vivo excision wound healing studies also supported the in vitro results suggesting that electrical stimulation of the wound in the presence of the conducting hydrogel and growth factors like vitamin D heals the wound much faster (within 12 days) compared to non-treated control wounds (requires 21 days for complete healing).

Conclusion

The results strongly suggested that the developed PANI-chitosan composite conducting hydrogel acts effectively as an electric current carrier to distribute the current uniformly across the wound surface. It also acted as a drug delivery vehicle for delivering vitamin D to the wound. The hydrogel provided a moist environment, a 3D matrix for free migration of the cells, and antimicrobial activity due to chitosan, all of which contributed to the electrotherapy's faster wound healing mechanism, confirmed through the in vitro and in vivo experiments.

Accelerated Skin Wound Healing by Electrical Stimulation

When the integrity of the skin got damaged, an endogenous electric field will be generated in the wound and a series of physiological reactions will be initiated to close the wound. The existence of the endogenous electric field of the wound has a promoting effect on all stages of wound healing. For wounds that cannot heal on their own, the exogenous electric field can assist the treatment. In this review, the effects of exogenous electrical stimulation on wound healing, such as the inflammation phase, blood flow, cell proliferation and migration, and the wound scarring is overviewed. This article also reviews the new electrical stimulation methods that have emerged in recent years, such as small power supplies, nanogenerators (NGs), and other physical, chemical or biological strategies. These new electrical stimulation methods and devices are safe, low-cost, stable, and small in size. The challenge and perspective are discussed for the future trends of the electrical stimulation treatment in accelerating skin wound healing.

Dielectrophoresis Prototypic Polystyrene Particle Synchronization toward Alive Keratinocyte Cells for Rapid Chronic Wound Healing

Diabetes patients are at risk of having chronic wounds, which would take months to years to resolve naturally. Chronic wounds can be countered using the electrical stimulation technique (EST) by dielectrophoresis (DEP), which is label-free, highly sensitive, and selective for particle trajectory. In this study, we focus on the validation of polystyrene particles of 3.2 and 4.8 μm to predict the behavior of keratinocytes to estimate their crossover frequency (fXO) using the DEP force (FDEP) for particle manipulation. MyDEP is a piece of java-based stand-alone software used to consider the dielectric particle response to AC electric fields and analyzes the electrical properties of biological cells. The prototypic 3.2 and 4.8 μm polystyrene particles have fXO values from MyDEP of 425.02 and 275.37 kHz, respectively. Fibroblast cells were also subjected to numerical analysis because the interaction of keratinocytes and fibroblast cells is essential for wound healing. Consequently, the predicted fXO from the MyDEP plot for keratinocyte and fibroblast cells are 510.53 and 28.10 MHz, respectively. The finite element method (FEM) is utilized to compute the electric field intensity and particle trajectory based on DEP and drag forces. Moreover, the particle trajectories are quantified in a high and low conductive medium. To justify the simulation, further DEP experiments are carried out by applying a non-uniform electric field to a mixture of different sizes of polystyrene particles and keratinocyte cells, and these results are well agreed. The alive keratinocyte cells exhibit NDEP force in a highly conductive medium from 100 kHz to 25 MHz. 2D/3D motion analysis software (DIPP-MotionV) can also perform image analysis of keratinocyte cells and evaluate the average speed, acceleration, and trajectory position. The resultant NDEP force can align the keratinocyte cells in the wound site upon suitable applied frequency. Thus, MyDEP estimates the Clausius-Mossotti factors (CMF), FEM computes the cell trajectory, and the experimental results of prototypic polystyrene particles are well correlated and provide an optimistic response towards keratinocyte cells for rapid wound healing applications.

Effects of electrical stimulation on skin surface

ABSTRACT

Skin is the largest organ in the body, and directly contact with the external environment. Articles on the role of micro-current and skin have emerged in recent years. The function of micro-current is various, including introducing various drugs into the skin locally or throughout the body, stimulating skin wounds healing through various currents, suppressing pain caused by various diseases, and promoting blood circulation for postoperative muscle rehabilitation, etc. This article reviews these efforts. Compared with various physical and chemical medical therapies, micro-current stimulation provides a relatively safe, non-invasive therapy with few side effects, giving modern medicine a more suitable treatment option. At the same time, the cost of the electrical stimulation generating device is relatively low, which makes it have wider space to and more clinical application value. The current micro-current stimulation technology has become more and more mature, but there are still many problems in its research. The design of the experiment and the selection of the current parameters not standardized and rigorous. Now, clear regulations are needed to regulate this field. Micro-current skin therapy has become a robust, reliable, and well-structured system.

In-situ doping of a conductive hydrogel with low protein absorption and bacterial adhesion for electrical stimulation of chronic wounds

Electrical stimulation (ES) via electrodes is promising for treating chronic wounds, but this electrode-based strategy is unable to stimulate the whole wound area and the therapeutic outcome may be compromised. In this study, a conductive poly(2-hydroxyethyl methacrylate) (polyHEMA)/polypyrrole (PPY) hydrogel was developed, and 3-sulfopropyl methacrylate was covalently incorporated in the hydrogel's network to in-situ dope the PPY and maintain the hydrogel's conductivity in the weak alkaline physiological environment. The obtained hydrogel was superior to the commercial Hydrosorb® dressing for preventing bacterial adhesion and protein absorption, and this is helpful to reduce the possibilities of infection and secondary damage during dressing replacement. The in vitro scratch assay demonstrates that ES through the hydrogel enhanced fibroblast migration, and this enhancement effect remained even after the ES was ended. The in vivo assay using diabetic rats shows that when ES was conducted with this polyHEMA/PPY hydrogel, the healing rate was faster than that achieved by the electrode-based ES strategy. Therefore, this polyHEMA/PPY hydrogel shows a great potential for developing the next generation of ES treatment for chronic wounds. STATEMENT OF SIGNIFICANCE: Electrical stimulation (ES) via separated electrodes is promising for treating chronic wounds, but this electrode-based strategy is unable to stimulate the whole wound area, compromising the therapeutic outcome. Herein, a hydrogel was developed with stable electrical conductivity in the physiological environment and strong resistance to protein absorption and bacterial adhesion. The in vitro and in vivo tests proved that ES applied through the flexible and conductive hydrogel that covered the wound was superior to ES through electrodes for promoting the healing of the chronic wound. This hydrogel-based ES strategy combines the advantages of ES and hydrogel dressing and will pave the way for the next generation of ES treatment for chronic wounds.

A Disposable Photovoltaic Patch Controlling Cellular Microenvironment for Wound Healing

Electrical stimulation (ES) is known to affect the wound healing process by modulating skin cell behaviors. However, the conventional clinical devices that can generate ES for promoting wound healing require patient hospitalization due to large-scale of the extracorporeal devices. Herein, we introduce a disposable photovoltaic patch that can be applied to skin wound sites to control cellular microenvironment for promoting wound healing by generating ES. In vitro experiment results show that exogenous ES could enhance cell migration, proliferation, expression of extracellular matrix proteins, and myoblast differentiation of fibroblasts which are critical for wound healing. Our disposable photovoltaic patches were attached to the back of skin wound induced mice. Our patch successfully provided ES, generated by photovoltaic energy harvested from the organic solar cell under visible light illumination. In vivo experiment results show that the patch promoted cutaneous wound healing via enhanced host-inductive cell proliferation, cytokine secretion, and protein synthesis which is critical for wound healing process. Unlike the current treatments for wound healing that engage passive healing processes and often are unsuccessful, our wearable photovoltaic patch can stimulate regenerative activities of endogenous cells and actively contribute to the wound healing processes.

Electrically stimulated cell migration and its contribution to wound healing

Naturally occurring electric fields are known to be morphogenetic cues and associated with growth and healing throughout mammalian and amphibian animals and the plant kingdom. Electricity in animals was discovered in the eighteenth century. Electric fields activate multiple cellular signaling pathways such as PI3K/PTEN, the membrane channel of KCNJ15/Kir4.2 and intracellular polyamines. These pathways are involved in the sensing of physiological electric fields, directional cell migration (galvanotaxis, also known as electrotaxis), and possibly other cellular responses. Importantly, electric fields provide a dominant and over-riding signal that directs cell migration. Electrical stimulation could be a promising therapeutic method in promoting wound healing and activating regeneration of chronic and non-healing wounds. This review provides an update of the physiological role of electric fields, its cellular and molecular mechanisms, its potential therapeutic value, and questions that still await answers.

Electrical Stimulation and Cutaneous Wound Healing: A Review of Clinical Evidence

Electrical stimulation (ES) has been shown to have beneficial effects in wound healing. It is important to assess the effects of ES on cutaneous wound healing in order to ensure optimization for clinical practice. Several different applications as well as modalities of ES have been described, including direct current (DC), alternating current (AC), high-voltage pulsed current (HVPC), low-intensity direct current (LIDC) and electrobiofeedback ES. However, no one method has been advocated as the most optimal for the treatment of cutaneous wound healing. Therefore, this review aims to examine the level of evidence (LOE) for the application of different types of ES to enhance cutaneous wound healing in the skin. An extensive search was conducted to identify relevant clinical studies utilising ES for cutaneous wound healing since 1980 using PubMed, Medline and EMBASE. A total of 48 studies were evaluated and assigned LOE. All types of ES demonstrated positive effects on cutaneous wound healing in the majority of studies. However, the reported studies demonstrate contrasting differences in the parameters and types of ES application, leading to an inability to generate sufficient evidence to support any one standard therapeutic approach. Despite variations in the type of current, duration, and dosing of ES, the majority of studies showed a significant improvement in wound area reduction or accelerated wound healing compared to the standard of care or sham therapy as well as improved local perfusion. The limited number of LOE-1 trials for investigating the effects of ES in wound healing make critical evaluation and assessment somewhat difficult. Further, better-designed clinical trials are needed to improve our understanding of the optimal dosing, timing and type of ES to be used.

The analgesic effect of electrostimulation (WoundEL®) in the treatment of leg ulcers

This study aims to demonstrate the analgesic efficacy of electrostimulation (ES), a recognised treatment for leg ulcers. Patients treated by ES for leg ulcers between 2011 and 2013 were included in the study. The pain score obtained with the numerical rating scale (NRS) was reported before the start of the ES (D0), after 3 days (D3) and 1 week following treatment initialisation. The analgesic treatments (AT) were reported at each assessment. Seventy-three patients were included (mean age 75·19 years): 31 venous leg ulcers, 21 mixed venous leg ulcers, 2 arterial ulcers, 17 hypertensive ischaemic ulcers, 1 Hydrea(®)-induced ulcer and an amputation stump ulcer. The NRS at D0 was on average 5·3 (median = 6) while it was 2·2 at D7 (median = 2), that is P < 0·001. The results were also significant between D0 and D3 (P < 0·001). A decrease in the number of AT used was observed between D0 (2·0 AT per patient on average) and D7 (1·7 AT on average) (P < 0·001). We also observed a decrease in the consumption of grade 3 analgesics on D0 and D7 (P = 0·03). This study demonstrates the rapid analgesic efficacy of ES in leg ulcers, with a clear impact on the NRS score and especially on the decrease in analgesic consumption.

Electrostimulation: Current Status, Strength of Evidence Guidelines, and Meta-Analysis

Significance: Delayed healing of skin wounds is a serious problem for the patients, clinicians, and society. The application of interventions with proven effectiveness to increase wound healing is relevant. Recent Advances: This article summarizes the results of effect studies with the application of electrostimulation (ES) as additional treatment to standard wound care (SWC). Therefore, five published narrative reviews are discussed. In addition, 15 studies with a clear randomized controlled trial design are analyzed systematically and the results are presented in four forest plots. The healing rate is expressed in the outcome measure percentage area reduction in 4 weeks of treatment (PAR4). This leads to a continuous measure with mean differences between the percentage healing in the experimental group (SWC plus ES) and in the control group (SWC alone or SWC plus placebo ES). Adding ES to SWC in all wound types increases PAR4 by an extra 26.7% (95% confidence interval [CI] 15.6, 37.8); adding unidirectional ES to SWC increases PAR4 by 30.8% (95% CI 20.9, 40.6) and adding unidirectional ES to the treatment of pressure ulcers increases PAR4 by 42.7% (95% CI 32.0, 53.3). Critical Issues: There is a discrepancy between the proven effectiveness of ES as additional treatment to SWC and the application of ES in real practice. Possible drawbacks are the lack of clinical expertise concerning the proper application of ES and the extra time effort and necessary equipment that are needed. Future Directions: Clinicians concerned about the optimal treatment of patients with delayed wound healing should improve their practical competency to be able to apply ES.

Harnessing the Electric Spark of Life to Cure Skin Wounds

Significance: Skin wounds cause great distress and are a huge economic burden, particularly with an increasingly aging population that heals poorly. There is an urgent need for better therapies that improve repair. Intracellular signaling pathways that regulate wound repair are activated by growth factors, hormones, and cytokines released at the wound. In addition, endogenous electric fields (EFs) are generated by epithelia in response to injury and are an important cue that coordinates cell behavior at wounds. Electrical stimulation (ES), therefore, holds the potential to be effective therapeutically in treating wounds. Recent Advances: ES of wounds is an old idea based on observations of the natural occurrence of EF at wound sites. However, it is now receiving increasing attention, because (1) the underpinning mechanisms are being clarified; (2) devices that measure skin wound currents are in place; and (3) medical devices that apply EF to poorly healing wounds are in clinical use with promising results. Critical Issues: Several signaling proteins transduce the EF influence to cells. However, a bigger picture of the EF-proteome is needed in order to understand this complex process and target it in a controlled manner. Future Directions: Dissecting the signaling pathways driving electrical wound healing will allow further identification of key molecular switches that control the cellular response to EFs. These findings herald the development of a new concept, the use of hydrogel electrodes impregnated with small molecules that target signaling pathways to explore the potential of dual electric-pharmacological therapies to repair wounds.

Influence of electrotaxis on cell behaviour

Understanding the mechanism of cell migration and interaction with the microenvironment is not only of critical significance to the function and biology of cells, but also has extreme relevance and impact on physiological processes and diseases such as morphogenesis, wound healing, neuron guidance, and cancer metastasis.

Current status of the use of modalities in wound care: electrical stimulation and ultrasound therapy

Wound healing is a complex pathway that requires cells, an appropriate biochemical environment (i.e., cytokines, chemokines), an extracellular matrix, perfusion, and the application of both macrostrain and microstrain. The process is both biochemically complex and energy dependent. Healing can be assisted in difficult cases through the use of physical modalities. In the current literature, there is much debate over which treatment modality, dosage level, and timing is optimal. The mechanism of action for both electrical stimulation and ultrasound are reviewed along with possible clinical applications for the plastic surgeon.

A novel in vitro assay for electrophysiological research on human skin fibroblasts: degenerate electrical waves downregulate collagen I expression in keloid fibroblasts

Electrical stimulation (ES) has been used for the treatment of wounds and has been shown to alter gene expression and protein synthesis in skin fibroblasts in vitro. Here, we have developed a new in vitro model system for testing the effects of precisely defined, different types of ES on the collagen expression of normal and keloid human skin fibroblasts. Keloid fibroblasts were studied because they show excessive collagen production. Both types of fibroblasts were electrically stimulated with alternating current (AC), direct current (DC) or degenerate waves (DW). Cells were subjected to 20, 75 and 150mV/mm electric field strengths at 10 and 60Hz frequencies. At lower electric fields, all types of ES upregulated collagen I in both cell types compared to controls. However, at higher electric field strength (150mV/mm) and frequency (60Hz), DW maximally downregulated collagen I in keloid fibroblasts, yet had significantly lower cytotoxic effects on normal fibroblasts than AC and DC. Compared to unstimulated cells, both normal skin and keloid fibroblasts showed a significant decrease in collagen I expression after 12h of DW and AC stimulation. In contrast, increasing amplitude of DC upregulated collagen I and PAI-1 gene transcription in normal and keloid fibroblasts, along with increased cytotoxicity effects. Thus, our new preclinical assay system shows highly differential effects of specific types of ES on human fibroblast collagen expression and cytotoxicity and identifies DW of electrical current (DW) as a promising, novel therapeutic strategy for suppressing excessive collagen I formation in keloid disease.