1.1. Skin Grafting Techniques

Tissue grafting has been explored for a long time now, with the initial use of autografts going back as far as the 6th century. Skin grafts come into play when the tissue loss or injury is chronic. The graft thickness could either be split-thickness or full-thickness skin grafts ^[1]. Typically, split-thickness grafts use the epidermis and the papillary dermis of healthy adult skin for repair ^[1]. Split-thickness grating is known to be the gold standard for a variety of cutaneous wounds, but it comes with certain limitations. Split-thickness procedures fail to repair if the skin loss is more than 1/3^rd of the total area of body skin ^[1]. While meshing can increase the graft sites’ surface area, balancing the meshing ratio, which ideally should be no more than 3:1 (graft: wound area), is hard as it is prone to contracting during repair ^[2]. Post-grafting symptoms of ache, redness, and inflammation are also observed in such skin grafts. Contrary to split-thickness grafts, full-thickness grafts use both the epidermal and complete dermal layers and are advantageous in repairing soft tissue defects. A full-thickness skin graft can handle chronic injuries well, with less skin shrinking and more aesthetically natural-looking post-healing, unlike split-thickness ones ^[3]. Full-thickness grafts, however, need a fully vascularized bed for grafting and are affected by donor skin unavailability ^[4]. Lately, autologous skin graft efficiency has been improved by combining it with scaffolds, gels, therapeutic agents, etc., to accomplish massive full-thickness injuries ^[3]. Allotransplantation or homografts obtained from genetically dissimilar members of the same species are often beneficial in traumatic wounds, where a temporary graft covering alleviates the recipient’s wound bed until autografting is done ^[3]. Homografts are immediately available, increase donor supply, and extended storage before use, thus giving them an upper hand in the grafting method. Regrettably, allotransplants are often subjected to viral contaminations such as human immunodeficiency virus, cytomegalovirus, and hepatitis ^[4]. They might induce strong recipient inflammatory immune reactions with the interference of T and B lymphocytes to ultimately reject the homograft ^[4]. Recent experiments have shown that implementing mixed chimeric molecules with the donor’s bone marrow could subdue recipient graft rejection in clinical therapies such as the in vitro assay on RA-iTreg cells (retinoic acid), which exhibits immunosuppressive T-cell proliferative activity and also prevents T-cell cytokine activity in mice models ^[5]. On the other hand, xenotransplants are obtained from heterologous species, with the most frequently used being porcine xenografts, which are ready for use but can cause secondary infections from other dissimilar species. Usually used with burn wounds where <25% of the total skin area is affected, xenografts reduce the implementation of surgical excisions and save time ^[6].

1.2. Wound Dressings

A dressing is considered ideal if it confers complete wound shielding, eliminates excess exudate, possesses antimicrobial efficacy, maintains a balance between optimum hydration and oxygen, is easy to handle, and has non-anaphylactic properties ^[7]. Most of the dressings have problems of frequent changing, contamination from the wound fluid, imbalance of wound moisture, difficulty to remove post-application, and insufficient antimicrobial protection. These problems were overcome by using cotton and polymeric bandages to treat dry wounds and those with mild exudation, like the nonocclusive dressing Xeroform ™, made up of a petroleum-based fine mesh gauze with 3% of bismuth tribromophenate, which was used for treating preliminary exudating wounds. Fabric-based non-allergic dressings saturated with paraffin and olive oil, such as Bactigras, Jelonet, Paratulle, etc., were commercially used non-adherent and gamma-sterilized dressings suitable for a superficial clean wound. However, these traditional dressings failed to provide an occlusive hydrated wound healing environment, which paved the way for modern alternatives, viz., contemporary formulated dressings applied directly onto wounds in the form of semi-solid creams, ointments, lotions, and liniments, as well as smart gels, thin self-adherent bioactive incorporated films, etc. The contemporary cotton gauge dressings incorporate chitosan-silver-zinc oxide nanocomposites for efficient moisture retention and antibacterial efficiency ^[7][8]. During the late 20th century, human amniotic membranes were used for exudate and fluid-laden burn wound dressings. These, as a non-cellular medium for adherence to mesenchymal stem cells, served as a vital platform for skin equivalent development ^[9]. Although such dressings were advantageous in providing temporary pain relief, balancing the optimum hydration in wounds, and were time- and cost-effective, the chance of infection spread was high ^[9]. Among polysaccharide dressings, chitosan and chitin are the most explored ones for clinical therapeutics because of their nontoxicity, biocompatibility, high durability, antibacterial efficiency, and suitability to be applied onto open wounds ^[7]. Their limitations include low tensile strength and elasticity. Algal extract-impregnated dressings have good absorbency, are hemostatic, and antimicrobial; thus, they are useful in exuding wounds ^[10]. The use of chitosan-alginate amalgamated dressings could improve the mechanical strength and stabilize the dressing ^[10]. Hyaluronic acid, a linear polysaccharide incorporated into dressings, is compatible with burn, chronic, and surgical wounds ^[8]. It gives structural sustenance to enable nutrient diffusion, clears wound debris by their interaction with the CD44 molecules, and balances hyperhydration during new tissue regeneration ^[8]. Hyaluronic acid dressings activate keratinocytes to migrate and proliferate wound sites for ready repair ^[11]. However, they are highly dissolvable and have less residence time in vivo. Microbial cellulose biosynthesized from Komagataeibacter xylinus, using diverse carbon and nitrogen sources, can precisely be made into dressings for the prophylaxis of extremely chronic injuries that require recurrent dressing changes ^[7][8]. Unlike other phytocelluloses, microbial ones show substantial pliability, strength, biocompatibility, and good absorbency, but their antimicrobial action limits their medical applications. In addition, they could be improved to a certain extent by the incorporation of nanoparticles like zinc-oxide nanoparticles. Hydrocolloid-based dressings are occlusive dressings for pressure ulcers ^[12]. They maintain an optimum water and oxygen balance within the wounds, but fail to hold a large amount of exudate. Their frequent changing is necessary to evade the maceration of tissues ^[12]. Foam dressings are bilaminar structurally with a hydrophilic end with moderate exudate absorbency for wounds with exposed bone. Foam dressings can be rightly called the new substitute to conventional dressings to treat venous pressure ulcers in preventing hospital-acquired pressure ulcers in critically ill individuals. However, they do not yet have much adherence to wound bed and hence are not indorsed for heavy exudative wounds ^[13]. Adhesive transparent film dressings are suitably conglomerated with hydrogels that allow for optimum wound hydration, maintain skin integrity, and easily monitor the wounds ^[8]. Research to expand their antimicrobial effectiveness has led to their combination with chlorhexidine, which displays high adherence and declines catheter-related infection to improve vascularization.

1.3. Natural, Phytochemical, and Antiseptic Therapies

Natural and plant-based products have been the traditional ancestral therapies used in skin wound care and management before the rise of pharmaceutical and clinical alternatives. For centuries, these products, because of their potent antimicrobial, anti-inflammatory, anti-analgesic, and cell-stimulating characteristics, were implemented as traditional medicine for acute and chronic wounds. Owing to the existing incidence of diabetes and severe cardiac and vascular implications, chronic wound interventions seek significant attention, making the use of natural therapies for healing applications of specific interest. Natural amalgams encompass a widespread assortment of substances, antioxidants, phenols, terpenes, flavones, and many more organic and inorganic constituents that act as specific targets in the healing process ^[15]. These constituents have been clinically tested for their efficiency through in vitro and in vivo models. Since wound repair is a complex cascade of biochemical events, it is of utmost importance to stimulate a reparation process without microbial infections. Hence, traditional therapeutic agents and plant-based natural products have shown exemplary outcomes. Further scientific investigation on the progress of various extraction and purification methods, their precise mechanism of action, safety, and quality control assessments, etc., is obligatory. Traditional therapies are cost complaint and beneficial for primary wound care and management. Still, inconsistency in their batch-to-batch results, sudden immunologic reactions, and adverse after-effects can restrict their implication in multidisciplinary wound management ^[15].

In antimicrobial wound management, topical antiseptics form the first line of a cure for primary wound infection and reduce the microbial bioburden. Antiseptics permeate into wound biofilms, curb bacteria’s growth, and target a broad spectrum of microbial communities, unlike selectively specific antibiotic medications. The most frequently used antiseptics are povidone-iodine, chlorhexidine, alcohol, acetate, hydrogen peroxide, boric acid, silver nitrate, and silver sulfadiazine ^[16]. Ethanol, isopropanol, and n-propanol are the most suitable agents for surface decontamination and skin asepsis. Their antibactericidal spectrum targets both Gram-positive and Gram-negative bacteria. Another antiseptic used for centuries is iodine and its compounds, which act as a topical agent for preoperative skin preparations ^[17]. Cadexomer iodine, a hydrophilic modified-starch polymer bead, has been explored for the sustained and controlled release for treating wound exudates ^[18]. Chlorhexidine, belonging to the class of biguanide, has been extensively investigated as a biocide antiseptic in dermal and oral products either as a 0.05% dilution for wound cleansing or a 4% solution for surgical skin preparation and hand scrub ^[19]. Polyhexanide biguanide hydrogels have been explored for their cytotoxicity against methicillin-resistant Staphylococcus aureus on dermal wounds and their ability to clinically eradicate the infection. Bisphenols, viz., triclosan and hexachlorophene, are skin-compatible antiseptics effective against Gram-positives. Similarly, silver compounds in the form of solutions, creams, and ointments or nanocrystalline silver have long been used as antimicrobial agents. Their mechanical action is either through cell membrane lysis, the disruption of cellular protein and electron transport chains, or DNA levels by blocking transcription initiation ^[20]. The expediency of antiseptics on the skin surface, though they are fairly well-established and used, and their utilization as a prophylactic anti-infective agent for open wounds, remains a debatable and unexplored area in the present time. It is relevant to state that a combined traditional and modern therapy approach can target repair faster with negligible side effects, such as silver-impregnated nanofibers, aloe vera extract-embedded alginate hydrogels, propolis wound dressings, honey-based post-operative bandages, etc., could likely expand modern medicine.

1.4. Mechanical Adjuncts and Physical Agents

Despite several attempts to equilibrate the cellular, biomolecular events during wound repair and preserve an optimal hydrated healing environment, there are times when wounds become chronic non-healing sites. A series of mechanical adjuncts and physical agents in use does contribute to such wound reparation processes and provide constructive and adjunctive functions. Hydrotherapy, ultraviolet C radiation (UV-C), vacuum-assisted closure, hyperbaric oxygen, and electrical stimulation are a few worth naming ^[21]. Hydrotherapy, being one of the oldest adjuvant therapies, is effective for burn wounds where a continuous rotation of water and air eliminates debris and toxic components and dilutes microbial colonization ^[22]. Hydrotherapy is advantageous for individuals with venous stasis dermatitis, pyoderma gangrenosum, peripheral artery disease, teeth lacerations, and rarely, diabetes mellitus acute wounds. This method effectively upholds optimal moisture in and around the wound surface for better revascularization and dermal regeneration. With several advantages, there are also a few disadvantages. A particular pressure of the water circulation is needed at the wound surface for rinsing of granulation tissue, which might impair the developing granulation tissue, restrict epidermal cell migration, and cause skin maceration ^[22]. In addition, bacterial infections can emerge if the moisture circulation is prolonged and proper drying of the wound is not done. Pulsed lavage therapy has currently become a replacement for hydrotherapy in terms of its use of an irrigating solution maintained at a particular pressure by a powered device ^[22]. The therapy improves the rate of granulation and better remodeling of wounded tissues. Ultraviolet C radiation (UV-C) ranges from 200–280 nm, and erythemal effectivity is accomplished at wavelengths of 250 nm where nucleic acid absorption happens, leading to accelerated DNA synthesis in fibroblasts, increased oxygenation and capillary blood flow for granulation tissue formation, and antibacterial and antiviral effects on wound surfaces. UV radiations can contribute to wound healing by upsurging epithelial cell turnover and hyperplasia to release prostaglandins and initiate cell proliferation for re-epithelialization. A dose-dependent application of these radiations may also cause shedding of peri-ulcer epidermal cells and sloughing of necrotic tissues and eschar ^[23]. Vacuum-assisted wound closure is applied to seal the wound area and place a negative pressure onto the wound surface that produces adhesive friction to the tissues and contracts wound depth for efficient closure ^[24]. This therapy can significantly and observably reduce water loss of the split-thickness graft area, curtail post-wounding duration, and restrict the relapse of infection during wound repair ^[24]. The accomplishment of vacuum-assisted closure therapy in treating chronic injuries has now led to its use in specialized clinical situations such as temporary abdominal closure, skin avulsion, poststernotomy mediastinitis, acute and subacute wounds, wound with bony prominence, osteomyelitis, as a graft reinforcement ^[24][25], and in reconstructive surgeries. Hyperbaric oxygen therapy confines a hundred percent oxygen at one atmospheric pressure to enhance oxygen inundation in the blood by forming oxyhemoglobin. Hyperoxic environments endorse wound repair through an increase in growth factors and formation of iNOS that regulates collagen formation, wound contraction, and endothelial progenitor cell proliferation ^[21][26]. This therapy has been utilized in chronic and poorly healing wounds, acute wounds, and diabetic foot ulcers. A systematic assessment of the healing capacity of hyperbaric oxygen therapy in diabetic foot ulcer patients was found to be clearly superior in comparison to other surgical procedures. Electrical simulation gathers both positive and negative charged cells, viz., neutrophils, phagocytes, epidermal cells, and fibroblasts, onto the wounded area so that each of the cells performs their specific cellular activities of wound healing. The endogenic electric field plays an imperative role in wound healing largely by triggering protein synthesis and cell migration. Clinical investigations have confirmed that electrical stimulation with steady direct currents is advantageous in wound acceleration. Human fibroblasts cells subjected to high-voltage pulsed current stimulation (HVPCS) did intensify the healing rate of soft tissue wounds as per reports ^[27]. Both protein and DNA synthesis rates became higher by applying specific blends of HVPCS voltages and pulse rates. Besides, both cell migration and a significant increase in the TGF-1β levels were prominent near the wound area in response to an endogenic electrical field that promoted early contraction and collagen synthesis (electrotaxis: the directional migration of cells toward the anodic or cathodic electrode of an applied electrical field) ^[27]. Researcher Yung Shin Sun experimentally aimed at optimizing the direct current stimulation therapy for enhancing the progression of wound repair. Via the finite element method (FEM), he standardized the distribution of endogenous electric fields produced around the wound area under the influence of different electrode configurations, including sizes and positions and the total power dissipation within different skin layers ^[28]. Extracorporeal shock wave therapy (ESWT) has been clinically relevant in being the cost-complaint effective intraoperative treatment for quite a few orthopedic and traumatic applications, together with challenging soft tissue wounds. These low-energy pulse waves were first clinically explored to treat urinary calcinosis, which later was utilized for treating bone and tendon injuries. Recently, ESWT has been studied to healing soft tissue wound injuries like burns, ulcers, etc., where these waves not only accelerate tissue repair, but also stimulate neovascularization in the underlying damaged tissues ^[29]. Additionally, these therapeutic shock waves also recruit newer mesenchymal stem cells, stimulate cell proliferation and differentiation, possess anti-inflammatory and antimicrobial effects, and block the toxic sensory pain receptors ^[29]. The underlying principle for ESWT employs short-term momentary acoustic pulsations with a simultaneous rise and fall in peak pressure time. The electro-hydraulic shock wave is generated within a metal inclusion, reflecting the shock waves towards the therapeutic target. Shock waves are electrically or mechanically produced energy waves that can traverse through a liquid or a gas medium. These waves either occur through electromagnetic, piezoelectric, or electrohydraulic wave pulses released from a high-voltage electrode water vaporization system ^[30]. During an injury, hypoxically challenged immunocompromised tissues are also subjected to ischemia. The application of ESWT onto the tissues increases tissue perfusion and reduces necrosis, as seen in experimental iatrogenic ischemia conditions ^[29]. Clinical research on experimental transgenic mice models displayed stimulation and upregulation of VEGF receptor 2, a mediator of angiogenesis, during ESWT treatments ^[31]. ESWT treatments also showed higher vessel densities in ischemic tissue formation experiments observed in immunohistopathological sections ^[32]. Another form of physical medication that uses low-level lasers or light-emitting diodes onto the body surface, known as the low-level laser therapy (LLLT), which has been effectively used as a therapeutic system to repair deferred wounds. This photothermal method comprises a monochromatic and coherent light source that produces a healing effect when the emitted photons are absorbed onto the wavelength-sensitive injured tissues/cells and trigger a set of complex biochemical arrays, ultimately resulting in accelerated healing of chronic wounds ^[33]. Lasers also employ their applications in burns, amputation wounds, skin grafting, infected wounds, etc. ^[34]. Low-intensity irradiations work between 500 and 1100 nm with laser output powers between 10 and 90 mW at the therapeutic site, capable of mediating cell proliferation and enhancing cellular activity. Visible red light, having the longest wavelength, is frequently used in LLLT, and has been seen to trigger faster healing of tissues by irradiating the mitochondrial complex and plasmalemma of the damaged cells, where the absorbed photons activate a set of enzymatic reactions and cytochromes, and energy conversions happen to yield adenosine triphosphates that, in turn, regulate cell function, relieve inflammation and pain, and accelerate healing ^[34]. Reports on the growth inhibition of Pseudomonas aeruginosa, Escherichia coli, and Staphylococcus aureus upon irradiation with 1–20 J/cm² at wavelengths of 630 nm were seen in preventing wound infections ^[33]. LLLT may also show substantial positive results in stimulation and co-adjuvanted therapies. A study conducted by Pessoa et al. to inspect the co-effect of LLLT with steroid cortisone did show a co-adjuvanted effect of LLLT on cortisone to not only speed up the tissue healing process, but also to stabilize the harmful effects of steroids on tissues ^[35]. Neat corticosteroid, neat 5-fluorouracil, a pulsed dye laser (585-nm), and the amalgamation of all the three showed a significant enhancement in keloidal and hypertrophic scars post-treatment. Pulsed dye laser enhanced the scar surface and improved long-term adverse hypopigmentation, telangiectasia, and skin atrophy, unlike the corticosteroid ^[36].