Exosomes are nano-sized vesicles that serve as mediators for cell-to-cell communication. With their unique nucleic acids, proteins, and lipids cargo compositions that reflect the characteristics of producer cells, exosomes can be utilized as cell-free therapeutics. Among exosomes derived from various cellular origins, mesenchymal stem cell-derived exosomes (MSC-exosomes) have gained great attention due to their immunomodulatory and regenerative functions. Indeed, many studies have shown anti-inflammatory, anti-aging and wound healing effects of MSC-exosomes in various in vitro and in vivo models. In addition, recent advances in the field of exosome biology have enabled development of specific guidelines and quality control methods, which will ultimately lead to clinical application of exosomes. This review highlights recent studies that investigate therapeutic potential of MSC-exosomes and relevant mode of actions for skin diseases, as well as quality control measures required for development of exosome-derived therapeutics.

Mesenchymal Stem/Stromal Cell-Derived Exosomes for Immunomodulatory Therapeutics and Skin Regeneration.

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.
Highlights:
1 The design and application of conductive biomaterials for wound healing are comprehensively reviewed, including versatile conductive agents, the various forms of conductive wound dressings, and different in vivo applications.2 Three main strategies of which conductive biomaterials realizing their applications in wound healing and skin tissue engineering are discussed.3 The challenges and perspectives in designing multifunctional conductive biomaterials and further clinical translation are proposed.

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

Significance: Chronic wounds impact the quality of life (QoL) of nearly 2.5% of the total population in the United States and the management of wounds has a significant economic impact on health care. Given the aging population, the continued threat of diabetes and obesity worldwide, and the persistent problem of infection, it is expected that chronic wounds will continue to be a substantial clinical, social, and economic challenge. In 2020, the coronavirus disease (COVID) pandemic dramatically disrupted health care worldwide, including wound care. A chronic nonhealing wound (CNHW) is typically correlated with comorbidities such as diabetes, vascular deficits, hypertension, and chronic kidney disease. These risk factors make persons with CNHW at high risk for severe, sometimes lethal outcomes if infected with severe acute respiratory syndrome coronavirus 2 (pathogen causing COVID-19). The COVID-19 pandemic has impacted several aspects of the wound care continuum, including compliance with wound care visits, prompting alternative approaches (use of telemedicine and creation of videos to help with wound dressing changes among others), and encouraging a do-it-yourself wound dressing protocol and use of homemade remedies/substitutions. Recent Advances: There is a developing interest in understanding how the social determinants of health impact the QoL and outcomes of wound care patients. Furthermore, addressing wound care in the light of the COVID-19 pandemic has highlighted the importance of telemedicine options in the continuum of care. Future Directions: The economic, clinical, and social impact of wounds continues to rise and requires appropriate investment and a structured approach to wound care, education, and related research.

Human Wound and Its Burden: Updated 2020 Compendium of Estimates.

The cells secrete extracellular vesicles (EV) that may have an endosomal origin, or from evaginations of the plasma membrane. The former are usually called exosomes, with sizes ranging from 50 to 100 nm. These EV contain a lipid bilayer associated to membrane proteins. Molecules such as nucleic acids (DNA, mRNA, miRNA, lncRNA, etc.) and proteins may be stored inside. The EV composition depends on the producer cell type and its physiological conditions. Through them, the cells modify their microenvironment and the behavior of neighboring cells. That is accomplished by transferring factors that modulate different metabolic and signaling pathways. Due to their properties, EV can be applied as a diagnostic and therapeutic tool in medicine. The mesenchymal stromal cells (MSC) have immunomodulatory properties and a high regenerative capacity. These features are linked to their paracrine activity and EV secretion. Therefore, research on exosomes produced by MSC has been intensified for use in cell-free regenerative medicine. In this area, the use of EV for the treatment of chronic skin ulcers (CSU) has been proposed. Such sores occur when normal healing does not resolve properly. That is usually due to excessive prolongation of the inflammatory phase. These ulcers are associated with aging and diseases, such as diabetes, so their prevalence is increasing with the one of such latter disease, mainly in developed countries. This has very important socio-economic repercussions. In this review, we show that the application of MSC-derived EV for the treatment of CSU has positive effects, including accelerating healing and decreasing scar formation. This is because the EV have immunosuppressive and immunomodulatory properties. Likewise, they have the ability to activate the angiogenesis, proliferation, migration, and differentiation of the main cell types involved in skin regeneration. They include endothelial cells, fibroblasts, and keratinocytes. Most of the studies carried out so far are preclinical. Therefore, there is a need to advance more in the knowledge about the conditions of production, isolation, and action mechanisms of EV. Interestingly, their potential application in the treatment of CSU opens the door for the design of new highly effective therapeutic strategies.

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Extracellular Vesicles Derived From Mesenchymal Stem Cells (MSC) in Regenerative Medicine: Applications in Skin Wound Healing.

Biofilms in chronic wounds, including diabetic foot ulcers, pressure ulcers, and venous leg ulcers, pose a major challenge to wound management. Herein, we report a Janus-type antimicrobial dressing for eradication of biofilms in chronic wounds. The dressing consists of electrospun nanofiber membranes coupled with dissolvable microneedle arrays to enable effective delivery of a database-designed antimicrobial peptide to both inside and outside biofilms. This antimicrobial dressing exhibited high efficacy against a broad spectrum of resistant pathogens in vitro. Importantly, such a dressing was able to eradicate methicillin-resistant Staphylococcus aureus (MRSA) biofilms in both an ex vivo human skin wound infection model and a type II diabetic mouse wound infection model after daily treatment without applying surgical debridement. Most importantly, the dressing can also completely remove the Pseudomonas aeruginosa and MRSA, dual-species biofilm in an ex vivo human skin infection model. In addition, our computational simulations also suggested that microneedles were more effective in the delivery of peptides to the biofilms than free drugs. Our results indicate that the Janus-type antimicrobial dressings may provide an effective treatment and management of chronic wound polymicrobial infections.

Dissolvable Microneedles Coupled with Nanofiber Dressings Eradicate Biofilms via Effectively Delivering a Database-Designed Antimicrobial Peptide.

Significance: A 2018 retrospective analysis of Medicare beneficiaries identified that ∼8.2 million people had wounds with or without infections. Medicare cost estimates for acute and chronic wound treatments ranged from $28.1 billion to $96.8 billion. Highest expenses were for surgical wounds followed by diabetic foot ulcers, with a higher trend toward costs associated with outpatient wound care compared with inpatient. Increasing costs of health care, an aging population, recognition of difficult-to-treat infection threats such as biofilms, and the continued threat of diabetes and obesity worldwide make chronic wounds a substantial clinical, social, and economic challenge. Recent Advances: Chronic wounds are not a problem in an otherwise healthy population. Underlying conditions ranging from malnutrition, to stress, to metabolic syndrome, predispose patients to chronic, nonhealing wounds. From an economic point of view, the annual wound care products market is expected to reach $15-22 billion by 2024. The National Institutes of Health's (NIH) Research Portfolio Online Reporting Tool (RePORT) now lists wounds as a category. Future Directions: A continued rise in the economic, clinical, and social impact of wounds warrants a more structured approach and proportionate investment in wound care, education, and related research.

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Chandan K. Sen

Papers

Human Wounds and Its Burden: An Updated Compendium of Estimates.

Human Wound and Its Burden: Updated 2020 Compendium of Estimates.

Human Wounds and Its Burden: An Updated Compendium of Estimates