Regenerative Engineering Approaches to Scar-Free Skin Regeneration

Blends of Silk Waste Protein and Polysaccharides for Enhanced Wound Healing and Tissue Regeneration: Mechanisms, Applications, and Future Perspectives

Wound healing is a highly sophisticated process, and therefore, a pioneering approach for designing excellent wound dressings with desirable characteristics vital for maintaining the external wound environment by assessing the inherent conditions of a patient for effective wound healing. Silk fibroin (SF), a versatile biocompatible material, has garnered significant attention for its potential in the field of wound healing and tissue regeneration. When SF is blended with polysaccharides, their synergistic properties can result in a material with enhanced bioactivity and tunable mechanical properties that facilitate the controlled release of therapeutic agents. This review explores how SF interacts with certain polysaccharides such as cellulose, chitosan, alginate, and hyaluronic acid (HA) and also delves into the underlying mechanisms through which these SF-polysaccharide blends induce processes such as cell adhesion, proliferation, and differentiation for enhanced wound healing and tissue regeneration. This review also emphasizes the potential of the aforementioned blends in diverse wound healing applications in conjunction with other treatment approaches, further addressing the current challenges in this domain and future directions for optimizing SF-polysaccharide blends for clinical research.

Phlomis crinita Cav. From Algeria: A source of bioactive compounds possessing antioxidant and wound healing activities

ETHNOPHARMACOLOGICAL RELEVANCE

Phlomis crinita Cav. (Lamiaceae), locally known as "El Khayata" or "Kayat El Adjarah", is traditionally used in Algeria for its wound-healing properties.

AIM OF THE STUDY

Investigate, for the first time, the phytochemical profile, safety, antioxidant and wound-healing activities of the flowering tops methanolic extract of P. crinita (PCME) collected from Bouira Province in the North of Algeria.

MATERIALS AND METHODS

Preliminary phytochemical assays were carried out on PCME to quantify the main classes of bioactive compounds, such as total phenols, flavonoids, and tannins. An in-depth LC-DAD-ESI-MS analysis was carried out to elucidate the phytochemical profile of this plant species. Antioxidant activity was investigated by several colorimetric and fluorimetric assays (DPPH, TEAC, FRAP, ORAC, β-carotene bleaching and ferrozine assay). The acute oral toxicity of PCME (2000 mg/kg b.w.) was tested in vivo on Swiss albino mice, whereas the acute dermal toxicity and wound-healing properties of the PCME ointment (1-5% PCMO) were tested in vivo on Wistar albino rats. Biochemical and histological analyses were carried out on biological samples.

RESULTS

The phytochemical screening highlighted a high content of phenolic compounds (175.49 ± 0.8 mg of gallic acid equivalents/g of dry extract), mainly flavonoids (82.28 ± 0.44 mg of quercetin equivalents/g of dry extract). Fifty-seven compounds were identified by LC-DAD-ESI-MS analysis, belonging mainly to the class of flavones (32.27%), with luteolin 7-(6″-acetylglucoside) as the most abundant compound and phenolic acids (32.54%), with salvianolic acid C as the most abundant compound. A conspicuous presence of phenylethanoids (15.26%) was also found, of which the major constituent is forsythoside B. PCME showed a strong antioxidant activity with half-inhibitory activity (IC50) ranging from 1.88 to 37.88 μg/mL and a moderate iron chelating activity (IC50 327.44 μg/mL). PCME appears to be safe with Lethal Dose 50 (LD50) ≥ 2000 mg/kg b.w. No mortality or toxicity signs, including any statistically significant changes in body weight gain and relative organs' weight with respect to the control group, were recorded. A significant (p < 0.001) wound contraction was observed in the 5% PCMO-treated group with respect to the untreated and petroleum jelly groups between 8 and 20 days, whereas no statistically significant results were observed at the two lower doses (1 and 2% PCMO). In addition, the 5% PCMO-treated group showed a statistically significant (p < 0.05) wound healing activity with respect to the reference drug-treated group, showing, at the end of the study, the highest wound contraction percentage (88.00 ± 0.16%).

CONCLUSION

PCME was safe and showed strong antioxidant and wound-healing properties, suggesting new interesting pharmaceutical applications for P. crinita based on its traditional use.

Classes of Stem Cells: From Biology to Engineering

Purpose

The majority of adult tissues are limited in self-repair and regeneration due to their poor intrinsic regenerative capacity. It is widely recognized that stem cells are present in almost all adult tissues, but the natural regeneration in adult mammals is not sufficient to recover function after injury or disease. Historically, 3 classes of stem cells have been defined: embryonic stem cells (ESCs), adult mesenchymal stem cells (MSCs), and induced pluripotent stem cells (iPSCs). Here, we have defined a fourth fully engineered class: the synthetic artificial stem cell (SASC). This review aims to discuss the applications of these stem cell classes in musculoskeletal regenerative engineering.

Method

We screened articles in PubMed and bibliographic search using a combination of keywords. Relevant and high-cited articles were chosen for inclusion in this narrative review.

Results

In this review, we discuss the different classes of stem cells that are biologically derived (ESCs and MSCs) or semi-engineered/engineered (iPSCs, SASC). We also discuss the applications of these stem cell classes in musculoskeletal regenerative engineering. We further summarize the advantages and disadvantages of using each of the classes and how they impact the clinical translation of these therapies.

Conclusion

Each class of stem cells has advantages and disadvantages in preclinical and clinical settings. We also propose the engineered SASC class as a potentially disease-modifying therapy that harnesses the paracrine action of biologically derived stem cells to mimic regenerative potential.

Lay Summary

The majority of adult tissues are limited in self-repair and regeneration, even though stem cells are present in almost all adult tissues. Historically, 3 classes of stem cells have been defined: embryonic stem cells (ESCs), adult mesenchymal stem cells (MSCs), and induced pluripotent stem cells (iPSCs). Here, we have defined a fourth, fully engineered class: the synthetic artificial stem cell (SASC). In this review, we discuss the applications of each of these stem cell classes in musculoskeletal regenerative engineering. We further summarize the advantages and disadvantages of using each of these classes and how they impact the clinical translation of these therapies.

Development of porcine skeletal muscle extracellular matrix-derived hydrogels with improved properties and low immunogenicity

Hydrogels derived from decellularized extracellular matrices (ECM) of animal origin show immense potential for regenerative applications due to their excellent cytocompatibility and biomimetic properties. Despite these benefits, the impact of decellularization protocols on the properties and immunogenicity of these hydrogels remains relatively unexplored. In this study, porcine skeletal muscle ECM (smECM) underwent decellularization using mechanical disruption (MD) and two commonly employed decellularization detergents, sodium deoxycholate (SDC) or Triton X-100. To mitigate immunogenicity associated with animal-derived ECM, all decellularized tissues were enzymatically treated with α-galactosidase to cleave the primary xenoantigen-the α-Gal antigen. Subsequently, the impact of the different decellularization protocols on the resultant hydrogels was thoroughly investigated. All methods significantly reduced total DNA content in hydrogels. Moreover, α-galactosidase treatment was crucial for cleaving α-Gal antigens, suggesting that conventional decellularization methods alone are insufficient. MD preserved total protein, collagen, sulfated glycosaminoglycan, laminin, fibronectin, and growth factors more efficiently than other protocols. The decellularization method impacted hydrogel gelation kinetics and ultrastructure, as confirmed by turbidimetric and scanning electron microscopy analyses. MD hydrogels demonstrated high cytocompatibility, supporting satellite stem cell recruitment, growth, and differentiation into multinucleated myofibers. In contrast, the SDC and Triton X-100 protocols exhibited cytotoxicity. Comprehensive in vivo immunogenicity assessments in a subcutaneous xenotransplantation model revealed MD hydrogels' biocompatibility and low immunogenicity. These findings highlight the significant influence of the decellularization protocol on hydrogel properties. Our results suggest that combining MD with α-galactosidase treatment is an efficient method for preparing low-immunogenic smECM-derived hydrogels with enhanced properties for skeletal muscle regenerative engineering and clinical applications.

Oxygen generating biomaterials at the forefront of regenerative medicine: advances in bone regeneration

Globally, an annual count of more than two million bone transplants is conducted, with conventional treatments, including metallic implants and bone grafts, exhibiting certain limitations. In recent years, there have been significant advancements in the field of bone regeneration. Oxygen tension regulates cellular behavior, which in turn affects tissue regeneration through metabolic programming. Biomaterials with oxygen release capabilities enhance therapeutic effectiveness and reduce tissue damage from hypoxia. However, precise control over oxygen release is a significant technical challenge, despite its potential to support cellular viability and differentiation. The matrices often used to repair large-size bone defects do not supply enough oxygen to the stem cells being used in the regeneration process. Hypoxia-induced necrosis primarily occurs in the central regions of large matrices due to inadequate provision of oxygen and nutrients by the surrounding vasculature of the host tissues. Oxygen generating biomaterials (OGBs) are becoming increasingly significant in enhancing our capacity to facilitate the bone regeneration, thereby addressing the challenges posed by hypoxia or inadequate vascularization. Herein, we discussed the key role of oxygen in bone regeneration, various oxygen source materials and their mechanism of oxygen release, the fabrication techniques employed for oxygen-releasing matrices, and novel emerging approaches for oxygen delivery that hold promise for their potential application in the field of bone regeneration.

Fetal milieu-simulating hyaluronic acid-dopamine-chondroitin sulfate hydrogel promoting angiogenesis and hair regeneration for wound healing

Wound regeneration with complete functions and skin appendages is still challenging in wound dressing application. Inspired by the efficient wound healing in the fetal environment, we developed a fetal milieu-mimicking hydrogel for accelerating wound healing simultaneously with hair follicle regeneration. To mimic the fetal extracellular matrix (ECM), which contains high content of glycosaminoglycans, hyaluronic acid (HA) and chondroitin sulfate (CS) were selected to fabricate hydrogels. Meanwhile, dopamine (DA) modification endowed hydrogels with satisfactory mechanical properties and multi-functions. The hydrogel encapsulated atorvastatin (ATV) and zinc citrate (ZnCit), namely HA-DA-CS/Zn-ATV, exhibited tissue adhesion, self-healing capacity, good biocompatibility, excellent anti-oxidant ability, high exudate absorption, and hemostasis property. In vitro results revealed that hydrogels exerted significant angiogenesis and hair follicle regeneration efficacy. In vivo results confirmed that hydrogels significantly promoted wound healing, and the closure ratio reached over 94 % after 14 days of hydrogels-treatment. The regenerated skin exhibited a complete epidermis, dense and ordered collagen. Furthermore, the number of neovessels and hair follicles in the HA-DA-CS/Zn-ATV group were 1.57- and 3.05-fold higher than those of the HA-DA-CS group. Thus, HA-DA-CS/Zn-ATV serves as multifunctional hydrogels for simulating the fetal milieu and achieving efficient skin reconstruction with hair follicle regrowth, exhibiting potential in clinical wound healing.

Oxygen-Generating Biomaterials for Translational Bone Regenerative Engineering

Successful regeneration of critical-size defects remains one of the significant challenges in regenerative engineering. These large-scale bone defects are difficult to regenerate and are often reconstructed with matrices that do not provide adequate oxygen levels to stem cells involved in the regeneration process. Hypoxia-induced necrosis predominantly occurs in the center of large matrices since the host tissue's local vasculature fails to provide sufficient nutrients and oxygen. Indeed, utilizing oxygen-generating materials can overcome the central hypoxic region, induce tissue in-growth, and increase the quality of life for patients with extensive tissue damage. This article reviews recent advances in oxygen-generating biomaterials for translational bone regenerative engineering. We discussed different oxygen-releasing and delivery methods, fabrication methods for oxygen-releasing matrices, biology, oxygen's role in bone regeneration, and emerging new oxygen delivery methods that could potentially be used for bone regenerative engineering.

Wound Healing Properties of Natural Products: Mechanisms of Action

A wound is the loss of the normal integrity, structure, and functions of the skin due to a physical, chemical, or mechanical agent. Wound repair consists of an orderly and complex process divided into four phases: coagulation, inflammation, proliferation, and remodeling. The potential of natural products in the treatment of wounds has been reported in numerous studies, emphasizing those with antioxidant, anti-inflammatory, and antimicrobial properties, e.g., alkaloids, saponins, terpenes, essential oils, and polyphenols from different plant sources, since these compounds can interact in the various stages of the wound healing process. This review addresses the most current in vitro and in vivo studies on the wound healing potential of natural products, as well as the main mechanisms involved in this activity. We observed sufficient evidence of the activity of these compounds in the treatment of wounds; however, we also found that there is no consensus on the effective concentrations in which the natural products exert this activity. For this reason, it is important to work on establishing optimal treatment doses, as well as an appropriate route of administration. In addition, more research should be carried out to discover the possible side effects and the behavior of natural products in clinical trials.

New insights into balancing wound healing and scarless skin repair

Scars caused by skin injuries after burns, wounds, abrasions and operations have serious physical and psychological effects on patients. In recent years, the research of scar free wound repair has been greatly expanded. However, understanding the complex mechanisms of wound healing, in which various cells, cytokines and mechanical force interact, is critical to developing a treatment that can achieve scarless wound healing. Therefore, this paper reviews the types of wounds, the mechanism of scar formation in the healing process, and the current research progress on the dual consideration of wound healing and scar prevention, and some strategies for the treatment of scar free wound repair.

Overexpression of NDST1 Attenuates Fibrotic Response in Murine Adipose-Derived Stem Cells

Adipose-derived stem cells (ADSCs) hold tremendous potential for treating diseases and repairing damaged tissues. Heparan sulfate (HS) plays various roles in cellular signaling mechanisms. The importance of HS in stem cell function has been reported and well documented. However, there has been little progress in using HS for therapeutic purposes. We focused on one of the sulfotransferases, NDST1, which influences overall HS chain extent and sulfation pattern, with the expectation to enhance stem cell function by increasing the N-sulfation level. We herein performed transfections of a green fluorescent protein-vector control and NDST1-vector into mouse ADSCs to evaluate stem cell functions. Overexpression of NDST1 suppressed the osteogenic differentiation of ADSCs. There was no pronounced effect observed on the stemness, inflammatory gene expression, nor any noticeable effect in adipogenic and chondrogenic differentiation. Under the tumor necrosis factor-alpha stimulation, NDST1 overexpression induced several chemokine productions that attract neutrophils and macrophages. Finally, we identified an antifibrotic response in ADSCs overexpressing NDST1. This study provides a foundation for the evaluation of HS-related effects in ADSCs undergoing ex vivo gene manipulation.