Perspectives on the Current State of Bioprinted Skin Substitutes for Wound Healing

Something Old and Something New-A Pilot Study of Shrinkage and Modern Imaging Devices

Shrinkage, a heat-induced process, reorganizes collagen fibers, thereby reducing wound surface area. This technique, commonly applied in surgeries like periareolar mastopexy and skin grafting, is well-established. Despite its widespread use, modern imaging has recently enabled detailed observation of shrinkage's effects on tissue temperature and oxygenation. The aim of this study is to investigate the effects of shrinkage on histological level, temperature, and tissue oxygenation. Skin flaps were collected, marked, and subjected to shrinkage in vitro, with wound dimensions recorded before and after shrinkage. Biopsy samples were analyzed histologically. In our clinical set up, Snapshot NIR® and FLIR thermography were used to assess tissue oxygenation and temperature changes before and after shrinkage. Shrinkage significantly reduced wound area by almost 47% ± 8.5%, with a 16.5% ± 6.0% reduction in length and a 36.5% ± 7.7% reduction in width. Tissue temperature rose by an average of 38.3 °C post-shrinkage, reaching approximately 65 °C. A slight decrease in oxygen saturation was observed following shrinkage. Histological analyses reveal collagen fiber denaturation and structural reorganization. Thermal shrinkage is an effective method for reducing wound size and tension, demonstrating potential for facilitating larger full-thickness skin grafts. Although minor decreases in oxygenation were observed, shrinkage may enhance wound healing by reducing tension at wound edges. Further studies are needed to quantify its impact on functional and cosmetic outcomes.

Bioinspired shape-changing nanofiber dressings for intelligent wrapping and promoting healing of superficial wounds

The use of dressings in clinical settings is common for the purpose of wound wrapping and creating an optimal microenvironment to enhance the healing process. Proper coverage of wounds with dressings serves as the fundamental basis for effective wound healing. Unfortunately, non-standard coverage by hands can cause pain and secondary damage to patients, while slow manual application during treatment of extensive burns may increase the risk of wound infection. Herein, drawing inspiration from the microstructure and hygroscopic deformation observed in pine cones, we propose a polyvinyl alcohol/polysulfone (PVA/PSF) smart dressing. This bioinspired smart dressing exhibits rapid bending deformation under high moisture condition, allowing easy adjustment of bending amplitude, speed, and direction. Moreover, the smart dressing is capable of rapid bending and autonomous wrapping around "artificial wounds" on a doll's body, as well as fitting irregularly shaped "hand wounds" and extensive "arm wounds" on human subjects. By integrating two layers into one dressing design, we endow it with dual functionality: The hygroscopic PVA layer facilitates transversal liquid transport to effectively reduce exudate accumulation in the wound bed while maintaining proper moisture levels; meanwhile, the highly hydrophobic PSF layer repels various aqueous solutions to protect against external contaminants. In vivo results confirm that this multifunctional smart dressing promotes collagen synthesis and accelerates angiogenesis for accelerated wound healing. We believe that this innovative multifunctional approach to wound management will provide valuable insights into wound healing therapy.

Advances in 3D printing for the repair of tympanic membrane perforation: a comprehensive review

Tympanic membrane perforation (TMP) is one of the most common conditions in otolaryngology worldwide, and hearing damage caused by inadequate or prolonged healing can be distressing for patients. This article examines the rationale for utilizing three-dimensional (3D) printing to produce scaffolds for repairing TMP, compares the advantages and disadvantages of 3D printed and bioprinted grafts with traditional autologous materials and other tissue engineering materials in TMP repair, and highlights the practical and clinical significance of 3D printing in TMP repair while discussing the current progress and promising future of 3D printing and bioprinting. There is a limited number of reviews specifically dedicated to 3D printing for TMP repair. The majority of reviews offer a general overview of the applications of 3D printing in the broader realm of tissue regeneration, with some mention of TMP repair. Alternatively, they explore the biopolymers, cells, and drug molecules utilized for TMP repair. However, more in-depth analysis is needed on the strategies for selecting bio-inks that integrate biopolymers, cells, and drug molecules for tympanic membrane repair.

A vascularized in vivo melanoma model suitable for metastasis research of different tumor stages using fundamentally different bioinks

Although 2D cancer models have been the standard for drug development, they don't resemble in vivo properties adequately. 3D models can potentially overcome this. Bioprinting is a promising technique for more refined models to investigate central processes in tumor development such as proliferation, dormancy or metastasis. We aimed to analyze bioinks, which could mimic these different tumor stages in a cast vascularized arteriovenous loop melanoma model in vivo. It has the advantage to be a closed system with a defined microenvironment, supplied only with one vessel-ideal for metastasis research. Tested bioinks showed significant differences in composition, printability, stiffness and microscopic pore structure, which led to different tumor stages (Matrigel and Alg/HA/Gel for progression, Cellink Bioink for dormancy) and resulted in different primary tumor growth (Matrigel significantly higher than Cellink Bioink). Light-sheet fluorescence microscopy revealed differences in vascularization and hemorrhages with no additional vessels found in Cellink Bioink. Histologically, typical human melanoma with different stages was demonstrated. HMB-45-positive tumors in progression inks were infiltrated by macrophages (CD163), highly proliferative (Ki67) and metastatic (MITF/BRN2, ATX, MMP3). Stainings of lymph nodes revealed metastases even without significant primary tumor growth in Cellink Bioink. This model can be used to study tumor pathology and metastasis of different tumor stages and therapies.

A novel method for the establishment of autologous skin cell suspensions: characterisation of cellular sub-populations, epidermal stem cell content and wound response-enhancing biological properties

Introduction: Autologous cell suspension (ACS)-based therapy represents a highly promising approach for burns and chronic wounds. However, existing technologies have not achieved the desired clinical success due to several limitations. To overcome practical and cost-associated obstacles of existing ACS methods, we have established a novel methodology for rapid, enzymatic disaggregation of human skin cells and their isolation using a procedure that requires no specialist laboratory instrumentation and is performed at room temperature. Methods: Cells were isolated using enzymatic disaggregation of split-thickness human skin followed by several filtration steps for isolation of cell populations, and cell viability was determined. Individual population recovery was confirmed in appropriate culture medium types, and the presence of epidermal stem cells (EpSCs) within keratinocyte sub-populations was defined by flow cytometry via detection of CD49 and CD71. Positive mediators of wound healing secreted by ACS-derived cultures established on a collagen-based wound-bed mimic were detected by proteome arrays and quantified by ELISA, and the role of such mediators was determined by cell proliferation assays. The effect of ACS-derived conditioned-medium on myofibroblasts was investigated using an in-vitro model of myofibroblast differentiation via detection of α-SMA using immunoblotting and immunofluorescence microscopy. Results: Our methodology permitted efficient recovery of keratinocytes, fibroblasts and melanocytes, which remained viable upon long-term culture. ACS-derivatives comprised sub-populations with the CD49-high/CD71-low expression profile known to demarcate EpSCs. Via secretion of mitogenic factors and wound healing-enhancing mediators, the ACS secretome accelerated keratinocyte proliferation and markedly curtailed cytodifferentiation of myofibroblasts, the latter being key mediators of fibrosis and scarring. Discussion: The systematic characterisation of the cell types within our ACS isolates provided evidence for their superior cell viability and the presence of EpSCs that are critical drivers of wound healing. We defined the biological properties of ACS-derived keratinocytes, which include ability to secrete positive mediators of wound healing as well as suppression of myofibroblast cytodifferentiation. Thus, our study provides several lines of evidence that the established ACS isolates comprise highly-viable cell populations which can physically support wound healing and possess biological properties that have the potential to enhance not only the speed but also the quality of wound healing.

Cutaneous Redox Senescence

Our current understanding of skin cell senescence involves the role of environmental stressors (UV, O3, cigarette smoke, particulate matter, etc.), lifestyle (diet, exercise, etc.) as well as genetic factors (metabolic changes, hormonal, etc.). The common mechanism of action of these stressors is the disturbance of cellular redox balance characterized by increased free radicals and reactive oxygen species (ROS), and when these overload the intrinsic antioxidant defense system, it can lead to an oxidative stress cellular condition. The main redox mechanisms that activate cellular senescence in the skin involve (1) the oxidative damage of telomeres causing their shortening; (2) the oxidation of proteomes and DNA damage; (3) an a in lysosomal mass through the increased activity of resident enzymes such as senescence-associated β-galactosidase (SA-β-gal) as well as other proteins that are products of lysosomal activity; (4) and the increased expression of SASP, in particular pro-inflammatory cytokines transcriptionally regulated by NF-κB. However, the main targets of ROS on the skin are the proteome (oxi-proteome), followed by telomeres, nucleic acids (DNAs), lipids, proteins, and cytoplasmic organelles. As a result, cell cycle arrest pathways, lipid peroxidation, increased lysosomal content and dysfunctional mitochondria, and SASP synthesis occur. Furthermore, oxidative stress in skin cells increases the activity of p16INK4A and p53 as inhibitors of Rb and CDks, which are important for maintaining the cell cycle. p53 also promotes the inactivation of mTOR-mediated autophagic and apoptotic pathways, leading to senescence. However, these markers alone cannot establish the state of cellular senescence, and multiple analyses are encouraged for confirmation. An updated and more comprehensive approach to investigating skin senescence should include further assays of ox-inflammatory molecular pathways that can consolidate the understanding of cutaneous redox senescence.