The Development of a Novel 3D Bioprinted Smart Responsive Dressing to Treat Skin Scars

The skin is the largest organ in the human body with a primary role of protecting against environmental insults such as infection and dehydration. Skin injuries affect millions of people worldwide and can lead to significant morbidity such as the loss of a body part, disfiguration, or even death. After large injuries, the skin is unable to regenerate, instead healing through intense wound contraction that leads to non-functional scar tissue formation. To overcome this limitation, the primary research goal of this thesis was to develop a new bilayered ‘responsive’ skin scaffold with dual action i.e., preventing bacterial infection while enhancing skin wound healing, ultimately promoting successful regeneration of a healthy, scar-less, full thickness skin tissue

3D-printed gelatin methacrylate scaffolds with controlled architecture and stiffness modulate the fibroblast phenotype towards dermal regeneration

Impaired skin wound healing due to severe injury often leads to dysfunctional scar tissue formation as a result of excessive and persistent myofibroblast activation, characterised by the increased expression of α-smooth muscle actin (αSMA) and extracellular matrix (ECM) proteins. Yet, despite extensive research on impaired wound healing and the advancement in tissue-engineered skin substitutes, scar formation remains a significant clinical challenge. This study aimed to first investigate the effect of methacrylate gelatin (GelMA) biomaterial stiffness on human dermal fibroblast behaviour in order to then design a range of 3D-printed GelMA scaffolds with tuneable structural and mechanical properties and understand whether the introduction of pores and porosity would support fibroblast activity, while inhibiting myofibroblast-related gene and protein expression. Results demonstrated that increasing GelMA stiffness promotes myofibroblast activation through increased fibrosis-related gene and protein expression. However, the introduction of a porous architecture by 3D printing facilitated healthy fibroblast activity, while inhibiting myofibroblast activation. A significant reduction was observed in the gene and protein production of αSMA and the expression of ECM-related proteins, including fibronectin I and collagen III, across the range of porous 3D-printed GelMA scaffolds. These results show that the 3D-printed GelMA scaffolds have the potential to improve dermal skin healing, whilst inhibiting fibrosis and scar formation, therefore potentially offering a new treatment for skin repair

Biocompatible polypeptide-based interpenetrating network (IPN) hydrogels with enhanced mechanical properties

Hydrogels are widely used for biomedical applications such as drug delivery, tissue engineering, or wound healing owing to their mimetic properties in relation to biological tissues. The generation of peptide-based hydrogels is a topic of interest due to their potential to increase biocompatibility. However, their usages can be limited when compared to other synthetic hydrogels because of their inferior mechanical properties. Herein, we present the synthesis of novel synthetic polypeptide-based interpenetrating network (IPN) hydrogels with enhanced mechanical properties. The polypeptide single network is obtained from alkyne functional polypeptides crosslinked with di, tri and tetra azide functional PEG by copper-catalysed alkyne-azide cycloaddition (CuAAC). Interpenetrating networks were subsequently obtained by loading of the polypeptide single network with PEG-dithiol and orthogonally UV-crosslinking with varying molar ratios of pentaerythritol tetraacrylate. The characteristics, including the mechanical strength (i.e. compressive strength (UCS), fracture strain (εbreak), and Young's modulus (E)) and cell compatibility (i.e. metabolic activity and Live/Dead of human Mesenchymal Stem Cells), of each synthetic polypeptide-based IPN hydrogel were studied and evaluated in order to demonstrate their potential as mechanically robust hydrogels for use as artificial tissues. Moreover, 1H NMR diffusometry was carried out to examine the water mobility (DH2O) within the polypeptide-based hydrogels and IPNs. It was found that both the mechanical and morphological properties could be tailored concurrently with the hydrophilicity, rate of water diffusion and 'swellability'. Finally it was shown that the polypeptide-based IPN hydrogels exhibited good biocompatibility, highlighting their potential as soft tissue scaffolds

3D printed scaffolds incorporated with platelet-rich plasma show enhanced angiogenic potential while not inducing fibrosis

Successful therapeutic strategies for wound healing rely on proper vascularization while inhibiting fibrosis. However, scaffolds designed for skin tissue engineering generally lack the biochemical cues that can enhance their vascularization without inducing fibrosis. Therefore, the objective of this work is to incorporate platelet-rich plasma (PRP), a natural source of angiogenic growth factors, into a gelatin methacrylate (GelMA) hydrogel, yielding a bioink that can subsequently be used to 3D print a novel regenerative scaffold with defined architecture for skin wound healing. A PRP-activated bioink is successfully 3D printed, and the resulting scaffolds present similar structural, rheological, and mechanical properties compared to GelMA-only scaffolds. Furthermore, 3D printed PRP-activated scaffolds facilitate controlled release of PRP-derived growth factors for up to 14 days, presenting superior angiogenic potential in vitro (e.g., tubulogenesis assay) and in vivo (chick chorioallantoic membrane) compared to GelMA-only scaffolds, while not inducing a myofibroblastic phenotype in fibroblasts (e.g., α-smooth muscle actin expression). This disruptive technology offers the opportunity for a patient's autologous growth factors to be incorporated into a tailored 3D-printed scaffold in theatre prior to implantation, as part of a single-stage procedure, and has potential in other tissue engineering applications in which enhanced vascularization with limited fibrosis is desired.</p

Mechanomodulatory biomaterials prospects in scar prevention and treatment

Scarring is a major clinical issue that affects a considerable number of patients. The associated problems go beyond the loss of skin functionality, as scars bring aesthetic, psychological, and social difficulties. Therefore, new strategies are required to improve the process of healing and minimize scar formation. Research has highlighted the important role of mechanical forces in the process of skin tissue repair and scar formation, in addition to the chemical signalling. A more complete understanding of how engineered biomaterials can modulate these mechanical stimuli and modify the mechanotransduction signals in the wound microenvironment is expected to enable scar tissue reduction. The present review aims to provide an overview of our current understanding of skin biomechanics and mechanobiology underlying wound healing and scar formation, with an emphasis on the development of novel mechanomodulatory wound dressings with the capacity to offload mechanical tension in the wound environment. Furthermore, a broad overview of current challenges and future perspectives of promising mechanomodulatory biomaterials for this application are provided. Statement of significance: Scarring still is one of the biggest challenges in cutaneous wound healing. Beyond the loss of skin functionality, pathological scars, like keloids and hypertrophic, are associated to aesthetic, psychological, and social distress. Nonetheless, the understanding of the pathophysiology behind the formation of those scars remains elusive, which has in fact hindered the development of effective therapeutics. Therefore, in this review we provide an overview of our current understanding of skin biomechanics and mechanobiology underlying wound healing and scar formation, with an emphasis on the development of novel mechanomodulatory wound dressings with the capacity to offload mechanical tension in the wound environment