Photocrosslinkable poly(propylene glycol-co-lactide) dimethacrylate-based microneedle patch for scarless wound healing of soft tissues

Abstract

Soft tissues, including skin, muscle, tendons, fat, cover almost all of the human body. Soft tissue injuries caused by trauma, disease, or overexertion are common in daily life but still lack targeted and effective repairing devices. This project aims to develop novel microneedle systems, involving special structure designs and multiple functions (e.g., programmable drug release, mechanical regulation, electrical stimulation) to better assist wound healing and tissue regeneration. Central to the systems was poly (lactide-co-propylene glycol-co-lactide) dimethacrylate (PmLnDMA; m and n represent the unit length of propylene glycol and lactide), a photocrosslinkable bioink developed by our group previously. We first designed a bioinspired microneedle system loaded with exosomes and mangiferin for fast and scarless wound healing. The microneedle had a core-shell structure with a gelatin methacryloyl (GelMA) hydrogel shell and a P7L2DMA core. The swelling of GelMA tip provided a reliable contact between the wound tissue and the microneedle. At the early stage, the GelMA shell rapidly released small molecule mangiferin to suppress macrophage-initiated inflammation. Then, the P7L2DMA core sustainably released macromolecule exosomes for angiogenesis of human umbilical vein endothelial cells (HUVECs). In vivo results further confirmed the promising effects of combining mangiferin with exosomes on anti-inflammation, angiogenesis, and even scar reduction. Secondly, we designed a contractile microneedle patch microneedle patch to regulate the stress environment in the wound and thereby reduce scar formation. Specifically, a skin wound bed has two kinds of forces: (1) the intrinsic tension force generated by the surrounding tissue and (2) the traction force generated during wound healing by fibroblasts and myofibroblasts. To counter those two forces, our microneedle system consisted of three parts: the backing layer, the middle part, and the tilted part. The backing layer was made of P68L8DMA, which was flexible and elastic enough to resist tension force of the surrounding tissue. The middle part was made of P7L2DMA, which was stiffer for relieving the local stress generated by myofibroblasts. The tilted part was also made of P7L2DMA and was inserted into the surrounding tissue for tissue adhesion and force transduction. The contractile microneedle patch showed better tissue adhesion than pure backing layer and common microneedle patches. Using a fibroblast-loaded collagen system as an in vitro scar model, the proposed microneedle system significantly reduced some scar-related protein (α-SMA, CXCL14) expressions. RNA sequencing revealed that our patch could decrease the scar formation by downregulating some mechanical signaling pathways, including ECM-receptor interaction, PI3K signaling pathway, and focal adhesion. Finally, we designed a self-powered patch integrated with microneedle and aligned piezoelectric polyvinylidene fluoride (PVDF) microfibers for cardiac tissue regeneration. The microneedle tip was made of stiff P7L2DMA for tissue anchoring while the backing layer was made of elastic P68L8DMA which could withstand long-term cyclic stretching (no breaking under 20% strain). The aligned PVDF fibers were fabricated by electrohydrodynamic (EHD) printing and attached on the P68L8DMA backing layer. Once the microneedle was inserted into the cardiac tissue and deformed with cyclic stretching by heartbeats, the aligned PVDF fibers could generate electrical stimulation to cells and provide topological induction for cell growth. Under dynamic cell culture, the electrical stimulation caused by the PVDF fiber significantly enhanced the cardiac functional protein (connexin 43) expression in H9c2 cardiomyocytes and induced oriented growth with elongated cell morphology. In summary, based on different microneedle systems, we investigated the effects of different treatments, including drug therapy, mechanical regulation, and electrical stimulation, on wound healing and scar formation. We found that long-term drug treatment augmenting the wound healing process was important for healing acceleration and scar reduction. Mechanical regulation is also crucial to scar reduction as stress relaxation in wound area during wound healing could effectively reduce fibroblast proliferation and scar-related protein expressions. In addition, electrical stimulation could promote cardiomyocyte functions, slowing down or even reversing myocardial infarction.