Cell Interactions with Vascular Regenerative MAA-Based Materials in the Context of Wound Healing

Actuation-Mediated Compression of a Mechanoresponsive Hydrogel by Soft Robotics to Control Release of Therapeutic Proteins

Therapeutic proteins, the fastest growing class of pharmaceuticals, are subject to rapid proteolytic degradation in vivo, rendering them inactive. Sophisticated drug delivery systems that maintain protein stability, prolong therapeutic effects, and reduce administration frequency are urgently required. Herein, a mechanoresponsive hydrogel is developed contained within a soft robotic drug delivery (SRDD) device. In a step-change from previously reported systems, pneumatic actuation of this system releases the cationic therapeutic protein Vascular Endothelial Growth Factor (VEGF) in a bioactive form which is required for therapeutic angiogenesis, the growth of new blood vessels, in numerous clinical conditions. The ability of the SRDD device to release bioactive VEGF in a spatiotemporal manner from the hydrogel is tested in diabetic rats - a model in which angiogenesis is difficult to stimulate. Daily actuation of the SRDD device in the diabetic rat model significantly increased cluster of differentiation 31+ (CD31+) blood vessel number (p = 0.0335) and the diameter of alpha-smooth muscle actin+ (α-SMA+) blood vessels (p = 0.0025) compared to passive release of VEGF from non-actuated devices. The SRDD device combined with the mechanoresponsive hydrogel offers the potential to deliver an array of bioactive therapeutics in a spatiotemporal manner to mimic their natural release in vivo.

Self-Assembled Nanoflowers from Natural Building Blocks with Antioxidant, Antibacterial, and Antibiofilm Properties

Polyphenols, natural compounds abundant in phenolic structures, have received widespread attention due to their antioxidant, anti-inflammatory, antibacterial, and anticancer properties, making them valuable for biomedical applications. However, the green synthesis of polyphenol-based materials with economical and environmentally friendly strategies is of great significance. In this study, a multifunctional wound dressing was achieved by introducing polyphenol-based materials of copper phosphate-tannic acid with a flower-like structure (Cu-TA NFs), which show the reactive oxygen species scavenging performance. This strategy endowed the electrospun wound dressing, composed of poly(caprolactone)-coated gum arabic-poly(vinyl alcohol) nanofibers (GPP), with the antibacterial and antibiofilm properties. Our research demonstrates that GPP/Cu-TA NFs are effective against Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa. Furthermore, the developed GPP/Cu-TA NFs showed excellent hemocompatibility and biocompatibility. These results suggest that the synergistic properties of this multifunctional polyphenol platform (GPP/Cu-TA NFs) make it a promising candidate for the further development of wound dressing materials.

The effect of silicon groups on the physicochemical property and bioactivity of L-phenylalanine derived poly(amide-imide)

Poly(amide-imide) (PAI), serving as a synthetic polymer, has been widely used in industry for excellent mechanical properties, chemical resistance and high thermal stability. However, lack of suitable cell niche and biological activity limited the further application of PAI in biomedical engineering. Herein, silicon modified L-phenylalanine derived poly(amide-imide) (PAIS) was synthesized by introducing silica to L-phenylalanine derived PAI to improve physicochemical and biological performances. The influence of silicon amount on physicochemical, immune, and angiogenic performances of PAIS were systemically studied. The results show that PAIS exerts excellent hydrophilic, mechanical, biological activity. PAIS shows no effects on the number of macrophages, but can regulate macrophage polarization and angiogenesis in a dose-dependent manner. This study advanced our understanding of silicon modification in PAI can modulate cell responses via initiating silicon concentration regulation. The acquired knowledge will provide a new strategy to design and optimize biomedical PAI in the future.

Immunomodulatory biomaterials on chemokine signaling in wound healing

Normal wound healing occurs through a careful orchestration of cytokine and chemokine signaling in response to injury. Chemokines are a small family of chemotactic cytokines that are secreted by immune cells in response to injury and are primarily responsible for recruiting appropriate immune cell types to injured tissue at the appropriate time. Dysregulation of chemokine signaling is suspected to contribute to delayed wound healing and chronic wounds in diseased states. Various biomaterials are being used in the development of new therapeutics for wound healing and our understanding of their effects on chemokine signaling is limited. It has been shown that modifications to the physiochemical properties of biomaterials can affect the body's immune reaction. Studying these effects on chemokine expression by various tissues and cell type can help us develop novel biomaterial therapies. In this review, we summarize the current research available on both natural and synthetic biomaterials and their effects on chemokine signaling in wound healing. In our investigation, we conclude that our knowledge of chemokines is still limited and that many in fact share both pro-inflammatory and anti-inflammatory properties. The predominance of either a pro-inflammatory or anti-inflammatory profile is mostly likely dependent on timing after injury and exposure to the biomaterial. More research is needed to better understand the interaction and contribution of biomaterials to chemokine activity in wound healing and their immunomodulatory effects.

Advances in modified hyaluronic acid-based hydrogels for skin wound healing

Hyaluronic acid (HA) is a natural linear anionic polysaccharide with many unique characteristics such as excellent biocompatibility and biodegradability, native biofunctionality, hydrophilicity, and non-immunoreactivity. HA plays crucial roles in numerous biological processes, including the inflammatory response, cell adhesion, migration, proliferation, differentiation, angiogenesis, and tissue regeneration. All these properties and biological functions of HA make it an appealing material for the synthesis of biomedical hydrogels for skin wound healing. Since HA is not able to be gelate alone, it must be processed and functionalized through chemical modifications and crosslinking to generate versatile HA-based hydrogels. In recent years, different physical and chemical crosslinking strategies for HA-based hydrogels have been developed and designed, such as radical polymerization, Schiff-base crosslinking, enzymatic crosslinking, and dynamic covalent crosslinking, and they have broad and promising applications in skin wound healing and tissue engineering. In this review, we focus on chemical modification and crosslinking strategies for HA-based hydrogels, aiming to provide an overview of the latest advances in the development of HA-based hydrogels for skin wound healing. We summarize and propose feasible measures for the application of HA-based hydrogels for skin treatment, and discuss future application trends, which may ultimately promote HA-based hydrogels as a promising biomaterial for clinical applications.

Alloyed nanostructures integrated metal-phenolic nanoplatform for synergistic wound disinfection and revascularization

New materials for combating bacteria-caused infection and promoting the formation of microvascular networks during wound healing are of vital importance. Although antibiotics can be used to prevent infection, treatments that can disinfect and accelerate wound healing are scarce. Herein, we engineer a coating that is both highly compatible with current wound dressing substrates and capable of simultaneously disinfecting and revascularizing wounds using a metal-phenolic nanoplatform containing an alloyed nanostructured architecture (Ag@Cu-MPN_NC). The alloyed nanostructure is formed by the spontaneous co-reduction and catalytic disproportionation reaction of multiple metal ions on a foundation metal-phenolic supramolecular layer. This synergistic presence of metals greatly improves the antibacterial activity against both Gram-negative and Gram-positive pathogenic bacteria, while demonstrating negligible cytotoxicity to normal tissue. In infected rat models, the Ag@Cu-MPN_NC could kill bacteria efficiently, promoting revascularization and accelerate wound closure with no adverse side effects in infected in vivo models. In other words, this material acts as a combination therapy by inhibiting bacterial invasion and modulating bio-nano interactions in the wound.

Nitric oxide-releasing polyurethane/S-nitrosated keratin mats for accelerating wound healing

Nitric oxide (NO) plays an important role in wound healing, due to its ability to contract wound surfaces, dilate blood vessels, participate in inflammation as well as promote collagen synthesis, angiogenesis and fibroblast proliferation. Herein, keratin was first nitrosated to afford S-nitrosated keratin (KSNO). As a NO donor, KSNO was then co-electrospun with polyurethane (PU). These as-spun PU/KSNO biocomposite mats could release NO sustainably for 72 h, matching the renewal time of the wound dressing. Moreover, these mats exhibited excellent cytocompatibility with good cell adhesion and cell migration. Further, the biocomposite mats exhibited antibacterial properties without inducing severe inflammatory responses. The wound repair in vivo demonstrated that these mats accelerated wound healing by promoting tissue formation, collagen deposition, cell migration, re-epithelialization and angiogenesis. Overall, PU/KSNO mats may be promising candidates for wound dressing.

Mobilizing Endogenous Repair Through Understanding Immune Reaction With Biomaterials

With few exceptions, humans are incapable of fully recovering from severe physical trauma. Due to these limitations, the field of regenerative medicine seeks to find clinically viable ways to repair permanently damaged tissue. There are two main approaches to regenerative medicine: promoting endogenous repair of the wound, or transplanting a material to replace the injured tissue. In recent years, these two methods have fused with the development of biomaterials that act as a scaffold and mobilize the body's natural healing capabilities. This process involves not only promoting stem cell behavior, but by also inducing activity of the immune system. Through understanding the immune interactions with biomaterials, we can understand how the immune system participates in regeneration and wound healing. In this review, we will focus on biomaterials that promote endogenous tissue repair, with discussion on their interactions with the immune system.

Construction of nanofibrous scaffolds with interconnected perfusable microchannel networks for engineering of vascularized bone tissue

Vascularization and bone regeneration are two closely related processes during bone reconstruction. A three-dimensional (3D) scaffold with porous architecture provides a suitable microenvironment for vascular growth and bone formation. Here, we present a simple and general strategy to construct a nanofibrous poly(l-lactide)/poly(ε-caprolactone) (PLLA/PCL) scaffold with interconnected perfusable microchannel networks (IPMs) based on 3D printing technology by combining the phase separation and sacrificial template methods. The regular and customizable microchannel patterns within the scaffolds (spacings: 0.4 mm, 0.5 mm, and 0.6 mm; diameters: 0.8 mm, 1 mm, and 1.2 mm) were made to investigate the effect of microchannel structure on angiogenesis and osteogenesis. The results of subcutaneous embedding experiment showed that 0.5/0.8-IPMs (spacing/diameter = 0.5/0.8) and 0.5/1-IPMs (spacing/diameter = 0.5/1) scaffolds exhibited more vascular network formation as compared with other counterparts. After loading with vascular endothelial growth factor (VEGF), VEGF@IPMs-0.5/0.8 scaffold prompted better human umbilical vein endothelial cells (HUVECs) migration and neo-blood vessel formation, as determined by Transwell migration, scratch wound healing, and chorioallantoic membrane (CAM) assays. Furthermore, the microangiography and rat cranial bone defects experiments demonstrated that VEGF@IPMs-0.5/0.8 scaffold exhibited better performance in vascular network formation and new bone formation compared to VEGF@IPMs-0.5/1 scaffold. In summary, our results suggested that the microchannel structure within the scaffolds could be tailored by an adjustable caramel-based template strategy, and the combination of interconnected perfusion microchannel networks and angiogenic factors could significantly enhance vascularization and bone regeneration.

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3D-printed sacrificial templates are used to construct the scaffold with interconnected perfusable microchannel networks.

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The microchannel structure within scaffolds can be tailored by changing the template specifications.

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The introduction of VEGF in the microchannel of scaffold promotes the vascular network formation.

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Microchannel structure and angiogenic factor within scaffold significantly enhance vascularization and bone regeneration.

Skin wound healing assisted by angiogenic targeted tissue engineering: A comprehensive review of bioengineered approaches

Skin injuries and in particular, chronic wounds, are one of the major prevalent medical problems, worldwide. Due to the pivotal role of angiogenesis in tissue regeneration, impaired angiogenesis can cause several complications during the wound healing process and skin regeneration. Therefore, induction or promotion of angiogenesis can be considered as a promising approach to accelerate wound healing. This article presents a comprehensive overview of current and emerging angiogenesis induction methods applied in several studies for skin regeneration, which are classified into the cell, growth factor, scaffold, and biological/chemical compound-based strategies. In addition, the advantages and disadvantages of these angiogenic strategies along with related research examples are discussed in order to demonstrate their potential in the treatment of wounds.

A Biomimetic Approach toward Enhancing Angiogenesis: Recombinantly Expressed Domain V of Human Perlecan Is a Bioactive Molecule That Promotes Angiogenesis and Vascularization of Implanted Biomaterials

Angiogenic therapy involving delivery of pro-angiogenic growth factors to stimulate new blood vessel formation in ischemic disease is promising but has seen limited clinical success due to issues associated with the need to deliver supra-physiological growth factor concentrations. Bio-inspired growth factor delivery utilizing the native growth factor signaling roles of the extracellular matrix proteoglycans has the potential to overcome many of the drawbacks of angiogenic therapy. In this study, the potential of the recombinantly expressed domain V (rDV) of human perlecan is investigated as a means of promoting growth factor signaling toward enhanced angiogenesis and vascularization of implanted biomaterials. rDV is found to promote angiogenesis in established in vitro and in vivo angiogenesis assays by potentiating endogenous growth factor signaling via its glycosaminoglycan chains. Further, rDV is found to potentiate fibroblast growth factor 2 (FGF2) signaling at low concentrations that in the absence of rDV are not biologically active. Finally, rDV immobilized on 3D porous silk fibroin biomaterials promotes enhanced vascular ingrowth and integration of the implanted scaffolds with the surrounding tissue. Together, these studies demonstrate the important role of this biologically active perlecan fragment and its potential in the treatment of ischemia in both native and bioengineered tissues.

Vascular Pedicle and Microchannels: Simple Methods Toward Effective In Vivo Vascularization of 3D Scaffolds

Poor vascularization remains a key limiting factor in translating advances in tissue engineering to clinical applications. Vascular pedicles (large arteries and veins) isolated in plastic chambers are known to sprout an extensive capillary network. This study examined the effect vascular pedicles and scaffold architecture have on vascularization and tissue integration of implanted silk scaffolds. Porous silk scaffolds with or without microchannels are manufactured to support implantation of a central vascular pedicle, without a chamber, implanted in the groin of Sprague Dawley rats, and assessed morphologically and morphometrically at 2 and 6 weeks. At both time points, blood vessels, connective tissue, and an inflammatory response infiltrate all scaffold pores externally, and centrally when a vascular pedicle is implanted. At week 2, vascular pedicles significantly increase the degree of scaffold tissue infiltration, and both the pedicle and the scaffold microchannels significantly increase vascular volume and vascular density. Interestingly, microchannels contribute to increased scaffold vascularity without affecting overall tissue infiltration, suggesting a direct effect of biomaterial architecture on vascularization. The inclusion of pedicles and microchannels are simple and effective proangiogenic techniques for engineering thick tissue constructs as both increase the speed of construct vascularization in the early weeks post in vivo implantation.

A review of accelerated wound healing approaches: biomaterial- assisted tissue remodeling

Nowadays, due to a growing number of tissue injuries, in particular, skin wounds, induction and promotion of tissue healing responses can be considered as a crucial step towards a complete regeneration. Recently, biomaterial design has been oriented towards promoting a powerful, effective, and successful healing. Biomaterials with wound management abilities have been developed for different applications such as providing a native microenvironment and supportive matrices that induce the growth of tissue, creating physical obstacles against microbial contamination, and to be used as delivery systems for therapeutic reagents. Until now, numerous strategies aiming to accelerate the wound healing process have been utilized and studied with their own pros and cons. In this review, tissue remodeling phenomena, wound healing mechanisms, and their related factors will be discussed. In addition, different methods for induction and acceleration of healing via cell therapy, bioactive therapeutic delivery, and/or biomaterial-based approaches will be reviewed.

The role of insulin growth factor-1 on the vascular regenerative effect of MAA coated disks and macrophage-endothelial cell crosstalk

The IGF-1 signaling pathway and IGF-1-dependent macrophage/endothelial cell crosstalk was found to be critical features of the vascular regenerative effect displayed by implanted methacrylic acid -co-isodecyl acrylate (MAA-co-IDA; 40% MAA) coated disks in CD1 mice. Inhibition of IGF-1 signaling using AG1024 an IGF1-R tyrosine kinase inhibitor abrogated vessel formation 14 days after disk implantation in a subcutaneous pocket. Explanted tissue had increased arginase 1 expression and reduced iNOS expression consistent with the greater shift from "M1" ("pro-inflammatory") macrophages to "M2" ("pro-angiogenic") macrophages for MAA coated disks relative to control MM (methyl methacrylate-co-IDA) disks; the latter did not generate a vascular response and the polarization shift was muted with AG1024. In vitro, medium conditioned by macrophages (both human dTHP1 cells and mouse bone marrow derived macrophages) had elevated IGF-1 mRNA and protein levels, while the cells had reduced IGF1-R but elevated IGFBP-3 mRNA levels. These cells also had reduced iNOS and elevated Arg1 expression, consistent with the in vivo polarization results, including the inhibitory effects of AG1024. On the other hand, HUVEC exposed to dTHP1 conditioned medium migrated and proliferated faster suggesting that the primary target of the macrophage released IGF-1 was endothelial cells. Although further investigation is warranted, IGF-1 appears to be a key feature underpinning the observed vascularization. Why MAA based materials have this effect remains to be defined, however.

Effect of methacrylic acid beads on the sonic hedgehog signaling pathway and macrophage polarization in a subcutaneous injection mouse model

Poly(methacrylic acid-co-methyl methacrylate) (MAA) beads promote a vascular regenerative response when used in diabetic wound healing. Previous studies reported that MAA beads modulated the expression of sonic hedgehog (Shh) and inflammation related genes in diabetic wounds. The aim of this work was to follow up on these observations in a subcutaneous injection model to study the host response in the absence of the confounding factors of diabetic wound healing. In this model, MAA beads improved vascularization in healthy mice of both sexes compared to control poly(methyl methacrylate) (MM) beads, with a stronger effect seen in males than females. MAA-induced vessels were perfusable, as evidenced from the CLARITY-processed images. In Shh-Cre-eGFP/Ptch1-LacZ non-diabetic transgenic mice, the increased vessel formation was accompanied by a higher density of cells expressing GFP (Shh) and β-Gal (patched 1, Ptch1) suggesting MAA enhanced the activation of the Shh pathway. Ptch1 is the Shh receptor and a target of the pathway. MAA beads also modulated the inflammatory cell infiltrate in CD1 mice: more neutrophils and more macrophages were noted with MAA relative to MM beads at days 1 and 7, respectively. In addition, MAA beads biased macrophages towards a MHCII-CD206+ ("M2") polarization state. This study suggests that the Shh pathway and an altered inflammatory response are two elements of the complex mechanism whereby MAA-based biomaterials effect vascular regeneration.