Biochemical and Biophysical Cues in Matrix Design for Chronic and Diabetic Wound Treatment

Current Advances in Wound Healing and Regenerative Medicine

Treating chronic wounds is a common and costly challenge worldwide. More advanced treatments are needed to improve wound healing and prevent severe complications such as infection and amputation. Like other medical fields, there have been advances in new technologies promoting wound healing potential. Regenerative medicine as a new method has aroused hope in treating chronic wounds. The technology improving wound healing includes using customizable matrices based on synthetic and natural polymers, different types of autologous and allogeneic cells at different differentiation phases, small molecules, peptides, and proteins as a growth factor, RNA interference, and gene therapy. In the last decade, various types of wound dressings have been designed. Emerging dressings include a variety of interactive/ bioactive dressings and tissue-engineering skin options. However, there is still no suitable and effective dressing to treat all chronic wounds. This article reviews different wounds and common treatments, advanced technologies and wound dressings, the advanced wound care market, and some interactive/bioactive wound dressings in the market.

Nanogels designed for cell-free nucleic acid sequestration

Chronic wounds exhibit over-expression of cell-free deoxyribonucleic acid (cfDNA), leading to a prolonged inflammation and non-healing wounds. Scavenging excessive cfDNA molecules is a promising strategy for chronic wound treatment. Nanoscopic particles act as efficient cfDNA scavengers due to their large surface area, however their efficiency in cfDNA uptake was limited by adsorption solely on the nanoparticle surface. In contrast, nanogels may provide multiple cfDNA binding sites in the nanoparticle interior, however their use for cfDNA scavenging is yet to be explored. Herein, we report cationic nanogels derived from a copolymer of chitosan and poly{2-[(acryloyloxy)ethyl]trimethylammonium chloride} end-grafted to the chitosan backbone as side chains. The nanogels retain their positive charge at the pH and ionic strength of chronic wound exudate, enabling electrostatically driven cfDNA scavenging. The network structure of the nanogels leads to the cfDNA sequestration in the nanogel interior, in addition to surface attachment. A key factor in cfDNA sequestration is the ratio of the pore size of the nanogel-to-cfDNA molecular dimensions. The enhanced cfDNA scavenging efficiency, along with biocompatibility of the nanogels, makes them a promising component of dressings for chronic wound treatment.

Fabrication and Characterization of Oxygen-Generating Polylactic Acid/Calcium Peroxide Composite Filaments for Bone Scaffolds

The latest advancements in bone scaffold technology have introduced novel biomaterials that have the ability to generate oxygen when implanted, improving cell viability and tissue maturation. In this paper, we present a new oxygen-generating polylactic acid (PLA)/calcium peroxide (CPO) composite filament that can be used in 3D printing scaffolds. The composite material was prepared using a wet solution mixing method, followed by drying and hot melting extrusion. The concentration of calcium peroxide in the composite varied from 0% to 9%. The prepared filaments were characterized in terms of the presence of calcium peroxide, the generated oxygen release, porosity, and antibacterial activities. Data obtained from scanning electron microscopy and X-ray diffraction showed that the calcium peroxide remained stable in the composite. The maximum calcium and oxygen release was observed in filaments with a 6% calcium peroxide content. In addition, bacterial inhibition was achieved in samples with a calcium peroxide content of 6% or higher. These results indicate that an optimized PLA filament with a 6% calcium peroxide content holds great promise for improving bone generation through bone cell oxygenation and resistance to bacterial infections.

Preparation and characterization of vaccarin, hypaphorine and chitosan nanoparticles and their promoting effects on chronic wounds healing

Chronic wounds have become an important factor hindering human health, affecting tens of millions of people worldwide, especially diabetic wounds. Based on the antibacterial properties of chitosan, the angiogenesis promoting effect of vaccarin (VAC) and the anti-inflammatory effect of hypaphorine (HYP), nanoparticles with high bioavailability were prepared. VAC, HYP and chitosan nanoparticles (VAC + HYP-NPS) were used to the treatment of chronic wounds. Transmission electron microscopy (TEM) images showed the nanoparticles were spherical. ZetaPALS showed the potential of nanoparticles were -12.8 ± 5.53 mV and the size were 166.8 ± 29.95 nm. Methyl thiazolyl tetrazolium (MTT) assay showed that VAC + HYP-NPS had no toxicity and the biocompatibility was satisfactory. In the treatment of chronic wounds in diabetic rats, VAC + HYP-NPS significantly promoted the re-epithelialization of chronic wounds and accelerated the healing of chronic wounds. In the process of chronic wounds healing, VAC + HYP-NPS played the antibacterial effect of chitosan, the angiogenic effect of VAC and the anti-inflammatory effect of HYP, and finally promoted the chronic wounds healing. Overall, the developed VAC + HYP-NPS have potential application in chronic wounds healing. In view of the complexity of the causes of chronic wounds, multi-target drug administration may be an effective way to treat chronic wounds.

Allergies caused by textiles: control, research and future perspective in the medical field

Textile production forms one of the most polluting industries worldwide. However, other than damaging environmental effects, chemical waste products, such as formaldehyde or thiazolinone, are problematic for human health, as allergic potential is present in these compounds. Mostly, contact dermatitis occurs when human skin is exposed to textiles. Moreover, non-eczemous variants are mainly associated to textiles. In order to diagnose the possible allergy of the patient towards these compounds, in vivo and in vitro methods ca be performed, such as patch testing or cytokine detection assays, respectively. Newest research focuses on medical textiles such as garments or sutures to help in diagnosis, therapy and recovery of the patients. Sutures and dressings with antimicrobial properties, with the release of oxygen and growth factors offer greater properties. In this review, state of the art in the field as well as future perspectives will be discussed, which are based on the smart textiles that are going to become more important and probably widespread after the current limits exceeded.

Bioactive Injectable Hydrogel Dressings for Bacteria-Infected Diabetic Wound Healing: A "Pull-Push" Approach

Chronic diabetic wound healing remains a challenge due to the existence of excessive danger molecules and bacteria in the inflammatory microenvironment. There is an urgent need for advanced wound dressings that target both inflammation and infection. Here, a bioactive hydrogel without loading any anti-inflammatory ingredients is rationally designed to achieve a "Pull-Push" approach for efficient and safe bacteria-infected diabetic wound healing by integrating danger molecule scavenging (Pull) with antibiotic delivery (Push) in the inflammatory microenvironment. The cationic hydrogel, termed the OCMC-Tob/PEI hydrogel, is fabricated by the conjugation of polyethylenimine (PEI) and tobramycin (Tob) on an oxidized carboxymethyl cellulose (OCMC) backbone via the Schiff base reaction with injectable, self-healing, and biocompatible properties. The OCMC-Tob/PEI hydrogel not only displays the remarkable capability of capturing multiple negatively charged danger molecules (e.g., cell-free DNA, lipopolysaccharides, and tumor necrosis factor-α) to ameliorate anti-inflammation effects but also achieves controllable long-term antibacterial activity by the pH-sensitive release of Tob. Consequently, this multifunctional hydrogel greatly expedites the wound closure rate with combined anti-inflammation and anti-infection effects on Pseudomonas aeruginosa-infected diabetic wounds. Our work provides a highly versatile treatment approach for chronic diabetic wounds and a promising dressing for regenerative medicine.

Biophysical and Biochemical Cues of Biomaterials Guide Mesenchymal Stem Cell Behaviors

Mesenchymal stem cells (MSCs) have been widely used in the fields of tissue engineering and regenerative medicine due to their self-renewal capabilities and multipotential differentiation assurance. However, capitalizing on specific factors to precisely guide MSC behaviors is the cornerstone of biomedical applications. Fortunately, several key biophysical and biochemical cues of biomaterials that can synergistically regulate cell behavior have paved the way for the development of cell-instructive biomaterials that serve as delivery vehicles for promoting MSC application prospects. Therefore, the identification of these cues in guiding MSC behavior, including cell migration, proliferation, and differentiation, may be of particular importance for better clinical performance. This review focuses on providing a comprehensive and systematic understanding of biophysical and biochemical cues, as well as the strategic engineering of these signals in current scaffold designs, and we believe that integrating biophysical and biochemical cues in next-generation biomaterials would potentially help functionally regulate MSCs for diverse applications in regenerative medicine and cell therapy in the future.

Needle-injectable microcomposite cryogel scaffolds with antimicrobial properties

Porous three-dimensional hydrogel scaffolds have an exquisite ability to promote tissue repair. However, because of their high water content and invasive nature during surgical implantation, hydrogels are at an increased risk of bacterial infection. Recently, we have developed elastic biomimetic cryogels, an advanced type of polymeric hydrogel, that are syringe-deliverable through hypodermic needles. These needle-injectable cryogels have unique properties, including large and interconnected pores, mechanical robustness, and shape-memory. Like hydrogels, cryogels are also susceptible to colonization by microbial pathogens. To that end, our minimally invasive cryogels have been engineered to address this challenge. Specifically, we hybridized the cryogels with calcium peroxide microparticles to controllably produce bactericidal hydrogen peroxide. Our novel microcomposite cryogels exhibit antimicrobial properties and inhibit antibiotic-resistant bacteria (MRSA and Pseudomonas aeruginosa), the most common cause of biomaterial implant failure in modern medicine. Moreover, the cryogels showed negligible cytotoxicity toward murine fibroblasts and prevented activation of primary bone marrow-derived dendritic cells ex vivo. Finally, in vivo data suggested tissue integration, biodegradation, and minimal host inflammatory responses when the antimicrobial cryogels, even when purposely contaminated with bacteria, were subcutaneously injected in mice. Collectively, these needle-injectable microcomposite cryogels show great promise for biomedical applications, especially in tissue engineering and regenerative medicine.

Crosslinking Strategies for 3D Bioprinting of Polymeric Hydrogels

Three-dimensional (3D) bioprinting has recently advanced as an important tool to produce viable constructs that can be used for regenerative purposes or as tissue models. To develop biomimetic and sustainable 3D constructs, several important processing aspects need to be considered, among which crosslinking is most important for achieving desirable biomechanical stability of printed structures, which is reflected in subsequent behavior and use of these constructs. In this work, crosslinking methods used in 3D bioprinting studies are reviewed, parameters that affect bioink chemistry are discussed, and the potential toward improving crosslinking outcomes and construct performance is highlighted. Furthermore, current challenges and future prospects are discussed. Due to the direct connection between crosslinking methods and properties of 3D bioprinted structures, this Review can provide a basis for developing necessary modifications to the design and manufacturing process of advanced tissue-like constructs in future.

Hydrogel Production Platform with Dynamic Movement Using Photo-Crosslinkable/Temperature Reversible Chitosan Polymer and Stereolithography 4D Printing Technology

BACKGROUND

Three-dimensional (3D) printing using hydrogel has made great strides when it comes to mimicking 3D artificial tissue in the medical field. However, most structures do not mimic the dynamic movement of the tissues. Without imitating dynamic movements, there are limitations on the extent to which the proper implementation of the tissue's own functions can be achieved.

METHOD

In this study, we intend to present an approach to solving this problem using hydroxybutyl methacrylated chitosan (HBC-MA), a photo-crosslinkable/temperature reversible chitosan polymer. In addition, stereolithography-3D (SLA-3D) printing technology was used, which is more likely to mimic the complex microstructure. As a control, a 3D structure made with pristine poly(ethylene glycol) dimethacrylate (PEG-DMA) was created, and a 4D structure was prepared by adding HBC-MA to poly(ethylene glycol) dimethacrylate (PEG-DMAP) resin.

RESULTS

HBC-MA caused the expansion of water into the polymer matrix at low temperature, and the 4D structure resulted in expansion of the polymer volume, generating dynamic movement due to the expansion of water. Conversely, as the temperature rose, deswelling occurred, followed by a decrease in the volume, showing a shape memory property of returning to the existing structure. Morphological, swelling, and mechanical analysis further confirmed the principle of dynamic movement. In addition, parameters were provided through calculation of the bending ratio angle (θ).

CONCLUSION

Through this, it is suggested that HBC-MA can be applied as a core polymer for SLA-4D printing, and has high potential for realizing the dynamic movement of tissue.

Oxygen-Releasing Antibacterial Nanofibrous Scaffolds for Tissue Engineering Applications

Lack of suitable auto/allografts has been delaying surgical interventions for the treatment of numerous disorders and has also caused a serious threat to public health. Tissue engineering could be one of the best alternatives to solve this issue. However, deficiency of oxygen supply in the wounded and implanted engineered tissues, caused by circulatory problems and insufficient angiogenesis, has been a rate-limiting step in translation of tissue-engineered grafts. To address this issue, we designed oxygen-releasing electrospun composite scaffolds, based on a previously developed hybrid polymeric matrix composed of poly(glycerol sebacate) (PGS) and poly(ε-caprolactone) (PCL). By performing ball-milling, we were able to embed a large percent of calcium peroxide (CP) nanoparticles into the PGS/PCL nanofibers able to generate oxygen. The composite scaffold exhibited a smooth fiber structure, while providing sustainable oxygen release for several days to a week, and significantly improved cell metabolic activity due to alleviation of hypoxic environment around primary bone-marrow-derived mesenchymal stem cells (BM-MSCs). Moreover, the composite scaffolds also showed good antibacterial performance. In conjunction to other improved features, such as degradation behavior, the developed scaffolds are promising biomaterials for various tissue-engineering and wound-healing applications.

An insight into cell-laden 3D-printed constructs for bone tissue engineering

In this review, we have spotlighted various combinations of bioinks to optimize the biofabrication of 3D bone constructs.

Viscoelasticity in natural tissues and engineered scaffolds for tissue reconstruction

Viscoelasticity of living tissues plays a critical role in tissue homeostasis and regeneration, and its implication in disease development and progression is being recognized recently. In this review, we first explored the state of knowledge regarding the potential application of tissue viscoelasticity in disease diagnosis. In order to better characterize viscoelasticity with local resolution and non-invasiveness, emerging characterization methods have been developed with the potential to be supplemented to existing facilities. To understand cellular responses to matrix viscoelastic behaviors in vitro, hydrogels made of natural polymers have been developed and the relationships between their molecular structure and viscoelastic behaviors, are elucidated. Moreover, how cells perceive the viscoelastic microenvironment and cellular responses including cell attachment, spreading, proliferation, differentiation and matrix production, have been discussed. Finally, some future perspective on an integrated mechanobiological comprehension of the viscoelastic behaviors involved in tissue homeostasis, cellular responses and biomaterial design are highlighted. STATEMENT OF SIGNIFICANCE: Tissue- or organ-scale viscoelastic behavior is critical for homeostasis, and the molecular basis and cellular responses of viscoelastic materials at micro- or nano-scale are being recognized recently. We summarized the potential applications of viscoelasticity in disease diagnosis enabled by emerging non-invasive characterization technologies, and discussed the underlying mechanism of viscoelasticity of hydrogels and current understandings of cell regulatory functions of them. With a growing understanding of the molecular basis of hydrogel viscoelasticity and recognition of its regulatory functions on cell behaviors, it is important to bring the clinical insights on how these characterization technologies and engineered materials may contribute to disease diagnosis and treatment. This review explains the basics in characterizing viscoelasticity with our hope to bridge the gap between basic research and clinical applications.

Theranostic biocomposite scaffold membrane

Acute and chronic wounds affect millions and are associated with billions of dollars in healthcare costs. The use of healing markers, biochemical cues from biocompatible matrices and materials, and their correlation with wound healing has the potential to generate valuable diagnostic, prognostic, and therapeutic information. In this study, we developed a collagen-dextran oxygen-sensing biocomposite scaffold membrane in which a phosphorescent oxygen sensor was incorporated to monitor physiological oxygen using in vivo phosphorescence imaging in a preclinical mouse model of wound healing. The oxygen-sensing biocomposite scaffold membrane enabled the noninvasive and longitudinal monitoring of oxygenation changes in vivo in an approach compatible with commercially available preclinical in vivo imaging system instruments. This study provides a new and novel capability where a biocomposite material can serve as a biocompatible, biodegradable theranostic platform to promote and assess tissue oxygenation during wound healing.

In-situ doping of a conductive hydrogel with low protein absorption and bacterial adhesion for electrical stimulation of chronic wounds

Electrical stimulation (ES) via electrodes is promising for treating chronic wounds, but this electrode-based strategy is unable to stimulate the whole wound area and the therapeutic outcome may be compromised. In this study, a conductive poly(2-hydroxyethyl methacrylate) (polyHEMA)/polypyrrole (PPY) hydrogel was developed, and 3-sulfopropyl methacrylate was covalently incorporated in the hydrogel's network to in-situ dope the PPY and maintain the hydrogel's conductivity in the weak alkaline physiological environment. The obtained hydrogel was superior to the commercial Hydrosorb® dressing for preventing bacterial adhesion and protein absorption, and this is helpful to reduce the possibilities of infection and secondary damage during dressing replacement. The in vitro scratch assay demonstrates that ES through the hydrogel enhanced fibroblast migration, and this enhancement effect remained even after the ES was ended. The in vivo assay using diabetic rats shows that when ES was conducted with this polyHEMA/PPY hydrogel, the healing rate was faster than that achieved by the electrode-based ES strategy. Therefore, this polyHEMA/PPY hydrogel shows a great potential for developing the next generation of ES treatment for chronic wounds. STATEMENT OF SIGNIFICANCE: Electrical stimulation (ES) via separated electrodes is promising for treating chronic wounds, but this electrode-based strategy is unable to stimulate the whole wound area, compromising the therapeutic outcome. Herein, a hydrogel was developed with stable electrical conductivity in the physiological environment and strong resistance to protein absorption and bacterial adhesion. The in vitro and in vivo tests proved that ES applied through the flexible and conductive hydrogel that covered the wound was superior to ES through electrodes for promoting the healing of the chronic wound. This hydrogel-based ES strategy combines the advantages of ES and hydrogel dressing and will pave the way for the next generation of ES treatment for chronic wounds.

A synergistic antibacterial effect between terbium ions and reduced graphene oxide in a poly(vinyl alcohol)–alginate hydrogel for treating infected chronic wounds

A graphene and rare earth ion-containing hydrogel was developed to effectively promote the healing of infected chronic wounds without using antibiotics.

Advances and Future Perspectives in 4D Bioprinting

Three-dimensionally printed constructs are static and do not recapitulate the dynamic nature of tissues. Four-dimensional (4D) bioprinting has emerged to include conformational changes in printed structures in a predetermined fashion using stimuli-responsive biomaterials and/or cells. The ability to make such dynamic constructs would enable an individual to fabricate tissue structures that can undergo morphological changes. Furthermore, other fields (bioactuation, biorobotics, and biosensing) will benefit from developments in 4D bioprinting. Here, the authors discuss stimuli-responsive biomaterials as potential bioinks for 4D bioprinting. Natural cell forces can also be incorporated into 4D bioprinted structures. The authors introduce mathematical modeling to predict the transition and final state of 4D printed constructs. Different potential applications of 4D bioprinting are also described. Finally, the authors highlight future perspectives for this emerging technology in biomedicine.

Synergetic topography and chemistry cues guiding osteogenic differentiation in bone marrow stromal cells through ERK1/2 and p38 MAPK signaling pathway

Both the topographic surface and chemical composition modification can enhance rapid osteogenic differentiation and bone formation. Till now, the synergetic effects of topography and chemistry cues guiding biological responses have been rarely reported. Herein, the ordered micro-patterned topography and classically essential trace element of strontium (Sr) ion doping were selected to imitate topography and chemistry cues, respectively. The ordered micro-patterned topography on Sr ion-doped bioceramics was successfully duplicated using the nylon sieve as the template. Biological response results revealed that the micro-patterned topography design or Sr doping could promote cell attachment, ALP activity, and osteogenic differentiation of bone marrow-derived mesenchymal stem cells (BMSCs). Most importantly, the samples both with micro-patterned topography and Sr doping showed the highest promotion effects, and could synergistically activate the ERK1/2 and p38 MAPK signaling pathways. The results suggested that the grafts with both specific topography and chemistry cues have synergetic effects on osteogenic activity of BMSCs and provide an effective approach to design functional bone grafts and cell culture substrates.

Skin Tissue Substitutes and Biomaterial Risk Assessment and Testing

Tremendous progress has been made over the past few decades to develop skin substitutes for the management of acute and chronic wounds. With the advent of tissue engineering and the ability to combine advanced manufacturing technologies with biomaterials and cell culture systems, more biomimetic tissue constructs have been emerged. Synthetic and natural biomaterials are the main constituents of these skin-like constructs, which play a significant role in tissue grafting, the body's immune response, and the healing process. The act of implanting biomaterials into the human body is subject to the body's immune response, and the complex nature of the immune system involves many different cell types and biological processes that will ultimately determine the success of a skin graft. As such, a large body of recent studies has been focused on the evaluation of the performance and risk assessment of these substitutes. This review summarizes the past and present advances in in vitro, in vivo and clinical applications of tissue-engineered skins. We discuss the role of immunomodulatory biomaterials and biomaterials risk assessment in skin tissue engineering. We will finally offer a roadmap for regulating tissue engineered skin substitutes.

Restoring vasculogenic potential of endothelial cells from diabetic patients through spheroid formation

Introduction

Diabetes is an emerging epidemic in the developing world and represents a major risk factor for cardiovascular disease. Among other issues, patients with diabetes suffer from diminished endothelial cell (EC) function, which contributes to impaired vasculogenesis and recovery from ischemic insult. The formation of cells into three-dimensional spheroids promotes cell survival and activates key signaling pathways through the upregulation of cell-cell contacts, providing an opportunity to overcome shortcomings associated with individual autologous cells.

Methods

We hypothesized that forming human microvascular endothelial cells (HMVECs) from diabetic patients into spheroids would restore their vasculogenic potential following upregulation of these cell-cell interactions. HMVEC spheroids were formed and suspended in fibrin gels to quantify vasculogenic potential.

Results

Individual HMVECs from diabetic patients exhibited similar proliferative and chemotactic potential to cells from healthy donors but reduced tubulogenesis. HMVEC spheroids formed from diabetic donors formed more sprouts than spheroids from healthy donors, and more sprouts than individual cells from either population.

Conclusions

Compared to cells from healthy donors, sprout formation was more efficiently abrogated in HMVECs from diabetic patients by blocking matrix metalloproteinase activity. This study demonstrates a promising approach for restoring the diminished vasculogenic potential of endothelial cells in diabetic patients.

Instructive microenvironments in skin wound healing: Biomaterials as signal releasing platforms

Skin wound healing aims to repair and restore tissue through a multistage process that involves different cells and signalling molecules that regulate the cellular response and the dynamic remodelling of the extracellular matrix. Nowadays, several therapies that combine biomolecule signals (growth factors and cytokines) and cells are being proposed. However, a lack of reliable evidence of their efficacy, together with associated issues such as high costs, a lack of standardization, no scalable processes, and storage and regulatory issues, are hampering their application. In situ tissue regeneration appears to be a feasible strategy that uses the body's own capacity for regeneration by mobilizing host endogenous stem cells or tissue-specific progenitor cells to the wound site to promote repair and regeneration. The aim is to engineer instructive systems to regulate the spatio-temporal delivery of proper signalling based on the biological mechanisms of the different events that occur in the host microenvironment. This review describes the current state of the different signal cues used in wound healing and skin regeneration, and their combination with biomaterial supports to create instructive microenvironments for wound healing.

Organ-On-A-Chip Platforms: A Convergence of Advanced Materials, Cells, and Microscale Technologies

Significant advances in biomaterials, stem cell biology, and microscale technologies have enabled the fabrication of biologically relevant tissues and organs. Such tissues and organs, referred to as organ-on-a-chip (OOC) platforms, have emerged as a powerful tool in tissue analysis and disease modeling for biological and pharmacological applications. A variety of biomaterials are used in tissue fabrication providing multiple biological, structural, and mechanical cues in the regulation of cell behavior and tissue morphogenesis. Cells derived from humans enable the fabrication of personalized OOC platforms. Microscale technologies are specifically helpful in providing physiological microenvironments for tissues and organs. In this review, biomaterials, cells, and microscale technologies are described as essential components to construct OOC platforms. The latest developments in OOC platforms (e.g., liver, skeletal muscle, cardiac, cancer, lung, skin, bone, and brain) are then discussed as functional tools in simulating human physiology and metabolism. Future perspectives and major challenges in the development of OOC platforms toward accelerating clinical studies of drug discovery are finally highlighted.