The 3D printed conductive grooved topography hydrogel combined with electrical stimulation for synergistically enhancing wound healing of dermal fibroblast cells

Electrowriting patterns and electric field harness directional cell migration for skin wound healing

Directional cell migration is a crucial step in wound healing, influenced by electrical and topographic stimulations. However, the underlying mechanism and the combined effects of these two factors on cell migration remain unclear. This study explores cell migration under various combinations of guided straight line (SL) spacing, conductivity, and the relative direction of electric field (EF) and SL. Electrowriting is employed to fabricate conductive (multiwalled carbon nanotube/polycaprolactone (PCL)) and nonconductive (PCL) SL, with narrow (50 μm) and wide (400 μm) spacing that controls the topographic stimulation strength. Results show that various combinations of electrical and topographic stimulation yield significantly distinct effects on cell migration direction and speed; cells migrate fastest with the most directivity in the case of conductive, narrow-spacing SL parallel to EF. A physical model based on intercellular interactions is developed to capture the underlying mechanism of cell migration under SL and EF stimulations, in agreement with experimental observations. In vivo skin wound healing assay further confirmed that the combination of EF (1 V cm-1) and parallelly aligned conductive fibers accelerated the wound healing process. This study presents a promising approach to direct cell migration and enhance wound healing by optimizing synergistic electrical and topographic stimulations.

Recent Developments in 3D-(Bio)printed Hydrogels as Wound Dressings

Wound healing is a physiological process occurring after the onset of a skin lesion aiming to reconstruct the dermal barrier between the external environment and the body. Depending on the nature and duration of the healing process, wounds are classified as acute (e.g., trauma, surgical wounds) and chronic (e.g., diabetic ulcers) wounds. The latter take several months to heal or do not heal (non-healing chronic wounds), are usually prone to microbial infection and represent an important source of morbidity since they affect millions of people worldwide. Typical wound treatments comprise surgical (e.g., debridement, skin grafts/flaps) and non-surgical (e.g., topical formulations, wound dressings) methods. Modern experimental approaches include among others three dimensional (3D)-(bio)printed wound dressings. The present paper reviews recently developed 3D (bio)printed hydrogels for wound healing applications, especially focusing on the results of their in vitro and in vivo assessment. The advanced hydrogel constructs were printed using different types of bioinks (e.g., natural and/or synthetic polymers and their mixtures with biological materials) and printing methods (e.g., extrusion, digital light processing, coaxial microfluidic bioprinting, etc.) and incorporated various bioactive agents (e.g., growth factors, antibiotics, antibacterial agents, nanoparticles, etc.) and/or cells (e.g., dermal fibroblasts, keratinocytes, mesenchymal stem cells, endothelial cells, etc.).

Innovations in hydrogel-based manufacturing: A comprehensive review of direct ink writing technique for biomedical applications

Direct ink writing (DIW) stands as a pioneering additive manufacturing technique that holds transformative potential in the field of hydrogel fabrication. This innovative approach allows for the precise deposition of hydrogel inks layer by layer, creating complex three-dimensional structures with tailored shapes, sizes, and functionalities. By harnessing the versatility of hydrogels, DIW opens up possibilities for applications spanning from tissue engineering to soft robotics and wearable devices. This comprehensive review investigates DIW as applied to hydrogels and its multifaceted applications. The paper introduces a diverse range of printing techniques while providing a thorough exploration of DIW for hydrogel-based printing. The investigation aims to explain the progress made, challenges faced, and potential trajectories that lie ahead for DIW in hydrogel-based manufacturing. The fundamental principles underlying DIW are carefully examined, specifically focusing on rheological attributes and printing parameters, prompting a comprehensive survey of the wide variety of hydrogel materials. These encompass both natural and synthetic variations, all of which can be effectively harnessed for this purpose. Furthermore, the review explores the latest applications of DIW for hydrogels in biomedical areas, with a primary focus on tissue engineering, wound dressing, and drug delivery systems. The document not only consolidates the existing state of DIW within the context of hydrogel-based manufacturing but also charts potential avenues for further research and innovative breakthroughs.

Stimuli-Responsive 3D Printable Conductive Hydrogel: A Step toward Regulating Macrophage Polarization and Wound Healing

Conductive hydrogels (CHs) are promising alternatives for electrical stimulation of cells and tissues in biomedical engineering. Wound healing and immunomodulation are complex processes that involve multiple cell types and signaling pathways. 3D printable conductive hydrogels have emerged as an innovative approach to promote wound healing and modulate immune responses. CHs can facilitate electrical and mechanical stimuli, which can be beneficial for altering cellular metabolism and enhancing the efficiency of the delivery of therapeutic molecules. This review summarizes the recent advances in 3D printable conductive hydrogels for wound healing and their effect on macrophage polarization. This report also discusses the properties of various conductive materials that can be used to fabricate hydrogels to stimulate immune responses. Furthermore, this review highlights the challenges and limitations of using 3D printable CHs for future material discovery. Overall, 3D printable conductive hydrogels hold excellent potential for accelerating wound healing and immune responses, which can lead to the development of new therapeutic strategies for skin and immune-related diseases.

GelMA/PEDOT:PSS Composite Conductive Hydrogel-Based Generation and Protection of Cochlear Hair Cells through Multiple Signaling Pathways

Recent advances in cochlear implantology are exemplified by novel functional strategies such as bimodal electroacoustic stimulation, in which the patient has intact low-frequency hearing and profound high-frequency hearing pre-operatively. Therefore, the synergistic restoration of dysfunctional cochlear hair cells and the protection of hair cells from ototoxic insults have become a persistent target pursued for this hybrid system. In this study, we developed a composite GelMA/PEDOT:PSS conductive hydrogel that is suitable as a coating for the cochlear implant electrode for the potential local delivery of otoregenerative and otoprotective drugs. Various material characterization methods (e.g., 1H NMR spectroscopy, FT-IR, EIS, and SEM), experimental models (e.g., murine cochlear organoid and aminoglycoside-induced ototoxic HEI-OC1 cellular model), and biological analyses (e.g., confocal laser scanning microscopy, real time qPCR, flow cytometry, and bioinformatic sequencing) were used. The results demonstrated decent material properties of the hydrogel, such as mechanical (e.g., high tensile stress and Young's modulus), electrochemical (e.g., low impedance and high conductivity), biocompatibility (e.g., satisfactory cochlear cell interaction and free of systemic toxicity), and biosafety (e.g., minimal hemolysis and cell death) features. In addition, the CDR medicinal cocktail sustainably released by the hydrogel not only promoted the expansion of the cochlear stem cells but also boosted the trans-differentiation from cochlear supporting cells into hair cells. Furthermore, hydrogel-based drug delivery protected the hair cells from oxidative stress and various forms of programmed cell death (e.g., apoptosis and ferroptosis). Finally, using large-scale sequencing, we enriched a complex network of signaling pathways that are potentially downstream to various metabolic processes and abundant metabolites. In conclusion, we present a conductive hydrogel-based local delivery of bifunctional drug cocktails, thereby serving as a potential solution to intracochlear therapy of bimodal auditory rehabilitation and diseases beyond.

Multifunctional and theranostic hydrogels for wound healing acceleration: An emphasis on diabetic-related chronic wounds

Hydrogels represent intricate three-dimensional polymeric structures, renowned for their compatibility with living systems and their ability to naturally degrade. These networks stand as promising and viable foundations for a range of biomedical uses. The practical feasibility of employing hydrogels in clinical trials has been well-demonstrated. Among the prevalent biomedical uses of hydrogels, a significant application arises in the context of wound healing. This intricate progression involves distinct phases of inflammation, proliferation, and remodeling, often triggered by trauma, skin injuries, and various diseases. Metabolic conditions like diabetes have the potential to give rise to persistent wounds, leading to delayed healing processes. This current review consolidates a collection of experiments focused on the utilization of hydrogels to expedite the recovery of wounds. Hydrogels have the capacity to improve the inflammatory conditions at the wound site, and they achieve this by diminishing levels of reactive oxygen species (ROS), thereby exhibiting antioxidant effects. Hydrogels have the potential to enhance the growth of fibroblasts and keratinocytes at the wound site. They also possess the capability to inhibit both Gram-positive and Gram-negative bacteria, effectively managing wounds infected by drug-resistant bacteria. Hydrogels can trigger angiogenesis and neovascularization processes, while also promoting the M2 polarization of macrophages, which in turn mitigates inflammation at the wound site. Intelligent and versatile hydrogels, encompassing features such as pH sensitivity, reactivity to reactive oxygen species (ROS), and responsiveness to light and temperature, have proven advantageous in expediting wound healing. Furthermore, hydrogels synthesized using environmentally friendly methods, characterized by high levels of biocompatibility and biodegradability, hold the potential for enhancing the wound healing process. Hydrogels can facilitate the controlled discharge of bioactive substances. More recently, there has been progress in the creation of conductive hydrogels, which, when subjected to electrical stimulation, contribute to the enhancement of wound healing. Diabetes mellitus, a metabolic disorder, leads to a slowdown in the wound healing process, often resulting in the formation of persistent wounds. Hydrogels have the capability to expedite the healing of diabetic wounds, facilitating the transition from the inflammatory phase to the proliferative stage. The current review sheds light on the biological functionalities of hydrogels, encompassing their role in modulating diverse mechanisms and cell types, including inflammation, oxidative stress, macrophages, and bacteriology. Additionally, this review emphasizes the significance of smart hydrogels with responsiveness to external stimuli, as well as conductive hydrogels for promoting wound healing. Lastly, the discussion delves into the advancement of environmentally friendly hydrogels with high biocompatibility, aimed at accelerating the wound healing process.

Development of Electro-Conductive Composite Bioinks for Electrohydrodynamic Bioprinting with Microscale Resolution

Bioprinting has attracted extensive attention in the field of tissue engineering due to its unique capability in constructing biomimetic tissue constructs in a highly controlled manner. However, it is still challenging to reproduce the physical and structural properties of native electroactive tissues due to the poor electroconductivity of current bioink systems as well as the limited printing resolution of conventional bioprinting techniques. In this work, an electro-conductive hydrogel is prepared by introducing poly (3,4-ethylene dioxythiophene): poly (styrene sulfonate) (PEDOT: PSS) into an RGD (GGGGRGDSP)-functionalized alginate and fibrin system (RAF), and then electrohydrodynamic (EHD)-bioprinted to form living tissue constructs with microscale resolution. The addition of 0.1 (w/v%) PEDOT: PSS increases the electroconductivity to 1.95 ± 0.21 S m-1 and simultaneously has little effect on cell viability. Compared with pure RAF bioink, the presence of PEDOT: PSS expands the printable parameters for EHD-bioprinting, and hydrogel filaments with the smallest feature size of 48.91 ± 3.44 µm can be obtained by further optimizing process parameters. Furthermore, the EHD-bioprinted electro-conductive living tissue constructs with improved resolution show good viability (>85%). The synergy of the advanced electro-conductive hydrogel and EHD-bioprinting presented here may provide a promising approach for engineering electro-conductive and cell-laden constructs for electroactive tissue engineering.

The exosomal secretomes of mesenchymal stem cells extracted via 3D-printed lithium-doped calcium silicate scaffolds promote osteochondral regeneration

The development of surface modification techniques has brought about a major paradigm shift in the clinical applications of bone tissue regeneration. Biofabrication strategies enable the creation of scaffolds with specific microstructural environments and biological components. Lithium (Li) has been reported to exhibit anti-inflammatory, osteogenic, and chondrogenic properties by promoting several intracellular signaling pathways. Currently, research focuses on fabricating scaffolds with simultaneous dual bioactivities to enhance osteochondral regeneration. In this study, we modified the surface of calcium silicate (CS) scaffolds with Li using a simple immersion technique and evaluated their capabilities for bone regeneration. The results showed that Li ions could be easily coated onto the surfaces of CS scaffolds without affecting the microstructural properties of CS itself. Furthermore, the modifications did not affect the printing capabilities of the CS, and porous scaffolds could be fabricated via extrusion. Moreover, the presence of Li improved the surface roughness and hydrophilicity, thus leading to enhanced secretion of osteochondral-related regeneration factors, such as alkaline phosphatase (ALP), bone sialoprotein (BSP), and collagen II (Col II) proteins. Subsequent in vivo studies, including histological and micro-CT analyses, confirmed that the Li-modified CS scaffolds promoted osteochondral regeneration. The transcriptome analysis suggested that the enhanced osteochondrogenic capabilities of our scaffolds were influenced by paracrine exosomes. We hope this study will inspire further research on osteochondral regeneration.

3D-biofabricated chondrocyte-laden decellularized extracellular matrix-contained gelatin methacrylate auxetic scaffolds under cyclic tensile stimulation for cartilage regeneration

Three-dimensional (3D) hydrogel constructs can mimic features of the extracellular matrix (ECM) and have tailorable physicochemical properties to support and maintain the regeneration of articular cartilage. Various studies have shown that mechanical cues affect the cellular microenvironment and thereby influence cellular behavior. In this study, we fabricated an auxetic scaffold to investigate the effect of 3D tensile stimulation on chondrocyte behavior. Different concentrations of decellularized extracellular matrix (dECM) were mixed with fish gelatin methacrylate (FGelMa) and employed for the preparation of dECM/FGelMa auxetic bio-scaffolds using 3D biofabrication technology. We show that when human chondrocytes (HCs) were incorporated into these scaffolds, their proliferation and the expression of chondrogenesis-related markers increased with dECM content. The function of HC was influenced by cyclic tensile stimulation, as shown by increased production of the chondrogenesis-related markers, collagen II and glycosaminoglycans, with the involvement of the yes-associated protein 1 signaling pathway. The biofabricated auxetic scaffold represents an excellent platform for exploring interactions between cells and their mechanical microenvironment.

The Synergistic Effect of Electrical Stimulation and Dermal Fibroblast Cells-Laden 3D Conductive Hydrogel for Full-Thickness Wound Healing

Clinically, most patients with poor wound healing suffer from generalized skin damage, usually accompanied by other complications, so developing therapeutic strategies for difficult wound healing has remained extremely challenging until now. Current studies have indicated that electrical stimulation (ES) to cutaneous lesions enhances skin regeneration by activating intracellular signaling cascades and secreting skin regeneration-related cytokine. In this study, we designed different concentrations of graphene in gelatin-methacrylate (GelMa) to form the conductive composite commonly used in wound healing because of its efficiency compared to other conductive thermo-elastic materials. The results demonstrated the successful addition of graphene to GelMa while retaining the original physicochemical properties of the GelMa bioink. In addition, the incorporation of graphene increased the interactions between these two biomaterials, leading to an increase in mechanical properties, improvement in the swelling ratio, and the regulation of degradation characteristics of the biocomposite scaffolds. Moreover, the scaffolds exhibited excellent electrical conductivity, increasing proliferation and wound healing-related growth factor secretion from human dermal fibroblasts. Overall, the HDF-laden 3D electroconductive GelMa/graphene-based hydrogels developed in this study are ideal biomaterials for skin regeneration applications in the future.

Self-powered enzyme-linked microneedle patch for scar-prevention healing of diabetic wounds

Diabetic wounds with complex pathological features and a difficult-to-heal nature remain a formidable challenge. To address this challenge, we design and fabricate a self-powered enzyme-linked microneedle (MN) patch composed of anode and cathode MN arrays, which respectively contain glucose oxidase (GOx) and horseradish peroxidase (HRP) encapsulated in ZIF-8 nanoparticles. The enzymatic cascade reaction in the MN patch can effectively reduce local hyperglycemia in diabetic wounds while generating stable microcurrents to promote rapid healing of diabetic wounds. Therefore, the diabetic wounds treated with this MN patch exhibit rapid, complete, and scar-preventative healing, which can be attributed to the synergistic actions of hypoglycemic, antibacterial, anti-inflammatory, and bioelectrical stimulation. In brief, the self-powered MN patch is an effective method to rapidly promote diabetic wound healing and prevent scar formation.

Additive manufacturing of barium-doped calcium silicate/poly-ε-caprolactone scaffolds to activate CaSR and AKT signalling and osteogenic differentiation of mesenchymal stem cells

3D-printed scaffolds are suitable for patient-specific implant preparation for bone regeneration in large-scale critical bone defects. In addition, these scaffolds should have mechanical and biological properties similar to those of natural bone tissue. In this study, 3D-printed barium-doped calcium silicate (BaCS)/poly-ε-caprolactone (PCL) composite scaffolds were fabricated as an alternative strategy for bone tissue engineering to achieve appropriate physicochemical characteristics and stimulate osteogenesis. Scaffolds containing 10% Ba (Ba10) showed optimal mechanical properties, preventing premature scaffold degradation during immersion while enabling ion release in a sustained manner to achieve the desired therapeutic goals. In addition, Wharton's jelly mesenchymal stem cells (WJMSCs) were used to assess biocompatibility and osteogenic differentiation behaviour. WJMSCs were cultured on the scaffold and permeabilised via ICP to analyse the presence of Si and Ba ions in the medium and cell lysates, suggesting that the ions released by the scaffold could effectively enter the cells. The protein expression of CaSR, PI3K, Akt, and JNK confirmed that CaSR could activate cells cultured in Ba10, thereby affecting the subsequent PI3k/Akt and JNK pathways and further promoting osteogenic differentiation. The in vivo performance of the proposed scaffolds was assessed using micro-CT and histological slices, which revealed that the BaCS scaffolds could further enhance bone regeneration, compared with bare scaffolds. These results suggest the potential use of 3D-printed BaCS/PCL scaffolds as next-generation substitutes for bone regeneration.

Self-curling 3D oriented scaffolds from fish scales for skeletal muscle regeneration

BACKGROUND

Volumetric muscle loss (VML) due to various reasons may cause motor dysfunction and tissue engineering has been proposed for muscle regeneration. However, developing three-dimensional (3D) tissue-engineered scaffolds that can mimic oriented cell growth of muscle tissues are challenging for regeneration medicine. Herein, we propose a novel self-curling 3D oriented scaffold (SCOS) composed of fish derived gelatin methacrylate (GelMA) and fish scales for repairing skeletal muscles.

METHODS

Fish scales of tilapia were decellularized and decalcified. Then, SCOSs were constructed by ultraviolet-coating methylated fish gelatin on the back of fish scales. C2C12 myoblasts were cultured on SCOSs, and after induction of myogenic differentiation, SCOS/C2C12 transplants were prepared for in vivo experiments.

RESULTS

Decellularized and decalcified fish scales (DDFSs) became soft and retained the original oriented microgroove surface structure that could induce oriented cell growth. SCOSs could self-curl into 3D structures when immersing in culture medium due to different swelling properties of fish GelMA and DDFSs. Cell experiments demonstrated that SCOSs enhanced the oriented growth and myogenic differentiation of C2C12 myoblasts. By integrating SCOSs and myogenic differentiated C2C12 myoblasts, the resultant SCOS/C2C12 transplants promoted de novo muscle regeneration and functional restoration of muscle activity in the mouse model of VML.

CONCLUSIONS

Our results suggest that SCOSs loaded with myogenic differentiated C2C12 myoblasts can promote muscle regeneration in mice with skeletal muscle injuries, indicating application prospects of such scaffolds in muscle tissue engineering and other related fields.

Effect of mussel-inspired polydopamine on the reinforced properties of 3D printed β-tricalcium phosphate/polycaprolactone scaffolds for bone regeneration

Bioceramic/polymer scaffolds have been considered as potential grafts used for facilitating bone healing. Unfortunately, the poor interfacial interaction between polymer matrices and bioceramic fillers limited their use in practical medicine. Thus, a facile strategy for reinforcing the three-dimensional printed β-tricalcium phosphate/polycaprolactone scaffolds through employing polydopamine modified-ceramics as fillers. The effects of the dopamine precursor on the compressive strength, degradability, cell proliferation, osteogenic differentiation, and in vivo osteogenicity were measured. The results indicated that the concentration of dopamine could remarkably affect the thickness and density of the polydopamine layer on fillers, further varying the compressive strength (1.23-fold to 1.64-fold), degradability, and osteogenicity of the scaffolds. More importantly, the presence of polydopamine in the three-dimensional printed composite scaffolds not only facilitated the proliferation, alkaline phosphatase activity and mineralization of mesenchymal stem cells, but also stimulated the formation of neo-bone tissue in femur defects. Taking together, the proposed scaffolds might serve as a candidate for bone regeneration.

Synergistic Effect of Static Magnetic Fields and 3D-Printed Iron-Oxide-Nanoparticle-Containing Calcium Silicate/Poly-ε-Caprolactone Scaffolds for Bone Tissue Engineering

In scaffold-regulated bone regeneration, most three-dimensional (3D)-printed scaffolds do not provide physical stimulation to stem cells. In this study, a magnetic scaffold was fabricated using fused deposition modeling with calcium silicate (CS), iron oxide nanoparticles (Fe₃O₄), and poly-ε-caprolactone (PCL) as the matrix for internal magnetic sources. A static magnetic field was used as an external magnetic source. It was observed that 5% Fe₃O₄ provided a favorable combination of compressive strength (9.6 ± 0.9 MPa) and degradation rate (21.6 ± 1.9% for four weeks). Furthermore, the Fe₃O₄-containing scaffold increased in vitro bioactivity and Wharton's jelly mesenchymal stem cells' (WJMSCs) adhesion. Moreover, it was shown that the Fe₃O₄-containing scaffold enhanced WJMSCs' proliferation, alkaline phosphatase activity, and the osteogenic-related proteins of the scaffold. Under the synergistic effect of the static magnetic field, the CS scaffold containing Fe₃O₄ can not only enhance cell activity but also stimulate the simultaneous secretion of collagen I and osteocalcin. Overall, our results demonstrated that Fe₃O₄-containing CS/PCL scaffolds could be fabricated three dimensionally and combined with a static magnetic field to affect cell behaviors, potentially increasing the likelihood of clinical applications for bone tissue engineering.