Recent Development of Conductive Hydrogels for Tissue Engineering: Review and Perspective

Tuning conductivity while maintaining mechanical properties in perylene bisimide hydrogels at physiological pH

By using different salts as a method to achieve gelation of two different amino-acid-functionalised perylene bisimides, we were able to tune reduction potentials while maintaining the mechanical and optical properties of the system all at pH 7.4.

Resorbable conductive materials for optimally interfacing medical devices with the living

Implantable and wearable bioelectronic systems are arising growing interest in the medical field. Linking the microelectronic (electronic conductivity) and biological (ionic conductivity) worlds, the biocompatible conductive materials at the electrode/tissue interface are key components in these systems. We herein focus more particularly on resorbable bioelectronic systems, which can safely degrade in the biological environment once they have completed their purpose, namely, stimulating or sensing biological activity in the tissues. Resorbable conductive materials are also explored in the fields of tissue engineering and 3D cell culture. After a short description of polymer-based substrates and scaffolds, and resorbable electrical conductors, we review how they can be combined to design resorbable conductive materials. Although these materials are still emerging, various medical and biomedical applications are already taking shape that can profoundly modify post-operative and wound healing follow-up. Future challenges and perspectives in the field are proposed.

A review of advanced hydrogels for cartilage tissue engineering

With the increase in weight and age of the population, the consumption of tobacco, inappropriate foods, and the reduction of sports activities in recent years, bone and joint diseases such as osteoarthritis (OA) have become more common in the world. From the past until now, various treatment strategies (e.g., microfracture treatment, Autologous Chondrocyte Implantation (ACI), and Mosaicplasty) have been investigated and studied for the prevention and treatment of this disease. However, these methods face problems such as being invasive, not fully repairing the tissue, and damaging the surrounding tissues. Tissue engineering, including cartilage tissue engineering, is one of the minimally invasive, innovative, and effective methods for the treatment and regeneration of damaged cartilage, which has attracted the attention of scientists in the fields of medicine and biomaterials engineering in the past several years. Hydrogels of different types with diverse properties have become desirable candidates for engineering and treating cartilage tissue. They can cover most of the shortcomings of other treatment methods and cause the least secondary damage to the patient. Besides using hydrogels as an ideal strategy, new drug delivery and treatment methods, such as targeted drug delivery and treatment through mechanical signaling, have been studied as interesting strategies. In this study, we review and discuss various types of hydrogels, biomaterials used for hydrogel manufacturing, cartilage-targeting drug delivery, and mechanosignaling as modern strategies for cartilage treatment.

Recent advances in composite hydrogels: synthesis, classification, and application in the treatment of bone defects

Bone defects are often difficult to treat due to their complexity and specificity, and therefore pose a serious threat to human life and health. Currently, the clinical treatment of bone defects is mainly surgical. However, this treatment is often more harmful to patients and there is a potential risk of rejection and infection. Hydrogels have a unique three-dimensional structure that can accommodate a variety of materials, including particles, polymers and small molecules, making them ideal for treating bone defects. Therefore, emerging composite hydrogels are considered one of the most promising candidates for the treatment of bone defects. This review describes the use of different types of composite hydrogel in the treatment of bone defects. We present the basic concepts of hydrogels, different preparation techniques (including chemical and physical crosslinking), and the clinical requirements for hydrogels used to treat bone defects. In addition, a review of numerous promising designs of different types of hydrogel doped with different materials (e.g., nanoparticles, polymers, carbon materials, drugs, and active factors) is also highlighted. Finally, the current challenges and prospects of composite hydrogels for the treatment of bone defects are presented. This review will stimulate research efforts in this field and promote the application of new methods and innovative ideas in the clinical field of composite hydrogels.

Emerging 4D fabrication of next-generation nerve guiding conduits: a critical perspective

The latest advancements in the field of manufacturing for biomedicine, digital health, targeted therapy, and personalized medicine have fuelled the fabrication of smart medical devices. Four-dimensional (4D) fabrication strategies, which combine the manufacturing of three-dimensional (3D) parts with smart materials and/or design, have proved beneficial in creating customized and self-fitting structures that change their properties on demand with time. These frontier techniques that yield dynamic implants can indeed alleviate various drawbacks of current clinical practices, such as the use of sutures and complex microsurgeries and associated inflammation, among others. Among various clinical applications, 4D fabrication has lately made remarkable progress in the development of next-generation nerve-guiding conduits for treating peripheral nerve injuries (PNIs) by improving the end-to-end co-aptation of transected nerve endings. The current perspective highlights the relevance of 4D fabrication in developing state-of-the-art technologies for the treatment of PNIs. Various 4D fabrication/bio-fabrication techniques for PNI treatment are summarized while identifying the challenges and opportunities for the future. Such advancements hold immense promise for improving the quality of life of patients suffering from nerve damage and the potential for extending the treatment of many other disorders. Although the techniques are being described for PNIs, they will lend themselves suitably to certain cases of cranial nerve injuries as well.

Nanotechnology development in surgical applications: recent trends and developments

This paper gives a detailed analysis of nanotechnology's rising involvement in numerous surgical fields. We investigate the use of nanotechnology in orthopedic surgery, neurosurgery, plastic surgery, surgical oncology, heart surgery, vascular surgery, ophthalmic surgery, thoracic surgery, and minimally invasive surgery. The paper details how nanotechnology helps with arthroplasty, chondrogenesis, tissue regeneration, wound healing, and more. It also discusses the employment of nanomaterials in implant surfaces, bone grafting, and breast implants, among other things. The article also explores various nanotechnology uses, including stem cell-incorporated nano scaffolds, nano-surgery, hemostasis, nerve healing, nanorobots, and diagnostic applications. The ethical and safety implications of using nanotechnology in surgery are also addressed. The future possibilities of nanotechnology are investigated, pointing to a possible route for improved patient outcomes. The essay finishes with a comment on nanotechnology's transformational influence in surgical applications and its promise for future breakthroughs.

Rational Design of Multifunctional Hydrogels for Wound Repair

The intricate microenvironment at the wound site, coupled with the multi-phase nature of the healing process, pose significant challenges to the development of wound repair treatments. In recent years, applying the distinctive benefits of hydrogels to the development of wound repair strategies has yielded some promising results. Multifunctional hydrogels, by meeting the different requirements of wound healing stages, have greatly improved the healing effectiveness of chronic wounds, offering immense potential in wound repair applications. This review summarized the recent research and applications of multifunctional hydrogels in wound repair. The focus was placed on the research progress of diverse multifunctional hydrogels, and their mechanisms of action at different stages of wound repair were discussed in detail. Through a comprehensive analysis, we found that multifunctional hydrogels play an indispensable role in the process of wound repair by providing a moist environment, controlling inflammation, promoting angiogenesis, and effectively preventing infection. However, further implementation of multifunctional hydrogel-based therapeutic strategies also faces various challenges, such as the contradiction between the complexity of multifunctionality and the simplicity required for clinical translation and application. In the future, we should work to address these challenges, further optimize the design and preparation of multifunctional hydrogels, enhance their effectiveness in wound repair, and promote their widespread application in clinical practice.

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.

Antimicrobial and Mechanical Properties of Ag@Ti3C2Tx-Modified PVA Composite Hydrogels Enhanced with Quaternary Ammonium Chitosan

Polyvinyl alcohol (PVA) is a polymeric material with good biocompatibility, excellent hydrophilicity, and a large number of hydroxyl groups. However, due to its insufficient mechanical properties and poor inhibition of bacteria, it has a lack of applications in wound dressings, stent materials, and other fields. In this study, a simple method was used to prepare composite gel materials: Ag@MXene-HACC-PVA hydrogels with a double-network structure were prepared using an acetal reaction. Due to the double cross-linked interaction, the hydrogel has good mechanical properties and is resistant to swelling. The adhesion and bacterial inhibition were enhanced due to the addition of HACC. In addition, the strain sensing properties of this conductive hydrogel were stable, and the GF (specification factor) was 1.7617 at 40-90% strain. Therefore, the dual-network hydrogel with excellent sensing properties, adhesion properties, antibacterial properties, and cytocompatibility has potential applications in biomedical materials, especially as a tissue engineering repair material.

Conductive and Adhesive Granular Alginate Hydrogels for On-Tissue Writable Bioelectronics

Conductive hydrogels are promising materials in bioelectronics that ensure a tissue-like soft modulus and re-enact the electrophysiological function of damaged tissues. However, recent approaches to fabricating conductive hydrogels have proved difficult: fixing of the conductive hydrogels on the target tissues hydrogels requires the aids from other medical glues because of their weak tissue-adhesiveness. In this study, an intrinsically conductive and tissue-adhesive granular hydrogel consisting of a PEDOT:PSS conducting polymer and an adhesive catechol-conjugated alginate polymer was fabricated via an electrohydrodynamic spraying method. Because alginate-based polymers can be crosslinked by calcium ions, alginate-catechol polymers mixed with PEDOT:PSS granular hydrogels (ACP) were easily fabricated. The fabricated ACP exhibited not only adhesive and shear-thinning properties but also conductivity similar to that of muscle tissue. Additionally, the granular structure makes the hydrogel injectable through a syringe, enabling on-tissue printing. This multifunctional granular hydrogel can be applied to soft and flexible electronics to connect humans and machines.

Integration of hydrogels in microfabrication processes for bioelectronic medicine: Progress and outlook

Recent research aiming at the development of electroceuticals for the treatment of medical conditions such as degenerative diseases, cardiac arrhythmia and chronic pain, has given rise to microfabricated implanted bioelectronic devices capable of interacting with host biological tissues in synergistic modalities. Owing to their multimodal affinity to biological tissues, hydrogels have emerged as promising interface materials for bioelectronic devices. Here, we review the state-of-the-art and forefront in the techniques used by research groups for the integration of hydrogels into the microfabrication processes of bioelectronic devices, and present the manufacturability challenges to unlock their further clinical deployment.

Surface Modification of Decellularized Heart Valve by the POSS-PEG Hybrid Hydrogel to Prepare a Composite Scaffold Material with Anticalcification Potential

Tissue-engineered heart valves (TEHVs) are the most promising replacement for heart valve transplantation. Decellularized heart valve (DHV) is one of the most common scaffold materials for TEHVs. In actual clinical applications, the most widely used method for treating DHV is cross-linking it with glutaraldehyde, but this method could cause serious problems such as calcification. In this study, we introduced polyhedral oligomeric silsesquioxane (POSS) nanoparticles into a poly(ethylene glycol) (PEG) hydrogel to prepare a POSS-PEG hybrid hydrogel, and then coated them on the surface of DHV to prepare the composite scaffold. The chemical structures, microscopic morphologies, cell compatibilities, blood compatibilities, and anticalcification properties were further investigated. Experimental results showed that the composite scaffold had good blood compatibility and excellent cell compatibility and could promote cell adhesion and proliferation. In vivo and in vitro anticalcification experiments showed that the introduction of POSS nanoparticles could reduce the degree of calcification significantly and the composite scaffold had obvious anticalcification ability. The DHV surface-coated with the POSS-PEG hybrid hydrogel is an alternative scaffold material with anticalcification potential for an artificial heart valve, which provides an idea for the preparation of TEHVs.