Biodegradable and electroconductive poly(3,4-ethylenedioxythiophene)/carboxymethyl chitosan hydrogels for neural tissue engineering

Hydrogel Properties and Their Impact on Regenerative Medicine and Tissue Engineering

Hydrogels (HGs), as three-dimensional structures, are widely used in modern medicine, including regenerative medicine. The use of HGs in wound treatment and tissue engineering is a rapidly developing sector of medicine. The unique properties of HGs allow researchers to easily modify them to maximize their potential. Herein, we describe the physicochemical properties of HGs, which determine their subsequent applications in regenerative medicine and tissue engineering. Examples of chemical modifications of HGs and their applications are described based on the latest scientific reports.

Electroconductive Hydrogels for Tissue Engineering: Current Status and Future Perspectives

Over the past decade, electroconductive hydrogels, integrating both the biomimetic attributes of hydrogels and the electrochemical properties of conductive materials, have gained significant attention. Hydrogels, three-dimensional and swollen hydrophilic polymer networks, are an important class of tissue engineering (TE) scaffolds owing to their microstructural and mechanical properties, ability to mimic the native extracellular matrix, and promote tissue repair. However, hydrogels are intrinsically insulating and therefore unable to emulate the complex electrophysiological microenvironment of cardiac and neural tissues. To overcome this challenge, electroconductive materials, including carbon-based materials, nanoparticles, and polymers, have been incorporated within nonconductive hydrogels to replicate the electrical and biological characteristics of biological tissues. This review gives a brief introduction on the rational design of electroconductive hydrogels and their current applications in TE, especially for neural and cardiac regeneration. The recent progress and development trends of electroconductive hydrogels, their challenges, and clinical translatability, as well as their future perspectives, with a focus on advanced manufacturing technologies, are also discussed.

Potential of Chitosan and Its Derivatives for Biomedical Applications in the Central Nervous System

It is well known that the central nervous system (CNS) has a limited regenerative capacity and that many therapeutic molecules cannot cross the blood brain barrier (BBB). The use of biomaterials has emerged as an alternative to overcome these limitations. For many years, biomedical applications of chitosan have been studied due to its remarkable biological properties, biocompatibility, and high versatility. Moreover, the interest in this biomaterial for CNS biomedical implementation has increased because of its ability to cross the BBB, mucoadhesiveness, and hydrogel formation capacity. Several chitosan-based biomaterials have been applied with promising results as drug, cell and gene delivery vehicles. Moreover, their capacity to form porous scaffolds and to bear cells and biomolecules has offered a way to achieve neural regeneration. Therefore, this review aims to bring together recent works that highlight the potential of chitosan and its derivatives as adequate biomaterials for applications directed toward the CNS. First, an overview of chitosan and its derivatives is provided with an emphasis on the properties that favor different applications. Second, a compilation of works that employ chitosan-based biomaterials for drug delivery, gene therapy, tissue engineering, and regenerative medicine in the CNS is presented. Finally, the most interesting trends and future perspectives of chitosan and its derivatives applications in the CNS are shown.

Doped Poly(3-hexylthiophene) Coatings onto Chitosan: A Novel Approach for Developing a Bio-Based Flexible Electronic

Conductive and flexible bio-based materials consisting of chitosan films coated with conductive poly(3-hexylthiophene) (P3HT) were prepared. Thermal, optical, mechanical, morphological, wettability, and conductive properties were analyzed. In a very simple and effective method of chitosan film modification, a controlled volume of a P3HT solution was deposited onto a previously formed chitosan film, assisted by the spin coating method. Later, P3HT-coated chitosan films were doped by simple contact with an aqueous solution of HAuCl₄. The use of HAuCl₄ becomes attractive because the reports on the doping process in this type of material using this reagent are still scarce and recent to date. In addition, since this acid is a well-known metal nanoparticle precursor, its use opens new future perspectives for these materials into new applications. The effect of P3HT concentration and doping times on film properties was studied. Attenuated total reflectance spectroscopy and UV-Vis spectroscopy allowed us to demonstrate that the presence of the P3HT coating and its doping induce significant changes in the vibrational modes and optoelectronic properties of samples. Additionally, the images obtained by scanning electron microscopy showed a well-distributed and homogeneous coating on the surface of chitosan films. Measured conductivity values of doped film samples fall in the range from 821.3 to 2017.4 S/m, representing, to the best of our knowledge, the highest values reported in the literature for chitosan/chitin-based materials. Indeed, these values are around or even higher than those obtained for some materials purely consisting of conductive polymers.

Three-Dimensional Printing and Injectable Conductive Hydrogels for Tissue Engineering Application

The goal of tissue engineering scaffolds is to simulate the physiological microenvironment, in which the electrical microenvironment is an important part. Hydrogel is an ideal material for tissue engineering scaffolds because of its soft, porous, water-bearing, and other extracellular matrix-like properties. However, the hydrogel matrix is usually not conductive and can hinder the communication of electrical signals between cells, which promotes researchers' attention to conductive hydrogels. Conductive hydrogels can promote the communication of electrical signals between cells and simulate the physiological microenvironment of electroactive tissues. Hydrogel formation is an important step for the application of hydrogels in tissue engineering. In situ forming of injectable hydrogels and customized forming of three-dimensional (3D) printing hydrogels represent two most potential advanced forming processes, respectively. In this review, we discuss (i) the classification, properties, and advantages of conductive hydrogels, (ii) the latest development of conductive hydrogels applied in myocardial, nerve, and bone tissue engineering, (iii) advanced forming processes, including injectable conductive hydrogels in situ and customized 3D printed conductive hydrogels, (iv) the challenges and opportunities of conductive hydrogels for tissue engineering. Impact Statement Biomimetic construction of electro-microenvironment is a challenge of tissue engineering. The development of conductive hydrogels provides possibility for the construction of biomimetic electro-microenvironment. However, the importance of conductive hydrogels in tissue engineering has not received enough attention so far. Herein, various conductive hydrogels and their tissue engineering applications are systematically reviewed. Two potential methods of conductive hydrogel forming, in situ forming of injectable conductive hydrogels and customized forming of three-dimensional printing conductive hydrogels, are introduced. The current challenges and future development directions of conductive hydrogels are comprehensively overviewed. This review provides a guideline for tissue engineering applications of conductive hydrogels.

Improved cellular response on functionalized polypyrrole interfaces

Neuroregeneration strategies involve multiple factors to stimulate nerve regeneration. Neural support with chemical and physical cues to optimize neural growth and replacing the lesion neuron and axons are crucial for designing neural scaffolds, which is a promising treatment approach. In this study, polypyrrole polymerization and its functionalization at the interface developed by glycine and gelatin for further optimization of cellular response. Nanofibrous scaffolds were fabricated by electrospinning of polyvinyl alcohol and chitosan solutions. The electrospun scaffolds were polymerized on the surface by pyrrole monomers to form an electroactive interface for further applications in neural tissue engineering. The polymerized polypyrrole showed a positive zeta potential value of 57.5 ± 5.46 mV. The in vitro and in vivo biocompatibility of the glycine and gelatin-functionalized polypyrrole-coated scaffolds were evaluated. No inflammatory cells were observed for the implanted scaffolds. Further, DAPI nucleus staining showed a superior cell attachment on the gelatin-functionalized polypyrrole-coated scaffolds. The topography and tuned positively charged polypyrrole interface with gelatin functionalization is expected to be particularly efficient physical and chemical simultaneous factors for promoting neural cell adhesion.

Human Neural Tissues from Neural Stem Cells Using Conductive Biogel and Printed Polymer Microelectrode Arrays for 3D Electrical Stimulation

Electricity is important in the physiology and development of human tissues such as embryonic and fetal development, and tissue regeneration for wound healing. Accordingly, electrical stimulation (ES) is increasingly being applied to influence cell behavior and function for a biomimetic approach to in vitro cell culture and tissue engineering. Here, the application of conductive polymer (CP) poly(3,4-ethylenedioxythiophene)-polystyrenesulfonate (PEDOT:PSS) pillars is described, direct-write printed in an array format, for 3D ES of maturing neural tissues that are derived from human neural stem cells (NSCs). NSCs are initially encapsulated within a conductive polysaccharide-based biogel interfaced with the CP pillar microelectrode arrays (MEAs), followed by differentiation in situ to neurons and supporting neuroglia during stimulation. Electrochemical properties of the pillar electrodes and the biogel support their electrical performance. Remarkably, stimulated constructs are characterized by widespread tracts of high-density mature neurons and enhanced maturation of functional neural networks. Formation of tissues using the 3D MEAs substantiates the platform for advanced clinically relevant neural tissue induction, with the system likely amendable to diverse cell types to create other neural and non-neural tissues. The platform may be useful for both research and translation, including modeling tissue development, function and dysfunction, electroceuticals, drug screening, and regenerative medicine.

Bionanotube/Poly(3,4-ethylenedioxythiophene) Nanohybrid as an Electrode for the Neural Interface and Dopamine Sensor

Poly(3,4-ethylene dioxythiophene) (PEDOT) is a promising conductive material widely used for interfacing with tissues in biomedical fields because of its unique properties. However, obtaining high charge injection capability and high stability remains challenging. In this study, pristine carbon nanotubes (CNTs) modified by dopamine (DA) self-polymerization on the surface polydopamine (PDA@CNTs) were utilized as dopants of PEDOT to prepare hybrid films through electrochemical deposition on the indium tin oxide (ITO) electrode. The PDA@CNTs-PEDOT film of the nanotube network topography exhibited excellent stability and strong adhesion to the ITO substrate compared with PEDOT and PEDOT/ p-toulene sulfonate. The PDA@CNTs-PEDOT-coated ITO electrodes demonstrated lower impedance and enhanced charge storage capacity than the bare ITO. When applying exogenous electrical stimulation (ES), robust long neurites sprouted from the dorsal root ganglion (DRG) neurons cultured on the PDA@CNTs-PEDOT film. Moreover, ES promoted Schwann cell migration out from the DRG spheres and enhanced myelination. The PDA@CNTs-PEDOT film served as an excellent electrochemical sensor for the detection of DA in the presence of biomolecule interferences. Results would shed light into the advancement of conducting nanohybrids for applications in the multifunctional bioelectrode in neuroscience.

Relevance and Recent Developments of Chitosan in Peripheral Nerve Surgery

Developments in tissue engineering yield biomaterials with different supporting strategies to promote nerve regeneration. One promising material is the naturally occurring chitin derivate chitosan. Chitosan has become increasingly important in various tissue engineering approaches for peripheral nerve reconstruction, as it has demonstrated its potential to interact with regeneration associated cells and the neural microenvironment, leading to improved axonal regeneration and less neuroma formation. Moreover, the physiological properties of its polysaccharide structure provide safe biodegradation behavior in the absence of negative side effects or toxic metabolites. Beneficial interactions with Schwann cells (SC), inducing differentiation of mesenchymal stromal cells to SC-like cells or creating supportive conditions during axonal recovery are only a small part of the effects of chitosan. As a result, an extensive body of literature addresses a variety of experimental strategies for the different types of nerve lesions. The different concepts include chitosan nanofibers, hydrogels, hollow nerve tubes, nerve conduits with an inner chitosan layer as well as hybrid architectures containing collagen or polyglycolic acid nerve conduits. Furthermore, various cell seeding concepts have been introduced in the preclinical setting. First translational concepts with hollow tubes following nerve surgery already transferred the promising experimental approach into clinical practice. However, conclusive analyses of the available data and the proposed impact on the recovery process following nerve surgery are currently lacking. This review aims to give an overview on the physiologic properties of chitosan, to evaluate its effect on peripheral nerve regeneration and discuss the future translation into clinical practice.

Stretchable Conductive Polymers and Composites Based on PEDOT and PEDOT:PSS

The conductive polymer poly(3,4-ethylenedioxythiophene) (PEDOT), and especially its complex with poly(styrene sulfonate) (PEDOT:PSS), is perhaps the most well-known example of an organic conductor. It is highly conductive, largely transmissive to light, processible in water, and highly flexible. Much recent work on this ubiquitous material has been devoted to increasing its deformability beyond flexibility-a characteristic possessed by any material that is sufficiently thin-toward stretchability, a characteristic that requires engineering of the structure at the molecular- or nanoscale. Stretchability is the enabling characteristic of a range of applications envisioned for PEDOT in energy and healthcare, such as wearable, implantable, and large-area electronic devices. High degrees of mechanical deformability allow intimate contact with biological tissues and solution-processable printing techniques (e.g., roll-to-roll printing). PEDOT:PSS, however, is only stretchable up to around 10%. Here, the strategies that have been reported to enhance the stretchability of conductive polymers and composites based on PEDOT and PEDOT:PSS are highlighted. These strategies include blending with plasticizers or polymers, deposition on elastomers, formation of fibers and gels, and the use of intrinsically stretchable scaffolds for the polymerization of PEDOT.

3D Scaffolds Based on Conductive Polymers for Biomedical Applications

3D scaffolds appear to be a cost-effective ultimate answer for biomedical applications, facilitating rapid results while providing an environment similar to in vivo tissue. These biomaterials offer large surface areas for cell or biomaterial attachment, proliferation, biosensing and drug delivery applications. Among 3D scaffolds, the ones based on conjugated polymers (CPs) and natural nonconductive polymers arranged in a 3D architecture provide tridimensionality to cellular culture along with a high surface area for cell adherence and proliferation as well electrical conductivity for stimulation or sensing. However, the scaffolds must also obey other characteristics: homogeneous porosity, with pore sizes large enough to allow cell penetration and nutrient flow; elasticity and wettability similar to the tissue of implantation; and a suitable composition to enhance cell-matrix interactions. In this Review, we summarize the fabrication methods, characterization techniques and main applications of conductive 3D scaffolds based on conductive polymers. The main barrier in the development of these platforms has been the fabrication and subsequent maintenance of the third dimension due to challenges in the manipulation of conductive polymers. In the last decades, different approaches to overcome these barriers have been developed for the production of conductive 3D scaffolds, demonstrating a huge potential for biomedical purposes. Finally, we present an overview of the emerging strategies developed to manufacture 3D conductive scaffolds, the techniques used to fully characterize them, and the biomedical fields where they have been applied.

Natural and synthetic materials based CMCh/PVA hydrogels for oxaliplatin delivery: Fabrication, characterization, In-Vitro and In-Vivo safety profiling

In this study, the chemically crosslinked hydrogels of carboxymethyl chitosan and polyvinyl alcohol were fabricated by the free radical polymerization. Successful polymerization was confirmed by Fourier transform infrared spectroscopy, while x-ray diffraction, thermogravimetric analysis, and differential scanning calorimetric measurements helped in investigating crystallinity and thermal behavior of the products. Morphological characterization was performed by scanning electron microscopy. The increased incorporation of carboxymethyl chitosan and polyvinyl alcohol enhanced the swelling, drug loading, and in-vitro drug release while crosslinking agent acted inversely. The blanked hydrogels were cytocompatible while oxaliplatin loaded hydrogels showed dose-dependent controlled cytotoxicity against HCT-116 and MCF-7. Oral biocompatibility in albino rabbits showed that the hydrogel suspension was tolerable up to 3600 mg/kg as no toxic or histopathological changes were observed upon comparison with the control group. Results of the studies confirmed that the developed hydrogels can be a potential candidate for controlled oxaliplatin delivery and targeting in cancer therapy.

Tissue Engineering Scaffolds Fabricated in Dissolvable 3D-Printed Molds for Patient-Specific Craniofacial Bone Regeneration

The current gold standard treatment for oral clefts is autologous bone grafting. This treatment, however, presents another wound site for the patient, greater discomfort, and pediatric patients have less bone mass for bone grafting. A potential alternative treatment is the use of tissue engineered scaffolds. Hydrogels are well characterized nanoporous scaffolds and cryogels are mechanically durable, macroporous, sponge-like scaffolds. However, there has been limited research on these scaffolds for cleft craniofacial defects. 3D-printed molds can be combined with cryogel/hydrogel fabrication to create patient-specific tissue engineered scaffolds. By combining 3D-printing technology and scaffold fabrication, we were able to create scaffolds with the geometry of three cleft craniofacial defects. The scaffolds were then characterized to assess the effect of the mold on their physical properties. While the scaffolds were able to completely fill the mold, creating the desired geometry, the overall volumes were smaller than expected. The cryogels possessed porosities ranging from 79.7% to 87.2% and high interconnectivity. Additionally, the cryogels swelled from 400% to almost 1500% of their original dry weight while the hydrogel swelling did not reach 500%, demonstrating the ability to fill a defect site. Overall, despite the complex geometry, the cryogel scaffolds displayed ideal properties for bone reconstruction.