Hydrogel – based biopolymers for regenerative medicine applications: a critical review

Biological Functions of Macromolecular Protein Hydrogels in Constructing Osteogenic Microenvironment

Irreversible bone defects resulting from trauma, infection, and degenerative illnesses have emerged as a significant health concern. Structurally and functionally controllable hydrogels made by bone tissue engineering (BTE) have become promising biomaterials. Natural proteins are able to establish connections with autologous proteins through unique biologically active regions. Hydrogels based on proteins can simulate the bone microenvironment and regulate the biological behavior of stem cells in the tissue niche, making them candidates for research related to bone regeneration. This article reviews the biological functions of various natural macromolecular proteins (such as collagen, gelatin, fibrin, and silk fibroin) and highlights their special advantages as hydrogels. Then the latest research trends on cross-linking modified macromolecular protein hydrogels with improved mechanical properties and composite hydrogels loaded with exogenous micromolecular proteins have been discussed. Finally, the applications of protein hydrogels, such as 3D printed hydrogels, microspheres, and injectable hydrogels, were introduced, aiming to provide a reference for the repair of clinical bone defects.

Modern advances in spinal cord regeneration: hydrogel combined with neural stem cells

Severe spinal cord injuries (SCI) lead to loss of functional activity of the body below the injury site, affect a person's ability to self-care and have a direct impact on performance. Due to the structural features and functional role of the spinal cord in the body, the consequences of SCI cannot be completely overcome at the expense of endogenous regenerative potential and, developing over time, lead to severe complications years after injury. Thus, the primary task of this type of injury treatment is to create artificial conditions for the regenerative growth of damaged nerve fibers through the area of the SCI. Solving this problem is possible using tissue neuroengineering involving the technology of replacing the natural tissue environment with synthetic matrices (for example, hydrogels) in combination with stem cells, in particular, neural/progenitor stem cells (NSPCs). This approach can provide maximum stimulation and support for the regenerative growth of axons of damaged neurons and their myelination. In this review, we consider the currently available options for improving the condition after SCI (use of NSC transplantation or/and replacement of the damaged area of the SCI with a matrix, specifically a hydrogel). We emphasise the expediency and effectiveness of the hydrogel matrix + NSCs complex system used for the reconstruction of spinal cord tissue after injury. Since such a complex approach (a combination of tissue engineering and cell therapy), in our opinion, allows not only to creation of conditions for supporting endogenous regeneration or mechanical reconstruction of the spinal cord, but also to strengthen endogenous regeneration, prevent the spread of the inflammatory process, and promote the restoration of lost reflex, motor and sensory functions of the injured area of spinal cord.

Nanocrystalline cellulose as a reinforcing agent for poly (vinyl alcohol)/ gellan-gum-based composite film for moxifloxacin ocular delivery

Nanocrystalline cellulose (NCC) is a star material in drug delivery applications due to its good biocompatibility, large specific surface area, high tensile strength (TS), and high hydrophilicity. Poly(Vinyl Alcohol)/Gellan-gum-based innovative composite film has been prepared using nanocrystalline cellulose (PVA/GG/NCC) as a strengthening agent for ocular delivery of moxifloxacin (MOX) via solvent casting method. Impedance analysis was studied using the capacitive sensing technique for examining new capacitance nature of the nanocomposite MOX film. Antimicrobial properties of films were evaluated using Pseudomonas aeruginosa and Staphylococcus aureus as gram-negative and gram-positive bacteria respectively by disc diffusion technique. XRD revealed the characteristic peak of NCC and the amorphous form of the drug. Sustained in vitro release and enhanced corneal permeation of drug were noticed in the presence of NCC. Polymer matrix enhanced the mechanical properties (tensile strength 22.05 to 28.41 MPa) and impedance behavior (resistance 59.23 to 213.23 Ω) in the film due to the presence of NCC rather than its absence (16.78 MPa and 39.03 Ω respectively). Occurrence of NCC brought about good antimicrobial behavior (both gram-positive and gram-negative) of the film. NCC incorporated poly(vinyl alcohol)/gellan-gum-based composite film exhibited increased mechanical properties and impedance behavior for improved ocular delivery of moxifloxacin.

Construction methods and biomedical applications of PVA-based hydrogels

Polyvinyl alcohol (PVA) hydrogel is favored by researchers due to its good biocompatibility, high mechanical strength, low friction coefficient, and suitable water content. The widely distributed hydroxyl side chains on the PVA molecule allow the hydrogels to be branched with various functional groups. By improving the synthesis method and changing the hydrogel structure, PVA-based hydrogels can obtain excellent cytocompatibility, flexibility, electrical conductivity, viscoelasticity, and antimicrobial properties, representing a good candidate for articular cartilage restoration, electronic skin, wound dressing, and other fields. This review introduces various preparation methods of PVA-based hydrogels and their wide applications in the biomedical field.

Polyvinyl Alcohol-Chitosan Scaffold for Tissue Engineering and Regenerative Medicine Application: A Review

Tissue engineering and regenerative medicine (TERM) holds great promise for addressing the growing need for innovative therapies to treat disease conditions. To achieve this, TERM relies on various strategies and techniques. The most prominent strategy is the development of a scaffold. Polyvinyl alcohol-chitosan (PVA-CS) scaffold emerged as a promising material in this field due to its biocompatibility, versatility, and ability to support cell growth and tissue regeneration. Preclinical studies showed that the PVA-CS scaffold can be fabricated and tailored to fit the specific needs of different tissues and organs. Additionally, PVA-CS can be combined with other materials and technologies to enhance its regenerative capabilities. Furthermore, PVA-CS represents a promising therapeutic solution for developing new and innovative TERM therapies. Therefore, in this review, we summarized the potential role and functions of PVA-CS in TERM applications.

Anionic Polysaccharide Cryogels: Interaction and In Vitro Behavior of Alginate-Gum Arabic Composites

In the present study, polysaccharide-based cryogels demonstrate their potential to mimic a synthetic extracellular matrix. Alginate-based cryogel composites with different gum arabic ratios were synthesized by an external ionic cross-linking protocol, and the interaction between the anionic polysaccharides was investigated. The structural features provided by FT-IR, Raman, and MAS NMR spectra analysis indicated that a chelation mechanism is the main process linking the two biopolymers. In addition, SEM investigations revealed a porous, interconnected, and well-defined structure suitable as a scaffold in tissue engineering. The in vitro tests confirmed the bioactive character of the cryogels through the development of the apatite layer on the surface of the samples after immersion in simulated body fluid, identifying the formation of a stable phase of calcium phosphate and a small amount of calcium oxalate. Cytotoxicity tests performed on fibroblast cells demonstrated the non-toxic effect of alginate-gum arabic cryogel composites. In addition, an increase in flexibility was noted for samples with a high gum arabic content, which determines an appropriate environment to promote tissue regeneration. The newly obtained biomaterials that exhibit all these properties can be successfully involved in the regeneration of soft tissues, wound management, or controlled drug release systems.

Novel Strategy for Surface Modification of Titanium Implants towards the Improvement of Osseointegration Property and Antibiotic Local Delivery

The topography and chemical composition modification of titanium (Ti) implants play a decisive role in improving biocompatibility and bioactivity, accelerating osseointegration, and, thus, determining clinical success. In spite of the development of surface modification strategies, bacterial contamination is a common cause of failure. The use of systemic antibiotic therapy does not guarantee action at the contaminated site. In this work, we proposed a surface treatment for Ti implants that aim to improve their osseointegration and reduce bacterial colonization in surgery sites due to the local release of antibiotic. The Ti discs were hydrothermally treated with 3M NaOH solution to form a nanostructured layer of titanate on the Ti surface. Metronidazole was impregnated on these nanostructured surfaces to enable its local release. The samples were coated with poly(vinyl alcohol)-PVA films with different thickness to evaluate a possible control of drug release. Gamma irradiation was used to crosslink the polymer chains to achieve hydrogel layer formation and to sterilize the samples. The samples were characterized by XRD, SEM, FTIR, contact angle measurements, "in vitro" bioactivity, and drug release analysis. The alkaline hydrothermal treatment successfully produced intertwined, web-like nanostructures on the Ti surface, providing wettability and bioactivity to the Ti samples (Ti + TTNT samples). Metronidazole was successfully loaded and released from the Ti + TTNT samples coated or not with PVA. Although the polymeric film acted as a physical barrier to drug delivery, all groups reached the minimum inhibitory concentration for anaerobic bacteria. Thus, the surface modification method presented is a potential approach to improve the osseointegration of Ti implants and to associate local drug delivery with dental implants, preventing early infections and bone failure.

Acoustic Force Elastography Microscopy

OBJECTIVE

Hydrogel scaffolds have attracted attention to develop cellular therapy and tissue engineering platforms for regenerative medicine applications. Among factors, local mechanical properties of scaffolds drive the functionalities of cell niche. Dynamic mechanical analysis (DMA), the standard method to characterize mechanical properties of hydrogels, restricts development in tissue engineering because the measurement provides a single elasticity value for the sample, requires direct contact, and represents a destructive evaluation preventing longitudinal studies on the same sample. We propose a novel technique, acoustic force elastography microscopy (AFEM), to evaluate elastic properties of tissue engineering scaffolds.

RESULTS

AFEM can resolve localized and two-dimensional (2D) elastic properties of both transparent and opaque materials with advantages of being non-contact and non-destructive. Gelatin hydrogels, neat synthetic oligo[poly(ethylene glycol)fumarate] (OPF) scaffolds, OPF hydroxyapatite nanocomposite scaffolds and ex vivo biological tissue were examined with AFEM to evaluate the elastic modulus. These measurements of Young's modulus range from approximately 2 kPa to over 100 kPa were evaluated and are in good agreement with finite element simulations, surface wave measurements, and DMA tests.

CONCLUSION

The AFEM can resolve localized and 2D elastic properties of hydrogels, scaffolds and thin biological tissues. These materials can either be transparent or non-transparent and their evaluation can be done in a non-contact and non-destructive manner, thereby facilitating longitudinal evaluation.

SIGNIFICANCE

AFEM is a promising technique to quantify elastic properties of scaffolds for tissue engineering and will be applied to provide new insights for exploring elastic changes of cell-laden scaffolds for tissue engineering and material science.

Effectiveness of Epidermal Growth Factor Loaded Carboxymethylcellulose (EGF-CMC) Hydrogel in Biofilm Formation in Wounds of Diabetic Patients: A Randomized Clinical Trial

Diabetic patients frequently develop wounds, which can be colonized by bacteria, mainly Staphylococcus aureus and Pseudomonas aeruginosa, with the ability to form biofilms. This study aimed to evaluate the colonization and biofilm formation of Staphylococcus aureus and Pseudomonas aeruginosa in chronic wounds of diabetic patients treated with a bioactive dressing (EGF-CMC), which consisted of a 2% carboxymethylcellulose (CMC) hydrogel loaded with epidermal growth factor (EGF). This randomized clinical trial was conducted with 25 participants: 14 treated with EGF-CMC hydrogel and 11 treated with CMC hydrogel for 12 weeks. Participants with type 2 diabetes mellitus were selected. All had diabetic foot ulcers or chronic venous ulcers. Swab collections were performed on weeks 1, 6, and 12. The laboratory analyses included the identification of strains, microbial quantification, virulence gene investigation, and the evaluation of biofilm formation. In total, 13 S. aureus strains and 15 P. aeruginosa strains were isolated. There were no statistically significant differences regarding bacterial loads and virulence genes. However, EGF-CMC-hydrogel-treated wounds were colonized by strains with lower biofilm formation abilities. The probability of isolating biofilm-producing strains from CMC-hydrogel-treated wounds was 83% greater than the probability of isolating biofilm-producing strains from EGF-CMC-treated wounds.

Automated analysis of soft material microindentation

An understanding of the mechanical properties of soft hydrogel materials over multiple length scales is important for their application in many fields. Typical measurement methods provide either bulk mechanical properties (compression, tensile, rheology) or probing of nano or microscale properties and heterogeneity (nanoindentation, AFM). In this work we demonstrate the complementarity of instrumented microindentation to these techniques, as it provides representative Young's moduli for soft materials with minimal influence of the experimental parameters chosen, and allows mechanical property mapping across macroscopic areas. To enable automated analysis of the large quantities of data required for these measurements, we develop a new fitting algorithm to process indentation data. This method allows for the determination of Young's moduli from imperfect data by automatic selection of a region of the indentation curve which does not display inelastic deformation or substrate effects. We demonstrate the applicability of our approach with a range of hydrogels, including materials with patterns and gradients in stiffness, and expect the techniques described here to be useful developments for the mechanical analysis of a wide range of soft and biological systems.

Advancements in the Use of Hydrogels for Regenerative Medicine: Properties and Biomedical Applications

Due to their particular water absorption capacity, hydrogels are the most widely used scaffolds in biomedical studies to regenerate damaged tissue. Hydrogels can be used in tissue engineering to design scaffolds for three-dimensional cell culture, providing a novel alternative to the traditional two-dimensional cell culture as hydrogels have a three-dimensional biomimetic structure. This material property is crucial in regenerative medicine, especially for the nervous system, since it is a highly complex and delicate structure. Hydrogels can move quickly within the human body without physically disturbing the environment and possess essential biocompatible properties, as well as the ability to form a mimetic scaffold in situ. Therefore, hydrogels are perfect candidates for biomedical applications. Hydrogels represent a potential alternative to regenerating tissue lost after removing a brain tumor and/or brain injuries. This reason presents them as an exciting alternative to highly complex human physiological problems, such as injuries to the central nervous system and neurodegenerative disease.

Natural Polymeric Scaffolds for Tissue Engineering Applications

Natural polymeric scaffolds can be used for tissue engineering applications such as cell delivery and cell-free supporting of native tissues. This is because of their desirable properties such as; high biocompatibility, tunable mechanical strength and conductivity, large surface area, porous- and extracellular matrix (ECM)-mimicked structures. Specifically, their less toxicity and biocompatibility makes them suitable for several tissue engineering applications. For these reasons, several biopolymeric scaffolds are currently being explored for numerous tissue engineering applications. To date, research on the nature, chemistry, and properties of nanocomposite biopolymers are been reported, while the need for a comprehensive research note on more tissue engineering application of these biopolymers remains. As a result, this present study comprehensively reviews the development of common natural biopolymers as scaffolds for tissue engineering applications such as cartilage tissue engineering, cornea repairs, osteochondral defect repairs, and nerve regeneration. More so, the implications of research findings for further studies are presented, while the impact of research advances on future research and other specific recommendations are added as well.