Injectable and tunable hyaluronic acid hydrogels releasing chemotactic and angiogenic growth factors for endodontic regeneration

Hydrogels for Treatment of Oral and Maxillofacial Diseases: Current Research, Challenge, and Future Directions

Oral and maxillofacial diseases such as infection and trauma often involve various organs and tissues, resulting in structural defects, dysfunctions and/or adverse effects on facial appearance. Hydrogels have been applied...

Materials for Dentoalveolar Bioprinting: Current State of the Art

Although current treatments can successfully address a wide range of complications in the dentoalveolar region, they often still suffer from drawbacks and limitations, resulting in sub-optimal treatments for specific problems. In recent decades, significant progress has been made in the field of tissue engineering, aiming at restoring damaged tissues via a regenerative approach. Yet, the translation into a clinical product is still challenging. Novel technologies such as bioprinting have been developed to solve some of the shortcomings faced in traditional tissue engineering approaches. Using automated bioprinting techniques allows for precise placement of cells and biological molecules and for geometrical patient-specific design of produced biological scaffolds. Recently, bioprinting has also been introduced into the field of dentoalveolar tissue engineering. However, the choice of a suitable material to encapsulate cells in the development of so-called bioinks for bioprinting dentoalveolar tissues is still a challenge, considering the heterogeneity of these tissues and the range of properties they possess. This review, therefore, aims to provide an overview of the current state of the art by discussing the progress of the research on materials used for dentoalveolar bioprinting, highlighting the advantages and shortcomings of current approaches and considering opportunities for further research.

Platelet lysate functionalized gelatin methacrylate microspheres for improving angiogenesis in endodontic regeneration

Rapid angiogenesis is one of the challenges in endodontic regeneration. Recently, tailored polymeric microsphere system that loaded pro-angiogenic growth factors (GFs) is promising in facilitating vascularization in dental pulp regeneration. In addition, the synergistic effect of multiple GFs is considered more beneficial, but combination usage of them is rather complex and costly. Herein, we aimed to incorporate human platelet lysate (PL), a natural-derived pool of multiple GFs, into gelatin methacrylate (GelMA) microsphere system (GP), which was further modified by Laponite (GPL), a nanoclay with efficient drug delivery ability. These hybrid microspheres were successfully fabricated by electrostatic microdroplet technique with suitable size range (180∼380 µm). After incorporation of the PL and Laponite with GelMA, the Young's modulus of the hybrid hydrogel increased up to about 3-fold and the swelling and degradation rate decreased simultaneously. The PL-derived GFs continued to release up to 28 days from both the GP and GPL microspheres, while the latter released relatively more slowly. What's more, the released GFs could effectively induce tubule formation of human umbilical endothelial cells (HUVECs) and also promote human dental pulp stem cells (hDPSCs) migration. Additionally, the PL component in the GelMA microspheres significantly improved the proliferation, spreading, and odontogenic differentiation of the encapsulated hDPSCs. As further verified by the subcutaneous implantation results, both of the GP and GPL groups enhanced microvascular formation and pulp-like tissue regeneration. This work demonstrated that PL-incorporating GelMA microsphere system was a promising functional vehicle for promoting vascularized endodontic regeneration. STATEMENT OF SIGNIFICANCE: Polymeric microsphere system loaded with pro-angiogenic growth factors (GFs) shows great promise for regeneration of vascularized dental pulp. Herein, we prepared a functional GelMA microsphere system incorporated with human platelet lysates (PL) and nanoclay Laponite by the electrostatic microdroplet method. The results demonstrated that the GelMA/PL/Laponite microspheres significantly improved the spreading, proliferation, and odontogenic differentiation of the encapsulated hDPSCs compared with pure GelMA microspheres. Moreover, they also enhanced microvascular formation and pulp-like tissue regeneration in vivo. This hybrid microsphere system has great potential to accelerate microvessel formation in regenerated dental pulp and other tissues.

Evaluation of Injectable Hyaluronic Acid-Based Hydrogels for Endodontic Tissue Regeneration

Dental pulp tissue engineering (TE) endeavors to regenerate dentin/pulp complex by combining a suitable supporting matrix, stem cells, and biochemical stimuli. Such procedures foresee a matrix that can be easily introduced into the root canal system (RCS) and tightly adhere to dentin walls to assure the dentin surface’s proper colonization with progenitor cells capable of restoring the dentin/pulp complex. Herein was investigated an injectable self-setting hyaluronic acid-based (HA) hydrogel system, formed by aldehyde-modified (a-HA) with hydrazide-modified (ADH), enriched with platelet lysate (PL), for endodontic regeneration. The hydrogels’ working (wT) and setting (sT) times, the adhesion to the dentine walls, the hydrogel’s microstructure, and the delivery of human dental pulp cells (DPCs) were studied in vitro. Hydrogels incorporating PL showed a suitable wT and sT and a porous microstructure. The tensile tests showed that the breaking point occurs after 4.3106 ± 1.8677 mm deformation, while in the indentation test after 1.4056 ± 0.3065 mm deformation. Both breaking points occur in the hydrogel extension. The HA/PL hydrogels exhibited supportive properties and promoted cell migration toward dentin surfaces in vitro. Overall, these results support using PL-laden HA injectable hydrogels (HA/PL) as a biomaterial for DPCs encapsulation, thereby displaying great clinical potential towards endodontic regenerative therapies.

Polymeric Scaffolds for Dental, Oral, and Craniofacial Regenerative Medicine

Dental, oral, and craniofacial (DOC) regenerative medicine aims to repair or regenerate DOC tissues including teeth, dental pulp, periodontal tissues, salivary gland, temporomandibular joint (TMJ), hard (bone, cartilage), and soft (muscle, nerve, skin) tissues of the craniofacial complex. Polymeric materials have a broad range of applications in biomedical engineering and regenerative medicine functioning as tissue engineering scaffolds, carriers for cell-based therapies, and biomedical devices for delivery of drugs and biologics. The focus of this review is to discuss the properties and clinical indications of polymeric scaffold materials and extracellular matrix technologies for DOC regenerative medicine. More specifically, this review outlines the key properties, advantages and drawbacks of natural polymers including alginate, cellulose, chitosan, silk, collagen, gelatin, fibrin, laminin, decellularized extracellular matrix, and hyaluronic acid, as well as synthetic polymers including polylactic acid (PLA), polyglycolic acid (PGA), polycaprolactone (PCL), poly (ethylene glycol) (PEG), and Zwitterionic polymers. This review highlights key clinical applications of polymeric scaffolding materials to repair and/or regenerate various DOC tissues. Particularly, polymeric materials used in clinical procedures are discussed including alveolar ridge preservation, vertical and horizontal ridge augmentation, maxillary sinus augmentation, TMJ reconstruction, periodontal regeneration, periodontal/peri-implant plastic surgery, regenerative endodontics. In addition, polymeric scaffolds application in whole tooth and salivary gland regeneration are discussed.

Injectable hydrogels for vascular embolization and cell delivery: The potential for advances in cerebral aneurysm treatment

Cerebral aneurysms are vascular lesions caused by the biomechanical failure of the vessel wall due to hemodynamic stress and inflammation. Aneurysmal rupture results in subarachnoid hemorrhage often leading to death or disability. Current treatment options include open surgery and minimally invasive endovascular options aimed at secluding the aneurysm from the circulation. Cerebral aneurysm embolization with appropriate materials is a therapeutic approach to prevent rupture and the resultant clinical sequelae. Metallic platinum coils are a typical, practical option to embolize cerebral aneurysms. However, the development of an alternative treatment modality is of interest because of poor occlusion permanence, coil migration, and coil compaction. Moreover, minimizing the implanted foreign materials during therapy is of importance not just to patients, but also to clinicians in the event an open surgical approach has to be pursued in the future. Polymeric injectable hydrogels have been investigated for transcatheter embolization and cell therapy with the potential for permanent aneurysm repair. This review focuses on how the combination of injectable embolic biomaterials and cell therapy may achieve minimally invasive remodeling of a degenerated cerebral artery with promise for superior outcomes in treatment of this devastating disease.

Local Drug Delivery Systems for Vital Pulp Therapy: A New Hope

Vital pulp therapy (VPT) is deliberated as an ultraconservative/minimally invasive approach for the conservation of vital pulpal tissues, preservation of dental structure, and maintenance of tooth function in the oral cavity. In VPT, following the exposure of the dental pulp, the environment is prepared for the possible healing and probable refunctionalisation of pulpal connective tissue. However, to succeed in VPT, specific biomaterials are used to cover and/or dress the exposed pulp, lower the inflammation, heal the dental pulp, provoke the remaining odontoblastic cells, and induce the formation of a hard tissue, i.e., the dentinal bridge. It can be assumed that if the employed biomaterial is transferred to the target site using a specially designed micro-/nanosized local drug delivery system (LDDS), the biomaterial would be placed in closer proximity to the connective tissue, may be released in a controlled and sustained pattern, could properly conserve the remaining dental pulp and might appropriately enhance hard-tissue formation. Furthermore, the loaded LDDS could help VPT modalities to be more ultraconservative and may minimise the manipulation of the tooth structure as well as pulpal tissue, which could, in turn, result in better VPT outcomes.

Recent Progress on Polysaccharide-Based Hydrogels for Controlled Delivery of Therapeutic Biomolecules

A plethora of applications using polysaccharides have been developed in recent years due to their availability as well as their frequent nontoxicity and biodegradability. These polymers are usually obtained from renewable sources or are byproducts of industrial processes, thus, their use is collaborative in waste management and shows promise for an enhanced sustainable circular economy. Regarding the development of novel delivery systems for biotherapeutics, the potential of polysaccharides is attractive for the previously mentioned properties and also for the possibility of chemical modification of their structures, their ability to form matrixes of diverse architectures and mechanical properties, as well as for their ability to maintain bioactivity following incorporation of the biomolecules into the matrix. Biotherapeutics, such as proteins, growth factors, gene vectors, enzymes, hormones, DNA/RNA, and antibodies are currently in use as major therapeutics in a wide range of pathologies. In the present review, we summarize recent progress in the development of polysaccharide-based hydrogels of diverse nature, alone or in combination with other polymers or drug delivery systems, which have been implemented in the delivery of biotherapeutics in the pharmaceutical and biomedical fields.

Hydrogel Composites with Different Dimensional Nanoparticles for Bone Regeneration

The treatment of large segmental bone defects and complex types of fractures caused by trauma, inflammation, or tumor resection is still a challenge in the field of orthopedics. Various natural or synthetic biological materials used in clinical applications cannot fully replicate the structure and performance of raw bone. This highlights how to endow materials with multiple functions and biological properties, which is a problem that needs to be solved in practical applications. Hydrogels with outstanding biocompatibility, for their casting into any shape, size, or form, are suitable for different forms of bone defects. Therefore, they have been used in regenerative medicine more widely. In this review, versatile hydrogels are compounded with nanoparticles of different dimensions, and many desirable features of these materials in bone regeneration are introduced, including drug delivery, cell factor vehicle, cell scaffolds, which have potential in bone regeneration applications. The combination of hydrogels and nanoparticles of different dimensions encourages better filling of bone defect areas and has higher adaptability. This is due to the minimally invasive properties of the material and ability to match irregular defects. These biological characteristics make composite hydrogels with different dimensional nanoparticles become one of the most attractive options for bone regeneration materials.

In Situ Oxygen Generation Enhances the SCAP Survival in Hydrogel Constructs

Prolonged and severe hypoxia is the main cause of death of transplanted cells prior to the establishment of functional circulation. In situ generation of oxygen by oxygen-producing scaffolds-a unique solution that could produce and deliver oxygen to the adjacent cells independently of blood perfusion-has attracted considerable attention to enhance the survivability of the transplanted cells. However, the application of oxygen-generating scaffolds for facilitating cell survival in pulp-like tissue regeneration is yet to be explored. In this study, gelatin methacryloyl (GelMA)-a biocompatible scaffolding material that closely mimics the native extracellular matrix and is conducive to cell proliferation and differentiation-was used to fabricate oxygen-generating scaffolds by loading various concentrations of CaO₂. The CaO₂ distribution, topography, swelling, and pore size of CaO₂-GelMA hydrogels were characterized in detail. The release of O₂ by the scaffold and the viability, spreading, and proliferation of stem cells from apical papilla (SCAPs) encapsulated in the GelMA hydrogels with various concentrations of CaO₂ under hypoxia were evaluated. In addition, cellular constructs were engineered into root canals, and cell viability within the apical, middle, and coronal portions was assessed. Our findings showed that 0.5% CaO₂-GelMA was sufficient to supply in situ oxygen for maintaining the embedded SCAP viability for 1 wk. Furthermore, the 0.5% CaO₂-GelMA hydrogels improved the survivability of SCAPs within the coronal portion of the engineered cellular constructs within the root canals. This work demonstrated that 0.5% CaO₂-GelMA hydrogels offer a potential promising scaffold that enhances survival of the embedded SCAPs in endodontic regeneration.

Human Platelet Lysate-Loaded Poly(ethylene glycol) Hydrogels Induce Stem Cell Chemotaxis In Vitro

Platelet lysates (PL) contain a selection of proteins and growth factors (GFs) that are known to mediate cell activity. Many of these biomolecules have been identified as chemoattractants with the capacity to induce cell migration. In order to effectively deliver and retain these biomolecules to the site of injury, a scaffold containing PL could be an option. We use poly(ethylene glycol) (PEG) hydrogels consisting of 90 vol % PL to investigate their migratory potential on human mesenchymal stem cells (hMSCs). Cells exposed to these hydrogels were tracked, resulting in cell trajectories and detailed migratory parameters (velocity, Euclidean distance, directness, and forward migration index). Volumetric swelling ratios, hydrogel mechanical properties, and the release kinetics of proteins and GFs from hydrogels were also assessed. Furthermore, hMSC spheroids were encapsulated within the hydrogels to qualitatively assess cell invasion by means of sprouting and disintegration of the spheroid. Cell spheroids encapsulated within the PL-PEG gels exhibited initial outgrowths and eventually colonized the 3D matrix successfully. Results from this study confirmed that hMSCs exhibit directional migration toward the PL-loaded hydrogel with increased velocity and directness, compared to the controls. Overall, the incorporation of PL renders the PEG hydrogel bioactive. This study demonstrates the capacity of PL-loaded hydrogel constructs to attract stem cells for endogenous tissue engineering purposes.

Structurally Dynamic Hydrogels for Biomedical Applications: Pursuing a Fine Balance between Macroscopic Stability and Microscopic Dynamics

Owing to their unique chemical and physical properties, hydrogels are attracting increasing attention in both basic and translational biomedical studies. Although the classical hydrogels with static networks have been widely reported for decades, a growing number of recent studies have shown that structurally dynamic hydrogels can better mimic the dynamics and functions of natural extracellular matrix (ECM) in soft tissues. These synthetic materials with defined compositions can recapitulate key chemical and biophysical properties of living tissues, providing an important means to understanding the mechanisms by which cells sense and remodel their surrounding microenvironments. This review begins with the overall expectation and design principles of dynamic hydrogels. We then highlight recent progress in the fabrication strategies of dynamic hydrogels including both degradation-dependent and degradation-independent approaches, followed by their unique properties and use in biomedical applications such as regenerative medicine, drug delivery, and 3D culture. Finally, challenges and emerging trends in the development and application of dynamic hydrogels are discussed.

Platform technologies for regenerative endodontics from multifunctional biomaterials to tooth-on-a-chip strategies

OBJECTIVES

The aim of this review is to highlight recent progress in the field of biomaterials-mediated dental pulp tissue engineering. Specifically, we aim to underscore the critical design criteria of biomaterial platforms that are advantageous for pulp tissue engineering, discuss models for preclinical evaluation, and present new and innovative multifunctional strategies that hold promise for clinical translation.

MATERIALS AND METHODS

The current article is a comprehensive overview of recent progress over the last 5 years. In detail, we surveyed the literature in regenerative pulp biology, including novel biologic and biomaterials approaches, and those that combined multiple strategies, towards more clinically relevant models. PubMed searches were performed using the keywords: "regenerative dentistry," "dental pulp regeneration," "regenerative endodontics," and "dental pulp therapy."

RESULTS

Significant contributions to the field of regenerative dentistry have been made in the last 5 years, as evidenced by a significant body of publications. We chose exemplary studies that we believe are progressive towards clinically translatable solutions. We close this review with an outlook towards the future of pulp regeneration strategies and their clinical translation.

CONCLUSIONS

Current clinical treatments lack functional and predictable pulp regeneration and are more focused on the treatment of the consequences of pulp exposure, rather than the restoration of healthy dental pulp.

CLINICAL RELEVANCE

Clinically, there is great demand for bioinspired biomaterial strategies that are safe, efficacious, and easy to use, and clinicians are eager for their clinical translation. In particular, we place emphasis on strategies that combine favorable angiogenesis, mineralization, and functional tissue formation, while limiting immune reaction, risk of microbial infection, and pulp necrosis.

Synthesis and Evaluation of AlgNa-g-Poly(QCL-co-HEMA) Hydrogels as Platform for Chondrocyte Proliferation and Controlled Release of Betamethasone

Hydrogels obtained from combining different polymers are an interesting strategy for developing controlled release system platforms and tissue engineering scaffolds. In this study, the applicability of sodium alginate-g-(QCL-co-HEMA) hydrogels for these biomedical applications was evaluated. Hydrogels were synthesized by free-radical polymerization using a different concentration of the components. The hydrogels were characterized by Fourier transform-infrared spectroscopy, scanning electron microscopy, and a swelling degree. Betamethasone release as well as the in vitro cytocompatibility with chondrocytes and fibroblast cells were also evaluated. Scanning electron microscopy confirmed the porous surface morphology of the hydrogels in all cases. The swelling percent was determined at a different pH and was observed to be pH-sensitive. The controlled release behavior of betamethasone from the matrices was investigated in PBS media (pH = 7.4) and the drug was released in a controlled manner for up to 8 h. Human chondrocytes and fibroblasts were cultured on the hydrogels. The MTS assay showed that almost all hydrogels are cytocompatibles and an increase of proliferation in both cell types after one week of incubation was observed by the Live/Dead^® assay. These results demonstrate that these hydrogels are attractive materials for pharmaceutical and biomedical applications due to their characteristics, their release kinetics, and biocompatibility.

Recent advances in the production of biomedical systems based on polyhydroxyalkanoates and exopolysaccharides

In recent years, growing attention has been devoted to naturally occurring biological macromolecules and their ensuing application in agriculture, cosmetics, food and pharmaceutical industries. They inherently have antigenicity, low immunogenicity, excellent biocompatibility and cytocompatibility, which are ideal properties for the design of biomedical devices, especially for the controlled delivery of active ingredients in the most diverse contexts. Furthermore, these properties can be modulated by chemical modification via the incorporation of other (macro)molecules in a random or controlled way, aiming at improving their functionality for each specific application. Among the wide variety of natural polymers, microbial polyhydroxyalkanoates (PHAs) and exopolysaccharides (EPS) are often considered for the development of original biomaterials due to their unique physicochemical and biological features. Here, we aim to fullfil a gap on the present associated literature, bringing an up-to-date overview of ongoing research strategies that make use of PHAs (poly (3-hydroxybutyrate), poly (3-hydroxybutyrate-co-3-hydroxyvalerate), poly (3-hydroxyoctanoate), poly(3-hydroxypropionate), poly (3-hydroxyhexanoate-co-3-hydroxyoctanoate), and poly (3-hydroxybutyrate-co-3-hydroxyhexanoate)) and EPS (bacterial cellulose, alginates, curdlan, pullulan, xanthan gum, dextran, hyaluronan, and schizophyllan) as sources of interesting and versatile biomaterials. For the first time, a monograph addressing the properties, pros and cons, status, challenges, and recent progresses regarding the application of these two important classes of biopolymers in biomedicine is presented.

Polysaccharide-Based Materials Created by Physical Processes: From Preparation to Biomedical Applications

Polysaccharide-based materials created by physical processes have received considerable attention for biomedical applications. These structures are often made by associating charged polyelectrolytes in aqueous solutions, avoiding toxic chemistries (crosslinking agents). We review the principal polysaccharides (glycosaminoglycans, marine polysaccharides, and derivatives) containing ionizable groups in their structures and cellulose (neutral polysaccharide). Physical materials with high stability in aqueous media can be developed depending on the selected strategy. We review strategies, including coacervation, ionotropic gelation, electrospinning, layer-by-layer coating, gelation of polymer blends, solvent evaporation, and freezing-thawing methods, that create polysaccharide-based assemblies via in situ (one-step) methods for biomedical applications. We focus on materials used for growth factor (GFs) delivery, scaffolds, antimicrobial coatings, and wound dressings.

Advances in Injectable and Self-healing Polysaccharide Hydrogel Based on the Schiff Base Reaction

Injectable hydrogel possesses great application potential in disease treatment and tissue engineering, but damage to gel often occurs due to the squeezing pressure from injection devices and the mechanical forces from limb movement, and leads to the rapid degradation of gel matrix and the leakage of the load material. The self-healing injectable hydrogels can overcome these drawbacks via automatically repairing gel structural defects and restoring gel function. The polysaccharide hydrogels constructed through the Schiff base reaction own advantages including simple fabrication, injectability, and self-healing under physiological conditions, and therefore have drawn extensive attention and investigation recently. In this short review, the preparation and self-healing properties of the polysaccharide hydrogels that is established on the Schiff base reaction are focused on and their biological applications in drug delivery and cell therapy are discussed.

Fibronectin-loaded Collagen/Gelatin Hydrogel Is a Potent Signaling Biomaterial for Dental Pulp Regeneration

INTRODUCTION

Guided tissue regeneration has been considered a promising biological strategy to replace conventional endodontic therapies of teeth with incomplete root formation. Therefore, in the present study, a collagen/gelatin hydrogel either containing dosages of fibronectin (FN), or not, was developed and assessed concerning their bioactive and chemotactic potential on human apical papilla cells (hAPCs).

METHODS

Hydrogels were prepared by varying the ratio of collagen and gelatin (Col/Gel; v/v), and used to establish the following groups: Collagen (positive control); Col/Gel 4:6; Col/Gel 6:4; Col/Gel 8:2. The viability, adhesion, and spreading of cells seeded on the hydrogels were evaluated. Different concentrations of FN (0, 5, or 10 μg/mL) were incorporated into the best formulation of the collagen/gelatin hydrogel selected. Then, the hAPCs seeded on the biomaterials were assessed concerning the cell migration, viability, adhesion and spreading, and gene expression of ITGA5, ITGAV, COL1A1, and COL3A1.

RESULTS

The Col/Gel 8:2 group exhibited better cell viability, adhesion and spreading in comparison with Control. Higher values of hAPC migration, viability, adhesion, spreading and gene expression of pulp regeneration markers were found, the higher the concentration was of FN incorporated into the collagen/gelatin hydrogel.

CONCLUSION

Collagen/gelatin hydrogel with 10 μg/mL of FN had potent bioactive and chemotactic effects on cultured hAPCs.

Which experimental models and explorations to use in regenerative endodontics? A comprehensive review on standard practices

Since the discovery of dental pulp stem cells, a lot of teams have expressed an interest in dental pulp regeneration. Many approaches, experimental models and biological explorations have been developed, each including the use of stem cells and scaffolds with the final goal being clinical application in humans. In this review, the authors' objective was to compare the experimental models and strategies used for the development of biomaterials for tissue engineering of dental pulp with stem cells. Electronic queries were conducted on PubMed using the following terms: pulp regeneration, scaffold, stem cells, tissue engineering and biomaterial. The extracted data included the following information: the strategy envisaged, the type of stem cells, the experimental models, the exploration or analysis methods, the cytotoxicity or viability or proliferation cellular tests, the tests of scaffold antibacterial properties and take into account the vascularization of the regenerated dental pulp. From the 71 selected articles, 59% focused on the "cell-transplantation" strategy, 82% used in vitro experimentation, 58% in vivo animal models and only one described an in vivo in situ human clinical study. 87% used dental pulp stem cells. A majority of the studies reported histology (75%) and immunohistochemistry explorations (66%). 73% mentioned the use of cytotoxicity, proliferation or viability tests. 48% took vascularization into account but only 6% studied the antibacterial properties of the scaffolds. This article gives an overview of the methods used to regenerate dental pulp from stem cells and should help researchers create the best development strategies for research in this field.

The Potential Translational Applications of Nanoparticles in Endodontics

Nanotechnology has substantially progressed in the past decades, giving rise to numerous possible applications in different biomedical fields. In particular, the use of nanoparticles in endodontics has generated significant interest due to their unique characteristics. As a result of their nanoscale dimensions, nanoparticles possess several properties that may enhance the treatment of endodontic infections, such as heightened antibacterial activity, increased reactivity and the capacity to be functionalized with other reactive compounds. Effective disinfection and sealing of the root canal system are the hallmarks for successful endodontic treatment. However, the presence of bacterial biofilms and resistance to endodontic disinfectants pose a significant challenge to this goal. This has encouraged the investigation of antibacterial nanoparticle-based irrigants and intracanal medicaments, which may improve the elimination of endodontic infections. In addition, photosynthesizer-functionalized nanoparticles could also serve as a worthy adjunct to root canal disinfection strategies. Furthermore, despite the myriad of commercially available options for endodontic obturation, the "ideal" material has yet to be conceived. This has led to the development of various experimental nanoparticle-incorporated obturation materials and sealers that exhibit a range of favourable physicochemical properties including enhanced antibacterial efficacy and bioactivity. Nanoparticle applications also show promise in the field of regenerative endodontics, such as supporting the release of bioactive molecules and enhancing the biophysical properties of scaffolds. Given the constantly growing body of research in this field, this article aims to present an overview of the current evidence pertaining to the potential translational applications of nanoparticles in endodontics.

Injectable, macroporous scaffolds for delivery of therapeutic genes to the injured spinal cord

Biomaterials are being developed as therapeutics for spinal cord injury (SCI) that can stabilize and bridge acute lesions and mediate the delivery of transgenes, providing a localized and sustained reservoir of regenerative factors. For clinical use, direct injection of biomaterial scaffolds is preferred to enable conformation to unique lesions and minimize tissue damage. While an interconnected network of cell-sized macropores is necessary for rapid host cell infiltration into-and thus integration of host tissue with-implanted scaffolds, injectable biomaterials have generally suffered from a lack of control over the macrostructure. As genetic vectors have short lifetimes in vivo, rapid host cell infiltration into scaffolds is a prerequisite for efficient biomaterial-mediated delivery of transgenes. We present scaffolds that can be injected and assembled in situ from hyaluronic acid (HA)-based, spherical microparticles to form scaffolds with a network of macropores (∼10 μm). The results demonstrate that addition of regularly sized macropores to traditional hydrogel scaffolds, which have nanopores (∼10 nm), significantly increases the expression of locally delivered transgene to the spinal cord after a thoracic injury. Maximal cell and axon infiltration into scaffolds was observed in scaffolds with more regularly sized macropores. The delivery of lentiviral vectors encoding the brain-derived neurotrophic factor (BDNF), but not neurotrophin-3, from these scaffolds further increased total numbers and myelination of infiltrating axons. Modest improvements to the hindlimb function were observed with BDNF delivery. The results demonstrate the utility of macroporous and injectable HA scaffolds as a platform for localized gene therapies after SCI.

Mechanical properties of cell- and microgel bead-laden oxidized alginate-gelatin hydrogels

3D-printing technologies, such as biofabrication, capitalize on the homogeneous distribution and growth of cells inside biomaterial hydrogels, ultimately aiming to allow for cell differentiation, matrix remodeling, and functional tissue analogues. However, commonly, only the mechanical properties of the bioinks or matrix materials are assessed, while the detailed influence of cells on the resulting mechanical properties of hydrogels remains insufficiently understood. Here, we investigate the properties of hydrogels containing cells and spherical PAAm microgel beads through multi-modal complex mechanical analyses in the small- and large-strain regimes. We evaluate the individual contributions of different filler concentrations and a non-fibrous oxidized alginate-gelatin hydrogel matrix on the overall mechanical behavior in compression, tension, and shear. Through material modeling, we quantify parameters that describe the highly nonlinear mechanical response of soft composite materials. Our results show that the stiffness significantly drops for cell- and bead concentrations exceeding four million per milliliter hydrogel. In addition, hydrogels with high cell concentrations (≥6 mio ml^-1) show more pronounced material nonlinearity for larger strains and faster stress relaxation. Our findings highlight cell concentration as a crucial parameter influencing the final hydrogel mechanics, with implications for microgel bead drug carrier-laden hydrogels, biofabrication, and tissue engineering.

Combination Therapy of Killing Diseases by Injectable Hydrogels: From Concept to Medical Applications

The complexity of hard-to-treat diseases strongly undermines the therapeutic potential of available treatment options. Therefore, a paradigm shift from monotherapy toward combination therapy has been observed in clinical research to improve the efficiency of available treatment options. The advantages of combination therapy include the possibility of synchronous alteration of different biological pathways, reducing the required effective therapeutic dose, reducing drug resistance, and lowering the overall costs of treatment. The tunable physical properties, excellent biocompatibility, facile preparation, and ease of administration with minimal invasiveness of injectable hydrogels (IHs) have made them excellent candidates to solve the clinical and pharmacological limitations of present systems for multitherapy by direct delivery of therapeutic payloads and improving therapeutic responses through the formation of depots containing drugs, genes, cells, or a combination of them in the body after a single injection. In this review, currently available methods for the design and fabrication of IHs are systematically discussed in the first section. Next, as a step toward establishing IHs for future multimodal synergistic therapies, recent advances in cancer combination therapy, wound healing, and tissue engineering are addressed in detail in the following sections. Finally, opportunities and challenges associated with IHs for multitherapy are listed and further discussed.

State-of-the-Art of Eggshell Waste in Materials Science: Recent Advances in Catalysis, Pharmaceutical Applications, and Mechanochemistry

Eggshell waste is among the most abundant waste materials coming from food processing technologies. Despite the unique properties that both its components (eggshell, ES, and eggshell membrane, ESM) possess, it is very often discarded without further use. This review article aims to summarize the recent reports utilizing eggshell waste for very diverse purposes, stressing the need to use a mechanochemical approach to broaden its applications. The most studied field with regards to the potential use of eggshell waste is catalysis. Upon proper treatment, it can be used for turning waste oils into biodiesel and moreover, the catalytic effect of eggshell-based material in organic synthesis is also very beneficial. In inorganic chemistry, the eggshell membrane is very often used as a templating agent for nanoparticles production. Such composites are suitable for application in photocatalysis. These bionanocomposites are also capable of heavy metal ions reduction and can be also used for the ozonation process. The eggshell and its membrane are applicable in electrochemistry as well. Due to the high protein content and the presence of functional groups on the surface, ESM can be easily converted to a high-performance electrode material. Finally, both ES and ESM are suitable for medical applications, as the former can be used as an inexpensive Ca2+ source for the development of medications, particles for drug delivery, organic matrix/mineral nanocomposites as potential tissue scaffolds, food supplements and the latter for the treatment of joint diseases, in reparative medicine and vascular graft producing. For the majority of the above-mentioned applications, the pretreatment of the eggshell waste is necessary. Among other options, the mechanochemical pretreatment has found an inevitable place. Since the publication of the last review paper devoted to the mechanochemical treatment of eggshell waste, a few new works have appeared, which are reviewed here to underline the sustainable character of the proposed methodology. The mechanochemical treatment of eggshell is capable of producing the nanoscale material which can be further used for bioceramics synthesis, dehalogenation processes, wastewater treatment, preparation of hydrophobic filters, lithium-ion batteries, dental materials, and in the building industry as cement.

hDPSC-laden GelMA microspheres fabricated using electrostatic microdroplet method for endodontic regeneration

The microsphere system has attracted considerable attention as a stem-cell delivery vehicle in regeneration medicine owing to its injectability, fast substance transfer ability, and mimicry of the three-dimensional native environment. However, suitable biomaterials for preparation of microspheres optimal for endodontic regeneration are still being explored. Owing to its excellent bioactivity and biodegradability, gelatin methacryloyl (GelMA) was used to fabricate hydrogel microspheres by the electrostatic microdroplet method, and the potential of GelMA microspheres applied in endodontic regeneration was studied. The average size of GelMA microspheres encapsulating human dental pulp stem cells (hDPSCs) was ~200 μm, and the Young's modulus was approximately 582.8 ± 66.0 Pa, which was close to that of the natural human dental pulp. The encapsulated hDPSCs could effectively adhere, spread, proliferate, and secrete extracellular matrix proteins in the microspheres, and tended to occupy the outer layer. Moreover, the cell-laden GelMA microsphere system could withstand cryopreservation, and the thawed cells exhibited normal functions. After subcutaneous implantation in a nude mouse model, more vascularized pulp-like tissues were generated in the cell-laden GelMA microsphere group compared with that in the cell-laden bulk GelMA group, and this was accompanied by a suitable degradation rate. The GelMA microspheres showed remarkable performances and great potential as cell delivery vehicles in endodontic regeneration.

Injectable hyaluronic acid and platelet lysate-derived granular hydrogels for biomedical applications

Towards the repair of damaged tissues, numerous scaffolds have been fabricated to recreate the complex extracellular matrix (ECM) environment to support desired cell behaviors; however, it is often challenging to design scaffolds with the requisite cell-anchorage sites, mechanical stability, and tailorable physicochemical properties necessary for many applications. To address this and to improve on the properties of hyaluronic acid (HA) hydrogels, we combined photocrosslinkable norbornene-modified HA (NorHA) with human platelet lysate (PL). These PL-NorHA hybrid hydrogels supported the adhesion of cells when compared to NorHA hydrogels without PL, exhibited tailorable physicochemical properties based on the concentration of individual components, and released proteins over time. Using microfluidic techniques with on-chip mixing of NorHA and PL and subsequent photocrosslinking, spherical PL-NorHA microgels with a hierarchical fibrillar network were fabricated that exhibited the sustained delivery of PL proteins. Microgels could be jammed into granular hydrogels that exhibited shear-thinning and self-healing properties, enabling ejection from syringes and the fabrication of stable 3D constructs with 3D printing. Again, the inclusion of PL enhanced cellular interactions with the microgel structures. Overall, the combination of biomolecules and fibrin self-assembly arising from the enriched milieu of PL-derived proteins improved the bioactivity of HA-based hydrogels, enabling the formation of dynamic systems with modular design. The granular systems can be engineered to meet the complex demands of functional tissue repair using versatile processing techniques, such as with 3D printing.

Nanocellulose: Recent Fundamental Advances and Emerging Biological and Biomimicking Applications

In the effort toward sustainable advanced functional materials, nanocelluloses have attracted extensive recent attention. Nanocelluloses range from rod-like highly crystalline cellulose nanocrystals to longer and more entangled cellulose nanofibers, earlier denoted also as microfibrillated celluloses and bacterial cellulose. In recent years, they have spurred research toward a wide range of applications, ranging from nanocomposites, viscosity modifiers, films, barrier layers, fibers, structural color, gels, aerogels and foams, and energy applications, until filtering membranes, to name a few. Still, nanocelluloses continue to show surprisingly high challenges to master their interactions and tailorability to allow well-controlled assemblies for functional materials. Rather than trying to review the already extensive nanocellulose literature at large, here selected aspects of the recent progress are the focus. Water interactions, which are central for processing for the functional properties, are discussed first. Then advanced hybrid gels toward (multi)stimuli responses, shape-memory materials, self-healing, adhesion and gluing, biological scaffolding, and forensic applications are discussed. Finally, composite fibers are discussed, as well as nanocellulose as a strategy for improvement of photosynthesis-based chemicals production. In summary, selected perspectives toward new directions for sustainable high-tech functional materials science based on nanocelluloses are described.

Hypoxia-mimicking cobalt-doped multi-walled carbon nanotube nanocomposites enhance the angiogenic capacity of stem cells from apical papilla

Adequate and timely vascularization is crucial for the success of dental pulp tissue engineering. Hypoxia, an important driving force of angiogenesis, plays an important role in this process. However, few studies have investigated the fabrication of hypoxia-simulating biomaterials for dental applications. In this study, a novel hypoxia-mimicking, multi-walled carbon nanotubes/cobalt (MWCNTs/Co) nanocomposite was prepared using the metal-organic framework (MOF) route for the in situ insertion of MWCNTs into Co₃O₄ polyhedra. The obtained nanocomposites were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and thermogravimetric analysis (TGA). Cobalt ion release of MWCNTs/Co was analyzed in vitro. Cell viability and proliferation were assessed by culturing stem cells from apical papilla (SCAP) with MWCNTs/Co nanocomposites. The angiogenic capacity of SCAP after exposure to nanocomposites was evaluated by enzyme-linked immunosorbent assay (ELISA), western blotting and the Matrigel angiogenesis assay. Our results proved that the synthesized MWCNTs/Co nanocomposites possessed a well-designed connecting structure and could release cobalt ions in a sustained way. The MWCNTs/Co nanocomposites at 50 μg/mL significantly upregulated hypoxia-inducible factor-1α (HIF-1α) and vascular endothelial growth factor (VEGF) protein expression in SCAP, with no apparent cellular cytotoxicity. The conditioned medium collected from SCAP treated with MWCNTs/Co markedly promoted endothelial cells vessel formation. In conclusion, hypoxia-mimicking MWCNTs/Co nanocomposites exhibit promising angiogenic potential for dental tissue engineering and might provide an alternative solution for translational applications.

Hydrogels and Dentin-Pulp Complex Regeneration: From the Benchtop to Clinical Translation

Dentin-pulp complex is a term which refers to the dental pulp (DP) surrounded by dentin along its peripheries. Dentin and dental pulp are highly specialized tissues, which can be affected by various insults, primarily by dental caries. Regeneration of the dentin-pulp complex is of paramount importance to regain tooth vitality. The regenerative endodontic procedure (REP) is a relatively current approach, which aims to regenerate the dentin-pulp complex through stimulating the differentiation of resident or transplanted stem/progenitor cells. Hydrogel-based scaffolds are a unique category of three dimensional polymeric networks with high water content. They are hydrophilic, biocompatible, with tunable degradation patterns and mechanical properties, in addition to the ability to be loaded with various bioactive molecules. Furthermore, hydrogels have a considerable degree of flexibility and elasticity, mimicking the cell extracellular matrix (ECM), particularly that of the DP. The current review presents how for dentin-pulp complex regeneration, the application of injectable hydrogels combined with stem/progenitor cells could represent a promising approach. According to the source of the polymeric chain forming the hydrogel, they can be classified into natural, synthetic or hybrid hydrogels, combining natural and synthetic ones. Natural polymers are bioactive, highly biocompatible, and biodegradable by naturally occurring enzymes or via hydrolysis. On the other hand, synthetic polymers offer tunable mechanical properties, thermostability and durability as compared to natural hydrogels. Hybrid hydrogels combine the benefits of synthetic and natural polymers. Hydrogels can be biofunctionalized with cell-binding sequences as arginine-glycine-aspartic acid (RGD), can be used for local delivery of bioactive molecules and cellularized with stem cells for dentin-pulp regeneration. Formulating a hydrogel scaffold material fulfilling the required criteria in regenerative endodontics is still an area of active research, which shows promising potential for replacing conventional endodontic treatments in the near future.

Intraarticular Injection of Infliximab-Loaded Thermosensitive Hydrogel Alleviates Pain and Protects Cartilage in Rheumatoid Arthritis

Purpose

Pain and cartilage destruction caused by rheumatoid arthritis (RA) are major challenges during clinical treatment. Traditional systemic administration not only has obvious side effects but also provides limited relief for local symptoms in major joints. Local delivery of therapeutics for RA treatment is a potential strategy but is limited by rapid intraarticular release.

Materials and Methods

In this study, we prepared a thermoresponsive injectable hydrogel by mixing pluronic F127 (F127) and hyaluronic acid (HA) with poly (γ-glutamic acid) (PGA) incorporating infliximab (IFX), a new generation monoclonal antibody drug. We investigated the biocompatibility of the hydrogel and its IFX release profile. In vivo, we studied the clinical manifestations (articular skin temperature and joint diameter), detected cytokines in the synovial fluid and cartilage, performed behavioral studies on pain relief, and evaluated the cartilage protection effect.

Results

A thermoresponsive hydrogel was successfully prepared by mixing F127, HA, and PGA with injectable properties. The F127-HA-PGA hydrogel had a porous structure with interconnected pores. The infliximab-loaded thermosensitive hydrogel exhibited good biocompatibility and biodegradability and sustained release properties. Intraarticular injection of the IFX-loaded F127-HA-PGA hydrogel could alleviate the expression of inflammatory cytokines, such as tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), interleukin-6 (IL-6), and interleukin-17 (IL-17), in the synovial fluid and cartilage as well as relieve pain and inhibit cartilage destruction in RA.

Conclusion

The double effect on pain relief and cartilage protection indicated the significant potential of the IFX-loaded injectable hydrogel for RA treatment in major joint lesions.

Hyaluronic acid as a bioactive component for bone tissue regeneration: Fabrication, modification, properties, and biological functions

Hyaluronic acid (HA) is widely distributed in the human body, and it is heavily involved in many physiological functions such as tissue hydration, wound repair, and cell migration. In recent years, HA and its derivatives have been widely used as advanced bioactive polymers for bone regeneration. Many medical products containing HA have been developed because this natural polymer has been proven to be nontoxic, noninflammatory, biodegradable, and biocompatible. Moreover, HA-based composite scaffolds have shown good potential for promoting osteogenesis and mineralization. Recently, many HA-based biomaterials have been fabricated for bone regeneration by combining with electrospinning and 3D printing technology. In this review, the polymer structures, processing, properties, and applications in bone tissue engineering are summarized. The challenges and prospects of HA polymers are also discussed.

Alginate/laponite hydrogel microspheres co-encapsulating dental pulp stem cells and VEGF for endodontic regeneration

Considering the complicated and irregular anatomical structure of root canal systems, injectable microspheres have received considerable attention as cell carriers in endodontic regeneration. Herein, we developed injectable hybrid RGD-alginate/laponite (RGD-Alg/Lap) hydrogel microspheres, co-encapsulating human dental pulp stem cells (hDPSCs) and vascular endothelial growth factor (VEGF). These microspheres were prepared by the electrostatic microdroplet method with an average size of 350~450 μm. By adjusting the content of laponite, the rheological properties and the degradation rate of the microspheres in vitro could be conditioned. The release of VEGF from the RGD-Alg/0.5%Lap microspheres was in a sustained manner for 28 days while the bioactivity of VEGF was preserved. In addition, the encapsulated hDPSCs were evenly distributed in microspheres with a cell viability exceeding 85%. The deposition of abundant extracellular matrix such as fibronectin (FN) and collagen type I (Col-I) was shown in microspheres after 7 days. The laponite in the system significantly up-regulated the expression of odontogenic-related genes of hDPSCs at day 7. Furthermore, after subcutaneous implantation with tooth slices in a nude mouse model for 1 month, the hDPSCs-laden RGD-Alg/0.5%Lap+VEGF microspheres significantly promoted the regeneration of pulp-like tissues as well as the formation of new micro-vessels. These results demonstrated the great potential of laponite-enhanced hydrogel microspheres in vascularized dental pulp regeneration. STATEMENT OF SIGNIFICANCE: Injectable cell-laden microspheres have recently gained great attention in endodontic regeneration. Here we first developed hybrid alginate/laponite hydrogel microspheres (size about 350~450 μm) by electrostatic microdroplet method, which exhibited tunability in mechanical property and sustained release ability. The incorporation of laponite and the sustained release of VEGF supported not only dental pulp stem cells differentiation in vitro but neotissue regeneration in vivo. These features combined with the simplicity in preparation, made the microspheres ideally suited to simultaneous cells and growth factors delivery in dental pulp regeneration and even other tissue regeneration application.

Intrinsically Bioactive Cryogels Based on Platelet Lysate Nanocomposites for Hemostasis Applications

The currently used hemostatic agents are highly effective in stopping hemorrhages but have a limited role in the modulation of the wound-healing environment. Herein, we propose an intrinsically bioactive hemostatic cryogel based on platelet lysate (PL) and aldehyde-functionalized cellulose nanocrystals (a-CNCs). PL has attracted great attention as an inexpensive milieu of therapeutically relevant proteins; however, its application as a hemostatic agent exhibits serious constraints (e.g., structural integrity and short shelf-life). The incorporation of a-CNCs reinforced the low-strength PL matrix by covalent cross-linking its amine groups that exhibit an elastic interconnected porous network after full cryogelation. Upon blood immersion, the PL-CNC cryogels absorbed higher volumes of blood at a faster rate than commercial hemostatic porcine gelatin sponges. Simultaneously, the cryogels released biomolecules that increased stem cell proliferation, metabolic activity, and migration as well as downregulated the expression of markers of the fibrinolytic process. In an in vivo liver defect model, PL-CNC cryogels showed similar hemostatic performance in comparison with gelatin sponges and normal material-induced tissue response upon subcutaneous implantation. Overall, owing to their structure and bioactive composition, the proposed PL-CNC cryogels provide an alternative off-the-shelf hemostatic and antibacterial biomaterial with the potential to deliver therapeutically relevant proteins in situ.

Challenges of Engineering Biomimetic Dental and Paradental Tissues

BACKGROUND

Loss of the dental and paradental tissues resulting from trauma, caries or from systemic diseases considered as one of the most significant and frequent clinical problem to the healthcare professionals. Great attempts have been implemented to recreate functionally, healthy dental and paradental tissues in order to substitute dead and diseased tissues resulting from secondary trauma of car accidents, congenital malformations of cleft lip and palate or due to acquired diseases such as cancer and periodontal involvements.

METHOD

An extensive literature search has been done on PubMed database from 2010 to 2019 about the challenges of engineering a biomimetic tooth (BioTooth) regarding basic biology of the tooth and its supporting structures, strategies, and different techniques of obtaining biological substitutes for dental tissue engineering.

RESULTS

It has been found that great challenges need to be considered before engineering biomimetic individual parts of the tooth such as enamel, dentin-pulp complex and periodontium. In addition, two approaches have been adopted to engineer a BioTooth. The first one was to engineer a BioTooth as an individual unit and the other was to engineer a BioTooth with its supporting structures.

CONCLUSION

Engineering of BioTooth with its supporting structures thought to be in the future will replace the traditional and conventional treatment modalities in the field of dentistry. To accomplish this goal, different cell lines and growth factors with a variety of scaffolds at the nano-scale level are now in use. Recent researches in this area of interest are dedicated for this objective, both in vivo and in vitro. Despite progress in this field, there are still many challenges ahead and need to be overcome, many of which related to the basic tooth biology and its supporting structures and some others related to the sophisticated techniques isolating cells, fabricating the needed scaffolds and obtaining the signaling molecules.

Bioactive molecule carrier systems in endodontics

INTRODUCTION

Bioactive molecule carrier systems (BACS) are biomaterial-based substrates that facilitate the delivery of active signaling molecules for different biologically based therapeutic applications, which include regenerative endodontic procedures. Tissue regeneration or organized repair in regenerative endodontic procedures is governed by the dynamic orchestration of interactions between stem/progenitor cells, bioactive molecules, and extracellular matrix. BACS aid in mimicking some of the complex physiological processes, overcoming some of the challenges faced in the clinical translation of regenerative endodontic procedures.

AREAS COVERED

This narrative review addresses the role of BACS in stem/progenitor cell proliferation, migration, and differentiation with the application for dentin-pulp tissue engineering both in vitro and in vivo. BACS shield the bioactivity of the immobilized molecules against environmental factors, while its design allows the pre-programmed release of bioactive molecules in a spatial and temporal-controlled manner. The polymeric and non-polymeric materials used to synthesize micro and nanoscale-based BACS are reviewed.

EXPERT OPINION

Comprehensive characterization of well-designed and customized BACS is necessary to be able to deliver multiple bioactive molecules in spatiotemporally controlled manner and to address the release kinetics required for potential in vivo application. This warrants further laboratory-based experiments and rigorous clinical investigations to enable their clinical translation for regenerative endodontic procedures.

Injectable Biomaterials for Dental Tissue Regeneration

Injectable biomaterials scaffolds play a pivotal role for dental tissue regeneration, as such materials are highly applicable in the dental field, particularly when compared to pre-formed scaffolds. The defects in the maxilla-oral area are normally small, confined and sometimes hard to access. This narrative review describes different types of biomaterials for dental tissue regeneration, and also discusses the potential use of nanofibers for dental tissues. Various studies suggest that tissue engineering approaches involving the use of injectable biomaterials have the potential of restoring not only dental tissue function but also their biological purposes.

Platelet-rich Blood Derivatives for Tendon Regeneration

Tendon injuries constitute a significant healthcare problem with variable clinical outcomes. The complex interplay of tissue homeostasis, degeneration, repair, and regeneration makes the development of successful delivery therapeutic strategies challenging. Platelet-rich hemoderivatives, a source of supra-physiologic concentrations of human therapeutic factors, are a promising application to treat tendon injuries from the perspective of tendon tissue engineering, although the outcomes remain controversial.

Platelet-rich plasma combined with injectable hyaluronic acid hydrogel for porcine cartilage regeneration: a 6-month follow-up

Based on our previous study, the utilization of an ultraviolet light photo-cross-linkable hyaluronic acid (HA) hydrogel integrated with a small molecule kartogenin-encapsulated nanoparticles obtained good reconstruction of osteochondral defects in a rabbit model, indicating the superiority of injectable hydrogel-based scaffolds in cartilage tissue engineering. Platelet-rich plasma (PRP), rich in various growth factors, proteins and cytokines, is considered to facilitate cartilage healing by stimulating cell proliferation and inducing chondrogenesis in cartilage defect site. The aim of this study was to test the therapeutic feasibility of autologous PRP combined with injectable HA hydrogel on cartilage repair. The focal cartilage defects with different critical sizes in the medial femoral condyle of a porcine model were used. At 6 months, the minipigs were sacrificed for assessment of macroscopic appearance, magnetic resonance imaging, micro-computed tomography, histology staining and biomechanics. The HA hydrogel combined with PRP-treated group showed more hyaline-like cartilage exhibited by macroscopic appearance and histological staining in terms of extracellular matrix and type II collagen without formation of hypertrophic cartilage, indicating its capacity to improve cartilage healing in the minipig model evaluated at 6 months, with full-thickness cartilage defect of 8.5 mm diameter and osteochondral defect of 6.5 mm diameter, 5 mm depth exhibiting apparent regeneration.

The application of hyaluronic acid in bone regeneration

Hyaluronic acid (HA) exists naturally as an important component of the extracellular matrix (ECM) in the human body. In recent decades, HA has been widely used in bone regeneration, and is currently a popular topic, particularly in the craniofacial and dental fields. From maxilla augmentation to craniofacial bone trauma, there is now a large demand for bone regenerative therapy. Serving as a cell-seeding scaffold or a carrier for bioactive components, hyaluronic acid-incorporated scaffolds and carriers in bone regeneration can be fabricated into either rigid or colloidal forms. Since the type of material used is a critical factor in the biological properties of a scaffold, HA derivatives or HA-incorporated composite scaffolds have shown excellent potential for improving osteogenesis and mineralization. Furthermore, in order to better enhance osteogenesis, local delivery carriers based on hyaluronic acid derivatives, rather than specifically serving as scaffolds, can be established by loading different osteoinductive or osteogenetic components and acquiring different release patterns. Such osteoinductive carriers immobilized on implant surfaces are also effective in improving osseointegration. Thus, as such a competent biomaterial, hyaluronic acid should be considered a promising tool in bone regeneration.

Injectable Click-Crosslinked Hyaluronic Acid Depot To Prolong Therapeutic Activity in Articular Joints Affected by Rheumatoid Arthritis

The aim of this study was to design a click-crosslinked hyaluronic acid (HA) (Cx-HA) depot via a click crosslinking reaction between tetrazine-modified HA and trans-cyclooctene-modified HA for direct intra-articular injection into joints affected by rheumatoid arthritis (RA). The Cx-HA depot had significantly more hydrogel-like features and a longer in vivo residence time than the HA depot. Methotrexate (MTX)-loaded Cx-HA (MTX-Cx-HA)-easily prepared as an injectable formulation-quickly formed an MTX-Cx-HA depot that persisted at the injection site for an extended period. In vivo MTX biodistribution in MTX-Cx-HA depots showed that a high concentration of MTX persisted at the intra-articular injection site for an extended period, with little distribution of MTX to normal tissues. In contrast, direct intra-articular injection of MTX alone or MTX-HA resulted in rapid clearance from the injection site. After intra-articular injection of MTX-Cx-HA into rats with RA, we noted the most significant RA reversal, measured by an articular index score, increased cartilage thickness, extensive generation of chondrocytes and glycosaminoglycan deposits, extensive new bone formation in the RA region, and suppression of tumor necrosis factor-α or interleukin-6 expression. Therefore, MTX-Cx-HA injected intra-articularly persists at the joint site in therapeutic MTX concentrations for an extended period, thus increasing the duration of RA treatment, resulting in an improved relief of RA.

Acellular biomaterial strategies for endodontic regeneration

Dental decay is treated by removing infected dental tissues such as dentine and restoring the tooth with a material. However, the vast majority of these materials have been designed to be mechanically robust and bioinert, whereas the potential regenerative properties of a biomaterial have not been considered. In endodontics for example, materials are used to seal the pulp cavity to avoid bacterial colonisation of the tooth and prevent further infection. While these treatments are effective in the short term, many of these materials have not been designed to interface with the pulp tissue in a biocompatible manner and are often cytotoxic. This can lead to less favourable long-term outcomes such as devitalisation of the tooth via root-canal therapy or extraction of the tooth. Clinical outcomes could be improved if regenerative approaches were followed whereby the biology of the tooth is engineered for repair and regeneration often with the support of a biomaterial. Within these, acellular or cell homing approaches are particularly interesting, as some regulatory hurdles associated with cellular therapies could be circumvented which may aid their clinical translation. In this review, we highlight progress in regenerative dentistry and focus on exciting developments using acellular biomaterials for regenerating dental tissues.

A review on cellulose nanocrystals as promising biocompounds for the synthesis of nanocomposite hydrogels

Hydrogels are hydrophilic cross-linked polymer networks formed via the simple reaction of one or more monomers with the ability to retain a significant extent of water. Owing to an increased demand for environmentally friendly, biodegradable, and biocompatible products, cellulose nanocrystals (CNCs) with high hydrophilicity have emerged as a promising sustainable material for the formation of hydrogels. The cytocompatibility, swellability, and non-toxicity make CNC hydrogels of great interest in biomedical, biosensing, and wastewater treatment applications. There has been a considerable progress in the research of CNC hydrogels, as the number of scientific publications has exponentially increased (>600%) in the last five years. In this paper, recent progress in CNC hydrogels with particular emphasis on design, materials, and fabrication techniques to control hydrogel architecture, and advanced applications are discussed.

Photocrosslinked hydrogels from coumarin derivatives of hyaluronic acid for tissue engineering applications

Hydrogels are an increasingly attractive choice in the fields of regenerative medicine, wound care and tissue engineering as important forms of bio-scaffolds. For many clinical needs, injectable in situ crosslinkable hydrogels are strongly preferred, due to treatment effectiveness and ease of use. In this study, hyaluronic acid (HA), containing side-arms linked to photo-active coumarin moieties, was used for the preparation of wall-to-wall hydrogels. This photocrosslinkable HA, hereafter called HA-TEG-coumarin, produces colourless aqueous solutions that solidify upon near-UV irradiation (at a specific wavelength of 365 nm) via a clean [2 + 2] photocycloaddition reaction, without by-products formation. The crosslinking event, a robust and non-cytotoxic process, does not require catalysts or radical initiators: in the field of hyaluronan photocrosslinking, this innovative feature is significant to ensure the whole biocompatibility and to avoid collateral reactions. Mechanical and rheological tests showed that hyaluronan derivatives became hydrogels after 3-5 min of irradiation, with average values for bulk and surface elastic moduli of about 32 kPa and 193 kPa, respectively. Fluorescence recovery after photobleaching (FRAP) assay showed that the hydrogels are porous and allow a good permeation for nutrients and growth factors. Cell metabolism and proliferation assays revealed that hydrogel-encapsulated fibroblasts maintained their viability and that HA-TEG-coumarin sustained the proliferation of non-adherent myoblasts. For all of these reasons and thanks to a safe free-radical approach, this novel hyaluronan coumarin derivative could be a good candidate for tissue engineering and regenerative medicine applications.

Growth Factors and Cell Homing in Dental Tissue Regeneration

Purpose of Review

To summarize current views on the role and therapeutic potential of growth factors (GFs) within endodontic cell homing.

Recent Findings

Cell homing/revitalization techniques aim to regenerate dentin and pulp using endogenous cells. Clinically, revitalization has successfully created new vital tissue in necrotic permanent teeth with an open apex; however, there is no evidence of new odontoblasts, pulp tissue, or predictable extension in root length. Although the response is reparative rather than regenerative, exciting opportunities to improve these biologically-based strategies remain by (1) efficiently sequestering dentin-matrix-components (DMCs) using irrigants and dental materials (2) designing next-generation GF-releasing scaffold materials and (3) utilizing other sources of GF such as cells and plasma-rich plasma and plasma-rich fibrin.

Summary

GFs can promote reparative-dentinogenesis and pulp-like tissue formation. The future development and clinical approval of GF-functionalized-scaffolds is a priority; however, current focus should be to harness DMCs and target the interaction of stem cells and GFs.