A Tetra-PEG Hydrogel Based Aspirin Sustained Release System Exerts Beneficial Effects on Periodontal Ligament Stem Cells Mediated Bone Regeneration

Material-Mediated Immunotherapy to Regulate Bone Aging and Promote Bone Repair

As the global population ages, an increasing number of elderly people are experiencing weakened bone regenerative capabilities, resulting in slower bone repair processes and associated risks of various complications. This review outlines the research progress on biomaterials that promote bone repair through immunotherapy. This review examines how manufacturing technologies such as 3D printing, electrospinning, and microfluidic technology contribute to enhancing the therapeutic effects of these biomaterials. Following this, it provides detailed introductions to various anti-osteoporosis drug delivery systems, such as injectable hydrogels, nanoparticles, and engineered exosomes, as well as bone tissue engineering materials and coatings used in immunomodulation. Moreover, it critically analyzes the current limitations of biomaterial-mediated bone immunotherapy and explores future research directions for material-mediated bone immunotherapy. This review aims to inspire new approaches and broaden perspectives in addressing the challenges of bone repair and aging by exploring innovative biomaterial-mediated immunotherapy strategies.

Composite Graphene for the Dimension- and Pore-Size-Mediated Stem Cell Differentiation to Bone Regenerative Medicine

As one of the most promising means to repair diseased tissues, stem cell therapy with immense potential to differentiate into mature specialized cells has been rapidly developed. However, the clinical application of stem-cell-dominated regenerative medicine was heavily hindered by the loss of pluripotency during the long-term in vitro expansion. Here, a composite three-dimensional (3D) graphene-based biomaterial, denoted as GO-Por-CMP@CaP, with hierarchical pore structure (micro- to macropore), was developed to guide the directional differentiation of human umbilical cord MSCs (hucMSCs) into osteoblasts. GO-Por-CMP@CaP could act as a high-efficiency living composite material without a "dead space", effectively regulating the cellular response. The 3D topological structure generated via the two-step modification on two-dimensional graphene could effectively mimic the natural 3D microenvironment of cells, enhancing the stem cell attachment, which is not only conducive for the proliferation of stem cells but also beneficial for the osteogenic differentiation. Meanwhile, the wide existence of interconnected macropores was favorable for bone ingrowth, capillary formation, as well as the nutrients transportation. Furthermore, the concurrent existence of micro- and mesopores significantly promoted the extracellular matrix (ECM) adsorption, which ensured cellular attachment, leading to multiscale osteointegration. Both in vitro and in vivo assay demonstrated the above three factors collaborated mutually with nanosized calcium phosphate (CaP, with chemical similarities to the inorganic components of bone), which provided abundant adhesive sites to adequately induce osteogenic differentiation in the absence of any soluble growth factors. Proteomic analysis experiments confirmed that GO-Por-CMP@CaP promoted the differentiation of hucMSCs cells into osteoblasts by affecting the PI3K-Akt signaling pathway through the up-regulation of SPP1 protein. Our study offers a pure material-based stem cell differentiation regulating behavior via engineering the dimension and porosity of material, which provides insights into the design and development of substitutes to bone repair materials.

Aspirin Inhibits the In Vitro Adipogenic Differentiation of Human Adipose Tissue-Derived Stem Cells in a Dose-Dependent Manner

Aspirin (ASA) is one of the most used medications worldwide and has shown various effects on cellular processes, including stem cell differentiation. However, the effect of ASA on adipogenesis of adipose tissue-derived stem cells (ASCs) remains largely unknown. Considering the potential application of ASCs in regenerative medicine and cell-based therapies, this study investigates the effects of ASA on adipogenic differentiation in human ASCs. ASCs were exposed to varying concentrations of ASA (0 µM, 400 µM, and 1000 µM) and evaluated for changes in morphology, migration, and adipogenic differentiation. While ASA exposure did not affect self-renewal potential, migration ability, or cell morphology, it significantly reduced lipid vacuole formation at 1000 µM after 21 days of adipogenic differentiation (p = 0.0025). This visible inhibition correlated with decreased expression of adipogenic markers (PPARG, ADIPOQ, and FABP4) and the proliferation marker MKi67 under ASA exposure in comparison to the control (ns). Overall, the findings demonstrate that ASA inhibits adipogenic differentiation of human ASCs in a dose-dependent manner in vitro, contrasting its known role in promoting osteogenic differentiation. This research highlights ASA's complex effects on ASCs and emphasizes the need for further investigation into its mechanisms and potential therapeutic applications in obesity and metabolic diseases. The inhibitory effects of ASA on adipogenesis should be considered in cell-based therapies using ASCs.

Prospective and challenges of locally applied repurposed pharmaceuticals for periodontal tissue regeneration

Periodontitis is a persistent inflammatory condition that causes periodontal ligament degradation, periodontal pocket development, and alveolar bone destruction, all of which lead to the breakdown of the teeth's supporting system. Periodontitis is triggered by the accumulation of various microflora (especially anaerobes) in the pockets, which release toxic substances and digestive enzymes and stimulate the immune system. Periodontitis can be efficiently treated using a variety of techniques, both regional and systemic. Effective therapy is dependent on lowering microbial biofilm, minimizing or eradicating pockets. Nowadays, using local drug delivery systems (LDDSs) as an adjuvant therapy to phase I periodontal therapy is an attractive option since it controls drug release, resulting in improved efficacy and lesser adverse reactions. Choosing the right bioactive agent and mode of delivery is the foundation of an efficient periodontal disease management approach. The objective of this paper is to shed light on the issue of successful periodontal regeneration, the drawbacks of currently implemented interventions, and describe the potential of locally delivered repurposed drugs in periodontal tissue regeneration. Because of the multiple etiology of periodontitis, patients must get customized treatment with the primary goal of infection control. Yet, it is not always successful to replace the lost tissues, and it becomes more challenging as the defect gets worse. Pharmaceutical repurposing offers a viable, economical, and safe alternative for non-invasive, and predictable periodontal regeneration. This article clears the way in front of researchers, decision-makers, and pharmaceutical companies to explore the potential, effectiveness, and efficiency of the repurposed pharmaceuticals to generate more economical, effective, and safe topical pharmaceutical preparations for periodontal tissue regeneration.

Application of hydrogel-loaded dental stem cells in the field of tissue regeneration

Mesenchymal stem cells (MSCs) are highly favored in clinical trials due to their unique characteristics, which have isolated from various human tissues. Derived from dental tissues, dental stem cells (DSCs) are particularly notable for their applications in tissue repair and regenerative medicine, attributed to their readily available sources, absence of ethical controversies, and minimal immunogenicity. Hydrogel-loaded stem cell therapy is widespread across a variety of injuries and diseases, and has good repair capabilities for both soft and hard tissues. This review comprehensively summarizes the regenerative and differentiation potential of various DSCs encapsulated in hydrogels across different tissues. In addition, the existing problems and future direction are also addressed. The application of hydrogel-DSCs composite has gained substantial progress in the field of tissue regeneration and need in-depth study in the future.

Research Status and Trends in Periodontal Ligament Stem Cells: A Bibliometric Analysis over the Past Two Decades

Objective

Currently, the summaries of research on periodontal ligament stem cells (PDLSCs) are mainly reviews, and the systematic evaluation of all relevant studies is lacking. The aim of our study was to reveal the research status and developmental trends of PDLSCs using bibliometric analyses.

Methods

Publications on PDLSC from 2004 to 2023 in the PubMed database were searched and then screened according to certain inclusion and exclusion criteria. Two researchers browsed the included papers and recorded information such as the research type and research model. The VOSviewer software was used to analyze the distribution of authors, journals, and institutions. The contents and directions of PDLSC research were summarized by analyzing high-frequency keywords. The CiteSpace software was used to monitor burst words, determine hot factors, and indicate developmental trends.

Results

During the past two decades, the number of studies on PDLSCs increased. China published the most related papers. The primary type of article was basic research. Among core journals, the Journal of Periodontal Research had the highest number of publications. The Fourth Military Medical University (China) was leading in the number of articles on PDLSCs. Research topics mainly included mechanism of periodontal diseases, tissue engineering and regeneration, biological characteristics of PDLSCs, and comparison with other stem cells. Infectious inflammation and mechanical stimulation were important pathological conditions and research topics.

Conclusion

The research of PDLSCs is still in a rapid development stage. Our study provides new insights into the current research status and future trend in this field.

Characterization and biocompatibility of a bilayer PEEK-based scaffold for guiding bone regeneration

BACKGROUND

Polyetheretherketone (PEEK) is well known for its excellent physical-chemical properties and biosafety. The study aimed to open up a new method for clinical application of PEEK to reconstruct large-scale bone defects.

METHODS

A bilayer scaffold for bone regeneration was prepared by combining a sulfonated PEEK barrier framework (SPEEK) with a hydrogel layer loaded with aspirin (ASA) and nano-hydroxyapatite (nHAP) by the wet-bonding of Polydopamine (PDA).

RESULTS

The hydrogel was successfully adhered to the surface of SPEEK, resulting in significant changes including the introduction of bioactive groups, improved hydrophilicity, and altered surface morphology. Subsequent tests confirmed that the bilayer scaffold exhibited enhanced compression resistance and mechanical compatibility with bone compared to a single hydrogel scaffold. Additionally, the bilayer scaffold showed stable and reliable bonding properties, as well as excellent biosafety verified by cell proliferation and viability experiments using mouse embryo osteoblast precursor (MC3T3-E1) cells.

CONCLUSION

The bilayer bone regeneration scaffold prepared in this study showed promising potential in clinical application for bone regeneration.

Aspirin Stimulates the Osteogenic Differentiation of Human Adipose Tissue-Derived Stem Cells In Vitro

This study investigates the impact of acetylsalicylic acid (ASA), also known as aspirin, on adipose tissue-derived stem cells (ASCs), aiming to elucidate its dose-dependent effects on morphology, viability, proliferation, and osteogenic differentiation. Isolated and characterized human ASCs were exposed to 0 µM, 100 µM, 200 µM, 400 µM, 800 µM, 1000 µM, 10,000 µM, and 16,000 µM of ASA in vitro. Cell morphology, viability, and proliferation were evaluated with fluorescent live/dead staining, alamarBlue viability reagent, and CyQUANT® cell proliferation assay, respectively. Osteogenic differentiation under stimulation with 400 µM or 1000 µM of ASA was assessed with alizarin red staining and qPCR of selected osteogenic differentiation markers (RUNX2, SPP1, ALPL, BGLAP) over a 3- and 21-day-period. ASA doses ≤ 1000 µM showed no significant impact on cell viability and proliferation. Live/dead staining revealed a visible reduction in viable cell confluency for ASA concentrations ≥ 1000 µM. Doses of 10,000 µM and 16,000 µM of ASA exhibited a strong cytotoxic and anti-proliferative effect in ASCs. Alizarin red staining revealed enhanced calcium accretion under the influence of ASA, which was macro- and microscopically visible and significant for 1000 µM of ASA (p = 0.0092) in quantification if compared to osteogenic differentiation without ASA addition over a 21-day-period. This enhancement correlated with a more pronounced upregulation of osteogenic markers under ASA exposure (ns). Our results indicate a stimulatory effect of 1000 µM of ASA on the osteogenic differentiation of ASCs. Further research is needed to elucidate the precise molecular mechanisms underlying this effect; however, this discovery suggests promising opportunities for enhancing bone tissue engineering with ASCs as cell source.

Hydrogels promote periodontal regeneration

Periodontal defects involve the damage and loss of periodontal tissue, primarily caused by periodontitis. This inflammatory disease, resulting from various factors, can lead to irreversible harm to the tissues supporting the teeth if not treated effectively, potentially resulting in tooth loss or loosening. Such outcomes significantly impact a patient's facial appearance and their ability to eat and speak. Current clinical treatments for periodontitis, including surgery, root planing, and various types of curettage, as well as local antibiotic injections, aim to mitigate symptoms and halt disease progression. However, these methods fall short of fully restoring the original structure and functionality of the affected tissue, due to the complex and deep structure of periodontal pockets and the intricate nature of the supporting tissue. To overcome these limitations, numerous biomaterials have been explored for periodontal tissue regeneration, with hydrogels being particularly noteworthy. Hydrogels are favored in research for their exceptional absorption capacity, biodegradability, and tunable mechanical properties. They have shown promise as barrier membranes, scaffolds, carriers for cell transplantation and drug delivery systems in periodontal regeneration therapy. The review concludes by discussing the ongoing challenges and future prospects for hydrogel applications in periodontal treatment.

Advances in Hydrogels for Periodontitis Treatment

Periodontitis is a common condition characterized by a bacterial infection and the disruption of the body's immune-inflammatory response, which causes damage to the teeth and supporting tissues and eventually results in tooth loss. Current therapy involves the systemic and local administration of antibiotics. However, the existing treatments cannot exert effective, sustained release and maintain an effective therapeutic concentration of the drug at the lesion site. Hydrogels are used to treat periodontitis due to their low cytotoxicity, exceptional water retention capability, and controlled drug release profile. Hydrogels can imitate the extracellular matrix of periodontal cells while offering suitable sites to load antibiotics. This article reviews the utilization of hydrogels for periodontitis therapy based on the pathogenesis and clinical manifestations of the disease. Additionally, the latest therapeutic strategies for smart hydrogels and the main techniques for hydrogel preparation have been discussed. The information will aid in designing and preparing future hydrogels for periodontitis treatment.

Matrix Metalloproteinase-Responsive Hydrogel with On-Demand Release of Phosphatidylserine Promotes Bone Regeneration Through Immunomodulation

Inflammation-responsive hydrogels loaded with therapeutic factors are effective biomaterials for bone tissue engineering and regenerative medicine. In this study, a matrix metalloproteinase (MMP)-responsive injectable hydrogel is constructed by integrating an MMP-cleavable peptide (pp) into a covalent tetra-armed poly-(ethylene glycol) (PEG) network for precise drug release upon inflammation stimulation. To establish a pro-regenerative environment, phosphatidylserine (PS) is encapsulated into a scaffold to form the PEG-pp-PS network, which could be triggered by MMP to release a large amount of PS during the early stage of inflammation and retain drug release persistently until the later stage of bone repair. The hydrogel is found to be mechanically and biologically adaptable to the complex bone defect area. In vivo and in vitro studies further demonstrated the ability of PEG-pp-PS to transform macrophages into the anti-inflammatory M2 phenotype and promote osteogenic differentiation, thus, resulting in new bone regeneration. Therefore, this study provides a facile, safe, and promising cell-free strategy on simultaneous immunoregulation and osteoinduction in bone engineering.

Preparation of PEG/P(U-AM-ChCl) composite hydrogels using ternary DES light polymerization and their properties

Deep eutectic solvents (DES) were prepared using urea (U) and acrylamide (AM) as hydrogen bond donors (HBD) and choline chloride (ChCl) as hydrogen bond acceptor (HBA), and polyethylene glycol (PEG) was selected as a filler and uniformly dispersed in DES to prepare PEG/P(U-AM-ChCl) composite hydrogels by light polymerization. The composite hydrogels were characterized by scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). The effects of the content of PEG on the swelling properties, mechanical properties and fatigue resistance of the composite hydrogels were investigated. The results showed that the compressive strength and fatigue strength of the composite hydrogels were gradually enhanced with the increase of the PEG content in the composite hydrogels, in which the maximum compressive strength of the hydrogels with 1 wt% PEG added was increased by 1.86 times. The composite hydrogel had excellent swelling properties, and the equilibrium swelling degree of the hydrogel with 1 wt% PEG added reached 10.15. Meanwhile, the PEG/P(U-AM-ChCl) composite hydrogel had excellent self-healing properties, and the self-healing rate of the composite hydrogel with a PFG content of 1 wt% could reach 91.93% after 48 hours of healing. This study provides a convenient and efficient method to prepare composite hydrogels with superior swelling properties and self-healing properties.

Rational design of viscoelastic hydrogels for periodontal ligament remodeling and repair

The periodontal ligament (PDL) is a distinctive yet critical connective tissue vital for maintaining the integrity and functionality of tooth-supporting structures. However, PDL repair poses significant challenges due to the complexity of its mechanical microenvironment encompassing hard-soft-hard tissues, with the viscoelastic properties of the PDL being of particular interest. This review delves into the significant role of viscoelastic hydrogels in PDL regeneration, underscoring their utility in simulating biomimetic three-dimensional microenvironments. We review the intricate relationship between PDL and viscoelastic mechanical properties, emphasizing the role of tissue viscoelasticity in maintaining mechanical functionality. Moreover, we summarize the techniques for characterizing PDL's viscoelastic behavior. From a chemical bonding perspective, we explore various crosslinking methods and characteristics of viscoelastic hydrogels, along with engineering strategies to construct viscoelastic cell microenvironments. We present a detailed analysis of the influence of the viscoelastic microenvironment on cellular mechanobiological behavior and fate. Furthermore, we review the applications of diverse viscoelastic hydrogels in PDL repair and address current challenges in the field of viscoelastic tissue repair. Lastly, we propose future directions for the development of innovative hydrogels that will facilitate not only PDL but also systemic ligament tissue repair. STATEMENT OF SIGNIFICANCE.

Soft and Conductive Polyethylene Glycol Hydrogel Electrodes for Electrocardiogram Monitoring

The measurement of biosignals in the clinical and healthcare fields is fundamental; however, conventional electrodes pose challenges such as incomplete skin contact and skin-related issues, hindering accurate biosignal measurement. To address these challenges, conductive hydrogels, which are valuable owing to their biocompatibility and flexibility, have been widely developed and explored for electrode applications. In this study, we fabricated a conductive hydrogel by mixing polyethylene glycol diacrylate (PEGDA) with poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) polymers dissolved in deionized water, followed by light-triggered crosslinking. Notably, this study pioneered the use of a PEGDA-PEDOT:PSS hydrogel for electrocardiogram (ECG) monitoring- a type of biosignal. The resulting PEGDA-PEDOT:PSS hydrogel demonstrated remarkable conductivity while closely approximating the modulus of skin elasticity. Additionally, it demonstrated biocompatibility and a high signal-to-noise ratio in the waveforms. This study confirmed the exceptional suitability of the PEGDA-PEDOT:PSS hydrogel for accurate biosignal measurements with potential applications in various wearable devices designed for biosignal monitoring.

Acetylsalicylic Acid Promotes Osteogenic Differentiation of Human Dental Pulp Mesenchymal Stem Cells and Regeneration of Alveolar Bone in Experimental Periodontitis Rats

Background

Periodontitis is characterized by bone resorption and periodontal tissue destruction owing to oral microbiota, mechanical stress, and systemic diseases such as diabetes mellitus. Human dental pulp mesenchymal stem cells (hDPMSCs) were analyzed as potential candidates for periodontal tissue regeneration. Acetylsalicylic acid (ASA), also known as aspirin, has been shown to promote osteogenic differentiation of mesenchymal stem cells. We investigated the effect of ASA pretreatment on periodontitis in order to achieve a more appealing prognosis of bone resorption.

Methods

The effect of ASA on cell proliferation was detected by the CCK-8 assay, and alkaline phosphatase (ALP) staining, alizarin red staining (ARS), and western blot were used to investigate the effect of different ASA concentrations on hDPMSCs' osteogenic differentiation and possible signaling pathways. Periodontitis was induced for 4 weeks. Stem cells pretreated with 50 µg/mL of ASA were transplanted into six-week-old male Sprague-Dawley rats by local and systemic injection once a week for two weeks. Four weeks after cell therapy, the rats were sacrificed for sampling to complete the molecular and morphological experiments.

Results

In vitro experiments revealed that 50 µg/mL of ASA had a significant effect on cell osteogenic differentiation. That is, when ASA was administered, the MAPK signaling pathway was activated. Notably, further vivo experiments revealed that ASA-hDPMSCs increased the area of bone regeneration and the OPG/RANKL ratio, suppressed TNF-α and IL-1 expression, and promote alveolar bone repair.

Conclusion

Our study extends the findings of previous research, firstly demonstrating that the use of ASA-pretreated hDPMSCs offers a novel therapy for the treatment of periodontitis for future clinical application.

Advances in combined application of dental stem cells and small-molecule drugs in regenerative medicine

Teeth are a kind of masticatory organs of special histological origin, unique to vertebrates, playing an important role in chewing, esthetics, and auxiliary pronunciation. In the past decades, with the development of tissue engineering and regenerative medicine, the studies of mesenchymal stem cells (MSCs) gradually attracted the interest of researchers. Accordingly, several types of MSCs have been successively isolated in teeth or teeth-related tissues, including dental pulp stem cells, periodontal ligament stem cells, stem cells from human exfoliated deciduous teeth, dental follicle stem cells, stem cells from apical papilla and gingival mesenchymal stem cells. These dental stem cells (DSCs) are easily accessible, possess excellent stem cell characteristics, such as high proliferation rates and profound immunomodulatory properties. Small-molecule drugs are widely used and show great advantages in clinical practice. As research progressed, small-molecule drugs are found to have various complex effects on the characteristics of DSCs, especially the enhancement of biological characteristics of DSCs, which has gradually become a hot issue in the field of DSCs research. This review summarizes the background, current status, existing problems, future research directions, and prospects of the combination of DSCs with three common small-molecule drugs: aspirin, metformin, and berberine.

Aspirin synergizes with mineral particle-coated macroporous scaffolds for bone regeneration through immunomodulation

Rationale: Mineral particles have been widely used in bone tissue engineering scaffolds due to their osteoconductive and osteoinductive properties. Despite their benefits, mineral particles can induce undesirable inflammation and subsequent bone resorption. Aspirin (Asp) is an inexpensive and widely used anti-inflammatory drug. The goal of this study is to assess the synergistic effect of Asp and optimized mineral particle coating in macroporous scaffolds to accelerate endogenous bone regeneration and reduce bone resorption in a critical-sized bone defect model. Methods: Four commonly used mineral particles with varying composition (hydroxyapatite v.s. tricalcium phosphate) and size (nano v.s. micro) were used. Mineral particles were coated onto gelatin microribbon (µRB) scaffolds. Macrophages (Mφ) were cultured on gelatin µRB scaffolds containing various particles, and Mφ polarization was assessed using PCR and ELISA. The effect of conditioned medium from Mφ on mesenchymal stem cell (MSC) osteogenesis was also evaluated in vitro. Scaffolds containing optimized mineral particles were then combined with varying dosages of Asp to assess the effect in inducing endogenous bone regeneration using a critical-sized cranial bone defect model. In vivo characterization and in vitro cell studies were performed to elucidate the effect of tuning Asp dosage on Mφ polarization, osteoclast (OC) activity, and MSC osteogenesis. Results: Micro-sized tricalcium phosphate (mTCP) particles were identified as optimal in promoting M2 Mφ polarization and rescuing MSC-based bone formation in the presence of conditioned medium from Mφ. When implanted in vivo, incorporating Asp with mTCP-coated µRB scaffolds significantly accelerated endogenous bone formation in a dose-dependent manner. Impressively, mTCP-coated µRB scaffolds containing 20 µg Asp led to almost complete bone healing of a critical-sized cranial bone defect as early as week 2 with no subsequent bone resorption. Asp enhanced M2 Mφ polarization, decreased OC activity, and promoted MSC osteogenesis in a dosage-dependent manner in vivo. These results were further validated using in vitro cell studies. Conclusions: Here, we demonstrate Asp and mineral particle-coated microribbon scaffold provides a promising therapy for repairing critical-sized cranial bone defects via immunomodulation. The leading formulation supports rapid endogenous bone regeneration without the need for exogenous cells or growth factors, making it attractive for translation. Our results also highlight the importance of optimizing mineral particles and Asp dosage to achieve robust bone healing while avoiding bone resorption by targeting Mφ and OCs.

Adult Mesenchymal Stem Cells from Oral Cavity and Surrounding Areas: Types and Biomedical Applications

Adult mesenchymal stem cells are those obtained from the conformation of dental structures (DMSC), such as deciduous and permanent teeth and other surrounding tissues. Background: The self-renewal and differentiation capacities of these adult stem cells allow for great clinical potential. Because DMSC are cells of ectomesenchymal origin, they reveal a high capacity for complete regeneration of dental pulp, periodontal tissue, and other biomedical applications; their differentiation into other types of cells promotes repair in muscle tissue, cardiac, pancreatic, nervous, bone, cartilage, skin, and corneal tissues, among others, with a high predictability of success. Therefore, stem and progenitor cells, with their exosomes of dental origin and surrounding areas in the oral cavity due to their plasticity, are considered a fundamental pillar in medicine and regenerative dentistry. Tissue engineering (MSCs, scaffolds, and bioactive molecules) sustains and induces its multipotent and immunomodulatory effects. It is of vital importance to guarantee the safety and efficacy of the procedures designed for patients, and for this purpose, more clinical trials are needed to increase the efficacy of several pathologies. Conclusion: From a bioethical and transcendental anthropological point of view, the human person as a unique being facilitates better clinical and personalized therapy, given the higher prevalence of dental and chronic systemic diseases.

New Challenges and Prospective Applications of Three-Dimensional Bioactive Polymeric Hydrogels in Oral and Craniofacial Tissue Engineering: A Narrative Review

Regenerative medicine, and dentistry offers enormous potential for enhancing treatment results and has been fueled by bioengineering breakthroughs over the previous few decades. Bioengineered tissues and constructing functional structures capable of healing, maintaining, and regenerating damaged tissues and organs have had a broad influence on medicine and dentistry. Approaches for combining bioinspired materials, cells, and therapeutic chemicals are critical in stimulating tissue regeneration or as medicinal systems. Because of its capacity to maintain an unique 3D form, offer physical stability for the cells in produced tissues, and replicate the native tissues, hydrogels have been utilized as one of the most frequent tissue engineering scaffolds during the last twenty years. Hydrogels' high water content can provide an excellent conditions for cell viability as well as an architecture that mimics real tissues, bone, and cartilage. Hydrogels have been used to enable cell immobilization and growth factor application. This paper summarizes the features, structure, synthesis and production methods, uses, new challenges, and future prospects of bioactive polymeric hydrogels in dental and osseous tissue engineering of clinical, exploring, systematical and scientific applications.

PSAT1 positively regulates the osteogenic lineage differentiation of periodontal ligament stem cells through the ATF4/PSAT1/Akt/GSK3β/β-catenin axis

BACKGROUND

Periodontal ligament stem cells (PDLSCs) are important seed cells for tissue engineering to realize the regeneration of alveolar bone. Understanding the gene regulatory mechanisms of osteogenic lineage differentiation in PDLSCs will facilitate PDLSC-based bone regeneration. However, these regulatory molecular signals have not been clarified.

METHODS

To screen potential regulators of osteogenic differentiation, the gene expression profiles of undifferentiated and osteodifferentiated PDLSCs were compared by microarray and bioinformatics methods, and PSAT1 was speculated to be involved in the gene regulation network of osteogenesis in PDLSCs. Lentiviral vectors were used to overexpress or knock down PSAT1 in PDLSCs, and then the proliferation activity, migration ability, and osteogenic differentiation ability of PDLSCs in vitro were analysed. A rat mandibular defect model was built to analyse the regulatory effects of PSAT1 on PDLSC-mediated bone regeneration in vivo. The regulation of PSAT1 on the Akt/GSK3β/β-catenin signalling axis was analysed using the Akt phosphorylation inhibitor Ly294002 or agonist SC79. The potential sites on the promoter of PSAT1 that could bind to the transcription factor ATF4 were predicted and verified.

RESULTS

The microarray assay showed that the expression levels of 499 genes in PDLSCs were altered significantly after osteogenic induction. Among these genes, the transcription level of PSAT1 in osteodifferentiated PDLSCs was much lower than that in undifferentiated PDLSCs. Overexpressing PSAT1 not only enhanced the proliferation and osteogenic differentiation abilities of PDLSCs in vitro, but also promoted PDLSC-based alveolar bone regeneration in vivo, while knocking down PSAT1 had the opposite effects in PDLSCs. Mechanistic experiments suggested that PSAT1 regulated the osteogenic lineage fate of PDLSCs through the Akt/GSK3β/β-catenin signalling axis. PSAT1 expression in PDLSCs during osteogenic differentiation was controlled by transcription factor ATF4, which is realized by the combination of ATF4 and the PSAT1 promoter.

CONCLUSION

PSAT1 is a potential important regulator of the osteogenic lineage differentiation of PDLSCs through the ATF4/PSAT1/Akt/GSK3β/β-catenin signalling pathway. PSAT1 could be a candidate gene modification target for enhancing PDLSCs-based bone regeneration.

Drug delivery systems based on polyethylene glycol hydrogels for enhanced bone regeneration

Drug delivery systems composed of osteogenic substances and biological materials are of great significance in enhancing bone regeneration, and appropriate biological carriers are the cornerstone for their construction. Polyethylene glycol (PEG) is favored in bone tissue engineering due to its good biocompatibility and hydrophilicity. When combined with other substances, the physicochemical properties of PEG-based hydrogels fully meet the requirements of drug delivery carriers. Therefore, this paper reviews the application of PEG-based hydrogels in the treatment of bone defects. The advantages and disadvantages of PEG as a carrier are analyzed, and various modification methods of PEG hydrogels are summarized. On this basis, the application of PEG-based hydrogel drug delivery systems in promoting bone regeneration in recent years is summarized. Finally, the shortcomings and future developments of PEG-based hydrogel drug delivery systems are discussed. This review provides a theoretical basis and fabrication strategy for the application of PEG-based composite drug delivery systems in local bone defects.

Applications of regenerative techniques in adult orthodontics

Management of the growing adult orthodontic patient population must contend with challenges particular to orthodontic treatment in adults. These include a limited rate of tooth movement, increased incidence of periodontal complications, higher risk of iatrogenic root resorption and pulp devitalisation, resorbed edentulous ridges, and lack of growth potential. The field of regenerative dentistry has evolved numerous methods of manipulating cellular and molecular processes to rebuild functional oral and dental tissues, and research continues to advance our understanding of stem cells, signalling factors that stimulate repair and extracellular scaffold interactions for the purposes of tissue engineering. We discuss recent findings in the literature to synthesise our understanding of current and prospective approaches based on biological repair that have the potential to improve orthodontic treatment outcomes in adult patients. Methods such as mesenchymal stem cell transplantation, biomimetic scaffold manipulation, and growth factor control may be employed to overcome the challenges described above, thereby reducing adverse sequelae and improving orthodontic treatment outcomes in adult patients. The overarching goal of such research is to eventually translate these regenerative techniques into clinical practice, and establish a new gold standard of safe, effective, autologous therapies.

Controlled Delivery of Corticosteroids Using Tunable Tough Adhesives

Hydrogel-based drug delivery systems typically aim to release drugs locally to tissue in an extended manner. Tissue adhesive alginate-polyacrylamide tough hydrogels are recently demonstrated to serve as an extended-release system for the corticosteroid triamcinolone acetonide. Here, the stimuli-responsive controlled release of triamcinolone acetonide from the alginate-polyacrylamide tough hydrogel drug delivery systems (TADDS) and evolving new approaches to combine alginate-polyacrylamide tough hydrogel with drug-loaded nano and microparticles, generating composite TADDS is described. Stimulation with ultrasound pulses or temperature changes is demonstrated to control the release of triamcinolone acetonide from the TADDS. The incorporation of laponite nanoparticles or PLGA microparticles into the tough hydrogel is shown to further enhance the versatility to control and modulate the release of triamcinolone acetonide. A first technical exploration of a TADDS shelf-life concept is performed using lyophilization, where lyophilized TADDS are physically stable and the bioactive integrity of released triamcinolone acetonide is demonstrated. Given the tunability of properties, the TADDS are a suggested technology platform for controlled drug delivery.

Advances of Hydrogel Therapy in Periodontal Regeneration-A Materials Perspective Review

Hydrogel, a functional polymer material, has emerged as a promising technology for therapies for periodontal diseases. It has the potential to mimic the extracellular matrix and provide suitable attachment sites and growth environments for periodontal cells, with high biocompatibility, water retention, and slow release. In this paper, we have summarized the main components of hydrogel in periodontal tissue regeneration and have discussed the primary construction strategies of hydrogels as a reference for future work. Hydrogels provide an ideal microenvironment for cells and play a significant role in periodontal tissue engineering. The development of intelligent and multifunctional hydrogels for periodontal tissue regeneration is essential for future research.

Investigation of heparin-loaded poly(ethylene glycol)-based hydrogels as anti-thrombogenic surface coatings for extracorporeal membrane oxygenation

Extracorporeal membrane oxygenation (ECMO), a critical life-sustaining tool, faces significant challenges for the maintenance of normal haemostasis due to the large volume of circulating blood continuously in contact with artificial surfaces, hyperoxia and excessive shear stresses of the extracorporeal circuit. From a biomaterials perspective, it has been hypothesised that drug eluting coatings composed of haemocompatible hydrogels loaded with an anticoagulant drug could potentially enhance the haemocompatibility of the circuit. Poly(ethylene glycol) (PEG) has been well established as a biocompatible and anti-fouling material with wide biomedical application. Unfractionated heparin is the most commonly used anticoagulant for ECMO. In the present study, the feasibility of using heparin-loaded PEG-based hydrogels as anti-thrombogenic surface coatings for ECMO was investigated. The hydrogels were synthesised by photopolymerisation using poly(ethylene glycol) diacrylate (PEGDA) as the crosslinking monomer and poly(ethylene glycol) methacrylate (PEGMA) as the hydrophilic monomer, with heparin loaded into the pre-gel solution. Factors which could affect the release of heparin were investigated, including the ratio of PEGDA/PEGMA, water content, loading level of heparin and the flow of fluid past the hydrogel. Our results showed that increased crosslinker content and decreased water content led to slower heparin release. The hydrogels with water contents of 60 wt% and 70 wt% could achieve a sustained heparin release by adjusting the ratio of PEGDA/PEGMA. The anticoagulation efficacy of the released heparin was evaluated by measuring the activated clotting time of whole blood. The hydrogels with desirable heparin release profiles were prepared onto poly(4-methyl-1-pentene) (PMP) films with the same chemical composition as the PMP ECMO membranes. The coatings showed sustained heparin release with a cumulative release of 70-80% after 7 days. Haemocompatibility tests demonstrated that PEG hydrogel coatings significantly reduced platelet adhesion and prolonged plasma recalcification time. These results suggest that heparin-loaded PEG hydrogels are potential anti-thrombogenic coatings for ECMO.

Aspirin effect on bone remodeling and skeletal regeneration: Review article

Bone tissues are one of the most complex tissues in the body that regenerate and repair themselves spontaneously under the right physiological conditions. Within the limitations of treating bone defects, mimicking tissue engineering through the recruitment of scaffolds, cell sources and growth factors, is strongly recommended. Aspirin is one of the non-steroidal anti-inflammatory drugs (NSAIDs) and has been used in clinical studies for many years due to its anti-coagulant effect. On the other hand, aspirin and other NSAIDs activate cytokines and some mediators in osteoclasts, osteoblasts and their progenitor cells in a defect area, thereby promoting bone regeneration. It also stimulates angiogenesis by increasing migration of endothelial cells and the newly developed vessels are of emergency in bone fracture repair. This review covers the role of aspirin in bone tissue engineering and also, highlights its chemical reactions, mechanisms, dosages, anti-microbial and angiogenesis activities.

Facile fabrication of a biocompatible composite gel with sustained release of aspirin for bone regeneration

Hydrogels are extracellular-matrix-like biomimetic materials that have wide biomedical applications in tissue engineering and drug delivery. However, most hydrogels cannot simultaneously fulfill the mechanical and cell compatibility requirements. In the present study, we prepared a semi-interpenetrating network composite gel (CG) by incorporating short chain chitosan (CS) into a covalent tetra-armed poly(ethylene glycol) network. In addition to satisfying physicochemical, mechanics, biocompatibility, and cell affinity requirements, this CG easily encapsulated acetylsalicylic acid (ASA) via electrostatic interactions and chain entanglement, achieving sustained release for over 14 days and thus promoting periodontal ligament stem cell (PDLSC) proliferation and osteogenic differentiation. In vivo studies corroborated the capacity of PDLSCs and ASA-laden CG to enhance new bone regeneration in situ using a mouse calvarial bone defect model. This might be attributed to PDLSCs and host mesenchymal stem cells expressing monocyte chemoattractant protein-1, which upregulated M2 macrophage recruitment and polarization in situ, indicating its appealing potential in bone tissue engineering.

Fabrication of Naturally Derived Double-Network Hydrogels With a Sustained Aspirin Release System for Facilitating Bone Regeneration

Continuous efforts on pursuit of effective drug delivery systems for engineering hydrogel scaffolds is considered a promising strategy for the bone-related diseases. Here, we developed a kind of acetylsalicylic acid (aspirin, ASA)-based double-network (DN) hydrogel containing the positively charged natural chitosan (CS) and methacrylated gelatin (GelMA) polymers. Combination of physical chain-entanglement, electrostatic interactions, and a chemically cross-linked methacrylated gelatin (GelMA) network led to the formation of a DN hydrogel, which had a suitable porous structure and favorable mechanical properties. After in situ encapsulation of aspirin agents, the resulting hydrogels were investigated as culturing matrices for adipose tissue-derived stromal cells (ADSCs) to evaluate their excellent biocompatibility and biological capacities on modulation of cell proliferation and differentiation. We further found that the long-term sustained ASA in the DN hydrogels could contribute to the anti-inflammation and osteoinductive properties, demonstrating a new strategy for bone tissue regeneration.

Human periodontal ligament stem cells with distinct osteogenic potential induce bone formation in rat calvaria defects

Aim: This study aimed to evaluate the ability of human periodontal ligament stem cells (PDLSCs) with high (HP-PDLSCs) and low (LP-PDLSCs) osteogenic potential, in addition to mixed cells, to repair bone tissue. Methods: Cell phenotype, proliferation and differentiation were evaluated. Undifferentiated PDLSCs were injected into rat calvarial defects and the new bone was evaluated by μCT, histology and real-time PCR. Results: PDLSCs exhibited a typical mesenchymal stem cell phenotype and HP-PDLSCs showed lower proliferative and higher osteogenic potential than LP-PDLSCs. PDLSCs induced similar bone formation and histological analysis suggests a remodeling process, confirmed by osteogenic and osteoclastogenic markers, especially in tissues derived from defects treated with HP-PDLSCs. Conclusion: PDLSCs induced similar bone formation irrespective of their in vitro osteogenic potential.

The application of human periodontal ligament stem cells and biomimetic silk scaffold for in situ tendon regeneration

BACKGROUND

With the development of tissue engineering, enhanced tendon regeneration could be achieved by exploiting suitable cell types and biomaterials. The accessibility, robust cell amplification ability, superior tendon differentiation potential, and immunomodulatory effects of human periodontal ligament stem cells (hPDLSCs) indicate their potential as ideal seed cells for tendon tissue engineering. Nevertheless, there are currently no reports of using PDLSCs as seed cells. Previous studies have confirmed the potential of silk scaffold for tendon tissue engineering. However, the biomimetic silk scaffold with tendon extracellular matrix (ECM)-like structure has not been systematically studied for in situ tendon regeneration. Therefore, this study aims to evaluate the effects of hPDLSCs and biomimetic silk scaffold on in situ tendon regeneration.

METHODS

Human PDLSCs were isolated from extracted wisdom teeth. The differentiation potential of hPDLSCs towards osteo-, chondro-, and adipo-lineage was examined by cultured in different inducing media. Aligned and random silk scaffolds were fabricated by the controlled directional freezing technique. Scaffolds were characterized including surface structure, water contact angle, swelling ratio, degradation speed and mechanical properties. The biocompatibility of silk scaffolds was evaluated by live/dead staining, SEM observation, cell proliferation determination and immunofluorescent staining of deposited collagen type I. Subsequently, hPDLSCs were seeded on the aligned silk scaffold and transplanted into the ruptured rat Achilles tendon. Scaffolds without cells served as control groups. After 4 weeks, histology evaluation was carried out and macrophage polarization was examined to check the repair effects and immunomodulatory effects.

RESULTS

Human PDLSCs were successfully isolated, and their multi-differentiation potential was confirmed. Compared with random scaffold, aligned silk scaffold had more elongated and aligned pores and promoted the proliferation and ordered arrangement of hPDLSCs. After implantation into rat Achilles tendon defect, hPDLSCs seeded aligned silk scaffold enhanced tendon repair with more tendon-like tissue formation after 4 weeks, as compared to the scaffold-only groups. Higher expression of CD206 and lower expression of iNOS, IL-1β and TNF-α were found in the hPDLSCs seeded aligned silk scaffold group, which revealed its modulation effect of macrophage polarization from M1 to M2 phenotype.

CONCLUSIONS

In summary, this study demonstrates the efficacy of hPDLSCs as seed cells and aligned silk scaffold as a tendon-mimetic scaffold for enhanced tendon tissue engineering, which may have broad implications for future tendon tissue engineering and regenerative medicine researches.

Aspirin impacts on stem cells: Implications for therapeutic targets

Despite the regenerative potential of stem cell therapy in pre-clinical investigations, clinical translation of cell-based therapy has not been completely clarified. In recent years, the importance of lifestyle, patient comorbidities, and prescribed medication has attracted more attention in the efficacy of cell therapy. As a nonsteroidal anti-inflammatory drug, aspirin is one of the most prevalent prescribed medications in the clinic for various disorders. Hence, aspirin treatment might affect the efficacy of stem cell therapy. In this regard, the current review focused on the impacts of aspirin on the viability, proliferation, differentiation, and immunomodulatory properties of stem cells in vitro as well as in experimental animal models.

Activated Carbon Fiber Cloth/Biomimetic Apatite: A Dual Drug Delivery System

A biomaterial that is both bioactive and capable of controlled drug release is highly attractive for bone regeneration. In previous works, we demonstrated the possibility of combining activated carbon fiber cloth (ACC) and biomimetic apatite (such as calcium-deficient hydroxyapatite (CDA)) to develop an efficient material for bone regeneration. The aim to use the adsorption properties of an activated carbon/biomimetic apatite composite to synthetize a biomaterial to be used as a controlled drug release system after implantation. The adsorption and desorption of tetracycline and aspirin were first investigated in the ACC and CDA components and then on ACC/CDA composite. The results showed that drug adsorption and release are dependent on the adsorbent material and the drug polarity/hydrophilicity, leading to two distinct modes of drug adsorption and release. Consequently, a double adsorption approach was successfully performed, leading to a multifunctional and innovative ACC-aspirin/CDA-tetracycline implantable biomaterial. In a second step, in vitro tests emphasized a better affinity of the drug (tetracycline or aspirin)-loaded ACC/CDA materials towards human primary osteoblast viability and proliferation. Then, in vivo experiments on a large cortical bone defect in rats was carried out to test biocompatibility and bone regeneration ability. Data clearly highlighted a significant acceleration of bone reconstruction in the presence of the ACC/CDA patch. The ability of the aspirin-loaded ACC/CDA material to release the drug in situ for improving bone healing was also underlined, as a proof of concept. This work highlights the possibility of bone patches with controlled (multi)drug release features being used for bone tissue repair.

Bioinformatics Analysis Identified miR-584-5p and Key miRNA-mRNA Networks Involved in the Osteogenic Differentiation of Human Periodontal Ligament Stem Cells

Human periodontal ligament cells (PDLCs) play an important role in periodontal tissue stabilization and function. In the process of osteogenic differentiation of PDLSCs, the regulation of molecular signal pathways are complicated. In this study, the sequencing results of three datasets on GEO were used to comprehensively analyze the miRNA-mRNA network during the osteogenic differentiation of PDLSCs. Using the GSE99958 and GSE159507, a total of 114 common differentially expressed genes (DEGs) were identified, including 62 up-regulated genes and 52 down-regulated genes. GO enrichment analysis was performed. The up-regulated 10 hub genes and down-regulated 10 hub genes were screened out by protein-protein interaction network (PPI) analysis and STRING in Cytoscape. Similarly, differentially expressed miRNAs (DEMs) were selected by limma package from GSE159508. Then, using the miRwalk website, we further selected 11 miRNAs from 16 DEMs that may have a negative regulatory relationship with hub genes. In vitro RT-PCR verification revealed that nine DEMs and 18 hub genes showed the same trend as the RNA-seq results during the osteogenic differentiation of PDLSCs. Finally, using miR-584-5p inhibitor and mimics, it was found that miR-584-5p negatively regulates the osteogenic differentiation of PDLSCs in vitro. In summary, the present results found several potential osteogenic-related genes and identified candidate miRNA-mRNA networks for the further study of osteogenic differentiation of PDLSCs.

Dental-Derived Mesenchymal Stem Cells: State of the Art

Mesenchymal stem cells (MSCs) could be identified in mammalian teeth. Currently, dental-derived MSCs (DMSCs) has become a collective term for all the MSCs isolated from dental pulp, periodontal ligament, dental follicle, apical papilla, and even gingiva. These DMSCs possess similar multipotent potential as bone marrow-derived MSCs, including differentiation into cells that have the characteristics of odontoblasts, cementoblasts, osteoblasts, chondrocytes, myocytes, epithelial cells, neural cells, hepatocytes, and adipocytes. Besides, DMSCs also have powerful immunomodulatory functions, which enable them to orchestrate the surrounding immune microenvironment. These properties enable DMSCs to have a promising approach in injury repair, tissue regeneration, and treatment of various diseases. This review outlines the most recent advances in DMSCs' functions and applications and enlightens how these advances are paving the path for DMSC-based therapies.

Preparation and osteogenic properties of nanocomposite hydrogel beads loaded with nanometric bioactive glass particles

Bone reconstruction in the oral and maxillofacial region presents particular challenges related to the development of biomaterials with osteoinductive properties and suitable physical characteristics for their surgical use in irregular bony defects. In this work, the preparation and bioactivity of chitosan-gelatin (ChG) hydrogel beads loaded with either bioactive glass nanoparticles (nBG) or mesoporous bioactive glass nanospheres (nMBG) were studied.In vitrotesting of the bionanocomposite beads was carried out in simulated body fluid, and through viability and osteogenic differentiation assays using dental pulp stem cells (DPSCs).In vivobone regenerative properties of the biomaterials were assessed using a rat femoral defect model and compared with a traditional maxillary allograft (Puros®). ChG hydrogel beads containing homogeneously distributed BG nanoparticles promoted rapid bone-like apatite mineralization and induced the osteogenic differentiation of DPSCsin vitro. The bionanocomposite beads loaded with either nBG or nMBG also produced a greater bone tissue formationin vivoas compared to Puros® after 8 weeks of implantation. The osteoinductivity capacity of the bionanocomposite hydrogel beads coupled with their physical properties make them promissory for the reconstruction of irregular and less accessible maxillary bone defects.

A review of biomimetic scaffolds for bone regeneration: Toward a cell-free strategy

In clinical terms, bone grafting currently involves the application of autogenous, allogeneic, or xenogeneic bone grafts, as well as natural or artificially synthesized materials, such as polymers, bioceramics, and other composites. Many of these are associated with limitations. The ideal scaffold for bone tissue engineering should provide mechanical support while promoting osteogenesis, osteoconduction, and even osteoinduction. There are various structural complications and engineering difficulties to be considered. Here, we describe the biomimetic possibilities of the modification of natural or synthetic materials through physical and chemical design to facilitate bone tissue repair. This review summarizes recent progresses in the strategies for constructing biomimetic scaffolds, including ion-functionalized scaffolds, decellularized extracellular matrix scaffolds, and micro- and nano-scale biomimetic scaffold structures, as well as reactive scaffolds induced by physical factors, and other acellular scaffolds. The fabrication techniques for these scaffolds, along with current strategies in clinical bone repair, are described. The developments in each category are discussed in terms of the connection between the scaffold materials and tissue repair, as well as the interactions with endogenous cells. As the advances in bone tissue engineering move toward application in the clinical setting, the demonstration of the therapeutic efficacy of these novel scaffold designs is critical.

Influence of Materials Properties on Bio-Physical Features and Effectiveness of 3D-Scaffolds for Periodontal Regeneration

Periodontal diseases are multifactorial disorders, mainly due to severe infections and inflammation which affect the tissues (i.e., gum and dental bone) that support and surround the teeth. These pathologies are characterized by bleeding gums, pain, bad breath and, in more severe forms, can lead to the detachment of gum from teeth, causing their loss. To date it is estimated that severe periodontal diseases affect around 10% of the population worldwide thus making necessary the development of effective treatments able to both reduce the infections and inflammation in injured sites and improve the regeneration of damaged tissues. In this scenario, the use of 3D scaffolds can play a pivotal role by providing an effective platform for drugs, nanosystems, growth factors, stem cells, etc., improving the effectiveness of therapies and reducing their systemic side effects. The aim of this review is to describe the recent progress in periodontal regeneration, highlighting the influence of materials' properties used to realize three-dimensional (3D)-scaffolds, their bio-physical characteristics and their ability to provide a biocompatible platform able to embed nanosystems.

A Current Overview of Scaffold-Based Bone Regeneration Strategies with Dental Stem Cells

Bone defects due to trauma or diseases still pose a clinical challenge to be resolved in the current tissue engineering approaches. As an alternative to traditional methods to restore bone defects, such as autografts, bone tissue engineering aims to achieve new bone formation via novel biomaterials used in combination with multipotent stem cells and bioactive molecules. Mesenchymal stem cells (MSCs) can be successfully isolated from various dental tissues at different stages of development including dental pulp, apical papilla, dental follicle, tooth germ, deciduous teeth, periodontal ligament and gingiva. A wide range of biomaterials including polymers, ceramics and composites have been investigated for their potential as an ideal bone scaffold material. This article reviews the properties and the manufacturing methods of biomaterials used in bone tissue engineering, and provides an overview of bone tissue regeneration approaches of scaffold and dental stem cell combinations as well as their limitations.

Gold nanorods enable noninvasive longitudinal monitoring of hydrogels in vivo with photoacoustic tomography

Longitudinal in vivo monitoring is essential for the design and evaluation of biomaterials. An ideal method would provide three-dimensional quantitative information, high spatial resolution, deep tissue penetration, and contrast between tissue and material structures. Photoacoustic (PA) or optoacoustic imaging is a hybrid technique that allows three-dimensional imaging with high spatial resolution. In addition, photoacoustic imaging allows for imaging of vascularization based on the intrinsic contrast of hemoglobin. In this study, we investigated photoacoustic computed tomography (PACT) as a tool for longitudinal monitoring of an implanted hydrogel in a small animal model. Hydrogels were loaded with gold nanorods to enhance contrast and imaged weekly for 8 weeks. PACT allowed non-invasive three-dimensional, quantitative imaging of the hydrogels over the entire 8 weeks. Quantitative volume analysis was used to evaluate the in vivo degradation kinetics of the implants which deviated slightly from in vitro predictions. Multispectral imaging allowed for the simultaneous analysis of hydrogel degradation and local vascularization. These results provide support for the substantial potential of PACT as a tool for insight into biomaterial performance in vivo.

The Delivery of RNA-Interference Therapies Based on Engineered Hydrogels for Bone Tissue Regeneration

RNA interference (RNAi) is an efficient post-transcriptional gene modulation strategy mediated by small interfering RNAs (siRNAs) and microRNAs (miRNAs). Since its discovery, RNAi has been utilized extensively to diagnose and treat diseases at both the cellular and molecular levels. However, the application of RNAi therapies in bone regeneration has not progressed to clinical trials. One of the major challenges for RNAi therapies is the lack of efficient and safe delivery vehicles that can actualize sustained release of RNA molecules at the target bone defect site and in surrounding cells. One promising approach to achieve these requirements is encapsulating RNAi molecules into hydrogels for delivery, which enables the nucleic acids to be delivered as RNA conjugates or within nanoparticles. Herein, we reviewed recent investigations into RNAi therapies for bone regeneration where RNA delivery was performed by hydrogels.

Synthesis, Characterization, and In Vitro and In Vivo Evaluations of Cellulose Hydrogels Enriched with Larrea tridentata for Regenerative Applications

Introduction

Tissue engineering is an elementary necessity for several applications in the biomedical field through the use of several biopolymers derived from plants. Larrea tridentata (LT) is a very used plant for various medicinal applications with interesting properties; however, its use into cellulose hydrogels for possible regenerative therapeutics is still limited. Cellulose films could be applied in medical field as wound healing, scaffold for connective tissue for periodontal applications, and so on. The aim of this study was to evaluate the mechanical properties and in vivo and in vitro biocompatibility of cellulose hydrogels that have been enriched with LT in a rat model.

Methods

By in vivo and in vitro assays, the concentration of LT was varied from 1 to 5 wt%, respectively. Hydrogel films were implanted intramuscularly into female Wistar rats, 250 g in weight and aged 2 months, to analyze their cytocompatibility and biocompatibility.

Results

No case showed any evidence of inflammation or toxicity. Regarding cell morphology and adhesion, the prepared LT cellulose films had better cytocompatibility values than when polystyrene (PS) dishes were used as the control. In all cases, the results suggest that the addition of LT to the hydrogel films did not affect their cytocompatibility or biocompatibility properties and increases their clinical application due to the reported uses of LT.

Conclusions

Cellulose hydrogel films enriched with LT have the potential to be used in the biomedical field acting as regenerative scaffolds.

Advancements in Hydrogel-Based Drug Sustained Release Systems for Bone Tissue Engineering

Bone defects caused by injury, disease, or congenital deformity remain a major health concern, and efficiently regenerating bone is a prominent clinical demand worldwide. However, bone regeneration is an intricate process that requires concerted participation of both cells and bioactive factors. Mimicking physiological bone healing procedures, the sustained release of bioactive molecules plays a vital role in creating an optimal osteogenic microenvironment and achieving promising bone repair outcomes. The utilization of biomaterial scaffolds can positively affect the osteogenesis process by integrating cells with bioactive factors in a proper way. A high water content, tunable physio-mechanical properties, and diverse synthetic strategies make hydrogels ideal cell carriers and controlled drug release reservoirs. Herein, we reviewed the current advancements in hydrogel-based drug sustained release systems that have delivered osteogenesis-inducing peptides, nucleic acids, and other bioactive molecules in bone tissue engineering (BTE).

Long-term delivery of alendronate through an injectable tetra-PEG hydrogel to promote osteoporosis therapy

Pharmacotherapy for hypercalcemia, which is mainly caused by osteoporosis, is an effective method to regulate the in vivo calcium equilibrium. From this perspective, the development of a minimally invasive gelling system for the prolonged local delivery of bisphosphonates has practical significance in the clinical therapy of bone osteoporosis. Here, a biocompatible and injectable hydrogel based on a uniform tetra-PEG network carrying a PEG-modified alendronate (ALN) prodrug for the localized elution and long-term sustained release of anti-osteoporotic small molecule drugs is reported. The obtained ALN-based tetra-PEG hydrogels exhibit rapid gel formation and excellent injectability, thereby allowing for the easy injection and consequent adaptation of hydrogels into the bone defects with irregular shapes, which promotes the ALN-based tetra-PEG hydrogels with depot formulation capacity for governing the on-demand release of ALN drugs and local reinforcement of bone osteoporosis at the implantation sites of animals. The findings imply that these injectable hydrogels mediate the optimized release of therapeutic cargoes and effectively promote in situ bone regeneration via minimally invasive procedures, which is effective for clinical osteoporosis therapy.

Nanoparticle diffusion during gelation of tetra poly(ethylene glycol) provides insight into nanoscale structural evolution

Single particle tracking (SPT) of PEG grafted nanoparticles (NPs) was used to examine the gelation of tetra poly(ethylene glycol) (TPEG) succinimidyl glutarate (TPEG-SG) and amine (TPEG-A) terminated 4-armed stars. As concentration was decreased from 40 to 20 mg mL-1, the onset of network formation, tgel, determined from rheometry increased from less than 2 to 44 minutes. NP mobility increased as polymer concentration decreased in the sol state, but remained diffusive at times past the tgel determined from rheometry. Once in the gel state, NP mobility decreased, became sub-diffusive, and eventually localized in all concentrations. The NP displacement distributions were investigated to gain insight into the nanoscale environment. In these relatively homogeneous gels, the onset of sub-diffusivity was marked by a rapid increase in dynamic heterogeneity followed by a decrease consistent with a homogeneous network. We propose a gelation mechanism in which clusters initially form a heterogeneous structure which fills in to form a fully gelled relatively homogenous network. This work aims to examine the kinetics of TPEG gelation and the homogeneity of these novel gels on the nanometer scale, which will aid in the implementation of these gels in biomedical or filtration applications.