Injectable Hydrogels as Three-Dimensional Network Reservoirs for Osteoporosis Treatment

Study of Injectable Hydrogel Based on ALN/nHA Promoting Osteogenesis and Inhibiting Osteoclasts in Osteoporotic Bone Defects Repair

Osteoporotic bone defects cannot withstand surgery with more significant trauma due to bone fragility, while systemic drug therapy has formidable adverse effects. Consequently, the present study introduces an innovatively devised injectable double-crosslinked hydrogel, as a potential therapeutic avenue for addressing varied shapes of osteoporotic bone defects via a minimally invasive approach. The injectable hydrogel is formed by the formation of Schiff base bonds between oxidized sodium alginate (OSA) and carboxymethyl chitosan, and the polymerization of gelatin methacrylate by UV light crosslinking. Additionally, alendronate sodium (ALN) is loaded into the hydrogel through Schiff base formation with OSA, and nanohydroxyapatite (nHA) is incorporated into the hydrogel via blending. The hydrogel demonstrates excellent injectability, and the nHA improves the mechanical properties of hydrogel and can promote bone formation. In addition, the hydrogel can sustain the release of ALN, which has the effect of inhibiting osteoclasts. Cell studies indicate that the hydrogel can promote the differentiation of osteoblasts and inhibit the activity of osteoclast, so as to obtain better osteogenic effect. Therefore, the injectable hydrogel can be used to repair osteoporotic bone defects through a minimally invasive, simple treatment modality.

Engineered cyclodextrin-based supramolecular hydrogels for biomedical applications

Cyclodextrin (CD)-based supramolecular hydrogels are polymer network systems with the ability to rapidly form reversible three-dimensional porous structures through multiple cross-linking methods, offering potential applications in drug delivery. Although CD-based supramolecular hydrogels have been increasingly used in a wide range of applications in recent years, a comprehensive description of their structure, mechanical property modulation, drug loading, delivery, and applications in biomedical fields from a cross-linking perspective is lacking. To provide a comprehensive overview of CD-based supramolecular hydrogels, this review systematically describes their design, regulation of mechanical properties, modes of drug loading and release, and their roles in various biomedical fields, particularly oncology, wound dressing, bone repair, and myocardial tissue engineering. Additionally, this review provides a rational discussion on the current challenges and prospects of CD-based supramolecular hydrogels, which can provide ideas for the rapid development of CD-based hydrogels and foster their translation from the laboratory to clinical medicine.

The Potential Therapeutic Effects of Platelet-Derived Biomaterials on Osteoporosis: A Comprehensive Review of Current Evidence

Osteoporosis is a chronic multifactorial condition that affects the skeletal system, leading to the deterioration of bone microstructure and an increased risk of bone fracture. Platelet-derived biomaterials (PDBs), so-called platelet concentrates, such as platelet-rich plasma (PRP) and platelet-rich fibrin (PRF), have shown potential for improving bone healing by addressing microstructural impairment. While the administration of platelet concentrates has yielded positive results in bone regeneration, the optimal method for its administration in the clinical setting is still debatable. This comprehensive review aims to explore the systemic and local use of PRP/PRF for treating various bone defects and acute fractures in patients with osteoporosis. Furthermore, combining PRP/PRF with stem cells or osteoinductive and osteoconductive biomaterials has shown promise in restoring bone microstructural properties, treating bony defects, and improving implant osseointegration in osteoporotic animal models. Here, reviewing the results of in vitro and in vivo studies, this comprehensive evaluation provides a detailed mechanism for how platelet concentrates may support the healing process of osteoporotic bone fractures.

Immune homeostasis modulation by hydrogel-guided delivery systems: a tool for accelerated bone regeneration

Immune homeostasis is delicately mediated by the dynamic balance between effector immune cells and regulatory immune cells. Local deviations from immune homeostasis in the microenvironment of bone fractures, caused by an increased ratio of effector to regulatory cues, can lead to excessive inflammatory conditions and hinder bone regeneration. Therefore, achieving effective and localized immunomodulation of bone fractures is crucial for successful bone regeneration. Recent research has focused on developing localized and specific immunomodulatory strategies using local hydrogel-based delivery systems. In this review, we aim to emphasize the significant role of immune homeostasis in bone regeneration, explore local hydrogel-based delivery systems, discuss emerging trends in immunomodulation for enhancing bone regeneration, and address the limitations of current delivery strategies along with the challenges of clinical translation.

Advances in materials-based therapeutic strategies against osteoporosis

Osteoporosis is caused by the disruption in homeostasis between bone formation and bone resorption. Conventional management of osteoporosis involves systematic drug administration and hormonal therapy. These treatment strategies have limited curative efficacy and multiple adverse effects. Biomaterials-based therapeutic strategies have recently emerged as promising alternatives for the treatment of osteoporosis. The present review summarizes the current status of biomaterials designed for managing osteoporosis. The advantages of biomaterials-based strategies over conventional systematic drug treatment are presented. Different anti-osteoporotic delivery systems are concisely addressed. These materials include injectable hydrogels and nanoparticles, as well as anti-osteoporotic bone tissue engineering materials. Fabrication techniques such as 3D printing, electrostatic spinning and artificial intelligence are appraised in the context of how the use of these adjunctive techniques may improve treatment efficacy. The limitations of existing biomaterials are critically analyzed, together with deliberation of the future directions in biomaterials-based therapies. The latter include discussion on the use of combination strategies to enhance therapeutic efficacy in the osteoporosis niche.

Hydrogel-based delivery system applied in the local anti-osteoporotic bone defects

Osteoporosis is an age-related systemic skeletal disease leading to bone mass loss and microarchitectural deterioration. It affects a large number of patients, thereby economically burdening healthcare systems worldwide. The low bioavailability and complications, associated with systemic drug consumption, limit the efficacy of anti-osteoporosis drugs currently available. Thus, a combination of therapies, including local treatment and systemic intervention, may be more beneficial over a singular pharmacological treatment. Hydrogels are attractive materials as fillers for bone injuries with irregular shapes and as carriers for local therapeutic treatments. They exhibit low cytotoxicity, excellent biocompatibility, and biodegradability, and some with excellent mechanical and swelling properties, and a controlled degradation rate. This review reports the advantages of hydrogels for adjuvants loading, including nature-based, synthetic, and composite hydrogels. In addition, we discuss functional adjuvants loaded with hydrogels, primarily focusing on drugs and cells that inhibit osteoclast and promote osteoblast. Selecting appropriate hydrogels and adjuvants is the key to successful treatment. We hope this review serves as a reference for subsequent research and clinical application of hydrogel-based delivery systems in osteoporosis therapy.

A ROS-Responsive Liposomal Composite Hydrogel Integrating Improved Mitochondrial Function and Pro-Angiogenesis for Efficient Treatment of Myocardial Infarction

Mitochondrial dysfunction of cardiomyocytes (CMs) has been identified as a significant pathogenesis of early myocardial infarction (MI). However, only a few agents or strategies have been developed to improve mitochondrial dysfunction for the effective MI treatment. Herein, a reactive oxygen species (ROS)-responsive PAMB-G-TK/4-arm-PEG-SG hydrogel is developed for localized drug-loaded liposome delivery. Notably, the liposomes contain both elamipretide (SS-31) and sphingosine-1-phosphate (S1P), where SS-31 acts as an inhibitor of mitochondrial oxidative damage and S1P as a signaling molecule for activating angiogenesis. Liposome-encapsulated PAMB-G-TK/4-arm-PEG-SG hydrogels demonstrate myocardium-like mechanical strength and electrical conductivity, and ROS-sensitive release of SS-31 and S1P-loaded liposomes. Further liposomal release of SS-31, which can target cytochrome c in the mitochondrial inner membrane of damaged CMs, inhibits pathological ROS production, improving mitochondrial dysfunction. Meanwhile, S1P released from the liposome induces endothelial cell angiogenesis by activating the S1PR1/PI3K/Akt pathway. In a rat MI model, the resulting liposomal composite hydrogel improves cardiac function by scavenging excess ROS, improving mitochondrial dysfunction, and promoting angiogenesis. This study reports for the first time a liposomal composite hydrogel that can directly target mitochondria of damaged CMs for a feedback-regulated release of encapsulated liposomes to consume the overproduced pathological ROS for improved CM activity and enhanced MI treatment.

Current Status of the Diagnosis and Management of Osteoporosis

Osteoporosis has been defined as the silent disease of the 21st century, becoming a public health risk due to its severity, chronicity and progression and affecting mainly postmenopausal women and older adults. Osteoporosis is characterized by an imbalance between bone resorption and bone production. It is diagnosed through different methods such as bone densitometry and dual X-rays. The treatment of this pathology focuses on different aspects. On the one hand, pharmacological treatments are characterized by the use of anti-resorptive drugs, as well as emerging regenerative medicine treatments such as cell therapies and the use of bioactive hydrogels. On the other hand, non-pharmacological treatments are associated with lifestyle habits that should be incorporated, such as physical activity, diet and the cessation of harmful habits such as a high consumption of alcohol or smoking. This review seeks to provide an overview of the theoretical basis in relation to bone biology, the existing methods for diagnosis and the treatments of osteoporosis, including the development of new strategies.

3D Printed Gene-Activated Sodium Alginate Hydrogel Scaffolds

Gene therapy is one of the most promising approaches in regenerative medicine to restore damaged tissues of various types. However, the ability to control the dose of bioactive molecules in the injection site can be challenging. The combination of genetic constructs, bioresorbable material, and the 3D printing technique can help to overcome these difficulties and not only serve as a microenvironment for cell infiltration but also provide localized gene release in a more sustainable way to induce effective cell differentiation. Herein, the cell transfection with plasmid DNA directly incorporated into sodium alginate prior to 3D printing was investigated both in vitro and in vivo. The 3D cryoprinting ensures pDNA structure integrity and safety. 3D printed gene-activated scaffolds (GAS) mediated HEK293 transfection in vitro and effective synthesis of model EGFP protein in vivo, thereby allowing the implementation of the developed GAS in future tissue engineering applications.

A dual crosslinked hydrogel-mediated integrated peptides and BMSC therapy for myocardial regeneration

The efficacy of myocardial regeneration strategies for myocardial infarction (MI) is significantly compromised by the complex structure and microenvironment of the myocardium. Although tissue engineering strategies based on cell therapy and/or pro-angiogenesis can somewhat improve cardiac function, the lack of proper myocardial materials that can withstand sustained deformability and adaptable mechanical properties severely affects myocardial wall integrity, systolic-diastolic cycles, and regeneration. Herein, we developed an integrated single "all-in-one" in situ dual crosslinking conductive hydrogel with favorable treatment properties termed as MaHA/B-G-SH/Fe³⁺ by ionic interactions and chemical covalency based on modified hyaluronic acid (HA), gelatin (G), and Fe³⁺. The resulting dual crosslinking dynamic hydrogel not only provides self-healing and mechanical properties adapted to the myocardial systolic-diastolic cycle with simultaneous electrical signal transmission to fibrous islands and normal tissue, but also leads to significant increase of the myocardial wall thickness very close to that of normal myocardium upon one single injection with complete degradation within 28 days. Notably, the hydrogel covalently conjugated with a tailored peptide sequence of GGR-KLT and encapsulated with bone mesenchymal stem cells (BMSCs) was further used for in situ injection in a rat MI model, which exhibited (i) efficient inhibition of excessive matrix degradation dependent on early MMP-2 expression, (ii) triggered on-demand release of KLT for at least 14 days and significant promotion of angiogenesis, and (iii) synergistic BMSCs considerably enhanced myocardial regeneration within 28 days. Taken together, the dual crosslinking conductive hydrogel-mediated synergistic peptide and cell therapy provides comprehensive recovery and regeneration of the structure and function of the injured myocardium, thus demonstrating great potential for clinical translations.