Dual-controlled release system of drugs for bone regeneration

Microenvironment-responsive living hydrogel containing engineered probiotic for treatment of massive bone defects

Self-activating and microenvironment-responsive biomaterials for tissue regeneration would address the escalating need for bone grafting, but remain challenging. The emergence of microbial living therapeutics offers vast potential in regenerative medicine, as genetically engineered probiotics possess efficient stimuli-responsiveness and tunable biological functions. Here, using elevated endogenous nitric oxide (NO) signals as a biological trigger in bone fracture injuries, a Living Responsive Regenerative Medicine (LRRM) strategy for in situ bone defect repair through real-time controlled release of bone morphogenetic protein-2 (BMP2) is proposed. The Escherichia coli Nissle 1917 (EcN) strain, genetically engineered to sense NO signals and correspondingly produce and secrete BMP2, was firstly encapsulated in gelatin methacryloyl (GelMA) microspheres and then embedded in a bulky hyaluronic acid methacryloyl (HAMA) hydrogel to form a living hydrogel device that circumvents immune attack and prevents bacterial leakage. In vivo multiple bone defect models demonstrated the efficacy of the living hydrogel in enhancing the maturation of bone callus, promoting neovascularization, and facilitating full-thickness bone union. Strategic incorporation of engineered probiotics and the bilayer-structured encapsulation system may emerge as an effective and microenvironment-responsive medicine approach for tissue regeneration.

A Review on Bone Tumor Management: Cutting-Edge Strategies in Bone Grafting, Bone Graft Substitute, and Growth Factors for Defect Reconstruction

Bone tumors present complex challenges in orthopaedic oncology, requiring precise management strategies to restore skeletal integrity and function with minimal morbidity. Traditional autologous bone grafting has been the gold standard due to its osteogenic, osteoconductive, and osteoinductive properties. However, limitations such as donor site morbidity and graft availability have prompted the development of alternative approaches.This review evaluates contemporary approaches in bone tumor management, focusing on advancements in bone grafting techniques, bone graft substitutes (eg, ceramics, polymers, bioactive materials), and growth factor-based therapies. The efficacy and safety of these substitutes are compared with autografts, examining their potential benefits and drawbacks.Recent innovations in bone graft substitutes show promise in overcoming autograft limitations. Ceramic, polymer, and bioactive materials offer diverse properties that may enhance bone regeneration. Growth factor-based therapies, including bone morphogenetic proteins (BMPs) and vascular endothelial growth factor (VEGF), have revolutionized bone healing by stimulating osteogenesis and angiogenesis.

Dual release scaffolds as a promising strategy for enhancing bone regeneration: an updated review

Advancements in tissue regeneration, particularly bone regeneration is key area of research due to potential of novel therapeutic approaches. Efforts to reduce reliance on autologous and allogeneic bone grafts have led to the development of biomaterials that promote synchronized and controlled bone healing. However, the use of growth factors is limited by their short half-life, slow tissue penetration, large molecular size and potential toxicity. These factors suggest that traditional delivery methods may be inadequate hence, to address these challenges, new strategies are being explored. These novel approaches include the use of bioactive substances within advanced delivery systems that enable precise spatiotemporal control. Dual-release composite scaffolds offer a promising solution by reducing the need for multiple surgical interventions and simplifying the treatment process. These scaffolds allow for sustained and controlled drug release, enhancing bone repair while minimizing the drawbacks of conventional methods. This review explores various dual-drug release systems, discussing their modes of action, types of drugs used and release mechanisms to improve bone regeneration.

Skeletal interoception and prospective application in biomaterials for bone regeneration

Accumulating research has shed light on the significance of skeletal interoception, in maintaining physiological and metabolic homeostasis related to bone health. This review provides a comprehensive analysis of how skeletal interoception influences bone homeostasis, delving into the complex interplay between the nervous system and skeletal system. One key focus of the review is the role of various factors such as prostaglandin E2 (PGE2) in skeletal health via skeletal interoception. It explores how nerves innervating the bone tissue communicate with the central nervous system to regulate bone remodeling, a process critical for maintaining bone strength and integrity. Additionally, the review highlights the advancements in biomaterials designed to utilize skeletal interoception for enhancing bone regeneration and treatment of bone disorders. These biomaterials, tailored to interact with the body's interoceptive pathways, are positioned at the forefront of innovative treatments for conditions like osteoporosis and fractures. They represent a convergence of bioengineering, neuroscience, and orthopedics, aiming to create more efficient and targeted therapies for bone-related disorders. In conclusion, the review underscores the importance of skeletal interoception in physiological regulation and its potential in developing more effective therapies for bone regeneration. It emphasizes the need for further research to fully understand the mechanisms of skeletal interoception and to harness its therapeutic potential fully.

Delivery of miRNAs Using Porous Silicon Nanoparticles Incorporated into 3D Hydrogels Enhances MSC Osteogenesis by Modulation of Fatty Acid Signaling and Silicon Degradation

Strategies incorporating mesenchymal stromal cells (MSC), hydrogels and osteoinductive signals offer promise for bone repair. Osteoinductive signals such as growth factors face challenges in clinical translation due to their high cost, low stability and immunogenicity leading to interest in microRNAs as a simple, inexpensive and powerful alternative. The selection of appropriate miRNA candidates and their efficient delivery must be optimised to make this a reality. This study evaluated pro-osteogenic miRNAs and used porous silicon nanoparticles modified with polyamidoamine dendrimers (PAMAM-pSiNP) to deliver these to MSC encapsulated within gelatin-PEG hydrogels. miR-29b-3p, miR-101-3p and miR-125b-5p are strongly pro-osteogenic and are shown to target FASN and ELOVL4 in the fatty acid biosynthesis pathway to modulate MSC osteogenesis. Hydrogel delivery of miRNA:PAMAM-pSiNP complexes enhanced transfection compared to 2D. The osteogenic potential of hBMSC in hydrogels with miR125b:PAMAM-pSiNP complexes is evaluated. Importantly, a dual-effect on osteogenesis occurred, with miRNAs increasing expression of alkaline phosphatase (ALP) and Runt-related transcription factor 2 (RUNX2) whilst the pSiNPs enhanced mineralisation, likely via degradation into silicic acid. Overall, this work presents insights into the role of miRNAs and fatty acid signalling in osteogenesis, providing future targets to improve bone formation and a promising system to enhance bone tissue engineering.

Spatiotemporal controlled released hydrogels for multi-system regulated bone regeneration

Bone defect is one of the urgent problems to be solved in clinics, and it is very important to construct efficient scaffold materials to facilitate bone tissue regeneration. Hydrogels, characterized by their unique three-dimensional network structure, serve as excellent biological scaffold materials. Their internal pores are capable of loading osteogenic drugs to expedite bone formation. The rate and quality of new bone formation are intimately linked with immune regulation and vascular remodeling. The strategic sequential release of drugs to balance inflammation and regulate vascular remodeling is crucial for initiating the osteogenic process. Through the design of hydrogel microstructures, it is possible to achieve sequential drug release and the drug action time can be prolonged, thereby catering to the multi-systemic collaborative regulation needs of osteosynthesis. The drug release rate within the hydrogel is governed by swelling control systems, physical control systems, chemical control systems, and environmental control systems. Utilizing these control systems to design hydrogel materials capable of multi-drug delivery optimizes the construction of the bone microenvironment. Consequently, this facilitates the spatiotemporal controlled released of drugs, promoting bone tissue regeneration. This paper reviews the principles of the controlled release system of various sustained-release hydrogels and the advancements in research on hydrogel multi-drug delivery systems for bone tissue regeneration.

Advances and Trends of Photoresponsive Hydrogels for Bone Tissue Engineering

The development of static hydrogels as an optimal choice for bone tissue engineering (BTE) remains a difficult challenge primarily due to the intricate nature of bone healing processes, continuous physiological functions, and pathological changes. Hence, there is an urgent need to exploit smart hydrogels with programmable properties that can effectively enhance bone regeneration. Increasing evidence suggests that photoresponsive hydrogels are promising bioscaffolds for BTE due to their advantages such as controlled drug release, cell fate modulation, and the photothermal effect. Here, we review the current advances in photoresponsive hydrogels. The mechanism of photoresponsiveness and its advanced applications in bone repair are also elucidated. Future research would focus on the development of more efficient, safer, and smarter photoresponsive hydrogels for BTE. This review is aimed at offering comprehensive guidance on the trends of photoresponsive hydrogels and shedding light on their potential clinical application in BTE.

Osteopontine-derived functional fragments coupled to RADA16 self-assembled peptide hydrogels promotes bone and vascular regeneration in vivo

Biomaterial scaffolds have been widely used in tissue engineering. A functionalized self-assembled peptide scaffold named RADA16-OPD was designed by linking the short functional motif of osteopontine (OPN)-derived functional fragments SVVYGLR (OPD) to the C-terminus of the self-assembled peptide RADA16. Atomic force microscopy (AFM) was used to analyze the self-assembling peptide's structural composition. The live/dead staining results showed that RADA16-OPD is not toxic to rASC. After creating a rat skull defect model artificially, micro-CT results revealed that the defect area treated with RADA16-OPD hydrogel had higher bone volume/total volume (BV/TV), a higher trabecular number (TB.N.), and higher bone density (BMD) at different treatment time points. Histological evaluation found that there was more new bone and mature collagen production in the RADA16-OPD group. Meanwhile, the RADA16-OPD group had higher expression of alkaline phosphatase (ALP) and osteocalcin (OCN) than the other two groups. Additionally, immunofluorescence revealed that the RADA16-OPD group had higher levels of platelet/endothelial cell adhesion molecule 1 (CD31) expression than the other two groups. It demonstrated the potential for clinical use of the RADA16-OPD peptide scaffold by promoting bone regeneration and blood vessel development in vivo.

Dual-controlled guest release from coordination cages

Despite having significant applications in the construction of controlled delivery systems with high anti-interference capability, to our knowledge dual-controlled molecular release has not yet been achieved based on small molecular/supramolecular entities. Herein, we report a dual-controlled release system based on coordination cages, for which releasing the guest from the cage demands synchronously altering the coordinative metal cations and the solvent. The cages, Hg5L2 and Ag5L2, are constructed via coordination-driven self-assembly of a corannulene-based ligand. While Hg5L2 shows a solvent-independent guest encapsulation in all the studied solvents, Ag5L2 is able to encapsulate the guests in only some of the solvents, such as acetone-d6, but will liberate the encapsulated guests in 1,1,2,2-tetrachloroethane-d2. Hg5L2 and Ag5L2 are interconvertible. Thus, the release of guests from Hg5L2 in acetone-d6 can be achieved, but requires two separate operations, including metal substitutions and a change of the solvent. Dual-controlled systems as such could be useful in complicated molecular release process to avoid those undesired stimulus-responses.

The development of magnesium-based biomaterials in bone tissue engineering: A review

Bone regeneration is a vital clinical challenge in massive or complicated bone defects. Recently, bone tissue engineering has come to the fore to meet the demand for bone repair with various innovative materials. However, the reported materials usually cannot satisfy the requirements, such as ideal mechanical and osteogenic properties, as well as biocompatibility at the same time. Mg-based biomaterials have considerable potential in bone tissue engineering owing to their excellent mechanical strength and biosafety. Moreover, the biocompatibility and osteogenic activity of Mg-based biomaterials have been the research focuses in recent years. The main limitation faced in the applications of Mg-based biomaterials is rapid degradation, which can produce excessive Mg2+ and hydrogen, affecting the healing of the bone defect. In order to overcome the limitations, researchers have explored several ways to improve the properties of Mg-based biomaterials, including alloying, surface modification with coatings, and synthesizing other composite materials to control the degradation rate upon implantation. This article reviewed the osteogenic mechanism and requirement for appropriate degradation rate and focused on current progress in the biomedical use of Mg-based biomaterials to inspire more clinical applications of Mg in bone regeneration in the future.

NIR light-facilitated bone tissue engineering

In the last decades, near-infrared (NIR) light has attracted considerable attention due to its unique properties and numerous potential applications in bioimaging and disease treatment. Bone tissue engineering for bone regeneration with the help of biomaterials is currently an effective means of treating bone defects. As a controlled light source with deeper tissue penetration, NIR light can provide real-time feedback of key information on bone regeneration in vivo utilizing fluorescence imaging and be used for bone disease treatment. This review provides a comprehensive overview of NIR light-facilitated bone tissue engineering, from the introduction of NIR probes as well as NIR light-responsive materials, and the visualization of bone regeneration to the treatment of bone-related diseases. Furthermore, the existing challenges and future development directions of NIR light-based bone tissue engineering are also discussed. This article is categorized under: Diagnostic Tools > In Vivo Nanodiagnostics and Imaging Implantable Materials and Surgical Technologies > Nanotechnology in Tissue Repair and Replacement.

Architecturally designed sequential-release hydrogels

Drug synergy has made significant strides in clinical applications in recent decades. However, achieving a platform that enables "single administration, multi-stage release" by emulating the natural physiological processes of the human body poses a formidable challenge in the field of molecular pharmaceutics. Hydrogels, as the novel generation of drug delivery systems, have gained widespread utilization in drug platforms owing to their exceptional biocompatibility and modifiability. Sequential drug delivery hydrogels (SDDHs), which amalgamate the advantages of hydrogel and sequential release platforms, offer a promising solution for effectively navigating the intricate human environment and accomplishing drug sequential release. Inspired by architectural design, this review establishes connections between three pivotal factors in SDDHs construction, namely mechanisms, carrier spatial structure, and stimuli-responsiveness, and three aspects of architectural design, specifically building materials, house structures, and intelligent interactive furniture, aiming at providing insights into recent developments in SDDHs. Furthermore, the dual-drug collocation and cutting-edge hydrogel preparation technologies as well as the prevailing challenges in the field were elucidated.

Investigations into the effects of scaffold microstructure on slow-release system with bioactive factors for bone repair

In recent years, bone tissue engineering (BTE) has played an essential role in the repair of bone tissue defects. Although bioactive factors as one component of BTE have great potential to effectively promote cell differentiation and bone regeneration, they are usually not used alone due to their short effective half-lives, high concentrations, etc. The release rate of bioactive factors could be controlled by loading them into scaffolds, and the scaffold microstructure has been shown to significantly influence release rates of bioactive factors. Therefore, this review attempted to investigate how the scaffold microstructure affected the release rate of bioactive factors, in which the variables included pore size, pore shape and porosity. The loading nature and the releasing mechanism of bioactive factors were also summarized. The main conclusions were achieved as follows: i) The pore shapes in the scaffold may have had no apparent effect on the release of bioactive factors but significantly affected mechanical properties of the scaffolds; ii) The pore size of about 400 μm in the scaffold may be more conducive to controlling the release of bioactive factors to promote bone formation; iii) The porosity of scaffolds may be positively correlated with the release rate, and the porosity of 70%-80% may be better to control the release rate. This review indicates that a slow-release system with proper scaffold microstructure control could be a tremendous inspiration for developing new treatment strategies for bone disease. It is anticipated to eventually be developed into clinical applications to tackle treatment-related issues effectively.

Bioactive Polyetheretherketone with Gelatin Hydrogel Leads to Sustained Release of Bone Morphogenetic Protein-2 and Promotes Osteogenic Differentiation

Polyetheretherketone (PEEK) is one of the most promising implant materials for hard tissues due to its similar elastic modulus; however, usage of PEEK is still limited owing to its biological inertness and low osteoconductivity. The objective of the study was to provide PEEK with the ability to sustain the release of growth factors and the osteogenic differentiation of stem cells. The PEEK surface was sandblasted and modified with polydopamine (PDA). Moreover, successful sandblasting and PDA modification of the PEEK surface was confirmed through physicochemical characterization. The gelatin hydrogel was then chemically bound to the PEEK by adding a solution of glutaraldehyde and gelatin to the surface of the PDA-modified PEEK. The binding and degradation of the gelatin hydrogel with PEEK (GPEEK) were confirmed, and the GPEEK mineralization was observed in simulated body fluid. Sustained release of bone morphogenetic protein (BMP)-2 was observed in GPEEK. When cultured on GPEEK with BMP-2, human mesenchymal stem cells (hMSCs) exhibited osteogenic differentiation. We conclude that PEEK with a gelatin hydrogel incorporating BMP-2 is a promising substrate for bone tissue engineering.

Tectorigenin: A Review of Its Sources, Pharmacology, Toxicity, and Pharmacokinetics

Tectorigenin is a well-known natural flavonoid aglycone and an active component that exists in numerous plants. Growing evidence suggests that tectorigenin has multiple pharmacological effects, such as anticancer, antidiabetic, hepatoprotective, anti-inflammatory, antioxidative, antimicrobial, cardioprotective, and neuroprotective. These pharmacological properties provide the basis for the treatment of many kinds of illnesses, including several types of cancer, diabetes, hepatic fibrosis, osteoarthritis, Alzheimer's disease, etc. The purpose of this paper is to provide a comprehensive summary and review of the sources, extraction and synthesis, pharmacological effects, toxicity, pharmacokinetics, and delivery strategy aspects of tectorigenin. Tectorigenin may exert certain cytotoxicity, which is related to the administration time and concentration. Pharmacokinetic studies have demonstrated that the main metabolic pathways in rats for tectorigenin are glucuronidation, sulfation, demethylation and methoxylation, but that it exhibits poor bioavailability. From our perspective, further research on tectorigenin should cover: exploring the pharmacological targets and mechanisms of action; finding an appropriate concentration to balance pharmacological effects and toxicity; attempting diversified delivery strategies to improve the bioavailability; and structural modification to obtain tectorigenin derivatives with higher pharmacological activity.

Molecular Beacon Imaging System to Discriminate the Differentiation State of Cells from Energy Metabolic Pathways

Metabolic pathways of energy production play an essential role as a function of cells. It is well recognized that the differentiation state of stem cells is highly associated with their metabolic profile. Therefore, visualization of the energy metabolic pathway makes it possible to discriminate the differentiation state of cells and predict the cell potential for reprogramming and differentiation. However, at present, it is technically difficult to directly assess the metabolic profile of individual living cells. In this study, we developed an imaging system of cationized gelatin nanospheres (cGNS) incorporating molecular beacons (MB) (cGNSMB) to detect intracellular pyruvate dehydrogenase kinase 1 (PDK1) and peroxisome proliferator-activated receptor γ, coactivator-1α (PGC-1α) mRNA of key regulators in the energy metabolism. The prepared cGNSMB was readily internalized into mouse embryonic stem cells, while their pluripotency was maintained. The high level of glycolysis in the undifferentiated state, the increased oxidative phosphorylation over the spontaneous early differentiation, and the lineage-specific neural differentiation were visualized based on the MB fluorescence. The fluorescence intensity corresponded well to the change of extracellular acidification rate and the oxygen consumption rate of representative metabolic indicators. These findings indicate that the cGNSMB imaging system is a promising tool to visually discriminate the differentiation state of cells from energy metabolic pathways.

Clindamycin phosphate and bone morphogenetic protein-7 loaded combined nanoparticle-graft and nanoparticle-film formulations for alveolar bone regeneration - An in vitro and in vivo evaluation

Commonly utilized techniques for healing alveolar bone destruction such as the use of growth factors, suffering from short half-life, application difficulties, and the ability to achieve bioactivity only in the presence of high doses of growth factor. The sustained release of growth factors through a scaffold-based delivery system offers a promising and innovative tool in dentistry. Furthermore, it is suggested to guide the host response by using antimicrobials together with growth factors to prevent recovery and achieve ideal regeneration. Herein, the aim was to prepare and an in vitro - in vivo evaluation of bone morphogenetic protein 7 (BMP-7) and clindamycin phosphate (CDP) loaded polymeric nanoparticles, and their loading into the alginate-chitosan polyelectrolyte complex film or alloplastic graft to accelerate hard tissue regeneration. PLGA nanoparticles containing CDP and BMP-7, separately or together, were prepared using the double emulsion solvent evaporation technique. Through in vitro assays, it was revealed that spherical particles were homogeneously distributed in the combination formulations, and sustained release could be achieved for >12 weeks with all formulations. Also, results from the micro-CT and histopathological analyses indicated that CDP and BMP-7 loaded nanoparticle-film formulations were more effective in treatment than the nanoparticle loaded grafts.

Icariin Has a Synergistic Effect on the Osteoinductivity of Bone Morphogenetic Protein 2 at Ectopic Sites

OBJECTIVE

Establishing biocompatible, biodegradable, osteoconductive, and osteoinductive bone materials remains a challenging subject in the research of bone healing and bone regeneration. Previously, we demonstrated the osteogenic and osteoconductive effects of biomimetic calcium phosphate (BioCaP) incorporating with Icariin and/or bone morphogenetic protein 2 (BMP-2) at orthotopic sites.

METHODS

By implanting the BioCaP granules incorporated Icariin and/or BMP-2 into the dorsal subcutaneous pockets of adult male Sprague-Dawley (S-D) rats (6-7 weeks old), we investigated the osteoinductive efficacy of the samples. Micro-computed tomography(micro-CT) observations and histological slices were used to verify the osteoinduction of this system on the 2^nd and 5^th week. Statistical significances was evaluated using Turkey's post hoc test of one-way analysis of variance.

RESULTS

The osteoinduction of the BioCaP incorporated with BMP-2 or both agents was confirmed as expected. BioCaP with Icariin alone could not generate bone formation at an ectopic sites. Nevertheless, co-administration of Icariin increased bone mineral density (BMD; p < 0.01) (628mg HA/cm³ vs 570mg HA/cm³ ) and completely changed the distribution of newly formed bone when compared with the granules with BMP-2 alone, even though there was no significant difference in the volume of newly formed bone. In contrast, the BioCaP with both agents (37.86%) had significantly fewer remaining materials than the other groups by the end of the fifth week (53.22%, 53.62% and 48.22%) (p < 0.01).

CONCLUSION

The co-administration of Icariin and BMP-2 increased BMD changed the distribution of newly formed bone, and reduced the amount of remaining materials. Therefore, Icariin can stimulate BMP-2 when incorporated into BioCaP granules at ectopic sites, which makes it useful for bone tissue engineering.

Recent advances in the biosynthesis, bioavailability, toxicology, pharmacology, and controlled release of citrus neohesperidin

Neohesperidin (hesperetin 7-O-neohesperidoside), a well-known flavanone glycoside widely found in citrus fruits, exhibits a variety of biological activities, with potential applications ranging from food ingredients to therapeutics. The purpose of this manuscript is to provide a comprehensive overview of the chemical, biosynthesis, and pharmacokinetics profiles of neohesperidin, as well as the therapeutic effects and mechanisms of neohesperidin against potential diseases. This literature review covers a wide range of pharmacological responses elicited by Neohesperidin, including neuroprotective, anti-inflammatory, antidiabetic, antimicrobial, and anticancer activities, with a focus on the mechanisms of those pharmacological responses. Additionally, the mechanistic pathways underlying the compound's osteoporosis, antiulcer, cardioprotective, and hepatoprotective effects have been outlined. This review includes detailed illustrations of the biosynthesis, biopharmacokinetics, toxicology, and controlled release of neohesperidine. Neohesperidin demonstrated a broad range of therapeutic and biological activities in the treatment of a variety of complex disorders, including neurodegenerative, hepato-cardiac, cancer, diabetes, obesity, infectious, allergic, and inflammatory diseases. Neohesperidin is a promising therapeutic candidate for the management of various etiologically complex diseases. However, further in vivo and in vitro studies on mechanistic potential are required before clinical trials to confirm the safety, bioavailability, and toxicity profiles of neohesperidin.

Dual drug delivery platforms for bone tissue engineering

The dual delivery platforms used in bone tissue engineering provide supplementary bioactive compounds that include distinct medicines and growth factors thereby aiding enhanced bone regeneration. The delivery of these compounds can be adjusted for a short or prolonged time based on the requirement by altering various parameters of the carrier platform. The platforms thus used are fabricated to mimic the niche of the bone microenvironment, either in the form of porous 3D structures, microspheres, or films. Thus, this review article focuses on the concept of dual drug delivery platform and its importance, classification of various platforms for dual drug delivery specific to bone tissue engineering, and finally highlights the foresight into the future direction of these techniques for better clinical applications.

Controlled magnesium ion delivery system for in situ bone tissue engineering

Magnesium cation (Mg²⁺) has been an emerging therapeutic agent for inducing vascularized bone regeneration. However, the therapeutic effects of current magnesium (Mg) -containing biomaterials are controversial due to the concentration- and stage-dependent behavior of Mg²⁺. Here, we first provide an overview of biochemical mechanism of Mg²⁺ in various concentrations and suggest that 2-10 mM Mg²⁺in vitro may be optimized. This review systematically summarizes and discusses several types of controlled Mg²⁺ delivery systems based on polymer-Mg composite scaffolds and Mg-containing hydrogels, as well as their design philosophy and several parameters that regulate Mg²⁺ release. Given that the continuous supply of Mg²⁺ may prevent biomineral deposition in the later stage of bone regeneration and maturation, we highlight the controlled delivery of Mg²⁺ based dual- or multi-ions system, especially for the hierarchical therapeutic ion release system, which shows enhanced biomineralization. Finally, the remaining challenges and perspectives of Mg-containing biomaterials for future in situ bone tissue engineering are discussed as well.

Gelatin Methacryloyl Hydrogels for Musculoskeletal Tissue Regeneration

Musculoskeletal disorders are a significant burden on the global economy and public health. Hydrogels have significant potential for enhancing the repair of damaged and injured musculoskeletal tissues as cell or drug delivery systems. Hydrogels have unique physicochemical properties which make them promising platforms for controlling cell functions. Gelatin methacryloyl (GelMA) hydrogel in particular has been extensively investigated as a promising biomaterial due to its tuneable and beneficial properties and has been widely used in different biomedical applications. In this review, a detailed overview of GelMA synthesis, hydrogel design and applications in regenerative medicine is provided. After summarising recent progress in hydrogels more broadly, we highlight recent advances of GelMA hydrogels in the emerging fields of musculoskeletal drug delivery, involving therapeutic drugs (e.g., growth factors, antimicrobial molecules, immunomodulatory drugs and cells), delivery approaches (e.g., single-, dual-release system), and material design (e.g., addition of organic or inorganic materials, 3D printing). The review concludes with future perspectives and associated challenges for developing local drug delivery for musculoskeletal applications.

Progress in Gelatin as Biomaterial for Tissue Engineering

Tissue engineering has become a medical alternative in this society with an ever-increasing lifespan. Advances in the areas of technology and biomaterials have facilitated the use of engineered constructs for medical issues. This review discusses on-going concerns and the latest developments in a widely employed biomaterial in the field of tissue engineering: gelatin. Emerging techniques including 3D bioprinting and gelatin functionalization have demonstrated better mimicking of native tissue by reinforcing gelatin-based systems, among others. This breakthrough facilitates, on the one hand, the manufacturing process when it comes to practicality and cost-effectiveness, which plays a key role in the transition towards clinical application. On the other hand, it can be concluded that gelatin could be considered as one of the promising biomaterials in future trends, in which the focus might be on the detection and diagnosis of diseases rather than treatment.

Nano Hydroxyapatite for Biomedical Applications Derived from Chemical and Natural Sources by Simple Precipitation Method

In the past, bone fractures due to accidents were rectified by surgery and reconstruction of bone structure. In recent times, researchers have been made to find a solution by producing alternate biomaterials. Hydroxyapatite (HAp) is one of the most important bioactive materials used as a substitute for human hard tissue because of its composition being very similar to human bones and teeth. A study has proved that HAp has been used for bone regeneration in clinical trials in the mid-1980. HAp has been used as implant coatings and graft materials and also used as granules, cement, and pastes for bone regenerative applications. HAp coatings on bioimplants improved biocompatibility, bioactivity, and biological fixation. Moreover, some of the deposition methods can be employed to increase the cellular responses of bone regeneration such as sputtering, spraying, electrodeposition, and pulsed layer deposition. The researcher has prepared hydroxyapatite from chemical and natural sources. The surface area and intrinsic properties of the HAp play a vital role in bone-related applications. This can be achieved by synthesizing the HAp from natural sources rather than synthetic materials. The HAp obtained from the chemical source is not fulfilling the requirements of the natural bone. A variety of biowaste materials such as eggshell, crab shell, snail shell, bovine bone, fishbone, and fish scales are available in nature and can be converted to useful calcium source for HAp. The present study is to produce the HAp from biowaste materials like eggshell and chemical sources using the wet precipitation method. The synthesized HAp is coated on the Ti6Al4V alloy using the electrodeposition method, and it is immersed in SBF solution at 37 °C for corrosion testing. The coated samples are investigated by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), electrochemical study, field emission scanning electron icroscopy (FESEM), energy dispersive X-ray analysis (EDAX), AFM, and antibacterial activity with two different microorganisms. FTIR and XRD confirm the functional groups and crystallinity of the HAp. The good antibacterial activity of the HAp is observed against two bacterial strains. The corrosion studies reveal that the HAp derived from a natural source is eco-friendly and nontoxic and has excellent corrosion resistivity and cell adhesion properties. A strong bond is formed between the naturally derived HAp with bone tissue which is involved in the bio-resorption process and does not pose any side effect to the human body compared to synthetically derived HAp. In addition, the biowaste materials are converted to useful biomaterials and can reduce environmental pollution.

Combining Mg–Zn–Ca Bulk Metallic Glass with a Mesoporous Silica Nanocomposite for Bone Tissue Engineering

Mg–Zn–Ca bulk metallic glass (BMG) is a promising orthopedic fixation implant because of its biodegradable and biocompatible properties. Structural supporting bone implants with osteoinduction properties for effective bone regeneration have been highly desired in recent years. Osteogenic growth peptide (OGP) can increase the proliferation and differentiation of mesenchymal stem cells and enhance the mineralization of osteoblast cells. However, the short half-life and non-specificity to target areas limit applications of OGP. Mesoporous silica nanoparticles (MSNs) as nanocarriers possess excellent properties, such as easy surface modification, superior targeting efficiency, and high loading capacity of drugs or proteins. Accordingly, we propose a system of combining the OGP-containing MSNs with Mg–Zn–Ca BMG materials to promote bone regeneration. In this work, we conjugated cysteine-containing OGP (cgOGP, 16 a.a.) to interior walls of channels in MSNs and maintained the dispersity of MSNs via PEGylation. An in vitro study showed that metal ions released from Mg–Zn–Ca BMG promoted cell proliferation and migration and elevated alkaline phosphatase (ALP) activity and mineralization. On treating cells with both BMG ion-containing Minimum Essential Medium Eagle-alpha modification (α-MEM) and OGP-conjugated MSNs, enhanced focal adhesion turnover and promoted differentiation were observed. Hematological analyses showed the biocompatible nature of this BMG/nanocomposite system. In addition, in vivo micro-computed tomographic and histological observations revealed that our system stimulated osteogenesis and new bone formation around the implant site.

Silencing Gene-Engineered Injectable Hydrogel Microsphere for Regulation of Extracellular Matrix Metabolism Balance

Extracellular matrix (ECM) metabolism balance is essential for maintaining tissue structure and function. However, the complex crosstalk between the ECM, resident cellular, and tissue microenvironment makes long-term maintenance of ECM metabolism balance in an abnormal microenvironment difficult to achieve. Herein, an injectable circRNA silencing-hydrogel microsphere (psh-circSTC2-lipo@MS) is constructed by grafting circSTC2 silencing genes-loaded 1,2-dioleoyl-3-trimethylammonium-propane/cholesterol/1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOTAP/Chol/DOPE) cationic liposomes on methacrylated hyaluronic acid (HAMA) microspheres via amide bonds, which could silence pathological genes in nucleus pulposus (NP) cells to regulate ECM metabolism balance in the nutrient-restricted microenvironment, thereby inhibiting intervertebral disc (IVD) degeneration. HAMA microspheres prepared by microfluidics displayed good degradability, swellability, and injectability. And lipoplexes can be efficiently loaded and released for 27 d through chemical grafting. Cocultured under nutrient-restricted conditions for 72 h, psh-circSTC2-lipo@MS significantly promotes the synthesis of ECM-related proteins and inhibits the secretion of ECM catabolism-related proteases in NP cells. In the rat IVD nutrient-restricted model, local injection of psh-circSTC2-lipo@MS promotes ECM synthesis and restored NP tissue after 8 weeks. In summary, this study confirms that psh-circSTC2-lipo@MS as a safe and controllable targeted gene delivery system has great potential in regulating the ECM metabolism balance under an abnormal microenvironment.

Modulation of Macrophage Response by Copper and Magnesium Ions in Combination with Low Concentrations of Dexamethasone

Macrophages have been deemed crucial for correct tissue regeneration, which is a complex process with multiple overlapping phases, including inflammation. Previous studies have suggested that divalent ions are promising cues that can induce an anti-inflammatory response, since they are stable cues that can be released from biomaterials. However, their immunomodulatory potential is limited in a pro-inflammatory environment. Therefore, we investigated whether copper and magnesium ions combined with low concentrations of the anti-inflammatory drug, dexamethasone (dex), could have a synergistic effect in macrophage, with or without pro-inflammatory stimulus, in terms of morphology, metabolic activity and gene expression. Our results showed that the combination of copper and dex strongly decreased the expression of pro-inflammatory markers, while the combination with magnesium upregulated the expression of IL-10. Moreover, in the presence of a pro-inflammatory stimulus, the combination of copper and dex induced a strong TNF-α response, suggesting an impairment of the anti-inflammatory actions of dex. The combination of magnesium and dex in the presence of a pro-inflammatory stimulus did not promote any improvement in comparison to dex alone. The results obtained in this study could be relevant for tissue engineering applications and in the design of platforms with a dual release of divalent ions and small molecules.

Enzymatically Crosslinked In Situ Synthesized Silk/Gelatin/Calcium Phosphate Hydrogels for Drug Delivery

Our research focuses on combining the valuable properties of silk fibroin (SF) and calcium phosphate (CaP). SF is a natural protein with an easily modifiable structure; CaP is a mineral found in the human body. Most of the new age biocomposites lack interaction between organic/inorganic phase, thus SF/CaP composite could not only mimic the natural bone, but could also be used to make drug delivery systems as well, which can ensure both healing and regeneration. CaP was synthesized in situ in SF at different pH values, and then crosslinked with gelatin (G), horseradish peroxide (HRP), and hydrogen peroxide (H₂O₂). In addition, dexamethasone phosphate (DEX) was incorporated in the hydrogel and drug delivery kinetics was studied. Hydrogel made at pH 10.0 was found to have the highest gel fraction 110.24%, swelling degree 956.32%, and sustained drug delivery for 72 h. The highest cell viability was observed for the hydrogel, which contained brushite (pH 6)-512.43%.

Local dual delivery therapeutic strategies: Using biomaterials for advanced bone tissue regeneration

Bone development is a complex process involving a vast number of growth factors and chemical substances. These factors include transforming growth factor-beta, platelet-derived growth factor, insulin-like growth factor, and most importantly, the bone morphogenetic protein, which exhibits excellent therapeutic value in bone repair. However, the spatial-temporal relationship in the expression of these factors during bone formation makes the bone repair a more complicated process to address. Thus, using a single therapeutic agent to address bone formation does not seem to provide a clinically effective option. Conversely, a dual delivery approach facilitating the co-delivery of agents has proved to be a dynamic alternative since such a strategy can provide more efficient spatial-temporal action. Such delivery systems can smartly target more than one pathway or differentiation lineage and thus offer more efficient bone regeneration. This review discusses various dual delivery strategies reported in the literature employed to achieve improved bone regeneration. These include concurrent use of different therapeutic agents (including growth factors and drugs), enhancing bone formation and cell recruitment, and improving the efficiency of bone healing.

Naringin as Sustained Delivery Nanoparticles Ameliorates the Anti-inflammatory Activity in a Freund's Complete Adjuvant-Induced Arthritis Model

Naringin (NAR), a naturally occurring essential flavonoid, present in grapefruit and Chinese herbal medicines, creates great interest in researchers due to its diverse biological and pharmacological activities. However, further development of NAR is hindered due to its poor water solubility and dissolution rates in GIT. To address these limitations, in this study, we report polymeric nanoparticles (NPs) of NAR (NAR-PLGA-NPs) for enhancing the oral NAR efficiency, with a biodegradable polymer (PLGA) to improve its absorption and bioavailability. NAR-PLGA-NPs were fabricated by a modified solvent emulsification-evaporation technique. Physicochemical properties were evaluated by SEM, particle size distribution, entrapment efficiency, Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and differential scanning calorimetry (DSC). In vitro drug release and ex vivo permeation studies were carried out in phosphate buffer (pH 6.8) for 24 h. Furthermore, in vivo anti-arthritic studies were performed on a mouse model, and the results were compared with free NAR. The modulation of inflammatory mediators was also evidently supported by docking studies. Optimized nanoformulation FN4 (NAR-PLGA-NPs) prepared with acetone-ethanol (2:1) as a solvent system in a combination of stabilizers, i.e., poloxamer-188 and sodium deoxylate (1:1), along with 2% PVA solution, was prepared. From size characterization studies, it was observed that nanoformulations possessed a low particle size (179.7 ± 2.05 nm), a low polydispersity index (0.206 ± 0.001), and a negative zeta potential (-9.18 ± 0.78 mV) with a maximum entrapment efficiency (74 ± 3.61%). The drug release followed a Korsmeyer-Peppas release kinetic model (anomalous non-Fickian diffusion), providing greater NAR release after lyophilization (82.11 ± 3.65%) drug release in pH 6.8 phosphate buffer for 24 h. Ex vivo permeation analysis through an isolated goat intestinal membrane revealed 80.02 ± 3.69% drug release in 24 h. Encapsulation of a drug into PLGA is well described by the results of FTIR, DSC, and XRD. Finally, the therapeutic efficacy of optimized FN4 (NAR-PLGA-NPs) and its possible application on RA were further confirmed in a Freund's complete adjuvant-induced rat arthritic model as against free NAR at a dose of 20 mg/kg body wt. Our findings demonstrate that sustained action of NAR from optimized FN4 NPs with a rate-controlling polymeric carrier system exhibited prolonged circulation time and reduced arthritic inflammation, hence indicating the possibility as a novel strategy to secure the unpropitious biological interactions of hydrophobic NAR in a gastric environment.

Controlled co-delivery system of magnesium and lanthanum ions for vascularized bone regeneration

For craniofacial bone regeneration, how to promote vascularized bone regeneration is still a significant problem, and the controlled release of trace elements vital to osteogenesis has attracted attention. In this study, an ion co-delivery system was developed to promote angiogenesis and osteogenesis. Magnesium ions (Mg²⁺) and lanthanum ions (La³⁺) were selected as biosignal molecules because Mg²⁺can promote angiogenesis and both of them can enhance bone formation. Microspheres made of poly(lactide-co-glycolide) were applied to load La₂(CO₃)₃, which was embedded into a MgO/MgCO₃-loaded cryogel made of photocrosslinkable gelatin methacryloyl to enable co-delivery of Mg²⁺and La³⁺. Evaluations of angiogenesis and osteogenesis were conducted via bothin vitrocell culture using human bone marrow mesenchymal stromal cells andin vivoimplantation using a rat model with calvarial defect (5 mm in diameter). Compared to systems releasing only Mg²⁺or La³⁺, the combination system demonstrated more significant effects on blood vessels formation, thereby promoting the regeneration of vascularized bone tissue. At 8 weeks post-implantation, the new bone volume/total bone volume ratio reached a value of 40.1 ± 0.9%. In summary, a properly designed scaffold system with the capacity to release ions of different bioactivities in a desired pattern can be a promising strategy to meet vascularized bone regeneration requirements.

Co-delivery of simvastatin and demineralized bone matrix hierarchically from nanosheet-based supramolecular hydrogels for osteogenesis

Supramolecular hydrogels are widely used as 3D scaffolds and delivery platforms in tissue engineering applications. However, hydrophobic therapeutic agents exhibit weak compatibility in hydrogel scaffolds along with aggregation and precipitation. Herein, simvastatin drugs used as BMP-2 stimulators are encapsulated into the layer space of LAPONITE® via electrostatic interactions and ion exchange efficiently, and supramolecular hydrogels could be fabricated with a self-healing, injectable and sustained drug release nature. Hydrogels encapsulated with 10 μg mL^-1 simvastatin drug show good osteogenic differentiation in vitro. Moreover, the loading of demineralized bone matrix particles could enhance the capacity for osteogenesis via improving the expression of BMP-2 synergistically. The integrated hydrogels could be implanted into cranial defect sites for bone regeneration in vivo. This work provides the first demonstration of molecular and supramolecular engineering of hydrogels to load osteoinductive agents hierarchically for bone regeneration, contributing to the development of a brand-new strategy for dealing with compatibility between scaffolds and osteogenic agents.

Evaluating Release Kinetics from Alginate Beads Coated with Polyelectrolyte Layers for Sustained Drug Delivery

Current approaches in stem cell-based bone tissue engineering require a release of bioactive compounds over up to 2 weeks. This study presents a polyelectrolyte-layered system featuring sustained release of water-soluble drugs with decreased burst release. The bioactive compounds adenosine 5'-triphosphate (ATP), suramin, and A740003 (a less water-soluble purinergic receptor ligand) were incorporated into alginate hydrogel beads subsequently layered with different polyelectrolytes (chitosan, poly(allyl amine), alginate, or lignosulfonate). Drug release into aqueous medium was monitored over 14 days and evaluated using Korsmeyer-Peppas, Peppas-Sahlin, Weibull models, and a Langmuir-like "Two-Stage" model. Release kinetics strongly depended on both the drug and the polyelectrolyte system. For ATP, five alternating layers of poly(allyl amine) and alginate proved to be most effective in sustaining the release. Release of suramin could be prolonged best with lignosulfonate as polyanion. A740003 showed prolonged release even without layering. Applying polyelectrolyte layers significantly slowed down the burst release. Release curves could be best described with the Langmuir-like model.

A Dual Peptide Sustained-Release System Based on Nanohydroxyapatite/Polyamide 66 Scaffold for Synergistic-Enhancing Diabetic Rats' Fracture Healing in Osteogenesis and Angiogenesis

Diabetes mellitus impairs fracture healing and function of stem cells related to bone regeneration; thus, effective bone tissue engineering therapies can intervene with those dysfunctions. Nanohydroxyapatite/polyamide 66 (n-HA/PA66) scaffold has been used in fracture healing, whereas the low bioactivity limits its further application. Herein, we developed a novel bone morphogenetic protein-2- (BMP-2) and vascular endothelial growth factor- (VEGF) derived peptides-decorated n-HA/PA66 (BVHP66) scaffold for diabetic fracture. The n-HA/PA66 scaffold was functionalized by covalent grafting of BMP-2 and VEGF peptides to construct a dual peptide sustained-release system. The structural characteristics and peptide release profiles of BVHP66 scaffold were tested by scanning electron microscopy, Fourier transform infrared spectroscopy, and fluorescence microscope. Under high glucose (HG) condition, the effect of BVHP66 scaffold on rat bone marrow mesenchymal stem cells’ (rBMSCs) adherent, proliferative, and differentiate capacities and human umbilical vein endothelial cells’ (HUVECs) proliferative and tube formation capacities was assessed. Finally, the BVHP66 scaffold was applied to fracture of diabetic rats, and its effect on osteogenesis and angiogenesis was evaluated. In vitro, the peptide loaded on the BVHP66 scaffold was in a sustained-release mode of 14 days. The BVHP66 scaffold significantly promoted rBMSCs’ and HUVECs’ proliferation and improved osteogenic differentiation of rBMSCs and tube formation of HUVECs in HG environment. In vivo, the BVHP66 scaffold enhanced osteogenesis and angiogenesis, rescuing the poor fracture healing in diabetic rats. Comparing with single peptide modification, the dual peptide-modified scaffold had a synergetic effect on bone regeneration in vivo. Overall, this study reported a novel BVHP66 scaffold with excellent biocompatibility and bioactive property and its application in diabetic fracture.

The design criteria and therapeutic strategy of functional scaffolds for spinal cord injury repair

Spinal cord injury (SCI) remains a therapeutic challenge in clinic. Current drug and cell therapeutics have obtained significant efficacy but are still in the early stages for complete neural and functional recovery. In the past few decades, functional scaffolds (FSs) have been rapidly developed to bridge the lesion and provide a framework for tissue regeneration in SCI repair. Moreover, a FS can act as an adjuvant for locally delivering drugs in the lesion with a designed drug release profile, and supplying a biomimetic environment for implanted cells. In this review, the design criteria of FSs for SCI treatment are summarized according to their biocompatibility, mechanical properties, morphology, architecture, and biodegradability. Subsequently, FSs designed for SCI repair in the scope of drug delivery, cell implantation and combination therapy are introduced, respectively. And how a FS promotes their therapeutic efficacy is analyzed. Finally, the challenges, perspectives, and potential of FSs for SCI treatment are discussed. Hopefully, this review may inspire the future development of potent FSs to facilitate SCI repair in clinic.

The effects of VEGF-centered biomimetic delivery of growth factors on bone regeneration

It is accepted that biomimetic supply of signaling molecules during bone regeneration can provide an appropriate environment for accelerated new bone formation. In this study, we developed a growth factor delivery system based on porous particles and a thermosensitive hydrogel that allowed fast, continuous, and delayed/continuous release of growth factors to mimic their biological production during bone regeneration. It was observed that the Continuous group (continuous release of growth factors) provides a better environment for the osteogenic differentiation of hPDCs than the Biomimetic group (biomimetic release of growth factors), and thus is anticipated to promote bone regeneration. However, contrary to expectation, the Biomimetic group promoted significant new bone formation compared to the Continuous group. From the systematic cell culture experiments, the initial supply of VEGF was considered to have more favorable effects on the osteoclastogenesis than osteogenesis, which may hinder bone regeneration. Our results indicated that the continuous supply of VEGF (in particular, at early stage) from VEGF-loaded biomaterial might not be conducive to new bone formation. Therefore, we suggest that a biomimetic supply of growth factors is a more pivotal parameter for sufficient tissue regeneration. Its use as a molecular delivery system may also serve as a useful tool for the investigation of biological processes and molecules during tissue regeneration processes.

Chitosan/Silver Nanoparticle/Graphene Oxide Nanocomposites with Multi-Drug Release, Antimicrobial, and Photothermal Conversion Functions

In this work, we designed and fabricated a multifunctional nanocomposite system that consists of chitosan, raspberry-like silver nanoparticles, and graphene oxide. The room temperature atmospheric pressure microplasma (RT-APM) process provides a rapid, facile, and environmentally-friendly method for introducing silver nanoparticles into the composite system. Our composite can achieve a pH controlled single and/or dual drug release. Under pH 7.4 for methyl blue loaded on chitosan, the drug release profile features a burst release during the first 10 h, followed by a more stabilized release of 70-80% after 40-50 h. For fluorescein sodium loaded on graphene oxide, the drug release only reached 45% towards the end of 240 h. When the composite acted as a dual drug release system, the interaction of fluorescein sodium and methyl blue slowed down the methyl blue release rate. Under pH 4, both single and dual drug systems showed a much higher release rate. In addition, our composite system demonstrated strong antibacterial abilities against E. coli and S. aureus, as well as an excellent photothermal conversion effect under irradiation of near infrared lasers. The photothermal conversion efficiency can be controlled by the laser power. These unique functionalities of our nanocomposite point to its potential application in multiple areas, such as multimodal therapeutics in healthcare, water treatment, and anti-microbials, among others.

An Elastic Mineralized 3D Electrospun PCL Nanofibrous Scaffold for Drug Release and Bone Tissue Engineering

Complex shaped and critical-sized bone defects have been a clinical challenge for many years. Scaffold-based strategies such as hydrogels provide localized drug release while filling complex defect shapes, but ultimately possess weaknesses in low mechanical strength alongside a lack of macroporous and collagen-mimicking nanofibrous structures. Thus, there is a demand for mechanically strong, extracellular matrix (ECM) mimicking scaffolds that can robustly fit complex shaped critical sized defects and simultaneously provide localized, sustained, multiple growth factor release. We therefore developed a composite, bi-phasic PCL/hydroxyapatite (HA) 3D nanofibrous (NF) scaffold for bone tissue regeneration by using our innovative electrospun-based thermally induced self-agglomeration (TISA) technique. One intriguing feature of our ECM-mimicking TISA scaffolds is that they are highly elastic and porous even after evenly coated with minerals and can easily be pressed to fit different defect shapes. Furthermore, the bio-mimetic mineral deposition technique allowed us to simultaneously encapsulate different type of drugs, e.g., proteins and small molecules, on TISA scaffolds under physiologically mild conditions. Compared to scaffolds with physically surface-adsorbed phenamil, a BMP2 signaling agonist, incorporated phenamil composite scaffolds indicated less burst release and longer lasting sustained release of phenamil with subsequently improved osteogenic differentiation of cells in vitro. Overall, our study indicated that the innovative press-fit 3D NF composite scaffold may be a robust tool for multiple-drug delivery and bone tissue engineering.

Visualization of Apoptosis in Three-Dimensional Cell Aggregates Based on Molecular Beacon Imaging

The objective of this study is to visualize cell apoptosis in three-dimensional (3D) cell aggregates based on molecular beacons (MB). Two types of MB for messenger RNA were used: caspase-3 MB as a target for apoptosis and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) MB as a control of stable fluorescence in cells. To enhance the MB internalization into cells, caspase-3 and GAPDH MB were incorporated in cationized gelatin nanospheres (cGNS), respectively (cGNS_{casp3 MB} and cGNS_{GAP MB}). In addition, cGNS co-incorporating caspase-3 and GAPDH MB (cGNS_{dual MB}) were prepared to perform the dual-color imaging for the same cell aggregate. The cGNS_MB were incubated with mouse mesenchymal stem cells to label with MB in the two-dimensional culture. The cell apoptosis mediated by the addition of antibody for a death receptor Fas was ratiometrically detected by the cGNS_{dual MB} to the same extent as single MB. The cell aggregates were prepared from MB-labeled cells, and the MB fluorescence was detected from almost all the cells even in the 3D aggregates to show the homogenous distribution. In addition to the Fas-mediated apoptosis, the aggregates were treated with camptothecin of a low-molecular weight apoptosis inducer. The fluorescence of caspase-3 MB was mainly distributed at the surface surrounding site of Fas-mediated apoptotic aggregates rather than the center site, while that of GAPDH MB was detected even in the interior site. On the other hand, in the camptothecin-induced apoptotic aggregates, both caspae-3 and GAPDH MB fluorescence were detected from the interior site of aggregates as well as the surrounding site. It is likely that the MB fluorescence reflected the localization of apoptotic position caused by the different molecular sizes of apoptosis inducer and the consequent penetration into the aggregates. It is concluded that the cGMS_MB are a promising system to visualize cell apoptosis in 3D cell aggregates without the destruction of aggregates.

Roles of oxygen level and hypoxia-inducible factor signaling pathway in cartilage, bone and osteochondral tissue engineering

The repair and treatment of articular cartilage injury is a huge challenge of orthopedics. Currently, most of the clinical methods applied in treating cartilage injuries are mainly to relieve pains rather than to cure them, while the strategy of tissue engineering is highly expected to achieve the successful repair of osteochondral defects. Clear understandings of the physiological structures and mechanical properties of cartilage, bone and osteochondral tissues have been established, but the understanding of their physiological heterogeneity still needs further investigation. Apart from the gradients in the micromorphology and composition of cartilage-to-bone extracellular matrixes, an oxygen gradient also exists in natural osteochondral tissue. The response of hypoxia-inducible factor (HIF)-mediated cells to oxygen would affect the differentiation of stem cells and the maturation of osteochondral tissue. This article reviews the roles of oxygen level and HIF signaling pathway in the development of articular cartilage tissue, and their prospective applications in bone and cartilage tissue engineering. The strategies for regulating HIF signaling pathway and how these strategies finding their potential applications in the regeneration of integrated osteochondral tissue are also discussed.

Multidrug-loaded electrospun micro/nanofibrous membranes: Fabrication strategies, release behaviors and applications in regenerative medicine

Electrospun micro/nanofibrous membranes (EFMs) have been widely investigated as local drug delivery systems. Multiple drugs can be simultaneously incorporated into one EFM to create synergistic effects, reduce side effects, and play their respective roles in the complex physiological processes of tissue regeneration and postoperative adhesion prevention. Due to the versatile electrospinning techniques, sustained and programmed release behaviors of multiple drugs could be achieved by modulating the structure of the EFMs and the location of the drugs. In this review, various multidrug incorporation approaches based on electrospinning are overviewed. In particular, the advantages and limitations of each drug incorporation technique, the methods to control drug release and the effect of one drug release on another are discussed. Then the applications of multidrug-loaded EFMs in regenerative medicine, including wound healing, bone regeneration, vascular tissue engineering, nerve regeneration, periodontal regeneration and adhesion prevention are comprehensively reviewed. Finally, the future perspectives and challenges in the research of multidrug-loaded EFMs are discussed.

Hydrogel Encapsulation of Mesenchymal Stem Cells and Their Derived Exosomes for Tissue Engineering

Tissue engineering has been an inveterate area in the field of regenerative medicine for several decades. However, there remains limitations to engineer and regenerate tissues. Targeted therapies using cell-encapsulated hydrogels, such as mesenchymal stem cells (MSCs), are capable of reducing inflammation and increasing the regenerative potential in several tissues. In addition, the use of MSC-derived nano-scale secretions (i.e., exosomes) has been promising. Exosomes originate from the multivesicular division of cells and have high therapeutic potential, yet neither self-replicate nor cause auto-immune reactions to the host. To maintain their biological activity and allow a controlled release, these paracrine factors can be encapsulated in biomaterials. Among the different types of biomaterials in which exosome infusion is exploited, hydrogels have proven to be the most user-friendly, economical, and accessible material. In this paper, we highlight the importance of MSCs and MSC-derived exosomes in tissue engineering and the different biomaterial strategies used in fabricating exosome-based biomaterials, to facilitate hard and soft tissue engineering.

Nanohydroxyapatite/polyamide 66 crosslinked with QK and BMP-2-derived peptide prevented femur nonunion in rats

A dual-peptide controlled released system based on nHA/PA66 scaffold for enhancing bone regeneration.

The effect of LyPRP/collagen composite hydrogel on osteogenic differentiation of rBMSCs

Although platelet-rich plasma (PRP) plays a significant role in the orthopedic clinical application, it still faces two major problems, namely, uncontrollable factors release, frequent preparation and extraction processes as well as the inconvenient form of usage. To overcome these shortcomings, freeze-dried PRP (LyPRP) was encapsulated into bioactive Col I hydrogel to induce osteogenic differentiation of rabbit bone marrow mesenchymal stem cells (rBMSCs). And PRP/Col І composite hydrogel was prepared as a control. Compared with Col І hydrogel, the introduction of platelets significantly improved the mechanical properties of hydrogels. Meanwhile, platelets were evenly distributed in the composite hydrogels network. The sustainable release of related factors in the composite hydrogels could last for more than 14 days to maintain its long-term biological activity. Further cell experiments confirmed that PRP and LyPRP could effectively alleviate the contraction of collagen hydrogel in vitro, and promote the adhesion, proliferation and osteogenesis differentiation of rBMSCs. The results of osteogenic gene expression indicated that the 10% LyPRP/Col І composite hydrogel could facilitate the early expression of BMP-2 and late osteogenic associated protein formation with higher expression of alkaline phosphatase and Osteocalcin (OCN). These results might provide new insights for the clinical application of 10% LyPRP/Col І composite hydrogel as practical bone repair injection.

A modular programmed biphasic dual-delivery system on 3D ceramic scaffolds for osteogenesis in vitro and in vivo

Single-factor delivery is the most common characteristic of bone tissue engineering techniques. However, bone regeneration is a complex process requiring multiple factors and specialized release mechanisms. Therefore, the development of a dual-delivery system allowing for programmed release kinetics would be highly desirable. Improvement of the molarity and versatility of the delivery system has rarely been studied. Herein, we report the development of a novel, modular programmed biphasic dual-release system (SCB), carrying a BMP2 and an engineered collagen I-derived recognition motif (Stath-DGEA), with a self-remodification feature on hydroxyapatite (HA)-based materials. The SCB system was loaded onto an additive manufactured (AM) scaffold in order to evaluate its bifactor osteogenic potential and its biphasic release behavior. Further, the biomechanical properties of the scaffold were studied by using the fluid-structure interaction (FSI) method. Section fluorescent labeling revealed that the HA scaffold has a relatively higher density and efficiency. Additionally, the results of the release and inhibition experiment suggested that the SCB system could facilitate the sustained release of therapeutic levels of two factors during the initial stage of implantation, thereby exhibiting a rapid high-dose release pattern at a specific time point during the second stage. The FSI prediction model indicated that the scaffold provides an excellent biomimetic mechanical and fluid dynamic microenvironment to promote osteogenesis. Our results indicated that incorporation of BMP2 with Stath-DGEA in the biphasic SCB system could have a synergetic effect in promoting the adhesion, proliferation, and differentiation of bone marrow mesenchymal stem cells (BMSCs) in vitro, under staged stimulations. Further, in vivo studies in both ectopic and orthotopic rat models showed that the SCB system loaded onto an AM scaffold could enhance osteointegration and osteoinduction throughout the osteogenic process. Thus, the novel synthetic SCB system described herein used on an AM scaffold provides a biomimetic extracellular environment that enhances bone regeneration and is a promising multifunctional, dual-release platform.

Synergistic use of biomaterials and licensed therapeutics to manipulate bone remodelling and promote non-union fracture repair

Disrupted bone metabolism can lead to delayed fracture healing or non-union, often requiring intervention to correct. Although the current clinical gold standard bone graft implants and commercial bone graft substitutes are effective, they possess inherent drawbacks and are limited in their therapeutic capacity for delayed union and non-union repair. Research into advanced biomaterials and therapeutic biomolecules has shown great potential for driving bone regeneration, although few have achieved commercial success or clinical translation. There are a number of therapeutics, which influence bone remodelling, currently licensed for clinical use. Providing an alternative local delivery context for these therapies, can enhance their efficacy and is an emerging trend in bone regenerative therapeutic strategies. This review aims to provide an overview of how biomaterial design has advanced from currently available commercial bone graft substitutes to accommodate previously licensed therapeutics that target local bone restoration and healing in a synergistic manner, and the challenges faced in progressing this research towards clinical reality.