Triple growth factor delivery promotes functional bone regeneration following composite musculoskeletal trauma

Collagen patches releasing phosphatidylserine liposomes guide M1-to-M2 macrophage polarization and accelerate simultaneous bone and muscle healing

Bilateral communication between bones and muscles is essential for healing composite bone-muscle injuries from orthopedic surgeries and trauma. However, these injuries are often characterized by exaggerated inflammation, which can disrupt bone-muscle crosstalk, thereby seriously delaying the healing of either tissue. Existing approaches are largely effective at healing single tissues. However, simultaneous healing of multiple tissues remains challenging, with little research conducted to date. Here we introduce collagen patches that overcome this overlooked issue by harnessing the plasticity of macrophage phenotypes. Phosphatidylserine liposomes (PSLs) capable of shifting the macrophage phenotype from inflammatory M1 into anti-inflammatory/prohealing M2 were coated on collagen patches via a layer-by-layer method. Original collagen patches failed to improve tissue healing under inflammatory conditions coordinated by M1 macrophages. In contrast, PSL-coated collagen patches succeeded in accelerating bone and muscle healing by inducing a microenvironment dominated by M2 macrophages. In cell experiments, differentiation of preosteoblasts and myoblasts was completely inhibited by secretions of M1 macrophages but unaffected by those of M2 macrophages. RNA-seq analysis revealed that type I interferon and interleukin-6 signaling pathways were commonly upregulated in preosteoblasts and myoblasts upon stimulation with M1 macrophage secretions, thereby compromising their differentiation. This study demonstrates the benefit of PSL-mediated M1-to-M2 macrophage polarization for simultaneous bone and muscle healing, offering a potential strategy toward simultaneous regeneration of multiple tissues. STATEMENT OF SIGNIFICANCE: Existing approaches for tissue regeneration, which primarily utilize growth factors, have been largely effective at healing single tissues. However, simultaneous healing of multiple tissues remains challenging and has been little studied. Here we demonstrate that collagen patches releasing phosphatidylserine liposomes (PSLs) promote M1-to-M2 macrophage polarization and are effective for simultaneous healing of bone and muscle. Transcriptome analysis using next-generation sequencing reveals that differentiation of preosteoblasts and myoblasts is inhibited by the secretions of M1 macrophages but promoted by those of M2 macrophages, highlighting the importance of timely regulation of M1-to-M2 polarization in tissue regeneration. These findings provide new insight to tissue healing of multiple tissues.

Recent advances of bone tissue engineering: carbohydrate and ceramic materials, fundamental properties and advanced biofabrication strategies ‒ a comprehensive review

Bone is a dynamic tissue that can always regenerate itself through remodeling to maintain biofunctionality. This tissue performs several vital physiological functions. However, bone scaffolds are required for critical-size damages and fractures, and these can be addressed by bone tissue engineering. Bone tissue engineering (BTE) has the potential to develop scaffolds for repairing critical-size damaged bone. BTE is a multidisciplinary engineered scaffold with the desired properties for repairing damaged bone tissue. Herein, we have provided an overview of the common carbohydrate polymers, fundamental structural, physicochemical, and biological properties, and fabrication techniques for bone tissue engineering. We also discussed advanced biofabrication strategies and provided the limitations and prospects by highlighting significant issues in bone tissue engineering. There are several review articles available on bone tissue engineering. However, we have provided a state-of-the-art review article that discussed recent progress and trends within the last 3-5 years by emphasizing challenges and future perspectives.

A Composite Hydrogel Functionalized by Borosilicate Bioactive Glasses and VEGF for Critical-Size Bone Regeneration

Critical-size bone defects pose a formidable challenge in clinical treatment, prompting extensive research efforts to address this problem. In this study, an inorganic-organic multifunctional composite hydrogel denoted as PLG-g-TA/VEGF/Sr-BGNPs is developed, engineered for the synergistic management of bone defects. The composite hydrogel demonstrated the capacity for mineralization, hydroxyapatite formation, and gradual release of essential functional ions and vascular endothelial growth factor (VEGF) and also maintained an alkaline microenvironment. The composite hydrogel promoted the proliferation and osteogenic differentiation of rat bone marrow mesenchymal stem cells (rBMSCs), as indicated by increased expression of osteogenesis-related genes and proteins in vitro. Moreover, the composite hydrogel significantly enhanced the tube-forming capability of human umbilical vein endothelial cells (HUVECs) and effectively inhibited the process of osteoblastic differentiation of nuclear factor kappa-B ligand (RANKL)-induced Raw264.7 cells and osteoclast bone resorption. After the implantation of the composite hydrogel into rat cranial bone defects, the expression of osteogenic and angiogenic biomarkers increased, substantiating its efficacy in promoting bone defect repair in vivo. The commendable attributes of the multifunctional composite hydrogel underscore its pivotal role in expediting hydrogel-associated bone growth and repairing critical bone defects, positioning it as a promising adjuvant therapy candidate for large-segment bone defects.

Engineering Innervated Musculoskeletal Tissues for Regenerative Orthopedics and Disease Modeling

Musculoskeletal (MSK) disorders significantly burden patients and society, resulting in high healthcare costs and productivity loss. These disorders are the leading cause of physical disability, and their prevalence is expected to increase as sedentary lifestyles become common and the global population of the elderly increases. Proper innervation is critical to maintaining MSK function, and nerve damage or dysfunction underlies various MSK disorders, underscoring the potential of restoring nerve function in MSK disorder treatment. However, most MSK tissue engineering strategies have overlooked the significance of innervation. This review first expounds upon innervation in the MSK system and its importance in maintaining MSK homeostasis and functions. This will be followed by strategies for engineering MSK tissues that induce post-implantation in situ innervation or are pre-innervated. Subsequently, research progress in modeling MSK disorders using innervated MSK organoids and organs-on-chips (OoCs) is analyzed. Finally, the future development of engineering innervated MSK tissues to treat MSK disorders and recapitulate disease mechanisms is discussed. This review provides valuable insights into the underlying principles, engineering methods, and applications of innervated MSK tissues, paving the way for the development of targeted, efficacious therapies for various MSK conditions.

Hydrogel-Based Growth Factor Delivery Platforms: Strategies and Recent Advances

Growth factors play a crucial role in regulating a broad variety of biological processes and are regarded as powerful therapeutic agents in tissue engineering and regenerative medicine in the past decades. However, their application is limited by their short half-lives and potential side effects in physiological environments. Hydrogels are identified as having the promising potential to prolong the half-lives of growth factors and mitigate their adverse effects by restricting them within the matrix to reduce their rapid proteolysis, burst release, and unwanted diffusion. This review discusses recent progress in the development of growth factor-containing hydrogels for various biomedical applications, including wound healing, brain tissue repair, cartilage and bone regeneration, and spinal cord injury repair. In addition, the review introduces strategies for optimizing growth factor release including affinity-based delivery, carrier-assisted delivery, stimuli-responsive delivery, spatial structure-based delivery, and cellular system-based delivery. Finally, the review presents current limitations and future research directions for growth factor-delivering hydrogels.

The Role of Vasculature and Angiogenic Strategies in Bone Regeneration

Bone regeneration is a complex process that involves various growth factors, cell types, and extracellular matrix components. A crucial aspect of this process is the formation of a vascular network, which provides essential nutrients and oxygen and promotes osteogenesis by interacting with bone tissue. This review provides a comprehensive discussion of the critical role of vasculature in bone regeneration and the applications of angiogenic strategies, from conventional to cutting-edge methodologies. Recent research has shifted towards innovative bone tissue engineering strategies that integrate vascularized bone complexes, recognizing the significant role of vasculature in bone regeneration. The article begins by examining the role of angiogenesis in bone regeneration. It then introduces various in vitro and in vivo applications that have achieved accelerated bone regeneration through angiogenesis to highlight recent advances in bone tissue engineering. This review also identifies remaining challenges and outlines future directions for research in vascularized bone regeneration.

Fundamental properties of smart hydrogels for tissue engineering applications: A review

Tissue engineering is an advanced and potential biomedical approach to treat patients suffering from lost or failed an organ or tissue to repair and regenerate damaged tissues that increase life expectancy. The biopolymers have been used to fabricate smart hydrogels to repair damaged tissue as they imitate the extracellular matrix (ECM) with intricate structural and functional characteristics. These hydrogels offer desired and controllable qualities, such as tunable mechanical stiffness and strength, inherent adaptability and biocompatibility, swellability, and biodegradability, all crucial for tissue engineering. Smart hydrogels provide a superior cellular environment for tissue engineering, enabling the generation of cutting-edge synthetic tissues due to their special qualities, such as stimuli sensitivity and reactivity. Numerous review articles have presented the exceptional potential of hydrogels for various biomedical applications, including drug delivery, regenerative medicine, and tissue engineering. Still, it is essential to write a comprehensive review article on smart hydrogels that successfully addresses the essential challenging issues in tissue engineering. Hence, the recent development on smart hydrogel for state-of-the-art tissue engineering conferred progress, highlighting significant challenges and future perspectives. This review discusses recent advances in smart hydrogels fabricated from biological macromolecules and their use for advanced tissue engineering. It also provides critical insight, emphasizing future research directions and progress in tissue engineering.

Vanadium-Doped Mesoporous Bioactive Glass Promotes Osteogenic Differentiation of rBMSCs via the WNT/β-Catenin Signaling Pathway

Pentavalent vanadium [V(V)] has been studied as bioactive ions to improve the bone defect repair; however, its osteogenic promotion mechanism is still not fully understood so far. In this study, a V-doped mesoporous bioactive glass (V-MBG) was prepared, and its effects on osteogenic differentiation of rat bone marrow mesenchymal stem cells (rBMSCs) and potential signaling pathways were investigated. The physicochemical characterization revealed that the incorporation of V slightly reduced the specific surface area and increased the mesoporous pore size, and the abundant mesopores of V-MBG were beneficial to the sustained dissolution of V(V) ions as well as calcium, silicon, and phosphorus ions. Cell proliferation results indicated that the high dilution ratio (>16) V-MBG extract markedly promoted the proliferation of rBMSCs compared with the control group and the same dilution ratio MBG extract. Compared with the same dilution ratio MBG extract, diluted V-MBG extracts markedly promoted the secretion of alkaline phosphatase (ALP) and osteocalcin (OCN) protein at day 7 but insignificantly stimulated the runt-related transcription factor 2 (RUNX2) and vascular endothelial growth factor (VEGF) protein synthesis. In depth, the diluted V-MBG extracts remarkably up-regulated the expression of WNT/β-catenin pathway direct target genes, including WNT3a, β-catenin, and AXIN2 genes in contrast to the same dilution ratio MBG extracts, suggesting that the released V(V) ions might promote osteogenic differentiation of rBMSCs via the WNT/β-catenin signaling pathway.

Reaming the intramedullary canal during tibial nailing does not affect in vivo intramuscular pH of the anterior tibialis

Many investigations have evaluated local and systemic consequences of intramedullary (IM) reaming and suggest that reaming may cause, or exacerbate, injury to the soft tissues adjacent to fractures. To date, no study has examined the effect on local muscular physiology as measured by intramuscular pH (IpH). Here, we observe in vivo IpH during IM reaming for tibia fractures.

Methods

Adults with acute tibia shaft fractures (level 1, academic, 2019-2021) were offered enrollment in an observational cohort. During IM nailing, a sterile, validated IpH probe was placed into the anterior tibialis (<5 cm from fracture, continuous sampling, independent research team). IpH before, during, and after reaming was averaged and compared through repeated measures ANOVA. As the appropriate period to analyze IpH during reaming is unknown, the analysis was repeated over periods of 0.5, 1, 2, 5, 10, and 15 minutes prereaming and postreaming time intervals.

Results

Sixteen subjects with tibia shaft fractures were observed during nailing. Average time from injury to surgery was 35.0 hours (SD, 31.8). Starting and ending perioperative IpH was acidic, averaging 6.64 (SD, 0.21) and 6.74 (SD, 0.17), respectively. Average reaming time lasted 15 minutes. Average IpH during reaming was 6.73 (SD, 0.15). There was no difference in IpH between prereaming, intrareaming, and postreaming periods. IpH did not differ regardless of analysis over short or long time domains compared with the duration of reaming.

Conclusions

Reaming does not affect IpH. Both granular and broad time domains were tested, revealing no observable local impact.

Synergistic Effect of QNZ, an Inhibitor of NF-κB Signaling, and Bone Morphogenetic Protein 2 on Osteogenic Differentiation in Mesenchymal Stem Cells through Fibroblast-Induced Yes-Associated Protein Activation

Biomaterials carrying recombinant human bone morphogenetic protein 2 (BMP2) have been developed to enhance bone regeneration in the treatment of bone defects. However, various reports have shown that in the bone repair microenvironment, fibroblasts can inhibit BMP2-induced osteogenic differentiation in mesenchymal stem cells (MSCs). Thus, factors that can target fibroblasts and improve BMP2-mediated osteogenesis should be explored. In this project, we focused on whether or not an inhibitor of the NF-κB signaling pathway, QNZ (EVP4593), could play a synergistic role with BMP2 in osteogenesis by regulating the activity of fibroblasts. The roles of QNZ in regulating the proliferation and migration of fibroblasts were examined. In addition, the effect of QNZ combined with BMP2 on the osteogenic differentiation of MSCs was evaluated both in vitro and in vivo. Furthermore, the detailed mechanisms by which QNZ improved BMP2-mediated osteogenesis through the modulation of fibroblasts were analyzed and revealed. Interestingly, we found that QNZ inhibited the proliferation and migration of fibroblasts. Thus, QNZ could relieve the inhibitory effects of fibroblasts on the homing and osteogenic differentiation of mesenchymal stem cells. Furthermore, biomaterials carrying both QNZ and BMP2 showed better osteoinductivity than did those carrying BMP2 alone both in vitro and in vivo. It was found that the mechanism of QNZ involved reactivating YAP activity in mesenchymal stem cells, which was inhibited by fibroblasts. Taken together, our results suggest that QNZ may be a candidate factor for assisting BMP2 in inducing osteogenesis. The combined application of QNZ and BMP2 in biomaterials may be promising for the treatment of bone defects in the future.

Engineering of an Osteoinductive and Growth Factor-Free Injectable Bone-Like Microgel for Bone Regeneration

Bone autografts remain the gold standard for bone grafting surgeries despite having increased donor site morbidity and limited availability. Bone morphogenetic protein-loaded grafts represent another successful commercial alternative. However, the therapeutic use of recombinant growth factors has been associated with significant adverse clinical outcomes. This highlights the need to develop biomaterials that closely approximate the structure and composition of bone autografts, which are inherently osteoinductive and biologically active with embedded living cells, without the need for added supplements. Here, injectable growth factor-free bone-like tissue constructs are developed, that closely approximate the cellular, structural, and chemical composition of bone autografts. It is demonstrated that these micro-constructs are inherently osteogenic, and demonstrate the ability to stimulate mineralized tissue formation and regenerate bone in critical-sized defects in-vivo. Furthermore, the mechanisms that allow human mesenchymal stem cells (hMSCs) to be highly osteogenic in these constructs, despite the lack of osteoinductive supplements, are assessed, whereby Yes activated protein (YAP) nuclear localization and adenosine signaling appear to regulate osteogenic cell differentiation. The findings represent a step toward a new class of minimally invasive, injectable, and inherently osteoinductive scaffolds, which are regenerative by virtue of their ability to mimic the tissue cellular and extracellular microenvironment, thus showing promise for clinical applications in regenerative engineering.

Combined application of BMP-2 and naturally occurring bioactive factor mixtures for the optimized therapy of segmental bone defects

Critical bone defects are the result of traumatic, infection- or tumor-induced segmental bone loss and represent a therapeutic problem that has not been solved by current reconstructive or regenerative strategies yet. Scaffolds functionalized with naturally occurring bioactive factor mixtures show a promising chemotactic and angiogenic potential in vitro and therefore might stimulate bone regeneration in vivo. To assess this prospect, the study targets at heparin-modified mineralized collagen scaffolds functionalized with naturally occurring bioactive factor mixtures and/or rhBMP-2. These scaffolds were implanted into a 2-mm segmental femoral defect in mice and analyzed in respect to newly formed bone volume (BV) and bone mineral density (BMD) by micro-computed tomography scans after an observation period of 6 weeks. To rate the degree of defect healing, the number of vessels, and the activity of osteoclasts and osteoblasts were analyzed histologically. The sole application of bioactive factor mixtures is inferior to the use of the recombinant growth factor rhBMP-2 regarding BV and degree of defect healing. A higher rhBMP-2 concentration or the combination with bioactive factor mixtures does not lead to a further enhancement in defect healing. Possibly, a synergistic effect can be achieved by further concentration or a prolonged release of bioactive factor mixtures. STATEMENT OF SIGNIFICANCE: The successful therapy of extended bone defects is still a major challenge in clinical routine. In this study we investigated the bone regenerative potential of naturally occuring bioactive factor mixtures derived from platelet concentrates, adipose tissue and cell secretomes as a cheap and promising alternative to recombinant growth factors in a murine segmental bone defect model. The mixtures alone were not able to induce complete bridging of the bone defect, but in combination with bone morphogenetic protein 2 bone healing seemed to be more physiological. The results show that naturally occuring bioactive factor mixtures are a promising add-on in a clinical setting.

Controlled growth factor delivery via a degradable poly(lactic acid) hydrogel microcarrier synthesized using degassed micromolding lithography

Controlled and targeted delivery of growth factors to biological environments is important for tissue regeneration. Polylactic acid (PLA) hydrogel microparticles are attractive carriers for the delivery of therapeutic cargoes based on their superior biocompatibility and biodegradability, uniform encapsulation of cargoes, and non-requirement of organic solvents during particle synthesis. In this study, we newly present controlled growth factor delivery utilizing PLA-based hydrogel microcarriers synthesized via degassed micromolding lithography (DML). Based on the direct gelation procedure from the single-phase aqueous precursor in DML, bovine serum albumin, a model protein of growth factor, and fibroblast growth factor were encapsulated into microparticles with uniform distribution. In addition, by tuning the monomer concentration and adding a hydrolytically stable crosslinker, the release of encapsulated cargoes was efficiently controlled and extended to 2 weeks. Finally, we demonstrated the biological activity of encapsulated FGF-2 in PLA-based microparticles using a fibroblast proliferation assay.

Nanoparticles based composite coatings with tunable vascular endothelial growth factor and bone morphogenetic protein-2 release for bone regeneration

Bone healing is a complex cascade involving precisely coordinated spatiotemporal presentation of multiple growth factors (GFs), including osteogenic and angiogenic GFs, and each stage of bone healing requires varying types and content of GFs. In this study, we fabricated a composite nanocoating with tunable vascular endothelial growth factor (VEGF) and bone morphogenetic protein-2 (BMP-2) that was coated on the surface of a polydopamine (PDA)-decorated tertiary calcium phosphate (TCP) scaffold using VEGF-loaded chitosan/bovine serum albumin nanoparticles (CS/BSA-NPs) and BMP-2-loaded poly-L-lysine/oxidized alginate nanoparticles (PLL/OALG-NPs). It was found that VEGF could be efficiently released to promote vascularization in early bone repair stages due to the rapid biodegradation of CS/BSA-NPs, while bone formation can be promoted by a sustained release of BMP-2 from the slowly degrading PLL/OALG-NPs. The composite coating and TCP scaffold can be conjugated due to the excellent adhesive property of PDA. The composite coating can achieve the rapid release of VEGF and sustained release of BMP-2, which can activate GFs for accelerating bone healing.

Advances in bone regeneration with growth factors for spinal fusion: A literature review

Bone tissue is regenerated via the spatiotemporal involvement of various cytokines. Among them, the bone morphogenetic protein (BMP), which plays a vital role in the bone regeneration process, has been applied clinically for the treatment of refractory orthopedic conditions. Although BMP therapy using a collagen carrier has shown efficiency in bone regeneration over the last two decades, a major challenge-considerable side effects associated with the acute release of high doses of BMPs-has also been revealed. To improve BMP efficiency, the development of new carriers and biologics that can be used in conjunction with BMPs is currently underway. In this review, we describe the current status and future prospects of bone regeneration therapy, with a focus on BMPs. Furthermore, we outline the characteristics and molecular signaling pathways involving BMPs, clinical applications of BMPs in orthopedics, clinical results of BMP use in human spinal surgeries, drugs combined with BMPs to provide synergistic effects, and novel BMP carriers.

Tissue Engineering as a Promising Treatment for Glottic Insufficiency: A Review on Biomolecules and Cell-Laden Hydrogel

Glottic insufficiency is widespread in the elderly population and occurs as a result of secondary damage or systemic disease. Tissue engineering is a viable treatment for glottic insufficiency since it aims to restore damaged nerve tissue and revitalize aging muscle. After injection into the biological system, injectable biomaterial delivers cost- and time-effectiveness while acting as a protective shield for cells and biomolecules. This article focuses on injectable biomaterials that transport cells and biomolecules in regenerated tissue, particularly adipose, muscle, and nerve tissue. We propose Wharton's Jelly mesenchymal stem cells (WJMSCs), induced pluripotent stem cells (IP-SCs), basic fibroblast growth factor (bFGF), vascular endothelial growth factor (VEGF), hepatocyte growth factor (HGF), insulin growth factor-1 (IGF-1) and extracellular vesicle (EV) as potential cells and macromolecules to be included into biomaterials, with some particular testing to support them as a promising translational medicine for vocal fold regeneration.

Spatiotemporal Delivery of pBMP2 and pVEGF by a Core-Sheath Structured Fiber-Hydrogel Gene-Activated Matrix Loaded with Peptide-Modified Nanoparticles for Critical-Sized Bone Defect Repair

The clinical translation of bioactive scaffolds for the treatment of large segmental bone defects remains a grand challenge. The gene-activated matrix (GAM) combining gene therapy and tissue engineering scaffold offers a promising strategy for the restoration of structure and function of damaged or dysfunctional tissues. Herein, a gene-activated biomimetic composite scaffold consisting of an electrospun poly(ε-caprolactone) fiber sheath and an alginate hydrogel core which carried plasmid DNA encoding bone morphogenetic protein 2 (pBMP2) and vascular endothelial growth factor (pVEGF), respectively, is developed. A peptide-modified polymeric nanocarrier with low cytotoxicity and high efficiency serves as the nonviral DNA delivery vector. The obtained GAM allows spatiotemporal release of pVEGF and pBMP2 and promotes osteogenic differentiation of preosteoblasts in vitro. In vivo evaluation using a critical-sized segmental femoral defect model in rats shows that the dual gene delivery system can significantly accelerate bone healing by activating angiogenesis and osteogenesis. These findings demonstrate the effectiveness of the developed dual gene-activated core-sheath structured fiber-hydrogel composite scaffold for critical-sized bone defect regeneration and the potential of cell-free scaffold-based gene therapy for tissue engineering.

Translating musculoskeletal bioengineering into tissue regeneration therapies

Musculoskeletal injuries and disorders are the leading cause of physical disability worldwide and a considerable socioeconomic burden. The lack of effective therapies has driven the development of novel bioengineering approaches that have recently started to gain clinical approvals. In this review, we first discuss the self-repair capacity of the musculoskeletal tissues and describe causes of musculoskeletal dysfunction. We then review the development of novel biomaterial, immunomodulatory, cellular, and gene therapies to treat musculoskeletal disorders. Last, we consider the recent regulatory changes and future areas of technological progress that can accelerate translation of these therapies to clinical practice.

A Metabolic Signature to Monitor Endothelial Cell Differentiation, Activation, and Vascular Organization

The formation of new blood vessels is an important step in the morphogenesis and organization of tissues and organs; hence, the success of regenerative medicine procedures is highly dependent on angiogenesis control. Despite the biotechnological advances, tissue engineering is still a challenge. Regarding vascular network formation, the regulators are well known, yet the identification of markers is pivotal in order to improve the monitoring of the differentiation and proliferation of endothelial cells, as well as the establishment of a vascular network supporting tissue viability for an efficacious implantation. The metabolic profile accompanies the physiological stages of cells involved in angiogenesis, being a fruitful hub of biomarkers, whose levels can be easily retrieved. Through NMR spectroscopy, we identified branched amino acids, acetate, and formate as central biomarkers of monocyte-to-endothelial-cell differentiation and endothelial cell proliferation. This study reinforces the successful differentiation process of monocytes into endothelial cells, allowing self-to-self transplantation of patient-derived vascular networks, which is an important step in tissue engineering, since monocytes are easily isolated and autologous transplantation reduces the immune rejection events.

Growth Factor Immobilization Strategies for Musculoskeletal Disorders

PURPOSE OF REVIEW

Tissue regenerative solutions for musculoskeletal disorders have become increasingly important with a growing aged population. Current growth factor treatments often require high dosages with the potential for off-target effects. Growth factor immobilization strategies offer approaches towards alleviating these concerns. This review summarizes current growth factor immobilization techniques (encapsulation, affinity interactions, and covalent binding) and the effects of immobilization on growth factor loading, release, and bioactivity.

RECENT FINDINGS

The breadth of immobilization techniques based on encapsulation, affinity, and covalent binding offer multiple methods to improve the therapeutic efficacy of growth factors by controlling bioactivity and release. Growth factor immobilization strategies have evolved to more complex systems with the capacity to load and release multiple growth factors with spatiotemporal control. The advancements in immobilization strategies allow for development of new, complex musculoskeletal tissue treatment strategies with improved spatiotemporal control of loading, release, and bioactivity.

Effects of a novel self-assembling peptide scaffold on bone regeneration and controlled release of two growth factors

RADA16 is a self-assembling peptide material with good bioactivity. To improve the bioactivity of a material, some specific functional motifs can be added to its peptide sequence. Here, we report a self-assembling peptide nanogel, RADA16-RGD, that has better bioactivity than RADA16 and can simultaneously carry and control the release of two growth factors, VEGF and BMP-2, which have synergistic effects on bone formation. The peptide materials were characterized by transmission electron microscopy and scanning electron microscopy. The mechanical properties of the peptides were evaluated by the rheology test. The biocompatibility of the materials was evaluated via the use of the CCK-8 test, live/dead staining and confocal laser scanning microscopy. Osteogenesis capability in vitro was evaluated by means of ALP staining, extracellular matrix mineralization and detection of osteogenic markers. The controlled release of growth factors was examined by ELISA. The results showed that RADA16-RGD exhibited a better ability than RADA16 to promote cell proliferation, adhesion and bone formation. In addition, RADA16-RGD had good biocompatibility and exhibited effective controlled release of VEGF and BMP-2. More importantly, compared with RADA16-RGD loaded with single growth factor or without growth factors, RADA16-RGD loaded with two growth factors exhibited a stronger ability to promote cell proliferation and osteogenesis. This study provides a promising strategy for the application of self-assembling peptides to promote osteogenesis and controlled release of proteins.

Nanoscale mineralization of cell-laden methacrylated gelatin hydrogels using calcium carbonate-calcium citrate core-shell microparticles

Conventional biomaterials developed for bone regeneration fail to fully recapitulate the nanoscale structural organization and complex composition of the native bone microenvironment. Therefore, despite promoting osteogenic differentiation of stem cells, they fall short of providing the structural, biochemical, and mechanical stimuli necessary to drive osteogenesis for bone regeneration and function. To address this, we have recently developed a novel strategy to engineer bone-like tissue using a biomimetic approach to achieve rapid and controlled nanoscale mineralization of a cell-laden matrix in the presence of osteopontin, a non-collagenous protein, and a supersaturated solution of calcium and phosphate medium. Here, we build on this approach to engineer bone regeneration scaffolds comprising methacrylated gelatin (GelMA) hydrogels incorporated with calcium citrate core-shell microparticles as a sustained and reliable source of calcium ions for in situ mineralization. We demonstrate successful biomineralization of GelMA hydrogels by embedded calcium carbonate-calcium citrate core-shell microparticles with the resultant mineral chemistry, structure, and organization reminiscent of that of native bone. The biomimetic mineralization was further shown to promote osteogenic differentiation of encapsulated human mesenchymal stem cells even in the absence of other exogenous osteogenic induction factors. Ultimately, by combining the superior biological response engendered by biomimetic mineralization with the intrinsic tissue engineering advantages offered by GelMA, such as biocompatibility, biodegradability, and printability, we envision that our system offers great potential for bone regeneration efforts.

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.