Preclinical safety study of a combined therapeutic bone wound dressing for osteoarticular regeneration

Recent advancements in cartilage tissue engineering innovation and translation

Articular cartilage was expected to be one of the first successfully engineered tissues, but today, cartilage repair products are few and they exhibit considerable limitations. For example, of the cell-based products that are available globally, only one is marketed for non-knee indications, none are indicated for severe osteoarthritis or rheumatoid arthritis, and only one is approved for marketing in the USA. However, advances in cartilage tissue engineering might now finally lead to the development of new cartilage repair products. To understand the potential in this field, it helps to consider the current landscape of tissue-engineered products for articular cartilage repair and particularly cell-based therapies. Advances relating to cell sources, bioactive stimuli and scaffold or scaffold-free approaches should now contribute to progress in therapeutic development. Engineering for an inflammatory environment is required because of the need for implants to withstand immune challenge within joints affected by osteoarthritis or rheumatoid arthritis. Bringing additional cartilage repair products to the market will require an understanding of the translational vector for their commercialization. Advances thus far can facilitate the future translation of engineered cartilage products to benefit the millions of patients who suffer from cartilage injuries and arthritides.

Chitosan-PNIPAM Thermogel Associated with Hydrogel Microspheres as a Smart Formulation for MSC Injection

Regenerative medicine based on cell therapy has emerged as a promising approach for the treatment of various medical conditions. However, the success of cell therapy heavily relies on the development of suitable injectable hydrogels that can encapsulate cells and provide a conducive environment for their survival, proliferation, and tissue regeneration. Herein, we address the medical need for cyto- and biocompatible injectable hydrogels by reporting on the synthesis of a hydrogel-forming thermosensitive copolymer. The copolymer was synthesized by grafting poly(N-isopropylacrylamide-co-carboxymethyl acrylate) (PNIPAM-COOH) onto chitosan through amide coupling. This chemical modification resulted in the formation of hydrogels that exhibit a sol-gel transition with an onset at approximately 27 °C, making them ideal for use in injectable applications. The hydrogels supported the survival and proliferation of cells for several days, which is critical for cell encapsulation. Furthermore, the study evaluates the addition of collagen/chitosan hybrid microspheres to support the adhesion of mesenchymal stem cells within the hydrogels. Altogether, these results demonstrate the potential of the PNIPAM-chitosan thermogel for cell encapsulation and its possible applications in regenerative medicine.

An Antibacterial Bionic Periosteum with Angiogenesis-Neurogenesis Coupling Effect for Bone Regeneration

The periosteum, rich in neurovascular networks, bone progenitor cells, and stem cells, is vital for bone repair. Current artificial periosteal materials face challenges in mechanical strength, bacterial infection, and promoting osteogenic differentiation and angiogenesis. To address these issues, we adjusted the electrospinning ratio of poly-ε-caprolactone and chitosan and incorporated Zn doping whitlockite with polydopamine coating into a nanofiber membrane. After a series of characterizations, optimal results were achieved with a poly-ε-caprolactone: chitosan ratio of 8:1 and 5% nanoparticle content. In vitro cell experiments and in vivo calvarial defect models, the sustained release of Mg2+ and Ca2+ promoted vascularization and new bone formation, respectively, while the release of Zn2+ was conducive to antibacterial and cooperated with Mg2+ to promote neurovascularization. Consequently, this antibacterial bionic periosteum with an angiogenesis-neurogenesis coupling effect demonstrates a promising potential for bone repair applications.

Composite Spheroid-Laden Bilayer Hydrogel for Engineering Three-Dimensional Osteochondral Tissue

A combination of hydrogels and stem cell spheroids has been used to engineer three-dimensional (3D) osteochondral tissue, but precise zonal control directing cell fate within the hydrogel remains a challenge. In this study, we developed a composite spheroid-laden bilayer hydrogel to imitate osteochondral tissue by spatially controlled differentiation of human adipose-derived stem cells. Meticulous optimization of the spheroid-size and mechanical strength of gelatin methacryloyl (GelMA) hydrogel enables the cells to homogeneously sprout within the hydrogel. Moreover, fibers immobilizing transforming growth factor beta-1 (TGF-β1) or bone morphogenetic protein-2 (BMP-2) were incorporated within the spheroids, which induced chondrogenic or osteogenic differentiation of cells in general media, respectively. The spheroids-filled GelMA solution was crosslinked to create the bilayer hydrogel, which demonstrated a strong interfacial adhesion between the two layers. The cell sprouting enhanced the adhesion of each hydrogel, demonstrated by increase in tensile strength from 4.8 ± 0.4 to 6.9 ± 1.2 MPa after 14 days of culture. Importantly, the spatially confined delivery of BMP-2 within the spheroids increased mineral deposition and more than threefold enhanced osteogenic genes of cells in the bone layer while the cells induced by TGF-β1 signals were apparently differentiated into chondrocytes within the cartilage layer. The results suggest that our composite spheroid-laden hydrogel could be used for the biofabrication of osteochondral tissue, which can be applied to engineer other complex tissues by delivery of appropriate biomolecules.

Endogenus chondrocytes immobilized by G-CSF in nanoporous gels enable repair of critical-size osteochondral defects

Injured articular cartilage is a leading cause for osteoarthritis. We recently discovered that endogenous stem/progenitor cells not only reside in the superficial zone of mouse articular cartilage, but also regenerated heterotopic bone and cartilage in vivo. However, whether critical-size osteochondral defects can be repaired by pure induced chemotatic cell homing of these endogenous stem/progenitor cells remains elusive. Here, we first found that cells in the superficial zone of articular cartilage surrounding surgically created 3 × 1 mm defects in explant culture of adult goat and rabbit knee joints migrated into defect-filled fibrin/hylaro1nate gel, and this migration was significantly more robust upon delivery of exogenous granulocyte-colony stimulating factor (G-CSF). Remarkably, G-CSF-recruited chondrogenic progenitor cells (CPCs) showed significantly stronger migration ability than donor-matched chondrocytes and osteoblasts. G-CSF-recruited CPCs robustly differentiated into chondrocytes, modestly into osteoblasts, and barely into adipocytes. In vivo, critical-size osteochondral defects were repaired by G-CSF-recruited endogenous cells postoperatively at 6 and 12 weeks in comparison to poor healing by gel-only group or defect-only group. ICRS and O'Driscoll scores of articular cartilage were significantly higher for both 6- and 12-week G-CSF samples than corresponding gel-only and defect-only groups. Thus, endogenous stem/progenitor cells may be activated by G-CSF, a Food and Drug Administration (FDA)-cleared bone-marrow stimulating factor, to repair osteochondral defects.

3D-bioprinted anisotropic bicellular living hydrogels boost osteochondral regeneration via reconstruction of cartilage-bone interface

Reconstruction of osteochondral (OC) defects represents an immense challenge due to the need for synchronous regeneration of special stratified tissues. The revolutionary innovation of bioprinting provides a robust method for precise fabrication of tissue-engineered OCs with hierarchical structure; however, their spatial living cues for simultaneous fulfilment of osteogenesis and chondrogenesis to reconstruct the cartilage-bone interface of OC are underappreciated. Here, inspired by natural OC bilayer features, anisotropic bicellular living hydrogels (ABLHs) simultaneously embedding articular cartilage progenitor cells (ACPCs) and bone mesenchymal stem cells (BMSCs) in stratified layers were precisely fabricated via two-channel extrusion bioprinting. The optimum formulation of the 7% GelMA/3% AlgMA hydrogel bioink was demonstrated, with excellent printability at room temperature and maintained high cell viability. Moreover, the chondrogenic ability of ACPCs and the osteogenic ability of BMSCs were demonstrated in vitro, confirming the inherent differential spatial regulation of ABLHs. In addition, ABLHs exhibited satisfactory synchronous regeneration of cartilage and subchondral bone in vivo. Compared with homogeneous hydrogels, the neo-cartilage and neo-bone in ABLHs were augmented by 23.5% and 20.8%, respectively, and more important, a more harmonious cartilage-bone interface was achieved by ABLHs due to their well-tuned cartilage-bone-vessel crosstalk. We anticipate that such a strategy of tissue-mimetic ABLH by means of bioprinting is capable of spatiotemporal cell-driven regeneration, offering insights into the fabrication of anisotropic living materials for the reconstruction of complex organ defects.

Review on vat photopolymerization additive manufacturing of bioactive ceramic bone scaffolds

Bone defects frequently occur in clinical settings due to trauma, disease, tumors, and other causes. The clinical use of autologous bones and allograft bone, however, has several limitations, such as limited sources, donor site morbidity, and immunological rejection. Nevertheless, there is newfound hope for regenerating and repairing bone defects through the development and integration of bone tissue engineering scaffold and additive manufacturing (AM) technology, also known as 3D printing. In particular, vat photopolymerization (VPP)-AM of bioactive ceramic bone scaffolds has garnered significant interest from interdisciplinary researchers in recent years. On the one hand, VPP-AM demonstrates clear advantages in printing accuracy and speed compared to other AM and non-AM technologies. On the other hand, bioactive ceramic materials exhibit superior bioactivity, biodegradability, and mechanical properties compared to metals, polymers, and bioinert ceramics, making them one of the most promising biomaterials for developing bone scaffolds. This paper reviews the research progress of VPP-AM of bioactive ceramic bone scaffolds, covering the process principles of various VPP-AM technologies, the performance requirements and preparation process of VPP ceramic slurry, the VPP process of bioactive ceramic bone scaffolds, and the research progress on different material types of VPP bioactive ceramic scaffolds. Firstly, we provide a brief introduction to the process principles and medical applications of various VPP technologies. Secondly, we explore the composition of the VPP ceramic slurry system, discussing the function of various components and their effects on printing quality. Thirdly, we delve into the performance requirements of bone scaffolds and summarize the research progress of VPP bioactive ceramic bone scaffolds of various material types including hydroxyapatite (HA), tricalcium phosphate (TCP), bioglass (BG), etc.; Finally, we discuss the challenges currently faced by VPP-AM bioactive ceramic bone scaffolds and propose possible development directions for the future.

A Review of 3D Polymeric Scaffolds for Bone Tissue Engineering: Principles, Fabrication Techniques, Immunomodulatory Roles, and Challenges

Over the last few years, biopolymers have attracted great interest in tissue engineering and regenerative medicine due to the great diversity of their chemical, mechanical, and physical properties for the fabrication of 3D scaffolds. This review is devoted to recent advances in synthetic and natural polymeric 3D scaffolds for bone tissue engineering (BTE) and regenerative therapies. The review comprehensively discusses the implications of biological macromolecules, structure, and composition of polymeric scaffolds used in BTE. Various approaches to fabricating 3D BTE scaffolds are discussed, including solvent casting and particle leaching, freeze-drying, thermally induced phase separation, gas foaming, electrospinning, and sol-gel techniques. Rapid prototyping technologies such as stereolithography, fused deposition modeling, selective laser sintering, and 3D bioprinting are also covered. The immunomodulatory roles of polymeric scaffolds utilized for BTE applications are discussed. In addition, the features and challenges of 3D polymer scaffolds fabricated using advanced additive manufacturing technologies (rapid prototyping) are addressed and compared to conventional subtractive manufacturing techniques. Finally, the challenges of applying scaffold-based BTE treatments in practice are discussed in-depth.

Updates on mesenchymal stem cell therapies for articular cartilage regeneration in large animal models

There is an unmet need for novel and efficacious therapeutics for regenerating injured articular cartilage in progressive osteoarthritis (OA) and/or trauma. Mesenchymal stem cells (MSCs) are particularly promising for their chondrogenic differentiation, local healing environment modulation, and tissue- and organism-specific activity; however, despite early in vivo success, MSCs require further investigation in highly-translatable models prior to disseminated clinical usage. Large animal models, such as canine, porcine, ruminant, and equine models, are particularly valuable for studying allogenic and xenogenic human MSCs in a human-like osteochondral microenvironment, and thus play a critical role in identifying promising approaches for subsequent clinical investigation. In this mini-review, we focus on [1] considerations for MSC-harnessing studies in each large animal model, [2] source tissues and organisms of MSCs for large animal studies, and [3] tissue engineering strategies for optimizing MSC-based cartilage regeneration in large animal models, with a focus on research published within the last 5 years. We also highlight the dearth of standard assessments and protocols regarding several crucial aspects of MSC-harnessing cartilage regeneration in large animal models, and call for further research to maximize the translatability of future MSC findings.

Material-Assisted Strategies for Osteochondral Defect Repair

The osteochondral (OC) unit plays a pivotal role in joint lubrication and in the transmission of constraints to bones during movement. The OC unit does not spontaneously heal; therefore, OC defects are considered to be one of the major risk factors for developing long-term degenerative joint diseases such as osteoarthritis. Yet, there is currently no curative treatment for OC defects, and OC regeneration remains an unmet medical challenge. In this context, a plethora of tissue engineering strategies have been envisioned over the last two decades, such as combining cells, biological molecules, and/or biomaterials, yet with little evidence of successful clinical transfer to date. This striking observation must be put into perspective with the difficulty in comparing studies to identify overall key elements for success. This systematic review aims to provide a deeper insight into the field of material-assisted strategies for OC regeneration, with particular considerations for the therapeutic potential of the different approaches (with or without cells or biological molecules), and current OC regeneration evaluation methods. After a brief description of the biological complexity of the OC unit, the recent literature is thoroughly analyzed, and the major pitfalls, emerging key elements, and new paths to success are identified and discussed.

Biomaterial Scaffolds Made of Chemically Cross-Linked Gelatin Microsphere Aggregates (C-GMSs) Promote Vascularized Bone Regeneration

Various scaffolding systems have been attempted to facilitate vascularization in tissue engineering by optimizing biophysical properties (e.g., vascular-like structures, porous architectures, surface topographies) or loading biochemical factors (e.g., growth factors, hormones). However, vascularization during ossification remains an unmet challenge that hampers the repair of large bone defects. In this study, reconstructing vascularized bones in situ against critical-sized bone defects is endeavored using newly developed scaffolds made of chemically cross-linked gelatin microsphere aggregates (C-GMSs). The rationale of this design lies in the creation and optimization of cell-material interfaces to enhance focal adhesion, proliferation, and function of anchorage-dependent functional cells. In vitro trials are carried out by coculturing human aortic endothelial cells (HAECs) and murine osteoblast precursor cells (MC3T3-E1) within C-GMS scaffolds, in which endothelialized bone-like constructs are yielded. Angiogenesis and osteogenesis induced by C-GMSs scaffold are further confirmed via subcutaneous-embedding trials in nude mice. In situ trials for the repair of critical-sized femoral defects are subsequently performed in rats. The acellular C-GMSs with interconnected macropores, exhibit the capability to recruit the endogenous cells (e.g., bone-forming cells, vascular forming cells, immunocytes) and then promote vascularized bone regeneration as well as integration with host bone.

Directed Regeneration of Osteochondral Tissue by Hierarchical Assembly of Spatially Organized Composite Spheroids

The use of engineered scaffolds or stem cells is investigated widely in the repair of injured musculoskeletal tissue. However, the combined regeneration of hierarchical osteochondral tissue remains a challenge due to delamination between cartilage and subchondral bone or difficulty in spatial control over differentiation of transplanted stem cells. Here, two types of composite spheroids are prepared using adipose-derived stem cells (hADSCs) and nanofibers coated with either transforming growth factor-β3 or bone morphogenetic growth factor-2 for chondrogenesis or osteogenesis, respectively. Each type of spheroid is then cultured within a 3D-printed microchamber in a spatially arranged manner to recapitulate the bilayer structure of osteochondral tissue. The presence of inductive factors regionally modulates in vitro chondrogenic or osteogenic differentiation of hADSCs within the biphasic construct without dedifferentiation. Furthermore, hADSCs from each spheroid proliferate and sprout and successfully connect the two layers mimicking the osteochondral interface without apertures. In vivo transplantation of the biphasic construct onto a femoral trochlear groove defect in rabbit knee joint results in 21.2 ± 2.8% subchondral bone volume/total volume and a cartilage score of 25.0 ± 3.7. The present approach can be an effective therapeutic platform to engineer complex tissue.

Combination of a Collagen Scaffold and an Adhesive Hyaluronan-Based Hydrogel for Cartilage Regeneration: A Proof of Concept in an Ovine Model

OBJECTIVE

Hyaluronic acid-transglutaminase (HA-TG) is an enzymatically crosslinkable adhesive hydrogel with chondrogenic properties demonstrated in vitro and in an ectopic mouse model. In this study, we investigated the feasibility of using HA-TG in a collagen scaffold to treat chondral lesions in an ovine model, to evaluate cartilage regeneration in a mechanically and biologically challenging joint environment, and the influence of the surgical procedure on the repair process.

DESIGN

Chondral defects of 6-mm diameter were created in the stifle joint of skeletally mature sheep. In a 3-month study, 6 defects were treated with HA-TG in a collagen scaffold to test the stability and biocompatibility of the defect filling. In a 6-month study, 6 sheep had 12 defects treated with HA-TG and collagen and 2 sheep had 4 untreated defects. Histologically observed quality of repair tissue and adjacent cartilage was semiquantitatively assessed.

RESULTS

HA-TG adhered to the native tissue and did not cause any detectable negative reaction in the surrounding tissue. HA-TG in a collagen scaffold supported infiltration and chondrogenic differentiation of mesenchymal cells, which migrated from the subchondral bone through the calcified cartilage layer. Additionally, HA-TG and collagen treatment led to better adjacent cartilage preservation compared with empty defects (P < 0.05).

CONCLUSIONS

This study demonstrates that the adhesive HA-TG hydrogel in a collagen scaffold shows good biocompatibility, supports in situ cartilage regeneration and preserves the surrounding cartilage. This proof-of-concept study shows the potential of this approach, which should be further considered in the treatment of cartilage lesions using a single-step procedure.

Repair of full-thickness articular cartilage defects using IEIK13 self-assembling peptide hydrogel in a non-human primate model

Articular cartilage is built by chondrocytes which become less active with age. This declining function of the chondrocytes, together with the avascular nature of the cartilage, impedes the spontaneous healing of chondral injuries. These lesions can progress to more serious degenerative articular conditions as in the case of osteoarthritis. As no efficient cure for cartilage lesions exist yet, cartilage tissue engineering has emerged as a promising method aiming at repairing joint defects and restoring articular function. In the present work, we investigated if a new self-assembling peptide (referred as IEIK13), combined with articular chondrocytes treated with a chondrogenic cocktail (BMP-2, insulin and T3, designated BIT) could be efficient to restore full-thickness cartilage defects induced in the femoral condyles of a non-human primate model, the cynomolgus monkey. First, in vitro molecular studies indicated that IEIK13 was efficient to support production of cartilage by monkey articular chondrocytes treated with BIT. In vivo, cartilage implant integration was monitored non-invasively by contrast-enhanced micro-computed tomography, and then by post-mortem histological analysis and immunohistochemical staining of the condyles collected 3 months post-implantation. Our results revealed that the full-thickness cartilage injuries treated with either IEIK13 implants loaded with or devoid of chondrocytes showed similar cartilage-characteristic regeneration. This pilot study demonstrates that IEIK13 can be used as a valuable scaffold to support the in vitro activity of articular chondrocytes and the repair of articular cartilage defects, when implanted alone or with chondrocytes.

Innovative Tissue-Engineered Strategies for Osteochondral Defect Repair and Regeneration: Current Progress and Challenges

Clinical treatments for the repair of osteochondral defects (OCD) are merely palliative, not completely curative, and thus enormously unfulfilled challenges. With the in-depth studies of biology, medicine, materials, and engineering technology, the conception of OCD repair and regeneration should be renewed. During the past decades, many innovative tissue-engineered approaches for repairing and regenerating damaged osteochondral units have been widely explored. Various scaffold-free and scaffold-based strategies, such as monophasic, biphasic, and currently fabricated multiphasic and gradient architectures have been proposed and evaluated. Meanwhile, progenitor cells and tissue-specific cells have also been intensively investigated in vivo as well as ex vivo. Concerning bioactive factors and drugs, they have been combined with scaffolds and/or living cells, and even released in a spatiotemporally controlled manner. Although tremendous progress has been achieved, further research and development (R&D) is needed to convert preclinical outcomes into clinical applications. Here, the osteochondral unit structure, its defect classifications, and diagnosis are summarized. Commonly used clinical reparative techniques, tissue-engineered strategies, emerging 3D-bioprinting technologies, and the status of their clinical applications are discussed. Existing challenges to translation are also discussed and potential solutions for future R&D directions are proposed.

A Biomimetic Biphasic Osteochondral Scaffold with Layer-Specific Release of Stem Cell Differentiation Inducers for the Reconstruction of Osteochondral Defects

There is a great challenge in regenerating osteochondral defects because they involve lesions of both cartilage and subchondral bone, which have remarkable differences in their chemical compositions and biological lineages. Thus, considering the complicated requirements in osteochondral reconstruction, a biomimetic biphasic osteochondral scaffold (BBOS) with the layer-specific release of stem cell differentiation inducers are developed. The cartilage regeneration layer (cartilage scaffold, CS) in the BBOS contains a hyaluronic acid hydrogel to mimic the composition of cartilage, which is mechanically enhanced by host-guest supramolecular units to control the release of kartogenin (KGN). Additionally, a 3D-printed hydroxyapatite (HAp) scaffold releasing alendronate (ALN) is employed as the bone-regeneration layer (bone scaffold, BS). The two layers are bound by semi-immersion and could regulate the hierarchical targeted differentiation behavior of the stem cells. Compared to the drug-free scaffold, the MSCs in the BBOS could be promoted to differentiate into both chondrocytes and osteoblasts. The in vivo results demonstrate the strong promotion of cartilage or bone regeneration in their respective layers. It is expected that this BBOS with layer-specific inducer release can become a new strategy for osteochondral regeneration.

Nanomaterial-based scaffolds for bone tissue engineering and regeneration

The global incidence of bone tissue injuries has been increasing rapidly in recent years, making it imperative to develop suitable bone grafts for facilitating bone tissue regeneration. It has been demonstrated that nanomaterials/nanocomposites scaffolds can more effectively promote new bone tissue formation compared with micromaterials. This may be attributed to their nanoscaled structural and topological features that better mimic the physiological characteristics of natural bone tissue. In this review, we examined the current applications of various nanomaterial/nanocomposite scaffolds and different topological structures for bone tissue engineering, as well as the underlying mechanisms of regeneration. The potential risks and toxicity of nanomaterials will also be critically discussed. Finally, some considerations for the clinical applications of nanomaterials/nanocomposites scaffolds for bone tissue engineering are mentioned.

Potential Implantable Nanofibrous Biomaterials Combined with Stem Cells for Subchondral Bone Regeneration

The treatment of osteochondral defects remains a challenge. Four scaffolds were produced using Food and Drug Administration (FDA)-approved polymers to investigate their therapeutic potential for the regeneration of the osteochondral unit. Polycaprolactone (PCL) and poly(vinyl-pyrrolidone) (PVP) scaffolds were made by electrohydrodynamic techniques. Hydroxyapatite (HAp) and/or sodium hyaluronate (HA) can be then loaded to PCL nanofibers and/or PVP particles. The purpose of adding hydroxyapatite and sodium hyaluronate into PCL/PVP scaffolds is to increase the regenerative ability for subchondral bone and joint cartilage, respectively. Human bone marrow-derived mesenchymal stem cells (hBM-MSCs) were seeded on these biomaterials. The biocompatibility of these biomaterials in vitro and in vivo, as well as their potential to support MSC differentiation under specific chondrogenic or osteogenic conditions, were evaluated. We show here that hBM-MSCs could proliferate and differentiate both in vitro and in vivo on these biomaterials. In addition, the PCL-HAp could effectively increase the mineralization and induce the differentiation of MSCs into osteoblasts in an osteogenic condition. These results indicate that PCL-HAp biomaterials combined with MSCs could be a beneficial candidate for subchondral bone regeneration.

Osteochondral repair combining therapeutics implant with mesenchymal stem cells spheroids

Functional articular cartilage regeneration remains challenging, and it is essential to restore focal osteochondral defects and prevent secondary osteoarthritis. Combining autologous stem cells with therapeutic medical device, we developed a bi-compartmented implant that could promote both articular cartilage and subchondral bone regeneration. The first compartment based on therapeutic collagen associated with bone morphogenetic protein 2, provides structural support and promotes subchondral bone regeneration. The second compartment contains bone marrow-derived mesenchymal stem cell spheroids to support the regeneration of the articular cartilage. Six-month post-implantation, the regenerated articular cartilage surface was 3 times larger than that of untreated animals, and the regeneration of the osteochondral tissue occurred during the formation of hyaline-like cartilage. Our results demonstrate the positive impact of this combined advanced therapy medicinal product, meeting the needs of promising osteochondral regeneration in critical size articular defects in a large animal model combining not only therapeutic implant but also stem cells.

Engineered three-dimensional scaffolds for enhanced bone regeneration in osteonecrosis

Osteonecrosis, which is typically induced by trauma, glucocorticoid abuse, or alcoholism, is one of the most severe diseases in clinical orthopedics. Osteonecrosis often leads to joint destruction, and arthroplasty is eventually required. Enhancement of bone regeneration is a critical management strategy employed in osteonecrosis therapy. Bone tissue engineering based on engineered three-dimensional (3D) scaffolds with appropriate architecture and osteoconductive activity, alone or functionalized with bioactive factors, have been developed to enhance bone regeneration in osteonecrosis. In this review, we elaborate on the ideal properties of 3D scaffolds for enhanced bone regeneration in osteonecrosis, including biocompatibility, degradability, porosity, and mechanical performance. In addition, we summarize the development of 3D scaffolds alone or functionalized with bioactive factors for accelerating bone regeneration in osteonecrosis and discuss their prospects for translation to clinical practice.

•

Engineered three-dimensional scaffolds boost bone regeneration in osteonecrosis.

•

The ideal properties of three-dimensional scaffolds for osteonecrosis treatment are discussed.

•

Bioactive factors-functionalized three-dimensional scaffolds are promising bone regeneration devices for osteonecrosis management.

•

The challenges and opportunities of engineered three-dimensional scaffolds for osteonecrosis therapy are predicted.

Regulation of MSC and macrophage functions in bone healing by peptide LL-37-loaded silk fibroin nanoparticles on a titanium surface

Titanium-based materials have been long regarded as effective bone implants for clinical use, yet the corresponding osteointegration ability needs to be optimized. This challenge can be overcome by fabricating titanium (Ti) materials with physiological functions. In this study, peptide LL-37-loaded silk fibroin nanoparticles (SFNPs) were immobilized on a titanium surface to facilitate osteointegration by regulating the physiological functions of mesenchymal stem cells (MSCs) and macrophages. According to our results, the cell viability, recruitment and paracrine responses of MSCs and macrophages were improved by the modified Ti samples. MSC differentiation was promoted by the macrophages incubated on the modified Ti samples, and the phenotype switch of macrophages was also modulated by the MSCs incubated on the modified Ti samples. In vivo studies proved that the modified Ti implant induced MSC and macrophage recruitments to injury sites and the inflammatory response was positively regulated. Moreover, better bone formation was achieved around the modified Ti implant 28 days after surgery. This suggested that the immobilization of peptide LL-37-loaded SFNPs on a titanium surface improves osteointegration via the regulation of physiological functions of MSCs and macrophages.

Injectable Multicomponent Biomimetic Gel Composed of Inter-Crosslinked Dendrimeric and Mesoporous Silica Nanoparticles Exhibits Highly Tunable Elasticity and Dual Drug Release Capacity

There is a growing need for cartilage defect grafts that are structurally adaptable to possess multifaceted functions to promote bone regeneration, sustain medication efficacy, and preferably remain injectable but solidify quickly upon injection. In this work, we developed an injectable multicomponent biomimetic gel (MBG) by integrating polyamidoamine dendrimer G3 (G3), mesoporous silica nanoparticles (MSNs), and dendrimer-templated silver nanoparticles (G3-Ag) into a well-defined cross-linked network. MBGs composed of one particulate component (G3 alone), i.e., MBG-1, two particulate components (G3 and MSN-NH2), i.e., MBG-2, and three particulate components (G3, MSN-NH2, and G3-Ag), i.e., MBG-3, were prepared by inter-cross-linking dendrimeric and mesoporous silica nanoparticles with poly(ethylene glycol) diglycidyl ether (PEG-DGE, Mn = 2000 g/mol) via the facile amine-epoxy click reaction. The water-soluble antibiotic isoniazid was loaded to the cross-linked PEG network, whereas the hydrophobic antibiotic rifampicin was encapsulated into mesoporous MSNs. Our studies revealed that elasticity and mechanical strengths could be modulated and enhanced significantly with the inclusion of MSNs and silver nanoparticles. Isoniazid was released rapidly while rifampicin was released over an extended period of time. In addition, MBGs showed injectability, high swelling capacity, structural stability, and cytocompatibility. Taken together, MBGs have shown structural features that allow for the development of injectable gel grafts with the ability to promote cartilage defect repair and offer antibiotic medication benefits.

Hierarchical assembly of nanostructured coating for siRNA-based dual therapy of bone regeneration and revascularization

Advancing bone implant engineering offers the opportunity to overcome crucial medical challenges and improve clinical outcomes. Although the establishment of a functional vascular network is crucial for bone development, its regeneration inside bone tissue has only received limited attention to date. Herein, we utilize siRNA-decorated particles to engineer a hierarchical nanostructured coating on clinically used titanium implants for the synergistic regeneration of skeletal and vascular tissues. Specifically, an siRNA was designed to target the regulation of cathepsin K and conjugated on nanoparticles. The functionalized nanoparticles were assembled onto the bone implant to form a hierarchical nanostructured coating. By regulating mRNA transcription, the coating significantly promotes cell viability and growth factor release related to vascularization. Moreover, microchip-based experiments demonstrate that the nanostructured coating facilitates macrophage-induced synergy in up-regulation of at least seven bone and vascular growth factors. Ovariectomized rat and comprehensive beagle dog models highlight that this siRNA-integrated nanostructured coating possesses all the key traits of a clinically promising candidate to address the myriad of challenges associated with bone regeneration.

Application of Chitosan in Bone and Dental Engineering

Chitosan is a deacetylated polysaccharide from chitin, the natural biopolymer primarily found in shells of marine crustaceans and fungi cell walls. Upon deacetylation, the protonation of free amino groups of the d-glucosamine residues of chitosan turns it into a polycation, which can easily interact with DNA, proteins, lipids, or negatively charged synthetic polymers. This positive-charged characteristic of chitosan not only increases its solubility, biodegradability, and biocompatibility, but also directly contributes to the muco-adhesion, hemostasis, and antimicrobial properties of chitosan. Combined with its low-cost and economic nature, chitosan has been extensively studied and widely used in biopharmaceutical and biomedical applications for several decades. In this review, we summarize the current chitosan-based applications for bone and dental engineering. Combining chitosan-based scaffolds with other nature or synthetic polymers and biomaterials induces their mechanical properties and bioactivities, as well as promoting osteogenesis. Incorporating the bioactive molecules into these biocomposite scaffolds accelerates new bone regeneration and enhances neovascularization in vivo.