Bioinspired trimodal macro/micro/nano-porous scaffolds loading rhBMP-2 for complete regeneration of critical size bone defect

Progress of research on the surface functionalization of tantalum and porous tantalum in bone tissue engineering

Tantalum and porous tantalum are ideal materials for making orthopedic implants due to their stable chemical properties and excellent biocompatibility. However, their utilization is still affected by loosening, infection, and peripheral inflammatory reactions, which sometimes ultimately lead to implant removal. An ideal bone implant should have exceptional biological activity, which can improve the surrounding biological microenvironment to enhance bone repair. Recent advances in surface functionalization have produced various strategies for developing compatibility between either of the two materials and their respective microenvironments. This review provides a systematic overview of state-of-the-art strategies for conferring biological functions to tantalum and porous tantalum implants. Furthermore, the review describes methods for preparing active surfaces and different bioactive substances that are used, summarizing their functions. Finally, this review discusses current challenges in the development of optimal bone implant materials.

Bio-integrated scaffold facilitates large bone regeneration dominated by endochondral ossification

Repair of large bone defects caused by severe trauma, non-union fractures, or tumor resection remains challenging because of limited regenerative ability. Typically, these defects heal through mixed routines, including intramembranous ossification (IMO) and endochondral ossification (ECO), with ECO considered more efficient. Current strategies to promote large bone healing via ECO are unstable and require high-dose growth factors or complex cell therapy that cause side effects and raise expense while providing only limited benefit. Herein, we report a bio-integrated scaffold capable of initiating an early hypoxia microenvironment with controllable release of low-dose recombinant bone morphogenetic protein-2 (rhBMP-2), aiming to induce ECO-dominated repair. Specifically, we apply a mesoporous structure to accelerate iron chelation, this promoting early chondrogenesis via deferoxamine (DFO)-induced hypoxia-inducible factor-1α (HIF-1α). Through the delicate segmentation of click-crosslinked PEGylated Poly (glycerol sebacate) (PEGS) layers, we achieve programmed release of low-dose rhBMP-2, which can facilitate cartilage-to-bone transformation while reducing side effect risks. We demonstrate this system can strengthen the ECO healing and convert mixed or mixed or IMO-guided routes to ECO-dominated approach in large-size models with clinical relevance. Collectively, these findings demonstrate a biomaterial-based strategy for driving ECO-dominated healing, paving a promising pave towards its clinical use in addressing large bone defects.

Engineering mesoporous bioactive glasses for emerging stimuli-responsive drug delivery and theranostic applications

Mesoporous bioactive glasses (MBGs), which belong to the category of modern porous nanomaterials, have garnered significant attention due to their impressive biological activities, appealing physicochemical properties, and desirable morphological features. They hold immense potential for utilization in diverse fields, including adsorption, separation, catalysis, bioengineering, and medicine. Despite possessing interior porous structures, excellent morphological characteristics, and superior biocompatibility, primitive MBGs face challenges related to weak encapsulation efficiency, drug loading, and mechanical strength when applied in biomedical fields. It is important to note that the advantageous attributes of MBGs can be effectively preserved by incorporating supramolecular assemblies, miscellaneous metal species, and their conjugates into the material surfaces or intrinsic mesoporous networks. The innovative advancements in these modified colloidal inorganic nanocarriers inspire researchers to explore novel applications, such as stimuli-responsive drug delivery, with exceptional in-vivo performances. In view of the above, we outline the fabrication process of calcium-silicon-phosphorus based MBGs, followed by discussions on their significant progress in various engineered strategies involving surface functionalization, nanostructures, and network modification. Furthermore, we emphasize the recent advancements in the textural and physicochemical properties of MBGs, along with their theranostic potentials in multiple cancerous and non-cancerous diseases. Lastly, we recapitulate compelling viewpoints, with specific considerations given from bench to bedside.

Exploring the role of polymers to overcome ongoing challenges in the field of extracellular vesicles

Extracellular vesicles (EVs) are naturally occurring nanoparticles released from all eucaryotic and procaryotic cells. While their role was formerly largely underestimated, EVs are now clearly established as key mediators of intercellular communication. Therefore, these vesicles constitute an attractive topic of study for both basic and applied research with great potential, for example, as a new class of biomarkers, as cell-free therapeutics or as drug delivery systems. However, the complexity and biological origin of EVs sometimes complicate their identification and therapeutic use. Thus, this rapidly expanding research field requires new methods and tools for the production, enrichment, detection, and therapeutic application of EVs. In this review, we have sought to explain how polymer materials actively contributed to overcome some of the limitations associated to EVs. Indeed, thanks to their infinite diversity of composition and properties, polymers can act through a variety of strategies and at different stages of EVs development. Overall, we would like to emphasize the importance of multidisciplinary research involving polymers to address persistent limitations in the field of EVs.

Polysaccharide-Based Composite Hydrogel with Hierarchical Microstructure for Enhanced Vascularization and Skull Regeneration

Critical-size skull defects caused by trauma, infection, and tumor resection raise great demands for efficient bone substitutes. Herein, a hybrid cross-linked hierarchical microporous hydrogel scaffold (PHCLS) was successfully assembled by a multistep procedure, which involved (i) the preparation of poly(lactic-co-glycolic)/nanohydroxyapatite (PLGA-HAP) porous microspheres, (ii) embedding the spheres in a solution of dopamine-modified hyaluronic acid and collagen I (Col I) and cross-linking via dopamine polyphenols binding to (i) Col I amino groups (via Michael addition) and (ii) PLGA-HAP (via calcium ion chelation). The introduction of PLGA-HAP not only improved the diversity of pore size and pore communication inside the matrix but also greatly enhanced the compressive strength (5.24-fold, 77.5 kPa) and degradation properties to construct a more stable mechanical structure. In particular, the PHCLS (200 mg, nHAP) promoted the proliferation, infiltration, and angiogenic differentiation of bone marrow mesenchymal stem cells in vitro, as well as significant ectopic angiogenesis and mineralization with a storage modulus enhancement of 2.5-fold after 30 days. Meanwhile, the appropriate matrix microenvironment initiated angiogenesis and early osteogenesis by accelerating endogenous stem cell recruitment in situ. Together, the PHCLS allowed substantial skull reconstruction in the rabbit cranial defect model, achieving 85.2% breaking load strength and 84.5% bone volume fractions in comparison to the natural cranium, 12 weeks after implantation. Overall, this study reveals that the hierarchical microporous hydrogel scaffold provides a promising strategy for skull defect treatment.

Photocurable 3D-Printed PMBG/TCP Scaffold Coordinated with PTH (1-34) Bidirectionally Regulates Bone Homeostasis to Accelerate Bone Regeneration

Bone defect repair remains a major clinical challenge that requires the construction of scaffolds that can regulate bone homeostasis. In this study, a photo-cured mesoporous bioactive glass (PMBG) precursor is developed as a tricalcium phosphate (TCP) agglomerant to obtain a double-phase PMBG/TCP scaffold via 3D printing. The scaffold exhibits multi-scale porous structures and large surface areas, making it a suitable carrier for the loading of parathyroid hormone (PTH) (1-34), which is used for the treatment of osteoporosis. In vitro and in vivo results demonstrate that PMBG/TCP scaffolds coordinated with PTH (1-34) can regulate bone homeostasis in a bidirectional manner to facilitate bone formation and inhibit bone resorption. Furthermore, bidirectional regulation of bone homeostasis by PTH (1-34) is achieved by inhibiting fibrogenic activation protein (FAP). Thus, PMBG/TCP scaffolds coordinated with PTH (1-34) are viable materials with considerable potential for application in the field of bone regeneration and provide an excellent solution for the design and development of clinical materials.

Optimization of a concentrated growth factor/mesoporous bioactive glass composite scaffold and its application in rabbit mandible defect regeneration

Maxillofacial bone defect repair and regeneration remains a tremendous challenge in the field of stomatology. However, the limited osteoinductivity of artificial materials and the high cost of bioactive agents restrain their clinical translation. This study aimed to construct an economical and efficient concentrated growth factor/mesoporous bioactive glass (CGF/MBG) composite scaffold for bone regeneration. The biochemical composition and biological effects of different forms of CGFs were systematically compared, and the results showed that CGF-conditioned medium effectively promoted proliferation, migration and osteogenesis of allogenic BMSCs. Gel phase CGF (gpCGF) exhibited superior bioactivity and osteoinductivity to liquid phase CGF (lpCGF) and liquid/gel mixed phase CGF (lgpCGF), and was further applied to construct CGF/MBG scaffolds. In vitro studies demonstrated that co-culture with gpCGF-conditioned medium further enhanced the biocompatibility of MBG, increasing cell adhesion and proliferation on the scaffold. On this basis, two compositing approaches to construct the scaffold by fibrin gel formation (CGF/FG/MBG) and freeze-drying (fdCGF/MBG) were applied, and the biological efficacy of CGFs was compared in vivo. In a rabbit mandibular defect model, higher osteogenic efficiency in in situ bone regeneration of CGF/FG/MBG composite scaffolds was proved, compared with fdCGF/MBG. Taken together, the CGF/FG/MBG composite scaffold is expected to be an efficient bone repairing therapy for clinical translation, and the CGF-composited scaffold using gpCGF and the fibrin gel formation method is a promising way to enhance the bioactivity and osteoinductivity of current clinical bone repairing materials, providing new thoughts on the development of future orthopedic biomaterials.

Sustained delivery of osteogenic growth peptide through injectable photoinitiated composite hydrogel for osteogenesis

One of the most challenging clinical issues continues to be the effective bone regeneration and rebuilding following bone abnormalities. Although osteogenic growth peptide (OGP) has been proven to be effective in promoting osteoblast activity, its clinical application is constrained by abrupt release and easily degradation. We developed a GelMA/HAMA dual network hydrogel loaded with OGP based on a combination of physical chain entanglement and chemical cross-linking effects to produce an efficient long-term sustained release of OGP. The hydrogel polymers were quickly molded under ultraviolet (UV) light and had the suitable physical characteristics, porosity structure and biocompatibility. Significantly, the GelMA/HAMA-OGP hydrogel could promote cell proliferation, adhesion, increase osteogenic-related gene and protein expression in vitro. In conclusion, the OGP sustained-release system based on GelMA/HAMA dual network hydrogel offers a fresh perspective on bone regeneration therapy.

Repurpose dasatinib and quercetin: Targeting senescent cells ameliorates postmenopausal osteoporosis and rejuvenates bone regeneration

Clinical therapies developed for estrogen-deficiency-driven postmenopausal osteoporosis (PMO) and related diseases, such as bone degeneration, show multiple adverse effects nowadays. Targeting senescent cells (SnCs) and the consequent senescence-associated secretory phenotype (SASP) with a combination of dasatinib and quercetin (DQ) is a recently developed novel therapy for multiple age-related diseases. Herein, we found that estrogen deficiency induced-bone loss was attributed to a pro-inflammatory microenvironment with SASP secretions and accelerated SnC accumulation, especially senescent mesenchymal stem cells (MSCs) characterized by exhaustion and dysfunction in middle aged rats. Systematically targeting SnCs with DQ strikingly ameliorated PMO and restored MSC function. Local administration of DQ and bone morphogenetic protein 2 (BMP2) in combination promoted osteogenic differentiation of MSCs and rejuvenated osteoporotic bone regeneration. Our results repurposed DQ as an attractive therapy for treating PMO and related diseases.

Polyvinylpyrrolidone Nanofibers Incorporating Mesoporous Bioactive Glass for Bone Tissue Engineering

Composite biomaterials that combine osteoconductive and osteoinductive properties are a promising approach for bone tissue engineering (BTE) since they stimulate osteogenesis while mimicking extracellular matrix (ECM) morphology. In this context, the aim of the present research was to produce polyvinylpyrrolidone (PVP) nanofibers containing mesoporous bioactive glass (MBG) 80S15 nanoparticles. These composite materials were produced by the electrospinning technique. Design of experiments (DOE) was used to estimate the optimal electrospinning parameters to reduce average fiber diameter. The polymeric matrices were thermally crosslinked under different conditions, and the fibers' morphology was studied using scanning electron microscopy (SEM). Evaluation of the mechanical properties of nanofibrous mats revealed a dependence on thermal crosslinking parameters and on the presence of MBG 80S15 particles inside the polymeric fibers. Degradation tests indicated that the presence of MBG led to a faster degradation of nanofibrous mats and to a higher swelling capacity. The assessment of in vitro bioactivity in simulated body fluid (SBF) was performed using MBG pellets and PVP/MBG (1:1) composites to assess if the bioactive properties of MBG 80S15 were kept when it was incorporated into PVP nanofibers. FTIR and XRD analysis along with SEM-EDS results indicated that a hydroxy-carbonate apatite (HCA) layer formed on the surface of MBG pellets and nanofibrous webs after soaking in SBF over different time periods. In general, the materials revealed no cytotoxic effects on the Saos-2 cell line. The overall results for the materials produced show the potential of the composites to be used in BTE.

Strontium Ion-Functionalized Nano-Hydroxyapatite/Chitosan Composite Microspheres Promote Osteogenesis and Angiogenesis for Bone Regeneration

Critical-size bone defects are an important problem in clinical practice, which usually occurs in severe trauma, or tumor resection, and cannot heal completely and autonomously. Implantation of grafts is often required to promote the regeneration of critical-size bone defects. Metal ions play an important role in human health, as they affect the body's metabolism and the tissue function. Strontium ions (Sr²⁺) can promote osteogenesis and angiogenesis. Herein, we prepared nano-hydroxyapatite (nHA)/chitosan (CS) composite microspheres with a uniform particle size distribution and an extracellular matrix-like nanofiber structure using microfluidic technology and direct alkali-induced gelation. Strontium ions were stably added into the microspheres by using polydopamine (PDA) to chelate metal ions forming a bone repair material (nHA/CS@PDA-Sr) with good bioactivity. The coordination reaction of PDA can effectively control the release of strontium ions and avoid the negative effects caused by the high strontium concentration. Our in vitro experiments showed that the composite microspheres had good biocompatibility and that the PDA coating promotes cell adhesion. The slow release of strontium ions can effectively promote mesenchymal stem cells osteogenic differentiation and the vascularization of endothelial cells. In addition, we injected composite microspheres into cranial defects of rats to evaluate osseointegration in vivo. The results showed that nHA/CS@PDA-Sr could effectively promote bone regeneration in the defect area. This study demonstrates that composite microspheres stimulate bone repair providing a promising way for bone-defect regeneration.

Injectable magnesium oxychloride cement foam-derived scaffold for augmenting osteoporotic defect repair

HYPOTHESIS

Cement augmentation has been widely applied to promote osteoporotic fracture healing, whereas the existing calcium-based products suffer from the excessively slow degradation, which may impede bone regeneration. Magnesium oxychloride cement (MOC) shows promising biodegradation tendency and bioactivity, which is expected to be a potential alternative to the classic calcium-based cement for hard-tissue-engineering applications.

EXPERIMENTS

Here, a hierarchical porous MOC foam (MOCF)-derived scaffold with favorable bio-resorption kinetic and superior bioactivity is fabricated through Pickering foaming technique. Then, a systematic characterization in terms of material properties and in vitro biological performance have been conducted to evaluate the feasibility of the as-prepared MOCF scaffold to be a bone-augmenting material for treating osteoporotic defects.

FINDINGS

The developed MOCF shows excellent handling performance in the paste state, while exhibiting sufficient load-bearing capacity after solidification. In comparison with the traditional bone cement, calcium deficient hydroxyapatite (CDHA), our porous MOCF scaffold demonstrates a much higher biodegradation tendency and better cell recruitment ability. Additionally, the eluted bioactive ions by MOCF commits to a biologically inductive microenvironment, where the in vitro osteogenesis is significantly enhanced. It is anticipated that this advanced MOCF scaffold will be competitive for clinical therapies to augment osteoporotic bone regeneration.

The effects of nano-hydroxyapatite/polyamide 66 scaffold on dog femoral head osteonecrosis model: a preclinical study

The lack of mechanical support in the bone tunnel formed after CD often results in a poor therapeutic effect in ONFH. The n-HA/P66 has excellent biocompatibility and mechanical properties and has been widely used in bone regeneration. The present study aimed to evaluate the effects of n-HA/P66 scaffold treatment in a dog model of ONFH. A FEA was performed to analyze the mechanical changes in the femoral head after CD and n-HA/P66 scaffold or tantalum rod implantation. Fifteen male beagles were selected to establish the model of ONFH by liquid nitrogen freezing method, and the models were identified by x-ray and MRI 4 weeks after modeling and randomly divided into three groups. Nine weeks later, femoral head samples were taken for morphology, micro-CT, and histological examination. The FEA showed that the n-HA/P66 scaffold proved the structural support in the bone tunnel, similar to the tantalum rod. The morphology showed that the femoral head with n-HA/P66 implantation is intact, while the femoral heads in the model group and CD group are collapsing. Moreover, the micro-CT results of the n-HA/P66 scaffold group were better than the model group and the CD group, and the interface between the n-HA/P66 scaffold and bone tissue is blurred. Furthermore, the histological result also verifies the alterations in micro-CT, and bone tissue grows in the bone tunnel with n-HA/P66 scaffold implanted while few in the CD group. The CD results in a lack of mechanical support in the femoral head subchondral bone and bone tunnel high stress. The n-HA/P66 scaffold implantation can provide mechanical support and relieve high stress induced by CD. The n-HA/P66 scaffold can treat femoral head necrosis and provide the bone tissue growth scaffold for the femoral head after CD to promote bone tissue regeneration.

A biomimetic and bioactive scaffold with intelligently pulsatile teriparatide delivery for local and systemic osteoporosis regeneration

Osteoporosis is one of the most disabling consequences of aging, osteoporotic fractures and higher risk of the subsequent fractures leading to substantial disability and deaths, indicating both local fractures healing and the early anti-osteoporosis therapy are of great significance. Teriparatide is strong bone formation promoter effective in treating osteoporosis, while side effects limit clinical applications. Traditional drug delivery is lack of sensitive and short-term release, finding a new non-invasive and easily controllable drug delivery to not only repair the local fractures but also improve total bone mass has remained a great challenge. Thus, bioinspired by the natural bone components, we develop appropriate interactions between inorganic biological scaffolds and organic drug molecules, achieving both loaded with the teriparatide in the scaffold and capable of releasing on demand. Herein, biomimetic bone microstructure of mesoporous bioglass, a near-infrared ray triggered switch, thermosensitive liposomes based on a valve, and polydopamine coated as a heater is developed rationally for osteoporotic bone regeneration. Teriparatide is pulsatile released from intelligent delivery, not only rejuvenating osteoporotic bone defect, but also presenting strong systemic anti-osteoporosis therapy. This biomimetic bone carrying novel drug delivery platform is well worth expecting to be a new promising strategy and clinically commercialized to help patients survive from the osteoporotic fracture.

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A novel NIR-triggered three-in-one smart platform was proposed.

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Highly NIR-sensitive in vivo controlled release and self-regulating pulsatile release can be achieved.

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Local precise pulsatile release accelerates osteoporotic bone healing.

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This study focused on the osteoporotic bone regeneration of both skull and femur at the same time.

Mesoporous bioglass capsule composite injectable hydrogels with antibacterial and vascularization promotion properties for chronic wound repair

Building an angiogenesis microenvironment and inhibiting wound infection are of great significance for chronic wound repair. In this paper, polydopamine-encapsulated mesoporous bioglass (MBG@PDA) capsules were constructed to realize the integration of angiogenesis and infection inhibition through the formation of a composite hydrogel with modified hyaluronic acid (HAMA) to promote wound healing. The experiments showed that the composite hydrogel had good adhesion and toughness and promoted the migration of fibroblasts to accelerate the epithelialization process. In addition, in the composite hydrogel, MBG@PDA could release Mg²⁺ to promote the proliferation and migration of vascular endothelial cells for angiogenesis. At the same time, MBG@PDA in the composite hydrogel could facilitate the long-term release of drugs to inhibit the growth of Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) for reducing the possibility of wound infection. Finally, the results of in vivo experiments showed that a multifunctional dressing could repair wounds more quickly by promoting angiogenesis and reducing the pathological areas. In summary, the construction of these composite hydrogels can provide a repair method in the wound-repair field.

Fabrication of BMP-2-peptide-Deferoxamine- and QK-peptide-functionalized nanoscaffolds and their application for bone defect treatment

The microenvironment in the healing process of large bone defects requires suitable conditions to promote osteogenesis and angiogenesis. Coaxial electrospinning is a mature method in bone tissue engineering (BTE) and allows functional modification. Appropriate modification methods can be used to improve the bioactivity of scaffolds for BTE. In this study, coaxial electrospinning with QK peptide (a Vascular endothelial growth factor mimetic peptide) and BMP-2 peptide-DFO (BD) was performed to produce double-modified PQBD scaffolds with vascularizing and osteogenic features. The morphology of coaxially electrospun scaffolds was verified by scanning electron microscopy (SEM) and transmission electron microscopy. Laser scanning confocal microscopy and Fourier transform infrared spectroscopy confirmed that BD covalently bound to the surface of the P and PQ scaffolds. In vitro, the PQBD scaffold promoted the adhesion and proliferation of bone marrow stromal cells (BMSCs). Both QK peptide and BD showed sustainable release and preservation of biological activity, enhancing the osteogenic differentiation of BMSCs and the migration of human umbilical vein endothelial cells and promoting angiogenesis. The combined ability of these factors to promote osteogenesis and angiogenesis is superior to that of each alone. In vivo, the PQBD scaffold was implanted into the bone defect, and after 8 weeks, the defect area was almost completely covered by new bone tissue. Histology showed more mature bone tissue and more blood vessels. PQBD scaffolds promote both angiogenesis and osteogenesis, offering a promising approach to enhance bone regeneration in the treatment of large bone defects.

Achievements in Mesoporous Bioactive Glasses for Biomedical Applications

Nowadays, mesoporous bioactive glasses (MBGs) are envisaged as promising candidates in the field of bioceramics for bone tissue regeneration. This is ascribed to their singular chemical composition, structural and textural properties and easy-to-functionalize surface, giving rise to accelerated bioactive responses and capacity for local drug delivery. Since their discovery at the beginning of the 21st century, pioneering research efforts focused on the design and fabrication of MBGs with optimal compositional, textural and structural properties to elicit superior bioactive behavior. The current trends conceive MBGs as multitherapy systems for the treatment of bone-related pathologies, emphasizing the need of fine-tuning surface functionalization. Herein, we focus on the recent developments in MBGs for biomedical applications. First, the role of MBGs in the design and fabrication of three-dimensional scaffolds that fulfil the highly demanding requirements for bone tissue engineering is outlined. The different approaches for developing multifunctional MBGs are overviewed, including the incorporation of therapeutic ions in the glass composition and the surface functionalization with zwitterionic moieties to prevent bacterial adhesion. The bourgeoning scientific literature on MBGs as local delivery systems of diverse therapeutic cargoes (osteogenic/antiosteoporotic, angiogenic, antibacterial, anti-inflammatory and antitumor agents) is addressed. Finally, the current challenges and future directions for the clinical translation of MBGs are discussed.

Preparation and In Vitro Bioactivity Study of a Novel Hollow Mesoporous Bioactive Glass Nanofiber Scaffold

In this study, a novel three-dimensional hollow mesoporous bioactive glass nanofiber scaffold has been synthesized with a template-assisted sol-gel method using bacterial cellulose (BC) as a template and nonionic triblock copolymer (P123) as a pore-directing agent, ethyl orthosilicate (TEOS), calcium nitrate tetrahydrate (CN), and triethyl phosphate (TEP) as glass precursors. Scanning and transmission electron microscopies, X-ray diffraction, nitrogen adsorption-desorption, and nuclear magnetic resonance method were applied to characterize the morphology, crystal structure, and chemical structure of the mesoporous bioactive glass nanofiber scaffold. Furthermore, the in vitro bioactivity and biocompatibility were also explored. The obtained scaffold depicted nanofiber-like morphology and interconnected three-dimensional network structure that replicated the BC template. The scaffold showed a large specific surface area (230.0 cm² g^-1) and pore volume (0.2 m³ g^-1). More importantly, the scaffold exhibited excellent apatite-forming ability and cellular biocompatibility. We believe that the hollow mesoporous bioactive glass nanofiber scaffold has great potential application in bone tissue regeneration.

Porous biomaterials for tissue engineering: a review

The field of biomaterials has grown rapidly over the past decades. Within this field, porous biomaterials have played a remarkable role in: (i) enabling the manufacture of complex three-dimensional structures; (ii) recreating mechanical properties close to those of the host tissues; (iii) facilitating interconnected structures for the transport of macromolecules and cells; and (iv) behaving as biocompatible inserts, tailored to either interact or not with the host body. This review outlines a brief history of the development of biomaterials, before discussing current materials proposed for use as porous biomaterials and exploring the state-of-the-art in their manufacture. The wide clinical applications of these materials are extensively discussed, drawing on specific examples of how the porous features of such biomaterials impact their behaviours, as well as the advantages and challenges faced, for each class of the materials.

Advances in surface modification of tantalum and porous tantalum for rapid osseointegration: A thematic review

After bone defects reach a certain size, the body can no longer repair them. Tantalum, including its porous form, has attracted increasing attention due to good bioactivity, biocompatibility, and biomechanical properties. After a metal material is implanted into the body as a medical intervention, a series of interactions occurs between the material’s surface and the microenvironment. The interaction between cells and the surface of the implant mainly depends on the surface morphology and chemical composition of the implant’s surface. In this context, appropriate modification of the surface of tantalum can guide the biological behavior of cells, promote the potential of materials, and facilitate bone integration. Substantial progress has been made in tantalum surface modification technologies, especially nano-modification technology. This paper systematically reviews the progress in research on tantalum surface modification for the first time, including physicochemical properties, biological performance, and surface modification technologies of tantalum and porous tantalum.

Osteogenic Effect of Fisetin Doping in Bioactive Glass/Poly(caprolactone) Hybrid Scaffolds

Treating large bone defects or fragile patients may require enhancing the bone regeneration rate to overcome a weak contribution from the body. This work investigates the osteogenic potential of nutrient fisetin, a flavonoid found in fruits and vegetables, as a doping agent inside the structure of a SiO₂-CaO bioactive glass-poly(caprolactone) (BG-PCL) hybrid scaffold. Embedded in the full mass of the BG-PCL hybrid during one-pot synthesis, we demonstrate fisetin to be delivered sustainably; the release follows a first-order kinetics with active fisetin concentration being delivered for more than 1 month (36 days). The biological effect of BG-PCL-fisetin-doped scaffolds (BG-PCL-Fis) has been highlighted by in vitro and in vivo studies. A positive impact is demonstrated on the adhesion and the differentiation of rat primary osteoblasts, without an adverse cytotoxic effect. Implantation in critical-size mouse calvaria defects shows bone remodeling characteristics and remarkable enhancement of bone regeneration for fisetin-doped scaffolds, with the regenerated bone volume being twofold that of nondoped scaffolds and fourfold that of a commercial trabecular bovine bone substitute. Such highly bioactive materials could stand as competitive alternative strategies involving biomaterials loaded with growth factors, the use of the latter being the subject of growing concerns.

An Insight of Nanomaterials in Tissue Engineering from Fabrication to Applications

Tissue engineering is a research domain that deals with the growth of various kinds of tissues with the help of synthetic composites. With the culmination of nanotechnology and bioengineering, tissue engineering has emerged as an exciting domain. Recent literature describes its various applications in biomedical and biological sciences, such as facilitating the growth of tissue and organs, gene delivery, biosensor-based detection, etc. It deals with the development of biomimetics to repair, restore, maintain and amplify or strengthen several biological functions at the level of tissue and organs. Herein, the synthesis of nanocomposites based on polymers, along with their classification as conductive hydrogels and bioscaffolds, is comprehensively discussed. Furthermore, their implementation in numerous tissue engineering and regenerative medicine applications is also described. The limitations of tissue engineering are also discussed here. The present review highlights and summarizes the latest progress in the tissue engineering domain directed at functionalized nanomaterials.

Effect of bone-shaped nanotube-hydrogel drug delivery system for enhanced osseointegration

Anodic titanium dioxide nanotubes (TNT) have a range of beneficial theranostic properties. However, a lack of effective osseointegration is a problem frequently associated with the titanium dental implant surface. Here, we investigated whether bone-shaped nanotube titanium implants could enhance osseointegration via promoting initial release of vascular endothelial growth factor 165 (VEGF165) and dual release of recombinant human bone morphogenetic protein-2 (rhBMP-2). Thus, we generated cylindrical-shaped nanotubes (TNT1) and bone-shaped nanotubes (TNT2) through voltage-varying and time-varying electrochemical anodization methods, respectively. Additionally, we prepared rhBMP-2-loaded cylindrical-shaped nanotubes/VEGF165-loaded hydrogel (TNT-F1) and rhBMP-2-loaded bone-shaped nanotubes/VEGF165-loaded hydrogel (TNT-F2) drug delivery systems. We evaluated the characteristics and release kinetics of the drug delivery systems, and then analyzed the cytocompatibility and osteogenic differentiation of these specimens with mesenchymal stem cells (MSCs) in vitro. Finally, we utilized a rat femur defect model to test the bone formation capacity of nanotube-hydrogel drug delivery system in vivo. Among these different nanotubes structures, the bone-shaped one was the optimum structure for growth factor release.

Advances in Regenerative Sports Medicine Research

Regenerative sports medicine aims to address sports and aging-related conditions in the locomotor system using techniques that induce tissue regeneration. It also involves the treatment of meniscus and ligament injuries in the knee, Achilles’ tendon ruptures, rotator cuff tears, and cartilage and bone defects in various joints, as well as the regeneration of tendon–bone and cartilage–bone interfaces. There has been considerable progress in this field in recent years, resulting in promising steps toward the development of improved treatments as well as the identification of conundrums that require further targeted research. In this review the regeneration techniques currently considered optimal for each area of regenerative sports medicine have been reviewed and the time required for feasible clinical translation has been assessed. This review also provides insights into the direction of future efforts to minimize the gap between basic research and clinical applications.

Effects of Channels and Micropores in Honeycomb Scaffolds on the Reconstruction of Segmental Bone Defects

The reconstruction of critical-sized segmental bone defects is a key challenge in orthopedics because of its intractability despite technological advancements. To overcome this challenge, scaffolds that promote rapid bone ingrowth and subsequent bone replacement are necessary. In this study, we fabricated three types of carbonate apatite honeycomb (HC) scaffolds with uniaxial channels bridging the stumps of a host bone. These HC scaffolds possessed different channel and micropore volumes. The HC scaffolds were implanted into the defects of rabbit ulnar shafts to evaluate the effects of channels and micropores on bone reconstruction. Four weeks postoperatively, the HC scaffolds with a larger channel volume promoted bone ingrowth compared to that with a larger micropore volume. In contrast, 12 weeks postoperatively, the HC scaffolds with a larger volume of the micropores rather than the channels promoted the scaffold resorption by osteoclasts and bone formation. Thus, the channels affected bone ingrowth in the early stage, and micropores affected scaffold resorption and bone formation in the middle stage. Furthermore, 12 weeks postoperatively, the HC scaffolds with large volumes of both channels and micropores formed a significantly larger amount of new bone than that attained using HC scaffolds with either large volume of channels or micropores, thereby bridging the host bone stumps. The findings of this study provide guidance for designing the pore structure of scaffolds.

Natural bone-mimicking nanopore-incorporated hydroxyapatite scaffolds for enhanced bone tissue regeneration

Background

A considerable number of studies has been carried out to develop alloplastic bone graft materials such as hydroxyapatite (HAP) that mimic the hierarchical structure of natural bones with multiple levels of pores: macro-, micro-, and nanopores. Although nanopores are known to play many essential roles in natural bones, only a few studies have focused on HAPs containing them; none of those studies investigated the functions of nanopores in biological systems.

Method

We developed a simple yet powerful method to introduce nanopores into alloplastic HAP bone graft materials in large quantities by simply pressing HAP nanoparticles and sintering them at a low temperature.

Results

The size of nanopores in HAP scaffolds can be controlled between 16.5 and 30.2 nm by changing the sintering temperature. When nanopores with a size of ~ 30.2 nm, similar to that of nanopores in natural bones, are introduced into HAP scaffolds, the mechanical strength and cell proliferation and differentiation rates are significantly increased. The developed HAP scaffolds containing nanopores (SNPs) are biocompatible, with negligible erythema and inflammatory reactions. In addition, they enhance the bone regeneration when are implanted into a rabbit model. Furthermore, the bone regeneration efficiency of the HAP-based SNP is better than that of a commercially available bone graft material.

Conclusion

Nanopores of HAP scaffolds are very important for improving the bone regeneration efficiency and may be one of the key factors to consider in designing highly efficient next-generation alloplastic bone graft materials.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40824-022-00253-x.

Eggshell Microparticle Reinforced Scaffolds for Regeneration of Critical Sized Cranial Defects

Scaffold-based approaches for bone regeneration have been studied using a wide range of biomaterials as reinforcing agents to improve the mechanical strength and bioactivity of the 3D constructs. Eggshells are sustainable and inexpensive materials with unique biological and chemical properties to support bone differentiation. The incorporation of eggshell particles within hydrogels yields highly osteoinductive and osteoconductive scaffolds. This study reveals the effects of microparticles of whole eggshells, eggshells without a membrane, and a pristine eggshell membrane on osteogenic differentiation in protein-derived hydrogels. The in vitro studies showed that gels reinforced with eggshells with and without a membrane demonstrated comparable cellular proliferation, osteogenic gene expression, and osteogenic differentiation. Subsequently, in vivo studies were performed to implant eggshell microparticle-reinforced composite hydrogel scaffolds into critical-sized cranial defects in Sprague Dawley (SD) rats for up to 12 weeks to study bone regeneration. The in vivo results showed that the eggshell microparticle-based scaffolds supported an average bone volume of 60 mm³ and a bone density of 2000 HU 12 weeks post implantation. Furthermore, histological analyses of the explanted scaffolds showed that the eggshell microparticle-reinforced scaffolds permitted tissue infiltration and induced bone tissue formation over 12 weeks. The histology staining also indicated that these scaffolds induced significantly higher bone regeneration at 6 and 12 weeks as compared to the blank (no scaffold) and pristine gel scaffolds. The eggshell microparticle-reinforced scaffolds also supported significantly higher bone formation, remodeling, and vascularization over 6 and 12 weeks as confirmed by immunohistochemistry analysis. Collectively, our results indicated that eggshell microparticle-reinforced scaffolds facilitated significant bone regeneration in critical-sized cranial defects.

Shape-Memory ECM-Mimicking Heparin-Modified Nanofibrous Gelatin Scaffold for Enhanced Bone Regeneration in Sinus Augmentation

Biomaterials with clinical maneuverability and predictable bone regeneration are needed in the field of maxillary sinus augmentation. Herein, gelatin was chemically modified with heparin that specifically interacted with and stabilized bone morphogenetic protein-2 (BMP-2). We then introduced thermally induced phase separation to form the injectable, shape-memory, highly porous scaffold for bone regeneration in sinus augmentation. The hydrated heparin-modified nanofibrous gelatin scaffolds (NH-GS) were demonstrated with high resilience and shape-memory property, both macroscopically and microscopically, making them injectable scaffolds and expected to be applied in sinus augmentation. This novel scaffold was verified to be biocompatible and an excellent matrix to support cell attachment, proliferation, and infiltration. Further, the growth factor-loaded NH-GS showed sustained release kinetics of BMP-2 through affinity-based scaffold-growth factor interaction, compared with BMP-2 loaded gelatin sponge (GS) and nanofibrous gelatin scaffold (NF). Both in vitro and in vivo experiments demonstrated that the BMP-2-loaded NH-GS exhibited the highest osteogenesis among the other groups. Taken together, this study introduces a new regenerative strategy in maxillary sinus augmentation, which is injectable with a predefined shape and structure and promotes bone regeneration through a more sustained BMP-2 release.

Spatiotemporal regulation of angiogenesis/osteogenesis emulating natural bone healing cascade for vascularized bone formation

Engineering approaches for growth factor delivery have been considerably advanced for tissue regeneration, yet most of them fail to provide a complex combination of signals emulating a natural healing cascade, which substantially limits their clinical successes. Herein, we aimed to emulate the natural bone healing cascades by coupling the processes of angiogenesis and osteogenesis with a hybrid dual growth factor delivery system to achieve vascularized bone formation. Basic fibroblast growth factor (bFGF) was loaded into methacrylate gelatin (GelMA) to mimic angiogenic signalling during the inflammation and soft callus phases of the bone healing process, while bone morphogenetic protein-2 (BMP-2) was bound onto mineral coated microparticles (MCM) to mimics osteogenic signalling in the hard callus and bone remodelling phases. An Initial high concentration of bFGF accompanied by a sustainable release of BMP-2 and inorganic ions was realized to orchestrate well-coupled osteogenic and angiogenic effects for bone regeneration. In vitro experiments indicated that the hybrid hydrogel markedly enhanced the formation of vasculature in human umbilical vein endothelial cells (HUVECs), as well as the osteogenic differentiation of mesenchymal stem cells (BMSCs). In vivo results confirmed the optimal osteogenic performance of our F/G-B/M hydrogel, which was primarily attributed to the FGF-induced vascularization. This research presents a facile and potent alternative for treating bone defects by emulating natural cascades of bone healing.

Synergic adhesive chemistry-based fabrication of BMP-2 immobilized silk fibroin hydrogel functionalized with hybrid nanomaterial to augment osteogenic differentiation of rBMSCs for bone defect repair

Bone defect repair and tissue engineering is specifically challenging process because of the distinctive morphological and structural behaviours of natural bone with complex healing and biochemical mechanisms. In the present investigation, we designed dopamine adhesive chemistry-based fabrication of silk fibroin hydrogel (SFD) with incorporation of nano-hydroxyapatite (nHA)-graphene oxide (GO) hybrid nanofillers with well-arranged porous morphology immobilized with bone morphogenic protein-2 (BMP-2) for the effective in vitro rabbit bone marrow derived mesenchymal stem cells loading compatibility and in vivo new bone regrowth and collagen deposition ability. We have achieved bone-specific hydrogel scaffolds with upgraded structural features, mechanical properties and particularly promoted in vitro osteogenic differentiation and compatibility of rabbit bone marrow mesenchymal stem cells (rBMSCs). Structural and microscopic analyses established greater distributions of components and well-ordered and aligned porous structure of the hydrogel network. In vivo result of new bone regrowth was promisingly higher in the Bm@nHG-SFD hydrogel (85%) group as compared to the other treatment groups of nHG-SFD (77%) and nH-SFD (64%) hydrogel. Overall, we summarized that morphologically improved hydrogel material with immobilization of BMP-2 could be have more attentions for new generation bone regeneration therapies.

3D-printed, bioactive ceramic scaffold with rhBMP-2 in treating critical femoral bone defects in rabbits using the induced membrane technique

Although autogenous bone grafts are an optimal filling material for the induced membrane technique, limited availability and complications at the harvest site have created a need for alternative graft materials. We aimed to investigate the effect of an rhBMP-2-coated, 3D-printed, macro/microporous CaO-SiO2 -P2 O5 -B2 O3 bioactive ceramic scaffold in the treatment of critical femoral bone defects in rabbits using the induced membrane technique. A 15-mm segmental bone defect was made in the metadiaphyseal area of the distal femur of 14 rabbits. The defect was filled with polymethylmethacrylate cement and stabilized with a 2.0 mm locking plate. After the membrane matured for 4 weeks, the scaffold was implanted in two randomized groups: Group A (3D-printed bioceramic scaffold) and Group B (3D-printed, bioceramic scaffold with rhBMP-2). Eight weeks after implantation, the radiographic assessment showed that the healing rate of the defect was significantly higher in Group B (7/7, 100%) than in Group A (2/7, 29%). The mean volume of new bone formation around and inside the scaffold doubled in Group B compared to that in Group A. The mean static and dynamic stiffness were significantly higher in Group B. Histological examination revealed newly formed bone in both groups. Extensive cortical bone formation along the scaffold was found in Group B. Successful bone reconstruction in critical-sized bone defects could be obtained using rhBMP-2-coated, 3D-printed, macro/microporous bioactive ceramic scaffolds. This grafting material demonstrated potential as an alternative graft material in the induced membrane technique for reconstructing critical-sized bone defects.

Comparative characteristic study from bone marrow-derived mesenchymal stem cells

Tissue engineering has been extensively investigated and proffered to be a potential platform for novel tissue regeneration. The utilization of mesenchymal stem cells (MSCs) from various sources has been widely explored and compared. In this regard, MSCs derived from bone marrow have been proposed and described as a promising cell resource due to their high yield of isolated cells with colony-forming potential, self-renewal capacity, MSC surface marker expression, and multi-lineage differentiation capacities in vitro. However, there is evidence for bone marrow MSCs (BM-MSCs) both in vitro and in vivo from different species presenting identical and distinct potential stemness characteristics. In this review, the fundamental knowledge of the growth kinetics and stemness properties of BM-MSCs in different animal species and humans are compared and summarized. Finally, to provide a full perspective, this review will procure results of current information studies focusing on the use of BM-MSCs in clinical practice.

Chitosan-anthracene hydrogels as controlled stiffening networks

In this study, we report the synthesis of single and dual-crosslinked anthracene-functional chitosan-based hydrogels in the absence of toxic initiators. Single crosslinking was achieved through dimerization of anthracene, whereas dual-crosslinked hydrogel was formed through dimerization of anthracene and free radical photopolymerization of methacrylated-chitosan in the presence of non-toxic initiator riboflavin, a well-known vitamin B2. Both single and dual-crosslinked hydrogels were found to be elastic, as was determined through rheological analysis. We observed that the dual-crosslinked hydrogels exhibited higher Young's modulus than the single-crosslinked hydrogels, where the modulus for single and dual-crosslinked hydrogels were measured as 9.2 ± 1.0 kPa and 26 ± 2.8 kPa, respectively resulting in significantly high volume of cells in dual-crosslinked hydrogel (2.2 × 10⁷ μm³) compared to single-crosslinked (4.9 × 10⁶ μm³). Furthermore, we investigated the cytotoxicity of both hydrogels towards 3T3-J2 fibroblast cells through CellTiter-Glo assay. Finally, immunofluorescence staining was carried out to evaluate the impact of hydrogel modulus on cell morphology. This study comprehensively presents functionalization of chitosan with anthracene, uses nontoxic initiator riboflavin, modulates the degree of crosslinking through dimerization of anthracene and free radical photopolymerization, and further modulates cell behavior through the alterations of hydrogel properties.

Review of emerging nanotechnology in bone regeneration: progress, challenges, and perspectives

The application of nanotechnology to regenerative medicine has increased over recent decades. The development of materials that can influence biology at the nanoscale has gained interest as our understanding of the interactions between cells and biomaterials at the nanoscale has grown. Materials that are either nanostructured or influence the nanostructure of the cellular microenvironment have been developed and shown to have advantages over their microscale counterparts. There are several reviews which have been published that discuss how nanomaterials have been used in regenerative medicine, particularly in bone regeneration. Most of these studies have explored this concept in specific areas, such as the application of glass-based nanocomposites, nanotechnology for targeted drug delivery to stimulate bone repair, and the progress in nanotechnology for the treatment of osteoporosis. In this review paper, the impact of nanotechnology in biomaterials development for bone regeneration will be discussed highlighting specifically, nanostructured materials that influence mechanical properties, biocompatibility, and osteoinductivity.

Spatiotemporal Immunomodulation Using Biomimetic Scaffold Promotes Endochondral Ossification-Mediated Bone Healing

Biomaterials play an important role in treating bone defects by promoting direct osteogenic healing through intramembranous ossification (IO). However, majority of the body's bones form via cartilaginous intermediates by endochondral ossification (EO), a process that has not been well mimicked by engineered scaffolds, thus limiting their clinical utility in treating large segmental bone defects. Here, by entrapping corticosteroid dexamethasone within biomimetic recombinant human bone morphogenetic protein (rhBMP)-loaded porous mesoporous bioglass scaffolds and regulating their release kinetics, significant degree of ectopic bone formation through endochondral ossification is achieved. By regulating the recruitment and polarization of immune suppressive macrophage phenotypes, the scaffold promotes rapid chondrogenesis by activating Hif-3α signaling pathway in mesenchymal stem cells, which upregulates the expression of downstream chondrogenic genes. Inhibition of Hif-3α signaling reverses the endochondral ossification phenotype. Together, these results reveal a strategy to facilitate developmental bone growth process using immune modulating biomimetic scaffolds, thus providing new opportunities for developing biomaterials capable of inducing natural tissue regeneration.

Foam Replica Method in the Manufacturing of Bioactive Glass Scaffolds: Out-of-Date Technology or Still Underexploited Potential?

Since 2006, the foam replica method has been commonly recognized as a valuable technology for the production of highly porous bioactive glass scaffolds showing three-dimensional, open-cell structures closely mimicking that of natural trabecular bone. Despite this, there are important drawbacks making the usage of foam-replicated glass scaffolds a difficult achievement in clinical practice; among these, certainly the high operator-dependency of the overall manufacturing process is one of the most crucial, limiting the scalability to industrial production and, thus, the spread of foam-replicated synthetic bone substitutes for effective use in routine management of bone defect. The present review opens a window on the versatile world of the foam replica technique, focusing the dissertation on scaffold properties analyzed in relation to various processing parameters, in order to better understand which are the real issues behind the bottleneck that still puts this technology on the Olympus of the most used techniques in laboratory practice, without moving, unfortunately, to a more concrete application. Specifically, scaffold morphology, mechanical and mass transport properties will be reviewed in detail, considering the various templates proposed till now by several research groups all over the world. In the end, a comprehensive overview of in vivo studies on bioactive glass foams will be provided, in order to put an emphasis on scaffold performances in a complex three-dimensional environment.

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

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

Developing a novel resorptive hydroxyapatite-based bone substitute for over-critical size defect reconstruction: physicochemical and biological characterization and proof of concept in segmental rabbit's ulna reconstruction

The aim of this study was to develop novel hydroxyapatite (HAP)-based bioactive bone replacement materials for segmental osteotomy reconstruction. Customized three-dimensional (3D) bone construct was manufactured from nanohydroxyapatite (nHAP) with poly(lactide-co-glycolide) (PLGA) coating using 3D models derived from the computed tomography (CT) scanning of the rabbit's ulna and gradient 3D printing of the bone substitute mimicking the anatomical shape of the natural bone defect. Engineered construct revealed adequate micro-architectural design for successful bone regeneration having a total porosity of 64% and an average pore size of 256 μm. Radiography and micro-CT analysis depicted new bone apposition through the whole length of the reconstructed ulna with a small area of non-resorbed construct in the central area of defect. Histological analysis revealed new bone formation with both endochondral and endesmal type of ossification. Immunohistochemistry analysis depicted the presence of bone formation indicators - bone morphogenetic protein (BMP), osteocalcin (OCN) and osteopontin (OPN) within newly formed bone. Manufactured personalized construct acts as a "smart" responsive biomaterial capable of modulating the functionality and potential for the personalized bone reconstruction on a clinically relevant length scale.

Gradient nanostructured titanium stimulates cell responses in vitro and enhances osseointegration in vivo

Background

Though titanium (Ti) is widely used as dental materials in the clinic, effective methods to treat Ti for higher surface biological activity still lack. Through Surface mechanical attrition treatment (SMAT) technology we could endow Ti with gradient nanostructured surface (GNS Ti). To investigate the biocompatibility of GNS Ti for its further application in dental implant field, we study the effects of GNS Ti on cell responses in vitro and osseointegration of the implant with surrounding bone tissues in vivo.

Methods

In this study, GNS Ti was fabricated by SMAT. In vitro experiment, we co-cultured GNS Ti with bone mesenchymal stem cells (BMSCs), surface characterization was detected by transmission electron microscope (TEM). Adhesion, proliferation and differentiation of BMSCs were evaluated by scanning electron microscope (SEM), MTT, flow cytometry (FCM), alkaline phosphatase (ALP) and osteocalcin (OCN) tests. In vivo experiment, the GNS Ti was implanted into the rabbit mandible. Osteogenesis and osseointegration were evaluated by Micro CT, toluidine blue staining, and immunohistochemical staining at 4, 8, and 12 weeks postoperatively.

Results

Both results showed that compared with the coarse grained (CG) Ti, the GNS Ti stimulated the adhesion, proliferation, and differentiation of BMSCs and improved osteogenesis and osseointegration.

Conclusions

This study indicates that gradient nanostructured Ti is a promising material for dental implant application.

The ultralong-term comparison of osteogenic behavior of three scaffolds with different matrices and degradability between one and two years

Attributed to their structure and composition manipulated to mimic natural bone tissue, porous scaffolds composed of inorganic nano-hydroxyapatite (n-HA) and organic polymers with different degrees of degradability have been proven to be a promising bone regeneration strategy. However, long-term and in-depth comparative research on the effects of scaffolds with different matrices and degrees of degradability on bone reconstruction is still lacking. In this study, the ultralong-term osteogenic performance of three polymeric composite scaffolds based on non-degradable polyamide 66 (PA66), slowly degradable polycaprolactone (PCL) and fast degradable poly (lactic-co-glycolic acid) (PLGA) were investigated comparatively after implanting the scaffolds into rabbit femoral defects for 12, 15, 18 and 21 months. The results demonstrated that the structural integrity of the scaffolds played a positive role in long-term bone reconstruction. Thus the n-HA/PA66 and n-HA/PCL scaffolds have a higher relative bone volume and bone density than the n-HA/PLGA scaffolds from 12 to 21 months. In addition, the favorable surface wettability and collagen-like molecular structure should endow the n-HA/PA66 scaffold with the best long-term osteogenic property among the three scaffolds. The ultralong-term comparative study reveals that a relatively stable scaffold integrity, together with favorable matrix molecular characteristics and hydrophilicity, may be more important for long-term osteogenesis besides the effect of scaffold pore structure, rather than the pursuit of fast scaffold degradation. The results also show that the space left by scaffold degradation is not easily occupied by new bone tissue, especially after bone tissue has formed a stable structure or the bone interface has become inert.

Optimized BMSC-derived osteoinductive exosomes immobilized in hierarchical scaffold via lyophilization for bone repair through Bmpr2/Acvr2b competitive receptor-activated Smad pathway

Mesenchymal stem cell-derived exosomes (MSC-exos), with its inherent capacity to modulate cellular behavior, are emerging as a novel cell-free therapy for bone regeneration. Herein, focusing on practical applying problems, the osteoinductivity of MSC-exos produced by different stem cell sources (rBMSCs/rASCs) and culture conditions (osteoinductive/common) were systematically compared to screen out an optimized osteogenic exosome (BMSC-OI-exo). Via bioinformatic analyses by miRNA microarray and in vitro pathway verification by gene silencing and miRNA transfection, we first revealed that the osteoinductivity of BMSC-OI-exo was attributed to multi-component exosomal miRNAs (let-7a-5p, let-7c-5p, miR-328a-5p and miR-31a-5p). These miRNAs targeted Acvr2b/Acvr1 and regulated the competitive balance of Bmpr2/Acvr2b toward Bmpr-elicited Smad1/5/9 phosphorylation. On these bases, lyophilized delivery of BMSC-OI-exo on hierarchical mesoporous bioactive glass (MBG) scaffold was developed to realize bioactivity maintenance and sustained release by entrapment in the surface microporosity of the scaffold. In a rat cranial defect model, the loading of BMSC-OI-exo efficiently enhanced the bone forming capacity of the scaffold and induced rapid initiation of bone regeneration. This paper could provide empirical bases of MSC-exo-based therapy for bone regeneration and theoretical bases of MSC-exo-induced osteogenesis mechanism. The BMSC-OI-exo-loaded MBG scaffold developed here represented a promising bone repairing strategy for future clinical application.

Mineralized Hydrogels Induce Bone Regeneration in Critical Size Cranial Defects

Sequential mineralization enables the integration of minerals within the 3D structure of hydrogels. Hydrolyzed collagen-based hydrogels are sequentially mineralized over 10 cycles. One cycle is defined as an incubation period in calcium chloride dihydrate followed by incubation in sodium phosphate dibasic dihydrate. Separate cycles are completed at 30-minute and 24-hour intervals. For the gels mineralized for 30 min and 24 h, the compressive moduli increases from 4.25 to 87.57 kPa and from 4.25 to 125.47 kPa, respectively, as the cycle number increases from 0 to 10. As indicated by X-ray diffraction (XRD) and Fourier transform infrared analysis (FTIR) analyses, the minerals in the scaffolds are mainly hydroxyapatite. In vitro experiments, which measure mechanical properties, porous structure, mineral content, and gene expression are performed to evaluate the physical properties and osteoinductivity of the scaffolds. Real time-quantitative polymerase chain reaction (RT-qPCR) demonstrates 4-10 fold increase in the expression of BMP-7 and osteocalcin. The in vivo subcutaneous implantation demonstrates that the scaffolds are biocompatible and 90% biodegradable. The critical size cranial defects in vivo exhibit nearly complete bone regeneration. Cycle 10 hydrogels mineralized for 24 h have a volume of 59.86 mm³ and a density of 1946.45 HU. These results demonstrate the suitability of sequentially mineralized hydrogel scaffolds for bone repair and regeneration.

Porous bioactive glass micro- and nanospheres with controlled morphology: developments, properties and emerging biomedical applications

In recent years, porous bioactive glass micro/nanospheres (PBGSs) have emerged as attractive biomaterials in various biomedical applications where such engineered particles provide suitable functions, from tissue engineering to drug delivery. The design and synthesis of PBGSs with controllable particle size and pore structure are critical for such applications. PBGSs have been successfully synthesized using melt-quenching and sol-gel based methods. The morphology of PBGSs is controllable by tuning the processing parameters and precursor characteristics during the synthesis. In this comprehensive review on PBGSs, we first overview the synthesis approaches for PBGSs, including both melt-quenching and sol-gel based strategies. Sol-gel processing is the primary technology used to produce PBGSs, allowing for control over the chemical compositions and pore structure of particles. Particularly, the influence of pore-forming templates on the morphology of PBGSs is highlighted. Recent progress in the sol-gel synthesis of PBGSs with sophisticated pore structures (e.g., hollow mesoporous, dendritic fibrous mesoporous) is also covered. The challenges regarding the control of particle morphology, including the influence of metal ion precursors and pore expansion, are discussed in detail. We also highlight the recent achievements of PBGSs in a number of biomedical applications, including bone tissue regeneration, wound healing, therapeutic agent delivery, bioimaging, and cancer therapy. Finally, we conclude with our perspectives on the directions of future research based on identified challenges and potential new developments and applications of PBGSs.

Enhancing the mechanical properties and cytocompatibility of magnesium potassium phosphate cement by incorporating oxygen-carboxymethyl chitosan

Incorporating bioactive substances into synthetic bioceramic scaffolds is challenging. In this work, oxygen-carboxymethyl chitosan (O-CMC), a natural biopolymer that is nontoxic, biodegradable and biocompatible, was introduced into magnesium potassium phosphate cement (K-struvite) to enhance its mechanical properties and cytocompatibility. This study aimed to develop O-CMC/magnesium potassium phosphate composite bone cement (OMPC), thereby combining the optimum bioactivity of O-CMC with the extraordinary self-setting properties and mechanical intensity of the K-struvite. Our results indicated that O-CMC incorporation increased the compressive strength and setting time of K-struvite and decreased its porosity and pH value. Furthermore, OMPC scaffolds remarkably improved the proliferation, adhesion and osteogenesis related differentiation of MC3T3-E1 cells. Therefore, O-CMC introduced suitable physicochemical properties to K-struvite and enhanced its cytocompatibility for use in bone regeneration.

Mesoporous Bioactive Glasses Cytocompatibility Assessment: A Review of In Vitro Studies

Thanks to their high porosity and surface area, mesoporous bioactive glasses (MBGs) have gained significant interest in the field of medical applications, in particular, with regards to enhanced bioactive properties which facilitate bone regeneration. The aim of this article is to review the state of the art regarding the biocompatibility evaluation of MBGs and provide a discussion of the various approaches taken. The research was performed using PubMed database and covered articles published in the last five years. From a total of 91 articles, 63 were selected after analyzing them according to our inclusion and exclusion criteria. In vitro methodologies and techniques used for biocompatibility assessment were investigated. Among the biocompatibility assessment techniques, scanning electron microscopy (SEM) has been widely used to study cell morphology and adhesion. Viability and proliferation were assessed using different assays including cell counting and/or cell metabolic activity measurement. Finally, cell differentiation tests relied on the alkaline phosphatase assay; however, these were often complemented by specific bimolecular tests according to the exact application of the mesoporous bioactive glass. The standardization and validation of all tests performed for MBG cytocompatibility is a key aspect and crucial point and should be considered in order to avoid inconsistencies, bias between studies, and unnecessary consumption of time. Therefore, introducing standard tests would serve an important role in the future assessment and development of MBG materials.

Construction of a hierarchical micro & nanoporous surface for loading genistein on the composite of polyetheretherketone/tantalum pentoxide possessing antibacterial activity and accelerated osteointegration

Nanoporous tantalum pentoxide (NTP) particles with a pore size of about 10 nm were synthesized and blended with polyetheretherketone (PEEK) to fabricate a PEEK/NTP composite (PN). Subsequently, PN was treated by concentrated sulfuric acid to create a microporous surface (pore size of around 2 μm) on sulfonated PN (SPN), which formed a hierarchical micro & nanoporous surface. Compared with PN, the porous surface of SPN exhibited higher roughness, hydrophilicity, and surface energy. In addition, genistein (GT) was loaded into the porous surface of SPN (SPNG), which showed high GT loading capacity and sustained release of GT into phosphate buffered saline (PBS). Moreover, SPNG revealed excellent antibacterial activity, which inhibited bacterial (E. coli and S. aureus) growth in vitro due to the synergistic effects of both sulfonic acid (SO3H) groups and the sustained release of GT. Compared with PN, SPN significantly improved the adhesion, proliferation, and osteogenic differentiation of bone mesenchymal stem cells in vitro. Moreover, compared with SPN, SPNG further enhances the cell responses. Compared with PN, SPN remarkably improved bone formation and osteointegration in vivo. Furthermore, compared with SPN, SPNG further enhanced the osteointegration. In short, SPNG with a micro & nanoporous surface, SO3H groups, and the sustained release of GT exhibited antibacterial activity and accelerated osteointegration, which would have tremendous potential as drug-loaded implants for bone substitute.