Polycaprolactone-coated 3D printed tricalcium phosphate scaffolds for bone tissue engineering: in vitro alendronate release behavior and local delivery effect on in vivo osteogenesis

Extrusion 3D-printed tricalcium phosphate-polycaprolactone biocomposites for quercetin-KCl delivery in bone tissue engineering

Critical-sized bone defects pose a significant challenge in advanced healthcare due to limited bone tissue regenerative capacity. The complex interplay of numerous overlapping variables hinders the development of multifunctional biocomposites. Phytochemicals show promise in promoting bone growth, but their dose-dependent nature and physicochemical properties halt clinical use. To develop a comprehensive solution, a 3D-printed (3DP) extrusion-based tricalcium phosphate-polycaprolactone (TCP-PCL) scaffold is augmented with quercetin and potassium chloride (KCl). This composite material demonstrates a compressive strength of 30 MPa showing promising stability for low load-bearing applications. Quercetin release from the scaffold follows a biphasic pattern that persists for up to 28 days, driven via diffusion-mediated kinetics. The incorporation of KCl allows for tunable degradation rates of scaffolds and prevents the initial rapid release. Functionalization of scaffolds facilitates the attachment and proliferation of human fetal osteoblasts (hfOB), resulting in a 2.1-fold increase in cell viability. Treated scaffolds exhibit a 3-fold reduction in osteosarcoma (MG-63) cell viability as compared to untreated substrates. Ruptured cell morphology and decreased mitochondrial membrane potential indicate the antitumorigenic potential. Scaffolds loaded with quercetin and quercetin-KCl (Q-KCl) demonstrate 76% and 89% reduction in bacterial colonies of Staphylococcus aureus, respectively. This study provides valuable insights as a promising strategy for bone tissue engineering (BTE) in orthopedic repair.

Drug delivery strategies through 3D-printed calcium phosphate

3D printing has revolutionized bone tissue engineering (BTE) by enabling the fabrication of patient- or defect-specific scaffolds to enhance bone regeneration. The superior biocompatibility, customizable bioactivity, and biodegradability have enabled calcium phosphate (CaP) to gain significance as a bone graft material. 3D-printed (3DP) CaP scaffolds allow precise drug delivery due to their porous structure, adaptable structure-property relationship, dynamic chemistry, and controlled dissolution. The effectiveness of conventional scaffold-based drug delivery is hampered by initial burst release and drug loss. This review summarizes different multifunctional drug delivery approaches explored in controlling drug release, including polymer coatings, formulation integration, microporous scaffold design, chemical crosslinking, and direct extrusion printing for BTE applications. The review also outlines perspectives and future challenges in drug delivery research, paving the way for next-generation bone repair methodologies.

In Vitro and In Vivo Evaluation of 3D Printed Poly(Ethylene Glycol) Dimethacrylate-Based Photocurable Hydrogel Platform for Bone Tissue Engineering

This study focuses to develop a unique hybrid hydrogel bioink formulation that incorporates poly(ethylene glycol) dimethacrylate (PEGDMA), gelatin (Gel), and methylcellulose (MC). This formulation achieves the necessary viscosity for extrusion-based three-dimensional (3D) printing of scaffolds intended for bone regeneration. After thorough optimization of the hybrid bioink system with Gel, three distinct scaffold groups are investigated in vitro: 0%, 3%, and 6% (w/v) Gel. These scaffold groups are examined for their morphology, mechanical strength, biodegradation, in vitro cell proliferation and differentiation, and in vivo bone formation using a rat cranial defect model. Among these scaffold compositions, the 3% Gel scaffold exhibits the most favorable characteristics, prompting further evaluation as a rat mesenchymal stem cell (rMSC) carrier in a critical-size cranial defect within a Lewis rat model. The compressive strength of all three scaffold groups range between 1 and 2 MPa. Notably, the inclusion of Gel in the scaffolds leads to enhanced bioactivity and cell adhesion. The Gel-containing scaffolds notably amplify osteogenic differentiation, as evidenced by alkaline phosphatase (ALP) and Western blot analyses. The in vivo results, as depicted by microcomputed tomography, showcase augmented osteogenesis within cell-seeded scaffolds, thus validating this innovative PEGDMA-based scaffold system as a promising candidate for cranial bone defect healing.

Citric Acid Loaded Hydrogel-Coated Stent for Dissolving Pancreatic Duct Calculi

In recent years, the incidence of chronic pancreatitis has increased significantly. Pancreatic calculi obstruct the pancreatic duct and induce abdominal pain in the patients. Pancreatic duct stenting is the major treatment option for chronic pancreatitis with calculi. In this study, a new kind of drug-eluting stent, a pancreatic stent coated by methacrylated gelatin (GelMA) hydrogel loaded with citric acid (CA), was designed for the interventional treatment of pancreatic duct calculi. The CA loading capacity reached up to 0.7 g CA/g hydrogel-coated stent. The GelMA hydrogel coating has higher mechanical strength and lower swelling performance after loading with CA. The in vitro experiments of stents exhibited good performance in CA sustained release and the calculi can be dissolved in almost 3 days. The stents also showed good blood compatibility and cell compatibility. This research has important clinical value in the treatment of chronic pancreatitis with pancreatic calculi.

Natural medicine delivery from 3D printed bone substitutes

Unmet medical needs in treating critical-size bone defects have led to the development of numerous innovative bone tissue engineering implants. Although additive manufacturing allows flexible patient-specific treatments by modifying topological properties with various materials, the development of ideal bone implants that aid new tissue regeneration and reduce post-implantation bone disorders has been limited. Natural biomolecules are gaining the attention of the health industry due to their excellent safety profiles, providing equivalent or superior performances when compared to more expensive growth factors and synthetic drugs. Supplementing additive manufacturing with natural biomolecules enables the design of novel multifunctional bone implants that provide controlled biochemical delivery for bone tissue engineering applications. Controlled release of naturally derived biomolecules from a three-dimensional (3D) printed implant may improve implant-host tissue integration, new bone formation, bone healing, and blood vessel growth. The present review introduces us to the current progress and limitations of 3D printed bone implants with drug delivery capabilities, followed by an in-depth discussion on cutting-edge technologies for incorporating natural medicinal compounds embedded within the 3D printed scaffolds or on implant surfaces, highlighting their applications in several pre- and post-implantation bone-related disorders.

Customized Additive Manufacturing in Bone Scaffolds-The Gateway to Precise Bone Defect Treatment

In the advancing landscape of technology and novel material development, additive manufacturing (AM) is steadily making strides within the biomedical sector. Moving away from traditional, one-size-fits-all implant solutions, the advent of AM technology allows for patient-specific scaffolds that could improve integration and enhance wound healing. These scaffolds, meticulously designed with a myriad of geometries, mechanical properties, and biological responses, are made possible through the vast selection of materials and fabrication methods at our disposal. Recognizing the importance of precision in the treatment of bone defects, which display variability from macroscopic to microscopic scales in each case, a tailored treatment strategy is required. A patient-specific AM bone scaffold perfectly addresses this necessity. This review elucidates the pivotal role that customized AM bone scaffolds play in bone defect treatment, while offering comprehensive guidelines for their customization. This includes aspects such as bone defect imaging, material selection, topography design, and fabrication methodology. Additionally, we propose a cooperative model involving the patient, clinician, and engineer, thereby underscoring the interdisciplinary approach necessary for the effective design and clinical application of these customized AM bone scaffolds. This collaboration promises to usher in a new era of bioactive medical materials, responsive to individualized needs and capable of pushing boundaries in personalized medicine beyond those set by traditional medical materials.

Mechanism of regulating macrophages/osteoclasts in attenuating wear particle-induced aseptic osteolysis

Joint replacement surgery is the most effective treatment for end-stage arthritis. Aseptic loosening caused by periprosthetic osteolysis is a common complication after joint replacement. Inflammation induced by wear particles derived from prosthetic biomaterials is a major cause of osteolysis. We emphasize that bone marrow-derived macrophages and their fusion-derived osteoclasts play a key role in this pathological process. Researchers have developed multiple intervention approaches to regulate macrophage/osteoclast activation. Aiming at wear particle-induced periprosthetic aseptic osteolysis, this review separately discusses the molecular mechanism of regulation of ROS formation and inflammatory response through intervention of macrophage/osteoclast RANKL-MAPKs-NF-κB pathway. These molecular mechanisms regulate osteoclast activation in different ways, but they are not isolated from each other. There is also a lot of crosstalk among the different mechanisms. In addition, other bone and joint diseases related to osteoclast activation are also briefly introduced. Therefore, we discuss these new findings in the context of existing work with a view to developing new strategies for wear particle-associated osteolysis based on the regulation of macrophages/osteoclasts.

Bisphosphonate-incorporated coatings for orthopedic implants functionalization

Bisphosphonates (BPs), the stable analogs of pyrophosphate, are well-known inhibitors of osteoclastogenesis to prevent osteoporotic bone loss and improve implant osseointegration in patients suffering from osteoporosis. Compared to systemic administration, BPs-incorporated coatings enable the direct delivery of BPs to the local area, which will precisely enhance osseointegration and bone repair without the systemic side effects. However, an elaborate and comprehensive review of BP coatings of implants is lacking. Herein, the cellular level (e.g., osteoclasts, osteocytes, osteoblasts, osteoclast precursors, and bone mesenchymal stem cells) and molecular biological regulatory mechanism of BPs in regulating bone homeostasis are overviewed systematically. Moreover, the currently available methods (e.g., chemical reaction, porous carriers, and organic material films) of BP coatings construction are outlined and summarized in detail. As one of the key directions, the latest advances of BP-coated implants to enhance bone repair and osseointegration in basic experiments and clinical trials are presented and critically evaluated. Finally, the challenges and prospects of BP coatings are also purposed, and it will open a new chapter in clinical translation for BP-coated implants.

Impact of beta-tricalcium phosphate on preventing tooth extraction-triggered bisphosphonate-related osteonecrosis of the jaw in rats

Antiresorptive or antiangiogenic drugs can cause medication-related osteonecrosis of the jaw that is refractory. Bisphosphonate-related osteonecrosis of the jaw (BRONJ) may be caused by procedures such as tooth extraction damage the alveolar bone, release bisphosphonates (BPs) and impede healing. This study investigated strategies for BRONJ prevention and molecular mechanisms of its onset. We assessed the effectiveness of filling extraction sockets with beta-tricalcium phosphate (β-TCP). Rats were administered zoledronic acid (ZA) 1.2 mg/kg once per week for 2 weeks, and a molar was extracted. They were randomly assigned to the β-TCP group (bone defects filled with 0.01 g of β-TCP) or control group. Tissue content measurements indicated 2.2 ng of ZA per socket in the β-TCP group and 4.9 ng in the control group, confirming BP distribution and BP adsorption by β-TCP in vivo. At 4 weeks after extraction, the β-TCP group had normal mucosal coverage without inflammation. Moreover, at 8 weeks after extraction, enhanced bone healing, socket coverage, and new bone formation were observed in the β-TCP group. Connective tissue in the extraction sockets suggested that local increases in BP concentrations may suppress the local autophagy mechanisms involved in BRONJ. Filling extraction sockets with β-TCP may prevent BRONJ.

Materials in the Na2O-CaO-SiO2-P2O5 System for Medical Applications

Calcium phosphate materials and materials based on silicon dioxide have been actively studied for more than 50 years due to their high biocompatibility and bioactivity. Hydroxyapatite and tricalcium phosphate are the most known among calcium phosphate materials, and Bioglass 45S5 is the most known material in the Na2O-CaO-SiO2-P2O5 system. Each of these materials has its application limits; however, some of them can be eliminated by obtaining composites based on calcium phosphate and bioglass. In this article, we provide an overview of the role of silicon and its compounds, including Bioglass 45S5, consider calcium phosphate materials, talk about the limits of each material, demonstrate the potential of the composites based on them, and show the other ways of obtaining composite ceramics in the Na2O-CaO-SiO2-P2O5 system.

Antimicrobial and Biodegradable 3D Printed Scaffolds for Orthopedic Infections

In bone tissue engineering, the performance of scaffolds underpins the success of the healing of bone. Microbial infection is the most challenging issue for orthopedists. The application of scaffolds for healing bone defects is prone to microbial infection. To address this challenge, scaffolds with a desirable shape and significant mechanical, physical, and biological characteristics are crucial. 3D printing of antibacterial scaffolds with suitable mechanical strength and excellent biocompatibility is an appealing strategy to surmount issues of microbial infection. The spectacular progress in developing antimicrobial scaffolds, along with beneficial mechanical and biological properties, has sparked further research for possible clinical applications. Herein, the significance of antibacterial scaffolds designed by 3D, 4D, and 5D printing technologies for bone tissue engineering is critically investigated. Materials such as antibiotics, polymers, peptides, graphene, metals/ceramics/glass, and antibacterial coatings are used to impart the antimicrobial features for the 3D scaffolds. Polymeric or metallic biodegradable and antibacterial 3D-printed scaffolds in orthopedics disclose exceptional mechanical and degradation behavior, biocompatibility, osteogenesis, and long-term antibacterial efficiency. The commercialization aspect of antibacterial 3D-printed scaffolds and technical challenges are also discussed briefly. Finally, the discussion on the unmet demands and prevailing challenges for ideal scaffold materials for fighting against bone infections is included along with a highlight of emerging strategies in this field.

Recent advances on 3D-printed PCL-based composite scaffolds for bone tissue engineering

Population ageing and various diseases have increased the demand for bone grafts in recent decades. Bone tissue engineering (BTE) using a three-dimensional (3D) scaffold helps to create a suitable microenvironment for cell proliferation and regeneration of damaged tissues or organs. The 3D printing technique is a beneficial tool in BTE scaffold fabrication with appropriate features such as spatial control of microarchitecture and scaffold composition, high efficiency, and high precision. Various biomaterials could be used in BTE applications. PCL, as a thermoplastic and linear aliphatic polyester, is one of the most widely used polymers in bone scaffold fabrication. High biocompatibility, low cost, easy processing, non-carcinogenicity, low immunogenicity, and a slow degradation rate make this semi-crystalline polymer suitable for use in load-bearing bones. Combining PCL with other biomaterials, drugs, growth factors, and cells has improved its properties and helped heal bone lesions. The integration of PCL composites with the new 3D printing method has made it a promising approach for the effective treatment of bone injuries. The purpose of this review is give a comprehensive overview of the role of printed PCL composite scaffolds in bone repair and the path ahead to enter the clinic. This study will investigate the types of 3D printing methods for making PCL composites and the optimal compounds for making PCL composites to accelerate bone healing.

In vivo and In vitro properties evaluation of curcumin loaded MgO doped 3D printed TCP scaffolds

The lack of site-specific chemotherapeutic agents to treat bone malignancy throws a significant challenge in the design of a delivery vehicle. The major scientific question posed in this study is, can we utilize curcumin-loaded magnesium oxide (MgO) doped 3D printed tricalcium phosphate (TCP) bone grafts as a localized delivery system that improves early stage in vivo osseointegration and in vitro chemoprevention, antibacterial properties? We have utilized curcumin as an alternative natural chemopreventive agent for bone cancer-specific delivery after direct incorporation on the 3D printed tricalcium phosphate (TCP) bone grafts. The addition of MgO as a dopant to TCP leads to ∼1.3 times enhancement in compressive strength. The designed drug delivery system shows up to ∼22% curcumin release in a physiological pH of 7.4 after 30 days. The presence of curcumin leads to up to ∼8.5 times reduction in osteosarcoma viability. In vitro results indicate that these scaffolds significantly enhance bone-forming osteoblast cells while reducing the bone-resorbing osteoclast cells. The in vivo rat distal femur model surgery followed by histological assessment with H&E, vWF, and Movat pentachrome staining results show that the designed scaffolds lead to new bone formation (up to ∼2.5 times higher than the control) after successful implantation. The presence of MgO and curcumin results in up to ∼71% antibacterial efficacy against osteomyelitis causing S. aureus. These 3D printed osteogenic and chemopreventive scaffolds can be utilized in patient-specific low load-bearing defect sites.

3D printing method for bone tissue engineering scaffold

3D printing technology is an emerging technology. It constructs solid bodies by stacking materials layer by layer, and can quickly and accurately prepare bone tissue engineering scaffolds with specific shapes and structures to meet the needs of different patients. The field of life sciences has received a great deal of attention. However, different 3D printing technologies and materials have their advantages and disadvantages, and there are limitations in clinical application. In this paper, the technology, materials and clinical applications of 3D printed bone tissue engineering scaffolds are reviewed, and the future development trends and challenges in this field are prospected.

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.

Review of Physical, Mechanical, and Biological Characteristics of 3D-Printed Bioceramic Scaffolds for Bone Tissue Engineering Applications

This review focuses on the advancements in additive manufacturing techniques that are utilized for fabricating bioceramic scaffolds and their characterizations leading to bone tissue regeneration. Bioscaffolds are made by mimicking the human bone structure, material composition, and properties. Calcium phosphate apatite materials are the most commonly used scaffold materials as they closely resemble live bone in their inorganic composition. The functionally graded scaffolds are fabricated by utilizing the right choice of the 3D printing method and material combinations to achieve the requirement of the bioscaffold. To tailor the physical, mechanical, and biological properties of the scaffold, certain materials are reinforced, doped, or coated to incorporate the functionality. The biomechanical loading conditions that involve flexion, torsion, and tension exerted on the implanted scaffold are discussed. The finite element analysis (FEA) technique is used to investigate the mechanical property of the scaffold before fabrication. This helps in reducing the actual number of samples used for testing. The FEA simulated results and the experimental result are compared. This review also highlights some of the challenges associated while processing the scaffold such as shrinkage, mechanical instability, cytotoxicity, and printability. In the end, the new materials that are evolved for tissue engineering applications are compiled and discussed.

How Efficient are Alendronate-Nano/Biomaterial Combinations for Anti-Osteoporosis Therapy? An Evidence-Based Review of the Literature

Osteoporosis is defined as a systemic skeletal disease characterized by low bone mass and microarchitectural deterioration of bone tissue, with a consequent increase in bone fragility and susceptibility to fracture. Because of the systemic nature of osteoporosis, the associated escalation in fracture risk affects virtually all skeletal sites. The problem is serious since it is estimated that more than 23 million men and women are at high risk of osteoporotic-like breakages in the European Union. Alendronate (ALN) is the most commonly prescribed oral nitrogen-containing bisphosphonate (BP) for the prevention and the therapy of osteoporosis. This is also one of the most intensely studied drugs in this field. However, ALN is characterized by restricted oral absorption and bioavailability and simultaneously its administration has serious side-effects (jaw osteonecrosis, irritation of the gastrointestinal system, nausea, musculoskeletal pain, and cardiovascular risks). Therefore, delivery systems enabling controlled release and local action of this drug are of great interest, being widely researched and presented in the literature. In this review, we discuss the current trends in the design of various types of alendronate carriers. Our paper is focused on the most recent developments in the field of nano/biomaterials-based systems for ALN delivery, including nano/microformulations, synthetic/natural polymeric and inorganic materials, hydrogel-based materials, scaffolds, coated-like structures, as well as organic-inorganic hybrids. Topics related to the treatment of complex bone diseases including osteoporosis have been covered in several more general reviews; however, the systems for this particular drug have not yet been discussed in detail.

Application of bioactive metal ions in the treatment of bone defects

The treatment of bone defects is an important problem in clinical practice. The rapid development of bone tissue engineering (BTE) may provide a new method for bone defect treatment. Metal ions have been widely studied in BTE and demonstrated a significant effect in promoting bone tissue growth. Different metal ions can be used to treat bone defects according to specific conditions, including promoting osteogenic activity, inhibiting osteoclast activity, promoting vascular growth, and exerting certain antibacterial effects. Multiple studies have confirmed that metal ions-modified composite scaffolds can effectively promote bone defect healing. By studying current extensive research on metal ions in the treatment of bone defects, this paper reviews the mechanism of metal ions in promoting bone tissue growth, analyzes the loading mode of metal ions, and lists some specific applications of metal ions in different types of bone defects. Finally, this paper summarizes the advantages and disadvantages of metal ions and analyzes the future research trend of metal ions in BTE. This article can provide some new strategies and methods for future research and applications of metal ions in the treatment of bone defects.

The Effect of Angiogenesis-Based Scaffold of MesoporousBioactive Glass Nanofiber on Osteogenesis

There is still an urgent need for more efficient biological scaffolds to promote the healing of bone defects. Vessels can accelerate bone growth and regeneration by transporting nutrients, which is an excellent method to jointly increase osteogenesis and angiogenesis in bone regeneration. Therefore, we aimed to prepare a composite scaffold that could promote osteogenesis with angiogenesis to enhance bone defect repair. Here, we report that scaffolds were prepared by coaxial electrospinning with mesoporous bioactive glass modified with amino (MBG-NH₂) adsorbing insulin-like growth factor-1 (IGF-1) as the core and silk fibroin (SF) adsorbing vascular endothelial growth factor (VEGF) as the shell. These scaffolds were named MBG-NH₂/IGF@SF/VEGF and might be used as repair materials to promote bone defect repair. Interestingly, we found that the MBG-NH₂/IGF@SF/VEGF scaffolds had nano-scale morphology and high porosity, as well as enough mechanical strength to support the tissue. Moreover, MBG-NH₂ could sustain the release of IGF-1 to achieve long-term repair. Additionally, the MBG-NH₂/IGF@SF/VEGF scaffolds could significantly promote the mRNA expression levels of osteogenic marker genes and the protein expression levels of Bmp2 and Runx2 in bone marrow mesenchymal stem cells (BMSCs). Meanwhile, the MBG-NH₂/IGF@SF/VEGF scaffolds promoted osteogenesis by simulating Runx2 transcription activity through the phosphorylated Erk1/2-activated pathway. Intriguingly, the MBG-NH₂/IGF@SF/VEGF scaffolds could also significantly promote the mRNA expression level of angiogenesis marker genes and the protein expression level of CD31. Furthermore, RNA sequencing verified that the MBG-NH₂/IGF@SF/VEGF scaffolds had excellent performance in promoting bone defect repair and angiogenesis. Consistent with these observations, we found that the MBG-NH₂/IGF@SF/VEGF scaffolds demonstrated a good repair effect on a critical skull defect in mice in vivo, which not only promoted the formation of blood vessels in the haversian canal but also accelerated the bone repair process. We concluded that these MBG-NH₂/IGF@SF/VEGF scaffolds could promote bone defect repair under accelerating angiogenesis. Our finding provides a new potential biomaterial for bone tissue engineering.

Translating musculoskeletal bioengineering into tissue regeneration therapies

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

Allicin-Loaded Hydroxyapatite: Enhanced Release, Cytocompatibility, and Antibacterial Properties for Bone Tissue Engineering Applications

Allicin, the active compound of garlic extract, is a naturally sourced biomolecule, which promotes a vast range of health benefits. However, the limited stability of allicin restricts its applications in tissue engineering. Additionally, the detailed effects of allicin in bone health are yet to be explored. Our work reports on the fabrication of a novel allicin-loaded hydroxyapatite drug delivery system with enhanced biological properties. The fabricated system shows excellent antibacterial efficiency against S. aureus after 36 h of bacterial interaction with a sample. The allicin release kinetics are enhanced with polycaprolactone (PCL). The obtained results after 20 days of drug release study indicate that PCL coating leads to an increase in cumulative allicin release from ~ 35% to 70% at a physiological pH of 7.4. These scaffolds maintain stability during the whole period of drug release. Cytocompatibility of tested compositions with osteoblasts indicates enhanced cell viability and good filopodial attachment on the sample surface at day 7. These allicin-loaded antibacterial and cytocompatible scaffolds can find applications as localized delivery vehicles for bone tissue engineering.

Three-dimensionally printed biphasic calcium phosphate blocks with different pore diameters for regeneration in rabbit calvarial defects

Background

Biphasic calcium phosphate (BCP) is the most frequently used synthetic bone substitutes, which comprises a combination of hydroxyapatite (HA) and beta-tricalcium phosphate (b-TCP). Thanks to the recent advances in digital dentistry and three-dimensional (3D) printing technology, synthetic block bone substitutes can be customized to fit individual defect morphologies. The diameter of the pores can influence the rate of bone formation and material resorption. The aim of this study was to compare three-dimensionally printed biphasic calcium phosphate (BCP) block bone substitutes with different pore diameters (0.8-, 1.0-, and 1.2- mm) for use in the regeneration of rabbit calvarial defects.

Methods

Four circular defects were formed on the calvaria of ten rabbits. Each defect was randomly allocated to one of the following study groups: (i) control group, (ii) 0.8-mm group, (iii) 1.0-mm group, and (iv) 1.2-mm group. All specimens were postoperatively harvested at 2 and 8 weeks, and radiographic and histomorphometric analyses were performed on the samples.

Results

Histologically, the BCP blocks remained unresorbed up to 8 weeks, and new bone formation occurred within the porous structures of the blocks. After the short healing period of 2 weeks, histomorphometric analysis indicated that new bone formation was significantly greater in the BCP groups compared with the control (p < 0.05). However, there were no significant differences between the groups with different pore diameters (p > 0.05). At 8 weeks, only the 1.0-mm group (3.42 ± 0.48 mm², mean ± standard deviation) presented a significantly larger area of new bone compared with the control (2.26 ± 0.59 mm²) (p < 0.05). Among the BCP groups, the 1.0- and 1.2-mm groups exhibited significantly larger areas of new bone compared with the 0.8-mm group (3.42 ± 0.48 and 3.04 ± 0.66 vs 1.60 ± 0.70 mm², respectively).

Conclusions

Within the limitations of this study, the BCP block bone substitutes can be applied to bone defects for successful bone regeneration. Future studies should investigate more-challenging defect configurations prior to considering clinical applications.

Zinc curcumin complex on fluoride doped hydroxyapatite with enhanced biological properties for dental and orthopedic applications

Since antiquity, curcumin, from turmeric is utilized in traditional Indian medicine (Ayurveda) to treat bone disorders. However, the hydrophobic nature and poor absorption of curcumin limit its clinical applications. There is a need to develop a novel strategy that can significantly enhance curcumin's biological properties. The current work reports the utilization of Zn²⁺-curcumin complex from a fluoride doped hydroxyapatite matrix for osteosarcoma inhibition, osteoblast growth, and anti-bacterial properties. The interaction between Zn²⁺ and curcumin increases curcumin release by ~ 2.5 folds. The fabricated drug delivery system shows up to ~ 1.6 times enhancement in osteoblast cell viability. The presence of curcumin results in ~ 4 times more osteosarcoma inhibition compared to control. The antibacterial efficacy of this system is confirmed against Staphylococcus aureus, due to the presence of antibacterial fluoride, zinc, and curcumin. This multifunctional drug delivery system can be utilized for various bone-tissue engineering and dental applications.

Bone morphogenetic protein (BMP)-modified graphene oxide-reinforced polycaprolactone-gelatin nanofiber scaffolds for application in bone tissue engineering

In this study, blend nanofibrous scaffolds were electrospun from polycaprolactone/gelatin (PCL/Gel) blend solutions reinforced by bone morphogenetic protein (BMP)-modified graphene oxide (GO). SEM results showed that uniform and bead-less nanofibers with 270 nm average diameter were obtained from electrospun of PCL/Gel blend solutions. Tensile strength test and contact angle measurement demonstrated that addition of PCL led to higher mechanical and physical properties of the resulting nanofibers. The addition of PCL as well as GO in the blend supports the suitable mechanical strength in the body media. The loading of BMP-modified graphene in the Gel/PCL structure caused the formation of nanofibrous substrate with great resemblance to bone tissue. Gel/PCL-G hybrid nanofibers revealed good biocompatibility in the presence of human osteosarcoma cells, and no trace of cellular toxicity was observed. The cells grown on the scaffolds exhibited a spindle-like and broad morphology and almost uniformly covered the entire nanofiber scaffold. Gel/PCL nanofibers reinforced by graphene oxide-immobilized bone morphogenetic protein was prepared as a promising safe and biocompatible nanofiber with high antibacterial activity for bone tissue engineering.

A programmed surface on polyetheretherketone for sequentially dictating osteoimmunomodulation and bone regeneration to achieve ameliorative osseointegration under osteoporotic conditions

Polyetheretherketone (PEEK) is a desirable alternative to conventional biomedical metals for orthopedic implants due to the excellent mechanical properties. However, the inherent bioinertness of PEEK contributes to inferior osseointegration of PEEK implants, especially under pathological conditions of osteoporosis. Herein, a programmed surface is designed and fabricated on PEEK to dictate osteoimmunomodulation and bone regeneration sequentially. A degradable hybrid coating consisting of poly(lactide-co-glycolide) and alendronate (ALN) loaded nano-hydroxyapatite is deposited on PEEK and then interleukin-4 (IL-4) is grafted onto the outer surface of the hybrid coating with the aid of N₂ plasma immersion ion implantation and subsequent immersion in IL-4 solution. Dominant release of IL-4 together with ALN and Ca²⁺ during the first few days synergistically mitigates the early acute inflammatory reactions and creates an osteoimmunomodulatory microenvironment that facilitates bone regeneration. Afterwards, slow and sustained delivery of ALN and Ca²⁺ in the following weeks boosts osteogenesis and suppresses osteoclastogenesis simultaneously, consequently ameliorating bone-implant osseointegration even under osteoporotic conditions. By taking into account the different phases in bone repair, this strategy of constructing advanced bone implants with sequential functions provides customizable and clinically viable therapy to osteoporotic patients.

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A programmed surface is designed and fabricated on PEEK to dictate osteoimmunomodulation and bone regeneration sequentially.

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A degradable coating consisting ALN loaded nano-HA is deposited on PEEK, with IL-4 being grafted onto the outmost surface.

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Dominant release of IL-4 together with ALN and Ca²⁺ synergistically mitigates the early acute inflammatory reactions.

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Slow and sustained delivery of ALN and Ca²⁺ boosts osteogenesis and suppresses osteoclastogenesis simultaneously.

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Sequential regulation of peri-implant biological responses is achieved to match the dynamic process of bone regeneration.

The Use of Fibers in Bone Tissue Engineering

Bone tissue engineering aims to restore and maintain the function of bone by means of biomaterial-based scaffolds. This review specifically focuses on the use of fibers in biomaterials used for bone tissue engineering as suitable environment for bone tissue repair and regeneration. We present a bioinspired rationale behind the use of fibers in bone tissue engineering and provide an overview of the most common fiber fabrication methods, including solution, melt, and microfluidic spinning. Subsequently, we provide a brief overview of the composition of fibers that are used in bone tissue engineering, including fibers composed of (i) natural polymers (e.g., cellulose, collagen, gelatin, alginate, chitosan, and silk, (ii) synthetic polymers (e.g., polylactic acid [PLA], polycaprolactone, polyglycolic acid [PGA], polyethylene glycol, and polymer blends of PLA and PGA), (iii) ceramic fibers (e.g., aluminium oxide, titanium oxide, and zinc oxide), (iv) metallic fibers (e.g., titanium and its alloys, copper and magnesium), and (v) composite fibers. In addition, we review the most relevant fiber modification strategies that are used to enhance the (bio)functionality of these fibers. Finally, we provide an overview of the applicability of fibers in biomaterials for bone tissue engineering, with a specific focus on mechanical, pharmaceutical, and biological properties of fiber-functionalized biomaterials for bone tissue engineering. Impact statement Natural bone is a complex composite material composed of an extracellular matrix of mineralized fibers containing living cells and bioactive molecules. Consequently, the use of fibers in biomaterial-based scaffolds offers a wide variety of opportunities to replicate the functional performance of bone. This review provides an overview of the use of fibers in biomaterials for bone tissue engineering, thereby contributing to the design of novel fiber-functionalized bone-substituting biomaterials of improved functionality regarding their mechanical, pharmaceutical, and biological properties.

Emerging zero-dimensional to four-dimensional biomaterials for bone regeneration

Bone is one of the most sophisticated and dynamic tissues in the human body, and is characterized by its remarkable potential for regeneration. In most cases, bone has the capacity to be restored to its original form with homeostatic functionality after injury without any remaining scarring. Throughout the fascinating processes of bone regeneration, a plethora of cell lineages and signaling molecules, together with the extracellular matrix, are precisely regulated at multiple length and time scales. However, conditions, such as delayed unions (or nonunion) and critical-sized bone defects, represent thorny challenges for orthopedic surgeons. During recent decades, a variety of novel biomaterials have been designed to mimic the organic and inorganic structure of the bone microenvironment, which have tremendously promoted and accelerated bone healing throughout different stages of bone regeneration. Advances in tissue engineering endowed bone scaffolds with phenomenal osteoconductivity, osteoinductivity, vascularization and neurotization effects as well as alluring properties, such as antibacterial effects. According to the dimensional structure and functional mechanism, these biomaterials are categorized as zero-dimensional, one-dimensional, two-dimensional, three-dimensional, and four-dimensional biomaterials. In this review, we comprehensively summarized the astounding advances in emerging biomaterials for bone regeneration by categorizing them as zero-dimensional to four-dimensional biomaterials, which were further elucidated by typical examples. Hopefully, this review will provide some inspiration for the future design of biomaterials for bone tissue engineering.

Ring-Opening Polymerization of ε-Caprolactone Mediated by Di-Zinc Complex Bearing Macrocyclic Thioether-phenolate [OSSO]-type Ligand

A unique example of zinc bromide complexes bearing macrocyclic [OSSO]-type thioetherphenolate ligand (Di-[OSSO]ZnBr) has been successfully explored toward ring-opening polymerization (ROP) of -caprolactone (ε-CL) in the presence of epoxides and...

Comprehensive Review on Design and Manufacturing of Bio-scaffolds for Bone Reconstruction

Bio-scaffolds are synthetic entities widely employed in bone and soft-tissue regeneration applications. These bio-scaffolds are applied to the defect site to provide support and favor cell attachment and growth, thereby enhancing the regeneration of the defective site. The progressive research in bio-scaffold fabrication has led to identification of biocompatible and mechanically stable materials. The difficulties in obtaining grafts and expenditure incurred in the transplantation procedures have also been overcome by the implantation of bio-scaffolds. Drugs, cells, growth factors, and biomolecules can be embedded with bio-scaffolds to provide localized treatments. The right choice of materials and fabrication approaches can help in developing bio-scaffolds with required properties. This review mostly focuses on the available materials and bio-scaffold techniques for bone and soft-tissue regeneration application. The first part of this review gives insight into the various classes of biomaterials involved in bio-scaffold fabrication followed by design and simulation techniques. The latter discusses the various additive, subtractive, hybrid, and other improved techniques involved in the development of bio-scaffolds for bone regeneration applications. Techniques involving multimaterial printing and multidimensional printing have also been briefly discussed.

A Review on Development of Bio-Inspired Implants Using 3D Printing

Biomimetics is an emerging field of science that adapts the working principles from nature to fine-tune the engineering design aspects to mimic biological structure and functions. The application mainly focuses on the development of medical implants for hard and soft tissue replacements. Additive manufacturing or 3D printing is an established processing norm with a superior resolution and control over process parameters than conventional methods and has allowed the incessant amalgamation of biomimetics into material manufacturing, thereby improving the adaptation of biomaterials and implants into the human body. The conventional manufacturing practices had design restrictions that prevented mimicking the natural architecture of human tissues into material manufacturing. However, with additive manufacturing, the material construction happens layer-by-layer over multiple axes simultaneously, thus enabling finer control over material placement, thereby overcoming the design challenge that prevented developing complex human architectures. This review substantiates the dexterity of additive manufacturing in utilizing biomimetics to 3D print ceramic, polymer, and metal implants with excellent resemblance to natural tissue. It also cites some clinical references of experimental and commercial approaches employing biomimetic 3D printing of implants.

Long-term pretreatment with alendronate inhibits calvarial defect healing in an osteoporotic rat model

INTRODUCTION

This study aimed to observe the effects of long-term alendronate pretreatment on the healing of osteoporotic calvarial defects, and further investigate the effect of alendronate combined with once-weekly parathyroid hormone following 12 weeks of alendronate treatment in ovariectomized rats.

MATERIALS AND METHODS

Thirty 3-month-old female rats were ovariectomized, and 24 rats received alendronate for 12 weeks. Then, a critical defect was created in the calvaria of all animals. Immediately after osteotomy, the animals received one of five treatments for 8 weeks: (1) continuation of vehicle (group E), (2) alendronate followed by vehicle (group A), (3) continuation of alendronate (group B), (4) alendronate followed by once-weekly parathyroid hormone alone (group C), or (5) continuation of alendronate combined with once-weekly parathyroid hormone (group D). Calvarial defect healing was assessed using dual-energy X-ray absorptiometry, micro-computed tomography, histology, and sequential fluorescence labeling.

RESULTS

Group E showed a significantly higher volume of newly formed bone than groups A, B, C, and D. Evidence of new dense bone formation in group E was observed histologically. In addition, the immunohistochemical expression of runt-related transcription factor 2 was increased in group E but inhibited in groups A, B, C, and D. Sequential immunofluorescence also showed inhibited mineral apposition in groups A, B, C, and D compared with group E.

CONCLUSION

The present study shows that long-term pretreatment with alendronate inhibited calvarial defect healing in osteoporotic rats, and this effect could not be reversed by stopping alendronate, switching to parathyroid hormone, or combining with once-weekly parathyroid hormone.

Addressing the Osteoporosis Problem-Multifunctional Injectable Hybrid Materials for Controlling Local Bone Tissue Remodeling

Novel multifunctional biomimetic injectable hybrid systems were synthesized. The physicochemical as well as biological in vitro and in vivo tests demonstrated that they are promising candidates for bone tissue regeneration. The hybrids are composed of a biopolymeric collagen/chitosan/hyaluronic acid matrix and amine group-functionalized silica particles decorated with apatite to which the alendronate molecules were coordinated. The components of these systems were integrated and stabilized by cross-linking with genipin, a compound of natural origin. They can be precisely injected into the diseased tissue in the form of a viscous sol or a partially cross-linked hydrogel, where they can serve as scaffolds for locally controlled bone tissue regeneration/remodeling by supporting the osteoblast formation/proliferation and maintaining the optimal osteoclast level. These materials lack systemic toxicity. They can be particularly useful for the repair of small osteoporotic bone defects.

An updated review on application of 3D printing in fabricating pharmaceutical dosage forms

The concept of "one size fits all" followed by the conventional healthcare system has drawbacks in providing precise pharmacotherapy due to variation in the pharmacokinetics of different patients leading to serious consequences such as side effects. In this regard, digital-based three-dimensional printing (3DP), which refers to fabricating 3D printed pharmaceutical dosage forms with variable geometry in a layer-by-layer fashion, has become one of the most powerful and innovative tools in fabricating "personalized medicine" to cater to the need of therapeutic benefits for patients to the maximum extent. This is achieved due to the tremendous potential of 3DP in tailoring various drug delivery systems (DDS) in terms of size, shape, drug loading, and drug release. In addition, 3DP has a huge impact on special populations including pediatrics, geriatrics, and pregnant women with unique or frequently changing medical needs. The areas covered in the present article are as follows: (i) the difference between traditional and 3DP manufacturing tool, (ii) the basic processing steps involved in 3DP, (iii) common 3DP methods with their pros and cons, (iv) various DDS fabricated by 3DP till date with discussing few research studies in each class of DDS, (v) the drug loading principles into 3D printed dosage forms, and (vi) regulatory compliance.

Enamel matrix derivative (EMD) enhances the osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs)

To investigate the EMD's capacity in BMSCs osteogenic differentiation. In vivo and in vitro, BMSCs were treated with EMD, scanning electron microscopy, and Alizarin Red staining were used to detect the changes in the osteogenic ability of BMSCs, and the proliferation ability of BMSCs was evaluated by CCK8. In addition, by adding xav939, a typical inhibitor of Wnt/β-catenin signaling pathway, the regulatory function of Wnt/β-catenin signaling was clarified. The results showed that EMD promote cell proliferation and 25 μg/ml EMD had the most significant effect. Cells inducing osteogenesis for 2 and 3 even 4 weeks, the cell staining is deeper in EMD treated group than that of the control (P < 0.05) by alizarin Red staining, suggesting more mineralization of BMSCs. In vivo implanting the titanium plate wrapped with 25 μg/ml EMD treated-BMSC film into nude mice for 8 weeks, more nodules were formed on the surface of the titanium plate than that the control (P < 0.05). HE showed that there is a little blue-violet immature bone-like tissue block. Besides, the expression of RUNX Family Transcription Factor 2 (Runx2), Osterix, Osteocalcin (OCN), collagen I (COLI), alkaline phosphatase (ALP) and β-catenin were inhibited in xav939 group (P < 0.05); Inversely, all were activated in EMD group (P < 0.05). In conclusion, EMD promoted the proliferation and osteogenic differentiation of BMSCs. EMD's function on BMSCs might be associated with the Wnt/β-catenin signaling pathway.

Extracorporeal Shock Wave Combined with Teriparatide-Loaded Hydrogel Injection Promotes Segmental Bone Defects Healing in Osteoporosis

BACKGROUND

Osteoporosis is a systemic bone disease characterized by decreased bone density and deterioration of bone microstructure, leading to an increased probability of fragility fractures. Once segmental bone defect occurs, it is easy to cause delayed union and nonunion.

METHODS

The aim of this study is to investigate the efficacy of extracorporeal shock wave (ESW) and teriparatide-loaded hydrogel (T-Gel) combined strategy on the cell activity and differentiation of osteoporosis derived bone marrow mesenchymal stem cells (OP-BMSCs) in vitro and bone regeneration in osteoporotic segmental bone defects in vivo.

RESULTS

In vitro, the strategy of combining ESW and T-Gel significantly enhanced OP-BMSCs proliferation, survival, migration, and osteogenic differentiation by up-regulating the alkaline phosphatase activity, mineralization, and expression of runt-related transcription factor-2, type I collagen, osteocalcin, and osteopontin. In the segmental bone defect models of osteoporotic rabbits, Micro-CT evaluation and histological observation demonstrated this ESW-combined with T-Gel injection significantly induced bone healing by enhancing the osteogenic activity of the local microenvironment in osteoporotic defects.

CONCLUSION

In conclusion, ESW-combined with T-Gel injection could regulate the poor osteogenic microenvironment in osteoporotic defects and show potential for enhancing fragility fractures healing.

Beta-phase Stabilization and Increased Osteogenic Differentiation of Stem Cells by Solid-State Synthesized Magnesium Tricalcium Phosphate

In this study, magnesium and strontium-doped β-tricalcium phosphates were synthesized to understand dopant impact on substrate chemistry and morphology, and proliferation and osteogenic differentiation of mesenchymal stem cells. Under solid-state synthesis, magnesium doping stabilized the β-phase in tricalcium phosphate, with 22% less α-phase content than control. Strontium doping increased α-phase formation by 17%, and also resulted in greater surface porosity, leading to greater crystal precipitation in vitro. Magnesium also significantly enhanced the proliferation of stem cells (P < 0.05) and differentiation into osteoblasts with increased alkaline phosphatase production (P < 0.05) at all time points. These results indicated that magnesium stabilizes β-tricalcium phosphate in vitro and enhanced early and late-time-point osteoconduction and osteoinduction of mesenchymal stem cells.

Nature-inspired materials and structures using 3D Printing

Emulating the unique combination of structural, compositional, and functional gradation in natural materials is exceptionally challenging. Many natural structures have proved too complex or expensive to imitate using traditional processing techniques despite recent advances. Recent innovations within the field of additive manufacturing (AM) or 3D Printing (3DP) have shown the ability to create structures that have variations in material composition, structure, and performance, providing a new design-for-manufacturing platform for the imitation of natural materials. AM or 3DP techniques are capable of manufacturing structures that have significantly improved properties and functionality over what could be traditionally-produced, giving manufacturers an edge in their ability to realize components for highly-specialized applications in different industries. To this end, the present work reviews fundamental advances in the use of naturally-inspired design enabled through 3DP / AM, how these techniques can be further exploited to reach new application areas, and the challenges that lie ahead for widespread implementation. An example of how these techniques can be applied towards a total hip arthroplasty application is provided to spur further innovation in this area.

Fabrication and characterization of bovine hydroxyapatite-gelatin-alendronate scaffold cross-linked by glutaraldehyde for bone regeneration

OBJECTIVES

Alendronate are widely used in the treatment of bone disorders characterized by inhibit osteoclast-mediated bone resorption such as Paget's disease, fibrous dysplasia, myeloma, bone metastases and osteoporosis. In recent studies alendronate improves proliferation and differentiation of osteoblasts, thereby facilitating for bone regeneration. The disadvantages of this class are their poor bioavailability and side effects on oral and intravenous application such as stomach irritation and osteonecrosis in jaw. Thus, local treatment of alendronate is needed in order to achieve high concentration of drug. Bovine hydroxyapatite-gelatin scaffold with alendronate was studied. Glutaraldehyde was used as cross-linking agent, increase the characteristics of this scaffold. The objectives of this study were to manufacture and characterize alendronate scaffold using bovine hydroxyapatite-gelatin and crosslinked by glutaraldehyde.

METHODS

Preparation of cross-linked bovine hydroxyapatite-gelatin and alendronate scaffold with different concentration of glutaraldehyde (0.00, 0.50, 0.75, and 1.00%). The scaffolds were characterized for compressive strength, porosity, density, swelling ratio, in vitro degradation, and cytotoxicity (the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide assay, shorted as MTT assay).

RESULTS

Bovine hydroxyapatite-gelatin-alendronate scaffold cross-linked with glutaraldehyde showed lower density than without glutaraldehyde. As glutaraldehyde concentration increased, porosity also increased. Eventually, it reduced compressive strength. Swelling ratio and in vitro degradation was negatively dependent on glutaraldehyde concentration. In addition, the scaffold has a good safety by MTT assay.

CONCLUSIONS

Bovine hydroxyapatite-gelatin-alendronate scaffold was fabricated with various concentrations of glutaraldehyde. The presence of glutaraldehyde on bovine hydroxyapatite-gelatin-alendronate is safe and suitable candidate scaffold for bone regeneration.

Advances in 3D Printing for Tissue Engineering

Tissue engineering (TE) scaffolds have enormous significance for the possibility of regeneration of complex tissue structures or even whole organs. Three-dimensional (3D) printing techniques allow fabricating TE scaffolds, having an extremely complex structure, in a repeatable and precise manner. Moreover, they enable the easy application of computer-assisted methods to TE scaffold design. The latest additive manufacturing techniques open up opportunities not otherwise available. This study aimed to summarize the state-of-art field of 3D printing techniques in applications for tissue engineering with a focus on the latest advancements. The following topics are discussed: systematics of the available 3D printing techniques applied for TE scaffold fabrication; overview of 3D printable biomaterials and advancements in 3D-printing-assisted tissue engineering.

Calcium alendronate-coated composite scaffolds promote osteogenesis of ADSCs via integrin and FAK/ERK signalling pathways

Bioceramic-biopolymer composites have been used extensively as bone tissue engineering scaffolds due to their bioactive properties. However, composite scaffolds are insufficient in inducing osteogenic differentiation of stem cells. In this study, a strategy for the local delivery of bioactive factors by coating calcium alendronate (ALC) on the surface of composite scaffolds was systematically evaluated for the first time. The coated ALC not only displayed excellent cytocompatibility and cell adhesion properties but also resulted in the significant upregulation of osteogenic related gene expression, osteogenic related protein levels, alkaline phosphatase (ALP) activity and calcium deposition of ADSCs. Furthermore, our results suggested that the molecular mechanism of ADSC osteogenic differentiation induced by the constructed ALC may be related to the integrin binding and the activation of FAK/ERK signalling pathways. These findings suggested that ALC-coated composite scaffolds can serve as bone tissue engineering scaffolds, providing a simple and universal method to improve the osteogenic differentiation of ADSCs by calcium phosphate-containing composite materials.

Advances in the Fabrication of Scaffold and 3D Printing of Biomimetic Bone Graft

The need for bone grafts is tremendous, and that leads to the use of autograft, allograft, and bone graft substitutes. The biology of the bone is quite complex regarding cellular composition and architecture, hence developing a mineralized connective tissue graft is challenging. Traditionally used bone graft substitutes including metals, biomaterial coated metals and biodegradable scaffolds, suffer from persistent limitations. With the advent and rise of additive manufacturing technologies, the future of repairing bone trauma and defects seems to be optimistic. 3D printing has significant advantages, the foremost of all being faster manipulation of various biocompatible materials and live cells or tissues into the complex natural geometries necessary to mimic and stimulate cellular bone growth. The advent of new-generation bioprinters working with high-precision, micro-dispensing and direct digital manufacturing is aiding in ground-breaking organ and tissue printing, including the bone. The future bone replacement for patients holds excellent promise as scientists are moving closer to the generation of better 3D printed bio-bone grafts that will be safer and more effective. This review aims to summarize the advances in scaffold fabrication techniques, emphasizing 3D printing of biomimetic bone grafts.

Regulation of extracellular bioactive cations in bone tissue microenvironment induces favorable osteoimmune conditions to accelerate in situ bone regeneration

The design of orthopedic biomaterials has gradually shifted from “immune-friendly” to “immunomodulatory,” in which the biomaterials are able to modulate the inflammatory response via macrophage polarization in a local immune microenvironment that favors osteogenesis and implant-to-bone osseointegration. Despite the well-known effects of bioactive metallic ions on osteogenesis, how extracellular metallic ions manipulate immune cells in bone tissue microenvironments toward osteogenesis and subsequent bone formation has rarely been studied. Herein, we investigate the osteoimmunomodulatory effect of an extracellular bioactive cation (Mg²⁺) in the bone tissue microenvironment using custom-made poly lactic-co-glycolic acid (PLGA)/MgO-alendronate microspheres that endow controllable release of magnesium ions. The results suggest that the Mg²⁺-controlled tissue microenvironment can effectively induce macrophage polarization from the M0 to M2 phenotype via the enhancement of anti-inflammatory (IL-10) and pro-osteogenic (BMP-2 and TGF-β1) cytokines production. It also generates a favorable osteoimmune microenvironment that facilitates the proliferation and osteogenic differentiation of bone marrow mesenchymal stem cells. The in vivo results further verify that a large amount of bony tissue, with comparable bone mineral density and mechanical properties, has been generated at an early post-surgical stage in rat intramedullary bone defect models. This study demonstrates that the concept of in situ immunomodulated osteogenesis can be realized in a controlled magnesium tissue microenvironment.

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Controlled release of Mg²⁺ was achieved by the microfluidic electrosprayed PLGA/MgO-alendronate microspheres.

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PLGA/MgO-alendronate microspheres with satisfied osteoimmunomodulatory properties accelerated bone regeneration in vivo.

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Extracellular Mg²⁺ induced macrophage switch to M2 phenotype with enhanced expressions of IL-10, BMP-2 and TGF-β1.

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Osteoimmune microenvironment favourably upregulated the osteogenic expressions of BMSCs.

Intraarticular Injection of Infliximab-Loaded Thermosensitive Hydrogel Alleviates Pain and Protects Cartilage in Rheumatoid Arthritis

Purpose

Pain and cartilage destruction caused by rheumatoid arthritis (RA) are major challenges during clinical treatment. Traditional systemic administration not only has obvious side effects but also provides limited relief for local symptoms in major joints. Local delivery of therapeutics for RA treatment is a potential strategy but is limited by rapid intraarticular release.

Materials and Methods

In this study, we prepared a thermoresponsive injectable hydrogel by mixing pluronic F127 (F127) and hyaluronic acid (HA) with poly (γ-glutamic acid) (PGA) incorporating infliximab (IFX), a new generation monoclonal antibody drug. We investigated the biocompatibility of the hydrogel and its IFX release profile. In vivo, we studied the clinical manifestations (articular skin temperature and joint diameter), detected cytokines in the synovial fluid and cartilage, performed behavioral studies on pain relief, and evaluated the cartilage protection effect.

Results

A thermoresponsive hydrogel was successfully prepared by mixing F127, HA, and PGA with injectable properties. The F127-HA-PGA hydrogel had a porous structure with interconnected pores. The infliximab-loaded thermosensitive hydrogel exhibited good biocompatibility and biodegradability and sustained release properties. Intraarticular injection of the IFX-loaded F127-HA-PGA hydrogel could alleviate the expression of inflammatory cytokines, such as tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), interleukin-6 (IL-6), and interleukin-17 (IL-17), in the synovial fluid and cartilage as well as relieve pain and inhibit cartilage destruction in RA.

Conclusion

The double effect on pain relief and cartilage protection indicated the significant potential of the IFX-loaded injectable hydrogel for RA treatment in major joint lesions.

Patient-Specific Bone Particles Bioprinting for Bone Tissue Engineering

Although bioinks with both high printability and shape fidelity while maintaining high cell viability are developed, the biofunctionality of the resulting bioprinted construct is often overlooked. To address this, a methacrylated gelatin (GelMA)-based bioink biofunctionalized with bone particles (BPs) is developed as a personalized treatment strategy for bone regeneration. The bioink consists of incorporating BPs of various sizes (0-500 µm) in GelMA at various concentrations (ranging from 5 to 15% w/v). The printability of the bioink is systematically investigated and it is demonstrated that a 15% w/v BP-loading results in high print quality for 10% and 12.5% GelMA concentrations. Rheological evaluation reveals a strong shear thinning behavior essential for printing and a high gel strength in bioink with 15% w/v 0-500 µm BPs for both GelMA concentrations. In addition, the printability of the bioink and the metabolic activity of the resulting scaffolds are dependent on both the concentration of hydrogel and size of the BPs. Importantly, the cells initially contained in the BPs are able to migrate and colonize the bioprinted scaffold while maintaining their capacity to express early osteogenic markers. This study demonstrates the feasibility of bioprinted viable BPs and may have some potential for chairside clinical translation.