Calcium phosphate bone cement/mesoporous bioactive glass composites for controlled growth factor delivery

Gingerol-zinc complex loaded 3D-printed calcium phosphate for controlled release application

The therapeutic potential of natural medicines in treating bone disorders is well-established. Modifications in formulation or molecular structure can enhance their efficacy. Gingerol, an osteogenic active compound derived from ginger roots (Zingiber officinale), can form metal ion complexes. Zinc (Zn), a trace element that combats bacterial infections and promotes osteoblast proliferation, can be complexed with gingerol to form a G-Zn+2 complex. This study investigates a porous 3D-printed (3DP) calcium phosphate (CaP) scaffold loaded with the G-Zn+2 complex for drug release and cellular interactions. The scaffold is coated with polycaprolactone (PCL) to control the drug release. Diffusion-mediated kinetics results in 50% release of the G-Zn+2 complex over 6 weeks. The G-Zn+2 complex demonstrates cytotoxicity against MG-63 osteosarcoma cells, indicated by the formation of apoptotic bodies and ruptured cell morphology on the scaffolds. G-Zn+2 PCL-coated scaffolds show a 1.2 ± 0.1-fold increase in osteoblast cell viability, and an 11.6 ± 0.5% increase in  alkaline phosphatase compared to untreated scaffolds. Treated scaffolds also exhibit reduced bacterial colonization against Staphylococcus aureus bacteria, highlighting the antibacterial potential of the G-Zn+2 complex. The functionalized 3DP CaP scaffold with the G-Zn+2 complex shows significant potential for enhancing bone regeneration and preventing infections in low-load-bearing applications.

Synergistic effects of silica-enriched bioactive glass and tri-calcium phosphate nanocomposites on BMP2 gene expression for bone repair and regeneration applications

This study focuses on the development of biomaterials for bone regeneration highlighting 59S bioactive glass (59S BG), tri-calcium phosphate (TCP), and their 1:1 composite (59S BG/TCP). The synthesized materials demonstrated excellent properties for bone tissue engineering. Characterization revealed their thermal stability up to 900 °C, as confirmed by thermogravimetric analysis (TGA), while X-ray diffraction (XRD) identified calcium phosphate and silicate phases. Functional groups and chemical bonding were elucidated using Fourier transform infrared spectroscopy (FTIR). The composite exhibited remarkable mechanical properties, with a hardness of 167.87 HV and a strength of 680.52 MPa, indicating its suitability for load-bearing applications. Biological evaluations confirmed promising performance, with in-vitro bioactivity showing apatite formation and reduced XRD peak intensity. Biocompatibility assessments revealed hemolysis below 5 % and a 300 % cell proliferation rate by day three ensuring minimal cytotoxicity and favorable blood compatibility. Protein adsorption studies demonstrated strong interactions with bovine serum albumin (BSA) and lysozyme, supporting protein stability. Additionally, the composite showed enhanced osteogenic potential with elevated BMP2 gene expression indicating its capacity to promote robust bone regeneration. The synergy between 59S BG and TCP underscores the composite's potential as a promising material for effective bone repair and regeneration.

Effect of pH and hydroxyapatite-like layer formation on the antibacterial properties of borophosphate bioactive glass incorporated poly(methyl methacrylate) bone cement

Infection is a leading cause of total joint arthroplasty failure. Current preventative measures incorporate antibiotics into the poly (methyl methacrylate) (PMMA) bone cement that anchors the implant into the natural bone. With bacterial resistance to antibiotics on the rise, the development of alternative antibacterial materials is crucial to mitigate infection. Borate bioactive glass, 13-93-B3, has been studied previously for use in orthopedic applications due to its ability to be incorporated into bone cements and other scaffolds, convert into hydroxyapatite (HA)-like layer, and enhance the osseointegration and antibacterial properties of the material. The purpose of this study is to better understand how glass composition and change in surrounding pH effects the composite's antibacterial characteristics by comparing the incorporation of 30% wt/wt 13-93-B3 glass and pH neutral borophosphate bioactive glass into PMMA bone cement. We also aim to elucidate how HA-like layer formation on the cement's surface may affect bacterial adhesion. These studies showed that 13-93-B3 incorporated cements had significant reduction of bacterial growth surrounding the composite beyond 24 h of exposure when compared to a neutral borate bioactive glass incorporated cement (p < 0.01) and cement only (p < 0.0001). Additionally, through soaking cement composites in simulated body fluid and then exposing them to a bioluminescent strand of staphylococcus aureus, we found that the presence of a HA-like layer on the 13-93-B3 or pH neutral glass incorporated cement disks resulted in an increase in bacterial attachment on the composite cement's surface, where p < 0.001, and p < 0.05 respectively. Overall, our studies demonstrated that borate bioactive glass incorporated PMMA bone cement has innate antimicrobial properties that make it a promising material to prevent infection in total joint arthroplasties.

Current and Future Perspectives of Bioactive Glasses as Injectable Material

This review covers recent compositions of bioactive glass, with a specific emphasis on both inorganic and organic materials commonly utilized as matrices for injectable materials. The major objective is to highlight the predominant bioactive glass formulations and their clinical applications in the biomedical field. Previous studies have highlighted the growing interest among researchers in bioactive glasses, acknowledging their potential to yield promising outcomes in this field. As a result of this increased interest, investigations into bioactive glass have prompted the creation of composite materials and, notably, the development of injectable composites as a minimally invasive method for administering the material within the human body. Injectable materials have emerged as a promising avenue to mitigate various challenges. They offer several advantages, including minimizing invasive surgical procedures, reducing patient discomfort, lowering the risk of postoperative infection and decreasing treatment expenses. Additionally, injectable materials facilitate uniform distribution, allowing for the filling of defects of any shape.

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.

Mesoporous Bioactive Glass-Incorporated Injectable Strontium-Containing Calcium Phosphate Cement Enhanced Osteoconductivity in a Critical-Sized Metaphyseal Defect in Osteoporotic Rats

In this study, the in vitro and in vivo bone formation behavior of mesoporous bioactive glass (MBG) particles incorporated in a pasty strontium-containing calcium phosphate bone cement (pS100G10) was studied in a metaphyseal fracture-defect model in ovariectomized rats and compared to a plain pasty strontium-containing calcium phosphate bone cement (pS100) and control (empty defect) group, respectively. In vitro testing showed good cytocompatibility on human preosteoblasts and ongoing dissolution of the MBG component. Neither the released strontium nor the BMG particles from the pS100G10 had a negative influence on cell viability. Forty-five female Sprague-Dawley rats were randomly assigned to three different treatment groups: (1) pS100 (n = 15), (2) pS100G10 (n = 15), and (3) empty defect (n = 15). Twelve weeks after bilateral ovariectomy and multi-deficient diet, a 4 mm wedge-shaped fracture-defect was created at the metaphyseal area of the left femur in all animals. The originated fracture-defect was substituted with pS100 or pS100G10 or left empty. After six weeks, histomorphometrical analysis revealed a statistically significant higher bone volume/tissue volume ratio in the pS100G10 group compared to the pS100 (p = 0.03) and empty defect groups (p = 0.0001), indicating enhanced osteoconductivity with the incorporation of MBG. Immunohistochemistry revealed a significant decrease in the RANKL/OPG ratio for pS100 (p = 0.004) and pS100G10 (p = 0.003) compared to the empty defect group. pS100G10 showed a statistically higher expression of BMP-2. In addition, a statistically significant higher gene expression of alkaline phosphatase, osteoprotegerin, collagen1a1, collagen10a1 with a simultaneous decrease in RANKL, and carbonic anhydrase was seen in the pS100 and pS100G10 groups compared to the empty defect group. Mass spectrometric imaging by time-of-flight secondary ion mass spectrometry (ToF-SIMS) showed the release of Sr2+ ions from both pS100 and pS100G10, with a gradient into the interface region. ToF-SIMS imaging also revealed that resorption of the MBG particles allowed for new bone formation in cement pores. In summary, the current work shows better bone formation of the injectable pasty strontium-containing calcium phosphate bone cement with incorporated mesoporous bioactive glass compared to the bioactive-free bone cement and empty defects and can be considered for clinical application for osteopenic fracture defects in the future.

Treatment of critical bone defects using calcium phosphate cement and mesoporous bioactive glass providing spatiotemporal drug delivery

Calcium phosphate cements (CPC) are currently widely used bone replacement materials with excellent bioactivity, but have considerable disadvantages like slow degradation. For critical-sized defects, however, an improved degradation is essential to match the tissue regeneration, especially in younger patients who are still growing. We demonstrate that a combination of CPC with mesoporous bioactive glass (MBG) particles led to an enhanced degradation in vitro and in a critical alveolar cleft defect in rats. Additionally, to support new bone formation the MBG was functionalized with hypoxia conditioned medium (HCM) derived from rat bone marrow stromal cells. HCM-functionalized scaffolds showed an improved cell proliferation and the highest formation of new bone volume. This highly flexible material system together with the drug delivery capacity is adaptable to patient specific needs and has great potential for clinical translation.

Vascular endothelial growth factor (VEGF) delivery approaches in regenerative medicine

The utilization of growth factors in the process of tissue regeneration has garnered significant interest and has been the subject of extensive research. However, despite the fervent efforts invested in recent clinical trials, a considerable number of these studies have produced outcomes that are deemed unsatisfactory. It is noteworthy that the trials that have yielded the most satisfactory outcomes have exhibited a shared characteristic, namely, the existence of a mechanism for the regulated administration of growth factors. Despite the extensive exploration of drug delivery vehicles and their efficacy in delivering certain growth factors, the development of a reliable predictive approach for the delivery of delicate growth factors like Vascular Endothelial Growth Factor (VEGF) remains elusive. VEGF plays a crucial role in promoting angiogenesis; however, the administration of VEGF demands a meticulous approach as it necessitates precise localization and transportation to a specific target tissue. This process requires prolonged and sustained exposure to a low concentration of VEGF. Inaccurate administration of drugs, either through off-target effects or inadequate delivery, may heighten the risk of adverse reactions and potentially result in tumorigenesis. At present, there is a scarcity of technologies available for the accurate encapsulation of VEGF and its subsequent sustained and controlled release. The objective of this review is to present and assess diverse categories of VEGF administration mechanisms. This paper examines various systems, including polymeric, liposomal, hydrogel, inorganic, polyplexes, and microfluidic, and evaluates the appropriate dosage of VEGF for multiple applications.

Research Progress of Design Drugs and Composite Biomaterials in Bone Tissue Engineering

Bone, like most organs, has the ability to heal naturally and can be repaired slowly when it is slightly injured. However, in the case of bone defects caused by diseases or large shocks, surgical intervention and treatment of bone substitutes are needed, and drugs are actively matched to promote osteogenesis or prevent infection. Oral administration or injection for systemic therapy is a common way of administration in clinic, although it is not suitable for the long treatment cycle of bone tissue, and the drugs cannot exert the greatest effect or even produce toxic and side effects. In order to solve this problem, the structure or carrier simulating natural bone tissue is constructed to control the loading or release of the preparation with osteogenic potential, thus accelerating the repair of bone defect. Bioactive materials provide potential advantages for bone tissue regeneration, such as physical support, cell coverage and growth factors. In this review, we discuss the application of bone scaffolds with different structural characteristics made of polymers, ceramics and other composite materials in bone regeneration engineering and drug release, and look forward to its prospect.

Additive Manufacturing of Bioactive Glass and Its Polymer Composites as Bone Tissue Engineering Scaffolds: A Review

Bioactive glass (BG) and its polymer composites have demonstrated great potential as scaffolds for bone defect healing. Nonetheless, processing these materials into complex geometry to achieve either anatomy-fitting designs or the desired degradation behavior remains challenging. Additive manufacturing (AM) enables the fabrication of BG and BG/polymer objects with well-defined shapes and intricate porous structures. This work reviewed the recent advancements made in the AM of BG and BG/polymer composite scaffolds intended for bone tissue engineering. A literature search was performed using the Scopus database to include publications relevant to this topic. The properties of BG based on different inorganic glass formers, as well as BG/polymer composites, are first introduced. Melt extrusion, direct ink writing, powder bed fusion, and vat photopolymerization are AM technologies that are compatible with BG or BG/polymer processing and were reviewed in terms of their recent advances. The value of AM in the fabrication of BG or BG/polymer composites lies in its ability to produce scaffolds with patient-specific designs and the on-demand spatial distribution of biomaterials, both contributing to effective bone defect healing, as demonstrated by in vivo studies. Based on the relationships among structure, physiochemical properties, and biological function, AM-fabricated BG or BG/polymer composite scaffolds are valuable for achieving safer and more efficient bone defect healing in the future.

Three-Dimensional Plotted Calcium Phosphate Scaffolds for Bone Defect Augmentation—A New Method for Regeneration

For sinus grafting, different methods and materials are available. One possible shortcoming of particulate bone grafts is either overfilling or augmenting the planned implant area insufficiently. To overcome this risk and to determine the implant position prior augmentation, we present an approach using three-dimensional printed scaffolds. A patient with a remaining anterior dentition and bilateral severely atrophied posterior maxilla was seeking oral rehabilitation. The cone beam computed tomography (CBCT) showed residual bone heights between one and two millimeters. Following the three-dimensional reconstruction of the CBCT data, the positions of the implants were determined in areas 16 and 26. Three-dimensional scaffolds adapted to the topography of the sinus were virtually designed and printed using a calcium phosphate cement paste. Bilateral sinus floor augmentation applying the printed scaffolds with an interconnecting porosity followed. After nine months, a satisfying integration of the scaffolds was obvious. At the re-entry, vital bone with sufficient blood supply was found. One implant could be placed in positions 16 and 26, respectively. After five months, the implants could be uncovered and were provided with a temporary denture. The application of three-dimensionally printed scaffolds from calcium phosphate cement paste seems to be a promising technique to graft the severely atrophied posterior maxilla for the placement of dental implants.

Composites consisting of calcium phosphate cements and mesoporous bioactive glasses as a 3D plottable drug delivery system

Calcium phosphate cements (CPC) and mesoporous bioactive glasses (MBG) are two well studied biomaterial groups widely under investigation on their applicability to treat bone defects in orthopaedics and maxillofacial surgery. Recently the extrusion properties of CPC-MBG composites using a pasty CPC based on a hydrophobic carrier-liquid were studied in our group demonstrating that such composites are suitable for low temperature 3D plotting. Based on this work, we show in this study that by variation of the MBG content in the composite the degradation of the final scaffolds can be influenced. Furthermore, by modifying the cement phase and/or the MBG with therapeutically active ions like strontium, the released ion concentration can be varied over a wide range. In a second step the MBG was functionalized exploiting the high specific surface area of the glass as a carrier system for proteins like lysozyme or grow factors. We developed a protocol that allows the incorporation of protein-laden MBG in CPC pastes without impairing the extrudability of the CPC-MBG composites. Additionally, we found that released proteins from pure MBG or 3D plotted composite-scaffolds maintained their biological activity. Therefore, the combination of CPC and MBG allows the creation of a highly flexible composite system making it a promising candidate for bone tissue engineering. STATEMENT OF SIGNIFICANCE: Calcium phosphate cements and mesoporous bioactive glasses are two promising degradable biomaterials for the regenerative treatment of bone defects. The combination of both materials to a 3D printable composite enables the creation of implants with patient specific geometry. By varying the composition of the composite, the degradation behaviour can be influenced and especially the release of therapeutically active ions is tailorable over a wide range. We demonstrated this for strontium, as it has been shown to stimulate bone formation. Moreover, the bioactive glass can be used as a carrier system for drugs or growth factors and we show the successful combination of such functionalised glass particles and a cement paste without affecting the printability.

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.

Calcium Phosphate-Based Biomaterials for Bone Repair

Traumatic, tumoral, and infectious bone defects are common in clinics, and create a big burden on patient's families and society. Calcium phosphate (CaP)-based biomaterials have superior properties and have been widely used for bone defect repair, due to their similarities to the inorganic components of human bones. The biological performance of CaPs, as a determining factor for their applications, are dependent on their physicochemical properties. Hydroxyapatite (HAP) as the most thermally stable crystalline phase of CaP is mostly used in the form of ceramics or composites scaffolds with polymers. Nanostructured CaPs with large surface areas are suitable for drug/gene delivery systems. Additionally, CaP scaffolds with hierarchical nano-/microstructures have demonstrated excellent ability in promoting bone regeneration. This review focuses on the relationships and interactions between the physicochemical/biological properties of CaP biomaterials and their species, sizes, and morphologies in bone regeneration, including synthesis strategies, structure control, biological behavior, and the mechanisms of CaP in promoting osteogenesis. This review will be helpful for scientists and engineers to further understand CaP-based biomaterials (CaPs), and be useful in developing new high-performance biomaterials for bone repair.

Alginate-modified mesoporous bioactive glass and its drug delivery, bioactivity, and osteogenic properties

Mesoporous bioactive glass (MBG) is widely used in bone tissue repairing and drug loading. However, burst release of drug and poor compatibility with other materials limited its application. It is an effective way to modify MBG with a polymer brush to improve the properties. Herein, an alginate-modified MBG was prepared, and then, the effects of ALG on the properties of MBG were investigated. The results demonstrate that ALG could improve the drug loading efficiency, prolong drug release times, and make orderly deposition of apatite on the surface of MBG. Furthermore, MBG@ALG significantly promoted the osteogenic differentiation of MC3T3-E1 cells, demonstrating that surface modification of MBG by ALG can improve its properties, which will further broaden the application of MBG in tissue engineering.

Highly bioactive bone cement microspheres based on α-tricalcium phosphate microparticles/mesoporous bioactive glass nanoparticles: Formulation, physico-chemical characterization and in vivo bone regeneration

Calcium phosphate cement (CPC) is a self-setting, biocompatible and osteoconductive bone cement, however its use as a bone substitute is still limited owing to its low bioactivity (i.e. its slow in vivo resorption and slow new bone formation rate) which is a challenging issue to be addressed. Herein, we report for the first time highly bioactive bone cement microspheres formulated from a cement paste containing α-tricalcium phosphate microparticles (α-TCP) and mesoporous calcium silicate bioactive glass nanoparticles (mesoporous BGn) using a water-in-oil emulsion method. Indeed, bioactive microspheres possess high potential as bone defect fillers for bone regeneration. The α-TCP microparticles were prepared by a solid state synthesis at 1400 ºC while mesoporous BGn were synthesized by template-assissted ultrasound-mediated sol-gel method. The particle size distribution of as-prepared cement microspheres was in the range of 200 - 450 µm with a sphericity index in the range of 0.92 - 0.94. The surface morphology of α-TCP microspheres revealed α-TCP micoparticles with smooth surfaces whereas α-TCP/BGn microspheres unveiled nano-roughened α-TCP microparticles. The as-prepared α-TCP/BGn cement microspheres exhibited larger specific surface area ca 18.6 m²/g, sustained release of soluble silicate (SiO₄^4-) ions (118 ppm within a week) and high protein adsorption capacity (252 mg/g). Notably, the α-TCP/BGn cement microspheres showed excellent in vitro surface bioactivity via formation of massive amounts of bone-like hydroxyapatite spherules and aggregates on their surfaces after soaking in simulated body fluid. Importantly, the in vivo implantation of as-prepared α-TCP/BGn cement microspheres in rat calvarial critical size bone defects for 6 weeks unveiled high in vivo bioactivity in terms of substantial new bone ingrowth and significant new bone formation within the bone defect as evidenced by histological analyses, X-ray radiography and micro-computed tomography evaluations.

The advances in nanomedicine for bone and cartilage repair

With the gradual demographic shift toward an aging and obese society, an increasing number of patients are suffering from bone and cartilage injuries. However, conventional therapies are hindered by the defects of materials, failing to adequately stimulate the necessary cellular response to promote sufficient cartilage regeneration, bone remodeling and osseointegration. In recent years, the rapid development of nanomedicine has initiated a revolution in orthopedics, especially in tissue engineering and regenerative medicine, due to their capacity to effectively stimulate cellular responses on a nanoscale with enhanced drug loading efficiency, targeted capability, increased mechanical properties and improved uptake rate, resulting in an improved therapeutic effect. Therefore, a comprehensive review of advancements in nanomedicine for bone and cartilage diseases is timely and beneficial. This review firstly summarized the wide range of existing nanotechnology applications in the medical field. The progressive development of nano delivery systems in nanomedicine, including nanoparticles and biomimetic techniques, which are lacking in the current literature, is further described. More importantly, we also highlighted the research advancements of nanomedicine in bone and cartilage repair using the latest preclinical and clinical examples, and further discussed the research directions of nano-therapies in future clinical practice.

Peptide-Modified Nano-Bioactive Glass for Targeted Immobilization of Native VEGF

A limiting factor in large bone defect regeneration is the slow and disorganized formation of a functional vascular network in the defect area, often resulting in delayed healing or implant failure. To overcome this, strategies that induce angiogenic processes should be combined with potent bone graft substitutes in new bone regeneration approaches. To this end, we describe a unique approach to immobilize the pro-angiogenic growth factor VEGF₁₆₅ in its native state on the surface of nanosized bioactive glass particles (nBGs) via a binding peptide (PR1P). We demonstrate that covalent coupling of the peptide to amine functional groups grafted on the nBG surface allows immobilization of VEGF with high efficiency and specificity. The amount of coupled peptide could be controlled by varying amine density, which eventually allows tailoring the amount of bound VEGF within a physiologically effective range. In vitro analysis of endothelial cell tube formation in response to VEGF-carrying nBG confirmed that the biological activity of VEGF is not compromised by the immobilization. Instead, comparable angiogenic stimulation was found for lower doses of immobilized VEGF compared to exogenously added VEGF. The described system, for the first time, employs a binding peptide for growth factor immobilization on bioactive glass nanoparticles and represents a promising strategy to overcome the problem of insufficient neovascularization in large bone defect regeneration.

Factors influencing the drug release from calcium phosphate cements

Thanks to their biocompatibility, biodegradability, injectability and self-setting properties, calcium phosphate cements (CPCs) have been the most economical and effective biomaterials of choice for use as bone void fillers. They have also been extensively used as drug delivery carriers owing to their ability to provide for a steady release of various organic molecules aiding the regeneration of defective bone, including primarily antibiotics and growth factors. This review provides a systematic compilation of studies that reported on the controlled release of drugs from CPCs in the last 25 years. The chemical, compositional and microstructural characteristics of these systems through which the control of the release rates and mechanisms could be achieved have been discussed. In doing so, the effects of (i) the chemistry of the matrix, (ii) porosity, (iii) additives, (iv) drug types, (v) drug concentrations, (vi) drug loading methods and (vii) release media have been distinguished and discussed individually. Kinetic specificities of in vivo release of drugs from CPCs have been reviewed, too. Understanding the kinetic and mechanistic correlations between the CPC properties and the drug release is a prerequisite for the design of bone void fillers with drug release profiles precisely tailored to the application area and the clinical picture. The goal of this review has been to shed light on these fundamental correlations.

Osteogenic Capability of Vaterite-Coated Nonwoven Polycaprolactone Scaffolds for In Vivo Bone Tissue Regeneration

In current orthopedic practice, bone implants used to-date often exhibit poor osteointegration, impaired osteogenesis, and, eventually, implant failure. Actively pursued strategies for tissue engineering could overcome these shortcomings by developing new hybrid materials with bioinspired structure and enhanced regenerative potential. In this study, the osteogenic and therapeutic potential of bioactive vaterite is investigated as a functional component of a fibrous polymeric scaffold for bone regeneration. Hybrid two-layered polycaprolactone scaffolds coated with vaterite (PCL/CaCO₃ ) are studied during their 28-days implantation period in a rat femur defect. After this period, the study of tissue formation in the defected area is performed by the histological study of femur cross-sections. Immobilization of alkaline phosphatase (ALP) into PCL/CaCO₃ scaffolds accelerates new bone tissue formation and defect repair. PCL/CaCO₃ and PCL/CaCO₃ /ALP scaffolds reveal 37.3% and 62.9% areas, respectively, filled with newly formed bone tissue in cross-sections compared to unmineralized PCL scaffold (17.5%). Bone turnover markers are monitored on the 7th and 28th days after implantation and reveal an increase of osteocalcin level for both PCL/CaCO₃ and PCL/CaCO₃ /ALP compared with PCL indicating the activation of osteogenesis. These findings indicate that vaterite, as an osteoconductive component of polymeric scaffolds, promotes osteogenesis, supports angiogenesis, and facilitates bone defect repair.

Injectable silanized hyaluronic acid hydrogel/biphasic calcium phosphate granule composites with improved handling and biodegradability promote bone regeneration in rabbits

Biphasic calcium phosphate (BCP) granules are osteoconductive biomaterials used in clinics to favor bone reconstruction. Yet, poor cohesivity, injectability and mechanical properties restrain their use as bone fillers. In this study, we incorporated BCP granules into in situ forming silanized hyaluronic acid (Si-HA) and hydroxypropylmethylcellulose (Si-HPMC) hydrogels. Hydrogel composites were shown to be easily injectable (F < 30 N), with fast hardening properties (<5 min), and similar mechanical properties (E∼ 60 kPa). In vivo, both hydrogels were well tolerated by the host, but showed different biodegradability with Si-HA gels being partially degraded after 21d, while Si-HPMC gels remained stable. Both composites were easily injected into critical size rabbit defects and remained cohesive. After 4 weeks, Si-HPMC/BCP led to poor bone healing due to a lack of degradation. Conversely, Si-HA/BCP composites were fully degraded and beneficially influenced bone regeneration by increasing the space available for bone ingrowth, and by accelerating BCP granules turnover. Our study demonstrates that the degradation rate is key to control bone regeneration and that Si-HA/BCP composites are promising biomaterials to regenerate bone defects.

The impact of leuprolide acetate-loaded calcium phosphate silicate cement to bone regeneration under osteoporotic conditions

Osteoporosis is detrimental to the health of skeletal structure and significantly increases the risks of bone fracture. Moreover, bone regeneration is adversely impaired by increased osteoclastic activities as a result of osteoporosis. In this study, we developed a novel formulation of injectable bone cement based on calcium phosphate silicate cement (CPSC) and leuprolide acetate (LA). Several combinations of LA-CPSC bone cement were characterized and, it is found that LA could increase the setting time and compressive strength of CPSC in a concentration-dependent manner. Moreover, thein vitroresults revealed that LA-CPSC was biocompatible and able to encourage the osteoblast proliferation via the mTOR signalling pathway. Furthermore, the LA-CPSC was implanted in the osteoporotic rats to evaluate its effectiveness to repair bone fractures under the osteoporotic conditions. The biomarker study and micro-CT analyses indicated that LA-CPSC could effectively reduce the osteoclast activities and promote the bone regeneration. In conclusion, our study demonstrated that LA-CPSC injectable bone cement should be a viable solution to repair bone fractures under the osteoporotic conditions.

Bioactive glass: A multifunctional delivery system

Bioactive glasses (BAGs) were invented five decades ago and have been widely used clinically in orthopedic and stomatology. However, in the past two decades, BAGs have been explored immensely by several researchers worldwide as a multifunctional delivery system for a multitude of therapeutics ranging from metal ions to small molecules (e.g., drugs) and macromolecules (e.g., DNA). The impetus for devising a BAG-based delivery system in the 21st century is based upon the facilitative properties it offers for entrapment of a wide range of therapeutic molecules and the tailorable controlled release kinetics to the target tissue site along with the biological activity of the ionic dissolution products in several pathological conditions such as osteoporosis, cancer, infection, and inflammation. This review comprises two parts: the first part discusses the need for a new delivery system and how the journey from melt quench progressed towards template-based sol-gel mesoporous. In the second part, we have comprehended the scientific advancements made so far, emphasizing BAGs as a delivery system ranging from therapeutic ions to phytopharmaceuticals. We have also highlighted a few loopholes that have prevented bench-to-bedside clinical translation of a plethora of elucidative researches done so far.

Moxifloxacin-loaded in situ synthesized Bioceramic/Poly(L-lactide-co-ε-caprolactone) composite scaffolds for treatment of osteomyelitis and orthopedic regeneration

High local intraosseous levels of antimicrobial agents are required for adequate long-term treatment of chronic osteomyelitis (OM). In this study, biodegradable composite scaffolds of poly-lactide-co-ε-caprolactone/calcium phosphate (CaP) were in-situ synthesized using two different polymer grades and synthesis pathways and compared to composites prepared by pre-formed (commercially available) CaP for delivery of the antibiotic moxifloxacin hydrochloride (MOX). Phase identification and characterization by Fourier transform infra-red (FTIR) spectroscopy, X-ray powder diffraction (XRPD) and scanning electron microscope (SEM) confirmed the successful formation of different CaP phases within the biodegradable polymer matrix. The selected in-situ formed CaP scaffold showed a sustained release for MOX for six weeks and adequate porosity. Cell viability study on MG-63 osteoblast-like cells revealed that the selected composite scaffold maintained the cellular proliferation and differentiation. Moreover, it was able to diminish the bacterial load, inflammation and sequestrum formation in the bones of OM-induced animals. The results of the present work deduce that the selected in-situ formed CaP composite scaffold is a propitious candidate for OM treatment, and further clinical experiments are recommended.

In vitro and in vivo effectiveness of a novel injectable calcitonin-loaded collagen/ceramic bone substitute

This study aimed to evaluate the effectiveness of a novel calcitonin-loaded calcium phosphate composite bone cement in vitro and in vivo. The novel composite bone cements were composed of NuROs injectable bone graft substitute, type I collagen, and/or salmon calcitonin. The setting time, porosity, wettability, compressive strength, compressive modulus, and crystallographic structures of cement specimens were determined. Degradation rate, calcitonin release rate, and osteoinductivity were assessed in vitro. In addition, osteogenic effect was examined in a rabbit model of femoral defect. The results revealed that addition of collagen/calcitonin did not substantially alter physical properties and degradation rate of bone cement specimens. Calcitonin was released into culture medium in a two-phase manner. Osteogenic effect of conditioned medium derived from calcitonin containing bone cement was observed. Finally, de novo bone growth and bone mineralization across the bone defect area were observed in rabbits after implantation of composite bone cement specimens. In conclusion, this novel calcitonin-loaded composite calcium phosphate bone cement exhibits biocompatibility, bioresorbability, osteoinductivity, and osteoconductivity, which may be suitable for clinical use.

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.

Advances in Growth Factor Delivery for Bone Tissue Engineering

Shortcomings related to the treatment of bone diseases and consequent tissue regeneration such as transplants have been addressed to some extent by tissue engineering and regenerative medicine. Tissue engineering has promoted structures that can simulate the extracellular matrix and are capable of guiding natural bone repair using signaling molecules to promote osteoinduction and angiogenesis essential in the formation of new bone tissues. Although recent studies on developing novel growth factor delivery systems for bone repair have attracted great attention, taking into account the complexity of the extracellular matrix, scaffolding and growth factors should not be explored independently. Consequently, systems that combine both concepts have great potential to promote the effectiveness of bone regeneration methods. In this review, recent developments in bone regeneration that simultaneously consider scaffolding and growth factors are covered in detail. The main emphasis in this overview is on delivery strategies that employ polymer-based scaffolds for spatiotemporal-controlled delivery of both single and multiple growth factors in bone-regeneration approaches. From clinical applications to creating alternative structural materials, bone tissue engineering has been advancing constantly, and it is relevant to regularly update related topics.

Mesoporous calcium silicate nanoparticles for superficial dental tissue reconstruction, in vitro and in vivo

The underlying dentin could be exposed to a humid atmosphere filled with bacteria if the covering enamel layer is broken because of external chemical and physical conditions. Accordingly, some diseases like bacterial invasion and dentin hypersensitivity often occur, which impact the daily life of patients. The study is aimed at evaluating the occluding effects of mesoporous calcium silicate nanoparticles (MCSNs) on the dentinal tubules in vitro and in vivo, as well as the antibacterial property and drug delivery ability when loaded with chlorhexidine (CHX) in vitro. MCSNs were synthesized according to the standard protocol. After a series of complimentary evaluations in vitro and in vivo, it was found that MCSNs and CHX–MCSNs could continually form apatite-like enamel layers on the exposed dentinal tubules and significantly reduced dentin permeability both in vitro and in vivo. Besides, MCSN and CHX–MCSN possessed low cytotoxicity in vitro, and only mild pulp inflammation was observed in two MCSNs containing groups in vivo. In addition, MCSN loaded with CHX released CHX sustainably and revealed a significant antibacterial effect against E. faecalis in vitro. Therefore, the results suggest that MCSN could be used as a promising biomaterial to occlude the dentinal tubules and carry antibiotics for avoiding further pulp infection.

MCSNs could be used as a promising biomaterial for occluding the dentinal tubules in vitro and in vivo. Also, the outstanding drug delivery and antibacterial properties enable it to carry antibiotics easily for inhibiting deeper pulp infection.

Mesoporous bioactive glass composition effects on degradation and bioactivity

Mesoporous bioactive glasses (MBGs) are promising materials for regenerative medicine, due to their favorable properties including bioactivity and degradability. These key properties, but also their surface area, pore structure and pore volume are strongly dependent on synthesis parameters and glass stoichiometry. However, to date no systematic study on MBG properties covering a broad range of possible compositions exists.

Here, 24 MBG compositions in the SiO₂–CaO–P₂O₅ system were synthesized by varying SiO₂ (60–90 mol %), CaO and P₂O₅ content (both 0 to 40 mol-%), while other synthesis parameters were kept constant. Mesopore characteristics, degradability and bioactivity were analysed.

The results showed that, within the tested range of compositions, mesopore formation required a molar SiO₂ content above 60% but was independent of CaO and P₂O₅ content. While mesopore size did not depend on glass stoichiometry, mesopore arrangement was influenced by the SiO₂ content. Specific surface area and pore volume were slightly altered by the SiO₂ content. All materials were degradable; however, degradation as well as bioactivity, i.e. the ability to form a CaP mineral on the surface, depended on stoichiometry. Major differences were found in early surface reactions in simulated body fluid: where some MBGs induced direct hydroxyapatite crystallization, high release of calcium in others resulted in calcite formation.

In summary, degradation and bioactivity, both key parameters of MBGs, can be controlled by glass stoichiometry over a broad range while leaving the unique structural parameters of MBGs relatively unaffected. This allows targeted selection of material compositions for specific regenerative medicine applications.

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Mesoporous bioactive glasses can be obtained over a broad range of compositions.

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In the SiO₂/CaO/P₂O₅ system up to 15 mol-% P₂O₅ allow ordered porosity.

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In SiO₂/P₂O₅ glasses, up to 30 mol-% P₂O₅ are possible.

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Bioactivity and degradation can be tailored by controlling stoichiometry.

Poloxamer: A versatile tri-block copolymer for biomedical applications

Poloxamers, also called Pluronic, belong to a unique class of synthetic tri-block copolymers containing central hydrophobic chains of poly(propylene oxide) sandwiched between two hydrophilic chains of poly(ethylene oxide). Some chemical characteristics of poloxamers such as temperature-dependent self-assembly and thermo-reversible behavior along with biocompatibility and physiochemical properties make poloxamer-based biomaterials promising candidates for biomedical application such as tissue engineering and drug delivery. The microstructure, bioactivity, and mechanical properties of poloxamers can be tailored to mimic the behavior of various types of tissues. Moreover, their amphiphilic nature and the potential to self-assemble into the micelles make them promising drug carriers with the ability to improve the drug availability to make cancer cells more vulnerable to drugs. Poloxamers are also used for the modification of hydrophobic tissue-engineered constructs. This article collects the recent advances in design and application of poloxamer-based biomaterials in tissue engineering, drug/gene delivery, theranostic devices, and bioinks for 3D printing. STATEMENT OF SIGNIFICANCE: Poloxamers, also called Pluronic, belong to a unique class of synthetic tri-block copolymers containing central hydrophobic chains of poly(propylene oxide) sandwiched between two hydrophilic chains of poly(ethylene oxide). The microstructure, bioactivity, and mechanical properties of poloxamers can be tailored to mimic the behavior of various types of tissues. Moreover, their amphiphilic nature and the potential to self-assemble into the micelles make them promising drug carriers with the ability to improve the drug availability to make cancer cells more vulnerable to drugs. However, no reports have systematically reviewed the critical role of poloxamer for biomedical applications. Research on poloxamers is growing today opening new scenarios that expand the potential of these biomaterials from "traditional" treatments to a new era of tissue engineering. To the best of our knowledge, this is the first review article in which such issue is systematically reviewed and critically discussed in the light of the existing literature.

Immobilization of Growth Factors for Cell Therapy Manufacturing

Cell therapy products exhibit great therapeutic potential but come with a deterring price tag partly caused by their costly manufacturing processes. The development of strategies that lead to cost-effective cell production is key to expand the reach of cell therapies. Growth factors are critical culture media components required for the maintenance and differentiation of cells in culture and are widely employed in cell therapy manufacturing. However, they are expensive, and their common use in soluble form is often associated with decreased stability and bioactivity. Immobilization has emerged as a possible strategy to optimize growth factor use in cell culture. To date, several immobilization techniques have been reported for attaching growth factors onto a variety of biomaterials, but these have been focused on tissue engineering. This review briefly summarizes the current landscape of cell therapy manufacturing, before describing the types of chemistry that can be used to immobilize growth factors for cell culture. Emphasis is placed to identify strategies that could reduce growth factor usage and enhance bioactivity. Finally, we describe a case study for stem cell factor.

Injectable and bioactive bone cement with moderate setting time and temperature using borosilicate bio-glass-incorporated magnesium phosphate

In this study, borosilicate bio-glass (BG) was incorporated into magnesium phosphate cement (MPC) for the purpose of developing an injectable and bioactive composite cement with suitable physicochemical and biocompatible performance. Results show that the BG-incorporated MPC possesses an excellent injectability, and can be used to fill in different 3D printed defect models using a syringe with a moderate setting time. Meanwhile, BG can retard the setting time and adjust the exothermic temperature of MPC. When the MPC/BG ratio was 3:1 (MPC3-BG), its corresponding setting time, peak temperature, anti-washout ratio and compressive strength were 9.9 ± 0.7 min, 45.8 ± 1.6 °C, 87%-90% and 13.5 MPa, respectively, which were suitable for injection and bone reparation. Characterizations of MPC3-BG showed that it had a faster degradation rate than MPC and the functional ions of boron and silicon could be released from the dissolution of the composite cement. In vitro and in vivo experiments also demonstrated that MPC3-BG had a stimulatory effect on the cell proliferation and new bone regeneration.

Chitosan-calcium phosphate composite scaffolds for control of post-operative osteomyelitis: Fabrication, characterization, and in vitro-in vivo evaluation

Osteomyelitis is a progressive inflammatory disease requiring prolonged systemic treatment with high antibiotic doses, and is very challenging to be treated. The use of locally applied antibiotics loaded on a biodegradable carrier at surgery sites is hypothesized to prevent post-operative osteomyelitis, while providing site-specific drug release. In this work, chitosan-based calcium phosphate composites were prepared and loaded with moxifloxacin hydrochloride. The in-situ formation of calcium phosphates within the composite was experimentally confirmed by Fourier transform infra-red spectroscopy, X-ray powder diffraction, and scanning electron microscopy. Results showed that the composites provided complete drug release over three days, and the selected composite formulation induced differentiation and proliferation of osteoblasts, while reducing bacterial count, inflammation and intra-medullary fibrosis in bone tissue specimens of osteomyelitis-induced animal model. Hence, we can conclude that the in situ prepared antibiotic-loaded calcium phosphate chitosan composite is promising in preventing post-operative osteomyelitis, and is worthy of clinical experimentation.

New insights into ToF-SIMS imaging in osteoporotic bone research

The present work focuses on the application of time-of-flight secondary ion mass spectrometry (ToF-SIMS) in osteoporotic bone research. In order to demonstrate the benefit, the authors present concrete application examples of ToF-SIMS in three different areas of bone research. ToF-SIMS as a mass spectrometric imaging technique allows simultaneous visualization of mineralized and nonmineralized bone tissue as well as implanted biomaterials and bone implant interphases. In the first example, the authors show that it is possible to study the incorporation and distribution of different components released from bone filler materials into bone with a single mass spectrometric measurement. This not only enables imaging of nonstained bone cross sections but also provides further insights beyond histologically obtained information. Furthermore, they successfully identified several mass fragments as markers for newly formed cartilage tissue and growth joint in bone. Different modes of ToF-SIMS as well as different SIMS instruments (IONTOF's TOF.SIMS 5 and M6 Hybrid SIMS, Ionoptika's J105) were used to identify these mass signals and highlight the high versatility of this method. In the third part, bone structure of cortical rat bone was investigated from bone sections embedded in technovit (polymethyl methacrylate, PMMA) and compared to cryosections. In cortical bone, they were able to image different morphological features, e.g., concentric arrangement of collagen fibers in so-called osteons as well as Haversian canals and osteocytes. In summary, the study provides examples of application and shows the strength of ToF-SIMS as a promising analytical method in the field of osteoporotic bone research.

3D Printing of Bone Grafts for Cleft Alveolar Osteoplasty - In vivo Evaluation in a Preclinical Model

One of the most common hereditary craniofacial anomalies in humans are cleft lip and cleft alveolar bone with or without cleft palate. Current clinical practice, the augmentation of the persisting alveolar bone defect by using autologous bone grafts, has considerable disadvantages motivating to an intensive search for alternatives. We developed a novel therapy concept based on 3D printing of biodegradable calcium phosphate-based materials and integration of osteogenic cells allowing fabrication of patient-specific, tissue-engineered bone grafts. Objective of the present study was the in vivo evaluation of implants in a rat alveolar cleft model. Scaffolds were designed according to the defect's geometry with two different pore designs (60° and 30° rotated layer orientation) and produced by extrusion-based 3D plotting of a pasty calcium phosphate cement. The scaffolds filled into the artificial bone defect in the palate of adult Lewis rats, showing a good support. Half of the scaffolds were colonized with rat mesenchymal stromal cells (rMSC) prior to implantation. After 6 and 12 weeks, remaining defect width and bone formation were quantified histologically and by microCT. The results revealed excellent osteoconductive properties of the scaffolds, a significant influence of the pore geometry (60° > 30°), but no enhanced defect healing by pre-colonization with rMSC.

In vivo behavior of biomicroconcretes based on α-tricalcium phosphate and hybrid hydroxyapatite/chitosan granules and sodium alginate

The current studies provide insights into how predictions based on results of physicochemical and in vitro tests are consistent with the results of in vivo studies. The new biomicroconcrete type materials were obtained by mixing the solid phase, composed of hybrid hydroxyapatite/chitosan granules and highly reactive α-tricalcium phosphate powder, used as the setting agent. This approach guaranteed a good adhesion of the continuous cement phase to the surface of granules. It has been demonstrated that developed biomicroconcretes are surgically handy, possessed favorable physicochemical and biological properties and can be considered as effective bone implant material. The hierarchical porosity and compressive strength (2-6 MPa) similar to cancellous bone made them suitable for low-load bearing applications. Despite the fact that final setting times of biomicroconcretes were longer than recommended in the literature (i.e., exceeded 15 min), their short cohesion time allows for a successful implantation in a rabbit femoral defect model. Histological analysis and Raman studies revealed newly formed bone tissues around the sides of implanted materials. Furthermore, the process of neovascularization and reconstruction of the bone tissue, as well as a reverse scaffolding process, was visible. No signs of inflammation or adverse tissue reactions were observed during the experiment.

An overview of advanced biocompatible and biomimetic materials for creation of replacement structures in the musculoskeletal systems: focusing on cartilage tissue engineering

Tissue engineering, as an interdisciplinary approach, is seeking to create tissues with optimal performance for clinical applications. Various factors, including cells, biomaterials, cell or tissue culture conditions and signaling molecules such as growth factors, play a vital role in the engineering of tissues. In vivo microenvironment of cells imposes complex and specific stimuli on the cells, and has a direct effect on cellular behavior, including proliferation, differentiation and extracellular matrix (ECM) assembly. Therefore, to create appropriate tissues, the conditions of the natural environment around the cells should be well imitated. Therefore, researchers are trying to develop biomimetic scaffolds that can produce appropriate cellular responses. To achieve this, we need to know enough about biomimetic materials. Scaffolds made of biomaterials in musculoskeletal tissue engineering should also be multifunctional in order to be able to function better in mechanical properties, cell signaling and cell adhesion. Multiple combinations of different biomaterials are used to improve above-mentioned properties of various biomaterials and to better imitate the natural features of musculoskeletal tissue in the culture medium. These improvements ultimately lead to the creation of replacement structures in the musculoskeletal system, which are closer to natural tissues in terms of appearance and function. The present review article is focused on biocompatible and biomimetic materials, which are used in musculoskeletal tissue engineering, in particular, cartilage tissue engineering.

Mesoporous bioactive glass combined with graphene oxide scaffolds for bone repair

Recently there has been an increasing interest in bioactive factors with robust osteogenic ability and angiogenesis function to repair bone defects. However, previously tested factors have not achieved satisfactory results due to low loading doses and a short protein half-life. Finding a validated stable substitute for these growth factors and apply it to the construction of porous scaffolds with the dual function of osteogenesis and angiogenesis is therefore vital for bone tissue regeneration engineering. Graphene oxide (GO) has attracted increasing attention due to its good biocompatibility, osteogenic, and angiogenic functions. This study aims to design a scaffold composed of mesoporous bioactive glasses (MBG) and GO to investigate whether the composite porous scaffold promotes local angiogenesis and bone healing. Our in vitro studies demonstrate that the MBG-GO scaffolds have better cytocompatibility and higher osteogenesis differentiation ability with rat bone marrow mesenchymal stem cells (rBMSCs) than the purely MBG scaffold. Moreover, MBG-GO scaffolds promote vascular ingrowth and, importantly, enhance bone repair at the defect site in a rat cranial defect model. The new bone was fully integrated not only with the periphery but also with the center of the scaffold. From these results, it is believed that the MBG-GO scaffolds possess excellent osteogenic-angiogenic properties which will make them appealing candidates for repairing bone defects. The novelty of this research is to provide a new material to treat bone defects in the clinic.

Mesoporous bioactive glasses for the combined application of osteosarcoma treatment and bone regeneration

In this study, mesoporous bioactive glass (MBG) sub-micro particles were prepared through sol-gel synthesis and possessed a uniform and spherical structure with particle size of 302 ± 43 nm, a pore size of 4 nm and a high surface area of 354 m² g^-1. Alendronate (AL) is often used for the treatment of bone associated diseases, in particular osteosarcoma. However, due to the low bioavailability and high toxicity at increased doses, local and sustained release would be an ideal approach to AL delivery. Here, MBGs and aminated MBGs (AMBG) were applied as carriers for AL loading. High encapsulation efficiency of 75% and 85% and loading efficiency of 60% and 63%, for MBG and AMBG, respectively, was achieved. The release profile of AL from AMBG showed a better sustained and controlled release mechanism compared to MBG. In vitro results demonstrated the non-cytotoxic nature of both MBG and AMBG following exposure to MG63 osteoblast like cell line. AL release from MBG and AMBG, even at lower concentration, provoked decreased MG63 proliferation. The osteogenic potential of MBG and AMBG following exposure to dental pulp stem cells was evaluated using alizarin red assay.

Biomaterial-assisted local and systemic delivery of bioactive agents for bone repair

Although bone tissues possess an intrinsic capacity for repair, there are cases where bone healing is either impaired or insufficient, such as fracture non-union, osteoporosis, osteomyelitis, and cancers. In these cases, treatments like surgical interventions are used, either alone or in combination with bioactive agents, to promote tissue repair and manage associated clinical complications. Improving the efficacy of bioactive agents often requires carriers, with biomaterials being a pivotal player. In this review, we discuss the role of biomaterials in realizing the local and systemic delivery of biomolecules to the bone tissue. The versatility of biomaterials enables design of carriers with the desired loading efficiency, release profile, and on-demand delivery. Besides local administration, systemic administration of drugs is necessary to combat diseases like osteoporosis, warranting bone-targeting drug delivery systems. Thus, chemical moieties with the affinity towards bone extracellular matrix components like apatite minerals have been widely utilized to create bone-targeting carriers with better biodistribution, which cannot be achieved by the drugs alone. Bone-targeting carriers combined with the desired drugs or bioactive agents have been extensively investigated to enhance bone healing while minimizing off-target effects. Herein, these advancements in the field have been systematically reviewed. STATEMENT OF SIGNIFICANCE: Drug delivery is imperative when surgical interventions are not sufficient to address various bone diseases/defects. Biomaterial-assisted delivery systems have been designed to provide drugs with the desired loading efficiency, sustained release, and on-demand delivery to enhance bone healing. By surveying recent advances in the field, this review outlines the design of biomaterials as carriers for the local and systemic delivery of bioactive agents to the bone tissue. Particularly, biomaterials that bear chemical moieties with affinity to bone are attractive, as they can present the desired bioactive agents to the bone tissue efficiently and thus enhance the drug efficacy for bone repair.

Development and Characterization of Composites Consisting of Calcium Phosphate Cements and Mesoporous Bioactive Glass for Extrusion-Based Fabrication

Calcium phosphate cements (CPC) and mesoporous bioactive glasses (MBG) are two degradable biomaterial groups widely under investigation concerning their applicability to treat bone defects. MBG-CPC composites were recently shown to possess enhanced degradation properties in comparison to pure CPC. In addition, modification of MBG allows an easy incorporation of therapeutically effective ions. Additive manufacturing of such composites enables the fabrication of patient-specific geometries with further improved degradation behavior due to control over macroporosity. In this study, we developed composites prepared from a non-aqueous carrier-liquid (cl) based CPC paste and MBG particles suitable for extrusion-based additive manufacturing (3D plotting). CPC with the addition of up to 10 wt % MBG were processible by adjusting the amount of cl. Scaffolds consisting of a 4, 6 and 8%-MBG-CPC composite were successfully manufactured by 3D plotting. While mechanically characterization of the scaffolds showed an influence of the MBG, no changes of microstructure were observed. During degradation of the composite, the release of Ca2+ and Sr2+ ions could be controlled by the MBG composition and plotted scaffolds with macropores showed a significant higher release than bulk samples of comparable mass. These findings demonstrate a high flexibility regarding ion release of the developed composites and suggest utilizing the drug binding capacities of MBG as a prospective delivery system for biologically active proteins.

Controlled in vivo Bone Formation and Vascularization Using Ultrasound-Triggered Release of Recombinant Vascular Endothelial Growth Factor From Poly(D,L-lactic-co-glycolicacid) Microbubbles

Bone defects are challenging to treat in musculoskeletal system due to the lack of vascularization. Biomaterials with internal vascularization ability and osteoinduction bioactivity are promising strategies for orthopedic applications. Vascular endothelial growth factor (VEGF) has been widely used for angiogenesis and osteogenesis. Here, we developed VEGF-loaded PLGA microbubbles (MBs) for improvement of angiogenesis and osteogenesis in bone defect repair in combination with ultrasound-targeted microbubble destruction (UTMD). Release profile showed UTMD promoted the burst release of VEGF from PLGA MBs. We subsequently investigated the combination of ultrasound application with VEGF MBs for in vitro osteogenesis. The results demonstrated that the expression of osteogenesis-related genes and calcium deposits were increased by VEGF MBs in combination of UTMD. Micro-computed tomography (micro-CT) and histological analysis were conducted 4 and 8 weeks post-surgery. In vivo results show that VEGF MBs in combination of UTMD could significantly enhance new bone formation and vascular ingrowth at the defect site in a rat calvarial defect model. In summary, VEGF MBs in combination of UTMD could augment bone regeneration and vascularization at calvarial bone defects and hold huge potential for clinical translation.

3D Plotted Biphasic Bone Scaffolds for Growth Factor Delivery: Biological Characterization In Vitro and In Vivo

Bioprinting enables the integration of biological components into scaffolds during fabrication that has the advantage of high loading efficiency and better control of release and/or spatial positioning. In this study, a biphasic scaffold fabricated by extrusion-based 3D multichannel plotting of a calcium phosphate cement (CPC) paste and an alginate/gellan gum (AlgGG) hydrogel paste laden with the angiogenic factor VEGF (vascular endothelial growth factor) is investigated with regard to biological response in vitro and in vivo. Rat mesenchymal stromal cells are able to adhere and grow on both CPC and AlgGG strands, and differentiate toward osteoblasts. A sustained VEGF release is observed, which is able to stimulate endothelial cell proliferation as well as angiogenesis in vitro that indicates maintenance of its biological activity. After implantation into a segmental bone defect in the femur diaphysis of rats, a clear reduction of the defect size by newly formed bone tissue occurs from the distal and proximal ends of the host bone within 12 weeks. The CPC component shows excellent osteoconductivity whereas the local VEGF release from the AlgGG hydrogel gives rise to an enhanced vascularization of the defect region. This work contributes to the development of novel therapeutic concepts for improved bone regeneration which are based on 3D bioprinting.

Melatonin decorated 3D-printed beta-tricalcium phosphate scaffolds promoting bone regeneration in a rat calvarial defect model

3D-printed β-TCP scaffolds decorated with melatonin via dopamine mussel-inspired chemistry enhance the osteogenesis and in vivo bone regeneration.

Enhanced Osteogenesis of Injectable Calcium Phosphate Bone Cement Mediated by Loading Chondroitin Sulfate

Toward repairing critical-sized bone defects, calcium phosphate cement (CPC) has been well recognized as a fairly promising bone graft because of its properties of injectability, self-setting, biocompatibility, and osteoconductivity. However, poor osteogenic capacity of CPC still limits its applications for meeting the demands of bone healing. In this work, chondroitin sulfate (CS), as an important component of the extracellular matrix network, was introduced into CPC to enhance its osteogenesis ability. Incorporation of CS had no evident effect on the phase, morphology, apparent porosity, and compressive strength of hydrated cement products, but it notably enhanced the injectability and improved the antiwashout property of the cement pastes. CS was able to be sustainably released from CS-CPCs in a CS-dose-dependent manner and supposed to have a long-term release potential for constant biological stimulation. CS-CPCs markedly accelerated the preferential adsorption of fibronectin. Furthermore, CS-CPCs significantly improved the adhesion, proliferation, and osteogenic differentiation of bone mesenchymal stem cells, which was synergistically mediated by the adhesion events of cells on the hydrated cements and the stimulation effects of CS molecules. Herein, utilization of CS is supposed to endow injectable calcium phosphate bone cements with enhanced osteogenic capacity and suitable physicochemical properties for numerous promising orthopedic applications.

Effects of a Pasty Bone Cement Containing Brain-Derived Neurotrophic Factor-Functionalized Mesoporous Bioactive Glass Particles on Metaphyseal Healing in a New Murine Osteoporotic Fracture Model

The development of new and better implant materials adapted to osteoporotic bone is still urgently required. Therefore, osteoporotic muscarinic acetylcholine receptor M3 (M3 mAChR) knockout (KO) and corresponding wild type (WT) mice underwent osteotomy in the distal femoral metaphysis. Fracture gaps were filled with a pasty α-tricalcium phosphate (α-TCP)-based hydroxyapatite (HA)-forming bone cement containing mesoporous bioactive CaP-SiO₂ glass particles (cement/MBG composite) with or without Brain-Derived Neurotrophic Factor (BDNF) and healing analyzed after 35 days. Histologically, bone formation was significantly increased in WT mice that received the BDNF-functionalized cement/MBG composite compared to control WT mice without BDNF. Cement/MBG composite without BDNF increased bone formation in M3 mAChR KO mice compared to equally treated WT mice. Mass spectrometric imaging showed that the BDNF-functionalized cement/MBG composite implanted in M3 mAChR KO mice was infiltrated by newly formed tissue. Leukocyte numbers were significantly lower in M3 mAChR KO mice treated with BDNF-functionalized cement/MBG composite compared to controls without BDNF. C-reactive protein (CRP) concentrations were significantly lower in M3 mAChR KO mice that received the cement/MBG composite without BDNF when compared to WT mice treated the same. Whereas alkaline phosphatase (ALP) concentrations in callus were significantly increased in M3 mAChR KO mice, ALP activity was significantly higher in WT mice. Due to a stronger effect of BDNF in non osteoporotic mice, higher BDNF concentrations might be needed for osteoporotic fracture healing. Nevertheless, the BDNF-functionalized cement/MBG composite promoted fracture healing in non osteoporotic bone.