Silicon-stabilized α-tricalcium phosphate and its use in a calcium phosphate cement: characterization and cell response

Stereolithography of ceramic scaffolds for bone tissue regeneration: Influence of hydroxyapatite/silica ratio on mechanical properties

In this paper, the results obtained in the development of ceramic resin feedstock for stereolithography are shown. Hydroxyapatite and silica are used as source of ceramic. Hydroxyapatite is extracted from bovine bone, which enhances bioactivity of ceramic scaffold. The influence of hydroxyapatite amount in polymer-based slurry on the viscosity and printability of feedstock is explored. Hydroxyapatite and silica containing scaffolds are successfully obtained by stereolithography. Influence of hydroxyapatite/silica ratio on the bioactivity, biodegradability and mechanical properties of the scaffolds is also studied. It was observed that higher concentrations of hydroxyapatite led to improved mechanical strength of the scuffolds but increased viscosity of the slurry, affecting printability. Cell viability assays and cell visualization experiments indicated that the scaffolds not cause significant cell toxicity.

Octacalcium phosphate phase forming cements as an injectable bone substitute materials: Preparation and in vitro structural study

In the realm of regenerating damaged or degenerated bones through minimally invasive techniques, injectable materials have emerged as exceptionally promising. Among these, calcium phosphate bone cements (CPCs) have garnered significant interest due to their remarkable bioactivity, setting it apart from non-degradable alternatives such as polymethyl methacrylate cements. α-Tricalcium phosphate (α-TCP) is a widely used solid phase component in CPCs. It can transform into calcium-deficient hydroxyapatite (CDHAp) when it comes in contact with water. In this study, we aimed to create an injectable, self-setting bone cement using low-temperature synthesized α-TCP powder as a single precursor of the powder phase. We found that changes in the pH of the liquid phase (pH 6.0, pH 6.2, pH 7.0 and pH 7.4) significantly altered the cement's setting, handling, and mechanical properties. The formation of the octacalcium phosphate (OCP) phase was identified in our study, which positively affects the osteoblastic cell response. Hardened OCP-forming bone cements prepared using a liquid phase with pH 7.0 and 7.4 showed better osteogenic cell attachment and proliferation than those prepared with pH 6.0 and 6.2. Our study suggests that changes in the pH of the liquid phase can significantly affect the properties of α-TCP-based bone cement, and the presence of the OCP phase is crucial for optimal cement performance.

The influence of silane coupling agents on the properties of α-TCP-based ceramic bone substitutes for orthopaedic applications

Biomaterials based on α-TCP are highly recommended for medical applications due to their ability to bond chemically with bone tissue. However, in order to improve their physicochemical properties, modifications are needed. In this work, novel, hybrid α-TCP-based bone cements were developed and examinated. The influence of two different silane coupling agents (SCAs) - tetraethoxysilane (TEOS) and 3-glycidoxypropyl trimethoxysilane (GPTMS) on the properties of the final materials was investigated. Application of modifiers allowed us to obtain hybrid materials due to the presence of different bonds in their structure, for example between calcium phosphates and SCA molecules. The use of SCAs increased the compressive strength of the bone cements from 7.24 ± 0.35 MPa to 12.17 ± 0.48 MPa. Moreover, modification impacted the final setting time of the cements, reducing it from 11.0 to 6.5 minutes. The developed materials displayed bioactive potential in simulated body fluid. Presented findings demonstrate the beneficial influence of silane coupling agents on the properties of calcium phosphate-based bone substitutes and pave the way for their further in vitro and in vivo studies.

Influence of Ag and/or Sr Dopants on the Mechanical Properties and In Vitro Degradation of β-Tricalcium Phosphate-Based Ceramics

β-tricalcium phosphate has good biodegradability and biocompatibility; it is widely perceived as a good material for treating bone deficiency. In this research, different contents of strontium (Sr) and silver (Ag) ion-doped β-tricalcium phosphate powders were prepared using the sol-gel method. After obtaining the best ratio of pore-forming agent and binder, the as-synthesized powders were sintered in a muffle for 5 h at 1000 °C to obtain the samples. Then, these samples were degraded in vitro in simulated body fluids. The samples were tested using a series of characterization methods before and after degradation. Results showed that the amount of Sr and/or Ag doping had an effect on the crystallinity and structural parameters of the samples. After degradation, though the compressive strength of these samples decreased overall, the compressive strength of the undoped samples was higher than that of the doped samples. Notably, apatite-like materials were observed on the surface of the samples. All the results indicate that Sr and/or Ag β-TCP has good osteogenesis and proper mechanical properties; it will be applied as a prospective biomaterial in the area of bone repair.

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.

α-TCP-based Calcium Phosphate Cements: a critical review

Calcium phosphates are promising materials for applications in bone repair and substitution, particularly for their bioactivity and ability to form self-setting cements. Among them, α-tricalcium phosphate (α-TCP) stands out due to its high solubility, its hydration reaction and bioresorbability. The synthesis of α-TCP is particularly complex and the interactions between some of the synthesis parameters are still not completely understood. The variety of methods available to synthesize α-TCP has provided a substantial variance in the properties of α-TCP-based cements and the decision about which method, parameters and starting reagents will be used for the powder's synthesis is determinant of the properties of the resulting material. Therefore, this review paper focuses on α-TCP's synthesis and properties, presenting the synthesis methods currently in use as well as a discussion of how the synthesis parameters and the cement preparation affect the reactivity and mechanical properties of the material, providing a guide for the selection of the most suitable process for each α-TCP application. STATEMENT OF SIGNIFICANCE: α-TCP is a calcium phosphate and it is currently one of the most investigated bioceramics for applications that explore its bioresorbability and the hydration reaction of α-TCP-based cements. Despite the increasing number of publications on the topic, there are still aspects not well understood. This review article aims at contributing to this fascinating subject by offering an update on the state of the art of α-TCP's synthesis methods, while also addressing topics that are not often discussed about this material, such as the preparation of α-TCP-based cements and how its parameters affect the properties of the resulting cements.

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.

Cytocompatibility and Bioactive Ion Release Profiles of Phosphoserine Bone Adhesive: Bridge from In Vitro to In Vivo

One major challenge when developing new biomaterials is translating in vitro testing to in vivo models. We have recently shown that a single formulation of a bone tissue adhesive, phosphoserine modified cement (PMC), is safe and resorbable in vivo. Herein, we screened many new adhesive formulations, for cytocompatibility and bioactive ion release, with three cell lines: MDPC23 odontoblasts, MC3T3 preosteoblasts, and L929 fibroblasts. Most formulations were cytocompatible by indirect contact testing (ISO 10993-12). Formulations with larger amounts of phosphoserine (>50%) had delayed setting times, greater ion release, and cytotoxicity in vitro. The trends in ion release from the adhesive that were cured for 24 h (standard for in vitro) were similar to release from the adhesives cured only for 5−10 min (standard for in vivo), suggesting that we may be able to predict the material behavior in vivo, using in vitro methods. Adhesives containing calcium phosphate and silicate were both cytocompatible for seven days in direct contact with cell monolayers, and ion release increased the alkaline phosphatase (ALP) activity in odontoblasts, but not pre-osteoblasts. This is the first study evaluating how PMC formulation affects osteogenic cell differentiation (ALP), cytocompatibility, and ion release, using in situ curing conditions similar to conditions in vivo.

Influence of Biomimetically Mineralized Collagen Scaffolds on Bone Cell Proliferation and Immune Activation

Collagen, as the main component of connective tissue, is frequently used in various tissue engineering applications. In this study, porous sponge-like collagen scaffolds were prepared by freeze-drying and were then mineralized in a simulated body fluid. The mechanical stability was similar in both types of scaffolds, but the mineralized scaffolds (MCS) contained significantly more calcium, magnesium and phosphorus than the unmineralized scaffolds (UCS). Although the MCS contained a lower percentage (~32.5%) of pores suitable for cell ingrowth (113–357 μm in diameter) than the UCS (~70%), the number of human-osteoblast-like MG-63 cells on days 1, 3 and 7 after seeding was higher on MCS than on UCS, and the cells penetrated deeper into the MCS. The cell growth in extracts prepared by eluting the scaffolds for 7 days in a cell culture medium was also markedly higher in the MCS extracts, as indicated by real-time monitoring in the sensory xCELLigence system for 7 days. From this point of view, MCS are more promising for bone tissue engineering than UCS. However, MCS evoked a more pronounced inflammatory response than UCS, as indicated by the production of tumor necrosis factor-alpha (TNF-α) in macrophage-like RAW 264.7 cells in cultures on these scaffolds.

Bioactive Calcium Phosphate-Based Composites for Bone Regeneration

Calcium phosphates (CaPs) are widely accepted biomaterials able to promote the regeneration of bone tissue. However, the regeneration of critical-sized bone defects has been considered challenging, and the development of bioceramics exhibiting enhanced bioactivity, bioresorbability and mechanical performance is highly demanded. In this respect, the tuning of their chemical composition, crystal size and morphology have been the matter of intense research in the last decades, including the preparation of composites. The development of effective bioceramic composite scaffolds relies on effective manufacturing techniques able to control the final multi-scale porosity of the devices, relevant to ensure osteointegration and bio-competent mechanical performance. In this context, the present work provides an overview about the reported strategies to develop and optimize bioceramics, while also highlighting future perspectives in the development of bioactive ceramic composites for bone tissue regeneration.

Silicate/zinc-substituted strontium apatite coating improves the osteoinductive properties of β-tricalcium phosphate bone graft substitute

Background

β-Tricalcium phosphate (β-TCP) is a popular synthetic bone graft substitute with excellent osteoconductive properties and bioabsorbability. However, its osteoinductive properties are inferior to those of autologous or allogeneic bone. Trace elements such as strontium (Sr), silica (Si), and zinc (Zn) have been reported to promote osteogenesis in materials. In this study, we aimed to determine whether a Si/Zn-substituted Sr apatite coating of β-TCP could enhance osteoinductive properties.

Methods

The apatite-coated β-TCP disks were prepared using nanoparticle suspensions of silicate-substituted Sr apatite (SrSiP) or silicate- and Zn-co-substituted Sr apatite (SrZnSiP).

Bone marrow mesenchymal cells (BMSCs) from rat femur were cultured and subsequently seeded at a density of 1.0 × 10⁶/cm² onto apatite-coated and non-coated β-TCP disks.

In vitro, the β-TCP disks were then placed in osteogenic medium, and lactate dehydrogenase (LDH) activity was measured from supernatants after culture for 2 days. Additionally, after culture for 14 days, the mRNA expression of genes encoding osteocalcin (OC), alkaline phosphatase (ALP), bone morphogenetic protein-2 (BMP-2), and vascular endothelial growth factor (VEGF) was evaluated by qRT-PCR. In vivo, the β-TCP disks were transplanted subcutaneously into rats that were sacrificed after 4 weeks. Then, the harvested disks were evaluated biochemically (ALP activity, OC content, mRNA expression of OC, ALP, BMP-2, and VEGF measured by qRT-PCR), radiologically, and histologically.

Results

Significantly higher mRNA expression of almost all evaluated osteogenic and angiogenic genes was observed in the SrZnSiP and SrSiP groups than in the non-coated group, with no significant cytotoxicity elicited by the apatite coating in vitro. Moreover, in vivo, the SrZnSiP and SrSiP groups showed significantly higher osteogenic and angiogenic gene expression and higher ALP activity and OC content than the non-coated group (P < 0.05). Radiological and histopathological findings revealed abundant bone formation in the apatite-coated group.

Conclusions

Our findings indicate that apatite coating of β-TCP improves osteoinductive properties without inducing significant cytotoxicity.

Nature-Inspired Unconventional Approaches to Develop 3D Bioceramic Scaffolds with Enhanced Regenerative Ability

Material science is a relevant discipline in support of regenerative medicine. Indeed, tissue regeneration requires the use of scaffolds able to guide and sustain the natural cell metabolism towards tissue regrowth. This need is particularly important in musculoskeletal regeneration, such as in the case of diseased bone or osteocartilaginous regions for which calcium phosphate-based scaffolds are considered as the golden solution. However, various technological barriers related to conventional ceramic processing have thus far hampered the achievement of biomimetic and bioactive scaffolds as effective solutions for still unmet clinical needs in orthopaedics. Driven by such highly impacting socioeconomic needs, new nature-inspired approaches promise to make a technological leap forward in the development of advanced biomaterials. The present review illustrates ion-doped apatites as biomimetic materials whose bioactivity resides in their unstable chemical composition and nanocrystallinity, both of which are, however, destroyed by the classical sintering treatment. In the following, recent nature-inspired methods preventing the use of high-temperature treatments, based on (i) chemically hardening bioceramics, (ii) biomineralisation process, and (iii) biomorphic transformations, are illustrated. These methods can generate products with advanced biofunctional properties, particularly biomorphic transformations represent an emerging approach that could pave the way to a technological leap forward in medicine and also in various other application fields.

Effect of Gold Nanoparticles and Silicon on the Bioactivity and Antibacterial Properties of Hydroxyapatite/Chitosan/Tricalcium Phosphate-Based Biomicroconcretes

Bioactive, chemically bonded bone substitutes with antibacterial properties are highly recommended for medical applications. In this study, biomicroconcretes, composed of silicon modified (Si-αTCP) or non-modified α-tricalcium phosphate (αTCP), as well as hybrid hydroxyapatite/chitosan granules non-modified and modified with gold nanoparticles (AuNPs), were designed. The developed biomicroconcretes were supposed to combine the dual functions of antibacterial activity and bone defect repair. The chemical and phase composition, microstructure, setting times, mechanical strength, and in vitro bioactive potential of the composites were examined. Furthermore, on the basis of the American Association of Textile Chemists and Colorists test (AATCC 100), adapted for chemically bonded materials, the antibacterial activity of the biomicroconcretes against S. epidermidis, E. coli, and S. aureus was evaluated. All biomicroconcretes were surgically handy and revealed good adhesion between the hybrid granules and calcium phosphate-based matrix. Furthermore, they possessed acceptable setting times and mechanical properties. It has been stated that materials containing AuNPs set faster and possess a slightly higher compressive strength (3.4 ± 0.7 MPa). The modification of αTCP with silicon led to a favorable decrease of the final setting time to 10 min. Furthermore, it has been shown that materials modified with AuNPs and silicon possessed an enhanced bioactivity. The antibacterial properties of all of the developed biomicroconcretes against the tested bacterial strains due to the presence of both chitosan and Au were confirmed. The material modified simultaneously with AuNPs and silicon seems to be the most promising candidate for further biological studies.

Tissue Engineering in Musculoskeletal Tissue: A Review of the Literature

Tissue engineering refers to the attempt to create functional human tissue from cells in a laboratory. This is a field that uses living cells, biocompatible materials, suitable biochemical and physical factors, and their combinations to create tissue-like structures. To date, no tissue engineered skeletal muscle implants have been developed for clinical use, but they may represent a valid alternative for the treatment of volumetric muscle loss in the near future. Herein, we reviewed the literature and showed different techniques to produce synthetic tissues with the same architectural, structural and functional properties as native tissues.

A Critical Review on the Synthesis of Natural Sodium Alginate Based Composite Materials: An Innovative Biological Polymer for Biomedical Delivery Applications

Sodium alginate (Na-Alg) is water-soluble, neutral, and linear polysaccharide. It is the derivative of alginic acid which comprises 1,4-β-d-mannuronic (M) and α-l-guluronic (G) acids and has the chemical formula (NaC6H7O6). It shows water-soluble, non-toxic, biocompatible, biodegradable, and non-immunogenic properties. It had been used for various biomedical applications, among which the most promising are drug delivery, gene delivery, wound dressing, and wound healing. For different biomedical applications, it is used in different forms with the help of new techniques. That is the reason it had been blended with different polymers. In this review article, we present a comprehensive overview of the combinations of sodium alginate with natural and synthetic polymers and their biomedical applications involving delivery systems. All the scientific/technical issues have been addressed, and we have highlighted the recent advancements.

Effects of Synthesis Conditions on the Formation of Si-Substituted Alpha Tricalcium Phosphates

Powders of α-TCP containing various amounts of silicon were synthesized by two different methods: Wet chemical precipitation and solid-state synthesis. The obtained powders were then physico–chemically studied using different methods: Scanning and transmission electron microscopy (TEM and SEM), energy-dispersive X-ray spectroscopy (EDS), powder X-ray diffractometry (PXRD), infrared and Raman spectroscopies (FT-IR and R), and solid-state nuclear magnetic resonance (ssNMR). The study showed that the method of synthesis affects the morphology of the obtained particles, the homogeneity of crystalline phase and the efficiency of Si substitution. Solid-state synthesis leads to particles with a low tendency to agglomerate compared to the precipitation method. However, the powders obtained by the solid-state method are less homogeneous and contain a significant amount of other crystalline phase, silicocarnotite (up to 7.33%). Moreover, the microcrystals from this method are more disordered. This might be caused by more efficient substitution of silicate ions: The silicon content of the samples obtained by the solid-state method is almost equal to the nominal values.

Development of injectable chitosan/biphasic calcium phosphate bone cement and in vitro and in vivo evaluation

Injectable biphasic calcium phosphate bone cements (BCPCs) composed of β-tricalcium phosphate (β-TCP) and hydroxyapatite (HA) have been intensively investigated because of their high rate of biodegradation, bioactivity and osteoconductivity, which can be adjusted by changing the ratio between β-TCP and HA phases after setting. The aim of this study was to evaluate the performance of 1 wt% chitosan fiber additive with biphasic calcium phosphate as an injectable bone cement both in vitro and in vivo. In vitro evaluation of compressive strength, degradation rate, morphology, and cell and alkaline phosphatase activities was done by comparison with bone cement without β-TCP. The in vivo results for micro-CT scanning and histological examinations for three groups (control, BCPC and commercial biphasic calcium phosphate granules) were characterized and compared. After the addition of 20 wt% β-TCP to calcium phosphate cement, the initial and final setting times of the sample were 3.92 min and 11.46 min, respectively, which were not significantly different from cement without β-TCP. The degradation time of the BCPC material was longer than that of calcium phosphate cement alone. The healing process was significantly faster for BCPC than for the control and commercial product groups. Therefore, this is the first evidence that BCPC is an attractive option for bone surgery due to its faster stimulation of healing and faster degradation rate.

Hydroxyethyl Chitosan-Reinforced Polyvinyl Alcohol/Biphasic Calcium Phosphate Hydrogels for Bone Regeneration

Fabrication of reinforced scaffolds for bone regeneration remains a significant challenge. The weak mechanical properties of the chitosan (CS)-based composite scaffold hindered its further application in clinic. Here, to obtain hydroxyethyl CS (HECS), some hydrogen bonds of CS were replaced by hydroxyethyl groups. Then, HECS-reinforced polyvinyl alcohol (PVA)/biphasic calcium phosphate (BCP) nanoparticle hydrogel was fabricated via cycled freeze-thawing followed by an in vitro biomineralization treatment using a cell culture medium. The synthesized hydrogel had an interconnected porous structure with a uniform pore distribution. Compared to the CS/PVA/BCP hydrogel, the HECS/PVA/BCP hydrogels showed a thicker pore wall and had a compressive strength of up to 5-7 MPa. The biomineralized hydrogel possessed a better compressive strength and cytocompatibility compared to the untreated hydrogel, confirmed by CCK-8 analysis and fluorescence images. The modification of CS with hydroxyethyl groups and in vitro biomineralization were sufficient to improve the mechanical properties of the scaffold, and the HECS-reinforced PVA/BCP hydrogel was promising for bone tissue engineering applications.

Injectable Biomaterials for Dental Tissue Regeneration

Injectable biomaterials scaffolds play a pivotal role for dental tissue regeneration, as such materials are highly applicable in the dental field, particularly when compared to pre-formed scaffolds. The defects in the maxilla-oral area are normally small, confined and sometimes hard to access. This narrative review describes different types of biomaterials for dental tissue regeneration, and also discusses the potential use of nanofibers for dental tissues. Various studies suggest that tissue engineering approaches involving the use of injectable biomaterials have the potential of restoring not only dental tissue function but also their biological purposes.

Improving osteogenesis of calcium phosphate bone cement by incorporating with manganese doped β-tricalcium phosphate

Lack of osteogenic capacity limits the bone repair effect of calcium phosphate cement (CPC). In present work, bivalent manganese ion (Mn²⁺) doped β-tricalcium phosphate (Mn-TCP) was incorporated into CPC to enhance its osteogenic ability. The incorporation of Mn-TCP promoted the hydration reaction of CPC. The presence of Mn²⁺ made the hydration products finer. When adding 10 wt% Mn-TCP in CPC (Mn-CPC-1), the setting time of CPC was shortened, whereas the strength and injectability were not changed. Mouse Bone marrow mesenchymal stem cells (mBMSCs) on Mn-CPC-1 and CPC with 20 wt% Mn-TCP (Mn-CPC-2) presented better adhesion and spreading behaviors. Besides, Mn-CPC-1 promoted the gene levels of ALP, Col-I and OC while Mn-CPC-2 promoted the gene levels of Runx2 and OC. Cellular behaviors were related to two points: one was the increase of adsorption capacity of proteins (e.g. BSA) after changing the surface properties of bone cements; and the other was the biological role of Mn²⁺ released from CPC in osteogenesis. All the results indicated that CPC incorporated with 10 wt% Mn-TCP has good osteogenesis and proper physicochemical properties, which will be a prospective biomaterial applying in the area of bone regeneration.

Biphasic Injectable Bone Cement with Fe3O4/GO Nanocomposites for the Minimally Invasive Treatment of Tumor-Induced Bone Destruction

Minimally invasive surgery will be gradually applied to the surgical treatment of bone tumors. One of the difficulties in the minimally invasive treatment of bone tumors is the lack of injectable materials that can be used to treat tumor-induced bone defects. Therefore, it is imperative to develop an injectable bone filler that can not only be injected into the defect site by minimally invasive methods to provide strong support and repair bone tissue but also inactivate residual tumor cells around the defect. To achieve this aim, in our study, for the first time, we doped Fe₃O₄/graphene oxide (GO) nanocomposites into α-tricalcium phosphate (α-TCP)/calcium sulfate (CS) biphasic bone cement to prepare an injectable magnetic bone cement (α-TCP/CS/Fe₃O₄/GO, αCFG), which can be applied in bone tumor minimally invasive surgery and fit ideally even if the area is irregular. The magnetothermal performance of the αCFG bone cement could be well adjusted by altering the content of Fe₃O₄/GO nanocomposites and the magnetic field parameters, but a 10 wt % Fe₃O₄/GO content formed the most stable bone cement with excellent magnetothermal performance. The αCFG bone cement not only promotes bone regeneration but also exhibits enhanced tumor treatment effects. Such multifunctional bone cement could provide a promising clinical strategy for the minimally invasive treatment of tumor-induced bone destruction.

Scaffolding Strategies for Tissue Engineering and Regenerative Medicine Applications

During the past two decades, tissue engineering and the regenerative medicine field have invested in the regeneration and reconstruction of pathologically altered tissues, such as cartilage, bone, skin, heart valves, nerves and tendons, and many others. The 3D structured scaffolds and hydrogels alone or combined with bioactive molecules or genes and cells are able to guide the development of functional engineered tissues, and provide mechanical support during in vivo implantation. Naturally derived and synthetic polymers, bioresorbable inorganic materials, and respective hybrids, and decellularized tissue have been considered as scaffolding biomaterials, owing to their boosted structural, mechanical, and biological properties. A diversity of biomaterials, current treatment strategies, and emergent technologies used for 3D scaffolds and hydrogel processing, and the tissue-specific considerations for scaffolding for Tissue engineering (TE) purposes are herein highlighted and discussed in depth. The newest procedures focusing on the 3D behavior and multi-cellular interactions of native tissues for further use for in vitro model processing are also outlined. Completed and ongoing preclinical research trials for TE applications using scaffolds and hydrogels, challenges, and future prospects of research in the regenerative medicine field are also presented.

Review of bone graft and bone substitutes with an emphasis on fracture surgeries

Background

Autogenous bone graft is the gold standard bone graft material. However, due to limitations of supply and morbidity associated with autograft harvest, various bone substitutes have been considered. This article aims to review the properties of the bone graft and various bone substitutes currently available in orthopedic surgery.

Main body

Synthetic bone substitutes consist of hydroxyapatite, tricalcium phosphate, calcium sulfate, or a combination of these minerals. Synthetic porous substitutes share several advantages over allografts, including unlimited supply, easy sterilization, and storage. However, they also have some disadvantages, such as brittle properties, variable rates of resorption, and poor performance in some clinical conditions. Recently, attention has been drawn to osteoinductive materials, such as demineralized bone matrix and bone morphogenetic proteins.

Conclusion

Despite tremendous efforts toward developing autograft alternatives, a single ideal bone graft substitute has not been developed. The surgeon should understand the properties of each bone graft substitute to facilitate appropriate selection in each specific clinical situation.

Effects of MgO, ZnO, SrO, and SiO2 in tricalcium phosphate scaffolds on in vitro gene expression and in vivo osteogenesis

β‑tricalcium phosphate (β‑TCP) is a versatile bioceramic for its use in many orthopedic and dental applications due to its excellent biocompatibility and biodegradability. Recently, the addition of additives to β‑TCP has been proven to improve bone repair and regeneration, however, the underlying mechanism of enhanced bone regeneration is still unknown. In this study, strontium oxide (SrO), silica (SiO2), magnesia (MgO), and zinc oxide (ZnO) were added to β‑TCP for dense discs fabrication followed by in vitro evaluation using a preosteoblast cell line. Cell viability and gene expression were analyzed at day 3 and day 9 during the cell culture. MgO and SiO2 were found to significantly enhance and expedite osteoblastic differentiation. A potential mechanism was introduced to explain the additive induced osteoblastic differentiation. In addition, in vivo characterizations showed that porous 3D printed MgO-SiO2-TCP scaffolds significantly improved new bone formation after 16 weeks of implantation. This study shows beneficial effects of additives on osteoblastic viability and differentiation in vitro as well as osteogenesis in vivo, which is crucial towards the development of bone tissue engineering scaffolds.

Optimized Bone Regeneration in Calvarial Bone Defect Based on Biodegradation-Tailoring Dual-shell Biphasic Bioactive Ceramic Microspheres

Bioceramic particulates capable of filling bone defects have gained considerable interest over the last decade. Herein, dual-shell bioceramic microspheres (CaP@CaSi@CaP, CaSi@CaP@CaSi) with adjustable beta-tricalcium phosphate (CaP) and beta-calcium silicate (CaSi) distribution were fabricated using a co-concentric capillary system enabling bone repair via a tailorable biodegradation process. The in vitro results showed the optimal concentration (1/16 of 200 mg/ml) of extracts of dual-shell microspheres could promote bone marrow mesenchymal cell (BMSC) proliferation and enhance the level of ALP activity and Alizarin Red staining. The in vivo bone repair and microsphere biodegradation in calvarial bone defects were compared using micro-computed tomography and histological evaluations. The results indicated the pure CaP microspheres were minimally resorbed at 18 weeks post-operatively and new bone tissue was limited; however, the dual-shell microspheres were appreciably biodegraded with time in accordance with the priority from CaSi to CaP in specific layers. The CaSi@CaP@CaSi group showed a significantly higher ability to promote bone regeneration than the CaP@CaSi@CaP group. This study indicates that the biphasic microspheres with adjustable composition distribution are promising for tailoring material degradation and bone regeneration rate, and such versatile design strategy is thought to fabricate various advanced biomaterials with tailorable biological performances for bone reconstruction.

Calcium Phosphates as Delivery Systems for Bisphosphonates

Bisphosphonates (BPs) are the most utilized drugs for the treatment of osteoporosis, and are usefully employed also for other pathologies characterized by abnormally high bone resorption, including bone metastases. Due to the great affinity of these drugs for calcium ions, calcium phosphates are ideal delivery systems for local administration of BPs to bone, which is aimed to avoid/limit the undesirable side effects of their prolonged systemic use. Direct synthesis in aqueous medium and chemisorptions from solution are the two main routes proposed to synthesize BP functionalized calcium phosphates. The present review overviews the information acquired through the studies on the interaction between bisphosphonate molecules and calcium phosphates. Moreover, particular attention is addressed to some important recent achievements on the applications of BP functionalized calcium phosphates as biomaterials for bone substitution/repair.

Calcium phosphate cements for bone engineering and their biological properties

Calcium phosphate cements (CPCs) are frequently used to repair bone defects. Since their discovery in the 1980s, extensive research has been conducted to improve their properties, and emerging evidence supports their increased application in bone tissue engineering. Much effort has been made to enhance the biological performance of CPCs, including their biocompatibility, osteoconductivity, osteoinductivity, biodegradability, bioactivity, and interactions with cells. This review article focuses on the major recent developments in CPCs, including 3D printing, injectability, stem cell delivery, growth factor and drug delivery, and pre-vascularization of CPC scaffolds via co-culture and tri-culture techniques to enhance angiogenesis and osteogenesis.

Addition of Wollastonite Fibers to Calcium Phosphate Cement Increases Cell Viability and Stimulates Differentiation of Osteoblast-Like Cells

Calcium phosphate cement (CPC) that is based on α-tricalcium phosphate (α-TCP) is considered desirable for bone tissue engineering because of its relatively rapid degradation properties. However, such cement is relatively weak, restricting its use to areas of low mechanical stress. Wollastonite fibers (WF) have been used to improve the mechanical strength of biomaterials. However, the biological properties of WF remain poorly understood. Here, we tested the response of osteoblast-like cells to being cultured on CPC reinforced with 5% of WF (CPC-WF). We found that both types of cement studied achieved an ion balance for calcium and phosphate after 3 days of immersion in culture medium and this allowed subsequent long-term cell culture. CPC-WF increased cell viability and stimulated cell differentiation, compared to nonreinforced CPC. We hypothesize that late silicon release by CPC-WF induces increased cell proliferation and differentiation. Based on our findings, we propose that CPC-WF is a promising material for bone tissue engineering applications.

Influence of Si substitution on the reactivity of α-tricalcium phosphate

Silicon substituted calcium phosphates have been widely studied over the last ten years due to their enhanced osteogenic properties. Notwithstanding, the role of silicon on α-TCP reactivity is not clear yet. Therefore, the aim of this work was to evaluate the reactivity and the properties of Si-α-TCP in comparison to α-TCP. Precursor powders have similar properties regarding purity, particle size distribution and specific surface area, which allowed a better comparison of the Si effects on their reactivity and cements properties. Both Si-α-TCP and α-TCP hydrolyzed to a calcium-deficient hydroxyapatite when mixed with water but their conversion rates were different. Si-α-TCP exhibited a slower setting rate than α-TCP, i.e. k_SSA for Si-TCP (0.021g·m^-2·h^-1) was almost four times lower than for α-TCP (0.072g·m^-2·h^-1). On the other hand, the compressive strength of the CPC resulting from fully reacted Si-α-TCP was significantly higher (12.80±0.38MPa) than that of α-TCP (11.44±0.54MPa), due to the smaller size of the entangled precipitated apatite crystals.

Fabrication of naturel pumice/hydroxyapatite composite for biomedical engineering

BACKGROUND

We evaluated the Bovine hydroxyapatite (BHA) structure. BHA powder was admixed with 5 and 10 wt% natural pumice (NP). Compression strength, Vickers micro hardness, Fourier transform infrared spectroscopy, scanning electron microscopy (SEM) and X-ray diffraction studies were performed on the final NP-BHA composite products. The cells proliferation was investigated by MTT assay and SEM. Furthermore, the antimicrobial activity of NP-BHA samples was interrogated.

RESULTS

Variances in the sintering temperature (for 5 wt% NP composites) between 1000 and 1300 °C, reveal about 700 % increase in the microhardness (~100 and 775 HV, respectively). Composites prepared at 1300 °C demonstrate the greatest compression strength with comparable result for 5 wt% NP content (87 MPa), which are significantly better than those for 10 wt% and those that do not include any NP (below 60 MPa, respectively).

CONCLUSION

The results suggested the optimal parameters for the preparation of NP-BHA composites with increased mechanical properties and biocompatibility. Changes in micro-hardness and compression strength can be tailored by the tuning the NP concentration and sintering temperature. NP-BHA composites have demonstrated a remarkable potential for biomedical engineering applications such as bone graft and implant.

Regulating the antibiotic drug release from β-tricalcium phosphate ceramics by atmospheric plasma surface engineering

Atmospheric plasma jet is a new promising tool that leads to the design of controlled drug release from bioceramic matrices.

Multiple characterization study on porosity and pore structure of calcium phosphate cements

Characterization of the intricate pore structure of calcium phosphate cements is a key step to successfully link the structural properties of these synthetic bone grafts with their most relevant properties, such as in vitro or in vivo behaviour, drug loading and release properties, or degradation over time. This is a challenging task due to the wide range of pore sizes in calcium phosphate cements, compared to most other ceramic biomaterials. This work provides a critical assessment of three different techniques based on different physical phenomena, namely mercury intrusion porosimetry (MIP), Nitrogen sorption, and thermoporometry (TPM) for the detailed characterization of four calcium phosphate cements with different textural properties in terms of total porosity, pore size distribution (PSD), and pore entrance size distribution (PESD). MIP covers a much wider size range than TPM and Nitrogen sorption, offering more comprehensive information at the micrometer level. TPM, and especially Nitrogen sorption, are non-destructive techniques and, although they cover a limited size range, provide complementary information regarding pore structure associated with crystal shape at the nanoscale, recording both PSD and PESD in a single experiment. MIP tended to register smaller sizes, especially at low L/P ratios, due to the network effect, which has a strong influence on the outcome of this technique.

STATEMENT OF SIGNIFICANCE

The detailed characterisation of the porosity of calcium phosphate cements is of paramount importance, since it is a key parameter influencing some of the most relevant features, like mechanical properties, degradation rate or drug loading and release kinetics. However, this is a challenging task because, once hardened, calcium phosphate cements present an intricate morphology, consisting of a network of precipitated crystals, which generate a high intrinsic micro/nano porosity, with pore sizes covering six orders of magnitude. This work provides for the first time a critical assessment of the advantages and limitations of three different techniques, namely mercury intrusion porosimetry, Nitrogen sorption and Thermoporometry, for the characterisation of the porosity of four calcium phosphate cements with different textural properties.

Inflammatory response to nano- and microstructured hydroxyapatite

The proliferation and activation of leukocytes upon contact with a biomaterial play a crucial role in the degree of inflammatory response, which may then determine the clinical failure or success of an implanted biomaterial. The aim of this study was to evaluate whether nano- and microstructured biomimetic hydroxyapatite substrates can influence the growth and activation of macrophage-like cells. Hydroxyapatite substrates with different crystal morphologies consisting of an entangled network of plate-like and needle-like crystals were evaluated. Macrophage proliferation was evaluated on the material surface (direct contact) and also in extracts i.e. media modified by the material (indirect contact). Additionally, the effect of supplementing the extracts with calcium ions and/or proteins was investigated. Macrophage activation on the substrates was evaluated by quantifying the release of reactive oxygen species and by morphological observations. The results showed that differences in the substrate's microstructure play a major role in the activation of macrophages as there was a higher release of reactive oxygen species after culturing the macrophages on plate-like crystals substrates compared to the almost non-existent release on needle-like substrates. However, the difference in macrophage proliferation was ascribed to different ionic exchanges and protein adsorption/retention from the substrates rather than to the texture of materials.

Novel bioactive nanocomposite cement formulations with potential properties: incorporation of the nanoparticle form of mesoporous bioactive glass into calcium phosphate cements

Novel calcium phosphate cements incorporated with bioactive glass nanoparticles demonstrate excellent properties for bone injectables.

Development of porous and antimicrobial CTS–PEG–HAP–ZnO nano-composites for bone tissue engineering

We have developed porous, antimicrobial, biodegradable, and pH and blood compatible CTS–PEG–HAP–ZnO nanocomposites having good mechanical properties and osteoblast cell proliferation abilities to mimic cancellous bone in bone tissue engineering.

Strontium modified calcium phosphate cements – approaches towards targeted stimulation of bone turnover

Strontium modified calcium phosphate cements can target local bone turnover by stimulating osteoblast proliferation and differentiation (1) as well as bone mineralisation (2), reducing osteoclastogenesis (3) and resorption activity, increase osteoclast apoptosis (4) and affect osteoblast/osteoclast paracrine signalling (5).

The pH-Dependent Properties of the Biphasic Calcium Phosphate for Bone Cements

Self-setting calcium phosphate cement (CPC) has been used in bone repair and substitution due to their excellent biocompatibility, bioactive as well as simplicity of preparation and use. The inherent brittleness and slow degradation are the major disadvantages for the use of calcium phosphate cements. To improve the degradation for the traditional CPC, the apatite cement formula incorporated with β-tricalcium phosphate (β-TCP) with varying concentration were studied and the effect of the pH value of liquid phase on the properties of this new calcium phosphate cement formula was evaluated. The apatite cements containing β-TCP for 10 and 40 wt.% were mixed into the aqueous solution with different pH values and then aging in absolute humidity at 37°C for 7 days. The setting time and phase analysis of the biphasic calcium phosphate were determined as compared to the apatite cement. For proper medical application, the compressive strength, the phase analysis and the degradation of the CPC samples at pH 7.0 and 7.4 were evaluated after soaking in the simulated body fluid (SBF) at 37°C for 7 days. The results indicated that the properties of the samples such as the setting time, the compressive strength related to the phase analysis of the set cements. The high degradation of the CPC was found in the cement with increasing β-TCP addition due to the phase after setting. Apatite formation with oriented plate-like morphology was also found to be denser on the surface of the biphasic bone cements after soaking in SBF for 7 days. The obtained results indicated that the cement containing β-TCP mixed with the liquid phase at pH 7.4 could be considered as a highly biodegradable and bioactive bone cement, as compared to the traditional CPC.

Osteogenesis and angiogenesis properties of dental pulp cell on novel injectable tricalcium phosphate cement by silica doped

β-Tricalcium phosphate (β-TCP) is an osteoconductive material in clinical. In this study, we have doped silica (Si) into β-TCP and enhanced its bioactive and osteostimulative properties. To check its effectiveness, a series of Si-doped with different ratios were prepared to make new bioactive and biodegradable biocomposites for bone repair. Formation of the diametral tensile strength, ions released and weight loss of cements was considered after immersion. In addition, we also examined the behavior of human dental pulp cells (hDPCs) cultured on Si-doped β-TCP cements. The results showed that setting time and injectability of the Si-doped β-TCP cements were decreased as the Si content was increased. At the end of the immersion point, weight losses of 30.1%, 36.9%, 48.1%, and 55.3% were observed for the cement doping 0%, 10%, 20%, and 30% Si into β-TCP cements, respectively. In vitro cell experiments show that the Si-rich cements promote human dental pulp cell (hDPC) proliferation and differentiation. However, when the Si-doped in the cement is more than 20%, the amount of cells and osteogenesis protein of hDPCs was stimulated by Si released from Si-doped β-TCP cements. The degradation of β-TCP and osteogenesis of Si gives a strong reason to believe that these Si-doped β-TCP cements may prove to be promising bone repair materials.

Furthering the understanding of silicate-substitution in α-tricalcium phosphate: an X-ray diffraction, X-ray fluorescence and solid-state nuclear magnetic resonance study

High-purity (SupT) and reagent-grade (ST), stoichiometric and silicate-containing α-tricalcium phosphate (α-TCP: ST0/SupT0 and Si-TCP x=0.10: ST10/SupT10) were prepared by solid-state reaction based on the substitution mechanism Ca3(PO4)(2-x)(SiO4)x. Samples were determined to be phase pure by X-ray diffraction (XRD), and Rietveld analysis performed on the XRD data confirmed inclusion of Si in the α-TCP structure as determined by increases in unit cell parameters; particularly marked increases in the b-axis and β-angle were observed. X-ray fluorescence (XRF) confirmed the presence of expected levels of Si in Si-TCP compositions as well as significant levels of impurities (Mg, Al and Fe) present in all ST samples; SupT samples showed both expected levels of Si and a high degree of purity. Phosphorus ((31)P) magic-angle-spinning solid-state nuclear magnetic resonance (MAS NMR) measurements revealed that the high-purity reagents used in the synthesis of SupT0 can resolve the 12 expected peaks in the (31)P spectrum of α-TCP compared to the low-purity ST0 that showed significant spectral line broadening; line broadening was also observed with the inclusion of Si which is indicative of induced structural disorder. Silicon ((29)Si) MAS NMR was also performed on both Si-TCP samples which revealed Q(0) species of Si with additional Si Q(1)/Q(2) species that may indicate a potential charge-balancing mechanism involving the inclusion of disilicate groups; additional Q(4) Si species were also observed, but only for ST10. Heating and cooling rates were briefly investigated by (31)P MAS NMR which showed no significant line broadening other than that associated with the emergence of β-TCP which was only realised with the reagent-grade sample ST0. This study provides an insight into the structural effects of Si-substitution in α-TCP and could provide a basis for understanding how substitution affects the physicochemical properties of the material.