Synthesis and characterization of nanostructured CaSiO3 biomaterial

Here we report a successful preparation of nanostructured calcium silicate by wet chemical approach. The synthesized sample was characterized by various physico-chemical methods. Thermal stability was investigated using thermo-gravimetric and differential thermal analysis (TG-DTA). Structural characterization of the sample was carried out by the X-ray diffraction technique (XRD) which confirmed its single phase hexagonal structure. Transmission electron microscopy (TEM) was used to study the nanostructure of the ceramics while homogeneous grain distribution was revealed by scanning electron microscopy studies (SEM). The elemental analysis data obtained from energy dispersive X-ray spectroscopy (EDAX) were in close agreement with the starting composition used for the synthesis. Superhydrophilic nature of CaSiO₃ was investigated at room temperature by sessile drop technique. Effect of porous nanosized CaSiO₃ on early adhesion and proliferation of human bone marrow mesenchymal stem cells (BMMSCs) and cord blood mesenchymal stem (CBMSCs) cells was measured in vitro. MTT cytotoxicity test and cell adhesion test showed that the material had good biocompatibility and promoted cell viability and cell proliferation. It has been stated that the cell viability and proliferation are significantly affected by time and concentration of CaSiO₃. These findings indicate that the CaSiO₃ ceramics has good biocompatibility and that it is promising as a biomaterial.     

Black Bioceramics: Combining Regeneration with Therapy

Bioceramics have been developed from bioinert to bioactive or biodegradable materials in the past few decades. However, at present, traditional bioceramics are still mainly used in bone tissue regeneration and dental restoration. In this work, a new generation of “black bioceramics,” extending the applications from tissue regeneration to disease therapy, is presented. Black bioceramics, through magnesium thermal reduction of traditional white ceramics, including silicate-based (e.g., CaSiO₃, MgSiO₃) and phosphate-based (e.g., Ca₃(PO₄)₂, Ca₅(PO₄)₃(OH)), are successfully synthesized. Due to the presence of oxygen vacancies and structural defects, the black bioceramics possess photothermal functionality while maintaining their initial high bioactivity and regenerative capacity. These black bioceramics show excellent photothermal antitumor effects for both skin and bone tumors. At the same time, they have significantly improved bioactivity for skin/bone tissue repair in vitro and in vivo. These fascinating properties award the black bioceramics with profound applications in both tumor therapy and tissue regeneration, which should greatly promote the scientific relevance and clinical application of bioceramics, representing a promising new direction of cell-instructive biomaterials.     

Recent advances in silicate-based crystalline bioceramics for orthopedic applications: a review

The present article critically reviewed the potentiality of Mg–Ca silicate-based crystalline bioceramics such as MgSiO₃, Mg₂SiO₄, CaSiO₃, Ca₂SiO₄, Ca₃SiO₅, CaMgSi₂O_6, Ca₂MgSi₂O₇, Ca₇MgSi₄O₁₆, CaMgSiO₄ and Ca₃MgSi₂O₈ as new generation orthopedic prosthetic implants. Mg²⁺, Ca²⁺ and Si⁴⁺ ions are abundant in bone and play a crucial role in various bone metabolic activities such as enhancing osteogenesis and inhibiting osteoporosis. The release rate of Mg²⁺, Ca²⁺ and Si⁴⁺ ions from these bioceramics depends on the crystal structure which consequently, influences their bioactivity and biocompatibility. In addition, the release rate of these ions can be tuned by tailoring the processing parameters/routes and compositional modifications and subsequently, bioactivity, cellular response as well as bone regeneration ability can be improved. Toward this end, the present article thoroughly reviewed and analyzed the influence of crystal structure, processing parameters/routes and compositional alteration on in vitro/in vivo biocompatibility and degradation behavior of the above ceramics. Further, a correlation between structure, processing and properties has been established.

     

Multifunctional hydroxyapatite and poly(d,l-lactide-co-glycolide) nanoparticles for the local delivery of cholecalciferol

Cholecalciferol, vitamin D₃, plays an important role in bone metabolism by regulating extracellular levels of calcium. Presented here is a study on the effects of the local delivery of cholecalciferol (D₃) using nanoparticulate carriers composed of hydroxyapatite (HAp) and poly(d,l-lactide-co-glycolide) (PLGA). Multifunctional nanoparticulate HAp-based powders were prepared for the purpose of: (a) either fast or sustained, local delivery of cholecalciferol, and (b) the secondary, osteoconductive and defect-filling effect of the carrier itself. Two types of HAp-based powders with particles of narrowly dispersed sizes in the nano range were prepared and tested in this study: HAp nanoparticles as direct cholecalciferol delivery agents and HAp nanoparticles coated with cholecalciferol-loaded poly(d,l)-lactide-co-glycolide (HAp/D₃/PLGA).Satisfying biocompatibility of particulate systems, when incubated in contact with MC3T3-E1 osteoblastic cells in vitro, was observed for HAp/D₃/PLGA and pure HAp. In contrast, an extensively fast release of cholecalciferol from the system comprising HAp nanoparticles coated with cholecalciferol (HAp/D3) triggered necrosis of the osteoblastic cells in vitro. Artificial defects induced in the osteoporotic bone of the rat mandible were successfully reconstructed following implantation of cholecalciferol-coated HAp nanoparticles as well as those comprising HAp nanoparticles coated with cholecalciferol-loaded PLGA (HAp/D₃/PLGA). The greatest levels of enhanced angiogenesis, vascularization, osteogenesis and bone structure differentiation were achieved upon the implementation of HAp/D₃/PLGA systems.     

Polyfunctional bioceramics modified by M-type hexagonal ferrite particles for medical applications

Magnetic bioceramics based on Ca₅(PO₄)₃OH hydroxyapatite and M-type hexagonal ferrite (HF) microcrystals has been synthesized and characterized. The material consists of a biocompatible apatite matrix containing dispersed M-type HF particles. The latter component makes the magnetic characteristics of synthesized ceramics significantly higher as compared to those of iron-oxide-modified bioglass ceramics currently used in medicine. These properties increase the efficiency and prospects of using the new bioceramics in medicine, in particular, for the hyperthermal treatment of malignant tumors. Thus, a new class of materials is created, which combine the necessary biocompatibility and biological activity of Ca₅(PO₄)₃OH hydroxyapatite and high magnetic characteristics of M-type HF microcrystals.     

Effect of mixing ceramics with a thermosensitive biodegradable hydrogel as composite graft

The composite of methoxy polyethylene glycol (mPEG) and poly(lactic-co-glycolic acid) (PLGA) thermosensitive hydrogel mixed with various portions of hydroxyapatite (HAP) or β-tricalcium phosphate (β-TCP) were used as bone graft substitutes. The physical properties of a series of composite gels, including the critical micelle concentration (CMC), particle sizes, zeta potential, rheological behavior, morphology of composite gels, and sol–gel transition, were characterized in vitro. These composite gels could form a gel at body temperature and could be controlled easily at room temperature, but showed only a small decline in pH, to between 6.33 and 6.66, whereas mPEG–PLGA gel without ceramic exhibited a more significant decrease in pH over a period of 5 days. The dissolution of ceramics results in an increase in the concentration of calcium and phosphate, which can buffer the degradation of mPEG–PLGA. Higher cell viability was observed in the composite gels with more bioceramics, as shown in the MTT assay and the live and dead stain. Mixing mPEG–PLGA with HAP or β-TCP may hold greater promise than mPEG–PLGA alone for repairing bone defects.     

Effect of mixing ceramics with a thermosensitive biodegradable hydrogel as composite graft

The composite of methoxy polyethylene glycol (mPEG) and poly(lactic-co-glycolic acid) (PLGA) thermosensitive hydrogel mixed with various portions of hydroxyapatite (HAP) or β-tricalcium phosphate (β-TCP) were used as bone graft substitutes. The physical properties of a series of composite gels, including the critical micelle concentration (CMC), particle sizes, zeta potential, rheological behavior, morphology of composite gels, and sol–gel transition, were characterized in vitro. These composite gels could form a gel at body temperature and could be controlled easily at room temperature, but showed only a small decline in pH, to between 6.33 and 6.66, whereas mPEG–PLGA gel without ceramic exhibited a more significant decrease in pH over a period of 5 days. The dissolution of ceramics results in an increase in the concentration of calcium and phosphate, which can buffer the degradation of mPEG–PLGA. Higher cell viability was observed in the composite gels with more bioceramics, as shown in the MTT assay and the live and dead stain. Mixing mPEG–PLGA with HAP or β-TCP may hold greater promise than mPEG–PLGA alone for repairing bone defects.     

Bioactivity of CaSiO<Subscript>3</Subscript>/poly-lactic acid (PLA) composites prepared by various surface loading methods of CaSiO<Subscript>3</Subscript> powder

Mixing bioactive ceramic powders with polymers is an effective method for generating bioactivity to the polymer-matrix composites but it is necessary to incorporate up to 40 vol% of bioactive ceramic powder. However, such a high mixing ratio offsets the advantages of the flexibility and formability of polymer matrix and it would be highly advantageous to lower the mixing ratio. Since surface loading of ceramic powders in the polymer is thought to be an effective way of reducing the mixing ratio of the ceramic powder while maintaining bioactive activity, CaSiO₃/poly-lactic acid (PLA) composites were prepared by three methods; (1) casting, (2) spin coating and (3) hot pressing. In methods (1) and (2), a suspension was prepared by dissolving PLA in chloroform and dispersing CaSiO₃ powder in it. The suspension was cast and dried to form a film in the case of method (1) while it was spin-coated on a PLA substrate in method (2). In method (3), CaSiO₃ powder was surface loaded on to a PLA substrate by hot-pressing. The bioactivity of these samples was investigated in vitro using simulated body fluid (SBF). Apatite formation was not observed in the samples prepared by method (1) but some apatite formation was achieved by mixing polyethylene glycol (PEG) with the PLA, producing a porous polymer matrix. In method (2), apatite was clearly observed after soaking for 7 days. Enhanced apatite formation was observed in method (3), the thickness of the resulting apatite layers becoming about 20 μm after soaking for 14 days. Since the amount of CaSiO₃ powder used in these samples was only ≤0.4 vol%, it is concluded that this preparation method is very effective in generating bioactivity in polymer-matrix composites by loading with only very small amounts of ceramic powder.     

Preparation and characterization of Sr-hardystonite (Sr2ZnSi2O7) for bone repair applications

In this work, the potential of Sr-hardystonite (Sr₂ZnSi₂O₇) ceramics for biomedical use was first detected. First, pure Sr₂ZnSi₂O₇ powders were successfully synthesized by sol-gel method, and then Sr₂ZnSi₂O₇ ceramics were prepared by sintering the powder compacts. The mechanical test showed that the bending strength and Young's modulus of Sr₂ZnSi₂O₇ ceramics could reach 82 MPa and 44 GPa, respectively, which were close to the values for human cortical bone. Degradation test in Tris-HCl buffer solution showed that Sr₂ZnSi₂O₇ ceramics had a low degradation rate with less than 3% weight loss after soaking for 28 days. Furthermore, the in vitro biocompatibility of the ceramics was evaluated by rabbit bone marrow stem cells (rBMSCs) adhesion and proliferation assay. The results showed that the ceramics supported the cells adhesion and proliferation. Taken together, Sr₂ZnSi₂O₇ might be a potential candidate for preparation of bone implants.     

Bioactivity of CaSiO<Subscript>3</Subscript>/poly-lactic acid (PLA) composites prepared by various surface loading methods of CaSiO<Subscript>3</Subscript> powder

Mixing bioactive ceramic powders with polymers is an effective method for generating bioactivity to the polymer-matrix composites but it is necessary to incorporate up to 40 vol% of bioactive ceramic powder. However, such a high mixing ratio offsets the advantages of the flexibility and formability of polymer matrix and it would be highly advantageous to lower the mixing ratio. Since surface loading of ceramic powders in the polymer is thought to be an effective way of reducing the mixing ratio of the ceramic powder while maintaining bioactive activity, CaSiO₃/poly-lactic acid (PLA) composites were prepared by three methods; (1) casting, (2) spin coating and (3) hot pressing. In methods (1) and (2), a suspension was prepared by dissolving PLA in chloroform and dispersing CaSiO₃ powder in it. The suspension was cast and dried to form a film in the case of method (1) while it was spin-coated on a PLA substrate in method (2). In method (3), CaSiO₃ powder was surface loaded on to a PLA substrate by hot pressing. The bioactivity of these samples was investigated in vitro using simulated body fluid (SBF). Apatite formation was not observed in the samples prepared by method (1) but some apatite formation was achieved by mixing polyethylene glycol (PEG) with the PLA, producing a porous polymer matrix. In method (2), apatite was clearly observed after soaking for 7 days. Enhanced apatite formation was observed in method (3), the thickness of the resulting apatite layers becoming about 20 μm after soaking for 14 days. Since the amount of CaSiO₃ powder used in these samples was only ≤0.4 vol%, it is concluded that this preparation method is very effective in generating bioactivity in polymer-matrix composites by loading with only very small amounts of ceramic powder.     

New nanocomposite based on poly(lactic-co-glycolic acid) copolymer and magnetite. Synthesis and characterization

The study presents the preparation of the new magnetic nanocomposite based on PLGA and magnetite. The PLGA used to obtain the magnetic nanocomposites was synthesized by the copolymerization of lactic acid with glycolic acid, in the presence of tin octanoate [Sn(Oct)₂] as catalyst, by polycondensation procedure. Magnetite was obtained by co-precipitation from aqueous salt solutions FeCl₂/FeCl₃. The particles size of magnetite was 420 nm, and the saturation magnetization 62.78 emu/g, while the PLGA/magnetite nanocomposite size was 864 nm and the saturation magnetization 39.44 emu/g. The magnetic nanocomposites were characterized by FT-IR, DLS technique, SEM, VSM and simultaneous thermal analyses (TG–FTIR–MS). The polymer matrix PLGA acts as a shell and carrier for the active component, while magnetite is the component which makes targeting possible by external magnetic field manipulation. Based on the gases resulted by thermal degradation of PLGA copolymer, using the simultaneous analysis TG–FTIR–MS, a possible degradation mechanism was proposed.     

Preparation and evaluation of a novel bioactive glass/lysozyme/PLGA composite microsphere

Objective: The objective of this study was to fabricate a novel nano-bioceramics incorporated lysozyme poly (d, l-lactide-co-glycolide) (PLGA) microsphere.

Methods: The nano-bioceramics was used as a biodegradable and sustained-release antacid to stabilize the lysozyme in the drug release process. First, the nano-bioceramics were prepared by sol-gel method, and then were characterized by energy dispersive X-ray analysis, dynamic light scattering and in vitro degradation test. Second, the lysozyme PLGA microsphere incorporated with nano-bioceramic was fabricated by the S/W/O/W emulsion solvent evaporation method. The microsphere was characterized by scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy and UV circular dichroism (UV CD). Finally the in vitro drug release and bioactivity test was carried out.

Results: The composition of the nano-bioceramics was 58% SiO₂, 36% CaO, 6% P₂O₅, and the average particle size was 295?nm. The nano-bioceramics incorporated lysozyme PLGA microspheres were prepared by the multi-emulsion method. The SEM results showed that the bioceramics was uniformly distributed in the PLGA microsphere. Results from in vitro lysozyme release test exhibited a prolonged release time for 1month. The FTIR and UVCD results suggested that the lysozyme in the drug release process had a similar secondary structure conformation to the native one. The Micrococcus lysodeikticus test showed that the microspheres incorporated with bioceramics provided long-term protein stability against the acidic environment resulted from PLGA’s degradates and more than 90% of the lysozyme released over the 1 month period was preserved in a bioactive form.

Conclusion: A novel bioceramics incorporated lysozyme PLGA microsphere was prepared with potentials for sustained protein release formulation.     

Effect of solid/solution ratio on apatite formation from CaSiO<Subscript>3</Subscript> ceramics in simulated body fluid

The effect of the solid/solution (S/S) ratio on apatite formation from CaSiO₃ ceramics in simulated body fluid (SBF) was investigated. CaSiO₃ ceramics with a Ca/Si ratio of 0.91 were prepared by sintering CaSiO₃ powder coprecipitated from ethanol solutions of Ca(NO₃)₂⋅4H₂O and Si(OC₂H₅)₄ using NH₄OH as the precipitant. These ceramics were reacted with SBF at S/S ratios of 1.0, 2.5 and 8.3 mg/ml at 36.5 ^∘C for various times. Formation of apatite was observed at all the S/S ratios after soaking for 1 day. The amount and microstructure of the apatite obtained at a S/S ratio of 8.3 mg/ml, however, differed largely from the product formed at the other two S/S ratios. The apatite formed at S/S = 8.3 mg/ml was of smaller particle size, formed in smaller amount and with less preferred orientation of the (00l) of apatite crystals compared with those formed at S/S = 1.0 and 2.5 mg/ml. An increase of Ca and decrease of the P components occurred in the soaked SBF at S/S = 8.3 mg/ml, the changes being much more marked than with the other two S/S ratios. These differences in the concentration changes in SBF at different S/S ratios are attributed to the difference in the apatite formation from the CaSiO₃ ceramics.     

Synthesis,Characterization and Bioactivity Evaluation of Porous Barium Titanate with Nanostructured Hydroxyapatite Coating for Biomedical Application

Nano phase hydroxyapatite (HA) bioceramics have gained importance in the biomedical field due to their superior biological properties. In this study, nanostructured HA coating was used to increase the bioactivity of a piezoelectric bioceramic, barium titanate (BT). Early reports on the influence of collagen piezoelectricity in remodeling of bone have attracted many researchers to piezoelectric bioceramics such as BT. Hence; porous BT was used as the matrix of a new bone graft composite and then coated with nanostructured HA. BT ceramic was foamed via a direct foaming method with a spray of polyurethane foam. The surface of the foam voids was coated with HA via sol–gel and dip‐coating methods. X‐ray diffraction (XRD), transmission electron microscopy (TEM), and scanning electron microscopy (SEM) techniques were used to characterize the prepared coated foam. XRD and TEM analysis showed that the HA coating had a nanostructure with crystallite size of 20–30 nm. SEM images of the prepared samples showed that the HA coating has about 25 µm thickness. The bioactivity of the prepared composite was evaluated in an in vitro study. The variation of Ca²⁺ and PO₄^3? ions versus time in simulated body fluid (SBF) solution were measured by inductively coupled plasma (ICP) analysis during 1 month and the results showed that the mineralization of calcium phosphate (Ca‐P) on HA coated porous samples was much more than that in non‐coated sample. The SEM micrographs and energy‐dispersive X‐ray spectroscopy (EDS or EDX) analysis of the samples after 1 month of immersing in SBF confirm that Ca‐P phase (bone‐like apatite) was significantly mineralized on HA coated porous BT samples. It was concluded that the nanostructured HA coating would improve the bioactivity of BT foam.     

Nanostructure effects on the bioactivity of forsterite bioceramic

Recently, forsterite (Mg₂SiO₄) has been introduced as a possible bioceramics due to its good biocompatibility. It has a better bending strength and fracture toughness than those of commercially available hydroxyapatite ceramics. In this study, nanostructure effects on the bioactivity of forsterite powder were investigated. For synthesizing forsterite powder, talc and magnesium carbonate powders were mechanically activated for various times. Then, the prepared powders were mixed with ammonium chloride (as a catalyst) and annealed at different temperatures. For bioactivity evaluation, the obtained forsterite powders were pressed in the form of tablets and then immersed in simulated body fluid (SBF). The results showed that nanostructure forsterite powder with crystallite size of about 31 nm, unlike micrometer-sized forsterite, possessed apatite formation ability and its bioactivity, biocompatibility, and good mechanical properties make it a suitable candidate for load bearing application in bone implant materials and open new horizons in tissue engineering.     

Calcite as a bone substitute. Comparison with hydroxyapatite and tricalcium phosphate with regard to the osteoblastic activity

Close to the bone mineral phase, the calcic bioceramics, such as hydroxyapatite (HA) and β-tricalcium phosphate (β-TCP), are commonly used as substitutes or filling materials in bone surgery. Besides, calcium carbonate (CaCO₃) is also used for their excellent biocompatibility and bioactivity. However, the problem with the animal-origin aragonite demands the new technique to synthesize pure calcite capable of forming 3D bone implant. This study aims to manufacture and evaluate a highly-pure synthetic crystalline calcite with good cytocompatibility regarding to the osteoblasts, comparing to that of HA and β-TCP. After the manufacture of macroporous bioceramic scaffolds with the identical internal architecture, their cytocompatibility is studied through MC3T3-E1 osteoblasts with the tests of cell viability, proliferation, vitality, etc. The results confirmed that the studied process is able to form a macroporous material with a controlled internal architecture, and this synthesized calcite is non-cytotoxic and facilitate the cell proliferation. Indeed requiring further improvement, the studied calcite is definitely an interesting alternative not only to coralline aragonite but also to calcium phosphate ceramics, particularly in bone sites with the large bone remodelling.     

In vitro characterization of laser ablation pseudowollastonite coating

Pseudowollastonite (CaSiO₃) coatings on titanium alloy substrates were prepared by laser ablation. The in vitro bioactivity of the coatings was examined for its biomedical applicability which was evaluated by immersion in human parotid saliva. The pseudowollastonite-coatings were soaked for various periods and characterized by SEM-EDS, XRD, FTIR, and TEM analysis, and the results indicated that the carbonated hydroxyapatite (CHA) was formed on the surface of the coatings within 1 day. In addition, cell attachment test showed that the pseudowollastonite-coatings supported the mesenchymal stem cells adhesion and spreading, and the cells established close contacts with the ceramics after 1 day of culture. These findings indicate that the pseudowollastonite-coatings possesses good bioactivity, biocompatibility and could be of interest in specific periodontal applications for bone restorative purposes.     

Subcritical CO2 sintering of microspheres of different polymeric materials to fabricate scaffolds for tissue engineering

The aim of this study was to use CO₂ at sub-critical pressures as a tool to sinter 3D, macroporous, microsphere-based scaffolds for bone and cartilage tissue engineering. Porous scaffolds composed of ~ 200 μm microspheres of either poly(lactic-co-glycolic acid) (PLGA) or polycaprolactone (PCL) were prepared using dense phase CO₂ sintering, which were seeded with rat bone marrow mesenchymal stromal cells (rBMSCs), and exposed to either osteogenic (PLGA, PCL) or chondrogenic (PLGA) conditions for 6 weeks. Under osteogenic conditions, the PLGA constructs produced over an order of magnitude more calcium than the PCL constructs, whereas the PCL constructs had far superior mechanical and structural integrity (125 times stiffer than PLGA constructs) at week 6, along with twice the cell content of the PLGA constructs. Chondrogenic cell performance was limited in PLGA constructs, perhaps as a result of the polymer degradation rate being too high. The current study represents the first long-term culture of CO₂-sintered microsphere-based scaffolds, and has established important thermodynamic differences in sintering between the selected formulations of PLGA and PCL, with the former requiring adjustment of pressure only, and the latter requiring the adjustment of both pressure and temperature. Based on more straightforward sintering conditions and more favorable cell performance, PLGA may be the material of choice for microspheres in a CO₂ sintering application, although a different PLGA formulation with the encapsulation of growth factors, extracellular matrix-derived nanoparticles, and/or buffers in the microspheres may be advantageous for achieving a more superior cell performance than observed here.     

Nanocomposite nanofibers of poly(d, l-lactic-co-glycolic acid) and graphene oxide nanosheets

Significant improvements in the thermomechanical and surface chemical properties of nanocomposite nanofibers of poly(d, l-lactic-co-glycolic acid) (PLGA) were achieved by adding 2-dimensional nanoscale fillers of graphene oxide (GO) nanosheets to PLGA nanofibers. The significant enhancement of storage and loss moduli of the PLGA/GO (2 wt.%.) nanocomposite nanofibers were presumably caused by enhanced chemical bonding between the oxygenated functional groups of the highly dispersible GO nanosheets and the hydroxyl groups of the polymer chains in the PLGA matrix, resulting in strong interfacial interactions between the nanofiller and polymer matrix. Enhanced hydrophilicity of nanocomposite nanofibers caused by embedded GO nanosheets also allowed for good biocompatibility of neuronal cells, resulting in enhanced cell proliferation and viability. Our findings indicate that nanocomposite biopolymer nanofibers embedded with GO nanosheets are attractive candidates for use in biomedical applications such as scaffolds.