Phase conversion of tricalcium phosphate into Ca-deficient apatite during sintering of hydroxyapatite–tricalcium phosphate biphasic ceramics

Regenerative Potential of Hydroxyapatite-Based Ceramic Biomaterial on Mandibular Cortical Bone: An In Vivo Study

Reconstruction of bone defects and maintaining the continuity of the mandible is still a challenge in the maxillofacial surgery. Nowadays, the biomedical research within bone defect treatment is focussed on the therapy of using innovative biomaterials with specific characteristics consisting of the body’s own substances. Hydroxyapatite ceramic scaffolds have fully acceptable phase compositions, microstructures and compressive strengths for their use in regenerative medicine. The innovative hydroxyapatite ceramics used by us were prepared using the tape-casting method, which allows variation in the shape of samples after packing hydroxyapatite paste to 3D-printed plastic form. The purpose of our qualitative study was to evaluate the regenerative potential of the innovative ceramic biomaterial prepared using this method in the therapy of the cortical bone of the lower jaw in four mature pigs. The mandible bone defects were evaluated after different periods of time (after 3, 4, 5 and 6 months) and compared with the control sample (healthy cortical bone from the opposite side of the mandible). The results of the morphological, clinical and radiological investigation and hardness examination confirmed the positive regenerative potential of ceramic implants after treatment of the mandible bone defects in the porcine mandible model.

Long-Bone-Regeneration Process in a Sheep Animal Model, Using Hydroxyapatite Ceramics Prepared by Tape-Casting Method

This study was designed to investigate the effects of hydroxyapatite (HA) ceramic implants (HA cylinders, perforated HA plates, and nonperforated HA plates) on the healing of bone defects, addressing biocompatibility, biodegradability, osteoconductivity, osteoinductivity, and osteointegration with the surrounding bone tissue. The HA ceramic implants were prepared using the tape-casting method, which allows for shape variation in samples after packing HA paste into 3D-printed plastic forms. In vitro, the distribution and morphology of the MC3T3E1 cells grown on the test discs for 2 and 9 days were visualised with a fluorescent live/dead staining assay. The growth of the cell population was clearly visible on the entire ceramic surfaces and very good osteoblastic cell adhesion and proliferation was observed, with no dead cells detected. A sheep animal model was used to perform in vivo experiments with bone defects created on the metatarsal bones, where histological and immunohistochemical tissue analysis as well as X-ray and CT images were applied. After 6 months, all implants showed excellent biocompatibility with the surrounding bone tissue with no observed signs of inflammatory reaction. The histomorphological findings revealed bone growth immediately over and around the implants, indicating the excellent osteoconductivity of the HA ceramic implants. A number of islands of bone tissue were observed towards the centres of the HA cylinders. The highest degree of biodegradation, bioresorption, and new bone formation was observed in the group in which perforated HA plates were applied. The results of this study suggest that HA cylinders and HA plates may provide a promising material for the functional long-bone-defect reconstruction and further research.

Molecular Dynamics Simulation of Biomimetic Biphasic Calcium Phosphate Nanoparticles

Biphasic calcium phosphate (BCP) is used as a bone substitute and bone tissue repair material due to its better control over bioactivity and biodegradability. It is crucial to stabilize the implanted biomaterial while promoting bone ingrowth. However, a lack of standard experimental and theoretical protocols to characterize the physicochemical properties of BCP limits the optimization of its composition and properties. Computational simulations can help us better to learn BCP at a nanoscale level. Here, the Voronoi tessellation method was combined with simulated annealing molecular dynamics to construct BCP nanoparticle models of different sizes, which were used to understand the physicochemical properties of BCP (e.g., melting point, infrared spectrum, and mechanical properties). We observed a ∼20 to 30 Å layer of calcium-deficient hydroxyapatite at the HAP/β-TCP interface due to particle migration, which may contribute to BCP stability. The BCP model may stimulate further research into BCP ceramics and multiphasic ceramics. Moreover, our study may facilitate the optimization of compositions of BCP-based biomaterials.

Sustained calcium ion release from bioceramics promotes CaSR-mediated M2 macrophage polarization for osteoinduction

Innate immune cells, especially macrophages, play a dual role in tissue repair and the defense against foreign bodies. Although biphasic calcium phosphate (BCP) ceramics have been confirmed as an excellent osteoimmunoregulatory biomaterial, it is unclear whether the ions release of BCP directly affects macrophage polarization and the mechanism by which the ions release is involved in osteoimmunomodulation. Herein, we verified the superior osteoinductive capacity of BCP in wild-type mice and showed its inability to promote this process in macrophage-deficient (LysM^-/- ) mice. Moreover, scanning electron microscopy, ion release curve, and calcein AM-staining results confirmed that BCP-released Ca²⁺ in a sustained manner, thereby maintaining the long-term induction of M2 macrophage polarization and promoting the differentiation of mesenchymal stem cells into osteoblasts during osteogenesis. Furthermore, Ca²⁺ targeted the Wnt/β-catenin signaling pathway and activated Arg1 and IL-10 (M2 marker genes) transcription through the calcium-sensing receptor (CaSR) in macrophages. Under treatment with a CaSR antagonist, macrophages cultured with the BCP fluid extract exhibited lower Ca²⁺ intake and weaker M2 macrophage polarization. These findings underscore the critical role of macrophages in bone regeneration and clarify the molecular mechanisms of Ca²⁺ -mediated osteoinduction by biomaterials, which is of great significance for the future design of biomaterial-oriented tissue regeneration engineering.

Dual-Wavelength Photosensitive Nano-in-Micro Scaffold Regulates Innate and Adaptive Immune Responses for Osteogenesis

The immune response of a biomaterial determines its osteoinductive effect. Although the mechanisms by which some immune cells promote regeneration have been revealed, the biomaterial-induced immune response is a dynamic process involving multiple cells. Currently, it is challenging to accurately regulate the innate and adaptive immune responses to promote osteoinduction in biomaterials. Herein, we investigated the roles of macrophages and dendritic cells (DCs) during the osteoinduction of biphasic calcium phosphate (BCP) scaffolds. We found that osteoinductive BCP directed M2 macrophage polarization and inhibited DC maturation, resulting in low T cell response and efficient osteogenesis. Accordingly, a dual-targeting nano-in-micro scaffold (BCP loaded with gold nanocage, BCP-GNC) was designed to regulate the immune responses of macrophages and DCs. Through a dual-wavelength photosensitive switch, BCP-GNC releases interleukin-4 in the early stage of osteoinduction to target M2 macrophages and then releases dexamethasone in the later stage to target immature DCs, creating a desirable inflammatory environment for osteogenesis. This study demonstrates that biomaterials developed to have specific regulatory capacities for immune cells can be used to control the early inflammatory responses of implanted materials and induce osteogenesis.

Modular microcarrier technologies for cell-based bone regeneration

A variety of materials-based approaches to accelerate the regeneration of damaged bone have been developed to meet the important clinical need for improved bone fillers. This comprehensive review covers the materials and technologies used in modular microcarrier-based methods for delivery of progenitor cells in orthopaedic repair applications. It provides an overview of the field and the rationale for using microcarriers combined with osteoprogenitor cells for bone regeneration in particular. The general concepts and methods used in microcarrier-based cell culture and delivery are described, and methods for fabricating and characterizing microcarriers designed for specific indications are presented. A comprehensive review of the current literature on the use of microcarriers in bone regeneration is provided, with emphasis on key developments in the field and their impact. The studies reviewed are organized according to the broad classes of materials that are used for fabricating microcarriers, including polysaccharides, proteins and peptides, ceramics, and synthetic polymers. In addition, composite microcarriers that incorporate multiple material types or that are mineralized biomimetically are included. In each case, the fabrication, processing, characterization, and resulting function of the microcarriers is described, with an emphasis on their ability to support osteogenic differentiation of progenitor cells in vitro, and their effectiveness in healing bone defects in vivo. In addition, a summary of the current state of the field is provided, as are future perspectives on how microcarrier technologies may be enhanced to create improved cell-based therapies for bone regeneration.

Preparation and biological effects of apatite nanosheet-constructed porous ceramics

A kind of apatite nanosheet-constructed porous ceramics could mediate the osteogenic differentiation of mesenchymal stem cells.

Biphasic calcium phosphates bioceramics (HA/TCP): Concept, physicochemical properties and the impact of standardization of study protocols in biomaterials research

Biphasic calcium phosphates (BCP) bioceramics have become the materials of choice in various orthopedic and maxillofacial bone repair procedures. One of their main advantages is their biodegradation rate that can be modified by changing the proportional ratio of the composition phases. For enhanced bone tissue regeneration, the bioactivity of BCP should be increased by optimizing their physicochemical properties. To date, the ideal physicochemical properties of BCP for bone applications have not been defined. This is mostly related to lack of standard study protocols in biomaterial science especially with regards to their characterizations and clinical applications. In this paper we provided a review on BCP and their physicochemical properties relevant to clinical applications. In addition, we summarized the available literature on their use in animal models and evaluated the influences of different composition ratios on bone healing. Controversies in literature with regards to ideal composition ratio of BCP have also been discussed in detail. We illustrated the discrepancies in study protocols among researchers in animal studies and emphasized the need to develop and follow a set of generally accepted standardized guidelines. Finally; we provided general recommendations for future pre-clinical studies that allow better standardization of study protocols. This will allow better comparison and contrast of newly developed bone substitute biomaterials that help further progress in the field of biomaterial science.

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.

Structural and phase characterization of bioceramics prepared from tetracalcium phosphate-monetite cement and in vitro osteoblast response

Biphasic porous calcium phosphate ceramics was prepared by sintering of transformed tetracalcium phosphate-monetite cement. After annealing hydroxyapatite, β- or α-TCP were found as main phases in ceramic substrates and a highly microporous microstructure of cement ceramics was created without an addition of porosifier. The origin microstructure features characteristic by the presence of hollow particle agglomerates in cement were preserved in microstructure of cement ceramics after annealing but the hydroxyapatite particles rose in size up to 2 µm and obtained a more regular shape. A small decrease in compressive strength was demonstrated in ceramics sintered up to 1150 °C and enhanced osteoblast proliferation was revealed on cement ceramic substrates in comparison with cement sample and conventional ceramics. The ALP activity of osteoblasts decreased with rise in sintering temperature. The prepared cement microporous ceramics could be utilized as carrier for antibiotics, drugs, growth factors, enzymes or other substances stimulating healing process.

Macrochanneled bioactive ceramic scaffolds in combination with collagen hydrogel: a new tool for bone tissue engineering

New tissue-engineering tool for bone regeneration is described to facilitate homogeneous cell seeding and effective osteogenic development. Calcium phosphate (CaP) scaffolds with macrochanneled and well-defined pore structure was developed, however, a large portion of the cells seeded directly within the scaffold easily penetrates without good adhesion to the scaffold surface. To overcome this, a method was exploited to dispense cells evenly throughout the CaP scaffold using collagen hydrogel. Rat bone marrow-derived mesenchymal stem cells (MSCs) were mixed within a neutralized collagen solution, which was then infiltrated into the macrochanneled pore space and gelled to result in macrochanneled bioceramic scaffold combined with MSCs-hydrogel. MSCs contained within the hydrogel-CaP scaffolds were highly viable, with similar growth pattern to those in the collagen hydrogel. Cells seeded by this approach were initially almost double in number compared with those seeded directly onto the CaP scaffold and had an active proliferation more than 14 days. Assessments of the MSCs showed significantly higher alkaline phosphatase levels in the combined scaffold, which was accompanied by enhanced osteogenesis including the expression of genes [collagen type I, bone sialoprotein, and osteopontin (OPN)] and proteins (OPN and osteocalcin). Extracellular calcium was also elevated significantly in the combined scaffold compared to the CaP scaffold. In addition, mechanical strength of the constructs was improved significantly in the combined scaffold compared to the CaP scaffold. Based on these, the cell culturing and tissue engineering strategy within the macrochanneled bioactive ceramic scaffolds could be improved greatly by the combinatory approach of using collagen hydrogel.

Biphasic, triphasic and multiphasic calcium orthophosphates

Biphasic, triphasic and multiphasic (polyphasic) calcium orthophosphates have been sought as biomaterials for reconstruction of bone defects in maxillofacial, dental and orthopedic applications. In general, this concept is determined by advantageous balances of more stable (frequently hydroxyapatite) and more resorbable (typically tricalcium orthophosphates) phases of calcium orthophosphates, while the optimum ratios depend on the particular applications. Therefore, all currently known biphasic, triphasic and multiphasic formulations of calcium orthophosphate bioceramics are sparingly soluble in water and, thus, after being implanted they are gradually resorbed inside the body, releasing calcium and orthophosphate ions into the biological medium and, hence, seeding new bone formation. The available formulations have already demonstrated proven biocompatibility, osteoconductivity, safety and predictability in vitro, in vivo, as well as in clinical models. More recently, in vitro and in vivo studies have shown that some of them might possess osteoinductive properties. Hence, in the field of tissue engineering biphasic, triphasic and multiphasic calcium orthophosphates represent promising biomaterials to construct various scaffolds capable of carrying and/or modulating the behavior of cells. Furthermore, such scaffolds are also suitable for drug delivery applications. This review summarizes the available information on biphasic, triphasic and multiphasic calcium orthophosphates, including their biomedical applications. New formulations are also proposed.

Concentration Effect of Aqueous Synthesis on Biphasic Hydroxyapatite – β-Tricalcium Phosphate Composition

Hydroxyapatite of calcium phosphate materials, one of the most frequently used ceramic material in biomedical application, has been produced via chemical reaction involves both calcium and phosphorus precursors. Effect of suspension concentration on available phases was investigated using a basis of 2 mole % excess of calcium oxide. The synthesis was performed at 90°C until paste was obtained. To improve crystallinity, hydroxyapatite was calcined at 900°C. However, β-TCP appeared as trace which varied in fraction with suspension concentration. Varying concentration is then one approaching method in designing phase composition through which a functional material could be attained.