Upgrading Calcium Phosphate Scaffolds for Tissue Engineering Applications

Porous scaffold hydroxyapatite from sand lobster shells (Panulirus homarus) using polyethylene oxide/chitosan as polymeric porogen for bone tissue engineering

The hydroxyapatite (HAp; Ca10 (PO4 )6 (OH)2 )) has good biocompatibility, bioactivity, and osteoconductivity as a bone implant because the main inorganic mineral of human bone is HAp. The use of scaffold HAp from biogenic resources that contain high calcium and polymer as a pore forming agent to support bone growth is a longstanding area of interest. In this study, porous scaffolds based on HAp were synthesized from sand lobster (SL; Panulirus homarus) shells as a source of calcium using the porogen leaching method with polyethylene oxide (PEO) and chitosan (Chs) as polymeric porogen. The present study aims to synthesize HAp derived from SL shells and evaluate the effect variations of PEO on the physicochemical properties of the scaffold and cytotoxicity in cell viability assay. Briefly, the SL shell powder was calcinated with temperature variations of 600°C, 800°C, and 1000°C for 6 h. Based on the characterization, it was shown that 1000°C was the optimum calcination temperature for SL shells to synthesize HAp using the precipitation method. The characterization results of HAp using energy dispersive x-ray (EDX) revealed that the molar ratio of Ca/P was 1.67. The Fourier transform infrared (FTIR) and x-ray diffractometer (XRD) spectral patterns indicated that HAp had been successfully synthesized with minor β-tricalcium phosphate (β-TCP), a calcium phosphate with high biocompatibility. Porous scaffolds were synthesized by varying the concentration of PEO at 0, 5, 10, and 15 wt %. Physicochemical analysis revealed that a higher concentration of PEO affected decreased crystallinity and compressive strength, but on the other hand, the porosity and pore sizes increased. Based on the physicochemical analysis, the synthesized porous scaffold showed that HAp/PEO/Chs 15 wt % had the most potential as a scaffold for biomedical applications. MTT Assay, after 24 h incubation, revealed that the scaffold was safe for use at low concentrations on the MC3T3E1 osteoblast cells, with a percentage of cell viability of 83.23 ± 3.18% at 23.4375 μg/mL. Although the cell viability decreased at higher concentrations, the HAp/PEO/Chs 15 wt % scaffold was cytocompatible with the cells. Thus, in the present study, HAp/PEO/Chs 15 wt % was the best scaffold based on pore structure, chemical composition, mechanical and crystalographic properties and cell viability.

Bilayer osteochondral graft in rabbit xenogeneic transplantation model comprising sintered 3D-printed bioceramic and human adipose-derived stem cells laden biohydrogel

Reconstruction of severe osteochondral defects in articular cartilage and subchondral trabecular bone remains a challenging problem. The well-integrated bilayer osteochondral graft design expects to be guided the chondrogenic and osteogenic differentiation for stem cells and provides a promising solution for osteochondral tissue repair in this study. The subchondral bone scaffold approach is based on the developed finer and denser 3D β-tricalcium phosphate (β-TCP) bioceramic scaffold process, which is made using a digital light processing (DLP) technology and the novel photocurable negative thermo-responsive (NTR) bioceramic slurry. Then, the concave-top disc sintered 3D-printed bioceramic incorporates the human adipose-derived stem cells (hADSCs) laden photo-cured hybrid biohydrogel (HG + 0.5AFnSi) comprised of hyaluronic acid methacryloyl (HAMA), gelatin methacryloyl (GelMA), and 0.5% (w/v) acrylate-functionalized nano-silica (AFnSi) crosslinker. The 3D β-TCP bioceramic compartment is used to provide essential mechanical support for cartilage regeneration in the long term and slow biodegradation. However, the apparent density and compressive strength of the 3D β-TCP bioceramics can be obtained for ~ 94.8% theoretical density and 11.38 ± 1.72 MPa, respectively. In addition, the in vivo results demonstrated that the hADSC + HG + 0.5AFnSi/3D β-TCP of the bilayer osteochondral graft showed a much better osteochondral defect repair outcome in a rabbit model. The other word, the subchondral bone scaffold of 3D β-TCP bioceramic could accelerate the bone formation and integration with the adjacent host cancellous tissue at 12 weeks after surgery. And then, a thicker cartilage layer with a smooth surface and uniformly aligned chondrocytes were observed by providing enough steady mechanical support of the 3D β-TCP bioceramic scaffold.

Functionalized cellulose nanofibrils in carbonate-substituted hydroxyapatite nanorod-based scaffold from long-spined sea urchin (Diadema setosum) shells reinforced with polyvinyl alcohol for alveolar bone tissue engineering

In this study, carbonate-substituted hydroxyapatite (C-HAp) nanorods were synthesised using a dissolution-precipitation reaction on hydroxyapatite (HAp) nanorods based on long-spined sea urchin (Diadema setosum) shells. From the EDS analysis, the Ca/P molar ratio of C-HAp was 1.705, which was very close to the Ca/P of natural bone apatite of 1.71. The FTIR and XRD analyses revealed the AB-type CHAp of the C-HAp nanorods. The TEM showed the rod-like shape of nanosize C-HAp with a high aspect ratio. The antibacterial test against Pseudomonas aeruginosa and Staphylococcus aureus also showed that C-HAp had a high antibacterial activity. The C-HAp/PVA-based scaffolds were fabricated, using a freeze-drying method, for use in alveolar bone tissue engineering applications. There were various scaffolds, with no filler, with microcrystalline cellulose (MCC) filler, and with cellulose nanofibrils (CNF) filler. The physicochemical analysis showed that adding PVA and cellulose caused no chemical decomposition but decreased the scaffold crystallinity, and the lower crystallinity created more dislocations that can help cells proliferate well. The antibacterial activity showed that the CNF induced the higher antibacterial level of the scaffold. According to the SEM results, the micropores of the C-HAp/PVA/CNF can provide a place for cells to grow, and its porosity can promote cell nutrient supply. The macropores of the C-HAp/PVA/CNF were also suitable for cells and new blood vessels. Therefore, the C-HAp/PVA/CNF scaffold was examined for its cytocompatibility using the MTT assay against NIH/3T3 fibroblast cells with a 24 h incubation. The C-HAp/PVA/CNF scaffold showed a high cell viability of 90.36 ± 0.37% at a low scaffold dose of 31.25 μg mL-1. The scaffold could also facilitate NIH/3T3 cells to attach to its surface. The IC50 value had also been estimated to be 2732 μg mL-1.

Surface-Modified Nano-Hydroxyapatite Uniformly Dispersed on High-Porous GelMA Scaffold Surfaces for Enhanced Osteochondral Regeneration

Purpose

This study aims to investigate the impact of enhancing subchondral bone repair on the efficacy of articular cartilage restoration, thereby achieving improved osteochondral regeneration outcomes.

Methods

In this study, we modified the surface of nano-hydroxyapatite (n-HAp) through alkylation reactions to prepare n-HApMA. Characterization techniques, including X-ray diffraction, infrared spectroscopy scanning, thermogravimetric analysis, particle size analysis, and electron microscopy, were employed to analyze n-HApMA. Bioinks were prepared using n-HApMA, high porosity GelMA hydrogel, and adipose tissue derived stromal cells (ADSCs). The rheological properties of the bioinks during photocuring were investigated using a rheometer. Based on these bioinks, a biphasic scaffold was constructed. The viability of cells within the scaffold was observed using live-dead cell staining, while the internal morphology was examined using scanning electron microscopy. The stiffness of the scaffold was evaluated through compression testing. Scaffolds were implanted into the osteochondral defects of New Zealand rabbit knees, and microCT was utilized to observe the subchondral bone repair. Hematoxylin and eosin (H&E) staining, Masson's trichrome staining, and Safranin O/Fast Green staining were performed to assess the regeneration of subchondral bone and cartilage. Furthermore, immunohistochemical staining was employed to detect the expression of osteogenic and chondrogenic-related molecules.

Results

Scaffold characterization revealed that surface modification enables the uniform distribution of n-HApMA within the GelMA matrix. The incorporation of 5% n-HApMA notably enhanced the elastic modulus and stiffness of the 6% high-porosity GelMA in comparison to n-HAp. Moreover, in-vivo study showed that the homogeneous dispersion of n-HApMA on the GelMA matrix facilitated the osteogenic differentiation of adipose-derived stem cells (ADSCs) and promoted osteochondral tissue regeneration.

Conclusion

These findings suggest potential applications of the n-HApMA/GelMA composite in the field of tissue engineering and regenerative medicine.

Clindamycin-Loaded Nanosized Calcium Phosphates Powders as a Carrier of Active Substances

Bioactive calcium phosphate ceramics (CaPs) are one of the building components of the inorganic part of bones. Synthetic CaPs are frequently used as materials for filling bone defects in the form of pastes or composites; however, their porous structure allows modification with active substances and, thus, subsequent use as a drug carrier for the controlled release of active substances. In this study, four different ceramic powders were compared: commercial hydroxyapatite (HA), TCP, brushite, as well as HA obtained by wet precipitation methods. The ceramic powders were subjected to physicochemical analysis, including FTIR, XRD, and determination of Ca/P molar ratio or porosity. These techniques confirmed that the materials were phase-pure, and the molar ratios of calcium and phosphorus elements were in accordance with the literature. This confirmed the validity of the selected synthesis methods. CaPs were then modified with the antibiotic clindamycin. Drug release was determined on HPLC, and antimicrobial properties were tested against Staphylococcus aureus. The specific surface area of the ceramic has been demonstrated to be a factor in drug release efficiency.

Biomedical applications of chitosan/silk fibroin composites: A review

Natural polymers have been used in the biomedical fields for decades, mainly derived from animals and plants with high similarities with biomacromolecules in the human body. As an alkaline polysaccharide, chitosan (CS) attracts much attention in tissue regeneration and drug delivery with favorable biocompatibility, biodegradation, and antibacterial activity. However, to overcome its mechanical properties and degradation behavior drawbacks, a robust fibrous protein-silk fibroin (SF) was introduced to prepare the CS/SF composites. Not only can CS be combined with SF via the amide and hydrogen bond formation, but also their functions are complementary and tunable with the blending ratio. To further improve the performances of CS/SF composites, natural (e.g., hyaluronic acid and collagen) and synthetic biopolymers (e.g., polyvinyl alcohol and hexanone) were incorporated. Also, the CS/SF composites acted as slow-release carriers for inorganic non-metals (e.g., hydroxyapatite and graphene) and metal particles (e.g., silver and magnesium), which could enhance cell functions, facilitate tissue healing, and inhibit bacterial growth. This review presents the state-of-the-art and future perspectives of different biomaterials combined with CS/SF composites as sponges, hydrogels, membranes, particles, and coatings. Emphasis is devoted to the biological potentialities of these hybrid systems, which look rather promising toward a multitude of applications.

Calcium Orthophosphate (CaPO4)-Based Bioceramics: Preparation, Properties, and Applications

Various types of materials have been traditionally used to restore damaged bones. In the late 1960s, a strong interest was raised in studying ceramics as potential bone grafts due to their biomechanical properties. A short time later, such synthetic biomaterials were called bioceramics. Bioceramics can be prepared from diverse inorganic substances, but this review is limited to calcium orthophosphate (CaPO4)-based formulations only, due to its chemical similarity to mammalian bones and teeth. During the past 50 years, there have been a number of important achievements in this field. Namely, after the initial development of bioceramics that was just tolerated in the physiological environment, an emphasis was shifted towards the formulations able to form direct chemical bonds with the adjacent bones. Afterwards, by the structural and compositional controls, it became possible to choose whether the CaPO4-based implants would remain biologically stable once incorporated into the skeletal structure or whether they would be resorbed over time. At the turn of the millennium, a new concept of regenerative bioceramics was developed, and such formulations became an integrated part of the tissue engineering approach. Now, CaPO4-based scaffolds are designed to induce bone formation and vascularization. These scaffolds are usually porous and harbor various biomolecules and/or cells. Therefore, current biomedical applications of CaPO4-based bioceramics include artificial bone grafts, bone augmentations, maxillofacial reconstruction, spinal fusion, and periodontal disease repairs, as well as bone fillers after tumor surgery. Prospective future applications comprise drug delivery and tissue engineering purposes because CaPO4 appear to be promising carriers of growth factors, bioactive peptides, and various types of cells.

3D printing of hierarchical porous biomimetic hydroxyapatite scaffolds: Adding concavities to the convex filaments

Porosity plays a key role on the osteogenic performance of bone scaffolds. Direct Ink Writing (DIW) allows the design of customized synthetic bone grafts with patient-specific architecture and controlled macroporosity. Being an extrusion-based technique, the scaffolds obtained are formed by arrays of cylindrical filaments, and therefore have convex surfaces. This may represent a serious limitation, as the role of surface curvature and more specifically the stimulating role of concave surfaces in osteoinduction and bone growth has been recently highlighted. Hence the need to design strategies that allow the introduction of concave pores in DIW scaffolds. In the current study, we propose to add gelatin microspheres as a sacrificial material in a self-setting calcium phosphate ink. Neither the phase transformation responsible for the hardening of the scaffold nor the formation of characteristic network of needle-like hydroxyapatite crystals was affected by the addition of gelatin microspheres. The partial dissolution of the gelatin resulted in the creation of spherical pores throughout the filaments and exposed on the surface, increasing filament porosity from 0.2 % to 67.9 %. Moreover, the presence of retained gelatin proved to have a significant effect on the mechanical properties, reducing the strength but simultaneously giving the scaffolds an elastic behavior, despite the high content of ceramic as a continuous phase. Notwithstanding the inherent difficulty of in vitro cultures with this highly reactive material an enhancement of MG-63 cell proliferation, as well as better spreading of hMSCs was recorded on the developed scaffolds. STATEMENT OF SIGNIFICANCE: Recent studies have stressed the role that concave surfaces play in tissue regeneration and, more specifically, in osteoinduction and osteogenesis. Direct ink writing enables the production of patient-specific bone grafts with controlled architecture. However, besides many advantages, it has the serious limitation that the surfaces obtained are convex. In this article, for the first time we develop a strategy to introduce concave pores in the printed filaments of biomimetic hydroxyapatite by incorporation and partial dissolution of gelatin microspheres. The retention of part of the gelatin results in a more elastic behavior compared to the brittleness of hydroxyapatite scaffolds, while the needle-shaped nanostructure of biomimetic hydroxyapatite is maintained and gelatin-coated concave pores on the surface of the filaments enhance cell spreading.

Porous Carbonated Hydroxyapatite-Based Paraffin Wax Nanocomposite Scaffold for Bone Tissue Engineering: A Physicochemical Properties and Cell Viability Assay Analysis

Porosity is one of the parameters of scaffold pore structure that must be developed using paraffin wax as a synthetic polymer for making porous bioceramics carbonated hydroxyapatite (CHA). This study fabricated CHA based on abalone mussel shells (Halioitis asinina); CHA/paraffin wax nanocomposite scaffolds were synthesized using paraffin wax with concentration variations of 10, 20, and 30 wt.%. The energy-dispersive X-ray spectroscopy (EDS) results showed that the Ca/P molar ratio of CHA was 1.72, which approaches the natural bone. The addition of paraffin wax in all concentration variation treatments caused the crystallographic properties of the CHA/paraffin wax nanocomposite scaffolds to decrease. The results of pore analysis suggest that the high concentration of paraffin wax in the CHA suspension is involved in the formation of more pores on the surface of the scaffold, but only CHA/paraffin wax 30 wt.% had a scaffold with potential to be used in media with a cellular growth orientation. The micropore analysis was also supported by the cell viability assay results for CHA/paraffin wax 30 wt.% nanocomposite scaffold, where serial doses of scaffold concentrations to mouse osteoblast cells were secure. Overall, based on this analysis, the CHA/paraffin wax scaffold can be a candidate for bone tissue engineering.

Carbonated Hydroxyapatite-Based Honeycomb Scaffold Coatings on a Titanium Alloy for Bone Implant Application—Physicochemical and Mechanical Properties Analysis

In this work, carbonated hydroxyapatite (CHA) based on abalone mussel shells (Haliotis asinina) is synthesized using the co-precipitation method. The synthesized CHA was mixed with honeycomb (HCB) 40 wt.% for the scaffold fabrication process. CHA and scaffold CHA/HCB 40 wt.% were used for coating a Titanium (Ti) alloy using the electrophoretic deposition dip coating (EP2D) method with immersion times of 10, 20, and 30 min. The synthesized B-type CHA with a stirring time of 45 min could have lower transmittance values and smaller crystallite size. Energy dispersive X-ray spectroscopy (EDS) showed that the Ca/P molar ratio was 1.79. The scaffold CHA/HCB 40 wt.% had macropore size, micropore size, and porosity of 102.02 ± 9.88 μm, 1.08 ± 0.086 μm, and 66.36%, respectively, and therefore it can also be applied in the coating process for bone implant applications due to the potential scaffold for bone growth. Thus, it has the potential for coating on Ti alloy applications. In this study, the compressive strength for all immersion time variations was about 54–83 MPa. The average compression strengths of human cancellous bone were about 0.2–80 MPa. The thickness obtained was in accordance with the thickness parameters required for a coating of 50–200 μm.

Multi-layered in vitro 3D-bone model via combination of osteogenic cell sheets with electrospun membrane interlayer

In this study, it was aimed to present an approach for the development of multi-layered tissue engineering constructs by using cell sheet engineering. Briefly, MC3T3-E1 mouse pre-osteoblast cells were cultured in temperature-responsive plates (Nunc Upcell®) in the presence of osteogenic medium and the resulting cell sheets were laminated with electrospun poly(L-lactic acid) (PLLA) membranes to obtain viable three-dimensional, thick constructs. The constructs prepared without PLLA membranes were used as control. The cell viability and death in the resulting structures were investigated by microscopic and colorimetric methods. The in vitro performance of the structures was discussed comparatively. Alkaline phosphatase (ALP) activity, collagen and sulfated glycosaminoglycan (sGAG) content values were calculated. The presented approach shows potential for engineering applications of complex tissues with at least two or more microenvironments such as osteochondral, corneal or vascular tissues.

Bone Grafts and Substitutes in Dentistry: A Review of Current Trends and Developments

After tooth loss, bone resorption is irreversible, leaving the area without adequate bone volume for successful implant treatment. Bone grafting is the only solution to reverse dental bone loss and is a well-accepted procedure required in one in every four dental implants. Research and development in materials, design and fabrication technologies have expanded over the years to achieve successful and long-lasting dental implants for tooth substitution. This review will critically present the various dental bone graft and substitute materials that have been used to achieve a successful dental implant. The article also reviews the properties of dental bone grafts and various dental bone substitutes that have been studied or are currently available commercially. The various classifications of bone grafts and substitutes, including natural and synthetic materials, are critically presented, and available commercial products in each category are discussed. Different bone substitute materials, including metals, ceramics, polymers, or their combinations, and their chemical, physical, and biocompatibility properties are explored. Limitations of the available materials are presented, and areas which require further research and development are highlighted. Tissue engineering hybrid constructions with enhanced bone regeneration ability, such as cell-based or growth factor-based bone substitutes, are discussed as an emerging area of development.

Structure-function assessment of 3D-printed porous scaffolds by a low-cost/open source fused filament fabrication printer

Additive manufacturing encompasses a plethora of techniques to manufacture structures from a computational model. Among them, fused filament fabrication (FFF) relies on heating thermoplastics to their fusion point and extruding the material through a nozzle in a controlled pattern. FFF is a suitable technique for tissue engineering, given that allows the fabrication of 3D-scaffolds, which are utilized for tissue regeneration purposes. The objective of this study is to assess a low-cost/open-source 3D printer (In-House), by manufacturing both solid and porous samples with relevant microarchitecture in the physiological range (100-500 μm pore size), using an equivalent commercial counterpart for comparison. For this, compressive tests in solid and porous scaffolds manufactured in both printers were performed, comparing the results with finite element analysis (FEA) models. Additionally, a microarchitectural analysis was done in samples from both printers, comparing the measurements of both pore size and porosity to their corresponding computer-aided design (CAD) models. Moreover, a preliminary biological assessment was performed using scaffolds from our In-House printer, measuring cell adhesion efficiency. Finally, Fourier transform infrared spectroscopy - attenuated total reflectance (FTIR-ATR) was performed to evaluate chemical changes in the material (polylactic acid) after fabrication in each printer. The results show that the In-House printer achieved generally better mechanical behavior and resolution capacity than its commercial counterpart, by comparing with their FEA and CAD models, respectively. Moreover, a preliminary biological assessment indicates the feasibility of the In-House printer to be used in tissue engineering applications. The results also show the influence of pore geometry on mechanical properties of 3D-scaffolds and demonstrate that properties such as the apparent elastic modulus (E_app) can be controlled in 3D-printed scaffolds.

Bioceramic hydroxyapatite-based scaffold with a porous structure using honeycomb as a natural polymeric Porogen for bone tissue engineering

Background

The application of bioceramic hydroxyapatite (HA) derived from materials high in calcium to tissue engineering has been of concern, namely scaffold. Scaffold pores allow for cell mobility metabolic processes, and delivery of oxygen and nutrients by blood vessel. Thus, pore architecture affects cell seeding efficiency, cell viability, migration, morphology, cell proliferation, cell differentiation, angiogenesis, mechanical strength of scaffolds, and, eventually, bone formation. Therefore, to improve the efficacy of bone regeneration, several important parameters of the pore architecture of scaffolds must be carefully controlled, including pore size, geometry, orientation, uniformity, interconnectivity, and porosity, which are interrelated and whose coordination affects the effectiveness of bone tissue engineering. The honeycomb (HCB) as natural polymeric porogen is used to pore forming agent of scaffolds. It is unique for fully interconnected and oriented pores of uniform size and high mechanical strength in the direction of the pores. The aim of this study was therefore to evaluate the effect of HCB concentration on macropore structure of the scaffolds.

Methods

Bioceramic hydroxyapatite (HA) was synthesized from abalone mussel shells (Halioitis asinina) using a precipitation method, and HA-based scaffolds were fabricated with honeycomb (HCB) as the porogen agent. Pore structure engineering was successfully carried out using HCB at concentrations of 10, 20, and 30 wt%.

Results

The Energy Dispersive X-Ray Spectroscopy (EDS) analysis revealed that the Ca/P molar ratio of HA was 1.67 (the stoichiometric ratio of HA). The Fourier Transform Infrared Spectroscopy (FTIR) spectra results for porous HA-based scaffolds and synthesized HA showed that no chemical decomposition occurred in the HA-based scaffold fabrication process. The porosity of the scaffold tended to increase when higher concentrations of HCB were added. XRD data show that the HCB was completely degraded from the scaffold material. The cell metabolic activity and morphology of the HA + HCB 30 wt% scaffold enable it to facilitate the attachment of MC3T3E1 cells on its surface.

Conclusion

HCB 30 wt% is the best concentration to fabricate the scaffold corresponding to the criteria for pores structure, crystallographic properties, chemical decomposition process and cell viability for bone tissue engineering.

Recent additive manufacturing methods categorized by characteristics of ceramic slurries for producing dual-scale porous ceramics

Porous ceramics have been utilized in various fields due to their advantages derived from characteristics of ceramics and porous structure and they were produced by versatile fabricating methods. However, the adoption of differently scaled pores in the porous ceramics by conventional pore forming strategies which results in dual-scale porosity has been studied to combine the specific functional abilities of each scaled pore. Those proposed strategies were supplemented to the recent additive manufacturing methods for constructing complicated structure with precisely controlled fabricating conditions. In this review, we provide the researches creating dual-scale porous ceramics with additive manufacturing which utilized the ceramic slurries containing homogeneous solution of photocurable monomers and terpenes. Introduction of the basic way to prepare photocurable monomer and terpene incorporated ceramic slurries which are suitable for specific printing mechanism was firstly discussed. And based on the characteristics of slurries, lithography-based and extrusion-based method are discussed with the experimental results. Subsequently, the remaining challenges of the techniques are further discussed with suggesting potentially capable approaches to overcome the limitations.

Bioactive calcium phosphate materials and applications in bone regeneration

BACKGROUND

Bone regeneration involves various complex biological processes. Many experiments have been performed using biomaterials in vivo and in vitro to promote and understand bone regeneration. Among the many biomaterials, calcium phosphates which exist in the natural bone have been conducted a number of studies because of its bone regenerative property. It can be directly contributed to bone regeneration process or assist in the use of other biomaterials. Therefore, it is widely used in many applications and has been continuously studied.

MAINBODY

Calcium phosphate has been widely used in bone regeneration applications because it shows osteoconductive and in some cases osteoinductive features. The release of calcium and phosphorus ions regulates the activation of osteoblasts and osteoclasts to facilitate bone regeneration. The control of surface properties and porosity of calcium phosphate affects cell/protein adhesion and growth and regulates bone mineral formation. Properties affecting bioactivity vary depending on the types of calcium phosphates such as HAP, TCP and can be utilized in various applications because of differences in ion release, solubility, stability, and mechanical strength. In order to make use of these properties, different calcium phosphates have been used together or mixed with other materials to complement their disadvantages and to highlight their advantages. Calcium phosphate has been utilized to improve bone regeneration in ways such as increasing osteoconductivity for bone ingrowth, enhancing osteoinductivity for bone mineralization with ion release control, and encapsulating drugs or growth factors.

CONCLUSION

Calcium phosphate has been used for bone regeneration in various forms such as coating, cement and scaffold based on its unique bioactive properties and bone regeneration effectiveness. Additionally, several studies have been actively carried out to improve the efficacy of calcium phosphate in combination with various healing agents. By summarizing the properties of calcium phosphate and its research direction, we hope that calcium phosphate can contribute to the clinical treatment approach for bone defect and disease.

Mesenchymal Stem Cells and Calcium Phosphate Bioceramics: Implications in Periodontal Bone Regeneration

In orthopedic medicine, a feasible reconstruction of bone structures remains one of the main challenges both for healthcare and for improvement of patients' quality of life. There is a growing interest in mesenchymal stem cells (MSCs) medical application, due to their multilineage differentiation potential, and tissue engineering integration to improve bone repair and regeneration. In this review we will describe the main characteristics of MSCs, such as osteogenesis, immunomodulation and antibacterial properties, key parameters to consider during bone repair strategies. Moreover, we describe the properties of calcium phosphate (CaP) bioceramics, which demonstrate to be useful tools in combination with MSCs, due to their biocompatibility, osseointegration and osteoconduction for bone repair and regeneration. Also, we overview the main characteristics of dental cavity MSCs, which are promising candidates, in combination with CaP bioceramics, for bone regeneration and tissue engineering. The understanding of MSCs biology and their interaction with CaP bioceramics and other biomaterials is critical for orthopedic surgical bone replacement, reconstruction and regeneration, which is an integrative and dynamic medical, scientific and bioengineering field of research and biotechnology.

Competent processing techniques for scaffolds in tissue engineering

Engineering a functional tissue ex vivo requires a synchronized effort towards developing technologies for ECM mimicking scaffold and cultivating tissue-specific cells in an integrated and controlled manner. Cell-interactive scaffolds in three dimensions (3D), designed and processed appropriately with an apt biomaterial to yield optimal porosity and mechanical strength is the key in tissue engineering (TE). In order to accomplish these facets in a 3D scaffold, multiple techniques and processes have been explored by researchers all over the world. New techniques offering reasonable flexibility to use blends of different materials for integrated tissue-specific mechanical strength and biocompatibility have an edge over conventional methods. They may allow a combinatorial approach with a mix of materials while incorporating multiple processing techniques for successful creation of tissue-specific ECM mimics. In this review, we analyze the material requirement from different TE perspectives, while discussing pros and cons of advanced fabrication techniques for scale-up manufacturing.

Hydroxyapatite–-Past, Present, and Future in Bone Regeneration

Hydroxyapatite (HA) is an essential element required for bone regeneration. Different forms of HA have been used for a long time. The essence of bone regeneration always revolves around the healthy underlying bone or it may be the surroundings that give enough strength. HA is well known for bone regeneration through conduction or by acting as a scaffold for filling of defects from ancient times, but emerging trends of osteoinductive property of HA are much promising for new bone regeneration. Emerging technology has made the dreams of clinicians to realize the use of HA in different forms for various regenerative purposes both in vivo and in vitro. The nanostructured calcium apatite plays an important role in the construction of calcified tissues. The nanostructured material has the ability to attach biological molecules such as proteins, which can be used as functional materials in many aspects, and the capability of synthesizing controlled structures of apatite to simulate the basic structure of bone and other calcified tissues. The process of regeneration requires a biomimetic and biocompatible nanostructured novel material. The nanostructured bioceramic particles are of interest in synthetic bone grafts and bone cements both injectable and controlled setting, so that such composites will reinforce the strength of bioceramics. Extensive research is being carried out for bone regeneration using nanotechnology. Artificial bone formation is not far from now. Nanotechnology has made many dreams come true. This paper gives comprehensive insights into the history and evolution with changing trends in the use of HA for various regenerative purposes.

Development and performance analysis of Si-CaP/fine particulate bone powder combined grafts for bone regeneration

Background

Although autogenous bone grafts as well as several bone graft substitute material have been used for some time, there is high demand for more efficient and less costly bone-substitute materials. Silicon-substituted calcium phosphates (Si-CaP) and fine particulate bone powder (FPBP) preparations have been previously shown to individually possess many of the required features of a bone graft substitute scaffold. However, when applied individually, these two materials fall short of an ideal substitute material. We investigated a new concept of combining Si-CaP with FPBP for improved performance in bone-repair.

Methods

We assessed Si-CaP/FPBP combined grafts in vitro, by measuring changes in pH, weight loss, water absorption and compressive strength over time.

Results

Si-CaP/FPBP combined grafts was found to produce conditions of alkaline pH levels compared to FPBP, and scaffold surface morphology conducive to bone cell adhesion, proliferation, differentiation, tissue growth and transport of nutrients, while maintaining elasticity and mechanical strength and degradation at a rate closer to osteogenesis.

Conclusion

Si-CaP/FPBP combined grafts was found to be superior to any of the two components individually.

Calcium Orthophosphate-Based Bioceramics

Various types of grafts have been traditionally used to restore damaged bones. In the late 1960s, a strong interest was raised in studying ceramics as potential bone grafts due to their biomechanical properties. A bit later, such synthetic biomaterials were called bioceramics. In principle, bioceramics can be prepared from diverse materials but this review is limited to calcium orthophosphate-based formulations only, which possess the specific advantages due to the chemical similarity to mammalian bones and teeth. During the past 40 years, there have been a number of important achievements in this field. Namely, after the initial development of bioceramics that was just tolerated in the physiological environment, an emphasis was shifted towards the formulations able to form direct chemical bonds with the adjacent bones. Afterwards, by the structural and compositional controls, it became possible to choose whether the calcium orthophosphate-based implants remain biologically stable once incorporated into the skeletal structure or whether they were resorbed over time. At the turn of the millennium, a new concept of regenerative bioceramics was developed and such formulations became an integrated part of the tissue engineering approach. Now calcium orthophosphate scaffolds are designed to induce bone formation and vascularization. These scaffolds are often porous and harbor different biomolecules and/or cells. Therefore, current biomedical applications of calcium orthophosphate bioceramics include bone augmentations, artificial bone grafts, maxillofacial reconstruction, spinal fusion, periodontal disease repairs and bone fillers after tumor surgery. Perspective future applications comprise drug delivery and tissue engineering purposes because calcium orthophosphates appear to be promising carriers of growth factors, bioactive peptides and various types of cells.

Development and evaluation of tetrapod-shaped granular artificial bones

We have developed a novel form of granular artificial bone "Tetrabones" with a homogeneous tetrapod shape and uniform size. Tetrabones are four armed structures that accumulate to form the intergranular pores that allow invasion of cells and blood vessels. In this study we evaluated the physicochemical characteristics of Tetrabones in vitro, and compared their biological and biomechanical properties in vivo to those of conventional β-tricalcium phosphate (β-TCP) granule artificial bone. Both the rupture strength and elastic modulus of Tetrabone particles were higher than those of β-TCP granules in vitro. The connectivity of intergranular pores 100, 300, and 400 μm in size were higher in Tetrabones than in the β-TCP granules. Tetrabones showed similar osteoconductivity and biomechanical stiffness to β-TCP at 2 months after implantation in an in vivo study of canine bone defects. These results suggest that Tetrabones may be a good bone graft material in bone reconstruction.

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.

Calcium orthophosphates: occurrence, properties, biomineralization, pathological calcification and biomimetic applications

The present overview is intended to point the readers' attention to the important subject of calcium orthophosphates. This type of materials is of special significance for human beings, because they represent the inorganic part of major normal (bones, teeth and antlers) and pathological (i.e., those appearing due to various diseases) calcified tissues of mammals. For example, atherosclerosis results in blood vessel blockage caused by a solid composite of cholesterol with calcium orthophosphates, while dental caries and osteoporosis mean a partial decalcification of teeth and bones, respectively, that results in replacement of a less soluble and harder biological apatite by more soluble and softer calcium hydrogenphosphates. Therefore, the processes of both normal and pathological calcifications are just an in vivo crystallization of calcium orthophosphates. Similarly, dental caries and osteoporosis might be considered an in vivo dissolution of calcium orthophosphates. Thus, calcium orthophosphates hold a great significance for humankind, and in this paper, an overview on the current knowledge on this subject is provided.

Calcium orthophosphates as bioceramics: state of the art

In the late 1960s, much interest was raised in regard to biomedical applications of various ceramic materials. A little bit later, such materials were named bioceramics. This review is limited to bioceramics prepared from calcium orthophosphates only, which belong to the categories of bioactive and bioresorbable compounds. There have been a number of important advances in this field during the past 30-40 years. Namely, by structural and compositional control, it became possible to choose whether calcium orthophosphate bioceramics were biologically stable once incorporated within the skeletal structure or whether they were resorbed over time. At the turn of the millennium, a new concept of calcium orthophosphate bioceramics-which is able to promote regeneration of bones-was developed. Presently, calcium orthophosphate bioceramics are available in the form of particulates, blocks, cements, coatings, customized designs for specific applications and as injectable composites in a polymer carrier. Current biomedical applications include artificial replacements for hips, knees, teeth, tendons and ligaments, as well as repair for periodontal disease, maxillofacial reconstruction, augmentation and stabilization of the jawbone, spinal fusion and bone fillers after tumor surgery. Exploratory studies demonstrate potential applications of calcium orthophosphate bioceramics as scaffolds, drug delivery systems, as well as carriers of growth factors, bioactive peptides and/or various types of cells for tissue engineering purposes.

Bioceramics of calcium orthophosphates

A strong interest in use of ceramics for biomedical applications appeared in the late 1960's. Used initially as alternatives to metals in order to increase a biocompatibility of implants, bioceramics have become a diverse class of biomaterials, presently including three basic types: relatively bioinert ceramics, bioactive (or surface reactive) and bioresorbable ones. Furthermore, any type of bioceramics could be porous to provide tissue ingrowth. This review is devoted to bioceramics prepared from calcium orthophosphates, which belong to the categories of bioresorbable and bioactive compounds. During the past 30-40 years, there have been a number of major advances in this field. Namely, after the initial work on development of bioceramics that was tolerated in the physiological environment, emphasis was shifted towards the use of bioceramics that interacted with bones by forming a direct chemical bond. By the structural and compositional control, it became possible to choose whether the bioceramics of calcium orthophosphates was biologically stable once incorporated within the skeletal structure or whether it was resorbed over time. At the turn of the millennium, a new concept of calcium orthophosphate bioceramics, which is able to regenerate bone tissues, has been developed. Current biomedical applications of calcium orthophosphate bioceramics include replacements for hips, knees, teeth, tendons and ligaments, as well as repair for periodontal disease, maxillofacial reconstruction, augmentation and stabilization of the jawbone, spinal fusion and bone fillers after tumor surgery. Potential future applications of calcium orthophosphate bioceramics will include drug-delivery systems, as well as they will become effective carriers of growth factors, bioactive peptides and/or various types of cells for tissue engineering purposes.