Dicalcium phosphate cements: brushite and monetite

The Effects of Crystal Phase and Particle Morphology of Calcium Phosphates on Proliferation and Differentiation of Human Mesenchymal Stromal Cells

Calcium phosphate (CaP) ceramics are extensively used for bone regeneration; however, their clinical performance is still considered inferior to that of patient's own bone. To improve the performance of CaP bone graft substitutes, it is important to understand the effects of their individual properties on a biological response. The aim of this study is to investigate the effects of the crystal phase and particle morphology on the behavior of human mesenchymal stromal cells (hMSCs). To study the effect of the crystal phase, brushite, monetite, and octacalcium phosphate (OCP) are produced by controlling the precipitation conditions. Brushite and monetite are produced as plate-shaped and as needle-shaped particles, to further investigate the effect of particle morphology. Proliferation of hMSCs is inhibited on OCP as compared to brushite and monetite in either morphology. Brushite needles consistently show the lowest expression of most osteogenic markers, whereas the expression on OCP is in general high. There is a trend toward a higher expression of the osteogenic markers on plate-shaped than on needle-shaped particles for both brushite and monetite. Within the limits of CaP precipitation, these data indicate the effect of both crystal phase and particle morphology of CaPs on the behavior of hMSCs.

Controlling Bone Graft Substitute Microstructure to Improve Bone Augmentation

Vertical bone augmentation procedures are frequently carried out to allow successful placement of dental implants in otherwise atrophic ridges and represent one of the most common bone grafting procedures currently performed. Onlay autografting is one of the most prevalent and predictable techniques to achieve this; however, there are several well documented complications and drawbacks associated with it and synthetic alternatives are being sought. Monetite is a bioresorbable dicalcium phosphate with osteoconductive and osteoinductive potential that has been previously investigated for onlay bone grafting and it is routinely made by autoclaving brushite to simultaneously sterilize and phase convert. In this study, monetite disc-shaped grafts are produced by both wet and dry heating methods which alter their physical properties such as porosity, surface area, and mechanical strength. Histological observations after 12 weeks of onlay grafting on rabbit calvaria reveal higher bone volume (38%) in autoclaved monetite grafts in comparison with the dry heated monetite grafts (26%). The vertical bone height gained is similar for both the types of monetite grafts (up to 3.2 mm). However, it is observed that the augmented bone height is greater in the lateral than the medial areas of both types of monetite grafts. It is also noted that the higher porosity of autoclaved monetite grafts increases the bioresorbability, whereas the dry heated monetite grafts having lower porosity but higher surface area resorb to a significantly lesser extent. This study provides information regarding two types of monetite onlay grafts prepared with different physical properties that can be further investigated for clinical vertical bone augmentation applications.

Characterization of alginate-brushite in-situ hydrogel composites

In the present study alginate-brushite composite hydrogels were in-situ synthetized and characterized with respect to preparation parameters. Specifically, the influence of initial pH value and initial concentration of phosphate precursor on the in-situ fabrication of the composite hydrogel were taken into account. The composite hydrogels were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), thermogravimetric (TGA, DTG) and differential thermal analysis (DTA). Finally, the cell viability tests were carried out (MTT) over the incubation time period of 3, 7, and 14days. The results revealed that the formation and the crystalline stability of brushite were highly dependent on the initial pH value. It was shown that as the pH reached to the value of 6, characteristics peaks of brushite appeared in the FTIR spectra. Besides, the XRD and thermal analysis results were in a good accordance with those of FTIR. In addition, the SEM images demonstrated that the plate like brushite was formed inside the alginate matrix. Also, a considerable impact of pH variation on the biocompatibility of samples was noticed so that the majority of samples especially those prepared in the acidic conditions were toxic.

Simvastatin-doped pre-mixed calcium phosphate cement inhibits osteoclast differentiation and resorption

Simvastatin, a cholesterol lowering drug, has been shown to have positive effects on fracture healing and bone regeneration based on its dual effect; bone anabolic and anti-resorptive. In this study the focus has been on the anti-resorptive effect of the drug and its impact on the degradation of acidic calcium phosphate cement. The drug was added to the pre-mixed acidic cement in three different doses (0.1, 0.25 and 0.5 mg/g cement) and the release was measured. Furthermore the effect of the loaded cements on osteoclast differentiation and resorption was evaluated by TRAP activity, number of multinucleated cells, gene expression and calcium ion concentration in vitro using murine bone marrow macrophages. The simvastatin did not affect the cell proliferation while it clearly inhibited osteoclastic differentiation at all three doses as shown by TRAP staining, TRAP activity and gene expression. Consistent with these results, simvastatin also impaired resorption of cements by osteoclasts as indicated by reduced calcium ion concentrations. In conclusion, our findings suggest that simvastatin-doped pre-mixed acidic calcium phosphate cement inhibits the osteoclastic mediated resorption of the cement thus slowing down the degradation rate. In addition with simvastatin's bone anabolic effect it makes the cement-drug combination a promising bone graft material, especially useful for sites with compromised bone formation.

Silver-Doped Calcium Phosphate Bone Cements with Antibacterial Properties

Calcium phosphate bone cements (CPCs) with antibacterial properties are demanded for clinical applications. In this study, we demonstrated the use of a relatively simple processing route based on preparation of silver-doped CPCs (CPCs-Ag) through the preparation of solid dispersed active powder phase. Real-time monitoring of structural transformations and kinetics of several CPCs-Ag formulations (Ag = 0 wt %, 0.6 wt % and 1.0 wt %) was performed by the Energy Dispersive X-ray Diffraction technique. The partial conversion of β-tricalcium phosphate (TCP) phase into the dicalcium phosphate dihydrate (DCPD) took place in all the investigated cement systems. In the pristine cement powders, Ag in its metallic form was found, whereas for CPC-Ag 0.6 wt % and CPC-Ag 1.0 wt % cements, CaAg(PO₃)₃ was detected and Ag (met.) was no longer present. The CPC-Ag 0 wt % cement exhibited a compressive strength of 6.5 ± 1.0 MPa, whereas for the doped cements (CPC-Ag 0.6 wt % and CPC-Ag 1.0 wt %) the reduced values of the compressive strength 4.0 ± 1.0 and 1.5 ± 1.0 MPa, respectively, were detected. Silver-ion release from CPC-Ag 0.6 wt % and CPC-Ag 1.0 wt % cements, measured by the Atomic Emission Spectroscopy, corresponds to the average values of 25 µg/L and 43 µg/L, respectively, rising a plateau after 15 days. The results of the antibacterial test proved the inhibitory effect towards pathogenic Escherichia coli for both CPC-Ag 0.6 wt % and CPC-Ag 1.0 wt % cements, better performances being observed for the cement with a higher Ag-content.

Gelatine modified monetite as a bone substitute material: An in vitro assessment of bone biocompatibility

Calcium phosphate phases are increasingly used for bone tissue substitution, and the load bearing properties of these inherently brittle biomaterials are increased by inclusion of organic components. Monetite prepared using mineralization of gelatine pre-structured through phosphate leads to a significantly increased biaxial strength and indirect tensile strength compared to gelatine-free monetite. Besides the mechanical properties, degradation in physiological solutions and osteoblast and osteoclast cell response were investigated. Human bone marrow stromal cells (hBMSCs) showed considerably higher proliferation rates on the gelatine modified monetite than on polystyrene reference material in calcium-free as well as standard cell culture medium (α-MEM). Osteogenic differentiation on the material was comparable to polystyrene in both medium types. Osteoclast-like cells derived from monocytes were able to actively resorb the biomaterial. Osteoblastic differentiation and perhaps even more important the cellular resorption of the biomaterial indicate that it can be actively involved in the bone remodeling process. Thus the behavior of osteoblasts and osteoclasts as well as the adequate degradation and mechanical properties are strong indicators for bone biocompatibility, although in vivo studies are still required to prove this.

STATEMENT OF SIGNIFICANCE

New and unique? A low temperature precipitationprocessforcalcium anhydrous hydrogen phosphateallows for the first time to produce monolithic compact composites of monetite and gelatine. The composite is degradable and resorbable. To prove that, the question arises: what is bone biocompatibility? The reaction of both mayor cell types of bone represents this biocompatibility. Therefore, human bone marrow stromal cells were seeded revealing the materials pro-osteogenic properties. Monocyte cultivation, becoming recently focus of interest, revealed the capability of the biomaterial to be actively resorbed by derived osteoclast-like cells. Not new but necessary ismechanical characterization, which is often only investigated as uniaxial property. Here, a biaxial method is applied, to characterize the materials properties closer to its application loads.

Strength reliability and in vitro degradation of three-dimensional powder printed strontium-substituted magnesium phosphate scaffolds

Strontium ions (Sr(2+)) are known to prevent osteoporosis and also encourage bone formation. Such twin requirements have motivated researchers to develop Sr-substituted biomaterials for orthopaedic applications. The present study demonstrates a new concept of developing Sr-substituted Mg3(PO4)2 - based biodegradable scaffolds. In particular, this work reports the fabrication, mechanical properties with an emphasis on strength reliability as well as in vitro degradation of highly biodegradable strontium-incorporated magnesium phosphate cements. These implantable scaffolds were fabricated using three-dimensional powder printing, followed by high temperature sintering and/or chemical conversion, a technique adaptable to develop patient-specific implants. A moderate combination of strength properties of 36.7MPa (compression), 24.2MPa (bending) and 10.7MPa (tension) were measured. A reasonably modest Weibull modulus of up to 8.8 was recorded after uniaxial compression or diametral tensile tests on 3D printed scaffolds. A comparison among scaffolds with varying compositions or among sintered or chemically hardened scaffolds reveals that the strength reliability is not compromised in Sr-substituted scaffolds compared to baseline Mg3(PO4)2. The micro-computed tomography analysis reveals the presence of highly interconnected porous architecture in three-dimension with lognormal pore size distribution having median in the range of 17.74-26.29μm for the investigated scaffolds. The results of extensive in vitro ion release study revealed passive degradation with a reduced Mg(2+) release and slow but sustained release of Sr(2+) from strontium-substituted magnesium phosphate scaffolds. Taken together, the present study unequivocally illustrates that the newly designed Sr-substituted magnesium phosphate scaffolds with good strength reliability could be used for biomedical applications requiring consistent Sr(2+)- release, while the scaffold degrades in physiological medium.

STATEMENT OF SIGNIFICANCE

The study investigates the additive manufacturing of scaffolds based on different strontium-substituted magnesium phosphate bone cements by means of three-dimensional powder printing technique (3DPP). Magnesium phosphates were chosen due to their higher biodegradability compared to calcium phosphates, which is due to both a higher solubility as well as the absence of phase changes (to low soluble hydroxyapatite) in vivo. Since strontium ions are known to promote bone formation by stimulating osteoblast growth, we aimed to establish such a highly degradable magnesium phosphate ceramic with an enhanced bioactivity for new bone ingrowth. After post-processing, mechanical strengths of up to 36.7MPa (compression), 24.2MPa (bending) and 10.7MPa (tension) could be achieved. Simultaneously, the failure reliability of those bioceramic implant materials, measured by Weibull modulus calculations, were in the range of 4.3-8.8. Passive dissolution studies in vitro proved an ion release of Mg(2+) and PO4(3-) as well as Sr(2+), which is fundamental for in vivo degradation and a bone growth promoting effect. In our opinion, this work broadens the range of bioceramic bone replacement materials suitable for additive manufacturing processing. The high biodegradability of MPC ceramics together with the anticipated promoting effect on osseointegration opens up the way for a patient-specific treatment with the prospect of a fast and complete healing of bone fractures.

Adsorption of malathion on mesoporous monetite obtained by mechanochemical treatment of brushite

Synthesis of mesoporous monetite by mechanochemical treatment brushite.

Surface micropatterning with zirconia and calcium phosphate ceramics by micromoulding in capillaries

Micropatterning of silicon surface with bioinert yttria-stabilised zirconia or bioactive calcium phosphate ceramic by micromoulding in capillaries.

Synthesis of calcium phosphate crystals with thin nacreous structure

Calcium phospate crystals with a thin nacreous structure were synthesized and characterized.

Effects of Silicon on Osteoclast Cell Mediated Degradation, In Vivo Osteogenesis and Vasculogenesis of Brushite Cement

Calcium phosphate cements (CPCs) are being widely used for treating small scale bone defects. Among the various CPCs, brushite (dicalcium phosphate dihydrate, DCPD) cement is widely used due to its superior solubility and ability to form new bone. In the present study, we have studied the physical, mechanical, osteoclast-like-cells differentiation and in vivo osteogenic and vasculogenic properties of silicon (Si) doped brushite cements. Addition of Si did not alter the phase composition of final product and regardless of Si level, all samples included β-tricalcium phosphate (β-TCP) and DCPD. 1.1 wt. % Si addition increased the compressive strength of undoped brushite cement from 4.78±0.21 MPa to 5.53±0.53 MPa, significantly. Cellular activity was studied using receptor activator of nuclear factor κβ ligand (RANKL) supplemented osteoclast-like-cells precursor RAW 264.7 cell. Phenotypic expressions of the cells confirmed successful differentiation of RAW264.7 monocytes to osteoclast-like-cells on undoped and doped brushite cements. An increased activity of osteoclast-like cells was noticed due to Si doping in the brushite cement. An excellent new bone formation was found in all cement compositions, with significant increase in Si doped brushite samples as early as 4 weeks post implantation in rat femoral model. After 4 weeks of implantation, no significant difference was found in blood vessel formation between the undoped and doped cements, however, a significant increase in vasculgenesis was found in 0.8 and 1.1 wt. % Si doped brushite cements after 8 weeks. These results show the influence of Si dopant on physical, mechanical, in vitro osteoclastogenesis and in vivo osteogenic and vasculogenic properties of brushite cements.

Mesoporous calcium phosphate bionanomaterials with controlled morphology by an energy-efficient microwave method

Calcium phosphate nanomaterials with controllable morphology and mesostructure were synthesized via a rapid and energy efficient microwave method. An increase in aspect ratio from nanoplates to nanorods was achieved by increasing the solvent chain length, accompanied by a subsequent about 23% increase in surface area and porosity. Control of mesoporosity was also achieved by varying the synthesis time and quantity of H2 O in the reaction solvent. Comparative studies were carried out using conventional heating (CON) and room temperature co-precipitation (RT) methods. It was found that microwave synthesis produces nanomaterials with about 50% higher yields, 7.5/1.7 times higher surface area and 3/5 times higher pore volume than RT/CON materials respectively, as well as having a lower distribution of particle size/shape (lower standard deviation values of their dimensions). Furthermore, in vitro protein loading tests of microwave synthesized mesoporous calcium phosphate materials showed an enhanced loading efficiency of bovine serum albumin (3-7 times), as compared with non-mesostructured products from room temperature precipitation, in accordance with their larger surface area and porosity.

Mechanisms of in Vivo Degradation and Resorption of Calcium Phosphate Based Biomaterials

Calcium phosphate ceramic materials are extensively used for bone replacement and regeneration in orthopedic, dental, and maxillofacial surgical applications. In order for these biomaterials to work effectively it is imperative that they undergo the process of degradation and resorption in vivo. This allows for the space to be created for the new bone tissue to form and infiltrate within the implanted graft material. Several factors affect the biodegradation and resorption of calcium phosphate materials after implantation. Various cell types are involved in the degradation process by phagocytic mechanisms (monocytes/macrophages, fibroblasts, osteoblasts) or via an acidic mechanism to reduce the micro-environmental pH which results in demineralization of the cement matrix and resorption via osteoclasts. These cells exert their degradation effects directly or indirectly through the cytokine growth factor secretion and their sensitivity and response to these biomolecules. This article discusses the mechanisms of calcium phosphate material degradation in vivo.

IGF-loaded silicon and zinc doped brushite cement: physico-mechanical characterization and in vivo osteogenesis evaluation

Dopants play critical roles in controlling the physical, mechanical, degradation kinetics, and in vivo properties of calcium phosphates. The aim of the present study was to evaluate the effects of silicon (Si) and zinc (Zn) dopants on the physico-mechanical and in vivo osteogenesis properties of brushite cements (BrCs) alone and in combination with insulin like growth factor 1 (IGF-1). Addition of 0.5 wt% Si did not alter the setting time, β-TCP content, and compressive strength of BrCs significantly; however, 0.25 wt% Zn incorporation was accompanied by a significant decrease in mechanical strength from 4.78 ± 0.21 MPa for pure BrC to 3.78 ± 0.59 MPa and 3.28 ± 0.22 MPa for Zn-BrC and Si/Zn-BrC, respectively. The in vivo bone regeneration properties of doped BrCs alone and in combination with IGF-1 were assessed and compared using chronological radiography, histology, scanning electron microscopy and fluorochrome labeling at 2 and 4 months post implantation in a rabbit femoral defect model. Based on in vivo characterization focusing on osteogenesis and vasculogenesis, Si-BrC and Si/Zn-BrC showed the best performance followed by Zn-BrC and pure BrCs. Addition of IGF-1 further improved bone regeneration. Our findings confirm that addition of Si and/or Zn alters the physico-mechanical properties of BrCs and promotes the early stage in vivo osseointegration and bone remodeling properties.

Fabrication of Poly-l-lactic Acid/Dicalcium Phosphate Dihydrate Composite Scaffolds with High Mechanical Strength-Implications for Bone Tissue Engineering

Scaffolds were fabricated from poly-l-lactic acid (PLLA)/dicalcium phosphate dihydrate (DCPD) composite by indirect casting. Sodium citrate and PLLA were used to improve the mechanical properties of the DCPD scaffolds. The resulting PLLA/DCPD composite scaffold had increased diametral tensile strength and fracture energy when compared to DCPD only scaffolds (1.05 vs. 2.70 MPa and 2.53 vs. 12.67 N-mm, respectively). Sodium citrate alone accelerated the degradation rate by 1.5 times independent of PLLA. Cytocompatibility of all samples were evaluated using proliferation and differentiation parameters of dog-bone marrow stromal cells (dog-BMSCs). The results showed that viable dog-BMSCs attached well on both DCPD and PLLA/DCPD composite surfaces. In both DCPD and PLLA/DCPD conditioned medium, dog-BMSCs proliferated well and expressed alkaline phosphatase (ALP) activity indicating cell differentiation. These findings indicate that incorporating both sodium citrate and PLLA could effectively improve mechanical strength and biocompatibility without increasing the degradation time of calcium phosphate cement scaffolds for bone tissue engineering purposes.

Toward accelerated bone regeneration by altering poly(D,L-lactic-co-glycolic) acid porogen content in calcium phosphate cement

This work aimed to compare in vitro degradation of dense PLGA microspheres and milled PLGA particles as porogens within CPC, considering that the manufacturing of milled PLGA is more cost-effective when compared with PLGA microspheres. Additionally, we aimed to examine the effect of porogen amount within CPC/PLGA on degradation and bone formation. Our in vitro results showed no differences between both forms of PLGA particles (as porogens in CPC; spherical for microspheres, irregular for milled) regarding morphology, porosity, and degradation. Using milled PLGA as porogens within CPC/PLGA, we evaluated the effect of porogen amount on degradation and bone forming capacity in vivo. Titanium landmarks surrounded by CPC/PLGA with 30 and 50 wt % PLGA, were implanted in forty femoral bone defects of twenty male Wistar rats. Histomorphometrical results showed a significant temporal decrease in the amount of CPC, for both formulas, and confirmed that 50 wt % PLGA degrades faster than 30 wt%, and allows for a 1.5-fold higher amount of newly formed bone. Taken together, this study demonstrated that (i) milled PLGA particles perform equal to PLGA microspheres, and (ii) tuning of the PLGA content in CPC/PLGA is a feasible approach to leverage material degradation and bone formation.

Long-Term In Vitro Degradation of a High-Strength Brushite Cement in Water, PBS, and Serum Solution

Bone loss and fractures may call for the use of bone substituting materials, such as calcium phosphate cements (CPCs). CPCs can be degradable, and, to determine their limitations in terms of applications, their mechanical as well as chemical properties need to be evaluated over longer periods of time, under physiological conditions. However, there is lack of data on how the in vitro degradation affects high-strength brushite CPCs over longer periods of time, that is, longer than it takes for a bone fracture to heal. This study aimed at evaluating the long-term in vitro degradation properties of a high-strength brushite CPC in three different solutions: water, phosphate buffered saline, and a serum solution. Microcomputed tomography was used to evaluate the degradation nondestructively, complemented with gravimetric analysis. The compressive strength, chemical composition, and microstructure were also evaluated. Major changes from 10 weeks onwards were seen, in terms of formation of a porous outer layer of octacalcium phosphate on the specimens with a concomitant change in phase composition, increased porosity, decrease in object volume, and mechanical properties. This study illustrates the importance of long-term evaluation of similar cement compositions to be able to predict the material's physical changes over a relevant time frame.

In vitro degradation and in vivo resorption of dicalcium phosphate cement based grafts

There are two types of DCP: dihydrated (brushite) and anhydrous (monetite). After implantation, brushite converts to hydroxyapatite (HA) which resorbs very slowly. This conversion is not observed after implantation of monetite cements and result in a greater of resorption. The precise mechanisms of resorption and degradation however of these ceramics remain uncertain. This study was designed to investigate the effect of: porosity, surface area and hydration on in vitro degradation and in vivo resorption of DCP. Brushite and two types of monetite cement based grafts (produced by wet and dry thermal conversion) were aged in phosphate buffered saline (PBS) and bovine serum solutions in vitro and were implanted subcutaneously in rats. Here we show that for high relative porosity grafts (50-65%), solubility and surface area does not play a significant role towards in vitro mass loss with disintegration and fragmentation being the main factors dictating mass loss. For grafts having lower relative porosity (35-45%), solubility plays a more crucial role in mass loss during in vitro ageing and in vivo resorption. Also, serum inhibited dissolution and the formation of HA in brushite cements. However, when aged in PBS, brushite undergoes phase conversion to a mixture of octacalcium phosphate (OCP) and HA. This phase conversion was not observed for monetite upon ageing (in both serum and PBS) or in subcutaneous implantation. This study provides greater understanding of the degradation and resorption process of DCP based grafts, allowing us to prepare bone replacement materials with more predictable resorption profiles.

Fabrication of interconnected pore forming α-tricalcium phosphate foam granules cement

Interconnected pore forming calcium phosphate cement is useful for the reconstruction of bone defects as well as scaffold fabrication in tissue engineering. In this study, interconnected pore forming calcium phosphate cement was fabricated using α-tricalcium phosphate (α-TCP) foam granules. When α-TCP foam granules were mixed with acidic calcium phosphate solution prepared from monocalcium phosphate monohydrate (MCPM) and phosphoric acid solution, brushite crystals were precipitated. These crystals bridged the α-TCP foam granules immediately upon mixing. As a result of the brushite bridge between the α-TCP foam granules, fully interconnected macroporous α-TCP was obtained. The amount of brushite precipitate and the mechanical strength of the set cement increased with acidic calcium phosphate concentration.

Biodegradable Materials for Bone Repair and Tissue Engineering Applications

This review discusses and summarizes the recent developments and advances in the use of biodegradable materials for bone repair purposes. The choice between using degradable and non-degradable devices for orthopedic and maxillofacial applications must be carefully weighed. Traditional biodegradable devices for osteosynthesis have been successful in low or mild load bearing applications. However, continuing research and recent developments in the field of material science has resulted in development of biomaterials with improved strength and mechanical properties. For this purpose, biodegradable materials, including polymers, ceramics and magnesium alloys have attracted much attention for osteologic repair and applications. The next generation of biodegradable materials would benefit from recent knowledge gained regarding cell material interactions, with better control of interfacing between the material and the surrounding bone tissue. The next generations of biodegradable materials for bone repair and regeneration applications require better control of interfacing between the material and the surrounding bone tissue. Also, the mechanical properties and degradation/resorption profiles of these materials require further improvement to broaden their use and achieve better clinical results.

Macrophages, Foreign Body Giant Cells and Their Response to Implantable Biomaterials

All biomaterials, when implanted in vivo, elicit cellular and tissue responses. These responses include the inflammatory and wound healing responses, foreign body reactions, and fibrous encapsulation of the implanted materials. Macrophages are myeloid immune cells that are tactically situated throughout the tissues, where they ingest and degrade dead cells and foreign materials in addition to orchestrating inflammatory processes. Macrophages and their fused morphologic variants, the multinucleated giant cells, which include the foreign body giant cells (FBGCs) are the dominant early responders to biomaterial implantation and remain at biomaterial-tissue interfaces for the lifetime of the device. An essential aspect of macrophage function in the body is to mediate degradation of bio-resorbable materials including bone through extracellular degradation and phagocytosis. Biomaterial surface properties play a crucial role in modulating the foreign body reaction in the first couple of weeks following implantation. The foreign body reaction may impact biocompatibility of implantation devices and may considerably impact short- and long-term success in tissue engineering and regenerative medicine, necessitating a clear understanding of the foreign body reaction to different implantation materials. The focus of this review article is on the interactions of macrophages and foreign body giant cells with biomaterial surfaces, and the physical, chemical and morphological characteristics of biomaterial surfaces that play a role in regulating the foreign body response. Events in the foreign body response include protein adsorption, adhesion of monocytes/macrophages, fusion to form FBGCs, and the consequent modification of the biomaterial surface. The effect of physico-chemical cues on macrophages is not well known and there is a complex interplay between biomaterial properties and those that result from interactions with the local environment. By having a better understanding of the role of macrophages in the tissue healing processes, especially in events that follow biomaterial implantation, we can design novel biomaterials-based tissue-engineered constructs that elicit a favorable immune response upon implantation and perform for their intended applications.

The effect of water on the mechanical properties of soluble and insoluble ceramic cements

Ceramic cements are good candidates for the stabilization of fractured bone due to their potential ease of application and biological advantages. New formulations of ceramic cements have been tested for their mechanical properties, including strength, stiffness, toughness and durability. The changes in the mechanical properties of a soluble cement (calcium sulfate) upon water-saturation (saturation) was reported in our previous study, highlighting the need to test ceramic cements using saturated samples. It is not clear if the changes in the mechanical properties of ceramic cements are exclusive to soluble cements. Therefore the aim of the present study was to observe the changes in the mechanical properties of soluble and insoluble ceramic cements upon saturation. A cement with high solubility (calcium sulfate dihydrate, CSD) and a cement with low solubility (dicalcium phosphate dihydrate, DCPD) were tested. Three-point bending tests were performed on four different groups of: saturated CSD, non-saturated CSD, saturated DCPD, and non-saturated DCPD samples. X-ray diffraction analysis and scanning electron microscopy were also performed on a sample from each group. Flexural strength, effective flexural modulus and flexural strain at maximum stress, lattice volume, and crystal sizes and shape were compared, independently, between saturated and non-saturated groups of CSD and DCPD. Although material dissolution did not occur in all cases, all calculated mechanical properties decreased significantly in both CSD and DCPD upon saturation. The results indicate that the reductions in the mechanical properties of saturated ceramic cements are not dependent on the solubility of a ceramic cement. The outcome raised the importance of testing any implantable ceramic cements in saturated condition to estimate its in vivo mechanical properties.

Dendritic Glycopolymer as Drug Delivery System for Proteasome Inhibitor Bortezomib in a Calcium Phosphate Bone Cement: First Steps Toward a Local Therapy of Osteolytic Bone Lesions

Establishment of drug delivery system (DDS) in bone substitute materials for local treatment of bone defects still requires ambitious solutions for a retarded drug release. We present two novel DDS, a weakly cationic dendritic glycopolymer and a cationic polyelectrolyte complex, composed of dendritic glycopolymer and cellulose sulfate, for the proteasome inhibitor bortezomib. Both DDS are able to induce short-term retarded release of bortezomib from calcium phosphate bone cement in comparison to a burst-release of the drug from bone cement alone. Different release parameters have been evaluated to get a first insight into the release mechanism from bone cements. In addition, biocompatibility of the calcium phosphate cement, modified with the new DDS was investigated using human mesenchymal stromal cells.

Bone Replacement Materials and Techniques Used for Achieving Vertical Alveolar Bone Augmentation

Alveolar bone augmentation in vertical dimension remains the holy grail of periodontal tissue engineering. Successful dental implant placement for restoration of edentulous sites depends on the quality and quantity of alveolar bone available in all spatial dimensions. There are several surgical techniques used alone or in combination with natural or synthetic graft materials to achieve vertical alveolar bone augmentation. While continuously improving surgical techniques combined with the use of auto- or allografts provide the most predictable clinical outcomes, their success often depends on the status of recipient tissues. The morbidity associated with donor sites for auto-grafts makes these techniques less appealing to both patients and clinicians. New developments in material sciences offer a range of synthetic replacements for natural grafts to address the shortcoming of a second surgical site and relatively high resorption rates. This narrative review focuses on existing techniques, natural tissues and synthetic biomaterials commonly used to achieve vertical bone height gain in order to successfully restore edentulous ridges with implant-supported prostheses.

Reinforcement Strategies for Load-Bearing Calcium Phosphate Biocements

Calcium phosphate biocements based on calcium phosphate chemistry are well-established biomaterials for the repair of non-load bearing bone defects due to the brittle nature and low flexural strength of such cements. This article features reinforcement strategies of biocements based on various intrinsic or extrinsic material modifications to improve their strength and toughness. Altering particle size distribution in conjunction with using liquefiers reduces the amount of cement liquid necessary for cement paste preparation. This in turn decreases cement porosity and increases the mechanical performance, but does not change the brittle nature of the cements. The use of fibers may lead to a reinforcement of the matrix with a toughness increase of up to two orders of magnitude, but restricts at the same time cement injection for minimal invasive application techniques. A novel promising approach is the concept of dual-setting cements, in which a second hydrogel phase is simultaneously formed during setting, leading to more ductile cement–hydrogel composites with largely unaffected application properties.

A mini-review on novel intraperiodontal pocket drug delivery materials for the treatment of periodontal diseases

Periodontal disease is defined as chronic inflammatory condition characterized by the destruction of the periodontal tissues causing loss of connective tissue attachment, loss of alveolar bone, and the formation of pathological pockets around the diseased teeth. The use of systemic antibiotics has been advocated for its treatment, but concerns emerged with respect to adverse drug reactions and its contribution to bacterial resistance. Thus local drug delivery devices have been developed that aim to deliver a high concentration of antimicrobial drugs directly to the affected site, while minimizing drug's systemic exposure. A burst release of antimicrobial agent from carrier, resulting in a short and inadequate exposure of bacteria residing in periodontal pocket to the agent, remains the main challenge of current local delivery systems for the treatment of periodontal disease. This review aims to investigate and compare different local antimicrobial delivery systems with regard to the treatment of periodontal disease.

Bone Regeneration Using Bone Morphogenetic Proteins and Various Biomaterial Carriers

Trauma and disease frequently result in fractures or critical sized bone defects and their management at times necessitates bone grafting. The process of bone healing or regeneration involves intricate network of molecules including bone morphogenetic proteins (BMPs). BMPs belong to a larger superfamily of proteins and are very promising and intensively studied for in the enhancement of bone healing. More than 20 types of BMPs have been identified but only a subset of BMPs can induce de novo bone formation. Many research groups have shown that BMPs can induce differentiation of mesenchymal stem cells and stem cells into osteogenic cells which are capable of producing bone. This review introduces BMPs and discusses current advances in preclinical and clinical application of utilizing various biomaterial carriers for local delivery of BMPs to enhance bone regeneration.

Resorption of monetite calcium phosphate cement by mouse bone marrow derived osteoclasts

Recently the interest for monetite based biomaterials as bone grafts has increased; since in vivo studies have demonstrated that they are degradable, osteoconductive and improve bone healing. So far osteoclastic resorption of monetite has received little attention. The current study focuses on the osteoclastic resorption of monetite cement using primary mouse bone marrow macrophages, which have the potential to differentiate into resorbing osteoclasts when treated with receptor activator NF-κB ligand (RANKL). The osteoclast viability and differentiation were analysed on monetite cement and compared to cortical bovine bone discs. After seven days live/dead stain results showed no significant difference in viability between the two materials. However, the differentiation was significantly higher on the bone discs, as shown by tartrate resistant acid phosphatase (TRAP) activity and Cathepsin K gene expression. Moreover monetite samples with differentiated osteoclasts had a 1.4 fold elevated calcium ion concentration in their culture media compared to monetite samples with undifferentiated cells. This indicates active resorption of monetite in the presence of osteoclasts. In conclusion, this study suggests that osteoclasts have a crucial role in the resorption of monetite based biomaterials. It also provides a useful model for studying in vitro resorption of acidic calcium phosphate cements by primary murine cells.

Development of nanosilica bonded monetite cement from egg shells

This work represents further effort from our group in developing monetite based calcium phosphate cements (CPC). These cements start with a calcium phosphate powder (MW-CPC) that is manufactured using microwave irradiation. Due to the robustness of the cement production process, we report that the starting materials can be derived from egg shells, a waste product from the poultry industry. The CPC were prepared with MW-CPC and aqueous setting solution. Results showed that the CPC hardened after mixing powdered cement with water for about 12.5±1 min. The compressive strength after 24h of incubation was approximately 8.45±1.29 MPa. In addition, adding colloidal nanosilica to CPC can accelerate the cement hardening (10±1 min) process by about 2.5 min and improve compressive strength (20.16±4.39 MPa), which is more than double the original strength. The interaction between nanosilica and CPC was monitored using an environmental scanning electron microscope (ESEM). While hardening, nanosilica can bond to the CPC crystal network for stabilization. The physical and biological studies performed on both cements suggest that they can potentially be used in orthopedics.

A novel chlorhexidine-releasing composite bone cement: Characterization of antimicrobial effectiveness and cement strength

The addition of calcium phosphate fillers or antimicrobials to bone cements seems to produce inferior materials. In this study, a two-solution bone cement composite was designed for high viscosity and high pseudoplasticity to improve injection and mitigate the risk of extravasation. By pre-mixing these cements, the fillers are incorporated into the matrix and should not detrimentally affect the performance properties. To expand the functionality of this cement system, the addition of bioactive and antimicrobial phases were explored. Brushite and chlorhexidine were used as calcium phosphate filler and the antimicrobial phase, respectively. By controlling the free radical quenching mechanism provided by the chlorhexidine molecule, it was possible to achieve high polymer conversion rates. This phenomenon led to cement strength retention while successfully preventing microbial proliferation in an environment exposed to the cement surface. Based on these results, two-solution cement composite prepared with high concentrations of brushite and chlorhexidine diacetate salt hydrate may provide an attractive bioactive and antimicrobial cement for load-bearing applications.

Induction suspension plasma sprayed biological-like hydroxyapatite coatings

Substituted hydroxyapatite coatings with different ions (Mg, Na, K, Cl, F) have been developed by the induction suspension plasma spray process. Suspensions were prepared with sol–gel. The main objective of this study was to demonstrate that induction suspension plasma spray technology possesses high material composition flexibility that allows as-sprayed coatings to closely mimic natural bone composition. Long-term in vitro behaviour of as-sprayed substituted coatings was evaluated with simulated body fluid. Data on the suspensions showed the formation of a pure hydroxyapatite phase. Transmission electron microscopy characterized various preparation stages of the suspensions. As-sprayed samples were distinguished by X-ray diffraction and scanning electron microscopy. Substituted elements were quantified by neutron activation. A well-crystallized hydroxyapatite phase was produced with concentration in various substitutions very close to natural bone composition. Ca/P and (Ca + Mg + Na + K)/P ratios provided evidence of the introduction of different cations into apatite structures. The immersion of samples into simulated body fluid led to the nucleation and growth of a flake-like octacalcium phosphate crystal layer at the surface of as-sprayed coatings after one week. Proof of octacalcium phosphate transformation and its partial dissolution and direct re-precipitation into apatite was disclosed by local energy dispersive spectroscopy and microstructure observation. Formation of a Ca/P ratio gradient from the precipitated layer surface to the as-sprayed coatings interface was observed after four weeks once the octacalcium phosphate crystals reached a critical size, resulting in the formation of a rich apatite layer at the interface after six weeks. A set of mechanisms has been proposed to explain these findings.

Dual-setting brushite-silica gel cements

The current study describes a dual-mechanism-setting cement that combines a brushite-forming cement paste with a second inorganic silica-based precursor. Materials were obtained by pre-hydrolyzing tetraethyl orthosilicate (TEOS) under acidic conditions following the addition of a calcium phosphate cement (CPC) powder mixed of β-tricalcium phosphate and monocalcium phosphate. Cement setting occurred by a dissolution-precipitation process, while changes in pH during setting simultaneously initiated the condensation reaction of the hydrolyzed TEOS. This resulted in an interpenetrating phase composite material in which the macropores of the CPC were infiltrated by the microporous silica gel, leading to a higher density and a compressive strength ∼5-10 times higher than the CPC reference. This also altered the release of vancomycin as a model drug, whereby in contrast to the quantitative release from the CPC reference, 25% of the immobilized drug remained in the composite matrix. By varying the TEOS content in the composite, the cement phase composition could be controlled to form either brushite, anhydrous monetite or a biphasic mixture of both. The composites with the highest silicate content showed a cell proliferation similar to a hydroxyapatite reference with a significantly higher activity per cell. Surprisingly, the biological response did not seem to be attributed to the released silicate ions, but to the release of phosphate and the adsorption of magnesium ions from the cell culture medium.

Structural changes and biological responsiveness of an injectable and mouldable monetite bone graft generated by a facile synthetic method

Brushite (dicalcium phosphate dihydrate) and monetite (dicalcium phosphate anhydrous) are of considerable interest in bone augmentation owing to their metastable nature in physiological fluids. The anhydrous form of brushite, namely monetite, has a finer microstructure with higher surface area, strength and bioresorbability, which does not transform to the poorly resorbable hydroxyapatite, thus making it a viable alternative for use as a scaffold for engineering of bone tissue. We recently reported the formation of monetite cements by a simple processing route without the need of hydrothermal treatment by using a high concentration of sodium chloride in the reaction mix of β-tricalcium phosphate and monocalcium phosphate monohydrate. In this paper, we report the biological responsiveness of monetite formed by this method. The in vitro behaviour of monetite after interaction and ageing both in an acellular and cellular environment showed that the crystalline phase of monetite was retained over three weeks as evidenced from X-ray diffraction measurements. The crystal size and morphology also remained unaltered after ageing in different media. Human osteoblast cells seeded on monetite showed the ability of the cells to proliferate and express genes associated with osteoblast maturation and mineralization. Furthermore, the results showed that monetite could stimulate osteoblasts to undergo osteogenesis and accelerate osteoblast maturation earlier than cells cultured on hydroxyapatite scaffolds of similar porosity. Osteoblasts cultured on monetite cement also showed higher expression of osteocalcin, which is an indicator of the maturation stages of osteoblastogenesis and is associated with matrix mineralization and bone forming activity of osteoblasts. Thus, this new method of fabricating porous monetite can be safely used for generating three-dimensional bone graft constructs.

Control of in vivo mineral bone cement degradation

The current study aimed to prevent the formation of hydroxyapatite reprecipitates in brushite-forming biocements by minimizing the availability of free Ca(2+) ions in the cement matrix. This was achieved by both maximizing the degree of cement setting to avoid unreacted, calcium-rich cement raw materials which can deliver Ca(2+) directly to the cement matrix after dissolution, and by a reduction in porosity to reduce Ca(2+) diffusion into the set cement matrix. In addition, a biocement based on the formation of the magnesium phosphate mineral struvite (MgNH4PO4·6H2O) was tested, which should prevent the formation of low-solubility hydroxyapatite reprecipitates due to the high magnesium content. Different porosity levels were fabricated by altering the powder-to-liquid ratio at which the cements were mixed and the materials were implanted into mechanically unloaded femoral defects in sheep for up to 10 months. While the higher-porosity brushite cement quantitatively transformed into crystalline octacalcium phosphate after 10 months, slowing down cement resorption, a lower-porosity brushite cement modification was found to be chemically stable with the absence of reprecipitate formation and minor cement resorption from the implant surface. In contrast, struvite-forming cements were much more degradable due to the absence of mineral reprecipitates and a nearly quantitative cement degradation was found after 10 months of implantation.

Development of monetite-nanosilica bone cement: a preliminary study

In this paper, we reported the results of our efforts in developing DCPA/nanosilica composite orthopedic cement. It is motivated by the significances of DCPA and silicon in bone physiological activities. More specifically, this paper examined the effects of various experimental parameters on the properties of such composite cements. In this work, DCPA cement powders were synthesized using a microwave synthesis technique. Mixing colloidal nanosilica directly with synthesized DCPA cement powders can significantly reduce the washout resistance of DCPA cement. In contrast, a DCPA-nanosilica cement powder prepared by reacting Ca(OH)2 , H3 PO4 and nanosilica together showed good washout resistance. The incorporation of nanosilica in DCPA can improve compressive strength, accelerate cement solidification, and intensify surface bioactivity. In addition, it was observed that by controlling the content of NaHCO3 during cement preparation, the resulting composite cement properties could be modified. Allowing for the development of different setting times, mechanical performance and crystal features. It is suggested that DCPA-nanosilica composite cement can be a potential candidate for bone healing applications.

Calcium phosphate cements for bone substitution: chemistry, handling and mechanical properties

Since their initial formulation in the 1980s, calcium phosphate cements (CPCs) have been increasingly used as bone substitutes. This article provides an overview on the chemistry, kinetics of setting and handling properties (setting time, cohesion and injectability) of CPCs for bone substitution, with a focus on their mechanical properties. Many processing parameters, such as particle size, composition of cement reactants and additives, can be adjusted to control the setting process of CPCs, concomitantly influencing their handling and mechanical performance. Moreover, this review shows that, although the mechanical strength of CPCs is generally low, it is not a critical issue for their application for bone repair--an observation not often realized by researchers and clinicians. CPCs with compressive strengths comparable to those of cortical bones can be produced through densification and/or homogenization of the cement matrix. The real limitation for CPCs appears to be their low fracture toughness and poor mechanical reliability (Weibull modulus), which have so far been only rarely studied.

Biphasic products of dicalcium phosphate-rich cement with injectability and nondispersibility

In this study, a calcium phosphate cement was developed using tetracalcium phosphate and surface-modified dicalcium phosphate anhydrous (DCPA). This developed injectable bone graft substitute can be molded to the shape of the bone cavity and set in situ through the piping system that has an adequate mechanical strength, non-dispersibility, and biocompatibility. The materials were based on the modified DCPA compositions of calcium phosphate cement (CPC), where the phase ratio of the surface-modified DCPA is higher than that of the conventional CPC for forming dicalcium phosphate (DCP)-rich cement. The composition and morphology of several calcium phosphate cement specimens during setting were analyzed via X-ray diffractometry and transmission electron microscopy coupled with an energy dispersive spectroscopy system. The compressive strength of DCP-rich CPCs was greater than 30MPa after 24h of immersion in vitro. The reaction of the CPCs produced steady final biphasic products of DCPs with apatite. The composites of calcium phosphate cements derived from tetracalcium phosphate mixed with surface-modified DCPA exhibited excellent mechanical properties, injectability, and interlocking forces between particles, and they also featured nondispersive behavior when immersed in a physiological solution.

Self-setting bioceramic microscopic protrusions for transdermal drug delivery

Self-setting bioceramic microneedles are fabricated using a simple manufacturing procedure under mild conditions and could be substitutes for current microneedles.

Monetite and brushite coated magnesium: in vivo and in vitro models for degradation analysis

The use of magnesium (Mg) as a biodegradable metallic replacement of permanent orthopaedic materials is a current topic of interest and investigation. The appropriate biocompatibility, elastic modulus and mechanical properties of Mg recommend its suitability for bone fracture fixation. However, the degradation rates of Mg can be rapid and unpredictable resulting in mass hydrogen production and potential loss of mechanical integrity. Thus the application of calcium phosphate coatings has been considered as a means of improving the degradation properties of Mg. Brushite and monetite are utilized and their degradation properties (alongside uncoated Mg controls) are assessed in an in vivo subcutaneous environment and the findings compared to their in vitro degradation behaviour in immersion tests. The current findings suggest monetite coatings have significant degradation protective effects compared to brushite coatings in vivo. Furthermore, it is postulated that an in vitro immersion test may be used as a tentative predictor of in vivo subcutaneous degradation behavior of calcium phosphate coated and uncoated Mg.

Quantifying effects of interactions between polyacrylic acid and chlorhexidine in dicalcium phosphate – forming cements

Polyacrylic acid has been shown to control setting and improve mechanical and antibacterial release properties of brushite bone cements.

Characterization of a biodegradable coralline hydroxyapatite/calcium carbonate composite and its clinical implementation

A partially converted, biodegradable coralline hydroxyapatite/calcium carbonate (CHACC) composite comprising a coral calcium carbonate scaffold enveloped by a thin layer of hydroxyapatite was used in the present study. The CHACC was characterized using powder x-ray diffraction, scanning electron microscopy and energy dispersive x-ray spectroscopy. The ability of the CHACC to promote conductive osteogenesis was assessed in vitro using human mesenchymal stem cells (hMSCs) and in vivo using an immunodeficient mouse model. The clinical performance of CHACC as a bone substitute to fill voids caused by excision of bone tumours was also observed in 16 patients. The CHACC was found to consist of two overlapping layers both morphologically and chemically. Hydroxyapatite formed a thin layer of nanocrystals on the surface and a thick rough crystal layer of around 30 µm in thickness enveloping the rock-like core calcium carbonate exoskeletal architecture. hMSCs cultured on CHACC in osteogenic medium demonstrated significant osteogenic differentiation. After subcutaneous implantation of CHACC incorporating osteogenically differentiated hMSCs and an anti-resorptive agent, risedronate, into an immunodeficient mouse model, bone formation was observed on the surface of the implants. Clinical application of CHACC alone in 16 patients for bone augmentation after tumour removal showed that after implantation, visible callus formation was observed at one month and clinical bone healing achieved at four months. The majority of the implanted CHACC was degraded in 18-24 months. In conclusion, CHACC appears to be an excellent biodegradable bone graft material. It biointegrates with the host, is osteoconductive, biodegradable and can be an attractive alternative to autogenous grafts.