Calcium-deficient Hydroxyapatite Research Articles

AZ31-calcium-deficient hydroxyapatite (CDHA) composites produced by friction stir processing: controlling the degradation by enhancing the biomineralisation

ABSTRACT In the present work, calcium deficient hydroxyapatite (CDHA) was dispersed into the surface of AZ31 Mg alloy within the solid state by friction stir processing and the role of the refined microstructure and the presence of nano-CDHA on biomineralization and corrosion performance was investigated. Fine grains (1.6 ± 2.1 µm) have been produced in AZ31-CDHA composite compared with base alloy (41 ± 6.1 µm) and nano-CDHA was observed as reinforced into AZ31 matrix. X-ray diffraction analysis confirms the texture change due to FSP in the composite. Wettability studies carried out by measuring contact angles on the surface of the composites indicated increased surface energy (37.27 ± 5.1 mJ/m2) compared with the base alloy (20.55 ± 3.4 mJ/m2) . From the potentiodynamic polarization studies, lower corrosion current density (1.69 ± 1.13 × 10-5 A/cm2) was observed for the composite. From the immersion studies in simulated body fluids, higher level of biomineralization on the composite helped to decrease the degradation rate as reflected from the lower weight loss (7.5 ± 1.1 %) compared with the base alloy (12.1 ± 1.3 %). The results demonstrate the promising role of enhanced biomineralization on controlling the degradation of AZ31-CDHA composite..

Vat photopolymerization of biomimetic bone scaffolds based on Mg, Sr, Zn-substituted hydroxyapatite: Effect of sintering temperature

In response to the urgent demand for innovative bone regeneration solutions, the focus of this study is to develop and characterize Mg, Sr, Zn-substituted calcium phosphate scaffolds that replicate the trabecular architecture of cancellous bone. Ion substitution represents a promising approach to improve the biological effectiveness of calcium phosphates and composite materials used in bone tissue engineering applications. Porous scaffolds mimicking the natural bone structure were additively manufactured from the photosensitive ceramic suspensions for vat photopolymerization using digital light processing. The impact of the selected trace elements (0, 1 and 5 mol.% substitution) and the sintering temperature (900, 1000, 1100, 1200, and 1300 °C) was investigated in relation to the obtained crystalline phase content, microstructure, elemental distribution, thermal stability, and mechanical properties. After sintering, in addition to hydroxyapatite, β-tricalcium phosphate was detected as a result of the added trace elements in the calcium-deficient hydroxyapatite used as a starting powder. The obtained scaffolds exhibited uniform distribution of the trace elements, and they feature 3D-designed porosity predominantly ranged from 10 to 900 μm in diameter, with an average pore size of 546.25 ± 10.95 μm. The total porosity of scaffolds was 76.24 ± 1.32 vol.% and an average wall thickness of 217.03 ± 8.98 μm, closely resembling the morphology of cancellous bone tissue. The mechanical properties of the scaffolds sintered at 1100°C, 1200°C, and 1300°C were in line with those typically observed in trabecular bone. The study demonstrates the feasibility of using custom made bioactive hydroxyapatite powders together with vat photopolymerization to design the porosity and properties of the bone scaffolds on demand, based on the requirements of individual bone defects.

Indirect 3D printing CDHA scaffolds with hierarchical porous structure to promote osteoinductivity and bone regeneration

Hierarchical porous structures, which include macropores, minor pores, and micropores in scaffolds, are essential in the multiple biological functions of bone repair and regeneration. In this study, patient-customized calcium-deficient hydroxyapatite (CDHA) scaffolds with the three-level hierarchical porous structure were fabricated by indirect 3D printing technology and particulate leaching method. The sacrificial template scaffolds were fabricated using a photo-curing 3D printer, which provided a prerequisite for the integral structure and interconnected macro pores of CDHA scaffolds. Additionally, the 20 wt% pore former was incorporated into the slurry to enhance the content of smaller pores within the CDHA-2 scaffolds, and then the CDHA-2 scaffolds were sintered to remove the sacrificial template scaffolds and pore former. The obtained CDHA-2 scaffolds exhibited interconnected macropores (300–400 μm), minor pores (∼10–100 μm), and micropores (< 10 μm) distributed throughout the scaffolds, which could promote bone tissue ingrowth, increase surface roughness, and enhance protein adsorption of scaffolds. In vitro studies identified that CDHA-2 scaffolds had nanocrystal grains, high specific surface area, and outstanding protein adsorption capacity, which could provide a microenvironment for cell adhesion, spreading, and proliferation. In addition, the murine intramuscular implantation experiment suggested that CDHA-2 scaffolds exhibited excellent osteoinductivity and were superior to traditional BCP ceramics under conditions without the addition of live cells and exogenous growth factors. The rabbit calvarial defect repair results indicated that CDHA-2 scaffolds could enhance in situ bone regeneration. In conclusion, these findings demonstrated that the hierarchical porous structure of CDHA scaffolds was a pivotal factor in modulating osteoinductivity and bone regeneration, and CDHA-2 scaffolds were a potential candidate for bone regeneration.

The impact of hydroxyapatite crystal structures and protein interactions on bone's mechanical properties

Hydroxyapatite (HAP) constitutes the primary mineral component of bones, and its crystal structure, along with the surface interaction with proteins, significantly influences the outstanding mechanical properties of bone. This study focuses on natural hydroxyapatite, constructing a surface model with calcium vacancy defects. Employing a representative model of aspartic acid residues, we delve into the adsorption mechanism on the crystal surface and scrutinize the adsorption forms of amino acid residues on HAP and calcium-deficient hydroxyapatite (CDHA) surfaces. The research also explores the impact of different environments on adsorption energy. Furthermore, a simplified sandwich structure of crystal-polypeptide-crystal is presented, analyzing the distribution of amino acid residue adsorption sites on the crystal surface of the polypeptide fragment. This investigation aims to elucidate how the stick–slip mechanism of polypeptide molecules on the crystal surface influences the mechanical properties of the system. By uncovering the interface mechanical behavior between HAP and osteopontin peptides, this article offers valuable theoretical insights for the construction and biomimetic design of biocomposites.

Calcination-based direct extraction of hydroxyapatite from bovine bone waste

ABSTRACT The main chemical components of waste cow bones are apatite minerals, especially those containing calcium and phosphorus. This study investigated whether this bone could produce extracted hydroxyapatite through calcining at 900° C for different holding times (1–6 h). An average mass loss of 45% occurred in this experiment during the preparation of bone powders, which involved crushing and further calcining at this temperature. The quantitative XRD analysis showed that 99.97 wt.% hydroxyapatite and over 0.3 wt.% calcite were present in the raw and as-calcined bone powders, with trace amounts of CaFe3O5 (calcium ferrite) phases appearing in the calcined product. Depending on the holding calcining times, SEM images of the calcined bovine powders revealed aggregate sizes ranging from 0.5–3 µm and crystallite (grain) sizes ranging from 70 to 340 nm in all calcium-phosphate powder products. Following EDX analysis of all sample surfaces, possible calcium-deficient hydroxyapatite instead of hydroxyapatite formed, as evidenced by the calcined product's Ca/P ratio exceeding 1.67. Additionally, calcining cow bones for 5–6 h at 900° C yielded a high-purity nano-crystalline hydroxyapatite powder precursor in biomedical applications.

Sporopollenin Capsules as Biomimetic Templates for the Synthesis of Hydroxyapatite and β-TCP.

Pollen grains, with their resilient sporopollenin exine and defined morphologies, have been explored as bio-templates for the synthesis of calcium phosphate minerals, particularly hydroxyapatite (HAp) and β-tricalcium phosphate (TCP). Various pollen morphologies from different plant species (black alder, dandelion, lamb's quarters, ragweed, and stargazer lily) were evaluated. Pollen grains underwent acid washing to remove allergenic material and facilitate subsequent calcification. Ragweed and lamb's quarter pollen grains were chosen as templates for calcium phosphate salts deposition due to their distinct morphologies. The calcification process yielded well-defined spherical hollow particles. The washing step, intended to reduce the protein content, did not significantly affect the final product; thus, justifying the removal of this low-yield step from the synthesis process. Characterisation techniques, including X-ray diffraction, scanning electron microscopy, Fourier-transform infrared spectroscopy, and thermal gravimetric analysis, confirmed the successful calcification of pollen-derived materials, revealing that calcified grains were principally composed of calcium deficient HAp. After calcination, biphasic calcium phosphate composed of HAp and TPC was obtained. This study demonstrated the feasibility of using pollen grains as green and sustainable bio-templates for synthesizing biomaterials with controlled morphology, showcasing their potential in biomedical applications such as drug delivery and bone regeneration.

Enhanced osteogenic and bactericidal performance of premixed calcium phosphate cement with photocrosslinked alginate thin film.

The increasing prevalence of implant-associated infections (IAI) in orthopedics remains a public health challenge. Calcium phosphates (CaPs) are critical biomaterials in dental treatments and bone regeneration. It is highly desirable to endow CaPs with antibacterial properties. To achieve this purpose, we developed a photocrosslinked methacrylated alginate co-calcium phosphate cement (PMA-co-PCPC) with antibacterial properties, using α-tricalcium phosphate (α-TCP) powders with 16% amorphous contents as solid phase, liquid phases containing CuCl2 and SrCl2 as an inhibitor, and CaCl2 as an activator to construct PCPC. When CaCl2 started to activate the hydration reaction, Sr2+ or Cu2+ ions were exchanged with Ca2+, and α-TCP dissolution was restarted and gradually hydrated to form calcium-deficient hydroxyapatite (CDHA). PMA was added to crosslink with Cu/Sr ions and form gel-layer-wrapped hydrated CDHA. This study explored the binding mechanism of PMA and PCPC and the ion release rule of Ca2+ → Sr2+/Cu2+, optimized the construction of several antibacterial PMA-co-PCPC materials, and analyzed the physical, chemical, and biological properties. Because of the combined effect of Cu and Sr ions, the scaffold exhibited a potential antibacterial activity, promoting bone formation and vascular regeneration. This work provides a basis for designing antibacterial calcium phosphate biomaterials with controllable treatment, which is an important characteristic for preventing IAI of biomaterials.

Characteristics of sintered calcium deficient hydroxyapatite scaffolds produced by 3D printing

This study investigates the parametric quality and reliability of 3D-printed scaffolds using a composite filament comprising a thermoplastic polymer and hydroxyapatite in 1:1 wt ratio. Employing a fused filament fabrication printer, we verified the 3D printing strategy, sintering temperature range, and preparation of hydroxyapatite scaffolds. To complete the study, in vitro cytotoxicity tests using animal and human cell models were conducted. The calcium-deficient hydroxyapatite (Ca/P ∼ 1.54) used in preparation of filament exhibited after sintering differences in crystalochemical phases in different rations, comparing to stoichiometric hydroxyapatite (Ca/P ≅ 1.67). The FFF process successfully produced scaffold macropores suitable for tissue vascularization (∼380 µm or smaller). Optimal sintering temperature for cell proliferation was identified at 1300 °C, especially effective for used investigated calcium-deficient hydroxyapatite. Cytotoxicity assessment with murine and human fibroblastic cells demonstrated differing behaviour, emphasizing the need for careful material property modifications for practical scaffold utilization.

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

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

One and two-step electrodeposition of composite films of calcium-deficient hydroxyapatite matrix with nanoscale Ag- and Zn-based particles

A fundamental study regarding the electrochemical synthesis of composite coatings with application in the orthopaedic field has been conducted. In particular, the electrodeposition of calcium phosphate coatings with Ag nanoparticles (AgNPs) from either a single electrolyte (one-step, 1S) or two electrolytes (two-step, 2S) on a β-Ti alloy (Ti-18Mo-6Nb-4Ta in wt%) was investigated. Pulse current deposition was implemented to produce the composite coatings by the 1S approach from a simple solution containing 42 mM Ca(NO3)2·4H2O, 25 mM NH4H2PO4, and 0.5 mM AgNO3 at 65°C. Meanwhile, the calcium phosphate matrix was also deposited by pulse current, and Ag was afterwards grown by direct current from 0.1 M KNO3 + x mM AgNO3 (x = 5, 10) at 25 °C (2S approach). The Ca/P ratio of the matrix was compatible with the formation of calcium-deficient hydroxyapatite (CDHA). The resulting Ag content in the composites could be varied between 4 and 13 wt% as a function of the working conditions. The 2S-derived coatings produced by electroplating Ag at j = –20.8 mA/cm2 from 0.1 M KNO3 + 10 mM AgNO3 furnished an optimal dispersion of the AgNPs on top of the CDHA matrix, while aggregation and/or dendritic growth was observed in other cases. Glow discharge optical emission spectrometry (GDOES) measurements indicated that a given amount of AgNPs becomes engulfed in the CDHA matrix during the 1S electrodeposition, whereas most of them decorate its outer surface in the 2S-derived coatings. The applicability of the two approaches was extended to the case of zinc oxide. ZnO-containing CDHA coatings in which the Zn element was homogeneously distributed across the film surface were obtained from 42 mM Ca(NO3)2·4H2O, 25 mM NH4H2PO4 and 1 mM Zn(NO3)2·6H2O at 65 °C (1S approach). On the contrary, ZnO-NPs could be clearly observed when deposition from 5 mM KNO3 + 5 mM Zn(NO3)2 was performed at 70 °C on top of previously grown CDHA (2S approach). The results indicated that the percentage and location of the antibacterial element (Ag, Zn) in the calcium phosphate matrix can be tuned on demand to a great extent by electrochemical means.

Enhancement of properties of a cell-laden GelMA hydrogel-based bioink via calcium phosphate phase transition

To improve the properties of the hydrogel-based bioinks, a calcium phosphate phase transition was applied, and the products were examined. We successfully enhanced the mechanical properties of the hydrogels by adding small amounts (< 0.5 wt%) of alpha-tricalcium phosphate (α-TCP) to photo-crosslinkable gelatin methacrylate (GelMA). As a result of the hydrolyzing calcium phosphate phase transition involving α-TCP, which proceeded for 36 h in the cell culture medium, calcium-deficient hydroxyapatite was produced. Approximately 18 times the compressive modulus was achieved for GelMA with 0.5 wt% α-TCP (20.96 kPa) compared with pure GelMA (1.18 kPa). Although cell proliferation decreased during the early stages of cultivation, both osteogenic differentiation and mineralization activities increased dramatically when the calcium phosphate phase transition was performed with 0.25 wt% α-TCP. The addition of α-TCP improved the printability and fidelity of GelMA, as well as the structural stability and compressive modulus (approximately six times higher) after three weeks of culturing. Therefore, we anticipate that the application of calcium phosphate phase transition to hydrogels may have the potential for hard tissue regeneration.

Phase and structural transformations during sintering of uncalcinated hydrolyzed and carbonated amorphous calcium phosphates

An uncalcinated carbonated amorphous calcium phosphate (CACP) compact during heating lost its absorbed and structural waters as well as volatile gases from residual by-products up to 600 °C and crystallized into a partially carbonated nanocrystalline calcium-deficient hydroxyapatite (CDHA) within 600–750 °C. The CDHA transformed into a mixture of stoichiometric HA and β-TCP (BCP) at 900 °C. These transformations in case of the preliminary uncalcinated CACP resulted in an increased density of the compact from 1.0 g cm−3 to 2.97 g cm−3, i.e., by a factor of about three. Such a high “green” density gave a ceramics of 95 % density (37/63 β-TCP/HA) for the BCP compact heated to 1000 °C practically with no holding time. This finding seems to be promising for the preparation of BCP ceramics with improved quality.

Preparation and Characterization of 3D Printed Hydroxyapatite-Whisker-Strengthened Hydroxyapatite Scaffold Coated with Biphasic Calcium Phosphate

This study investigates the in vitro degradation of calcium-deficient hydroxyapatite powder after heat treatment at different temperatures and analyzes the calculated phase composition, particle size distribution, degradation rate, and bioactivity of the powder after heat treatment. A mixture of hydroxyapatite and β-tricalcium phosphate (BCP) coatings was prepared on the surface of a 3D-printed hydroxyapatite-whisker-strengthened hydroxyapatite scaffold (HAw/HA) by vacuum impregnation and ultraviolet light curing combined with an optimized heat treatment process. The performance of the coatings under different methods was characterized. The composite scaffolds with highly interconnected pores and excellent mechanical properties were prepared, and their biodegradation performance, bioactivity, osteoconductivity, and osteoinductivity of the scaffolds were improved. The results showed that calcium-deficient hydroxyapatite began to transform into BCP between 600 °C and 800 °C, and the powder treated at 800 °C has better bioactivity. The BCP coating prepared by light curing was more uniform, resulting in a higher interfacial bonding strength, and has better osteoconductivity and osteoinductivity than that prepared by vacuum impregnation.

An alkali-responsive mineral self-healing agent with mechanical property enhancement for cementitious composites

Self-healing cementitious materials are regarded as an effective choice to increase the sustainability of the resource and environment. In this study, an alkali-responsive mineral self-healing agent (AMS) was prepared inspired by bone repair. The healing component, phosphate, was loaded into the halloysite nanotubes (HNTs) and encapsulated by the layer-by-layer (LbL) self-assembly method. The structure and alkali-responsive behavior of AMS, the effect of AMS on the mechanical properties of cement pastes, the stability of AMS before cement cracking, and its effect on the self-healing efficiency of the cement pastes were investigated with a range of analytical techniques. Results showed that AMS was successfully encapsulated and endowed with excellent alkali responsiveness. The incorporation of AMS was effective in reinforcing the mechanical performances of cement pastes. XRD analysis showed that the phosphate encapsulated in AMS can be mostly retained until cracks appear. When cracks occurred, the B-type carbonated calcium-deficient hydroxyapatite was found as the main product in the crack environment. The surface crack around 130 μm in the damaged specimens containing 5% AMS was fully sealed and healed, and its damaged compressive strength was almost completely recovered after curing for 28 days. The synergistic effect of autonomous healing triggered by AMS and autogenous healing behavior promotes the self-healing process and improves the self-healing efficiency of the hardened cement pastes.

Nature-inspired Apatite Production: Steam Processing of Calcium Carbonate and Tricalcium Phosphate Nanosized Powder Blends

Green production of materials is crucial to protect the environment. In this article, a low-temperature steam synthesis strategy for apatite production is shown for limiting chemical pollution and enabling the control of crystallinity. Steam processing produced apatite from calcium carbonate and tricalcium phosphate nanosized powders. Interdiffusion between amorphous precursors gave hydroxyapatite accompanied by calcium-deficient hydroxyapatite. This study unfolds the potential of hydrothermal processing in steam as a synthesis strategy that has been forgotten since the 1950s showing where two solid nanosized powders react to form a new product without creating waste, thereby emulating the clean processing route found in nature. This research reopens the consideration of steam processing for more chemically diverse alternatives and processing of various calcium resources readily available in nature, such as eggshell waste, for greener production. Furthermore, it presents a rarely found combination of apatite forms.

Fabrication of injectable antibiotic-loaded apatitic bone cements with prolonged drug delivery for treating post-surgery infections.

Antibiotic-loaded bioactive bone substitutes are widely used for treating various orthopedic diseases and prophylactically to avoid post implantation infection. Calcium deficient hydroxyapatite (also known as apatitic bone cement) is a potential bioactive bone substitute in orthopedics due to its chemical composition similar to that of natural bone minerals. In this study, fabrication of mannitol (a solid porogen) incorporated injectable synthetic (Syn) and eggshell derived (ESD) apatitic bone cements loaded with antibiotics (gentamicin/meropenem/ rifampicin/vancomycin) was investigated. The release kinetics of the antibiotics were studied by fitting them with different kinetic models. All the antibiotics-loaded apatitic bone cements set within clinically accepted setting time (20 ± 2 min) and with good injectability (>70%). The antibiotics released from these bone cements were found to be controlled and sustained throughout the study time. Weibull and Gompertz (applies in least initial burst and sustain drug release rate models) were the best models to predict the release behavior. They cements had acceptable compressive strength (6-10 MPa; in the range of trabecular bone) and were biodegradable (21%-27% within 12 weeks of incubation) in vitro in simulated body fluids at physiological conditions. These bone cements showed excellent antibacterial activity from day 1 onwards and no bacterial colony was found from day 3 onwards. The viability of MG63 cells in vitro after 72 h was significantly higher after 24 h (i.e., ~110%). The cells were well attached and spread over the surface of the cements with extended morphology. The ESD antibiotic-loaded apatitic bone cements showed better injectability, degradation and cytocompatibility compared when compared to Syn antibiotic-loaded apatitic bone cements. Thus, we believe that the ESD antibiotic-loaded apatitic bone cements are suitable as potential injectable bone substitutes to avoid post-operative implant associated and other acute or chronic bone infections.

Multifunctional bone substitute using carbon dot and 3D printed calcium-deficient hydroxyapatite scaffolds for osteoclast inhibition and fluorescence imaging.

Multifunctional bone substitute materials (BSM) have gained considerable attention with the exponential increase in aging populations. The development of hybrid materials for diagnosis and therapy of bone-related diseases and dysfunctions, especially, has been a significant challenge in the biological and the biomedical field, due to the shortage of agents with specificity and selectivity toward bone. In this study, a hybrid material, referred as Alen-CDs@CDHA, fabricated from alendronate-conjugated carbon dots (Alen-CDs) and calcium-deficient hydroxyapatite (CDHA, the mineral component of bones) scaffolds is offered as a novel multifunctional BSM for in vivo osteoclasts deactivation and fluorescence imaging. The fluorescent Alen-CDs were hydrothermally prepared using phytic acid as carbon source, followed by conjugating alendronate, for controlled alendronate release and fluorescent imaging under acidic conditions. As-prepared fluorescent Alen-CDs were consecutively immobilized on surfaces of CDHA scaffolds, exhibiting high affinity by bisphosphonate group, easily fabricated from α-tricalcium phosphate (α-TCP) paste using three-dimensional (3D) printing system. The resultant Alen-CDs@CDHA caused a significant decrease (> 50%) in viability of osteoclasts at 7 days after in vitro treatment. Furthermore, when Alen-CDs@CDHA was implanted in balb/c nude mice for in vivo evaluation, we found Alen-CDs@CDHA to be suitable for bone imaging through fluorescence signals, without necrosis or inflammatory symptoms in the epidermal tissues. Thus, these observations offer new opportunities for a novel and revolutionary use of Alen-CDs@CDHA as highly specific multifunctional BSM for bone diagnosis and imaging, and as bone-specific drug delivery materials, eventually providing anti-osteoclastogenic treatments solution for degenerative bone disorders. STATEMENT OF SIGNIFICANCE: Alen-CDs@CDHA significantly reduced the viability of osteoclasts and fluorescently imaged in vivo after transplantation, releasing drug via pH modulation. The development of fluorescence materials for bone imaging remains still a major challenge in the biomedical field owing to the shortage of selectivity and specificity. The results could lead to improvements in bone treatment strategies, as it could reduce the invasiveness of procedures and the associated negative outcomes, and increase the precision of strategies. Further, we believe that this study will be of interest to the readership of your journal as clearly focuses on the advancement of a biomaterial, where we have engineered a substance to substitute bone and integrate with a living system.

Effect of moisture on the reactivity of alpha-tricalcium phosphate

The ability of the high-temperature polymorph of tricalcium phosphate, α-TCP, to hydrolyse to calcium-deficient hydroxyapatite underlies many developments in the field of synthetic bone grafts, including calcium phosphate cements, foams, and self-setting inks. The objective of the present work was to investigate the effect of humidity on α-TCP powder reactivity. The results showed that a 3-week incubation at high relative humidity (80%) had no impact on reactivity, but, as the incubation was prolonged, the powder started to hydrolyse. This reactivity was associated to the presence of defects and to an amorphous phase induced during powder milling. Moisture studies performed under static/dynamic conditions gave comparable water adsorption percentages. The dynamic studies further proved irreversible water sorption, indicating that some water molecules reacted with the powder after short incubation times. Taken together, these results demonstrate that, although α-TCP powder adsorbs water from moisture immediately, the impact on reactivity appears only after several weeks of storage.

Injectable magnesium oxychloride cement foam-derived scaffold for augmenting osteoporotic defect repair

HypothesisCement augmentation has been widely applied to promote osteoporotic fracture healing, whereas the existing calcium-based products suffer from the excessively slow degradation, which may impede bone regeneration. Magnesium oxychloride cement (MOC) shows promising biodegradation tendency and bioactivity, which is expected to be a potential alternative to the classic calcium-based cement for hard-tissue-engineering applications. ExperimentsHere, a hierarchical porous MOC foam (MOCF)-derived scaffold with favorable bio-resorption kinetic and superior bioactivity is fabricated through Pickering foaming technique. Then, a systematic characterization in terms of material properties and in vitro biological performance have been conducted to evaluate the feasibility of the as-prepared MOCF scaffold to be a bone-augmenting material for treating osteoporotic defects. FindingsThe developed MOCF shows excellent handling performance in the paste state, while exhibiting sufficient load-bearing capacity after solidification. In comparison with the traditional bone cement, calcium deficient hydroxyapatite (CDHA), our porous MOCF scaffold demonstrates a much higher biodegradation tendency and better cell recruitment ability. Additionally, the eluted bioactive ions by MOCF commits to a biologically inductive microenvironment, where the in vitro osteogenesis is significantly enhanced. It is anticipated that this advanced MOCF scaffold will be competitive for clinical therapies to augment osteoporotic bone regeneration.

Can Differently Stabilized Silver Nanoparticles Modify Calcium Phosphate Precipitation?

Calcium phosphates (CaPs) composites with silver nanoparticles (AgNPs) attract attention as a possible alternative to conventional approaches to combating orthopedic implant-associated infections. Although precipitation of calcium phosphates at room temperatures was pointed out as an advantageous method for the preparation of various CaP-based biomaterials, to the best of our knowledge, no such study exists for the preparation of CaPs/AgNP composites. Motivated by this lack of data in this study we investigated the influence of AgNPs stabilized with citrate (cit-AgNPs), poly(vinylpyrrolidone) (PVP-AgNPs), and sodium bis(2-ethylhexyl) sulfosuccinate (AOT-AgNPs) in the concentration range 5-25 mg dm-3 on the precipitation of CaPs. The first solid phase to precipitate in the investigated precipitation system was amorphous calcium phosphate (ACP). The effect of AgNPs on ACP stability was significant only in the presence of the highest concentration of AOT-AgNPs. However, in all precipitation systems containing AgNPs, the morphology of ACP was affected, as gel-like precipitates formed in addition to the typical chain-like aggregates of spherical particles. The exact effect depended on the type of AgNPs. After 60 min of reaction time, a mixture of calcium-deficient hydroxyapatite (CaDHA) and a smaller amount of octacalcium phosphate (OCP) formed. PXRD and EPR data point out that the amount of formed OCP decreases with increasing AgNPs concentration. The obtained results showed that AgNPs can modify the precipitation of CaPs and that CaPs properties can be fine-tuned by the choice of stabilizing agent. Furthermore, it was shown that precipitation can be used as a simple and fast method for CaP/AgNPs composites preparation which is of special interest for biomaterials preparation.