Nano-sized Hydroxyapatite Particles Research Articles

Impact of Alkaline Immersion Time on Nano-Hydroxyapatite Synthesis from Broiler Eggshells with Electrochemical Method Using Constant Direct Current (CDC)

Calcium phosphate is widely used in biomaterials, especially as a bone substitute. One of the calcium phosphate compounds that is widely used is hydroxyapatite. In biomedical applications, nano-sized hydroxyapatite particles have better bioactivity than coarse crystals. Hydroxyapatite can be synthesized from various sources of calcium and phosphate. Broiler eggshells were chosen as a source of calcium in this study because they have a relatively high calcium content. The method used in the synthesis of nano-hydroxyapatite in this research is the electrochemical method. This research aims to examine the effect of varying NaOH immersion time on the size and structure of calcium phosphate particles produced using an electrochemical method made from chicken egg shells. The synthesis of nano-hydroxyapatite from chicken egg shells was carried out in 4 stages: material preparation, electrolysis, precipitate immersion, and characterization. Nanometer-sized particles can be acquired through an immersion process lasting at least four hours, and it is observed that the longer the duration of immersion, the greater the resemblance of the resulting structure to hydroxyapatite.

Nanohydroxyapatite in dentistry: A comprehensive review

Enamel, being the hardest and the highest mineralized tissue of the human body, contains nearly 96% inorganic components and 4% organic compounds and water. Dentin contains 65% inorganic components and 35% organicand water content. The translucency and white appearance of enamel are attributed to Hydroxyapatite (HA), which constitutes the major part of the inorganic component of dental hard tissue. With the advent of nanotechnology, the application of Nanohydroxyapatite (nHA) has piqued interest in dentistry due to its excellent mechanical, physical, and chemical properties. Compared to HA, nHA is found to have superior properties such as increased solubility, high surface energy and better biocompatibility. This is due to the morphological and structural similarity of nanosized hydroxyapatite particles to tooth hydroxyapatite crystals. These nanoparticles have been incorporated into various dental formulations for different applications to ensure comprehensive oral healthcare. To prevent dental caries, several nHA based dentifrices, mouth rinsing solutions and remineralizing pastes have been developed. nHA-based materials, such as nanocomposites, nano impression materials, and nanoceramics, have proven to be very effective in restoring tooth deformities (decay, fracture, and tooth loss). The nHA coating on the surface of the dental implant helps it bind to the bone by forming a biomimetic coating. A recent innovative strategy involves using nHA to reduce dentinal hypersensitivity and to reconstruct periodontal bone defects. The purpose of the present review is to discuss the different applications of nHA in dentistry, especially in preventive and restorative dentistry, dental implantology, bleaching and dentine hypersensitivity management.

Co-Delivery of Methotrexate and Nanohydroxyapatite with Polyethylene Glycol Polymers for Chemotherapy of Osteosarcoma

Neoadjuvant chemotherapy is an alternative treatment modality for tumors. Methotrexate (MTX) has been often used as a neoadjuvant chemotherapy reagent for osteosarcoma surgery. However, the large dosage, high toxicity, strong drug resistance, and poor improvement of bone erosion restricted the utilization of methotrexate. Here, we developed a targeted drug delivery system using nanosized hydroxyapatite particles (nHA) as the cores. MTX was conjugated to polyethylene glycol (PEG) through the pH-sensitive ester linkage and acted as both the folate receptor-targeting ligand and the anti-cancer drug due to the similarity to the structure of folic acid. Meanwhile, nHA could increase the concentration of calcium ions after being uptake by cells, thus inducing mitochondrial apoptosis and improving the efficacy of medical treatment. In vitro drug release studies of MTX-PEG-nHA in phosphate buffered saline at different pH values (5, 6.4 and 7.4) indicated that the system showed a pH-dependent release feature because of the dissolution of ester bonds and nHA under acidic conditions. Furthermore, the treatment on osteosarcoma cells (143B, MG63, and HOS) by using MTX-PEG-nHA was demonstrated to exhibit higher therapeutic efficacy. Therefore, the developed platform possesses the great potential for osteosarcoma therapy.

Influence of spark plasma sintering temperature and hydroxyapatite nanoparticles on properties of HA based functionally graded materials for bone prosthesis

Functionally graded materials (FGMs) have exhibited great potential to be used for biomedical implants, joint replacements, and bone prostheses. Variation of spark plasma sintering (SPS) temperature and nanoparticles have been utilized in the matrix to fabricate fully-densified FGMs based on hydroxyapatite (HA), and AISI 316L stainless steel. FGMs based on five layers of HA/AISI 316L composites were fabricated through spark plasma sintering (SPS) at 1000 and 1100 °C. To study the effect of the addition of HA nanoparticles, a mixture of micro− and nanosized HA particles was also used as a matrix for the AISI 316L reinforcements, along with 100 wt% micro-sized HA powders. The concentration of the AISI 316L particles in the layers ranged from 0 to 40 wt%. Results showed that the FGMs sintered at 1100 °C exhibited better mechanical properties than those prepared at 1000 °C. However, regardless of the sintering temperature, phase transformations and chemical reactions involving the HA and the AISI 316L precursors were observed. Furthermore, no microcracks were observed in the matrix around the AISI 316L particles and at interlayer boundaries. The addition of the HA nanoparticles in the matrix improved the physical and mechanical properties of the fabricated FGMs, making these comparable to the standard materials for a bone prosthesis.

Optimization of hydrothermal synthesis of hydroxyapatite from chicken eggshell waste for effective adsorption of aqueous Pb(II).

Proper disposal of the millions of tons of eggshell waste generated around the world every year is a significant environmental challenge. However, eggshell waste can be converted into new materials that may be useful for a wide range of applications. In this study, four methods, including the conventional subcritical hydrothermal method (CSHM), microwave-assisted subcritical hydrothermal method (MSHM), conventional low-temperature hydrothermal method (CLHM), and ultrasonic-assisted low-temperature hydrothermal method (ULHM) were used to convert eggshell waste into hydroxyapatite (HAP). For each hydrothermal method, increasing the reaction temperature increased production efficiency and improved the degree of crystallinity of HAP. X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) surface area analysis, Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) were used to characterize the preferred eggshell-derived HAP, which was produced by the MSHM at 180 °C in a period of only 1 h. For the MSHM, the HAP yield was 75.3%, the degree of HAP crystallinity was as high as 0.78, and pure, rod-like, nano-sized HAP particles with high specific surface area were produced. For the preferred HAP produced by the MSHM, the adsorption capacity of Pb2+and pH were positively related in the range of pH 1-6. Consequently, the HAP produced by the MSHM showed relatively high maximum adsorption (qm= 505.05 mg/g) of Pb2+ in aqueous solution. The adsorption process followed a pseudo-second-order reaction model, and the equilibrium adsorption was well fit by the Langmuir model.

Surface metal matrix nano-composite of magnesium/hydroxyapatite produced by stir-centrifugal casting

The present study aims to investigate a liquid state method of stir and centrifugal casting as an in-situ and cost-attractive processing technology for the production of magnesium/hydroxyapatite surface metal matrix nano-composites (Mg/HA surface metal matrix nano-composite). The main contribution of this study is to design the best condition for achieving a uniform Mg/HA surface nano-composite as a potential bone implant. It was shown how casting parameters and the distribution of hydroxyapatite affect mechanical properties of nano-composites measured using nano-indentation, nano-scratch, and compression tests. Response surface method in Design Expert software was used to predict the best model and the optimum condition of casting based on the experimentally measured data. The surface metal matrix nano-composites, consisting of a magnesium matrix with different amounts of nano-sized hydroxyapatite and silicon-doped hydroxyapatite (0.75-3 wt%) particles, were prepared. Hot isostatic pressing was used to homogenize the nano-composites in terms of particle distribution and to reduce porosity. It was shown that the weight percent of hydroxyapatite reinforcement is the parameter which is best suited to tailor targeted strength values. The target values of maximum compression strength (187 MPa) and elastic modulus (33 GPa) were achieved with a combination of the following parameters: 1.83 wt% hydroxyapatite, 800 rpm mold rotational speed, and a propeller rotational time of 6.3 min. A specimen prepared under these conditions had a homogeneous distribution of nano-hydroxyapatite in magnesium metal matrix after hot isostatic pressing at 450 °C and 100 MPa for a holding time of 120 min. It indicated the best mechanical resistance in terms of hardness and material loss during the nano-scratch testing. Moreover, the XRD results show that there is no considerable chemical reaction between the reinforcement particles of n-HA and Mg metallic matrix during casting at 700 °C and thermo-mechanical treatment of HIP at 450 °C.

Evaluation of Physicochemical Properties of Nano-Sized Hydroxyapatite Particles Synthesized from Cowbones

Pure and white Hydroxyapatite Ca10(PO4)6 (OH)2 powder was synthesized from animal bone (Cowbone) using thermal decomposition method. The physicochemical properties of the synthesized hydroxyapatite were evaluated using X-ray diffraction analysis and Fourier Transform Infrared spectroscopy. The X-ray diffraction results revealed crystalline phase of hydroxyapatite while Scanning Electron Microscope analysis revealed the microscopic structure and nano size of the hydroxyapatite particle. Fourier Transform Infrared spectroscopy was used to identify functional groups in the material and did not indicate any organic components of the bone. Thermo gravimetric analysis confirmed the thermal stability of the hydroxyapatite. The in-vivo cytotoxicity test using Wistar Albino Rats did not indicate any toxic effects of the material at acute level. The research has not only shown economic potentiality of producing nano hydroxyapatite from this waste but offers a means of impacting positively on the environment.

Enhancing the physical and mechanical properties of pellet-shaped hydroxyapatite by controlling micron- and nano-sized powder ratios

Hydroxyapatite (HA) was fabricated in microns as its basic size. The particle size distribution was controlled by mixing micron- and nano-sized HA to obtain the optimum amount of mixture to improve its properties. HA powder with a size of 2.5 μm was mixed with that with a size of 200 nm, with a variety of concentrations of up to 20 wt%. A green body was fabricated using the uniaxial pressing method at a pressure of 200 MPa. The sintering process was conducted at a temperature of 1200 °C, heating rate of 3 °C/min, and holding time of 2 h in air. The physical characteristics of the HA sintered body were determined using X-ray diffraction, scanning electron microscopy, linear shrinkage, and density testing. The mechanical properties of the HA sintered body were tested using compressive strength testing. The test results indicated that the mechanical properties of the HA sintered body increased with the addition of nano-sized HA. The mechanism of the increasing strength occurred because nano-sized HA particles filled the gaps between the micron-sized particles. In this study, the highest mechanical properties were obtained by adding 20 wt% nano-sized HA. The compressive strength in the sample without added nano-sized HA was 132.2 MPa and increased significantly to 208.6 MPa with the addition of nano-sized HA of 20 wt%. No change in the phase in HA was observed within a sintering temperature of 1200 °C.

Aggregation of Nanosized Hydroxyapatite Particles and Inhibition of Cell Adhesion on this Bio-Active Material as Key Factors that Limit its Biointegration

Abstract—Different synthetic calcium phosphate compounds are used as osteoplastic materials for filling of bone defects during surgical reconstruction of bone. Synthetic nanosized hydroxyapatite is of particular interest because of its similarity to the chemical composition of bone and its osteoinductive potential. However, it is also known that nanosized hydroxyapatite can inhibit the processes of biointegration of biomaterials, although we have no clear understanding of the mechanisms that are responsible for this effect. In our in vitro studies suppression of cell adhesion on nanosized hydroxyapatite that may lead to anoikis was shown. Studies in which rat subcutaneous heterotopic implantation methods were used showed that nanosized hydroxyapatite in vivo formed a slightly resorbable agglomerate that blocks cell migration into the material, as well as neocollagenesis processes in it, including the processes of encapsulation of the material. In this case, the processes of neocollagenesis along the periphery of the sample were observed only over a dense layer of dead cells (cellular debris) surrounding the agglomerated nanosized hydroxyapatite. Addition of demineralized bone collagen matrix to nanosized hydroxyapatite as a conductive component contributed to colonization of the material by the cells, resorption of nanosized hydroxyapatite, and active construction of the neocollagen matrix. These results show that modification of nanosized hydroxyapatite with a conductive component is required in order to prevent its agglomeration and thus increase its biointegration and osteoinductive potential in the body.

Correction To: Evaluation of mechanical and adhesion properties of glass ionomer cement incorporating nano-sized hydroxyapatite particles.

In the original publication of the article, the family name of the author.

Evaluation of mechanical and adhesion properties of glass ionomer cement incorporating nano-sized hydroxyapatite particles.

Glass ionomer cement is a widely used luting agent for indirect restorations but presents inferior mechanical properties compared to resin cement due to its low elastic modulus. This study evaluated the mechanical and adhesion properties of glass ionomer luting cements reinforced with nano-sized hydroxyapatite particles (HA). The nano-sized HA particles were synthesized using the co-precipitation technique and the resulting precipitate was characterized using X-ray diffraction analysis (XRD), field emission scanning electron (FESEM) and transmission electron microscopy (TEM). HA particles were incorporated into the glass powder (FUJI I, GC) and the luting agent was manipulated in a liquid to powder ratio of 3:1 into 6% by weight after determining the best ratio. The flexural strength of the luting agent and shear bond strength of dentin were analyzed and compared to other luting agents namely, (a) glass ionomer (FUJI I), (b) resin-modified glass ionomer (RelyX Luting Plus) and (c) adhesive resin cement (RelyX U200). Failure types after debonding from dentin were evaluated under SEM. Flexural strength and bond strength data were analyzed using one-way ANOVA and Tukey's tests (alpha = 0.001). Addition of 6 w% HA particles in the range of 80-150nm enhanced the flexural strength (30.97 ± 5.9 versus 11.65 ± 5.63) and shear bond strength (0.97 ± 0.41 versus 0.39 ± 0.16) of a conventional glass ionomer luting agent significantly compared to the non-reinforced ones when manipulated at a liquid to powder ratio of 3:1 (P < 0.001). While conventional glass ionomer, HA-reinforced glass ionomer and resin-modified glass ionomer specimens showed exclusively mixed type of failures, adhesive resin cement showed cohesive failures within the resin cement. Increased mechanical and adhesion potential of the experimental glass ionomer luting agent after incorporation of HA particles could expand the scope of application of this cement.

Effect of the reaction temperature on the morphology of nanosized HAp

We reported on the synthesis of nanosized hydroxyapatite particles by wet chemical precipitation method and the consolidation of the nanoparticles by spark plasma sintering. We studied the effect of the synthesis temperature on the particle size and phase composition of the obtained HAp. During synthesis beyond HAp, another phase supposedly nonstoichiometric HAp was also formed as a by-product that can be detected by thermal analysis combined with XRD. Its amount gradually decreased with the increase in synthesis temperature and practically disappeared at 80 °C. Using this nanopowder for sintering, the spark plasma-sintered ceramics retained their nanostructure comprising only HAp phase in contrast to the powders synthesized at lower temperature when transformed products of the nonstoichiometric HAp could also be detected.

Nano hydroxyapatite induces glioma cell apoptosis by suppressing NF-κB signaling pathway.

Nano-sized hydroxyapatite (nHA) particles have been demonstrated to exert anti-cancer effects on multiple cancer cell lines and animal models of cancer biology. However, the molecular mechanism underlying the effects of nHA particles on glioma cells remains unclear. The present study aimed to examine the effects of nHA on the behavior of glioma cells and investigate its underlying molecular mechanism. Rat glioma C6 cells and human glioma U87MG ATCC cells were exposed to nHA (20–100 µg/ml), and its effects on cell morphology, viability, apoptosis, cell cycle, invasion and nuclear factor (NF)-κB signaling were analyzed. Exposure of C6 and U87MG ATCC cells to 20 µg/ml nHA for 24 h caused cell detachment. Viability of C6 and U87MG ATCC cells were significantly reduced by nHA in a dose-dependent manner (P<0.05). Nuclear staining with Hoechst 33258 exhibited clear chromatin condensation in C6 cells following 24 h exposure to ≥25 µg/ml nHA. Flow cytometry revealed that nHA (20–100 µg/ml) significantly induced apoptosis and cell cycle G2/M arrest in C6 and U87MG ATCC cells (P<0.05). Transwell invasion assay demonstrated that nHA (20–60 µg/ml) significantly inhibited invasion of U87MG ATCC cells (P<0.05). Furthermore, western blotting and confocal immunofluorescence microscopy revealed that nHA (20–100 µg/ml) decreased NF-κB p65 protein expression and blocked NF-κB p65 nuclear translocation in C6 cells. The protein expression of NF-κB target molecules, such as B cell lymphoma 2, cyclooxygenase-2 and survivin, were also significantly reduced by nHA in a dose-dependent manner in both C6 and U87MG ATCC cells (P<0.05). In conclusion, it was demonstrated that the inhibitory effect of nHA on glioma cells is likely associated with the downregulation of NF-κB signaling.

Effect of Solution and Calcination Time on Sol-gel Synthesis of Hydroxyapatite

Nano-sized hydroxyapatite (HA) particles were synthesized by sol-gel through water and ethanol based mediums of phosphoric acid (H3PO4) and calcium hydroxide (Ca(OH)2) at pH = 11 for different calcination time (1 h, 2 h, 4 h). The effects of calcination time and solution on the crystallinity, morphology and impurity phases of the HA nanoparticles were examined via Fourier Transform Infrared (FTIR), Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDS) and X-ray Diffraction (XRD). It was found that crystallite size and the fraction crystallinity of the synthesized samples increased with calcination time. According to solution medium, only CaO as impurity was appeared in the water-based solvent, CaO and Ca(OH)2 impurities were appeared in the ethanol-based solvent. The lowest crystallinity was 0.92 and the highest crystallinity was 1.73 respectively, depending on the process parameters. The Ca/P atomic ratio closest to the bone was found as 1.5178. As a result, the employed water-based sol-gel processes for 1 h calcination time was determined as the optimum for the formation of nano-sized HA powders using calcium hydroxide and phosphoric acid.

Microstructural evolution and mechanical properties of a friction-stir processed Ti-hydroxyapatite (HA) nanocomposite

In this research, a new metal matrix nanocomposite with enhanced capability for biomedical applications was fabricated by incorporation of nano-sized hydroxyapatite (HA) particles within the titanium substrate using multi-pass friction-stir processing (FSP). These n-HA particles were dispersed effectively within the titanium matrix. Titanium metal-matrix was processed without introducing the HA nanoparticles, as well, for the aim of comparison. The results showed the formation of different regions with various microstructural features and mechanical property across the processed materials. A thin layer with ultra-fine grain structure and indentation hardness value of up to ~400 HV was formed on the surface after FSP modification of coarse-grained titanium substrate. This was due to severe shear deformation induced by the rotating shoulder as well as the surface absorption of N and O elements from the atmosphere inside the layer. Incorporation of nanoparticles and subsequent grain structural refinement owing to operative dynamic recrystallization mechanisms leads to a maximum hardness improvement of up to ~250 HV in the lower regions (as compared to the average hardness value of base metal ~150 HV). The FSP modified pure titanium exhibited a good combination of strength and ductility by refining the grain structure with a well-developed dimple-like structure on the fracture surface. For the nanocomposite specimen, the trend of the tensile property was found deteriorative showing the impaired features on the fracture surface. This is attributed to the complex structure of HA compound and low quality of interfacial bonding between the nanoparticles and titanium matrix.

Hydroxyapatite for Filling Bone Tissue Defects

Hydroxyapatite was synthesized in conditions of mechanoacoustic treatment of an aqueous reaction mixture consisting of ammonium hydrogen phosphate and calcium nitrate using a commercially available rotary pulsation apparatus. Mechanoacoustic treatment of the reaction mixture was found to lead to the formation of nanosized hydroxyapatite particles with a predominant mean diameter of about 20 nm. Purification of technical hydroxyapatite to remove traces of ammonium nitrate by thermal processing at 350°C is proposed. The crystalline phase of hydroxyapatite was found not to be dominant in the structure. The porosity of hydroxyapatite amounted to about 75% with a mean pore diameter of 2.8 × 103 nm. Thermal processing of hydroxyapatite in aqueous medium was found to yield a paste-like form. Hydroxyapatite paste had no cytotoxicity and did not prevent cell adhesion, though it almost completely inhibited cell spreading.

Biomechanical, histological, and computed X‐ray tomographic analyses of hydroxyapatite coated PEEK implants in an extended healing model in rabbit

A nanosized hydroxyapatite (HA) modification on polyetheretherketone (PEEK) using a novel spin coating technique was investigated in a rabbit model. Spin coating technique creates a 20-40 nm thick layer of nanosized HA particles with similar shape, size, and crystallinity as human bone. Some implants were designed with a perforating hole in the apical region to mimic a fusion chamber of a spinal implant. The coating nano-structures were assessed using a scanning electron microscope. The in vivo response to HA-PEEK was compared to untreated PEEK with respect to removal torque, histomorphometry, and computed microtomography. The HA-coated and pure PEEK implants were inserted in the tibia and femur bone according to simple randomization. The rabbits were sacrificed 20 weeks after implantation. Removal torque analysis showed significantly higher values for HA-PEEK. Qualitative histological evaluation revealed an intimate contact between PEEK and the bone at the threads and perforated hole. Histomorphometric assessment showed higher bone-implant and bone area values for HA-PEEK but without statistical significance. The effect of the HA coating showed most prominent effect in the removal torque which may be correlated to an alteration in the bone quality around the HA-PEEK implants. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 1440-1447, 2018.

Porous hydroxyapatite scaffolds fabricated from nano-sized powder via honeycomb extrusion

In this study, we have developed hydroxyapatite (HA) scaffolds for synthetic bone graft from nano-sized HA particles using ceramic extrusion. We also demonstrate that these HA scaffolds show enhanced compressive strength (29.4 MPa), whilst possessing large pore sizes (> 600 µm) that are suitable for bone grafting. The extrusion process involved forming a ceramic paste by mixing the HA powder with a binder and distilled water. The ceramic paste was then fabricated using a ram extruder that was fitted with a honeycomb die to impart large, structured pores. Several green bodies were extruded and then subjected to the same drying and thermal debinding treatment. The samples underwent three different sintering temperatures and two varied dwell times, in order to determine the optimum sintering parameters. The scaffolds were then analysed for their chemical, physical, mechanical and biological properties to elucidate the effects of the sintering parameters on extruded HA scaffolds. The results revealed that the nano-sized particles exhibited a high sinterability, and XRD analysis showed phase purity until 1300 o C. At 1300 o C, trace amounts of phase impurities were detected, however, scaffolds sintered at this temperature exhibited the highest mean compressive strength. The findings demonstrated that traces of phase impurities were not detrimental to the scaffold’s compressive strength. In addition, scanning electron microscopy and density measurements revealed a highly densified solid phase was attained.

Synthesis and characterization of pure and nanosized hydroxyapatite bioceramics

AbstractSynthetic nanosized hydroxyapatite (HA) particles (&lt;120 nm) were prepared using a co-precipitation technique by adopting two different routes – one from an aqueous solution of calcium nitrate tetrahydrate and diammonium hydrogen phosphate at pH 10 and the other by using calcium hydroxide and phosphoric acid as precursors at pH 8.5 and reaction temperature of 50°C. The lattice parameters of HA nanopowder were analogous to reference [Joint Committee on Powdered Diffraction Standards (JCPDS)] pattern no. 09-432. No decomposition of HA into other phases was observed even after heating at 1000°C in air for 1 h. This observation revealed the high-temperature stability of the HA nanopowder obtained using co-precipitation route. The effects of preliminary Ca/P molar ratio, precipitation, pH and temperature on the evolution of phase and crystallinity of the nanopowder were systematically examined and optimized. The product was evaluated by techniques such as X-ray-diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) and Raman spectroscopy analyses. The chemical structural analysis of the as-prepared HA sample was performed using X-ray photoelectron spectroscopy (XPS). After heat treatment at 1000°C for 1 h and ageing for 15 h, the product was obtained as a phase-pure, highly crystalline HA nanorods.

Long-lasting and bioactive hyaluronic acid-hydroxyapatite composite hydrogels for injectable dermal fillers: Physical properties and in vivo durability.

Hyaluronic acid (HAc)-hydroxyapatite (HAp) composite hydrogels were developed to improve the biostability and bioactivity of HAc for dermal filler applications. Two kinds of HAc-HAp composite fillers were generated: HAcmicroHAp and HAc-nanoHAp composites. HAc-microHAp was fabricated by mixing HAp microspheres with HAc hydrogels, and HAc-nanoHAp was made by in situ precipitation of nano-sized HAp particles in HAc hydrogels. Emphasis was placed on the effect of HAp on the durability and bioactivity of the fillers. Compared with the pure HAc filler, all of the HAc-HAp composite fillers exhibited significant improvements in volumetric maintenance based on in vivo tests owing to their reduced water content and higher degree of biointegration between the filler and surrounding tissues. HAc-HAp composite fillers also showed noticeable enhancement in dermis recovery, promoting collagen and elastic fiber formation. Based on their long-lasting durability and bioactivity, HAc-HAp composite fillers have great potential for soft tissue augmentation with multifunctionality.