Hot pressing of hydroxyapatite(HA)-Ti material and stability of HA

Hot pressing of hydroxyapatite(HA) Ti system material and the stability of HA component were investigated to supply the foundation of optimizing sintering procedure of HA Ti functionally graded material(FGM). The results show that the HA powders used have excellent thermal stability and no decomposition is observed at 1 300 ℃. The existence of Ti can promote the dehydration and decomposition of HA. However, no new compounds form between HA and Ti. By selecting sintering parameters properly, ideal HA Ti material can be acquired. The relative densities of the mixtures of HA and Ti are always lower than those of pure HA or Ti, which may be caused by the decomposition of HA in the mixtures.

The Effect of Material Surface Microstructure on the Enhancement of Bone-Bonding Ability of a Hydroxyapatite-Implant by Low-Intensity Pulsed Ultrasound (LIPUS)

Excellent firm bonding between the biomaterials and bone tissue (osseointegration and osteo-conductivity) has been desired for the stability in vivo of dental implants and artificial joints. Much has been learned about this concept, which has led to significant improvements in the design and surface modification of implants in the field of implant dentistry, orthopedic surgery. We have already reported that low-intensity pulsed ultrasound (LIPUS) irradiation can accelerate the bone bonding ability of the bio-conductive materials such as bioactive titanium and hydroxyapatite implant. However, it is still unclear whether the LIPUS could have same effect to different types of the bioactive-materials. Therefore, in this study, the differences of bone-like hydroxyapatite formation on some kind of hydroxyapatite surface in simulated body fluid (SBF) under the LIPUS irradiation were investigated. Two kinds of hydroxyapatite samples immersed in SBF was exposed to ultrasound waves, the bone-like apatite on the surface was analyzed by Scanning electron microscopy and X-ray diffraction. As a result, the enhancement of hydroxyapatite formation on the surface by LIPUS was confirmed, the initial epitaxial nucleation and crystal growth of apatite depended on crystal structure of the surface of matrix materials.

Improving the Corrosion Resistance of ZEK100 Magnesium Alloy by Combining High-Pressure Torsion Technology with Hydroxyapatite Coating

Recently,magnesium and its alloys have attracted more and more attention as promising implant materials due to their excellent properties such as good biocompatibility,biodegradation,non-toxicity and comparable mechanical properties with natural bone.They can be gradually degraded and absorbed so as to avoid the second surgery for implants removal after the tissues are healed completely.In addition,they are also able to prevent the stress shielding effect in human body environment because of the density,elastic modulus and yield strength of magnesium closer to the bone.Unfortunately,the high corrosion rate which causes early mechanical failure of the implants in physiological environment limits the widespread use of magnesium alloys for clinical application in biology.And the high corrosion process usually causes huge hydrogen evolution and alkalinization,resulting in problems against the implants as well as the surrounding tissues.In order to enhance the corrosion resistance of magnesium alloys,in this study,the ZEK100 magnesium alloy was pre-deformed with a highpressure torsion(HPT)process and then fabricated hydroxyapatite(HA)coatings with different contents of Mg(OH)2 nanopowder via hydrothermal method.The specimens were characterized by scanning electron microscope(SEM)and X-ray diffraction(XRD).At the same time,prior and after the HPT procedure,the metallography,microhardness and tensile tests of specimens were characterized.Meanwhile,the corrosion behavior of the specimens was evaluated by electrochemical impedance spectroscopy(EIS)and hydrogen evolution tests.And the interface bonding strength of the HA coating on the magnesium alloy substrate was evaluated by a tape adhesion test/scratch test.Results showed that HPT processing refined the grain size and introduced a great number of twins,resulting in the enhancement of microhardness and Young’s modulus of ZEK100 magnesium alloy,but hardness values at the edge were higher than those at the center due to the uneven shear strain.At the same conditions,the HA coating on HPT-ZEK was denser,thicker than that on ZEK sample and the crystal sizes of HA were smaller on HPT-ZEK.These were attributed to fine,uniform distributed secondary phases and lots of fine grains,twins,grain boundaries in HPT-ZEK substrates which can provide more nucleation sites for the HA crystal.In terms of the amount of Mg(OH)2 nanopowder,Mg(OH)2 nanopowder significantly influenced the microstructure and thickness of the HA coating.And at a 0.3 mg/mL content of Mg(OH)2 nanopowder,there was the densest,thickest HA coating on magnesium alloys,and the crystal size of HA was minimum.Specifically,the HA coating thickness on ZEK-03(0.3 mg/mL Mg(OH)2 nanopowder)was 1.8 times of that on ZEK-00(0 mg/mL Mg(OH)2 nanopowder),while the HA coating thickness on HPT-03 was 2.6 times of that on ZEK-00.And the adhesion strength of HA coating on HPT-03 substrate was better than that on ZEK-03.In addition,HPT technology and surface modification by HA coating simultaneously increased the corrosion resistance of ZEK100 magnesium alloy and the corrosion of HPT-ZEK samples occurred in a more uniform manner,while it was pitting on the surface of ZEK100 magnesium alloy.Therefore,there was the best corrosion resistance on HPT-03 sample,which could promote the application of magnesium alloys in biomedical fields.

Microwave assisted synthesis & properties of nano HA-TCP biphasic calcium phosphate

Biphasic calcium phosphate （BCP） nanopowders were synthesized by using microwave and non-microwave irradiation assisted processes. The synthesized powders were pressed under a pressure of 90 MPa, and then were sintered at 1000-1200℃ for 1 h. The mechanical properties of the samples were investigated. The formed phases and microstructures were characterized by X-ray diffraction （XRD） and scanning electron microscopy （SEM）. The results showed that the synthesis time was shorter, along with a more homogeneous microstructure, when the microwave irradiation assisted method was applied. The compression strength and the Young＇s modulus of the samples synthesized with microwave irradiation were about 60 MPa and 3 GPa, but those of the samples synthesized without microwave irradiation were about 30 MPa and 2 GPa, respectively. XRD patterns of the microwave irradiation assisted and non-microwave irradiation assisted nanopowders showed the coexistence of hydroxyapatite （HA） and lricalcium phosphate （TCP） phases in the system.

Enhanced Biocompatibility and Osseointegration of Calcium Titanate Coating on Titanium Screws in Rabbit Femur

This study aimed to examine the biocompatibility of calcium titanate(CaTiO3) coating prepared by a simplified technique in an attempt to assess the potential of CaTiO3coating as an alternative to current implant coating materials. CaTiO3-coated titanium screws were implanted with hydroxyapatite(HA)-coated or uncoated titanium screws into medial and lateral femoral condyles of 48 New Zealand white rabbits. Imaging, histomorphometric and biomechanical analyses were employed to evaluate the osseointegration and biocompatibility 12 weeks after the implantation. Histology and scanning electron microscopy revealed that bone tissues surrounding the screws coated with CaTiO3were fully regenerated and they were also well integrated with the screws. An interfacial fibrous membrane layer, which was found in the HA coating group, was not noticeable between the bone tissues and CaTiO3-coated screws. X-ray imaging analysis showed in the CaTiO3coating group, there was a dense and tight binding between implants and the bone tissues; no radiation translucent zone was found surrounding the implants as well as no detachment of the coating and femoral condyle fracture. In contrast, uncoated screws exhibited a fibrous membrane layer, as evidenced by the detection of a radiation translucent zone between the implants and the bone tissues. Additionally, biomechanical testing revealed that the binding strength of CaTiO3coating with bone tissues was significantly higher than that of uncoated titanium screws, and was comparable to that of HA coating. The study demonstrated that CaTiO3coating in situ to titanium screws possesses great biocompatibility and osseointegration comparable to HA coating.

Synthesis,characterization and biological activity in vitro of FeCrAl(f)/HA asymmetrical biological functionally gradient materials

FeCrAl(f)/HA biological functionally gradient materials(FGMs) were successfully fabricated by the hot pressing technique.Scanning electron microscope(SEM),energy dispersive spectrometer(EDS) and bending strength test machine were utilized to characterize the microstructure,component,mechanical properties and the formation of the Ca-deficient apatite on the surface of these materials.The results indicate that an asymmetrical FeCrAl(f)/HA FGM,consolidating powders prepared by mixing HA with 3%–15%(volume fraction) is successfully prepared.Both of the matrix and FeCrAl fiber are integrated very tightly and bite into each other very deeply.And counter diffusion takes place to some extent in two phase interfaces.The elemental compositions of the FeCrAl(f)/HA FGM change progressively.Ca and P contents increase gradually with immersion time increasing,and thereafter approach equilibrium.The bone-like apatite layer forms on the materials surface,which possesses benign bioactivity,and the favorable biocompatibility can provide potential firm fixation between FeCrAl(f)/HA asymmetrical FGM implants and human bone.

COMPUTATION OF FLEXURAL PROPERTIES OF HA/PLLA COMPOSITE USING A CELL MODEL APPROACH

A three-dimensional finite element analysis was conducted to evaluate the feasibility of predicting the flexural properties of hydroxyapatite-reinforced poly-L-lactide acid （HA/PLLA） biocomposite using three different schemes. The scheme 1, originated from a beam analysis, was used to determine the flexural modulus analytically while the scheme 2 and 3 were designed to have different loading and boundary conditions using a finite element cell modeling approach. An empirical approach using Chow＇s formula and experimental data were used for comparison with the predicted results. In order to reduce the computational time and save the storage space involved in determining the effect of varying particle volume fractions on the flexural properties of HA/PLLA, a superelement technique was applied. The results using the scheme 3 and the Chow＇s formula were found to be in reasonable agreement with experimental results over the range of particle volume fraction. In addition to the Chow＇s formula, local stress distribution and the failure processes in HA/PLLA were simulated using the finite element technique.

Study on biocompatibility of PDLLA/HA/DBM with co-cultured human osteoblasts in vitro

Objective: To evaluate the osteocompatibility of D, L-polylactic/hydroxyapatite/decalcifying bone matrix (PDLLA/HA/DBM), and compare with PDLLA and DBM. Methods: Human primary osteoblasts isolated from the femoral head of patients were inoculated onto PDLLA/HA/DBM, PLA and DBM respectively. The proliferation rate and collagen Ⅰ expression were detected. The interface between biomaterial and osteoblasts was investigated with phase contrast microscopy and electron scanning microscopy. Results: Best proliferation rate was observed with the PDLLA/HA/DBM and followed by DBM and PLA, suggesting that PDLLA/HA/DBM satisfying most requirements for the cultivation of human osteoblasts. Scanning electron microscopy showed the morphology of osteoblasts was correlated with the proliferation data. The cells, well spread and flattened, were attached closely on the surface of biomaterial with an arched structure and had normal morphology. The extracellular collagenous matrixs covered the surface of biomaterial and packed the granules of biomaterial. Conclusion: PDLLA/HA/DBM can form osteointerface early and have a good biocompability.

Mechanical property and biocompatibility of co-precipitated nano hydroxyapatite-gelatine composites

Uniform and well dispersed nano hydroxyapatite(HA)-gelatine composites were obtained by co-precipitation of hydroxyapatite and denatured calf skin collagen.The process allowed much higher concentration of hydroxyapatite to be produced over conventional hydrothermal process to improve the productivity.The effect of gelatine on the morphology,mechanical properties,and biocompatibility of hydroxyapatite particles was investigated.Fibroblast cell tests of the consolidated hydroxyapatite-gelatine composites showed that the composites have excellent biocompatibility.

Biomineralization of the Surface of PLGA-(ASP-PEG) Modified with the K_(16) and RGD-containing Peptide

K16 and RGD-containing peptide was used to modify the surface of three-dimensional PLGA-（ASP-PEG） matrix, then the modified PLGA-（ASP-PEG） was incubated in modified simulated body fluid （SBF）. The biomineralization of the modified PLGA- （ASP-PEG） was explored, and the peptide was synthesized with solid phase synthesis technology and linked cova-lently to PLGA-（ASP-PEG） through cross-linker （Sulfo-LC-SPDP）, which was characterized with XPS. The modified PLGA-（ASP-PEG） （Experiment group, EG） and PLGA-（ASP-PEG） （Control group, CG） were all incubated into SBF for 10 d, and the growth of hydroxyapatite （HA） nanocrys-tals was confirmed with XRD, EDS and SEM. HPLC shows that peptide purity is 94.13%, while MS analysis shows that molecular value of peptide is 2741.26. Binding energy of the sulphur in EG was 164 eV is detected by XPS, and the ratio of carbon and sulphur is 99.746：0.1014. SEM analysis demonstrates the better growth of bonelike HA nanocrystals in EG than that in CG. The component of mineral in EG consisted mainly of hydroxyapatite containing low crystalline nanocrystals, and the Ca/P ratio is about 1.60, which is similar to that of natural bone, while the Ca/P ratio in CG is 1.52. PLGA-（ASP-PEG） modified with peptide provided enough functional groups for biomineralization, and possessed the bonelike structure.

High performance hydroxyapatite ceramics and a triply periodic minimum surface structure fabricated by digital light processing 3D printing

High performance hydroxyapatite(HA)ceramics with excellent densification and mechanical properties were successfully fabricated by digital light processing(DLP)three-dimensional(3D)printing technology.It was found that the sintering atmosphere of wet C02 can dramatically improve the densification process and thus lead to better mechanical properties.HA ceramics with a relative density of 97.12%and a three-point bending strength of 92.4 MPa can be achieved at a sintering temperature of 1300℃,which makes a solid foundation for application in bone engineering.Furthermore,a relatively high compressive strength of 4.09 MPa can be also achieved for a DLP-printed p-cell triply periodic minimum surface(TPMS)structure with a porosity of 74%,which meets the requirement of cancellous bone substitutes.A further cell proliferation test demonstrated that the sintering atmosphere of wet CO2 led to improve cell vitality after 7 days of cell culture Moreover,with the possible benefit from the bio-inspired structure,the 3D-printed TPMS structure significantly improved the cell vitality,which is crucial for early osteogenesis and osteointegration.

Fabrication of a hydroxyapatite-PDMS microfluidic chip for bone-related cell culture and drug screening

Bone is an important part of the human body structure and plays a vital role in human health.A microfluidic chip that can simulate the structure and function of bone will provide a platform for bone-related biomedical research.Hydroxyapatite(HA),a bioactive ceramic material,has a similar structure and composition to bone mineralization products.In this study,we used HA as a microfluidic chip component to provide a highly bionic bone environment.HA substrates with different microchannel structures were printed by using ceramic stereolithography(SLA)technology,and the minimum trench width was 50μm.The HA substrate with microchannels was sealed by a thin polydimethylsiloxane(PDMS)layer to make a HA-PDMS microfluidic chip.Cell culture experiments demonstrated that compared with PDMS,HA was more conducive to the proliferation and osteogenic differentiation of the human foetal osteoblast cell line(hFOB).In addition,the concentration gradient of the model drug doxorubicin hydrochloride(DOX)was successfully generated on a Christmas tree structure HA-PDMS chip,and the half maximal inhibitory concentration(IC50)of DOX was determined.The findings of this study indicate that the HA-PDMS microfluidic chip has great potential in the field of high-throughput bonerelated drug screening and bone-related research.

Forsterite-hydroxyapatite composite scaffolds with photothermal antibacterial activity for bone repair

Bone engineering scaffolds with antibacterial activity satisfy the repair of bacterial infected bone defects,which is an expected issue in clinical.In this work,3D-printed polymer-derived forsterite scaffolds were proposed to be deposited with hydroxyapatite(HA)coating via a hydrothermal treatment,achieving the functions of photothermal-induced antibacterial ability and bioactivity.The results showed that polymer-derived forsterite scaffolds possessed the photothermal antibacterial ability to inhibit Staphylococcus aureus(S.aureus)and Escherichia coli(E.coli)in vitro,owing to the photothermal effect of free carbon embedded in the scaffolds.The morphology of HA coating on forsterite scaffolds could be controlled through changing the hydrothermal temperature and the pH value of the reaction solution during hydrothermal treatment.Furthermore,HA coating did not influence the mechanical strength and photothermal effect of the scaffolds,but facilitated the proliferation and osteogenic differentiation of rat bone mesenchymal stem cells(rBMSCs)on scaffolds.Hence,the HA-deposited forsterite scaffolds would be greatly promising for repairing bacterial infected bone defects.

Isotropic freeze casting of through-porous hydroxyapatite ceramics

It has well known that hydroxyapatite(HA) is a kind of excellent materials for biomolecular absorption and separation, and the absorption and separation performances of HA would be improved if HA had been processed into desirable porous structures. In this paper, we reported on the combination of gel casting and freeze casting to develop the through-porous hydroxyapatite ceramic monoliths. Experiments demonstrated that the gel-containing freeze casting technique was an isotropic pore-forming technique and could prepare the near-net-shape forming green bodies with good mechanical strength no matter what the HA content in green bodies was. Further green body sintering formed the through-porous ceramics whose grain size, pore size, and porosity depended on and could be controlled by the content of HA in green bodies. The formation of through-pores in ceramics resulted from the gels and water in green bodies, which acted as the templates of the pores with size < 1 μm and the pores with size > 1 μm, respectively. The gel–freeze casting technique is simple, repeatable, and cost-effective, therefore being hopeful for industrial applications.

Immobilization of pegylated AMP on hydroxyapatite nanorods for antibiosis

Infection is one of the major reasons whichinduce failure of percutaneous Ti implants.Covalent bonding of antimicrobial peptides(AMPs)on Ti surfaces can avoid AMPs'blast release by physical absorption,but the reduced mobility affects their antibacterial efficiency.In this paper,HHC36 was pegylated with PEG12 and immobilized on hydroxyapatite(HA)nanorods to endow Ti surface with antibacterial activity and improved cytocom-patibility simultaneously.The obtained results indicated that HA nanorods immobilized with HHC36 showed antibacterial activity,and pegylation obviously increased the antibacterial activity of immobilized HHC36 against staphylococcus aureus.They reached 99.5%and 97.0%in vitro and in vivo,respectively.PEG12 is flexible,and it increases mobility of HHC36 and enables lateral diffusion of peptide molecules into the lipid double layer of microbial membrane,resulting in highly antibacterial activity of HHC36.Furthermore,HA nanorods immobilized with pegylated HHC36 have reduced inflammatory response in an infection model and should be potentially applied on percutaneous Ti implants for reducing infection-induced failure and enhancing biointegration.

Coatings of needle/stripe-like fluoridated hydroxyapatite on H2O2-treated carbon/carbon composites prepared by induction heating and hydrothermal methods

A hydroxyapatite （HA） coating was achieved on H2O2-treated carbon/ carbon （C/C） composite through hydrothermally treating and induction heating deposited CaHPO4 coating in an ammonia solution under ultrasonic water bath. Then, this HA coating was placed in a NH4F solution and hydrothermally treated again to fabricate fluorinated hydroxyapatite （FHA） coatings for 24 h at 353, 373, 393 and 413 K, respectively. The structure, morphology and chemical composition of the HA and FHA coatings were characterized by SEM, XRD, EDS and FTIR, and the adhesiveness and chemical stability of these FHA coatings were examined by a scratch test and an immersion test, respectively. The results showed that the as-prepared FHA coatings contained needle-like or stripe-like crystals, different from those of the HA coating. As the fluoridation temperature rose, the adhesiveness of the FHA coating first increased from 34.8 to 40.9 N at a temperature between 353 and 393 K, and then decreased to 24.2 N at 413 K, while the dissolution rate of the FHA coating decreased steadily. The reasons for the property variation of the FHA coatings were proposed by analyzing the morphology, composition and structure of the coatings.

Enamel matrix proteins in promoting saliva lubrication

Anti-wear performance of human enamel in the mouth is closely related to the lubrication of salivary pellicle.It is well known that the inorganic hydroxyapatite(HA)of the enamel plays an important role in the adsorption and pellicle-forming of salivary proteins on the enamel,but the role of enamel matrix proteins remains unclear.In this study,the adsorption and lubrication behavior of salivary proteins on original,heated,and deproteinated enamel surfaces was comparatively investigated using an atomic force microscopy and nano-indentation/scratch techniques.Compared with that on the original enamel surface,the adsorption and lubrication behavior of salivary proteins remains almost unchanged on the heated enamel surface(where the enamel matrix proteins are denatured but the size of HA crystalline nanoparticles keeps constant)but exhibits an obvious compromise on the deproteinated enamel surface(where the enamel matrix proteins are removed and agglomeration of HA crystallites occurs).The HA agglomeration weakens the electrostatic interaction of enamel surfaces with salivary proteins to cause a distinct negative influence on the adsorption and pellicle-forming of salivary proteins.Further,the negative effect is confirmed with a quartz crystal microbalance with dissipation.In summary,by regulating enamel nanostructure for appropriate electrostatic interactions between salivary proteins and enamel surfaces,the enamel matrix proteins play an essential role in the adsorption and pellicle-forming of salivary proteins on human enamel,and then contribute to saliva lubrication,which provides the enamel with an anti-wear mechanism.The findings will promote and assist the design of enamel-inspired anti-wear materials.