Nanostructured Hydroxyapatite Coatings Research Articles

Application of Early Loading on Surface Implants with Nanostructured Hydroxyapatite Coating

The objective of this work was to describe the variation in the stability of nanostructured HA coatied implants installed in the upper premolar area by means of resonance frequency analysis (RFA, measured in ISQ) during the first 4 weeks, in partially edentulous patients. The study design is quantitative, observational, descriptive, longitudinal and prospective. The implants used were the UNITITE line of S.I.N Implant System® of 3.5 mm x 11.5 mm, which have HAnano® surface. These implants have a surface treatment with a nanostructured hydroxyapatite coating, which increases hydrophilicity and would accelerate the process of new bone formation and remodeling after installation. The surgeries were carried out by students of the Oral Maxillofacial Implantology department, at Universidad Mayor, Santiago. A descriptive analysis was performed on a sample of 8 implants, resulting in a variation of 1 to 2 ISQ points during the four weeks studied. The results suggest that as the stability of the implants keeps constant, it would be possible to carry out early loading at 4 weeks in the implants studied, however, a greater number of samples, comparative studies and longer-term studies are required to generate more robust conclusions on this subject.

Nanostructured hydroxyapatite coatings on NiTi shape memory alloys by ultrasonic mechanical coating and armouring

Mechanical energy-induced deposition on NiTi shape memory alloys (SMAs) is difficult to accomplish due to the pseudoelasticity of NiTi SMAs. In this study, a high-frequency ball-bombardment method called ultrasonic mechanical coating and armouring (UMCA) is introduced to synthesize a hydroxyapatite (HA)-containing coating on a NiTi SMA. The effects of treatment duration, Ti addition, and ball-to-powder ratio on the HA content of the coating are investigated. Results show that the HA content of the coating largely increased during the initial 10 s and decreased with further ball-bombardment. The addition of Ti powder into the chamber assisted HA anchoring on the NiTi SMA surface. Using a ball-to-powder ratio of 1:1 induced the highest HA content on the NiTi SMA as compared to the 1:2 and 2:1 ratios. Coating consisting of 10–50 nm nanoparticles of HA and Ti formed under localized compressive forces were induced through shot collisions. The bombardment also created a local amorphous structure of the NiTi SMA near the coating/NiTi SMA interface. Laser annealing induced oxidation of the coating, which improved the coating adhesion and corrosion resistance of the NiTi SMA in Hank's balanced salt solution. • HA-containing coatings on NiTi SMAs were synthesized by UMCA. • Coatings comprised HA and Ti nanoparticles (10–50 nm). • The NiTi SMA near the coating/substrate interface was amorphous. • Laser-annealed coating improved corrosion resistance of NiTi.

Pulsed laser deposition of nanostructured bioactive glass and hydroxyapatite coatings: Microstructural and electrochemical characterization

Bioactive coatings on metallic implants promote osseointegration between bone and implant interfaces. A suitable coating enhances the life span of the implant and reduces the requirement of revision surgery. The coating process needs to be optimized such that it does not alter the bioactivity of the material. To understand this, the biocompatibility of nanostructured bioactive glass and hydroxyapatite-coated Titanium substrate by pulsed laser deposition method is evaluated. Raman and IR spectroscopic techniques based on silica and phosphate functional groups mapping have confirmed homogeneity in coatings by pulse laser deposition method. Comparative studies on nanostructured bioactive glass and hydroxyapatite on titanium surface elaborated the significance of bioactivity, hemocompatibility, and cytocompatibility of the coated surface. Notably, both hydroxyapatite and bioactive glass show good hemocompatibility in powder form. Hemocompatibility and cytocompatibility results validate the enhanced sustenance for hydroxyapatite coating. These results signify the importance of the choice of coating methodology of bioceramics towards implant applications.

Electrochemical Deposition of Nanostructured Hydroxyapatite Coating on Titanium with Enhanced Early Stage Osteogenic Activity and Osseointegration.

PurposeThe aim of research is to fabricate nanostructured hydroxyapatite (HA) coatings on the titanium via electrochemical deposition (ED). Additionally, the biological properties of the ED-produced HA (EDHA) coatings with a plate-like nanostructure were evaluated in vitro and in vivo by undertaking comparisons with those prepared by acid/alkali (AA) treatment and by plasma spray-produced HA (PSHA) nanotopography-free coatings.Materials and MethodsNanoplate-like HA coatings were prepared through ED, and nanotopography-free PSHA coatings were fabricated. The surface morphology, phase composition, roughness, and wettability of these samples were investigated. Furthermore, the growth, proliferation, and osteogenic differentiation of MC3T3-E1 cells cultured on each sample were evaluated via in vitro experiments. Histological assessment and push-out tests for the bone–implant interface were performed to explore the effect of the EDHA coatings on the interfacial osseointegration in vivo.ResultsXRD analysis showed that the strongest intensity for the EDHA coatings was at the (002) plane rather than at the regular (211) plane. Relatively higher surface roughness and greater wettability were observed for the EDHA coatings. Cellular experiments revealed that the plate-like nanostructured EDHA coatings not only possessed an ability, similar to that of PSHA coatings, to promote the adhesion and proliferation of MC3T3-E1 cells but also demonstrated significantly enhanced early or intermediate markers of osteogenic differentiation. Significant osseointegration enhancement in the early stage of implantation period and great bonding strength were observed at the interface of bone and EDHA samples. In comparison, relatively weak osseointegration and bonding strength of the bone–implant interface were observed for the AA treatment.ConclusionThe biological performance of the plate-like nanostructured EDHA coating, which was comparable with that of the PSHA, improves early-stage osteogenic differentiation and osseointegration abilities and has great potential for enhancing the initial stability and long-term survival of uncemented or 3D porous titanium implants.

The Effect of Nanostructured Hydroxyapatite Coating on Distraction Osteogenesis

Dogs underwent high-frequency automated tibia lengthening with the Ilizarov apparatus over a 1.8-mm hydroxyapatite-coated intramedullary titanium wire. Daily distraction was 3.0 mm with a fraction of 0.125 mm/h and continued ten days. The regenerate was well vascularized, had zonal structure and was of normal or hyperplastic type to the end of distraction. Osteogenesis was fast and complete. The wire served for both mechanical and biological reinforcement of the bone callus and provided reduction of external fixation time. Mean consolidation time with the apparatus on the limb was 13.83±4.02 days. Overall, external fixation index was 10.5 days/cm and 4.8 days/cm in the consolidation phase.

The morphological effect of nanostructured hydroxyapatite coatings on the osteoinduction and osteogenic capacity of porous titanium.

Weak osteogenic activity affects the long-term fixation and lifespan of titanium (Ti) implants. Surface modification along with a built-in porous structure is a highly considerable approach to improve the osteoinduction and osseointegration capacity of Ti. Herein, the osteoinduction and osteogenic activities of electrochemically deposited (ED) nanoplate-like, nanorod-like and nanoneedle-like hydroxyapatite (HA) coatings (named EDHA-P, EDHA-R, and EDHA-N, respectively) were evaluated in vitro and in vivo by comparison with those of acid/alkali (AA) treatment. The results revealed that the apatite forming ability of all nanostructured EDHA coatings was excellent, and only 12 h of soaking in SBF was needed to induce a complete layer of apatite. More serum proteins adsorbed on EDHA-P than others. In cellular experiments, different from those on EDHA-R and EDHA-N, the cells on EDHA-P presented a polygonal shape with lamellipodia extension, and thus exhibited a relatively larger spreading area. Furthermore, EDHA-P was more favorable for the enhancement of the proliferation and ALP activity of BMSCs, and the up-regulation of OPN gene expression. Based on the good biological performance in vitro, EDHA-P was selected to further evaluate its osteoinduction and osteogenic activities in vivo by comparison with AA treatment. Interestingly, a greater ability of ectopic osteoinduction was observed in the EDHA-P group compared to that in the AA group. At the osseous site, EDHA-P promoted more bone on/ingrowth, and had a higher area percentage of newly formed bone in the bone-implant interface and inner pores of the implants than in the AA group. Thus, a nanoplate-like HA coating has good potential in improving the osteoinductivity and osteogenic activity of porous Ti implants in clinical applications.

Comparative study on microstructure and corrosion behavior of nanostructured hydroxyapatite coatings deposited by high velocity oxygen fuel and flame spraying on AZ61 magnesium based substrates

Hydroxyapatite coatings are biocompatible, osteoconductive and create a corrosion resistance surface on magnesium-based implants. Thermal decomposition of HA during thermal spraying limits its application. To overcome the challenges associated with thermal decomposition of HA during thermal spraying, high velocity oxygen fuel spraying with a good thermal stability for HA is proposed. In this work, the traditional flame spraying was compared to high velocity oxy-fuel (HVOF) for HA depositions on magnesium alloy substrates. The effect of process on microstructure, morphology, corrosion behavior and cellular response of HA layers were evaluated. X-ray diffraction analysis showed that the amount of secondary phases in the HVOF deposited sample was less than that in the flame sprayed coatings. Elemental weight percentage of calcium in corroded surfaces was 21% and 34.5% for HVOF and flame sprayed coatings, respectively. Contrary to the results of the electrochemical impedance spectroscopy measurements for HVOF coating performed during the early hours of immersion in the simulated body fluid (SBF), flame sprayed coating exhibited lower corrosion rate after 5 h immersion in SBF solution.

Optimally Hierarchical Nanostructured Hydroxyapatite Coatings for Superior Prosthesis Biointegration.

Bone osteogenesis is a complex phenomenon dependent on numerous microenvironmental cues, with their synchrony regulating cellular functions, such as mechanical signaling, survival, proliferation, and differentiation, as well as controlled regional specification of skeletal progenitor cell fate. Therefore, obtaining a mechanistic understanding of cellular response to a microenvironment is now coming into intense focus, which will facilitate the design of programmable biomaterials for regenerative medicine. State-of-the-art nanomaterial synthesis and self-assembly processes yield complex structures that mimic surface properties, composition, and partially the morphology of the extracellular matrix. However, determining key structural properties that control cell attachment has been challenging and contradictory results are reported regarding the mechanisms and roll of nanostructured materials. Here, we significantly improve osteogenesis on bioinert substrates, demonstrating an exemplary organic-inorganic interface for superior prosthesis biointegration. We identify critical microscale hierarchical features that drastically enhance the cellular response to the same nanoscale architecture. It was observed that hierarchical morphologies, with a porosity above 80%, promote early-stage osteoinduction, as indicated by extensive coating ingrowth and nanofilopodia formation. We determined that cellular integration was mediated by two-way recognition of specific nano- and microtopographical cues between the host tissue and cellular microenvironment. This has allowed us to detail a set of determinant features for the nanofabrication of advanced prosthesis coatings that may ultimately improve implant longevity.

Nanostructured Hydroxyapatite Coating on Bioalloy Substrates: Current Status and Future Directions

Nanostructured Hydroxyapatite Coating on Bioalloy Substrates: Current Status and Future Directions

Biomimetic nanostructured hydroxyapatite coatings on metallic implant materials

Metallic implant materials used in load-bearing applications are inert in nature in their native state. The surface properties of the material and its interaction with the surrounding physiological fluid determine the success of the biomedical implant. In this regard, bioactive nanostructured coatings are being recognised as potential approach to enhance the biological and corrosion properties of the conventional inert materials. In this review, recent advances in biomedical applications of nanostructured hydroxyapatite coatings on stainless steel implant materials are highlighted with special focus on the electrochemical deposition of hydroxyapatite and their consequent biological activity. Furthermore, osteoblasts functions and cellular activity on the nanostructured hydroxyapatite coatings processed by other techniques is also discussed. The potential application of such next generation materials as biomedical implants is also addressed.

Bioactive, nanostructured Si-substituted hydroxyapatite coatings on titanium prepared by pulsed laser deposition.

The aim of this work was to deposit silicon-substituted hydroxyapatite (Si-HAp) coatings on titanium for biomedical applications, since it is known that Si-HAp is able to promote osteoblastic cells activity, resulting in the enhanced bone ingrowth. Pulsed laser deposition (PLD) method was used for coatings preparation. For depositions, Si-HAp targets (1.4 wt % of Si), made up from nanopowders synthesized by wet method, were used. Microstructural and mechanical properties of the produced coatings, as a function of substrate temperature, were investigated by scanning electron and atomic force microscopies, X-ray diffraction, Fourier transform infrared spectroscopy, and Vickers microhardness. In the temperature range of 400-600°C, 1.4-1.5 µm thick Si-HAp films, presenting composition similar to that of the used target, were deposited. The prepared coatings were dense, crystalline, and nanostructured, characterized by nanotopography of surface and enhanced hardness. Whereas the substrate temperature of 750°C was too high and led to the HAp decomposition. Moreover, the bioactivity of coatings was evaluated by in vitro tests in an osteoblastic/osteoclastic culture medium (α-Modified Eagle's Medium). The prepared bioactive Si-HAp coatings could be considered for applications in orthopedics and dentistry to improve the osteointegration of bone implants.

Enhanced Adhesion Properties, Structure and Sintering Mechanism of Hydroxyapatite Coatings Obtained by Plasma Jet Deposition

Hydroxyapatite (HA) coatings were deposited on high purity titanium substrate by atmospheric plasma spraying (APS) with high electric energy input. Previously, the surface of the titanium was prepared by alkali etching with NaOH and subsequent diverse thermal treatments. The phase composition, structure and morphology of the nano-structured HA coatings were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and Auger electron spectroscopy (AES). The XRD pattern showed that the coatings deposited by APS consisted mainly of HA with crystallite sizes between 15.5 and 31 nm and small quantities of the amorphous HA phase. The SEM observation showed that the as-deposited coatings had very different morphology with typical features of micro-structural patterns, which are desirable for improving the biological performances of HA coatings. AES analysis of various spots of the titanium substrate-coating interface showed the presence of an oxide layer with implanted Ca ions owing to the high kinetic energy of the plasma jet. This layer caused a significant increase in the measured adhesive strength, showing values in the range of 51.8–62.5 MPa. The sintering mechanism was studied using several approaches that show that the dominant sintering mechanism was volume diffusion.

Fabrication, ultra-structure characterization and in vitro studies of RF magnetron sputter deposited nano-hydroxyapatite thin films for biomedical applications

A series of nanostructured low-crystalline hydroxyapatite (HA) coatings averaging 170, 250, and 440nm in thickness were deposited onto previously etched titanium substrates through radio-frequency (RF) magnetron sputtering. The HA coatings were analyzed using infrared spectroscopy (FTIR), X-ray diffraction (XRD), and scanning and transmission electron microscopy (SEM and TEM). Cross sections of the thin specimens were prepared by FIB to study the microstructure of the coatings by TEM. The deposition process formed nano-scale grains, generating an amorphous layer at the substrate/coating interface and inducing the growth of a columnar grain structure perpendicular to the substrate surface. A microstructural analysis of the film confirmed that the grain size and crystallinity increased when increasing the deposition time. The nanostructured HA coatings were not cytotoxic, as proven by in vitro assays using primary dental pulp stem cells and mouse fibroblast NCTC clone L929 cells. Low-crystallinity HA coatings with different thicknesses stimulated cells to attach, proliferate and form mineralized nodules on the surface better than uncoated titanium substrates.

Biodegradation assessment of nanostructured fluoridated hydroxyapatite coatings on biomedical grade magnesium alloy

The challenges associated with managing Mg degradation rate demand novel technologies to ensure its biological safety and reliability. Here, fluoridated hydroxyapatite nanopowders with different degrees of fluoridation were coated on microarc oxidized AZ91 magnesium alloy via the electrophoretic deposition method. Zeta potential and conductivity monitoring techniques were employed to offer appropriate conditions for the coatings. The bio-corrosion process and the associated mineralization were interpreted during the immersion in simulated body fluid solution. Based on the results, the 25% fluorine substituted hydroxyapatite coating on microarc-treated AZ91 implant was proposed to stimulate bone ingrowth in a minor invasive behavior and without post-operative complications during its lifespan.

Synthesis, Characterization and Bioactivity Evaluation of Porous Barium Titanate with Nanostructured Hydroxyapatite Coating for Biomedical Application

AbstractNano phase hydroxyapatite (HA) bioceramics have gained importance in the biomedical field due to their superior biological properties. In this study, nanostructured HA coating was used to increase the bioactivity of a piezoelectric bioceramic, barium titanate (BT). Early reports on the influence of collagen piezoelectricity in remodeling of bone have attracted many researchers to piezoelectric bioceramics such as BT. Hence; porous BT was used as the matrix of a new bone graft composite and then coated with nanostructured HA. BT ceramic was foamed via a direct foaming method with a spray of polyurethane foam. The surface of the foam voids was coated with HA via sol–gel and dip‐coating methods. X‐ray diffraction (XRD), transmission electron microscopy (TEM), and scanning electron microscopy (SEM) techniques were used to characterize the prepared coated foam. XRD and TEM analysis showed that the HA coating had a nanostructure with crystallite size of 20–30 nm. SEM images of the prepared samples showed that the HA coating has about 25 µm thickness. The bioactivity of the prepared composite was evaluated in an in vitro study. The variation of Ca2+ and PO43− ions versus time in simulated body fluid (SBF) solution were measured by inductively coupled plasma (ICP) analysis during 1 month and the results showed that the mineralization of calcium phosphate (Ca‐P) on HA coated porous samples was much more than that in non‐coated sample. The SEM micrographs and energy‐dispersive X‐ray spectroscopy (EDS or EDX) analysis of the samples after 1 month of immersing in SBF confirm that Ca‐P phase (bone‐like apatite) was significantly mineralized on HA coated porous BT samples. It was concluded that the nanostructured HA coating would improve the bioactivity of BT foam.

Fabrication of Nano-Structured HA/CNT Coatings on Ti6Al4V by Electrophoretic Deposition for Biomedical Applications

In order to improve the bone bioactivity and osteointegration of metallic implants, hydroxyapatite (HA) is often coated on their surface so that a real bond with the surrounding bone tissue can be formed. In the present study, cathodic electrophoretic deposition (EPD) has been attempted for depositing nanostructured HA coatings on titanium alloy Ti6Al4V followed by sintering at 800 degrees C. Nano-sized HA powder was used in the EPD process to produce dense coatings. Moreover, multiwalled carbon nanotubes (CNTs) were also used to reinforce the HA coating for enhancing its mechanical strength. The surface morphology, compositions and microstructure of the monolithic coating of HA and nanocomposite coatings of HA with different CNT contents (4 to 25%) on Ti6Al4V were investigated by scanning-electron microscopy, energy-dispersive X-ray spectroscopy and Xray diffractometry, respectively. Electrochemical corrosion behavior of the various coatings in Hanks' solution at 37 degrees C was investigated by means of open-circuit potential measurement and cyclic potentiodynamic polarization tests. Surface hardness, adhesion strength and bone bioactivity of the coatings were also studied. The HA and HA/CNT coatings had a thickness of about 10 microm, with corrosion resistance higher than that of the substrate and adhesion strength higher than that of plasma sprayed HA coating. The properties of the composite coatings were optimized by varying the CNT contents. The enhanced properties could be attributed to the use of nano-sized HA particles and CNTs. Compared with the monolithic HA coating, the CNT-reinforced HA coating markedly increased the coating hardness without deteriorating the corrosion resistance or adhesion strength.

Neutron diffraction residual strain measurements in nanostructured hydroxyapatite coatings for orthopaedic implants

The failure of an orthopaedic implant can be initiated by residual strain inherent to the hydroxyapatite coating (HAC). Knowledge of the through-thickness residual strain profile in the thermally sprayed hydroxyapatite coating/substrate system is therefore important in the development of a new generation of orthopaedic implants. As the coating microstructure is complex, non-destructive characterization of residual strain, e.g. using neutron diffraction, provides a useful measure of through thickness strain profile without altering the stress field. This first detailed study using a neutron diffraction technique, non-destructively evaluates the through thickness strain measurement in nanostructured hydroxyapatite plasma sprayed coatings on a titanium alloy substrate (as-sprayed, heat treated, and heat treated then soaked in simulated body fluid (SBF)). The influence of crystallographic plane orientation on the residual strain measurement is shown to indicate texturing in the coating. This texturing is expected to influence both the biological and fracture response of HA coatings. Results are discussed in terms of the influence of heat-treatment and SBF on the residual stress profile for these biomedical coatings. The results show that the through thickness residual strain in all three coatings was different for different crystallographic planes but was on average tensile. It is also concluded that the heat-treatment and simulated body fluid exposure had a significant effect on the residual strain profile in the top layers of HAC.

Characterization and formation mechanism of nano-structured hydroxyapatite coatings deposited by the liquid precursor plasma spraying process

Nano-structured hydroxyapatite (HA) coatings were deposited on the Ti-6Al-4V alloy substrate by the liquid precursor plasma spraying (LPPS) process. The thermal behavior of the HA liquid precursor was analyzed to interpret the phase change and structure transformation during the formation process of the nano-structured HA coatings. The phase composition, structure and morphology of the nano-structured HA coatings were characterized by x-ray diffraction (XRD), scanning electron microscope (SEM) and Fourier transform infrared (FTIR) spectroscopy. The XRD spectra showed that the coatings deposited by the LPPS process mainly consisted of the HA phase and the crystallite size was measured to be 56 nm. The SEM observation showed that the as-deposited LPPS coatings had small splat size, and nano-scale HA particles were found in certain regions of the coating surface. The FTIR spectroscopy showed the strong presence of the OH− group in the as-deposited LPPS coatings, indicating a superior structural integrity. In addition, the coatings deposited by the LPPS process were also carbonated HA coatings. The results indicate that the LPPS process is a promising plasma spraying technique for depositing nano-structured HA coatings with unique microstructural features that are desirable for improving the biological performance of the HA coatings.

Neutron Diffraction Residual Strain Measurements in Plasma Sprayed Nanostructured Hydroxyapatite Coatings for Orthopaedic Implants

Residual strains in plasma sprayed and heat-treated hydroxyapatite (HA) coatings deposited on a titanium alloy (Ti-6Al-4V) substrate were investigated by means of neutron diffraction. Strain measurements were performed in vertical scan (“z-scanning”) mode to provide a through thickness strain profile in the coating and substrate materials. Results are discussed in terms of the influence of heat-treatment on the residual strain profile of these biomedical coatings. This investigation concluded that the heat-treatment had a significant effect on the residual strain profile in HA coatings.

Dense Nanostructured Hydroxyapatite Coating on Titanium by Aerosol Deposition

In order to improve biocompatibility of Ti metal substrates, 1‐μm‐thick nanostructured hydroxyapatite (HAp) coatings were deposited on the substrates through aerosol deposition, which sprays HAp powder with an average particle size of 3.2 μm at room temperature in vacuum. The original HAp particles were fractured into nanoscale fragments to form highly dense coating during the deposition process. Density of the HAp coating was 98.5% theoretical density (TD). Transmission electron microscopy observation revealed that the as‐deposited coating consisted of HAp crystallites with average grain size of 16.2 nm and amorphous phase. Tensile adhesion strength between the coating and the substrate was 30.5±1.2 MPa. Annealing up to 500°C in air increased crystallinity and grain size in the coating without any delamination or crack according to X‐ray diffraction analysis and electron microscopy. MTS assay and alkaline phosphatase activity measurements with MC3T3‐E1 preosteoblast cell revealed that the biocompatibility was greatly improved by postdeposition heat treatment at 400°C in air due to well‐crystallized HAp with average grain size of 29.3 nm. However, further heat treatment at 500°C deteriorated biocompatibility due to rapid growth of HAp grains to average size of 99 nm. Cross section of the coating on a commercially available Ti dental implant revealed full coverage of the surface with HAp.