Structural influence from calcium phosphate coatings and its possible effect on enhanced bone integration

An Elastin-Derived Composite Matrix for Enhanced Vascularized and Innervated Bone Tissue Reconstruction: From Material Development to Preclinical Evaluation

Despite progress in bone tissue engineering, reconstruction of large bone defects remains an important clinical challenge. Here, a biomaterial designed to recruit bone cells, endothelial cells, and neuronal fibers within the same matrix is developed, enabling bone tissue regeneration. The bioactive matrix is based on modified elastin-like polypeptides (ELPs) grafted with laminin-derived adhesion peptides IKVAV and YIGSR, and the SNA15 peptide for retention of hydroxyapatite (HA) particles. The composite matrix shows suitable porosity, interconnectivity, biocompatibility for endothelial cells, and the ability to support neurites outgrowth by sensory neurons. Subcutaneous implantation leads to the formation of osteoid tissue, characterized by the presence of bone cells, vascular networks, and neuronal structures, while minimizing inflammation. Using a rat femoral condyle defect model, longitudinal micro-CT analysis is performed, which demonstrates a significant increase in the volume of mineralized tissue when using the ELP-based matrix compared to empty defects and a commercially available control (Collapat). Furthermore, visible blood vessel networks and nerve fibers are observed within the lesions after a period of two weeks. By incorporating multiple key components that support cell growth, mineralization, and tissue integration, this ELP-based composite matrix provides a holistic and versatile solution to enhance bone tissue regeneration.

Advanced applications of strontium-containing biomaterials in bone tissue engineering

Strontium (Sr) and strontium ranelate (SR) are commonly used therapeutic drugs for patients suffering from osteoporosis. Researches have showed that Sr can significantly improve the biological activity and physicochemical properties of materials in vitro and in vivo. Therefore, a large number of strontium containing biomaterials have been developed for repairing bone defects and promoting osseointegration. In this review, we provide a comprehensive overview of Sr-containing biomaterials along with the current state of their clinical use. For this purpose, the different types of biomaterials including calcium phosphate, bioactive glass, and polymers are discussed and provided future outlook on the fabrication of the next-generation multifunctional and smart biomaterials.

Advanced Surface Modification for 3D-Printed Titanium Alloy Implant Interface Functionalization

With the development of three-dimensional (3D) printed technology, 3D printed alloy implants, especially titanium alloy, play a critical role in biomedical fields such as orthopedics and dentistry. However, untreated titanium alloy implants always possess a bioinert surface that prevents the interface osseointegration, which is necessary to perform surface modification to enhance its biological functions. In this article, we discuss the principles and processes of chemical, physical, and biological surface modification technologies on 3D printed titanium alloy implants in detail. Furthermore, the challenges on antibacterial, osteogenesis, and mechanical properties of 3D-printed titanium alloy implants by surface modification are summarized. Future research studies, including the combination of multiple modification technologies or the coordination of the structure and composition of the composite coating are also present. This review provides leading-edge functionalization strategies of the 3D printed titanium alloy implants.

Calcium phosphate and silicate-based nanoparticles: history and emerging trends

Bulk calcium phosphates and silicate-based bioglasses have been extensively studied since the early 1970s due to their unique capacity to bind to host bone, which led to their clinical translation and commercialization in the 1980s. Since the mid-1990s, researchers have synthesized nanoscale calcium phosphate and silicate-based particles of increased specific surface area, chemical reactivity and solubility which offer specific advantages as compared to their bulk counterparts. This review provides a critical perspective on the history and emerging trends of these two classes of ceramic nanoparticles. Their synthesis and functional properties in terms of particle composition, size, shape, charge, dispersion, and toxicity are discussed as a function of relevant processing parameters. Specifically, emerging trends such as the influence of ion doping and mesoporosity on the biological and pharmaceutical performance of these nanoparticles are reviewed in more detail. Finally, a broad comparative overview is provided on the physicochemical properties and applicability of calcium phosphate and silicate-based nanoparticles within the fields of i) local delivery of therapeutic agents, ii) functionalization of biomaterial scaffolds or implant coatings, and iii) bio-imaging applications.

Stable sol-gel hydroxyapatite coating on zirconia dental implant for improved osseointegration

Aside from being known for its excellent mechanical properties and aesthetic effect, zirconia has recently attracted attention as a new dental implant material. Many studies have focused on hydroxyapatite (HA) coating for obtaining improved biocompatibility, however the coating stability was reduced by a byproduct produced during the high-temperature sintering process. In this study, to overcome this problem, we simply coated the zirconia surface with a sol-gel-derived hydroxyapatite (HA) layer and then sintered it at a varied temperature (<1000 °C). The surface showed a nanoporous structure, and there was no crystalline phase other than HA and zirconia when the sintering temperature was 800 °C. The adhesion strength of the HA layer (>40 MPa) was also appropriate as a dental implant application. In addition, in vitro cell experiments using a preosteoblast cell line revealed that the HA-coated zirconia surface acts as a preferable surface for cell attachment and proliferation than bare zirconia surface. In vivo animal experiments also demonstrated that the osteoconductivity of zirconia were dramatically enhanced by HA coating, which was comparable to that of Ti implant. These results suggest that the sol-gel-based HA-coated zirconia has a great potential for use as a dental implant material.

Evaluation of pulsed electromagnetic field protocols in implant osseointegration: in vivo and in vitro study

OBJECTIVES

The present study aims to evaluate two protocols of pulsed electromagnetic field (PEMF) on osseointegration and establish one that addresses ideal parameters for its use in dentistry, especially in the optimization of the implants osseointegration process.

MATERIALS AND METHODS

Sixty male rats (Wistar) were allocated into three experimental groups: control (GC), test A (GTA, 3 h exposed), and test B (GTB, 1 h exposed). All animals received titanium implants in both tibias, and PEMF application (15 Hz, ± 1 mT, 5 days/week) occurred only in the test groups. They were euthanized at 03, 07, 21, and 45 days after PEMF therapy. Removal torque, histomorphometric measurements, three-dimensional radiographic evaluation, and in vitro biological assay analyses were performed.

RESULTS

GTB showed better results compared with GTA in removal torque tests, in bone volume and bone mineral density, cell viability, total protein content, and mineralization nodules (p < 0.05). GTA showed better performance in trabecular bone thickness and cell proliferation compared with GTB (p < 0.05), especially at osseointegration early periods. In the histomorphometric analysis and number of trabeculae, there were no differences in the test groups.

CONCLUSION

PEMF as a biostimulator was effective in optimizing the events in bone tissue that lead to osseointegration, especially when applied for a shorter time and in the initial periods of bone healing.

CLINICAL RELEVANCE

The PEMF therapy is an effective alternative method for optimizing bone healing.

Heat and hydrothermal treatments on the microstructure evolution and mechanical properties of plasma sprayed hydroxyapatite coatings reinforced with graphene nanoplatelets

Recent demands in clinical applications drive a large amount of research to plasma sprayed hydroxyapatite (HA) composite coatings. Herein, graphene nanosheet (GNS) reinforced HA coating was fabricated using plasma spray, the effect of heat and hydrothermal treatments (hereafter referred to as thermal treatment) on microstructural evolution and mechanical properties of the composite coating were investigated. Thermally treated GNS/HA coating not only exhibited ~47.1% improvement in HA crystallinity and more denser microstructure, but also displayed increased surface roughness (3 times of that of the as-sprayed sample) due to the fact that GNSs facilitated HA nanoparticle precipitation on the coating surface. Fracture toughness of the as-sprayed HA coating increased by up to ~44.1% at 2.0 wt% GNSs owing to GNS pullout, GNS bridging and arresting of crack propagation by the embedded GNSs. As for thermally treated HA coatings, crack propagation arrested by the sintered regions was found to act as an important toughening mechanism, but thermal treatment introduced more structural defects into the GNSs and led to the reductions in their length and thickness, resulting in negligible enhancement in toughness of the GNS/HA coating.

Can implant surfaces affect implant stability during osseointegration? A randomized clinical trial

This randomized clinical trial evaluated the insertion torque (IT), primary, and secondary stability of dental implants with different surface treatments during the osseointegration period. Nineteen patients with bilateral partial edentulism in the posterior mandibular region were randomly allocated to two implant brand groups and received implants with different surface treatments in the opposite site of the arch: Osseotite and Nanotite or SLA and SLActive. During implant placement, the maximum IT was recorded using a surgical motor equipped with a graphical user interface. The implant stability quotient (ISQ) was assessed immediately after the IT, and was measured weekly via resonance frequency analysis during 3 months. The data were analyzed by a one-way ANOVA, the Bonferroni test, paired t tests and Pearson's correlation coefficient. The IT values were similar (p > 0.05) for all implant types ranging from 43.82 ± 6.50 to 46.84 ± 5.06. All implant types behaved similarly until the 28th day (p > 0.05). Between 35 and 56 days, Osseotite and SLActive showed lower ISQ values (p < 0.001) compared to Nanotite and SLA implants. After 56 days, only Osseotite maintained significantly lower ISQ values than the other implants (p < 0.05). After 91 days the ISQ values were significantly higher than the baseline for all four implant types (p < 0.001). The ISQ and IT values were significantly correlated at the baseline and at the final evaluation for Osseotite, Nanotite, and SLActive implants (p < 0.001). After 91 days, ISQ and IT values were only significantly correlated for the Osseotite implants (p < 0.05). All implants types exhibited acceptable primary and secondary stability.

Bone Response to Titanium Implants Coated with Double- or Single-Stranded DNA

We aimed to evaluate in vivo bone response and in vitro apatite formation to titanium (Ti) implants, coated with double-stranded DNA (DNA-d) or single-stranded DNA (DNA-s), and to compare the influence in different structure of DNA, double strand and single strand on bone response and apatite formation. The bone responses to multilayered DNA-d/protamine or DNA-s/protamine coating implants were evaluated after implantation into the extracted sockets of rat maxillary molars. Apatite formation on either coating surface after immersion in simulated body fluid (SBF) was evaluated using the quartz crystal microbalance (QCM) method. DNA-d/protamine and DNA-s/protamine coatings produced more roughened and hydrophilic surfaces than untreated Ti. Animal experiments showed that higher bone-to-implant ratios were achieved 3 and 6 weeks after implantation using DNA-d/protamine and DNA-s/protamine coatings compared with Ti. QCM measurements revealed that each coating contributed to significant earlier apatite formation in SBF. We conclude that both DNA-d/protamine and DNA-s/protamine coatings enhanced early bone formation. We suggest that a DNA-multilayer coating is useful for the surface modification of a Ti implant.

Enhanced Tribological and Bacterial Resistance of Carbon Nanotube with Ceria- and Silver-Incorporated Hydroxyapatite Biocoating

Pertaining to real-life applications (by scaling up) of hydroxyapatite (HA)-based materials, herein is a study illustrating the role of carbon nanotube (CNT) reinforcement with ceria (CeO₂) and silver (Ag) in HA on titanium alloy (TiAl6V4) substrate, utilizing the plasma-spraying processing technique, is presented. When compared with pure HA coating enhanced hardness (from 2.5 to 5.8 GPa), elastic modulus (from 110 to 171 GPa), and fracture toughness (from 0.7 to 2.2 MPa·m^1/2) elicited a reduced wear rate from 55.3 × 10⁻⁵ mm³·N⁻¹·m⁻¹ to 2.1 × 10⁻⁵ mm³·N⁻¹·m⁻¹ in HA-CNT-CeO₂-Ag. Besides, an order of magnitude lower Archard’s wear constant and a 41% decreased shear stress by for HA-CNT-CeO₂-Ag coating depicted the effect of higher hardness and modulus of a material to control its wear phenomenon. Antibacterial property of 46% (bactericidal) is ascribed to Ag in addition to CNT-CeO₂ in HA. Nonetheless, the composite coating also portrayed exaggerated L929 fibroblast cell growth (4.8 times more than HA), which was visualized as flat and elongated cells with multiple filopodial protrusions. Hence, synthesis of a material with enhanced mechanical integrity resulting in tribological resistance and cytocompatible efficacy was achieved, thereupon making HA-CNT-CeO₂-Ag a scalable potent material for real-life load-bearing implantable bio-coating.

Characterization and Bone Response of Carbonate-Containing Apatite-Coated Titanium Implants Using an Aqueous Spray Coating

We performed thin carbonate-containing apatite (CA) coating on titanium (Ti) by an aqueous spray coating (ASC) method that consisted of a Ca-CO₃-PO₄ complex. Two different CA coatings were produced by two different spray amounts and were heat-treated after spraying. We evaluated three-dimensional structures, adhesiveness to Ti, and durability of the CA film. In addition, we performed immersion experiments in simulated body fluid (SBF), and bone responses were evaluated after implantation into a femoral bone defect in rats. The bonding ability of ASC-coated implant into the bone was examined by push-in tests. Unique network structures with small particles were identified on CA coatings. Although heat treatment produced no significant difference in surface morphology, scratch tests revealed that heat treatment improved the adhesion of CA coatings to Ti. Crystal formation progressed on CA-coated specimens, and the sample placement direction influenced crystal formation and growth in SBF immersion. Animal implantation experiments revealed significantly greater bone-to-implant contact ratio and bone mass in both cortical and bone marrow, respectively, four weeks after implantation. Push-in tests suggested that the bonding of the CA coating to Ti is clinically acceptable. Therefore, we conclude that CA coating to Ti by the ASC method would be possible for clinical applications, including dentistry.

Increasing the Stability of Dental Implants: the Concept of Osseodensification

One of the most important factors that affect osseointegration is the primary stability of the implant. Dental implants inserted at the posterior region of the maxilla exhibit the lowest success rates as the low density bone in this area often jeopardize rigid fixation of the implant. Many surgical techniques have been developed to increase the primary stability of an implant placed in low density bone, such as bicortical fixation of the implant, undersized preparation of the implant bed and bone condensation by the use of osteotomes. A new promising technique, named osseodensification, has been recently developed that creates an autograft layer of condensed bone at the periphery of the implant bed by the aid of specially designed burs rotating in a clockwise and anti-clockwise direction. The purpose of this review is to emphasize that implant primary stability is strongly influenced by the surgical technique, to quote and briefly analyse the various surgical procedures laying weight to osseodensification procedure.

Deconvoluting the Bioactivity of Calcium Phosphate-Based Bone Graft Substitutes: Strategies to Understand the Role of Individual Material Properties

Calcium phosphate (CaP)-based ceramics are the most widely applied synthetic biomaterials for repair and regeneration of damaged and diseased bone. CaP bioactivity is regulated by a set of largely intertwined physico-chemical and structural properties, such as the surface microstructure, surface energy, porosity, chemical composition, crystallinity and stiffness. Unravelling the role of each individual property in the interaction between the biomaterial and the biological system is a prerequisite for evolving from a trial-and-error approach to a design-driven approach in the development of new functional biomaterials. This progress report critically reviews various strategies developed to decouple the roles of the individual material properties in the biological performance of CaP ceramics. It furthermore emphasizes on the importance of a comprehensive and adequate material characterization that is needed to enhance our knowledge of the property-function relationship of biomaterials used in bone regeneration, and in regenerative medicine in general.

Enhanced proliferation and differentiation effects of a CGRP- and Sr-enriched calcium phosphate cement on bone mesenchymal stem cells

INTRODUCTION

Because of its good osteoconductivity, strontium (Sr) ranelate has been extensively used as a bone substitute for the treatment of bone disorders. To facilitate treatment, Sr is also incorporated into calcium phosphate cement (Sr-CPC); however, the Sr from Sr-CPC is not sufficient to induce a significant increase of bone mass in an ovariectomized rat model. To improve the efficiency of Sr-CPC, we developed a calcitonin gene-related peptide (CGRP)- and Sr-enriched CPC (CGRP-Sr-CPC).

METHODS

We used X-ray diffraction and Fourier transform infrared spectroscopy to measure properties of CGRP-Sr-CPC. We also employed a cell proliferation assay, alkaline phosphatase (ALP) assay and real-time PCR to assess the effects of CPC implants on proliferation and differentiation of bone mesenchymal stem cells (BMSCs) from an ovariectomized rat model.

RESULTS

CGRP did not change the composition, pore sizes and compressive strength of the cement body as compared with Sr-CPC. Meanwhile, CGRP-Sr-CPC did not show cell cytotoxicity to BMSCs. Further, CGRP and Sr released from CGRP-Sr-CPC significantly enhanced the cell proliferation of BMSCs and increased the activity of ALP during differentiation of BMSCs, compared with CGRP- or Sr-CPC. Moreover, CGRP-Sr-CPC significantly up-regulated the expression levels of osteogenic differentiation-related genes including Alp, Bmp2, Osteonectin and Runx2 during differentiation.

CONCLUSIONS

These findings demonstrate the optimized effects of CGRP- and Sr-enriched CPC in promoting proliferation and osteogenic differentiation of BMSCs, suggesting the potential ability of this novel cement to assist the formation of new bone during osteoporosis-induced bone disorders.

Comparison of Removal Torques for Implants With Hydroxyapatite-Blasted and Sandblasted and Acid-Etched Surfaces

PURPOSE

Sandblasted and acid-etched (SLA) implants are widely known and used by many practitioners. A resorbable blasting media (RBM) surface is produced by blasting with bioceramic particles. We studied the correlation between the particle sizes of the media and the biomechanical force, evaluating the removal torque of hydroxyapatite-blasted implants.

MATERIALS AND METHODS

Commercial SLA implants comprised the control group, and RBM surface-treated implants of the same size and design comprised the experimental group. These implants were installed on both sides of rabbits' tibiae. Four weeks after the implants were installed, the implant removal torque was measured using a digital torque device. The roughness of the implant surface was analyzed using field-emission scanning electron microscopy and confocal laser scanning microscopy.

RESULTS

Both groups of surface textures exhibited a regular porosity. The 2 groups exhibited different surface roughness. No significant differences in removal torques were observed between the control and experimental groups.

CONCLUSION

There were no significant differences in our measures of osseointegration between hydroxyapatite-blasted and SLA implants.

Surface characterization and in vivo evaluation of laser sintered and machined implants followed by resorbable-blasting media process: A study in sheep

Background

This study aimed to compare the histomorphometric and histological bone response to laser-sintered implants followed by resorbable-blasting media (RBM) process relative to standard machined/RBM surface treated implants.

Material and Methods

Six male sheep (n=6) received 2 Ti-6Al-4V implants (1 per surface) in each side of the mandible for 6 weeks in vivo. The histomorphometric parameters bone-implant contact (BIC) and bone area fraction occupancy (BAFO) were evaluated.

Results

Optical interferometry revealed higher Sa and Sq values for the laser-sintered/RBM surface in relation to standard/RBM implants. No significant differences in BIC were observed between the two groups (p>0.2), but significantly higher BAFO was observed for standard/RBM implants (p<0.01).

Conclusions

The present study demonstrated that both surfaces were biocompatible and osseoconductive, and the combination of laser sintering and RBM has no advantage over the standard machined implants with subsequent RBM.

Key words:Dental implants, osseointegration, resorbable- blasting media, sheep, in vivo.

In vitro and in vivo evaluation of the inflammatory potential of various nanoporous hydroxyapatite biomaterials

Aim: To discriminate the most important physicochemical parameters for bone reconstruction, the inflammatory potential of seven nanoporous hydroxyapatite powders synthesized by hard or soft templating was evaluated both in vitro and in vivo. Materials & methods: After physical and chemical characterization of the powders, we studied the production of inflammatory mediators by human primary monocytes after 4 and 24 h in contact with powders, and the host response after 2 weeks implantation in a mouse critical size defect model. Results: In vitro results highlighted increases in the secretion of TNF-α, IL-1, -8, -10 and proMMP-2 and -9 and decreases in the secretion of IL-6 only for powders prepared by hard templating. In vivo observations confirmed an extensive inflammatory tissue reaction and a strong resorption for the most inflammatory powder in vitro. Conclusion: These findings highlight that the most critical physicochemical parameters for these nanoporous hydroxyapatite are, the crystallinity that controls dissolution potential, the specific surface area and the size and shape of crystallites.

Synthesis of bioactive β-TCP coatings with tailored physico-chemical properties on zirconia bioceramics

The objective of this work was to develop a synthesis procedure for the deposition of β-TCP coatings with tailored physico-chemical properties on zirconia bioceramics. The synthesis procedure involved two steps: (i) a rapid wet-chemical deposition of a biomimetic CaP coating and (ii) a subsequent post-deposition processing of the biomimetic CaP coating, which included a heat treatment between 800 and 1200 °C, followed by a short sonication in a water bath. By regulating the heating temperature the topography of the β-TCP coatings could be controlled. The average surface roughness (Ra) ranged from 42 nm for the coating that was heated at 900 °C (TCP-900) to 630 nm for the TCP-1200 coating. Moreover, the heating temperature also affected the dissolution rate of the coatings in a physiological solution, their protein-adsorption capacity and their bioactivity in a simulated body fluid.

Enhanced bone healing around nanohydroxyapatite-coated polyetheretherketone implants: An experimental study in rabbit bone

Objective

To investigate the bone response to threaded polyetheretherketone (PEEK) implants coated with nanohydroxyapatite.

Materials and methods

A total of 39 PEEK implants were coated with nanocrystalline hydroxyapatite and 39 uncoated implants were used as controls. The implant surface was characterized by optical interferometry and scanning electron microscope. The implants were inserted in the tibia and femur of 13 rabbits. After 6 weeks of healing, quantitative and qualitative analyses were performed.

Results

The test implants showed significantly higher removal torque test values compared with the control group. Histomorphometric evaluation demonstrated higher bone-to-implant contact for the test implants; however, there were no differences in bone area between the groups. Qualitative histological analyses demonstrated inflammatory cellular reactions in close vicinity of both implant surfaces. A two-cell layer of foreign body giant cells was observed irrespective of sample type.

Conclusion

Our findings demonstrate that implants with a threaded design render good stability to PEEK in both coated and uncoated implants. Nanohydroxyapatite-coated PEEK implants demonstrated improved bone formation compared with uncoated controls.

Nanometer scale titanium surface texturing are detected by signaling pathways involving transient FAK and Src activations

Background

It is known that physico/chemical alterations on biomaterial surfaces have the capability to modulate cellular behavior, affecting early tissue repair. Such surface modifications are aimed to improve early healing response and, clinically, offer the possibility to shorten the time from implant placement to functional loading. Since FAK and Src are intracellular proteins able to predict the quality of osteoblast adhesion, this study evaluated the osteoblast behavior in response to nanometer scale titanium surface texturing by monitoring FAK and Src phosphorylations.

Methodology

Four engineered titanium surfaces were used for the study: machined (M), dual acid-etched (DAA), resorbable media microblasted and acid-etched (MBAA), and acid-etch microblasted (AAMB). Surfaces were characterized by scanning electron microscopy, interferometry, atomic force microscopy, x-ray photoelectron spectroscopy and energy dispersive X-ray spectroscopy. Thereafter, those 4 samples were used to evaluate their cytotoxicity and interference on FAK and Src phosphorylations. Both Src and FAK were investigated by using specific antibody against specific phosphorylation sites.

Principal Findings

The results showed that both FAK and Src activations were differently modulated as a function of titanium surfaces physico/chemical configuration and protein adsorption.

Conclusions

It can be suggested that signaling pathways involving both FAK and Src could provide biomarkers to predict osteoblast adhesion onto different surfaces.

Osteoconductive Potential of Mesoporous Titania Implant Surfaces Loaded with Magnesium: An Experimental Study in the Rabbit

BACKGROUND

Mesoporous coatings enable incorporation of functional substances and sustainedly release them at the implant site. One bioactive substance that can be incorporated in mesoporous is magnesium, which is strongly involved in bone metabolism and in osteoblast interaction.

PURPOSE

The aim of this experimental study was to evaluate the effect of incorporation of magnesium into mesoporous coatings of oral implants on early stages of osseointegration.

MATERIAL AND METHODS

Titanium implants were coated with thin films of mesoporous TiO2 having pore diameters of 6 nm and were loaded with magnesium. The implant surfaces were extensively characterized by means of interferometry, atomic force microscopy, scanning electron microscopy, and energy-dispersive spectroscopy and then placed in the tibiae of 10 rabbits. After 3 weeks of healing, osseointegration was evaluated by means of removal torque testing and histology and histomorphometry.

RESULTS

Histological and biomechanical analyses revealed no side effects and successful osseointegration of the implants. The biomechanical evaluation evidenced a significant effect of magnesium doping on strengthening the implant-bone interface.

CONCLUSIONS

A local release of magnesium from the implant surfaces enhances implant retention at the early stage of healing (3 weeks after implantation), which is highly desirable for early loading of the implant.

Significance of calcium phosphate coatings for the enhancement of new bone osteogenesis--a review

A systematic analysis of results available from in vitro, in vivo and clinical trials on the effects of biocompatible calcium phosphate (CaP) coatings is presented. An overview of the most frequently used methods to prepare CaP-based coatings was conducted. Dense, homogeneous, highly adherent and biocompatible CaP or hybrid organic/inorganic CaP coatings with tailored properties can be deposited. It has been demonstrated that CaP coatings have a significant effect on the bone regeneration process. In vitro experiments using different cells (e.g. SaOS-2, human mesenchymal stem cells and osteoblast-like cells) have revealed that CaP coatings enhance cellular adhesion, proliferation and differentiation to promote bone regeneration. However, in vivo, the exact mechanism of osteogenesis in response to CaP coatings is unclear; indeed, there are conflicting reports of the effectiveness of CaP coatings, with results ranging from highly effective to no significant or even negative effects. This review therefore highlights progress in CaP coatings for orthopaedic implants and discusses the future research and use of these devices. Currently, an exciting area of research is in bioactive hybrid composite CaP-based coatings containing both inorganic (CaP coating) and organic (collagen, bone morphogenetic proteins, arginylglycylaspartic acid etc.) components with the aim of promoting tissue ingrowth and vascularization. Further investigations are necessary to reveal the relative influences of implant design, surgical procedure, and coating characteristics (thickness, structure, topography, porosity, wettability etc.) on the long-term clinical effects of hybrid CaP coatings. In addition to commercially available plasma spraying, other effective routes for the fabrication of hybrid CaP coatings for clinical use still need to be determined and current progress is discussed.

Bone responses to zirconia implants with a thin carbonate-containing hydroxyapatite coating using a molecular precursor method

Thin carbonate-containing hydroxyapatite (CA) films coating partially stabilized zirconia (Y-TZP) were prepared (CA-Y-TZP) to establish a metal-free implant system. CA was coated using a molecular precursor method. The CA film was deposited on the surface of Y-TZP using a precursor solution, which was a mixture of a calcium-ethylenediaminetetraacetic acid (EDTA) complex and phosphate compounds. The deposited CA film was characterized by X-ray diffraction, Fourier transform infrared spectroscopy, and energy dispersive X-ray spectroscopy measurements. A focus ion beam system technique revealed that the thickness of the CA film was less than 1.0 µm. Biological evaluations of CA-Y-TZP were performed by immersion experiments in simulated body fluid (SBF) and implantation experiments in the tibiae and femoral condyles of rabbits. In the SBF immersion experiment, apatite deposition progressed more on CA-Y-TZP at the early stage of immersion than on Y-TZP without the CA coating. Animal experiments revealed that bone formation on CA-Y-TZP was similar with than on Y-TZP. Histomorphometrical evaluations showed a significantly higher bone-to-implant contact ratio and bone mass on CA-Y-TZP after implantation into the femoral trabecular bone of rabbits. Therefore, CA-Y-TZP appears to be applicable as a metal-free implant.

Histologic and Biomechanical Evaluation of 2 Resorbable-Blasting Media Implant Surfaces at Early Implantation Times

This study evaluated 3 implant surfaces in a dog model: (1) resorbable-blasting media + acid-etched (RBMa), alumina-blasting + acid-etching (AB/AE), and AB/AE + RBMa (hybrid). All of the surfaces were minimally rough, and Ca and P were present for the RBMa and hybrid surfaces. Following 2 weeks in vivo, no significant differences were observed for torque, bone-to-implant contact, and bone-area fraction occupied measurements. Newly formed woven bone was observed in proximity with all surfaces.

Photocatalytically induced hydrophilicity influences bone remodelling at longer healing periods: a rabbit study

OBJECTIVES

Previously, we have reported that photocatalytically active hydrophilicity of the anatase titanium dioxide (TiO₂) nanoparticles coated onto commercially pure titanium discs presented significantly improved hydrophilicity after ultraviolet irradiation. As hydrophilicity has shown enhancement of osseointegration, the in vivo responses were of great interest. The aim of this study was to evaluate whether or not the photo-activated hydrophilicity generated at the time of implant placement has an effect on the longer healing periods for osseointegration.

MATERIALS AND METHODS

Photocatatytically active nanostructured TiO₂ powder (Degussa P-25), which consists of approximately 80% anatase and 20% rutile, was spin-coated onto commercially pure titanium discs and was heat-treated thereafter. These P25-coated discs were irradiated with ultraviolet (UV) light for the test (+UV) group, and non-irradiated discs were prepared for the control (-UV) group. Both groups of discs were placed in the rabbits' tibiae. After 12 weeks of healing period, histological analysis and gene expression analysis using real-time RT-PCR were performed.

RESULTS

From the histological analyses, there were no specific differences between -UV and +UV groups. However, from the gene expression analysis, ALP, RUNX-2 and IL-10 were significantly upregulated for the +UV group compared with the -UV group.

CONCLUSIONS

The biologically enhancing effect to photocatalytically activated surfaces remained even after 12 weeks of healing time in terms of genetic responses.

Physicochemical Characterization and In Vivo Evaluation of Amorphous and Partially Crystalline Calcium Phosphate Coatings Fabricated on Ti-6Al-4V Implants by the Plasma Spray Method

Objective. To characterize the topographic and chemical properties of 2 bioceramic coated plateau root form implant surfaces and evaluate their histomorphometric differences at 6 and 12 weeks in vivo. Methods. Plasma sprayed hydroxyapatite (PSHA) and amorphous calcium phosphate (ACP) surfaces were characterized by scanning electron microscopy (SEM), interferometry (IFM), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FT-IR). Implants were placed in the radius epiphysis, and the right limb of dogs provided implants that remained for 6 weeks, and the left limb provided implants that remained 12 weeks in vivo. Thin sections were prepared for bone-to-implant contact (BIC) and bone-area-fraction occupancy (BAFO) measurements (evaluated by Friedman analysis P < 0.05). Results. Significantly, higher S_a (P < 0.03) and S_q (P < 0.02) were observed for ACP relative to PSHA. Chemical analysis revealed significantly higher HA, calcium phosphate, and calcium pyrophosphate for the PSHA surface. BIC and BAFO measurements showed no differences between surfaces. Lamellar bone formation in close contact with implant surfaces and within the healing chambers was observed for both groups. Conclusion. Given topographical and chemical differences between PSHA and ACP surfaces, bone morphology and histomorphometric evaluated parameters showed that both surfaces were osseoconductive in plateau root form implants.

In vitro characterization and osteoblast responses to nanostructured photocatalytic TiO2 coated surfaces

The aims of the study were to characterize a nanostructured photoactive titanium dioxide (TiO(2)) coating and to compare the cellular response of human osteoblasts before and after ultraviolet (UV) irradiation of the coating. A specific nanostructured TiO(2) powder (Degussa P-25), which consists of approximately 80% anatase and 20% rutile, was spin-coated onto commercially pure titanium discs, and was heat-treated thereafter. After topographical, chemical and photocatalytic property characterizations, human osteoblasts were cultured on the coated discs before and after UV irradiation. Cell morphology was evaluated by scanning electron microscopy (SEM), and cell viability was analysed by 3-(4,5-dimethylthiazol)-2,5-diphenyltetrazolium bromide (MTT) assay. From the contact angle analysis, the wettability significantly improved after UV irradiation. The cultured cells were flattened with numerous elongated lammellipodia; however, no morphological differences were indicated between -UV and +UV surfaces. The MTT assay analysis showed that -UV surface presented significantly higher viability compared to the +UV surface except for one cell population group at 3h where there were no differences. The nanostructured photoactive TiO(2) surface improved its hydrophilicity by UV irradiation, however no enhancing effect in cell response was confirmed at the time tested compared to the non-irradiated surface.

Surface and Biomechanical Study of Titanium Implants Modified by Laser With and Without Hydroxyapatite Coating, in Rabbits

Surface and biomechanical analysis of titanium implant surfaces modified by laser beam with and without hydroxyapatite. Titanium implants with 3 different surfaces were inserted into the tibias of 30 rabbits: group I (GI) machined surface (control group), group II irradiated with laser (GII), and group III irradiated with laser and hydroxyapatite coating applied—biomimetic method (GIII). Topographical analysis with scanning electron microscopy was made before surgery in the tibia. These rabbits were distributed into 2 periods of observation: 4 and 8 weeks postsurgery, after which biomechanical analysis (removal torque) was conducted. Statistical analysis used the Student-Newman-Keuls method. Surface showed roughness in GII and GIII. Biomechanical analysis demonstrated values with significant differences in GII and GIII. Titanium implants modified by laser irradiation can increase osseointegration during the initial phase.

Osteoclast resorption of thermal spray hydoxyapatite coatings is influenced by surface topography

Coating characteristics such as composition, crystallite features and topography collectively impact the cell response. The influence from splats has not yet been assessed for hydroxyapatite (HAp) thermal spray coatings. The objective of this work is to (a) survey the topography on commercial implants, (b) ascertain topography formation from single splats, and (c) determine the osteoclast resorption pattern on a topographically refined coating compared to dentine. Coatings on dental implants, an orthopedic screw, a femoral stem and a knee implant were studied for reference. The effects of substrate pre-heat, roughness, spray distance and particle size on the coating roughness and topography were studied. Human-derived osteoclasts were placed on a coating with refined topography and compared to dentine, a polished coating and polished sintered HAp. A pre-heat of at least 200°C on titanium was required to form rounded splats. The greatest influence on coating roughness and topography arose from particle size. A 2-fold increase in the mean particle size from 30 to 72 μm produced a significant difference (P<0.001) in roughness from 4.8 and 9.7 μm. A model is shown to illustrate topography formation, nanostructure evolution on single splats, and the topography as seen in commercial implants. Osteoclasts showed a clear preference for activity on coatings with refined topography. A one-way ANOVA test revealed a significantly greater pit depth (P=0.022) for dentine (14 μm) compared to the as-sprayed and polished coating (5 μm). Coatings with topography display a similar number of resorption pits with dentine, but a 10-fold greater number than polished coatings, emphasizing the importance of flattened droplet topography on implant surfaces.

Commercially pure titanium implants with surfaces modified by laser beam with and without chemical deposition of apatite. Biomechanical and topographical analysis in rabbits

OBJECTIVES

The purpose of this study was to evaluate the surfaces of commercially pure titanium (cp Ti) implants modified by laser beam (LS), without and with hydroxyapatite deposition by the biomimetic method (HAB), without (HAB) and with thermal treatment (HABT), and compare them with implants with surfaces modified by acid treatment (AS) and with machined surfaces (MS), employing topographical and biomechanics analysis.

METHODS

Forty-five rabbits received 75 implants. After 30, 60, and 90 days, the implants were removed by reverse torque and the surfaces were topographically analyzed.

RESULTS

At 30 days, statistically significant difference (P < 0.05) was observed among all the surfaces and the MS, between HAB/HABT and AS and between HAB and LS. At 60 days, the reverse torque of LS, HAB, HABT, and AS differed significantly from MS. At 90 days, difference was observed between HAB and MS. The microtopographic analysis revealed statistical difference between the roughness of LS, HAB, and HABT when compared with AS and MS.

CONCLUSIONS

It was concluded that the implants LS, HAB, and HABT presented physicochemical and topographical properties superior to those of AS and MS and favored the osseointegration process in the shorter periods. In addition, HAB showed the best results when compared with other surfaces.

Genetic responses to nanostructured calcium-phosphate-coated implants

Nanostructured calcium phosphate (CaP) has been histologically and biomechanically proven to enhance osseointegration of implants; however, conventional techniques were not sufficiently sensitive to capture its biological effects fully. Here, we compared the conventional removal torque (RTQ) evaluation and gene expression in tissues around nanostructured CaP-coated implants, using real-time RT-PCR, with those of uncoated implants, in a rabbit model. At 2 wks, RTQ values were significantly higher, alkaline phosphatase (ALP) expression was significantly higher, and runt-related transcription factor 2 and tumor necrosis factor-α expressions were significantly lower in the coated than in the uncoated implants. This indicates that inflammatory responses were suppressed and osteoprogenitor activity increased around the CaP-coated surface. At 4 wks, although RTQ values did not significantly differ between the 2 groups, ALP and osteocalcin (OCN) were significantly up-regulated in the coated group, indicating progressive mineralization of the bone around the implant. Moreover, an osteoclast marker, adenosine triphosphatase, which indicates acidification of the resorption lacunae, was significantly higher for the coated implants, suggesting gradual resorption of the CaP coating. This study reveals detailed genetic responses to nanostructured CaP-coated implants and provides evidence that the effect of nanotopography is significant during the osseointegration cascade.

Histologic and biomechanical evaluation of alumina-blasted/acid-etched and resorbable blasting media surfaces

This study evaluated the early biomechanical fixation and bone-to-implant contact (BIC) of an alumina-blasted/acid-etched (AB/AE) compared with an experimental resorbable blasting media (RBM) surface in a canine model. Higher texturization was observed for the RBM than for the AB/AE surface, and the presence of calcium and phosphorus was only observed for the RBM surface. Time in vivo and implant surface did not influence torque. For both surfaces, BIC significantly increased from 2 to 4 weeks.