Relative contributions of chemistry and topography to the osseointegration of hydroxyapatite coatings

Choice of Spinal Interbody Fusion Cage Material and Design Influences Subsidence and Osseointegration Performance

OBJECTIVE

The objective of the study was to quantify the effect of cage material (titanium-alloy vs. polyetheretherketone or PEEK) and design (porous vs. solid) on subsidence and osseointegration.

METHODS

Three lateral cages (solid PEEK, solid titanium, and 3-dimension-printed porous titanium cages) were evaluated for cage stiffness, subsidence compression stiffness, and dynamic subsidence displacement under simulated postoperative spine loading. Dowel-shaped implants made of grit-blasted solid titanium alloy (solid titanium) and porous titanium were fabricated using commercially available processes. Samples were processed for mechanical push-out testing and polymethylmethacrylate histology following an established ovine bone implantation model.

RESULTS

The solid titanium cage exhibited the greatest stiffness (57.1 ± 0.6 kN/mm), followed by the porous titanium cage (40.4 ± 0.3 kN/mm) and the solid PEEK cage (37.1 ± 1.2 kN/mm). In the clinically relevant dynamic subsidence, the porous titanium cage showed the least amount of subsidence displacement (0.195 ± 0.012 mm), significantly less than that of the solid PEEK cage (0.328 ± 0.020 mm) and the solid titanium cage (0.538 ± 0.027 mm). Bony on-growth was noted histologically on all implant materials; however, only the porous titanium supported bony ingrowth with marked quantities of bone formed within the interconnected pores through 12 weeks. Functional differences in osseointegration were noted between groups during push-out testing. The porous titanium showed the highest maximum shear stress at 12 weeks and was the only group that demonstrated significant improvement (4-12 weeks).

CONCLUSIONS

The choice of material and design is critical to cage mechanical and biological performances. A porous titanium cage can reduce subsidence risk and generate biological stability through bone on-growth and ingrowth.

High Subsidence Rate After Primary Total Hip Arthroplasty Using a Zweymüller-type Noncemented Implant With a Matte Surface

Introduction:

The surface topography is one key factor that affects the initial fixation of prosthesis in total hip arthroplasty (THA). We aimed to evaluate the mid-term results of a Zweymüller-type noncemented femoral implant (Elance stem) that had a matte surface with a target average roughness of 1.0 to 2.5 μm. The prosthesis was subjected to alkali and heat treatments to enhance its bone-bonding property.

Methods:

In this retrospective study, 30 THAs (27 patients) done using an Elance stem from September 2012 to October 2014 were evaluated clinically and radiographically for a mean follow-up of 6.3 ± 1.7 years after the index THA.

Results:

Stem revision was indicated for six hips (20%). The survival rate with stem revision for any reason was 86.4% (95% confidence interval, 68.9%-94.8%) at 5 years. Stem subsidence >5 mm was noted in 17 hips (56.7%). The survival rate with stem subsidence >5 mm as the end point was 46.6% (95% confidence interval, 29.9%-64.2%) at 5 years.

Conclusion:

The Zweymüller-type noncemented stem with a low-roughness matte surface demonstrated a high subsidence rate, although the bone-bonding property was potentially enhanced by the alkali and heat treatments. Surgeons should be aware that an insufficient surface roughness could lead to poor mechanical fixation of the noncemented stem, even with an appropriate stem geometry and surface chemistry.

The effect of hydroxyapatite on titanium pedicle screw resistance: an electrical model

BACKGROUND CONTEXT

Intraoperative detection of a pedicle wall breach implicitly reduces surgical risk, but the reliability of intraoperative neuromonitoring has been contested. Hydroxyapatite (HA) has been promulgated to increase pedicle screw resistance and negatively influence the accuracy of electromyography.

PURPOSE

The primary purpose of this experiment is to evaluate the effect of HA on pedicle screw electrical resistance using a controlled laboratory model.

STUDY DESIGN

Controlled laboratory study.

METHODS

Stimulation of pedicle screws was performed in normal saline (0.9% NaCl). The experimental group included 8 HA coated (HAC) pedicle screws and matched manufacturer control pedicle screws without HAC (Ti6Al4V). All screws were stimulated at 5, 10-, 15-, 20-, and 25-mm submersion depths. Circuit current return was recorded, and pedicle screw electrical resistance was calculated according to Ohm's Law. Data were assessed for normality and variance. Mann-Whitney U and Kruskal-Wallis tests compared groups with Bonferroni correction for multiple testing. Effect size is reported with 95% confidence intervals (95CI). p values <.05 were considered significant.

RESULTS

Current return was detected for all screws (N=24) following subclinical 8.5 µA stimulation at 5, 10-, 15-, 20-, and 25-mm submersion depths (N=144). The effect estimate of HA on pedicle screw electrical resistance is -0.07 (-0.17 to 0.01 95CI). The estimated effect of HA on pedicle screw electrical resistance did not differ across manufacturers. Electrical resistance values were inversely related to submersion depth. Electrical resistance values were lower in the experimental group at 10 mm (p=.04), 15 mm (p=.04), and 25 mm (p=.02) submersion depths. The HA effect ranged from -0.03 to -0.08 as submersion depth varied.

CONCLUSIONS

We found no evidence that HA increased pedicle screw electrical resistance in a matched manufacturer control laboratory model. Electrical stimulation of pedicle screws may be reliable for pedicle breach detection in the presence of HA. Future research should investigate if laboratory findings translate to clinical practice and confirm that electrical stimulation of pedicle screws is a reliable method to detect pedicle breach in the presence of HA.

Biomimetic Composite Coatings for Activation of Titanium Implant Surfaces: Methodological Approach and In Vivo Enhanced Osseointegration

Innovative nanomaterials are required for the coatings of titanium (Ti) implants to ensure the activation of Ti surfaces for improved osseointegration, enhanced bone fracture healing and bone regeneration. This paper presents a systematic investigation of biomimetic composite (BC) coatings on Ti implant surfaces in a rat model of a diaphyseal femoral fracture. Methodological approaches of surface modification of the Ti implants via the usual joining methods (e.g., grit blasting and acid etching) and advanced physicochemical coating via a self-assembled dip-coating method were used. The biomimetic procedure used multi-substituted hydroxyapatite (ms-HAP) HAP-1.5 wt% Mg-0.2 wt% Zn-0.2 wt% Si nanoparticles (NPs), which were functionalized using collagen type 1 molecules (COL), resulting in ms-HAP/COL (core/shell) NPs that were embedded into a polylactic acid (PLA) matrix and finally covered with COL layers, obtaining the ms-HAP/COL@PLA/COL composite. To assess the osseointegration issue, first, the thickness, surface morphology and roughness of the BC coating on the Ti implants were determined using AFM and SEM. The BC-coated Ti implants and uncoated Ti implants were then used in Wistar albino rats with a diaphyseal femoral fracture, both in the absence and the presence of high-frequency pulsed electromagnetic shortwave (HF-PESW) stimulation. This study was performed using a bone marker serum concentration and histological and computer tomography (micro-CT) analysis at 2 and 8 weeks after surgical implantation. The implant osseointegration was evaluated through the bone–implant contact (BIC). The bone–implant interface was investigated using FE-SEM images and EDX spectra of the retrieved surgical implants at 8 weeks in the four animal groups. The obtained results showed significantly higher bone–implants contact and bone volume per tissue volume, as well as a greater amount of newly formed bone, in the BC-coated Ti implants than in the uncoated Ti implants. Direct bone–implant contact was also confirmed via histological examination. The results of this study confirmed that these biomimetic composite coatings on Ti implants were essential for a significant enhancement of osseointegration of BC-coated Ti implants and bone regeneration. This research provides a novel strategy for the treatment of bone fractures with possible orthopedic applications.

Iodine-Loaded Calcium Titanate for Bone Repair with Sustainable Antibacterial Activity Prepared by Solution and Heat Treatment

In the orthopedic and dental fields, simultaneously conferring titanium (Ti) and its alloy implants with antibacterial and bone-bonding capabilities is an outstanding challenge. In the present study, we developed a novel combined solution and heat treatment that controllably incorporates 0.7% to 10.5% of iodine into Ti and its alloys by ion exchange with calcium ions in a bioactive calcium titanate. The treated metals formed iodine-containing calcium-deficient calcium titanate with abundant Ti-OH groups on their surfaces. High-resolution XPS analysis revealed that the incorporated iodine ions were mainly positively charged. The surface treatment also induced a shift in the isoelectric point toward a higher pH, which indicated a prevalence of basic surface functionalities. The Ti loaded with 8.6% iodine slowly released 5.6 ppm of iodine over 90 days and exhibited strong antibacterial activity (reduction rate >99%) against methicillin-resistant Staphylococcus aureus (MRSA), S. aureus, Escherichia coli, and S. epidermidis. A long-term stability test of the antibacterial activity on MRSA showed that the treated Ti maintained a >99% reduction until 3 months, and then it gradually decreased after 6 months (to a 97.3% reduction). There was no cytotoxicity in MC3T3-E1 or L929 cells, whereas apatite formed on the treated metal in a simulated body fluid within 3 days. It is expected that the iodine-carrying Ti and its alloys will be particularly useful for orthopedic and dental implants since they reliably bond to bone and prevent infection owing to their apatite formation, cytocompatibility, and sustainable antibacterial activity.

The effect of simple heat treatment on apatite formation on grit-blasted/acid-etched dental Ti implants already in clinical use

Grit-blasted/acid-etched titanium dental implants have a moderately roughened surface that is suitable for cell adhesion and exhibits faster osseointegration. However, the roughened surface does not always maintain stable fixation over a long period. In this study, a simple heat treatment at 600°C was performed on a commercially available dental Ti implant with grit-blasting/acid-etching, and its effect on mineralization capacity was assessed by examining apatite formation in a simulated body fluid (SBF). The as-purchased implant displayed a moderately roughened surface at the micrometer scale. Its surface was composed of titanium hydride accompanied by a small amount of alumina particles derived from the grit-blasting. Heat treatment transformed the titanium hydride into rutile without evidently changing the surface morphology. The immersion in SBF revealed that apatite formed on the heated implant at 7 days. Furthermore, apatite formed on the Ti rod surface within 1 day when the metal was subjected to acid and heat treatment without blasting. These indicate that apatite formation was conferred on the commercially available dental implant by simple heat treatment, although its induction period was slightly affected by alumina particles remaining on the implant surface. The heat-treated implant should achieve stronger and more stable bone bonding due to its apatite formation.

The Use of Simulated Body Fluid (SBF) for Assessing Materials Bioactivity in the Context of Tissue Engineering: Review and Challenges

Some special implantable materials are defined as “bioactive” if they can bond to living bone, forming a tight and chemically-stable interface. This property, which is inherent to some glass compositions, or can be induced by applying appropriate surface treatments on otherwise bio-inert metals, can be evaluated in vitro by immersion studies in simulated body fluid (SBF), mimicking the composition of human plasma. As a result, apatite coating may form on the material surface, and the presence of this bone-like “biomimetic skin” is considered predictive of bone-bonding ability in vivo. This review article summarizes the story and evolution of in vitro bioactivity testing methods using SBF, highlighting the influence of testing parameters (e.g., formulation and circulation of the solution) and material-related parameters (e.g., composition, geometry, texture). Suggestions for future methodological refinements are also provided at the end of the paper.

New Insights into Osteointegration and Delamination from a Multidisciplinary Investigation of a Failed Hydroxyapatite-Coated Hip Joint Replacement

Hydroxyapatite (HA) coatings have become very popular in uncemented total hip arthroplasty (THA). Analysis of retrievals and tissue samples from an HA-coated femoral stem, which failed within 14 months after THA, provides exceptional insights into the failure mechanism, as well as the process of osteointegration of such an implant. Methods: Retrievals were photo-documented. Samples were examined by micro-computed tomography, X-ray diffraction (XRD) and embedded in polymethylmethacrylate for histology. Results: The coating had partially delaminated. The sandblasted surface of the stem was partially polished by the delaminated HA coating, indicating failure before revision. In the tissue samples, the HA coating was well integrated by newly formed bone trabeculae. No adverse biological reaction was observed. XRD analysis showed that residues of the HA coating were still present and could clearly be differentiated from the surrounding bone. Preferential orientation of the HA crystallites could be identified within the newly formed bone, representing a potential mechanical weakness induced either by physiologic strain or by the coating. Conclusion: current HA coatings, relatively thick and made of high crystallinity HA, may be prone to delamination, as also seen in our study. Recent efforts have aimed towards thinner (<1 μm) coatings with nanocrystalline HA structures that possibly relate to lower delamination risks. However, the question arises if HA coatings are beneficial since sandblasted non-coated stems offer similar results without the risk of delamination. XRD not only permits differentiation between the HA from the coating and the HA of the ongrown bone, it also provides new insights into the microstructure of this newly formed bone.

Nanotechnology Assisted Targeted Drug Delivery for Bone Disorders: Potentials and Clinical Perspectives

Nanotechnology and its allied modalities have brought revolution in tissue engineering and bone healing. The research on translating the findings of the basic and preclinical research into clinical practice is ongoing. Advances in the synthesis and design of nanomaterials along with advances in genomics and proteomics, and tissue engineering have opened a bright future for bone healing and orthopedic technology. Studies have shown promising outcomes in the design and fabrication of porous implant substrates that can be exploited as bone defect augmentation and drug-carrier devices. However, there are dozens of applications in orthopedic traumatology and bone healing for nanometer-sized entities, structures, surfaces, and devices with characteristic lengths ranging from tens 10s of nanometers to a few micrometers. Nanotechnology has made promising advances in the synthesis of scaffolds, delivery mechanisms, controlled modification of surface topography and composition, and biomicroelectromechanical systems. This study reviews the basic and translational sciences and clinical implications of the nanotechnology in tissue engineering and bone diseases. Recent advances in NPs assisted osteogenic agents, nanocomposites, and scaffolds for bone disorders are discussed.

Effects of Surface Topography and Chemistry on Polyether-Ether-Ketone (PEEK) and Titanium Osseointegration

STUDY DESIGN

An in vivo study examining the functional osseointegration of smooth, rough, and porous surface topographies presenting polyether-ether-ketone (PEEK) or titanium surface chemistry.

OBJECTIVE

To investigate the effects of surface topography and surface chemistry on implant osseointegration.

SUMMARY OF BACKGROUND DATA

Interbody fusion devices have been used for decades to facilitate fusion across the disc space, yet debate continues over their optimal surface topography and chemistry. Though both factors influence osseointegration, the relative effects of each are not fully understood.

METHODS

Smooth, rough, and porous implants presenting either a PEEK or titanium surface chemistry were implanted into the proximal tibial metaphyses of 36 skeletally mature male Sprague Dawley rats. At 8 weeks, animals were euthanized and bone-implant interfaces were subjected to micro-computed tomography analysis (n = 12), histology (n = 4), and biomechanical pullout testing (n = 8) to assess functional osseointegration and implant fixation.

RESULTS

Micro-computed tomography analysis demonstrated that bone ingrowth was 38.9 ± 2.8% for porous PEEK and 30.7 ± 3.3% for porous titanium (P = 0.07). No differences in fixation strength were detected between porous PEEK and porous titanium despite titanium surfaces exhibiting an overall increase in bone-implant contact compared with PEEK (P < 0.01). Porous surfaces exhibited increased fixation strength compared with smooth and rough surfaces regardless of surface chemistry (P < 0.05). Across all groups both surface topography and chemistry had a significant overall effect on fixation strength (P < 0.05), but topography accounted for 65.3% of the total variance (ω = 0.65), whereas surface chemistry accounted for 5.9% (ω = 0.06).

CONCLUSIONS

The effect of surface topography (specifically porosity) dominated the effect of surface chemistry in this study and could lead to further improvements in orthopedic device design. The poor osseointegration of existing smooth PEEK implants may be linked more to their smooth surface topography rather than their material composition.

LEVEL OF EVIDENCE

N/A.

The effect of strontium and silicon substituted hydroxyapatite electrochemical coatings on bone ingrowth and osseointegration of selective laser sintered porous metal implants

Additive manufactured, porous bone implants have the potential to improve osseointegration and reduce failure rates of orthopaedic devices. Substantially porous implants are increasingly used in a number of orthopaedic applications. HA plasma spraying-a line of sight process-cannot coat the inner surfaces of substantially porous structures, whereas electrochemical deposition of calcium phosphate can fully coat the inner surfaces of porous implants for improved bioactivity, but the osseous response of different types of hydroxyapatite (HA) coatings with ionic substitutions has not been evaluated for implants in the same in vivo model. In this study, laser sintered Ti6Al4V implants with pore sizes of Ø 700 μm and Ø 1500 μm were electrochemically coated with HA, silicon-substituted HA (SiHA), and strontium-substituted HA (SrHA), and implanted in ovine femoral condylar defects. Implants were retrieved after 6 weeks and histological and histomorphometric evaluation were compared to electrochemically coated implants with uncoated and HA plasma sprayed controls. The HA, SiHA and SrHA coatings had Ca:P, Ca:(P+Si) and (Ca+Sr):P ratios of 1.53, 1.14 and 1.32 respectively. Electrochemically coated implants significantly promoted bone attachment to the implant surfaces of the inner pores and displayed improved osseointegration compared to uncoated scaffolds for both pore sizes (p<0.001), whereas bone ingrowth was restricted to the surface for HA plasma coated or uncoated implants. Electrochemically coated HA implants achieved the highest osseointegration, followed by SrHA coated implants, and both coatings exhibited significantly more bone growth than plasma sprayed groups (p≤0.01 for all 4 cases). SiHA had significantly more osseointegration when compared against the uncoated control, but no significant difference compared with other coatings. There was no significant difference in ingrowth or osseointegration between pore sizes, and the bone-implant-contact was significantly higher in the electrochemical HA than in SiHA or SrHA. These results suggest that osseointegration is insensitive to pore size, whereas surface modification through the presence of an osteoconductive coating plays an important role in improving osseointegration, which may be critically important for extensively porous implants.

Tri-Functional Calcium-Deficient Calcium Titanate Coating on Titanium Metal by Chemical and Heat Treatment

The main problem of orthopedic and dental titanium (Ti) implants has been poor bone-bonding to the metal. Various coatings to improve the bone-bonding, including the hydroxyapatite and titania, have been developed, and some of them have been to successfully applied clinical use. On the other hand, there are still challenges to provide antibacterial activity and promotion of bone growth on Ti. It was shown that a calcium-deficient calcium titanate coating on Ti and its alloys exhibits high bone-bonding owing to its apatite formation. In this study, Sr and Ag ions, known for their promotion of bone growth and antibacterial activity, were introduced into the calcium-deficient calcium titanate by a three-step aqueous solution treatment combined with heat. The treated metal formed apatite within 3 days in a simulated body fluid and exhibited antibacterial activity to Escherichia coli without showing any cytotoxicity in MC3T3-E1 preosteoblast cells. Furthermore, the metal slowly released 1.29 ppm of Sr ions. The Ti with calcium-deficient calcium titanate doped with Sr and Ag will be useful for orthopedic and dental implants, since it should bond to bone because of its apatite formation, promote bone growth due to Sr ion release, and prevent infection owing to its antibacterial activity.

Characterization of bone ingrowth and interface mechanics of a new porous 3D printed biomaterial: an animal study

AIMS

The purpose of this study was to evaluate the biological fixation of a 3D printed porous implant, with and without different hydroxyapatite (HA) coatings, in a canine model.

MATERIALS AND METHODS

A canine transcortical model was used to evaluate the characteristics of bone ingrowth of Ti6Al4V cylindrical implants fabricated using laser rapid manufacturing (LRM). At four and 12 weeks post-implantation, we performed histological analysis and mechanical push-out testing on three groups of implants: a HA-free control (LRM), LRM with precipitated HA (LRM-PA), and LRM with plasma-sprayed HA (LRM-PSHA).

RESULTS

Substantial bone ingrowth was observed in all LRM implants, with and without HA, at both time periods. Bone ingrowth increased from 42% to 52% at four weeks, to 60% to 65% at 12 weeks. Mechanical tests indicated a minimum shear fixation strength of 20 MPa to 24 MPa at four weeks, and 34 MPa to 40 MPa at 12 weeks. There was no significant difference in the amount of bone ingrowth or in the shear strength between the three implant types at either time period.

CONCLUSION

At four and 12 weeks, the 3D printed porous implants exhibited consistent bone ingrowth and high mechanical shear strength. Based on the results of this study, we confirmed the suitability of this novel new additive manufacturing porous material for biological fixation by bone ingrowth. Cite this article: Bone Joint J 2019;101-B(6 Supple B):62-67.

Bioactive pedicle screws prepared by chemical and heat treatments improved biocompatibility and bone-bonding ability in canine lumbar spines

Background

Titanium (Ti)-6Al-4V alloy, which is widely used in spinal instrumentation with a pedicle screw (PS) system. However, significant clinical problems, including loosening and back-out of PSs, persist. During the last decade, a novel technology that produces bioactive Ti from chemical and heat treatments has been reported that induces the spontaneous formation of a hydroxyapatite (HA) layer on the surface of Ti materials. The purpose of this study was to study the effect of bioactivation of Ti-6Al-4V PSs on the ability of HA formation in vitro and its biocompatibility and bone-bonding ability in vivo.

Methods

Ti-6V-4Al alloy PSs were prepared and bioactivated by NaOH-CaCl₂-heat-water treatments. The HA-forming ability of bioactive PSs in simulated body fluid (SBF) was evaluated by field emission scanning electron microscopy (FE-SEM) and energy dispersive X-ray analysis (EDX). Six 11-month-old female beagle dogs were used for the in vivo study. Bioactive and control (without bioactivation) PSs were left and right randomly placed from L1 to L6. One and three months after surgery, lumbar spines were removed for biomechanical and histological analyses.

Results

In vitro: The surface analysis of bioactive PSs by FE-SEM and EDX showed substantial HA deposits over the entire surface. In vivo: The mean extraction torque was significantly higher for bioactive PSs compared to controls PSs (P<0.01); there was no significant difference in pull-out strength between control and bioactive PSs. Histologically, the contact area between bone tissue and screw surface showed no significant trend to be greater in bioactive PSs compared to control PSs (P = 0.06).

Conclusions

Bioactive PSs prepared by chemical and heat treatments formed layers of HA on the surface of screws in vitro that improved biocompatibility and bonding ability with bone in vivo. Bioactive PSs may reduce screw loosening to overcome the obstacles confronted in spinal instrumentation surgery.

Impact of Surface Potential on Apatite Formation in Ti Alloys Subjected to Acid and Heat Treatments

Titanium metal (Ti) and its alloys are widely used in orthopedic and dental fields. We have previously shown that acid and heat treatment was effective to introduce bone bonding, osteoconduction and osteoinduction on pure Ti. In the present study, acid and heat treatment with or without initial NaOH treatment was performed on typical Ti-based alloys used in orthopedic and dental fields. Dynamic movements of alloying elements were developed, which depended on the kind of treatment and type of alloy. It was found that the simple acid and heat treatment enriched/remained the alloying elements on Ti-6Al-4V, Ti-15Mo-5Zr-3Al and Ti-15Zr-4Nb-4Ta, resulting in neutral surface charges. Thus, the treated alloys did not form apatite in a simulated body fluid (SBF) within 3 days. In contrast, when the alloys were subjected to a NaOH treatment prior to an acid and heat treatment, alloying elements were selectively removed from the alloy surfaces. As a result, the treated alloys became positively charged, and formed apatite in SBF within 3 days. Thus, the treated alloys would be useful in orthopedic and dental fields since they form apatite even in a living body and bond to bone.

Bioactive treatment promotes osteoblast differentiation on titanium materials fabricated by selective laser melting technology

Selective laser melting (SLM) technology is useful for the fabrication of porous titanium implants with complex shapes and structures. The materials fabricated by SLM characteristically have a very rough surface (average surface roughness, Ra=24.58 µm). In this study, we evaluated morphologically and biochemically the specific effects of this very rough surface and the additional effects of a bioactive treatment on osteoblast proliferation and differentiation. Flat-rolled titanium materials (Ra=1.02 µm) were used as the controls. On the treated materials fabricated by SLM, we observed enhanced osteoblast differentiation compared with the flat-rolled materials and the untreated materials fabricated by SLM. No significant differences were observed between the flat-rolled materials and the untreated materials fabricated by SLM in their effects on osteoblast differentiation. We concluded that the very rough surface fabricated by SLM had to undergo a bioactive treatment to obtain a positive effect on osteoblast differentiation.

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.

Calcium Phosphate Bioceramics: A Review of Their History, Structure, Properties, Coating Technologies and Biomedical Applications

Calcium phosphate (CaP) bioceramics are widely used in the field of bone regeneration, both in orthopedics and in dentistry, due to their good biocompatibility, osseointegration and osteoconduction. The aim of this article is to review the history, structure, properties and clinical applications of these materials, whether they are in the form of bone cements, paste, scaffolds, or coatings. Major analytical techniques for characterization of CaPs, in vitro and in vivo tests, and the requirements of the US Food and Drug Administration (FDA) and international standards from CaP coatings on orthopedic and dental endosseous implants, are also summarized, along with the possible effect of sterilization on these materials. CaP coating technologies are summarized, with a focus on electrochemical processes. Theories on the formation of transient precursor phases in biomineralization, the dissolution and reprecipitation as bone of CaPs are discussed. A wide variety of CaPs are presented, from the individual phases to nano-CaP, biphasic and triphasic CaP formulations, composite CaP coatings and cements, functionally graded materials (FGMs), and antibacterial CaPs. We conclude by foreseeing the future of CaPs.

Long-term release of antibiotics by carbon nanotube-coated titanium alloy surfaces diminish biofilm formation by Staphylococcus epidermidis

Bacterial biofilms cause a considerable amount of prosthetic joint infections every year, resulting in morbidity and expensive revision surgery. To address this problem, surface modifications of implant materials such as carbon nanotube (CNT) coatings have been investigated in the past years. CNTs are biologically compatible and can be utilized as drug delivery systems. In this study, multi-walled carbon nanotube (MWCNT) coated TiAl6V4 titanium alloy discs were fabricated and impregnated with Rifampicin, and tested for their ability to prevent biofilm formation over a period of ten days. Agar plate-based assays were employed to assess the antimicrobial activity of these surfaces against Staphylococcus epidermidis. It was shown that vertically aligned MWCNTs were more stable against attrition on rough surfaces than on polished TiAl6V4 surfaces. Discs with coated surfaces caused a significant inhibition of biofilm formation for up to five days. Therefore, MWCNT-modified surfaces may be effective against pathogenic biofilm formation on endoprostheses.

Sliced Magnetic Polyacrylamide Hydrogel with Cell-Adhesive Microarray Interface: A Novel Multicellular Spheroid Culturing Platform

Cell-adhesive properties are of great significance to materials serving as extracellular matrix mimics. Appropriate cell-adhesive property of material interface can balance the cell-matrix interaction and cell-cell interaction and can promote cells to form 3D structures. Herein, a novel magnetic polyacrylamide (PAM) hydrogel fabricated via combining magnetostatic field induced magnetic nanoparticles assembly and hydrogel gelation was applied as a multicellular spheroids culturing platform. When cultured on the cell-adhesive microarray interface of sliced magnetic hydrogel, normal and tumor cells from different cell lines could rapidly form multicellular spheroids spontaneously. Furthermore, cells which could only form loose cell aggregates in a classic 3D cell culture model (such as hanging drop system) were able to be promoted to form multicellular spheroids on this platform. In the light of its simplicity in fabricating as well as its effectiveness in promoting formation of multicellular spheroids which was considered as a prevailing tool in the study of the microenvironmental regulation of tumor cell physiology and therapeutic problems, this composite material holds promise in anticancer drugs or hyperthermia therapy evaluation in vitro in the future.

Growth of Novel Ceramic Layers on Metals via Chemical and Heat Treatments for Inducing Various Biological Functions

The present authors' systematic studies on growth of novel ceramic layers on Ti metal and its alloys by chemical and heat treatments for inducing bone-bonding bioactivity and some other biological functions are reviewed. Ti metal formed an apatite on its surface in a simulated body fluid, when heat-treated after exposure to strong acid solutions to form rutile surface layer, or to strong alkali solutions to form sodium titanate surface layer. Both types of Ti metal tightly bonded to the living bone. The alkali and heat treatment was applied to the surface Ti metal of an artificial hip joint and successfully used in the clinic since 2007. The acid and heat treatments was applied to porous Ti metal to induce osteoconductivity as well as osteoinductivity. The resulting product was successfully used in clinical trials for spinal fusion devices. For the Ti-based alloys, the alkali and heat treatment was little modified to form calcium titanate surface layer. Bone-growth promoting Mg, Sr, and Zn ions as well as the antibacterial Ag ion were successfully incorporated into the calcium titanate layer.

Bisphosphonate-adsorbed ceramic nanoparticles increase bone formation in an injectable carrier for bone tissue engineering

Sucrose acetate isobutyrate (SAIB) is a sugar-based carrier. We have previously applied SAIB as a minimally invasive system for the co-delivery of recombinant human bone morphogenetic protein-2 (rhBMP-2) and found synergy when co-delivering zoledronic acid (ZA) and hydroxyapatite (HA) nanoparticles. Alternative bioceramics were investigated in a murine SAIB/rhBMP-2 injection model. Neither beta-tricalcium phosphate (TCP) nor Bioglass (BG) 45S5 had a significant effect on bone volume (BV) alone or in combination with the ZA. ¹⁴C-labelled ZA binding assays showed particle size and ceramic composition affected binding with nano-HA > micro-HA > TCP > BG. Micro-HA and nano-HA increased BV in a rat model of rhBMP-2/SAIB injection (+278% and +337%), and BV was further increased with ZA–adsorbed micro-HA and nano-HA (+530% and +889%). These data support the use of ZA–adsorbed nanoparticle-sized HA as an optimal additive for the SAIB/rhBMP-2 injectable system for bone tissue engineering.

Effects of a micro/nano rough strontium-loaded surface on osseointegration

We developed a hierarchical hybrid micro/nanorough strontium-loaded Ti (MNT-Sr) surface fabricated through hydrofluoric acid etching followed by magnetron sputtering and evaluated the effects of this surface on osseointegration. Samples with a smooth Ti (ST) surface, micro Ti (MT) surface treated with hydrofluoric acid etching, and strontium-loaded nano Ti (NT-Sr) surface treated with SrTiO₃ target deposited via magnetron sputtering technique were investigated in parallel for comparison. The results showed that MNT-Sr surfaces were prepared successfully and with high interface bonding strength. Moreover, slow Sr release could be detected when the MNT-Sr and NT-Sr samples were immersed in phosphate-buffered saline. In in vitro experiments, the MNT-Sr surface significantly improved the proliferation and differentiation of osteoblasts compared with the other three groups. Twelve weeks after the four different surface implants were inserted into the distal femurs of 40 rats, the bone–implant contact in the ST, MT, NT-Sr, and MNT-Sr groups were 39.70%±6.00%, 57.60%±7.79%, 46.10%±5.51%, and 70.38%±8.61%, respectively. In terms of the mineral apposition ratio, the MNT-Sr group increased by 129%, 58%, and 25% compared with the values of the ST, MT, and NT-Sr groups, respectively. Moreover, the maximal pullout force in the MNT-Sr group was 1.12-, 0.31-, and 0.69-fold higher than the values of the ST, MT, and NT-Sr groups, respectively. These results suggested that the MNT-Sr surface has a synergistic effect of hierarchical micro/nano-topography and strontium for enhanced osseointegration, and it may be a promising option for clinical use. Compared with the MT surface, the NT-Sr surface significantly improved the differentiation of osteoblasts in vitro. In the in vivo animal experiment, the MT surface significantly enhanced the bone-implant contact and maximal pullout force than the NT-Sr surface.

Nanotexturing of PC/n-HA nanocomposites by innovative and advanced spray system

Nanoscale texturing of n-HA filler on PC matrix is ameliorated by advanced engineered spray techniques viz. spary gun and centrifuged spray dryer, modifying properties of biomedical grade screw/plate coating application.

Novel anti-infective activities of chitosan immobilized titanium surface with enhanced osteogenic properties

We have covalently immobilized chitosan onto a titanium (Ti) surface to manage implant-related infection and poor osseointegration, two of the major complications of orthopedic implants. The Ti surface was first treated with sulfuric acid (SA) and then covalently grafted with chitosan. Surface roughness, contact angle and surface zeta potential of the samples were markedly increased by the sulfuric acid treatment and the subsequent chitosan immobilization. The chitosan-immobilized Ti (SA-CS-Ti) showed two novel antimicrobial roles: it (a) prevented the invasion and internalization of bacteria into the osteoblast-like cells, and (b) significantly increased the susceptibility of adherent bacteria to antibiotics. In addition, the sulfuric acid-treated Ti (SA-Ti) and SA-CS-Ti led to significantly increased (P<0.05) osteoblast-like cell attachment, enhanced cell proliferation, and better osteogenic differentiation and mineralization of osteoblast-like cells.

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.

The differential regulation of osteoblast and osteoclast activity by surface topography of hydroxyapatite coatings

The behavior of bone cells is influenced by the surface chemistry and topography of implants and scaffolds. Our purpose was to investigate how the topography of biomimetic hydroxyapatite (HA) coatings influences the attachment and differentiation of osteoblasts, and the resorptive activity of osteoclasts. Using strategies reported previously, we directly controlled the surface topography of HA coatings on polycaprolactone discs. Osteoblasts and osteoclasts were incubated on HA coatings having distinct isotropic topographies with submicrometer and micro-scale features. Osteoblast attachment and differentiation were greater on more complex, micro-rough HA surfaces (Ra ~2 μm) than on smoother topographies (Ra ~1 μm). In contrast, activity of the osteoclast marker tartrate-resistant acid phosphatase was greater on smoother than on micro-rough surfaces. Furthermore, scanning electron microscopy revealed the presence of resorption lacunae exclusively on smoother HA coatings. Inhibition of resorption on micro-rough surfaces was associated with disruption of filamentous actin sealing zones. In conclusion, HA coatings can be prepared with distinct topographies, which differentially regulate responses of osteoblasts, as well as osteoclastic activity and hence susceptibility to resorption. Thus, it may be possible to design HA coatings that induce optimal rates of bone formation and degradation specifically tailored for different applications in orthopedics and dentistry.

Effect of Ca contamination on apatite formation in a Ti metal subjected to NaOH and heat treatments

It has long been known that titanium (Ti) metal bonds to living bone through an apatite layer formed on its surface in the living body after it had previously been subjected to NaOH and heat treatments and as a result had formed sodium titanate on its surface. These treatments were applied to a porous Ti metal layer on a total hip joint and the resultant joint has been in clinical use since 2007. It has been also demonstrated that the apatite formation on the treated Ti metal in the living body also occurred in an acelullar simulated body fluid (SBF) with ion concentrations nearly equal to those of the human blood plasma, and hence bone-bonding ability of the treated Ti metal can be evaluated using SBF in vitro. However, it was recently found that certain Ti metals subjected to the same NaOH and heat treatments display apatite formation in SBF which is decreased with the increasing volume of the NaOH solution used in some cases. This indicates that bone-bonding ability of the treated Ti metal varies with the volume of the NaOH solution used. In the present study, this phenomenon was systematically investigated using commercial NaOH reagents and is considered in terms of the structure and composition of the surface layers of the treated Ti metals. It was found that a larger amount of the calcium contamination in the NaOH reagent is concentrated on the surface of the Ti metal during the NaOH treatment with an increasing volume of the NaOH solution, and that this inhibited apatite formation on the Ti metal in SBF by suppressing Na ion release from the sodium titanate into the surrounding fluid. Even a Ca contamination level of 0.0005 % of the NaOH reagent was sufficient to inhibit apatite formation. On the other hand, another NaOH reagent with a nominal purity of just 97 % did not exhibit any such inhibition, since it contained almost no Ca contamination. This indicates that NaOH reagent must be carefully selected for obtaining reliable bone-bonding implants of Ti metal by the NaOH and heat treatments.

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.

The Otto Aufranc Award: Demineralized bone matrix around porous implants promotes rapid gap healing and bone ingrowth

BACKGROUND

Noncemented revision arthroplasty is often complicated by the presence of bone implant gaps that reduce initial stability and biologic fixation. Demineralized bone matrix has osteoinductive properties and therefore the potential to enhance gap healing and porous implant fixation.

QUESTIONS/PURPOSES

We determined at what times and to what extent demineralized bone matrix promotes gap healing and bone ingrowth around a porous implant.

METHODS

We inserted porous titanium implants into the proximal metaphyses of canine femora and humeri, with an initial 3-mm gap between host cancellous bone and implants. We left the gaps empty (control; n = 12) or filled them with either demineralized bone matrix (n = 6) or devitalized demineralized bone matrix (negative control; n = 6) and left them in situ for 4 or 12 weeks. We quantified volume healing of the gap with new bone using three-dimensional micro-CT scanning and quantified apposition and ingrowth using backscattered scanning electron microscopy.

RESULTS

The density of bone inside gaps filled with demineralized bone matrix reached 64% and 93% of surrounding bone density by 4 and 12 weeks, respectively. Compared with empty controls and negative controls at 4 and 12 weeks, gap healing using demineralized bone matrix was two to three times greater and bone ingrowth and apposition were up to 15 times greater.

CONCLUSIONS

Demineralized bone matrix promotes rapid bone ingrowth and gap healing around porous implants.

CLINICAL RELEVANCE

Demineralized bone matrix has potential for enhancing implant fixation in revision arthroplasty.

Osteogenic protein-1 delivered by hydroxyapatite-coated implants improves bone ingrowth in extracortical bone bridging

BACKGROUND

Extracortical bone bridging for treatment of massive bone loss can improve stability and longevity of massive endoprostheses. Osteogenic protein-1 (OP-1), when used with allograft bone, reportedly improves extracortical bone bridging and bone ingrowth.

QUESTIONS/PURPOSES

We asked whether OP-1 delivered by hydroxyapatite (HA) without bone grafting could improve bone ingrowth and bone formation in the context of extracortical bone bridging.

METHODS

We implanted unilateral segmental femoral diaphyseal replacement prostheses in 18 dogs (three groups of six dogs). The groups consisted of an HA-coated group augmented with OP-1, an HA-coated group, and a plain porous group. Bone grafting techniques were not used to augment bone formation. The implants were retrieved at 12 weeks for histologic assessment.

RESULTS

After removing one specimen owing to a complication, 17 femora were analyzed (six HA-coated augmented with OP-1, five HA-coated, and six plain). We observed better bone ingrowth in the HA-coated OP-1 group than in the plain porous and HA-coated groups, with no difference between the latter two groups. There also was better bone apposition and callus height in the HA-coated OP-1 group than in the plain group but no differences between the HA-coated OP-1 and HA-coated groups or between the HA-coated and plain groups.

CONCLUSIONS

OP-1 (2.9 mg) delivered by HA-coated segmental replacement prostheses in this canine extracortical bone bridging model revealed improved bone ingrowth over HA-coated implants without OP-1 or plain porous-coated prostheses.

Relative influence of surface topography and surface chemistry on cell response to bone implant materials. Part 1: physico-chemical effects

Knowledge of the complexity of cell-material interactions is essential for the future of biomaterials and tissue engineering, but we are still far from achieving a clear understanding, as illustrated in this review. Many factors of the cellular or the material aspect influence these interactions and must be controlled systematically during experiments. On the material side, it is essential to illustrate surface topography by parameters describing the roughness amplitude as well as the roughness organization, and at the scales pertinent for the cell response, i.e., from the nano-scale to the micro-scale. Authors interested in this field must be careful to develop surfaces or methods systematically, allowing perfect control of the relative influences of surface topography and surface chemistry.

Bioactive Ti metal analogous to human cancellous bone: Fabrication by selective laser melting and chemical treatments

Selective laser melting (SLM) is a useful technique for preparing three-dimensional porous bodies with complicated internal structures directly from titanium (Ti) powders without any intermediate processing steps, with the products being expected to be useful as a bone substitute. In this study the necessary SLM processing conditions to obtain a dense product, such as the laser power, scanning speed, and hatching pattern, were investigated using a Ti powder of less than 45 μm particle size. The results show that a fully dense plate thinner than 1.8 mm was obtained when the laser power to scanning speed ratio was greater than 0.5 and the hatch spacing was less than the laser diameter, with a 30 μm thick powder layer. Porous Ti metals with structures analogous to human cancellous bone were fabricated and the compressive strength measured. The compressive strength was in the range 35-120 MPa when the porosity was in the range 75-55%. Porous Ti metals fabricated by SLM were heat-treated at 1300 °C for 1h in an argon gas atmosphere to smooth the surface. Such prepared specimens were subjected to NaOH, HCl, and heat treatment to provide bioactivity. Field emission scanning electron micrographs showed that fine networks of titanium oxide were formed over the whole surface of the porous body. These treated porous bodies formed bone-like apatite on their surfaces in a simulated body fluid within 3 days. In vivo studies showed that new bone penetrated into the pores and directly bonded to the walls within 12 weeks after implantation into the femur of Japanese white rabbits. The percentage bone affinity indices of the chemical- and heat-treated porous bodies were significantly higher than that of untreated implants.

Effect of heat treatments on apatite-forming ability of NaOH- and HCl-treated titanium metal

Titanium (Ti) metal was soaked in HCl solution after NaOH treatment and then subjected to heat treatments at different temperatures. Their apatite-forming abilities in a simulated body fluid (SBF) were discussed in terms of their surface structures and properties. The nanometer scale roughness formed on Ti metal after NaOH treatment remained after the HCl treatment and a subsequent heat treatment below 700°C. Hydrogen titanate was formed on Ti metal from an HCl treatment after NaOH treatment, and this was converted into titanium oxide of anatase and rutile phases by a subsequent heat treatment above 500°C. The scratch resistance of the surface layer increased with the formation of the titanium oxide after a heat treatment up to 700°C, and then decreased with increasing temperature. The Ti metal with a titanium oxide layer formed on its surface showed a high apatite-forming ability in SBF when the heat treatment temperature was in the range 500-700°C. The high apatite-forming ability was attributed to the positive surface charge in an SBF. These positive surface charges were ascribed to the presence of chloride ions, which were adsorbed on the surfaces and dissociated in the SBF to give an acid environment.

Tissue response to the components of a hydroxyapatite-coated composite femoral implant

Bone loss around femoral implants used for THA is a persistent clinical concern. It may be caused by stress shielding, generally attributed to a mismatch in stiffness between the implants and host bone. In this regard, a fatigue resistant, carbon fiber (CF) composite femoral implant with bone-matching stiffness has been developed. This study evaluated the tissue response to the three material components of this implant in normal and textured (blasted with 24 grit alumina) surfaces: the hydroxyapatite (HA) coating, the CF composite and the intermediate crystalline HA particulate composite layer to bond to the HA coating (blended). Sprague-Dawley rats underwent bilateral femoral implantation each receiving two rod-like implants. Bone apposition to the HA (37%) and textured Ti (41%) implants was not significantly different. Bone apposition to the untextured CF (14%) and blended (19%) implants and polished Ti (8%) implants was significantly lower. Bone apposition to the textured CF (9%) and blended (11%) implants was lower (but not statistically from the as received or untextured counterparts). Nearly all sections from femurs containing CF implants presented CF debris. There was no evidence of localized bone loss or any strong immune response associated with any of the implant materials. All materials were well tolerated with minimal inflammation despite the presence of particulate debris. The high degree of bone apposition to the HA-coated composite implants and the lack of short-term inflammation and adverse tissue response to the three material implant component support continued evaluation of this composite technology for use in THA.

Statistical approach of chemistry and topography effect on human osteoblast adhesion

Our objective in this work was to determine statistically the relative influence of surface topography and surface chemistry of metallic substrates on long-term adhesion of human bone cell quantified by the adhesion power (AP). Pure titanium, titanium alloy, and stainless steel substrates were processed with electro-erosion, sandblasting, or polishing giving various morphologies and amplitudes. The surface chemistry was characterized by X-ray photoelectron spectroscopy (XPS) associated with an extensive analysis of surface topography. The statistical analysis demonstrated that the effect on AP of the material composition was not significant. More, no correlation was found between AP and the surface element concentrations determined by XPS demonstrating that the surface chemistry was not an influencing parameter for long-term adhesion. In the same way, the roughness amplitude, independently of the process, had no influence on AP, meaning that roughness amplitude is not an intrinsic parameter of long-term adhesion. On the contrary, the elaboration process alone had a significant effect on AP. For a same surface elaboration process, the number of inflexion points, or G parameter, was the most pertinent roughness parameter for describing the topography influence on long-term adhesion. Thus, more the inflexion points, more the discontinuities, higher the long-term adhesion.

An in vivo evaluation of bone response to three implant surfaces using a rabbit intramedullary rod model

Our study was designed to evaluate osseointegration among implants with three surface treatments: plasma-sprayed titanium (P), plasma-sprayed titanium with hydroxyapatite (PHA), and chemical-textured titanium with hydroxyapatite (CHA). Average surface roughness (Ra) was 27 microns for the P group, 17 microns for the PHA group, and 26 microns for the CHA group. Bilateral distal intramedullary implants were placed in the femora of thirty rabbits. Histomorphometry of scanning electron microscopy images was used to analyze the amount of bone around the implants at 6 and 12 weeks after implantation. Greater amounts of osseointegration were observed in the hydroxyapatite-coated groups than in the noncoated group. For all implant surfaces, osseointegration was greater at the diaphyseal level compared to the metaphyseal level. No significant differences were seen in osseointegration between the 6 and 12 week time points. Although the average surface roughness of the P and the CHA groups was similar, osseointegration of the CHA implants was significantly greater. The results of this in vivo lapine study suggest that the presence of an hydroxyapatite coating enhances osseointegration despite similarities in average surface roughness.

Positively charged bioactive Ti metal prepared by simple chemical and heat treatments

A highly bioactive bone-bonding Ti metal was obtained when Ti metal was simply heat-treated after a common acid treatment. This bone-bonding property was ascribed to the formation of apatite on the Ti metal in a body environment. The formation of apatite on the Ti metal was induced neither by its surface roughness nor by the rutile phase precipitated on its surface, but by its positively charged surface. The surface of the Ti metal was positively charged because acid groups were adsorbed on titanium hydride formed on the Ti metal by the acid treatment, and remained even after the titanium hydride was transformed into titanium oxide by the subsequent heat treatment. These results provide a new principle based on a positively charged surface for obtaining bioactive materials.

Nanotechnology and bone healing

Nanotechnology and its attendant techniques have yet to make a significant impact on the science of bone healing. However, the potential benefits are immediately obvious with the result that hundreds of researchers and firms are performing the basic research needed to mature this nascent, yet soon to be fruitful niche. Together with genomics and proteomics, and combined with tissue engineering, this is the new face of orthopaedic technology. The concepts that orthopaedic surgeons recognize are fabrication processes that have resulted in porous implant substrates as bone defect augmentation and medication-carrier devices. However, there are dozens of applications in orthopaedic traumatology and bone healing for nanometer-sized entities, structures, surfaces, and devices with characteristic lengths ranging from 10s of nanometers to a few micrometers. Examples include scaffolds, delivery mechanisms, controlled modification of surface topography and composition, and biomicroelectromechanical systems. We review the basic science, clinical implications, and early applications of the nanotechnology revolution and emphasize the rich possibilities that exist at the crossover region between micro- and nanotechnology for developing new treatments for bone healing.

Early failure of the Dual coat Cormet 2000 metal on metal acetabular component

We report a 10% failure rate for aseptic loosening and overall revision rate of 15% at 5 years mean follow up in 190 patients using the Cormet 2000 Dual coat acetabular component. Between 2001 and 2004, the original Dual coat component was used in our region by 4 experienced arthroplasty surgeons. 142 were used with resurfacing heads. The average age was 54 and 99 were male. Revision for aseptic loosening was required in 20 cups (10%) at a mean interval of 23 months including five within 2 months. Persistent groin pain was seen in a further three patients who have declined further surgery. Failure of the backing of this implant to integrate reliably with bone has led to an unacceptably high early loosening rate of the original design which was phased out in 2003.

Enhanced osseointegration of grit-blasted, NaOH-treated and electrochemically hydroxyapatite-coated Ti-6Al-4V implants in rabbits

Osseointegration, in terms of the bone apposition ratio (BAR) and the new bone area (NBA), was measured by backscattered electron imaging. The results were compared for four implant types: grit-blasted and NaOH-treated Ti-6Al-4V (Uncoated-NaOH), electrodeposited with hydroxyapatite without alkali treatment (ED-HAp), electrodeposited with hydroxyapatite after alkali treatment (NaOH-ED-HAp), and plasma sprayed with hydroxyapatite (PS-HAp). No heat treatment was done after soaking in NaOH. The implants were press fitted into the intramedullary canal of mature New Zealand white rabbits and analyzed, both at the diaphyseal and at the metaphyseal zones, either 1week or 12weeks after surgery. NaOH-ED-HAp already exhibited a higher BAR value than the ED-HAp at 1week, and was as good as the commercial PS-HAp at 12weeks. The NBA value for NaOH-ED-HAp at 12weeks was the highest. The higher content of octacalcium phosphate in NaOH-ED-HAp, as evident from the X-ray photoelectron spectroscopy analysis of the oxygen shake-up peaks, and the associated increase in the solubility of this coating in vivo are considered responsible for the enhanced osseointegration. Taking into account also the reduced occurrence of delamination and the inherent advantages of the electrodeposition process, electrodeposition of HAp following soaking in NaOH may become an attractive alternative for the traditional plasma-sprayed process for coating of orthopedic and dental implants.

Applications of microscale technologies for regenerative dentistry

While widespread advances in tissue engineering have occurred over the past decade, many challenges remain in the context of tissue engineering and regeneration of the tooth. For example, although tooth development is the result of repeated temporal and spatial interactions between cells of ectoderm and mesoderm origin, most current tooth engineering systems cannot recreate such developmental processes. In this regard, microscale approaches that spatially pattern and support the development of different cell types in close proximity can be used to regulate the cellular microenvironment and, as such, are promising approaches for tooth development. Microscale technologies also present alternatives to conventional tissue engineering approaches in terms of scaffolds and the ability to direct stem cells. Furthermore, microscale techniques can be used to miniaturize many in vitro techniques and to facilitate high-throughput experimentation. In this review, we discuss the emerging microscale technologies for the in vitro evaluation of dental cells, dental tissue engineering, and tooth regeneration.