Bisphosphonate coating on titanium screws increases mechanical fixation in rat tibia after two weeks

Bisphosphonate-incorporated coatings for orthopedic implants functionalization

Bisphosphonates (BPs), the stable analogs of pyrophosphate, are well-known inhibitors of osteoclastogenesis to prevent osteoporotic bone loss and improve implant osseointegration in patients suffering from osteoporosis. Compared to systemic administration, BPs-incorporated coatings enable the direct delivery of BPs to the local area, which will precisely enhance osseointegration and bone repair without the systemic side effects. However, an elaborate and comprehensive review of BP coatings of implants is lacking. Herein, the cellular level (e.g., osteoclasts, osteocytes, osteoblasts, osteoclast precursors, and bone mesenchymal stem cells) and molecular biological regulatory mechanism of BPs in regulating bone homeostasis are overviewed systematically. Moreover, the currently available methods (e.g., chemical reaction, porous carriers, and organic material films) of BP coatings construction are outlined and summarized in detail. As one of the key directions, the latest advances of BP-coated implants to enhance bone repair and osseointegration in basic experiments and clinical trials are presented and critically evaluated. Finally, the challenges and prospects of BP coatings are also purposed, and it will open a new chapter in clinical translation for BP-coated implants.

Bioactive coatings with anti-osteoclast therapeutic agents for bone implants: Enhanced compliance and prolonged implant life

The use of therapeutic agents that inhibit bone resorption is crucial to prolong implant life, delay revision surgery, and reduce the burden on the healthcare system. These therapeutic agents include bisphosphonates, various nucleic acids, statins, proteins, and protein complexes. Their use in systemic treatment has several drawbacks, such as side effects and insufficient efficacy in terms of concentration, which can be eliminated by local treatment. This review focuses on the incorporation of osteoclast inhibitors (antiresorptive agents) into bioactive coatings for bone implants. The ability of bioactive coatings as systems for local delivery of antiresorptive agents to achieve optimal loading of the bioactive coating and its release is described in detail. Various parameters such as the suitable concentrations, release times, and the effects of the antiresorptive agents on nearby cells or bone tissue are discussed. However, further research is needed to support the optimization of the implant, as this will enable subsequent personalized design of the coating in terms of the design and selection of the coating material, the choice of an antiresorptive agent and its amount in the coating. In addition, therapeutic agents that have not yet been incorporated into bioactive coatings but appear promising are also mentioned. From this work, it can be concluded that therapeutic agents contribute to the biocompatibility of the bioactive coating by enhancing its beneficial properties.

Biofunctionalization of titanium surfaces with alendronate and albumin modulates osteoblast performance

BACKGROUND

Biofunctionalization of titanium surfaces can improve host responses, especially considering the time for osteointegration and patient recovery. This prompted us to modify titanium surfaces with alendronate and albumin and to investigate the behavior of osteoblasts on these surfaces.

METHODS

The biofunctionalization of titanium surfaces was characterized using classical physicochemical approaches and later used to challenge pre-osteoblast cells up to 24 h. Then their viability and molecular behavior were investigated using mitochondrial dehydrogenase activity and RTq-PCR technologies, respectively. Potential stimulus of extracellular remodeling was also investigated by zymography.

RESULTS

Our data indicates a differential behavior of cells responding to the surfaces, considering the activity of mitochondrial dehydrogenases. Molecularly, the differential expression of genes related with cell adhesion highlighted the importance of Integrin-β1, Fak, and Src. These 3 genes were significantly decreased in response to titanium surfaces modified with alendronate, but this behavior was reverted when alendronate was associated with albumin. Alendronate-modified surfaces promoted a significant increase on ECM remodeling, as well as culminating with greater gene activity related to the osteogenic phenotype (Runx2, Alp, Bsp).

CONCLUSION

Altogether, our study found interesting osteogenic behavior of cells in response to alendronate and albumin surfaces, which indicates the need for in vivo analyses to better consider these surfaces before clinical trials within the biomedical field.

The Influence of Local Pamidronate Application on Alveolar Dimensional Preservation after Tooth Extraction-An Animal Experimental Study

The aim of this randomized, controlled animal exploratory trial was to investigate the influence of local application of aminobisphosphonate pamidronate during the socket preservation procedure. Mandibular premolars were extracted in five Göttingen minipigs. Two animals underwent socket preservation using BEGO OSS (n = 8 sockets) and three animals using BEGO OSS + Pamifos (15 mg) (n = 12 sockets). After jaw impression, cast models (baseline, eight weeks postoperative) were digitized using an inLab X5 scanner (Dentsply Sirona) and the generated STL data were superimposed and analyzed with GOM Inspect 2018 (GOM, Braunschweig). After 16 weeks, the lower jaws were prepared and examined using standard histological methods. In the test group (BEGO OSS + pamidronate), buccooral dimensional loss was significantly lower, both vestibulary (−0.80 ± 0.57 mm vs. −1.92 ± 0.63 mm; p = 0.00298) and lingually (−1.36 ± 0.58 mm vs. −2.56 ± 0.65 mm; p = 0.00104) compared with the control group (BEGO OSS). The test group showed a significant difference between vestibular and lingual dimensional loss (p = 0.04036). Histology showed cortical and cancellous bone in the alveolar sockets without signs of local inflammation. Adjuvant application of pamidronate during socket preservation reduces alveolar dimensional loss significantly. Further investigations with regard to dose–response relationships, volume effects, side effects, and a verification of the suitability in combination with other bone substitute materials (BSMs) are necessary.

Osseointegration and current interpretations of the bone-implant interface

Complex physical and chemical interactions take place in the interface between the implant surface and bone. Various descriptions of the ultrastructural arrangement to various implant design features, ranging from solid and macroporous geometries to surface modifications on the micron-, submicron-, and nano- levels, have been put forward. Here, the current knowledge regarding structural organisation of the bone-implant interface is reviewed with a focus on solid devices, mainly metal (or alloy) intended for permanent anchorage in bone. Certain biomaterials that undergo surface and bulk degradation are also considered. The bone-implant interface is a heterogeneous zone consisting of mineralised, partially mineralised, and unmineralised areas. Within the meso-micro-nano-continuum, mineralised collagen fibrils form the structural basis of the bone-implant interface, in addition to accumulation of non-collagenous macromolecules such as osteopontin, bone sialoprotein, and osteocalcin. In the published literature, as many as eight distinct arrangements of the bone-implant interface ultrastructure have been described. The interpretation is influenced by the in vivo model and species-specific characteristics, healing time point(s), physico-chemical properties of the implant surface, implant geometry, sample preparation route(s) and associated artefacts, analytical technique(s) and their limitations, and non-compromised vs compromised local tissue conditions. The understanding of the ultrastructure of the interface under experimental conditions is rapidly evolving due to the introduction of novel techniques for sample preparation and analysis. Nevertheless, the current understanding of the interface zone in humans in relation to clinical implant performance is still hampered by the shortcomings of clinical methods for resolving the finer details of the bone-implant interface. STATEMENT OF SIGNIFICANCE: Being a hierarchical material by design, the overall strength of bone is governed by composition and structure. Understanding the structure of the bone-implant interface is essential in the development of novel bone repair materials and strategies, and their long-term success. Here, the current knowledge regarding the eventual structural organisation of the bone-implant interface is reviewed, with a focus on solid devices intended for permanent anchorage in bone, and certain biomaterials that undergo surface and bulk degradation. The bone-implant interface is a heterogeneous zone consisting of mineralised, partially mineralised, and unmineralised areas. Within the meso-micro-nano-continuum, mineralised collagen fibrils form the structural basis of the bone-implant interface, in addition to accumulation of non-collagenous macromolecules such as osteopontin, bone sialoprotein, and osteocalcin.

Clinical Applications of Bone Tissue Engineering in Orthopedic Trauma

Purpose of Review

Orthopaedic trauma is a major cause of morbidity and mortality worldwide. Although many fractures tend to heal if treated appropriately either by nonoperative or operative methods, delayed or failed healing, as well as infections, can lead to devastating complications. Tissue engineering is an exciting, emerging field with much scientific and clinical relevance in potentially overcoming the current limitations in the treatment of orthopaedic injuries.

Recent Findings

While direct translation of bone tissue engineering technologies to clinical use remains challenging, considerable research has been done in studying how cells, scaffolds, and signals may be used to enhance acute fracture healing and to address the problematic scenarios of nonunion and critical-sized bone defects. Taken together, the research findings suggest that tissue engineering may be considered to stimulate angiogenesis and osteogenesis, to modulate the immune response to fractures, to improve the biocompatibility of implants, to prevent or combat infection, and to fill large gaps created by traumatic bone loss. The abundance of preclinical data supports the high potential of bone tissue engineering for clinical application, although a number of barriers to translation must first be overcome.

Summary

This review focuses on the current and potential applications of bone tissue engineering approaches in orthopaedic trauma with specific attention paid to acute fracture healing, nonunion, and critical-sized bone defects.

Earlier effect of alendronate in mouse metaphyseal versus diaphyseal bone healing

Healing of injured cancellous bone is characterized by a transient stage of rapid bone formation throughout the traumatized bone volume, often followed by similarly rapid resorption. This is different from the slower diaphyseal healing via an external callus. We, therefore, hypothesized that antiresorptive treatment might have an earlier positive effect in cancellous bone healing than in diaphyseal fractures. One hundred and twenty-three male C57bl6 mice received either an internally stabilized diaphyseal osteotomy of the femur or a screw inserted into the tibial metaphysis. The mice were randomized to daily alendronate injections (200 μg/kg/day), or control injections, and killed for mechanical testing after 14, 21, or 28 days. The hypothesis was tested by a three-way Anova (time, site, and drug). The ultimate force was increased by bisphosphonate treatment in both models. There was a significant interaction between time, site, and drug (p < 0.001) so that the full positive effect of alendronate was evident in the metaphysis at 14 days, but first after 28 days in the diaphysis. While the early effect in the metaphysis might be translated into earlier healing, the late effect in the diaphysis was due to delayed remodeling of the callus, which might have less clinical importance. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:793-799, 2017.

Immobilization of alendronate on titanium via its different functional groups and the subsequent effects on cell functions

Immobilization of alendronate on orthopedic implants offers the possibility of enhancing osteogenesis without potentially adverse effects associated with systemic administration of this drug. In this work, alendronate was immobilized on titanium (Ti) via either its phosphate (Method 1) or amino (Method 2) groups, and responses of osteoblasts and human mesenchymal stem cells (hMSCs) on these surfaces were investigated. These modified substrates have similar surface roughness and are negatively charged. With similar amounts of immobilized alendronate, these two types of modified substrates showed comparable osteogenic stimulating effects in enhancing osteoblasts' alkaline phosphatase (ALP) activity and calcium deposition for the first 10days. However, alendronate immobilized via its phosphate groups was less stable, and gradually leached into the medium. As a result, its stimulating effect on osteoblast differentiation diminished with time. On the other hand, alendronate immobilized via its amino group stimulated osteoblast differentiation over 21days, and with 1655ng/cm2 of immobilized alendronate on the Ti substrate, calcium deposition by osteoblasts and hMSCs increased by 30% and 69%, respectively, compared to pristine Ti after 21days. The expressions of runt-related transcription factor 2, osterix, osteopontin and osteocalcin in hMSCs cultured on this substrate were monitored. The up-regulation of these genes is postulated to play a role in the acceleration of osteogenic differentiation of hMSCs cultured on the alendronate-modified substrate over those on pristine Ti.

Does Local Ibandronate and/or Pamidronate Delivery Enhance Osseointegration? A Systematic Review

PURPOSE

To our knowledge from indexed literature, the present study is the first one to systematically review the influence of local delivery of pamidronate (PAM) and/or ibandronate (IBA) on osseointegration enhancement. The aim of the present systematic review was to assess the efficacy of IBA and/or PAM local delivery (topically or coating on implants surfaces) in promoting osseointegration.

MATERIALS AND METHODS

To address the focused question, "Does local IBA and/or PAM delivery enhances osseointegration?," indexed databases were searched without time or language restrictions up to and including May 2016 using various combinations of the following keywords: "pamidronate," "ibandronate," "bisphosphonates," "osseointegration," and "topical administration." Letters to the Editor, historic reviews, commentaries, case series, and case reports were excluded.

RESULTS

Fifteen studies were included. Fourteen studies were performed in animals and 2 were clinical trials. One study reported an experimental model and a clinical trial in the same publication. Results from 12 experimental studies and 2 clinical studies reported improved biomechanical properties and/or osseointegration around implants with PAM and/or IBA. Two experimental studies showed that PAM and/or IBA did not improve osseointegration.

CONCLUSIONS

On experimental grounds, local IBA and/or PAM delivery seems to enhance osseointegration; however, from a clinical perspective, further randomized control trials are needed to assess the effectiveness of IBA and PAM in promoting osseointegration around dental implants.

Randomised trial of bisphosphonate-coated dental implants: Radiographic follow-up after five years of loading

The results of a randomised trial with bisphosphonate-coated dental implants have been reported previously. Each patient received one coated and one uncoated implant in a double-blind split-mouth design study. After 6 months of osseointegration, resonance frequency analysis indicated better fixation of the coated implants. Reduced marginal bone resorption was also shown. However, it was not known whether the advantage of the bisphosphonate coating would persist over time. The radiographic results at 5 years after implant installation are reported herein. A blinded investigator measured marginal resorption on fresh radiographs obtained for 14 of the 16 patients (two had died) and compared these with the post-implantation images. Non-parametric statistics were used. All implants functioned well. The median marginal bone loss for control implants was found to be 0.70mm, which is less than usually reported in the literature. The bisphosphonate-coated implants showed even less resorption (median 0.20mm). The median difference within each pair of implants after 5 years of use was 0.34mm (95% confidence interval 0.00-0.75mm; P=0.04). The present data suggest that bisphosphonate-coated implants enable prolonged preservation of the marginal bone.

Biomaterial strategies for engineering implants for enhanced osseointegration and bone repair

Bone tissue has a remarkable ability to regenerate and heal itself. However, large bone defects and complex fractures still present a significant challenge to the medical community. Current treatments center on metal implants for structural and mechanical support and auto- or allo-grafts to substitute long bone defects. Metal implants are associated with several complications such as implant loosening and infections. Bone grafts suffer from donor site morbidity, reduced bioactivity, and risk of pathogen transmission. Surgical implants can be modified to provide vital biological cues, growth factors and cells in order to improve osseointegration and repair of bone defects. Here we review strategies and technologies to engineer metal surfaces to promote osseointegration with the host tissue. We also discuss strategies for modifying implants for cell adhesion and bone growth via integrin signaling and growth factor and cytokine delivery for bone defect repair.

Osteoprotegerin and zoledronate bone effects during orthodontic tooth movement

OBJECTIVES

To assess the effects of local delivery of recombinant fusion protein osteoprotegerin (OPG-Fc) and bisphosphonate zoledronate on bone and periodontal ligament in a rat tooth movement model.

MATERIALS AND METHODS

Maxillary first molars of 36 male Sprague-Dawley rats were displaced mesially using a calibrated spring connected to an anterior mini-screw. Two different drugs were used: a single dose of Zoledronate (16 μg) and a twice-weekly dose of OPG-Fc (5.0 mg/kg) were injected. Tooth movement was measured on scanned plaster casts. Structural and immunohistochemical analysis of the orthodontic-induced changes in bone included receptor activator of nuclear factor ĸ (RANK), Runx, type 1 collagen, matrix metalloproteinases (MMPs) 2 and 9, tissue inhibitors of metalloproteinases (TIMPs) 1 and 2, and vimentin.

RESULTS

Both groups showed a reduction in mesial molar displacement. Animals receiving OPG-Fc demonstrated only 52%, 31%, and 21% of the total mesial molar displacement compared to control rats at 7, 14, and 21 days, respectively (*p < 0.001). For rats receiving zoledronate tooth displacement decreased significantly with 52%, 46% and 30%, respectively (*p < 0.001). At 14 and 21 days, OPG-Fc group showed significantly less molar displacement than the zoledronate group (*p < 0.001). RANK, Runx, vimentin, MMP-9 and tissues-inhibitor metalloproteinase 1 immunoreactivity were reduced in zoledronate treated animals and even more in OPG treated animals.

CONCLUSION

Local delivery of OPG-Fc or zoledronate inhibits bone resorption and therefore tooth movement. OPG-Fc was more effective than zoledronate in blocking the action of osteoclasts.

Simple coating with fibronectin fragment enhances stainless steel screw osseointegration in healthy and osteoporotic rats

Metal implants are widely used to provide structural support and stability in current surgical treatments for bone fractures, spinal fusions, and joint arthroplasties as well as craniofacial and dental applications. Early implant-bone mechanical fixation is an important requirement for the successful performance of such implants. However, adequate osseointegration has been difficult to achieve especially in challenging disease states like osteoporosis due to reduced bone mass and strength. Here, we present a simple coating strategy based on passive adsorption of FN7-10, a recombinant fragment of human fibronectin encompassing the major cell adhesive, integrin-binding site, onto 316-grade stainless steel (SS). FN7-10 coating on SS surfaces promoted α5β1 integrin-dependent adhesion and osteogenic differentiation of human mesenchymal stem cells. FN7-10-coated SS screws increased bone-implant mechanical fixation compared to uncoated screws by 30% and 45% at 1 and 3 months, respectively, in healthy rats. Importantly, FN7-10 coating significantly enhanced bone-screw fixation by 57% and 32% at 1 and 3 months, respectively, and bone-implant ingrowth by 30% at 3 months compared to uncoated screws in osteoporotic rats. These coatings are easy to apply intra-operatively, even to implants with complex geometries and structures, facilitating the potential for rapid translation to clinical settings.

Single-dose local simvastatin injection improves implant fixation via increased angiogenesis and bone formation in an ovariectomized rat model

Background

Statins have been reported to promote bone formation. However, taken orally, their bioavailability is low to the bones. Implant therapies require a local repair response, topical application of osteoinductive agents, or biomaterials that promote implant fixation.

Material/Methods

The present study evaluated the effect of a single local injection of simvastatin on screw fixation in an ovariectomized rat model of osteoporosis.

Results

Dual-energy X-ray absorptiometry, micro-computed tomography, histology, and biomechanical tests revealed that 5 and 10 mg simvastatin significantly improved bone mineral density by 18.2% and 22.4%, respectively (P<0.05); increased bone volume fraction by 51.0% and 57.9%, trabecular thickness by 16.4% and 18.9%, trabeculae number by 112.0% and 107.1%, and percentage of osseointegration by 115.7% and 126.3%; and decreased trabeculae separation by 34.1% and 36.6%, respectively (all P<0.01). Bone mineral apposition rate was significantly increased (P<0.01). Furthermore, implant fixation was significantly increased (P<0.05), and bone morphogenetic protein 2 (BMP2) expression was markedly increased. Local injection of a single dose of simvastatin also promoted angiogenesis. Vessel number, volume, thickness, surface area, and vascular volume per tissue volume were significantly increased (all P<0.01). Vascular endothelial growth factor (VEGF), VEGF receptor-2, von Willebrand factor, and platelet endothelial cell adhesion molecule-1 expression were enhanced.

Conclusions

A single local injection of simvastatin significantly increased bone formation, promoted osseointegration, and enhanced implant fixation in ovariectomized rats. The underlying mechanism appears to involve enhanced BMP2 expression and angiogenesis in the target bone.

Osteoporosis and bisphosphonate-related osteonecrosis in a dental school implant patient population

PURPOSE

Studies have demonstrated an inconsistent association between implant failure and bone mineral density. The prevalence of osteoporosis in US adults has been reported to range from 5% to 10% in women and from 2% to 4% in men. The prevalence of bisphosphonate (BP)-related osteonecrosis of the jaw (BRONJ) has been reported to range from 0% to 4.3% of patients taking oral BPs. The purpose of this study was to calculate the risk of dental implant loss and the incidence of BRONJ in patients with osteoporosis at the University of Kentucky College of Dentistry (UKCD).

MATERIALS AND METHODS

This study analyzed data collected from patients who had implants placed between 2000 and 2004 at UKCD. Data were gathered from patient interviews regarding implant survival and patient-satisfaction parameters, and interviews were conducted either chairside at a scheduled maintenance appointment or by telephone interview.

RESULTS

Among 203 patients who received 515 implants, the prevalence of osteoporosis was 23.3% for women and 1.2% for men. None of the 20 patients who reported a history of oral BP use exhibited BRONJ, and there were no implant failures in patients with a history of osteoporosis.

CONCLUSIONS

In this study, osteoporosis conferred no risk of implant failure, and oral BP therapy was not associated with BRONJ.

Time course of bone screw fixation following a local delivery of Zoledronate in a rat femoral model - a micro-finite element analysis

A good fixation of osteosynthesis implants is crucial for a successful bone healing but often difficult to achieve in osteoporotic patients. One possible solution to this issue is the local delivery of bisphosphonates in direct proximity to the implants, A critical aspect of this method, that has not yet been well investigated, is the time course of the implant fixation following the drug release. Usual destructive mechanical tests require large numbers of animals to produce meaningful results. Therefore, a micro-finite element (microFE) approach was chosen to analyze implant fixation. In vivo micro computed tomography (microCT) scans were obtained, first weekly and later bi-weekly, after implantation of polymeric screws in the femoral condyles of ovariectomized rats. In one half of the animals, Zoledronate was released from a hydrogel matrix directly in the peri-implant bone stock, the other animals were implanted only with screws as control. The time course of the implant fixation was investigated with linear elastic microFE models that were created based on in vivo microCT scans. The numerical models were validated against experimental pullout-tests measurements in an additional cadaver study. The microFE analysis revealed a significant increase in force at yield of the Zoledronate treated group compared to the control group. The force of the treated group was 28% higher after 17 days of screw implantation, 42% higher after 31 days. The significant difference persisted until the end of the in vivo study at day 58 (p<0.01). The early onset and prolonged duration of the implant anchorage improvement that was found in this study indicates the great potential of Zoledronate-loaded hydrogel for an enhancement of osteosynthesis implant fixation in impaired bone.

Bisphosphonate associated osteonecrosis of the jaw: an update on pathophysiology, risk factors, and treatment

Osteonecrosis of the jaw in patients treated with bisphosphonates is a relatively rare but well known complication at maxillofacial units around the world. It has been speculated that the medication, especially long-term i.v. bisphosphonate treatment, could cause sterile necrosis of the jaws. The aim of this narrative review of the literature was to elaborate on the pathological mechanisms behind the condition and also to gather an update on incidence, risk factors, and treatment of bisphosphonate associated osteonecrosis of the jaw. In total, ninety-one articles were reviewed. All were published in internationally recognized journals with referee systems. We can conclude that necrotic lesions in the jaw seem to be following upon exposure of bone, for example, after tooth extractions, while other interventions like implant placement do not increase the risk of osteonecrosis. Since exposure to the bacterial environment in the oral cavity seems essential for the development of necrotic lesions, we believe that the condition is in fact chronic osteomyelitis and should be treated accordingly.

Early tissue responses to zoledronate, locally delivered by bone screw, into a compromised cancellous bone site: a pilot study

Background

In fracture treatment, adequate fixation of implants is crucial to long-term clinical performance. Bisphosphonates (BP), potent inhibitors of osteoclastic bone resorption, are known to increase peri-implant bone mass and accelerate primary fixation. However, adverse effects are associated with systemic use of BPs. Thus, Zoledronic acid (ZOL) a potent BP was loaded on bone screws and evaluated in a local delivery model. Whilst mid- to long-term effects are already reported, early cellular events occurring at the implant/bone interface are not well described. The present study investigated early tissue responses to ZOL locally delivered, by bone screw, into a compromised cancellous bone site.

Methods

ZOL was immobilized on fibrinogen coated titanium screws. Using a bilateral approach, ZOL loaded test and non-loaded control screws were implanted into femoral condyle bone defects, created by an overdrilling technique. Histological analyses of the local tissue effects such as new bone formation and osteointegration were performed at days 1, 5 and 10.

Results

Histological evaluation of the five day ZOL group, demonstrated a higher osseous differentiation trend. At ten days an early influx of mesenchymal and osteoprogenitor cells was seen and a higher level of cellular proliferation and differentiation (p < 5%). In the ZOL group bone-to-screw contact and bone volume values within the defect tended to increase. Local drug release did not induce any adverse cellular effects.

Conclusion

This study indicates that local ZOL delivery into a compromised cancellous bone site actively supports peri-implant osteogenesis, positively affecting mesenchymal cells, at earlier time points than previously reported in the literature.

Raloxifene and alendronate containing thin mesoporous titanium oxide films improve implant fixation to bone

This study tested the hypothesis that osteoporosis drug-loaded mesoporous TiO2 implant coatings can be used to improve bone-implant integration. Two osteoporosis drugs, Alendronate (ALN) and Raloxifene (RLX), were immobilized in nanoporous oxide films prepared on Ti screws and evaluated in vivo in rat tibia. The drug release kinetics were monitored in vitro by quartz crystal microbalance with dissipation and showed sustained release of both drugs. The osteogenic response after 28days of implantation was evaluated by quantitative polymerase chain reaction (qPCR), removal torque, histomorphometry and ultrastructural interface analysis. The drug-loaded implants showed significantly improved bone fixation. In the case of RLX, stronger bone-remodelling activity was observed compared with controls and ALN-loaded implants. The ultrastructural interface analysis revealed enhanced apatite formation inside the RLX coating and increased bone density outside the ALN coating. Thus, this novel combination of a thin mesoporous TiO2 carrier matrix and appropriate drugs can be used to accelerate implant fixation in trabecular bone.

The effect of polyelectrolyte multilayer coated titanium alloy surfaces on implant anchorage in rats

Advances have been achieved in the design and biomechanical performance of orthopedic implants in the last decades. These include anatomically shaped and angle-stable implants for fracture fixation or improved biomaterials (e.g. ultra-high-molecular-weight polyethylene) in total joint arthroplasty. Future modifications need to address the biological function of implant surfaces. Functionalized surfaces can promote or reduce osseointegration, avoid implant-related infections or reduce osteoporotic bone loss. To this end, polyelectrolyte multilayer structures have been developed as functional coatings and intensively tested in vitro previously. Nevertheless, only a few studies address the effect of polyelectrolyte multilayer coatings of biomaterials in vivo. The aim of the present work is to evaluate the effect of polyelectrolyte coatings of titanium alloy implants on implant anchorage in an animal model. We test the hypotheses that (1) polyelectrolyte multilayers have an effect on osseointegration in vivo; (2) multilayers of chitosan/hyaluronic acid decrease osteoblast proliferation compared to native titanium alloy, and hence reduce osseointegration; (3) multilayers of chitosan/gelatine increase osteoblast proliferation compared to native titanium alloy, hence enhance osseointegration. Polyelectrolyte multilayers on titanium alloy implants were fabricated by a layer-by-layer self-assembly process. Titanium alloy (Ti) implants were alternately dipped into gelatine (Gel), hyaluronic acid (HA) and chitosan (Chi) solutions, thus assembling a Chi/Gel and a Chi/HA coating with a terminating layer of Gel or HA, respectively. A rat tibial model with bilateral placement of titanium alloy implants was employed to analyze the bones' response to polyelectrolyte surfaces in vivo. 48 rats were randomly assigned to three groups of implants: (1) native titanium alloy (control), (2) Chi/Gel and (3) Chi/HA coating. Mechanical fixation, peri-implant bone area and bone contact were evaluated by pull-out tests and histology at 3 and 8 weeks. Shear strength at 8 weeks was statistically significantly increased (p<0.05) in both Chi/Gel and Chi/HA groups compared to the titanium alloy control. No statistically significant difference (p>0.05) in bone contact or bone area was found between all groups. No decrease of osseointegration of Chi/HA-coated implants compared to non-coated implants was found. The results of polyelectrolyte coatings in a rat model showed that the Chi/Gel and Chi/HA coatings have a positive effect on mechanical implant anchorage in normal bone.

Locally enhanced early bone formation of zoledronic acid incorporated into a bone cement plug in vivo

OBJECTIVES

The aim of the study was to gain experience about the short-term effects of zoledronic acid (ZOL) on bone-implant contact (BIC), bone regeneration and bone area (BA).

METHODS

In this in-vivo study, ZOL was released locally from a drug-loaded pre-shaped calcium phosphate bone cement plug which was implanted into a bone defect in the proximal tibia of rats. At 1 and 3 weeks post implantation, tissue reactions as well as bone regeneration capabilities at the implant site were investigated. Furthermore, tissue samples, harvested at placebo and verum plug sites were used to analyse the gene expression of selected bone-specific markers by using quantitative polymerase chain reaction. Data were normalized against ribosomal RNA (Rn18s) subunits.

KEY FINDINGS

In the placebo interface a higher amount of cells could be detected as indicated by higher expression of small subunit Rn18s. Nevertheless, comparing the normalized data of the selected gene expression levels, no significant differences were detected. The histomorphometric results showed a significant higher BIC and BA for ZOL-loaded plugs at 3 weeks after implantation.

CONCLUSIONS

In this model, ZOL was demonstrated to be effective in impacting the bone regeneration process towards reduction of early bone resorption and enhanced bone formation.

Titanium as a Reconstruction and Implant Material in Dentistry: Advantages and Pitfalls

Commercial pure titanium (cpTi) has been the material of choice in several disciplines of dentistry due to its biocompatibility, resistance to corrosion and mechanical properties. Despite a number of favorable characteristics, cpTi as a reconstruction and oral implant material has several shortcomings. This paper highlights current knowledge on material properties, passive oxidation film formation, corrosion, surface activation, cell interactions, biofilm development, allergy, casting and machining properties of cpTi for better understanding and potential improvement of this material for its clinical applications.

Etanercept does not impair healing in rat models of tendon or metaphyseal bone injury

BACKGROUND AND PURPOSE

Should blockade of TNF-α be avoided after orthopedic surgery? Healing of injuries in soft tissues and bone starts with a brief inflammatory phase. Modulation of inflammatory signaling might therefore interfere with healing. For example, Cox inhibitors impair healing in animal models of tendon, ligament, and bone injury, as well as in fracture patients. TNF-α is expressed locally at increased levels during early healing of these tissues. We therefore investigated whether blocking of TNF-α with etanercept influences the healing process in established rat models of injury of tendons and metaphyseal bone.

METHODS

Rats were injected with etanercept, 3.5 mg/kg 3 times a week. Healing of transected Achilles tendons and bone healing around screws implanted in the tibial metaphysis were estimated by mechanical testing. Tendons were allowed to heal either with or without mechanical loading. Ectopic bone induction following intramuscular BMP-2 implants has previously been shown to be stimulated by etanercept in rodents. This was now tested as a positive control.

RESULTS

Tendon peak force after 10 days was not significantly influenced by etanercept. Changes exceeding 29% could be excluded with 95% confidence. Likewise, screw pull-out force was not significantly influenced. More than 25% decrease or 18% increase could be excluded with 95% confidence. However, etanercept treatment increased the amount of bone induced by intramuscular BMP-2 implants, as estimated by blind histological scoring.

INTERPRETATION

Etanercept does not appear to impair tendon or metaphyseal bone healing to any substantial degree.

A bisphosphonate-coating improves the fixation of metal implants in human bone. A randomized trial of dental implants

Many surgical procedures use metal implants in bone. The clinical results depend on the strength of the bone holding these implants. Our objective was to show that a drug released from the implant surface can improve parameters reflecting the quality or amount of this bone. Sixteen patients received paired dental titanium implants in the maxilla, in a randomized, double-blinded fashion. One implant in each pair was coated with a thin fibrinogen layer containing 2 bisphosphonates. The other implant was untreated. Fixation was evaluated by measurement of resonance frequency (implant stability quotient; ISQ) serving as a proxy for stiffness of the implant-bone construct. Increase in ISQ at 6months of follow-up was the primary variable. None of the patients had any complications. The resonance frequency increased 6.9 ISQ units more for the coated implants (p=0.0001; Cohen's d=1.3). The average difference in increase in ISQ, and the effect size, suggested a clinically relevant improvement. X-ray showed less bone resorption at the margin of the implant both at 2months (p=0.012) and at 6months (p=0.012). In conclusion, a thin, bisphosphonate-eluting fibrinogen coating might improve the fixation of metal implants in human bone. This might lead to new possibilities for orthopedic surgery in osteoporotic bone and for dental implants.

Effect of local zoledronate on implant osseointegration in a rat model

Background

An implant coating with poly(D, L-lactide) (PDLLA) releasing incorporated Zoledronic acid (ZOL) has already proven to positively effect osteoblasts, to inhibit osteoclasts and to accelerate fracture healing. Aim of this study was to investigate the release kinetics of the chosen coating and the effect of different concentrations of ZOL locally released from this coating on the osseointegration of implants.

Methods

For release kinetics the release of C14-labled ZOL out of the coating was monitored over a period of six weeks in vitro. For testing the osseointegration, titanium Kirschner wires were implanted into the medullary canal of right femurs of 100 Sprague Dawley rats. The animals were divided into five groups receiving implants either uncoated or coated with PDLLA, PDLLA/ZOL low (1.2% w/w) or PDLLA/ZOL high (2% w/w). Additionally, a group with uncoated implants received ZOL intravenously (i.v.). After 56 days animals were sacrificed, femurs dissected and either strength of fixation or histological bone/implant contacts and newly formed bone around the implants were determined.

Results

Release kinetics revealed an initial peak in the release of C14-ZOL with a slight further progression over the following weeks. There was no significant enhancement of osseointegration for both groups who received ZOL-coated implants or ZOL i.v. compared to the controls in biomechanical or histological analyses, except for a significant raise in strength of fixation of ZOL i.v. versus PDLLA.

Conclusions

Even though the investigated local ZOL application did not enhance the osseointegration of the implant, the findings might support its application in fracture treatment, since fracture stabilization devices are often explanted after consolidation.

Local bisphosphonate release versus hydroxyapatite coating for stainless steel screw fixation in rat tibiae

Implant fixation in bone can be improved by a coating that delivers bisphosphonates locally, or by a hydroxyapatite (HA) coating. In this study, we compared these different types of coatings. For mechanical testing, 30 rats were assigned into three groups, and similar screws were implanted bilaterally in the proximal tibiae. The rats received screws that were either uncoated, coated with nano-crystalline hydroxyapatite or coated with a bisphosphonate releasing protein matrix. After 4 weeks, one screw was subjected to pull-out testing, and the contra-lateral one to torsion testing. For morphology, 30 rats were assigned to similar treatment groups, but received only one screw each. Bisphosphonates enhanced the pull-out force by 41% (P = 0.02) compared to controls, HA increased the pull-out force although not significantly. Conversely, HA increased the maximal torque by 64% (P = 0.02). Morphometry showed higher bone volume around bisphosphonate screws in comparison to HA-coated screws (P < 0.001) and controls (P < 0.001). The results suggest that bisphosphonates improve fixation by increasing the amount of surrounding bone, whereas HA mainly improves bone to implant attachment.

Weak effect of strontium on early implant fixation in rat tibia

Strontium ranelate increases bone mass and is used in the treatment of osteoporosis. Its effects in metaphyseal bone repair are largely unknown. We inserted a stainless steel and a PMMA screw into each tibia of male Sprague-Dawley rats. The animals were fed with ordinary feed (n=20) or with addition of strontium ranelate (800 mg/kg/day; n=10). As a positive control, half of the animals on control feed received alendronate subcutaneously. The pullout force of the stainless steel screws was measured after 4 or 8 weeks, and µCT was used to assess bone formation around the PMMA screws. No significant effects of strontium treatment on pullout force were observed, but animals treated with bisphosphonate showed a doubled pullout force. Strontium improved the micro architecture of the cancellous bone below the primary spongiosa at the growth plate, but no significant effects were found around the implants. Strontium is known to improve bone density, but it appears that this effect is weak in conjunction with metaphyseal bone repair and early implant fixation.

In vivo assessment of local effects after application of bone screws delivering bisphosphonates into a compromised cancellous bone site

BACKGROUND

The primary stability of cancellous screw is difficult to obtain in bone of compromised quality and failure of screw fixation is common. To overcome this problem, it is proposed to locally deliver bisphosphonate from the screw. An in vivo validation of the increase in fixation of the cancellous screw is then needed in compromised bone.

METHODS

In this study, we used an overdrilling procedure, which enables consistent modeling of reduced screw stability comparable to compromised cancellous bone. Forty eight adult NZW rabbits were used in this study and all animals underwent bilateral femur implantation. One leg was implanted with the screw containing the bisphosphonate (biocoated group) while the other was used as control (control group) with the screw only. Mechanical testing and micro-CT imaging were used to assess the effect of local drug delivery of Zoledronate on screws fixation at 5 time points.

FINDINGS

At the early time points (1, 5, and 10 days), no significant difference could be seen between the biocoated and control groups. At 6 weeks, the bone volume fraction was significantly higher in the trabecular region of the biocoated group. However, this increase did not have a significant effect on the pull-out force. At the last time point, 11 weeks, both the bone volume fraction and the pull-out force were significantly higher in the biocoated group.

INTERPRETATION

The results of this study suggest that, in compromised bone, local delivery of bisphosphonate enhances the stability of bone screws.

Optimising implant anchorage (augmentation) during fixation of osteoporotic fractures: is there a role for bone-graft substitutes?

When stabilising a fracture the contact between the screw and the surrounding bone is crucial for mechanical strength. Through development of screws with new thread designs, as well as optimisation of other properties, improved screw purchase has been gained. Other alternatives to improve screw fixation in osteoporotic bone, as well as normal bone if needed, includes the use of various coatings on the screw that will induce a bonding between the implant surface and the bone implant, as well as application of drugs such as bisphosphonates locally in the screw hole to induce improved screw anchorage through their anticatabolic effect on the bone tissue. As failure of internal fixation of fractures in osteoporotic bone typically occurs through breakage of the bone that surrounds the implant, rather than the implant itself, an alternative strategy in osteoporotic bone can include augmentation of the bone around the screw. This is useful when screws alone are being used for fixation, as it will increase pull-out resistance, but also when conventional plates and screws are used. In angularly stable plate-screw systems, screw back-out is not a problem if the locking mechanism between the screws and the plate works. However, augmentation that will strengthen the bone around the screws can also be useful in conjunction with angle-stable plate-screw systems, as the augmentation will provide valuable support when subjected to loading that might cause cut-out. For many years conventional bone cement, polymethylmethacrylate (PMMA), has been used for augmentation, but due to side effects--including great difficulties if removal becomes necessary--the use of PMMA has never gained wide acceptance. With the introduction of bone substitutes, such as calcium phosphate cement, it has been shown that augmentation around screws can be achieved without the drawbacks seen with PMMA. When dealing with fixation of fractures in osteoporotic bone where screw stability might be inadequate, it therefore seems an attractive option to include bone substitutes for augmentation around screws as part of the armamentarium. Clinical studies now are needed to determine the indications in which bone augmentation with bone-graft substitutes (BGSs) would merit clinical usage.

The effects of Dickkopf-1 antibody on metaphyseal bone and implant fixation under different loading conditions

The secreted protein Dickkopf-1 (Dkk1) is an antagonist of canonical Wnt signaling, expressed during fracture healing. It is unclear how it is involved in the mechanical control of bone maintenance. We investigated the response to administration of a Dkk1 neutralizing antibody (Dkk1-ab) in metaphyseal bone under different loading conditions, with or without trauma. In this three part experiment, 120 rats had a screw or bone chamber inserted either unilaterally or bilaterally in the proximal tibia. Mechanical (pull-out) testing, μCT and histology were used for evaluation. The animals were injected with either 10mg/kg Dkk1-ab or saline every 14days for 14, 28, or 42days. Antibody treatment increased bone formation around the screws and improved their fixation. After 28days, the pull-out force was increased by over 100%. In cancellous bone, the bone volume fraction was increased by 50%. In some animals, one hind limb was paralyzed with Botulinum toxin A (Botox) to create a mechanically unloaded environment. This did not increase the response to antibody treatment with regard to screw fixation, but in cancellous bone, the bone volume fraction increased by 233%. Thus, the response in unloaded, untraumatized bone was proportionally larger, suggesting that Dkk1 may be up-regulated in unloaded bone. There was also an increase in thickness of the metaphyseal cortex. In bone chambers, the antibody treatment increased the bone volume fraction. The results suggest that antibodies blocking Dkk1 might be used to stimulate bone formation especially during implant fixation, fracture repair, or bone disuse. It also seems that Dkk1 is up-regulated both after metaphyseal trauma and after unloading, and that Dkk1 is involved in mechano-transduction.

Surface immobilized zoledronate improves screw fixation in rat bone: a new method for the coating of metal implants

Previous studies show that surface immobilized bisphosphonates improve the fixation of stainless steel screws in rat tibia after 2-8 weeks of implantation. We report here about the immobilization of a potent bisphosphonate, zoledronate, to crosslinked fibrinogen by the use of another technique, i.e. ethyl-dimethyl-aminopropylcarbodiimide (EDC)/imidazole immobilization. Bone fixation of zoledronate-coated screws was compared to screws coated with crosslinked fibrinogen only and ditto with EDC/N-hydroxy-succinimide immobilized pamidronate. Fixation in rat tibia was evaluated by a pull-out test at either 2 or 6 weeks after implantation. Both bisphosphonate coatings increased the pull-out force at both time points, and zoledronate showed a significantly higher pull-out force than pamidronate. To further evaluate the new coating technique we also performed a morphometric study, focusing on the area surrounding the implant. The zoledronate coating resulted in an increased bone density around the screws compared to controls. No pronounced increase was seen around the pamidronate coated screws. Together, the results demonstrate the possibility of obtaining a significant local therapeutic effect with minute amounts of surface immobilized zoledronate.

Sol-gel derived titania coating with immobilized bisphosphonate enhances screw fixation in rat tibia

A variety of surface modifications have been tested for the enhancement of screw fixation in bone, and locally delivered anti-osteoporosis drugs such as bisphosphonates (BP) are then of interest. In this in vivo study, the impact of surface immobilized BP was compared with systemic BP delivery and screws with no BP. After due in vitro characterization, differently treated stainless steel (SS) screws were divided into four groups with 10 rats each. Three of the groups received screws coated with sol-gel derived TiO(2) and calcium phosphate (SS+TiO(2)+CaP). One of these had no further treatment, one had alendronate (BP) adsorbed to calcium phosphate mineral, and one received systemic BP treatment. The fourth group received uncoated SS screws and no BP (control). The screw pullout force was measured after 4 weeks of implantation in rat tibiae. The immobilized amount and release rate of alendronate could be controlled by different immersion times. The SS+TiO(2)+CaP coating did not increase the pullout force compared to SS alone. Surface delivered alendronate enhanced the pullout force by 93% [p = 0.000; 95% Confidence Interval (CI): 67-118%] compared to SS, and by 39% (p = 0.044; 95% CI: 7-71%) compared to systemic alendronate delivery. Both surface immobilized and systemically delivered alendronate improved implant fixation. Also, locally delivered, that is, surface immobilized alendronate showed a better fixation than systemically delivered. Using sol-gel derived TiO(2) as a platform, it is possible to administer controllable amounts of a variety of BPs.

Titanium oral implants: surface characteristics, interface biology and clinical outcome

Bone-anchored titanium implants have revolutionized oral healthcare. Surface properties of oral titanium implants play decisive roles for molecular interactions, cellular response and bone regeneration. Nevertheless, the role of specific surface properties, such as chemical and phase composition and nanoscale features, for the biological in vivo performance remains to be established. Partly, this is due to limited transfer of state-of-the-art preparation techniques to complex three-dimensional geometries, analytical tools and access to minute, intact interfacial layers. As judged by the available results of a few randomized clinical trials, there is no evidence that any particular type of oral implant has superior long-term success. Important insights into the recruitment of mesenchymal stem cells, cell-cell communication at the interface and high-resolution imaging of the interface between the surface oxide and the biological host are prerequisites for the understanding of the mechanisms of osseointegration. Strategies for development of the next generation of material surface modifications for compromised tissue are likely to include time and functionally programmed properties, pharmacological modulation and incorporation of cellular components.