Hydroxyapatite particle shape affects screw attachment in cancellous bone when augmented with hydroxyapatite-containing hydrogels

Screw-bone construct failures are a true challenge in orthopaedic implant fixation, particularly in poor quality bone. Whilst augmentation with bone cement can improve the primary stability of screws, there are cements, e.g. PMMA, that may impede blood flow and nutrients and hamper bone remodelling. In this study, soft, non-setting biomaterials based on Hyalectin gels and hydroxyapatite (HA) particles with different morphological parameters were evaluated as potential augmentation materials, using a lapine ex vivo bone model. The pull-out force, stiffness, and work to fracture were considered in evaluating screw attachment. The pull-out force of constructs reinforced with Hyalectin containing irregularly shaped nano-HA and spherically shaped micro-HA particles were found to be significantly higher than the control group (no augmentation material). The pull-out stiffness increased for the micro-HA particles and the work to fracture increased for the irregular nano-HA particles. However, there were no significant augmentation effect found for the spherical shaped nano-HA particles. In conclusion, injectable Hyalectin gel loaded with hydroxyapatite particles was found to have a potentially positive effect on the primary stability of screws in trabecular bone, depending on the HA particle shape and size.

Determining primary stability for adhesively stabilized dental implants

OBJECTIVES

To examine factors influencing the primary stability of dental implants when stabilized in over-sized osteotomies using a calcium phosphate-based adhesive cement was the objective.

METHODS

Using implant removal torque measurements as a surrogate for primary stability, we examined the influence of implant design features (diameter, surface area, and thread design), along with cement gap size and curing time, on the resulting primary implant stability.

RESULTS

Removal torque values scaled with implant surface area and increasing implant diameters. Cement gap size did not alter the median removal torque values; however, larger gaps were associated with an increased spread of the measured values. Among the removal torque values measured, all were found to be above 32 Ncm which is an insertion torque threshold value commonly recommended for immediate loading protocols.

CONCLUSION

The adhesive cement show potential for offering primary implant stability for different dental implant designs. In this study, the primary parameters influencing the measured removal torque values were the implant surface area and diameter. As the liquid cement prevents the use of insertion torque, considering the relationship between insertion and removal torque, removal torque can be considered a reliable surrogate for primary implant stability for bench and pre-clinical settings.

CLINICAL RELEVANCE

At present, the primary stability of dental implants is linked to the quality of the host bone, the drill protocol, and the specific implant design. The adhesive cement might find applications in future clinical settings for enhancing primary stability of implants under circumstances where this cannot be achieved conventionally.

A new bone adhesive candidate- does it work in human bone? An ex-vivo preclinical evaluation in fresh human osteoporotic femoral head bone

INTRODUCTION

The fixation of small intraarticular bone fragments is clinically challenging and an obvious first orthopaedic indication for an effective bone adhesive. In the present study the feasibility of bonding freshly harvested human trabecular bone with OsStic^R, a novel phosphoserine modified cement, was evaluated using a bone cylinder model pull-out test and compared with a commercial fibrin tissue adhesive.

METHODS

Femoral heads (n=13) were collected from hip fracture patients undergoing arthroplasty and stored refrigerated overnight in saline medium prior to testing. Cylindrical bone cores with a pre-inserted bone screw, were prepared using a coring tool. Each core was removed and glued back in place with either the bone adhesive (α-tricalcium phosphate, phosphoserine and 20% trisodium citrate solution) or the fibrin glue. All glued bones were stored in bone medium at 37°C. Tensile loading, using a universal testing machine (5 kN load cell), was applied to each core/head. For the bone adhesive, bone cores were tested at 2 (n=13) and 24 (n=11) hours. For the fibrin tissue adhesive control group (n=9), bone cores were tested exclusively at 2 hours. The femoral bone quality was evaluated with micro-CT.

RESULTS

The ultimate pull-out load for the bone adhesive at 2 hours ranged from 36 to 171 N (mean 94 N, SD 42 N). At 24 hours the pull-out strength was similar, 47 to 198 N (mean 123 N, SD 43 N). The adhesive failure usually occurred through the adhesive layer, however in two samples, at 167 N and 198 N the screw pulled out of the bone core. The fibrin tissue adhesive group reached a peak force of 8 N maximally at 2 hours (range 2.8-8 N, mean 5.4 N, SD 1.6 N). The mean BV/TV for femoral heads was 0.15 and indicates poor bone quality.

CONCLUSION

The bone adhesive successfully glued wet and fatty tissue of osteoporotic human bone cores. The mean ultimate pull-out force of 123 N at 24 hours corresponds to ∼ 300 kPa shear stress acting on the bone core. These first ex-vivo results in human bone are a promising step toward potential clinical application in osteochondral fragment fixation.

Gluing Living Bone Using a Biomimetic Bioadhesive: From Initial Cut to Final Healing

Osteoporotic fractures are a growing issue due to the increasing incidence of osteoporosis worldwide. High reoperation rates in osteoporotic fractures call for investigation into new methods in improving fixation of osteoporotic bones. In the present study, the strength of a recently developed bone bioadhesive, OsStic^tm, was evaluated in vivo using a novel bone core assay in a murine animal model at 0, 3, 7, 14, 28, and 42 days. Histology and micro-CT were obtained at all time points, and the mean peak pull-out force was assessed on days 0–28. The adhesive provided immediate fixation to the bone core. The mean peak bone core pull-out force gradually decreased from 6.09 N (σ 1.77 N) at day 0 to a minimum of 3.09 N (σ 1.08 N) at day 7, recovering to 6.37 N (σ 4.18 N) by day 28. The corresponding fibrin (Tisseel) control mean peak bone core pull-out characteristic was 0.27 N (σ 0.27 N) at day 0, with an abrupt increase from 0.37 N (σ 0.28) at day 3, 6.39 N (σ 5.09 N) at day 7, and continuing to increase to 11.34 N (σ 6.5 N) by day 28. The bone cores failed either through core pull-out or by the cancellous part of the core fracturing. Overall, the adhesive does not interrupt healing with pathological changes or rapid resorption. Initially, the adhesive bonded the bone core to the femur, and over time, the adhesive was replaced by a vascularised bone of equivalent quality and quantity to the original bone. At the 42 day time point, 70% of the adhesive in the cancellous compartment and 50% in the cortical compartment had been replaced. The adhesive outwith the bone shell was metabolized by cells that are only removing the material excess with no ectopic bone formation. It is concluded that the adhesive is not a physical and biochemical barrier as the bone heals through the adhesive and is replaced by a normal bone tissue. This adhesive composition meets many of the clinical unmet needs expressed in the literature, and may, after further preclinical assessments, have potential in the repair of bone and osteochondral fragments.

An Intrinsically-Adhesive Family of Injectable and Photo-Curable Hydrogels with Functional Physicochemical Performance for Regenerative Medicine

Attaching hydrogels to soft internal tissues is crucial for the development of various biomedical devices. Tough sticky hydrogel patches present high adhesion, yet with lack of injectability and the need for treatment of contacting surface. On the contrary, injectable and photo-curable hydrogels are highly attractive owing to their ease of use, flexibility of filling any shape, and their minimally invasive character, compared to their conventional preformed counterparts. Despite recent advances in material developments, a hydrogel that exhibits both proper injectability and sufficient intrinsic adhesion is yet to be demonstrated. Herein, a paradigm shift is proposed toward the design of intrinsically adhesive networks for injectable and photo-curable hydrogels. The bioinspired design strategy not only provides strong adhesive contact, but also results in a wide window of physicochemical properties. The adhesive networks are based on a family of polymeric backbones where chains are modified to be intrinsically adhesive to host tissue and simultaneously form a hydrogel network via a hybrid cross-linking mechanism. With this strategy, adhesion is achieved through a controlled synergy between the interfacial chemistry and bulk mechanical properties. The functionalities of the bioadhesives are demonstrated for various applications, such as tissue adhesives, surgical sealants, or injectable scaffolds.

The Few Who Made It: Commercially and Clinically Successful Innovative Bone Grafts

Bone reconstruction techniques are mainly based on the use of tissue grafts and artificial scaffolds. The former presents well-known limitations, such as restricted graft availability and donor site morbidity, while the latter commonly results in poor graft integration and fixation in the bone, which leads to the unbalanced distribution of loads, impaired bone formation, increased pain perception, and risk of fracture, ultimately leading to recurrent surgeries. In the past decade, research efforts have been focused on the development of innovative bone substitutes that not only provide immediate mechanical support, but also ensure appropriate graft anchoring by, for example, promoting de novo bone tissue formation. From the countless studies that aimed in this direction, only few have made the big jump from the benchtop to the bedside, whilst most have perished along the challenging path of clinical translation. Herein, we describe some clinically successful cases of bone device development, including biological glues, stem cell-seeded scaffolds, and gene-functionalized bone substitutes. We also discuss the ventures that these technologies went through, the hindrances they faced and the common grounds among them, which might have been key for their success. The ultimate objective of this perspective article is to highlight the important aspects of the clinical translation of an innovative idea in the field of bone grafting, with the aim of commercially and clinically informing new research approaches in the sector.

The effect of two types of resorbable augmentation materials - a cement and an adhesive - on the screw pullout pullout resistance in human trabecular bone

Augmentation materials, such as ceramic and polymeric bone cements, have been frequently used to improve the physical engagement of screws inserted into bone. While ceramic, degradable cements may ultimately improve fixation stability, reports regarding their effect on early fixation stability have been inconsistent. On the other hand, a newly developed degradable ceramic adhesive that can bond with tissues surrounding the screw, may improve the pullout performance, ensure early stability, and subsequent bony integration. The aim of this study was to investigate failure mechanisms of screw/trabecular bone constructs by comparing non-augmented screws with screws augmented with a calcium phosphate cement or an adhesive, i.e. a phosphoserine-modified calcium phosphate. Pullout tests were performed on screws inserted into trabecular cylinders extracted from human femoral bone. Continuous and stepwise pullout loading was applied with and without real-time imaging in a synchrotron radiation micro-computed tomograph, respectively. Statistical analysis that took the bone morphology into account confirmed that augmentation with the adhesive supported significantly higher pullout loads compared to cement-augmented, or non-augmented screws. However, the adhesive also allowed for a higher injection volume compared to the cement. In-situ imaging showed cracks in the vicinity of the screw threads in all groups, and detachment of the augmentation materials from the trabecular bone in the augmented specimens. Additional cracks at the periphery of the augmentation and the bone-material interfaces were only observed in the adhesive-augmented specimen, indicating a contribution of surface bonding to the pullout resistance. An adhesive that has potential for bonding with tissues, displayed superior pullout resistance, compared to a brushite cement, and may be a promising material for cementation or augmentation of implants.

Synthesis of Phospho-Amino Acid Analogues as Tissue Adhesive Cement Additives

In this paper we report the synthesis of a library of phospho-amino acid analogues, via a novel single-step allyl-phosphoester protection/Pd-mediated deprotection strategy. These phosphoserine and phosphotyrosine analogues were then applied as additives to create adhesive calcium phosphate cements, allowing us to probe the chemical origins of the increased surface binding strength. We demonstrate the importance of multiple calcium binding motifs in mediating adhesion, as well as highlighting the crucial role played by substrate hydrophobicity and orientation in controlling binding strength.

In vivo safety assessment of a bio-inspired bone adhesive

A new class of materials, bone adhesives, could revolutionise the treatment of highly fragmented fractures. We present the first biological safety investigation of a bio-inspired bone adhesive. The formulation was based upon a modified calcium phosphate cement that included the amino acid phosphoserine. This material has recently been described as substantially stronger than other bioresorbable calcium phosphate cements. Four adhesive groups with the active substance (phosphoserine) and two control groups without phosphoserine were selected for in vitro and in vivo biocompatibility testing. The test groups were subject for cell viability assay and subcutaneous implantation in rats that was followed by gene expression analysis and histology assessment after 6 and 12 weeks. All adhesive groups supported the same rate of cell proliferation compared to the α-TCP control and had viability between 45-64% when compared to cell control. There was no evidence of an increased immune response or ectopic bone formation in vivo. To conclude, this bio-inspired bone adhesive has been proven to be safe, in the present study, without any harmful effects on the surrounding soft tissue.

Adhesive Cements That Bond Soft Tissue Ex Vivo

The aim of the present study was to evaluate the soft tissue bond strength of a newly developed, monomeric, biomimetic, tissue adhesive called phosphoserine modified cement (PMC). Two types of PMCs were evaluated using lap shear strength (LSS) testing, on porcine skin: a calcium metasilicate (CS1), and alpha tricalcium phosphate (αTCP) PMC. CS1 PCM bonded strongly to skin, reaching a peak LSS of 84, 132, and 154 KPa after curing for 0.5, 1.5, and 4 h, respectively. Cyanoacrylate and fibrin glues reached an LSS of 207 kPa and 33 kPa, respectively. αTCP PMCs reached a final LSS of ≈110 kPa. In soft tissues, stronger bond strengths were obtained with αTCP PMCs containing large amounts of amino acid (70-90 mol%), in contrast to prior studies in calcified tissues (30-50 mol%). When αTCP particle size was reduced by wet milling, and for CS1 PMCs, the strongest bonding was obtained with mole ratios of 30-50% phosphoserine. While PM-CPCs behave like stiff ceramics after setting, they bond to soft tissues, and warrant further investigation as tissue adhesives, particularly at the interface between hard and soft tissues.

A biomechanical test model for evaluating osseous and osteochondral tissue adhesives

Background

Currently there are no standard models with which to evaluate the biomechanical performance of calcified tissue adhesives, in vivo. We present, herein, a pre-clinical murine distal femoral bone model for evaluating tissue adhesives intended for use in both osseous and osteochondral tissue reconstruction.

Results

Cylindrical cores (diameter (Ø) 2 mm (mm) × 2 mm depth), containing both cancellous and cortical bone, were fractured out from the distal femur and then reattached using one of two tissue adhesives. The adhesiveness of fibrin glue (Tisseel^tm), and a novel, biocompatible, calcium phosphate-based tissue adhesive (OsStic^tm) were evaluated by pullout testing, in which glued cores were extracted and the peak force at failure recorded. The results show that Tisseel weakly bonded the metaphyseal bone cores, while OsStic produced > 30-fold higher mean peak forces at failure (7.64 Newtons (N) vs. 0.21 N). The failure modes were consistently disparate, with Tisseel failing gradually, while OsStic failed abruptly, as would be expected with a calcium-based material. Imaging of the bone/adhesive interface with microcomputed tomography revealed that, for OsStic, failure occurred more often within cancellous bone (75% of tested samples) rather than at the adhesive interface.

Conclusions

Despite the challenges associated with biomechanical testing in small rodent models the preclinical ex-vivo test model presented herein is both sensitive and accurate. It enabled differences in tissue adhesive strength to be quantified even for very small osseous fragments (<Ø4mm). Importantly, this model can easily be scaled to larger animals and adapted to fracture fragment fixation in human bone. The present model is also compatible with other long-term in vivo evaluation methods (i.e. in vivo imaging, histological analysis, etc.).

A Novel Class of Injectable Bioceramics that Glue Tissues and Biomaterials

Calcium phosphate cements (CPCs) are clinically effective void fillers that are capable of bridging calcified tissue defects and facilitating regeneration. However, CPCs are completely synthetic/inorganic, unlike the calcium phosphate that is found in calcified tissues, and they lack an architectural organization, controlled assembly mechanisms, and have moderate biomechanical strength, which limits their clinical effectiveness. Herein, we describe a new class of bioinspired CPCs that can glue tissues together and bond tissues to metallic and polymeric biomaterials. Surprisingly, alpha tricalcium phosphate cements that are modified with simple phosphorylated amino acid monomers of phosphoserine (PM-CPCs) bond tissues up to 40-fold stronger (2.5–4 MPa) than commercial cyanoacrylates (0.1 MPa), and 100-fold stronger than surgical fibrin glue (0.04 MPa), when cured in wet-field conditions. In addition to adhesion, phosphoserine creates other novel properties in bioceramics, including a nanoscale organic/inorganic composite microstructure, and templating of nanoscale amorphous calcium phosphate nucleation. PM-CPCs are made of the biocompatible precursors calcium, phosphate, and amino acid, and these represent the first amorphous nano-ceramic composites that are stable in liquids.

Joint academic and industrial efforts towards innovative and efficient solutions for clinical needs

The 4^th Translational Research Symposium (TRS) was organised at the annual meeting of the European Society for Biomaterials (ESB) 2017, Athens, Greece, with a focus on 'Academia-Industry Clusters of Research for Innovation Catalysis'. Collaborations between research institutes and industry can be sustained in several ways such as: European Union (EU) funded consortiums; syndicates of academic institutes, clinicians and industries; funding from national governments; and private collaborations between universities and companies. Invited speakers from industry and research institutions presented examples of these collaborations in the translation of research ideas or concepts into marketable products. The aim of the present article is to summarize the key messages conveyed during these lectures. In particular, emphasis is put on the challenges to appropriately identify and select unmet clinical needs and their translation by ultimately implementing innovative and efficient solutions achieved through joint academic and industrial efforts.

Influence of cement compressive strength and porosity on augmentation performance in a model of orthopedic screw pull-out

Disease and injuries that affect the skeletal system may require surgical intervention and internal fixation, i.e. orthopedic plate and screw insertion, to stabilize the injury and facilitate tissue repair. If the surrounding bone quality is poor the screws may migrate, or the bone may fail, resulting in fixation failure. While numerous studies have shown that cement augmentation of the interface between bone and implant can increase screw pull-out force, the physical properties of cement that influence pull-out force have not been investigated. The present study sought to determine how the physical properties of high strength calcium phosphate cements (hsCPCs, specifically dicalcium phosphate) affected the corresponding orthopedic screw pull-out force in urethane foam models of "healthy" and "osteoporotic" synthetic bone (Sawbones). In the simplest model, where only the bond strength between screw thread and cement (without Sawbone) was tested, the correlation between pull-out force and cement compressive strength (R² = 0.79) was weaker than correlation with total cement porosity (R² = 0.89). In open pore Sawbone that mimics "healthy" cancellous bone density the stronger cements produced higher pull-out force (50-60% increase). High strength, low porosity cements also produced higher pull-out forces (50-190% increase) in "healthy" Sawbones with cortical fixation if the failure strength of the cortical material was similar to, or greater than (a metal shell), actual cortical bone. This result is of particular clinical relevance where fixation with a metal plate implant is indicated, as the nearby metal can simulate a thicker cortical shell, thereby increasing the pull-out force of screws augmented with stronger cements. The improvement in pull-out force was apparent even at low augmentation volumes of 0.5mL (50% increase), which suggest that in clinical situations where augmentation volume is limited the stronger, lower porosity calcium phosphate cement (CPC) may still produce a significant improvement in screw pull-out force. When the correlation strength of all the tested models were compared both cement porosity and compressive strength accurately predicted pull-out force (R²=1.00, R²=0.808), though prediction accuracy depended upon the strength of the material surrounding the Sawbone. The correlations strength was low for bone with no, or weak, cortical fixation (R²=0.56, 0.36). Higher strength and lower porosity CPCs also produced greater pull-out force (1-1.5kN) than commercial CPC (0.2-0.5kN), but lower pull-out force than PMMA (2-3kN). The results of this study suggest that the likelihood of screw fixation failure may be reduced by selecting calcium phosphate cements with lower porosity and higher compressive strength, in patients with healthy bone mineral density and/or sufficient cortical thickness. This is of particular clinical relevance when fixation with metal plates is indicated, or where the augmentation volume is limited.

Studying health informatics from a distance: issues, problems and experiences

Sheffield University has recently introduced a new Health Informatics Masters degree by distance learning. This paper documents the initial experiences of setting up, managing and delivering this course. The three parts of the paper cover motivation and background, design and content, and the issues, observations and problems relating to the course respectively. The latter relate to the logistics of delivery and how best to utilize the features of WebCT, and also how to meet the aspirations of students from a wide range of backgrounds.

Innovating in the medical device industry - challenges & opportunities ESB 2015 translational research symposium

The European Society for Biomaterials 2015 Translational Research Symposium focused on 'Innovating in the Medical Device Industry - Challenges & Opportunities' from different perspectives, i.e., from a non-profit research organisation to a syndicate of small and medium-sized companies and large companies. Lecturers from regulatory consultants, industry and research institutions described the innovation process and regulatory processes (e.g., 510K, PMA, combination product) towards market approval. The aim of the present article is to summarise and explain the main statements made during the symposium, in terms of challenges and opportunities for medical device industries, in a constantly changing customer and regulatory environment.

Studying Health Information from a Distance: The Impact of a Multimedia Case Study

This paper describes a project to enhance the learning experience of students, in which a multimedia healthcare case study and associated tasks are being developed and evaluated within the Distance Learning MSc in Health Informatics programme at the University of Sheffield. The paper provides background context and motivation for the case study, followed by a description of its content, which is based upon a general practice change management scenario. The way in which this material was researched and developed is reviewed, covering rationale, methodology and the strategy for evaluation. Early evaluation suggests that the introduction of the case study is having a positive effect on the problem of isolation experienced by students on distance learning courses. The paper also reflects on the overheads of this project. Those with substantial experience in computer-assisted learning should be involved at an early stage, and planning and sequencing of both the case study itself and between the case study and the course should be given attention. The paper concludes that benefits of the approach are significant, and include better integration of course modules, shared decision making and group problem solving.

In vitro and in vivo investigation of bisphosphonate-loaded hydroxyapatite particles for peri-implant bone augmentation

Locally applied bisphosphonates, such as zoledronate, have been shown in several studies to inhibit peri-implant bone resorption and recently to enhance peri-implant bone formation. Studies have also demonstrated positive effects of hydroxyapatite (HA) particles on peri-implant bone regeneration and an enhancement of the anti-resorptive effect of bisphosphonates in the presence of calcium. In the present study, both hydroxyapatite nanoparticles (nHA) and zoledronate were combined to achieve a strong reinforcing effect on peri-implant bone. The nHA-zoledronate combination was first investigated in vitro with a pre-osteoclastic cell assay (RAW 264.7) and then in vivo in a rat model of postmenopausal osteoporosis. The in vitro study confirmed that the inhibitory effect of zoledronate on murine osteoclast precursor cells was enhanced by loading the drug on nHA. For the in vivo investigation, either zoledronate-loaded or pure nHA were integrated in hyaluronic acid hydrogel. The gels were injected in screw holes that had been predrilled in rat femoral condyles before the insertion of miniature screws. Micro-CT-based dynamic histomorphometry and histology revealed an unexpected rapid mineralization of the hydrogel in vivo through formation of granules, which served as scaffold for new bone formation. The delivery of zoledronate-loaded nHA further inhibited a degradation of the mineralized hydrogel as well as a resorption of the peri-implant bone as effectively as unbound zoledronate. Hyaluronic acid with zoledronate-loaded nHA, thanks to its dual effect on inducing a rapid mineralization and preventing resorption, is a promising versatile material for bone repair and augmentation. Copyright © 2015 John Wiley & Sons, Ltd.

Progressing innovation in biomaterials. From the bench to the bed of patients

A Translational Research Symposium was organized at the 2014 annual meeting of the European society for biomaterials. This brought together leading Tier one companies in clinical biomaterials and medical device markets, small and medium enterprises and entrepreneurial academics who shared their experiences on taking biomaterials technologies to commercial endpoints, in the clinics. The symposium focused on "Progressing Innovation in Biomaterials. From the Bench to the Bed of Patients". The aim of the present document is to illustrate the content of the symposium and to highlight the key lessons from selected lectures.

Bone Anchors—A Preliminary Finite Element Study of Some Factors Affecting Pullout

Bone anchors (or suture anchors) are used to provide attachment points for sutures to connect tissue such as tendons or ligaments to bone, and work by engaging a threaded portion—sometimes tapered—to the cancellous and/or cortical bone. Such repair is often needed after trauma, or as part of reconstructive surgery. This paper uses the finite element method to compare the pullout characteristics of one common type of bone anchor in different cancellous bone structures. Finite element models are created by using computed tomography (CT) scans of cancellous bone and building computer-aided design (CAD) models to define the cancellous bone geometry. Orthopedic surgeons will sometimes remove parts of the cortical shell and this paper also examines the mechanical effects of decortication. Furthermore, the importance of the connection between anchor and cortical layer is examined. One of the key outcomes from the model is that the coefficient of friction between bone and anchor determines potential mechanisms of pullout. The stiffness of anchors and the effect of the cortical layer are presented for different pullout angles to obtain the theoretical response. The results show the detailed modeling that includes the micro-architecture of the cancellous bone is necessary to capture the large variations that can exist.

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.

Biomechanical and antibacterial properties of Tobramycin loaded hydroxyapatite coated fixation pins

The present study investigates the use of nanoporous, biomimetic hydroxyapatite (HA) coatings deposited on TiO₂ coated fixation pins as functional implant surfaces for the local release of Tobramycin in order to prevent bacterial colonization. The impact of HA-coating thickness, coating morphology and biomechanical forces during insertion into synthetic bone on the drug loading and release properties are analyzed. The coatings are shown to exhibit bactericidal effects against Staphylococcus aureus in agar medium for a duration of 6 days after loading by adsorption with Tobramycin for only 5 min at elevated temperature and pressure. Furthermore, high performance liquid chromatography analysis shows a drug release in phosphate buffered saline for 8 days with antibiotic concentration remaining above the minimal inhibitory concentration for S. aureus during the entire release period. Biomechanical insertion tests into synthetic bone and conventional scratch testing demonstrate adhesive strength at the HA/TiO₂ interface. Biocompatibility is verified by cell viability tests. Outgrowth endothelial cells, as well as primary osteoblasts, are viable and firmly attached to both HA and TiO₂ surfaces. The results presented are encouraging and support the concept of functional HA coatings as local drug delivery vehicles for biomedical applications to treat as well as to prevent post-surgical infections.

Drug loading and release of Tobramycin from hydroxyapatite coated fixation pins

This paper evaluates the loading and release properties of Tobramycin incorporated by adsorptive loading from a solution into plasma sprayed and biomimetically coated Hydroxyapatite (HA) fixation pins. The aim of this study is to contribute towards designing a functional implant surface offering local release of the antibiotic agent to prevent post-surgical infections. Cathodic arc deposition is used to coat stainless steel fixation pins with a bioactive, anatase phase dominated, TiO₂ coating onto which a HA layer is grown biomimetically. The loading and release properties are evaluated by studying the subsequent release of Tobramycin using high performance liquid chromatography and correlated to the differences in HA coating microstructure and the physical conditions under loading. The results from these studies show that a dual loading strategy consisting of a solution temperature of 90 °C and a pressure of 6 bar during a loading time of 5 min release a sufficient amount of Tobramycin to guarantee the inhibition of Staphylococcus aureus up to 2 days for plasma sprayed HA coatings and for 8 days for biomimetic coatings. The present study emphasizes the advantages of the nanoporous structure of biomimetically deposited HA over the more dense structure of plasma sprayed HA coatings in terms of antibiotic incorporation and subsequent sustained release and provides a valuable outline for the design of implant surfaces aiming for a fast-loading and controlled, local drug administration.

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.

An approximate model for cancellous bone screw fixation

This paper presents a finite element (FE) model to identify parameters that affect the performance of an improved cancellous bone screw fixation technique, and hence potentially improve fracture treatment. In cancellous bone of low apparent density, it can be difficult to achieve adequate screw fixation and hence provide stable fracture fixation that enables bone healing. Data from predictive FE models indicate that cements can have a significant potential to improve screw holding power in cancellous bone. These FE models are used to demonstrate the key parameters that determine pull-out strength in a variety of screw, bone and cement set-ups, and to compare the effectiveness of different configurations. The paper concludes that significant advantages, up to an order of magnitude, in screw pull-out strength in cancellous bone might be gained by the appropriate use of a currently approved calcium phosphate cement.

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.

Bone substitute materials delivering zoledronic acid: Physicochemical characterization, drug load, and release properties

Calcium phosphate-like bone substitute materials have a long history of successful orthopedic applications such as bone void filling and augmentation. Based on the clinical indications, these materials may be loaded with active agents by adsorption offering a perspective for providing innovative drug-delivery systems. The highly effective bisphosphonate zoledronic acid (ZOL) demonstrated a strong affinity to biominerals and is known to significantly reduce osteoclastic activity. Support of early bone formation and reduction of bone resorption can be promoted after implantation of bioceramics releasing ZOL. The aim of this study was to develop an easy to handle approach to combine ZOL with bone substitutes by use of a dipping technique. The properties of three different materials were investigated by using a number of physicochemical methods such as light microscopy, scanning electron microscopy (SEM), dynamic vapor sorption (DVS), true density, and surface area measurement to evaluate the feasibility of being potential drug carriers. Besides physicochemical characterization, the bone substitutes were evaluated by their ZOL-loading capacity in a time- and concentration-dependent manner. Additionally, the materials were assessed as release systems in an in vitro study. Acontrolled ZOL load in a range of 0.04–1.86 µg/mg material and a release of 0.02–0.18 µg/mg within 30 min is demonstrated. The findings support using the investigated bioceramics as carrier systems to release ZOL. Overall, the results create the base for further development of drug-delivery systems with controlled drug loading and prolonged release and need to be further analyzed in an in vivo study.

In vivo tissue response to ultrasound assisted application of biodegradable pins into cortical and cancellous bone structures: a histological and densitometric analysis in rabbits

In orthopaedic traumatology biodegradable pins are increasingly used for fixation of small bone fragments. In the present study, the ultrasound-assisted anchoring technique (SonicFusion technique), a osteosynthesis method being recently introduced in cranial applications, in which ultrasonic energy is used to insert and anchor polymer pins in bone, was compared with the conventional pin application procedure. The aim of the present study was to assess the short and long term thermal impact of two different ultrasonic energy levels on different bone structures in the distal medial femur of rabbits. The treatment groups consisted of customized polylactide pins applied at a low and a high energy level, the Reference Control and a Negative Control. The thermal effect on bone tissues was evaluated by means of qualitative and semi-quantitative histology and micro-computerized tomography. Five days following surgery, all implant sites showed no tissue damage but normal signs of early ongoing tissue repair. Enhancing the energy level by about 30% had no significant impact on the tissue response. At 4 weeks after surgery test sites covered by ultrasound-aided implantation showed a significantly enhanced bone/implant contact as compared to pins applied by conventional application. In conclusion, the ultrasound assisted anchoring technique not only did not impair bone regeneration, but even improved implant integration.

Calcium phosphate cement augmentation of cancellous bone screws can compensate for the absence of cortical fixation

An obvious means to improve the fixation of a cancellous bone screw is to augment the surrounding bone with cement. Previous studies have shown that bone augmentation with Calcium Phosphate (CaP) cement significantly improves screw fixation. Nevertheless, quantitative data about the optimal distribution of CaP cement is not available. The present study aims to show the effect of cement distribution on the screw fixation strength for various cortical thicknesses and to determine the conditions at which cement augmentation can compensate for the absence of cortical fixation in osteoporotic bone. In this study, artificial bone materials were used to mimic osteoporotic cancellous bone and cortical bone of varying thickness. These bone constructs were used to test the fixation strength of cancellous bone screws in different cortical thicknesses and different cement augmentation depths. The cement distribution was measured with microCT. The maximum pullout force was measured experimentally. The microCT analysis revealed a pseudo-conic shape distribution of the cement around the screws. While the maximum pullout strength of the screws in the artificial bone only was 30±7N, it could increase up to approximately 1000N under optimal conditions. Cement augmentation significantly increased pullout force in all cases. The effect of cortical thickness on pullout force was reduced with increased cement augmentation depth. Indeed, cement augmentation without cortical fixation increased pullout forces over that of screws without cement augmentation but with cortical fixation. Since cement augmentation significantly increased pullout force in all cases, we conclude that the loss of cortical fixation can be compensated by cement augmentation.

Finite element analysis of intramedullary devices: The effect of the gap between the implant and the bone

This paper examines the interaction interface between the implant and the bone for an intramedullary femoral nailing system using a finite element (FE) model and specifically considers the hypothesis that the local geometry at the interface is significant to the resulting localized contact stress between the medial and lateral aspect of nail and endosteum. Contact mechanics algorithms are used in the FE modelling technique that can be developed to deal with any form of intramedullary device for which contact at the bone—implant interface is important.

Global stiffness data from the FE model are compared with available data from an experiment carried out on a construct of the bone and the device that uses intramedullary femoral nails. Acceptable agreement is obtained.

The results demonstrate that the mechanical interface between the implant and the bone is significantly affected by the gap geometry and magnitude. In particular, larger gaps lead to greater concentrations of stress on the medial side, while the distribution of stress is more uniform at the lateral contacts. Furthermore, the results show that the gap can have a marked effect on the stresses that occur on the fracture plane.

Intramedullary nails with two lag screws

OBJECTIVE

To investigate the structural integrity of intramedullary nails with two lag screws, and to give guidance to orthopaedic surgeons in the choice of appropriate devices.

DESIGN

Alternative designs of the construct are considered, and the use of a slotted upper lag screw insertion hole is analysed.

BACKGROUND

Intramedullary fixation devices with a single lag screw have been known to fail at the lag screw insertion hole. Using two lag screws is considered. It has also been proposed to use a slot in the nail for the upper lag screw to prevent the upper lag screw from sticking.

METHODS

Bending and torsion load cases are analysed using finite element method. Consideration of both load conditions is essential.

RESULTS

The results present the overall stiffness of the assembly, the load sharing between lag screws, and the possibility for cut-out to occur.

CONCLUSIONS

While the slot for the upper lag screw might be advantageous with regard to the stresses in the lag screws, it could be detrimental for cut-out occurring adjacent to the lag screws.

RELEVANCE

Comparative analyses demonstrate that two lag screws may be advantageous in patients whose cancellous bone quality is good and who impose large loads on the lag screw/nail interface. However, the use of two screws might pre-dispose to failure by cut-out of the lag screws. The addition of a slotted hole for the upper lag screw appears to do nothing significant to reduce the risk of such a failure.

Intramedullary nails: some design features of the distal end

Intramedullary nails are used to stabilise fractures of the proximal femur. The nail acts by transferring loads from the proximal fraction to the rest of the femoral shaft. The way in which this occurs depends to a large extent on the design of the distal end of the nail. This is not dissimilar to the situation with regard to load shedding (or load transfer) from the femoral component of a total hip replacement. A finite element model of a fractured femur with either a neck or a subtrochanteric fracture is set up to investigate the effects of nail length, nail distal stiffness and material stiffness on the structural behaviour of the system. Specifically what is considered is the influence of these parameters on the stress across the fracture and the normal pressure that the nail exerts on the endosteum of the femoral diaphysis. It is found that a longer nail could produce higher contact stress between the tip of the nail and the endosteum. Also, this contact stress is reduced when the distal region of the nail is made more flexible either by incorporating longitudinal slots or by using a material with a lower modulus of elasticity.

Intelligent systems for nursing education

Health care is one of the fastest growing areas in terms of care, treatment and the exploitation of new technology in Slovenia. There is a great need for new approaches ensuring that education and work of health care professionals will be built upon the state of the art in nursing. As a consequence the educational, governmental and "industrial" institutions from Slovenia, UK, Italy and Greece have determined to work on above problem. EU agreed to support the project under the Phare Tempus Framework and the aim of this paper is to present an educational approach based on intelligent systems and its application in nursing education.

Intramedullary femoral nails: one or two lag screws? A preliminary study

Failures of proximal femoral nails that treat unstable femoral fractures have been reported. In this communication, a finite element model to include a proximal femoral nail within a fractured femur was used to carry out preliminary investigations into configurations of single or double lag screws. The effects of the different types of fracture were investigated. The results show that in order to share the load evenly between two lag screws, a good configuration seems to be to have a slightly larger screw above the lower screw. This also ameliorates stresses in the nail at the lag screw insertion holes. However, using two screws in this way can lead to large stresses in the cancellous bone in the femoral head, and these stresses may be significant in the initiation of cut-out.

Information and communication systems for the assistance of carers based on ACTION

Recent advances in telecommunication technologies allow the design of information and communication systems for people who are caring for others in the home as family members or as professionals in the health or community centres. The present paper analyses and classifies the information flow and maps it to an information life cycle, which governs the design of the deployed hardware, software and the data-structure. This is based on the initial findings of ACTION (assisting carers using telematics interventions to meet older persons' needs) a European Union funded project. The proposed information architecture discusses different designs such as centralized or decentralized Web and Client server solutions. A user interface is developed reflecting the special requirements of the targeted user group, which influences the functionality and design of the software, data architecture and the integrated communication system using video-conferencing. ACTION has engineered a system using plain Web technology based on HTML, extended with JavaScript and ActiveX and a software switch enabling the integration of different types of videoconferencing and other applications providing manufacturer independence.

A unified model to support an information intensive health care environment

The two parts of this paper respectively analyses the mismatch between current systems and practice in health care, and present an outline design for enhanced Integrated Care Pathways (ICP) knowledge and information management based upon mature ICT technologies.

Finite element analysis of a Gamma nail within a fractured femur

Failures of Gamma nails which treat unstable femoral fractures have been reported. In this paper, a finite element model to include a Gamma nail within a fractured femur was used to investigate the stresses in the Gamma nail. The effects for different types of fracture were investigated. The results show that its use for subtrochanteric fractures will cause higher stresses at the lag screw and upper distal screw insertion holes in the nail than when used for femur neck fractures.

Geometric mismatch of the Gamma nail to the Chinese femur

The geometric mismatch of the femoral component of the Gamma nail to the Chinese femora resulted in intraoperative complications. To provide scientific data for modification of the implant, 28 pairs of normal Chinese femora were studied with the 3-dimensional reconstruction from the computed tomography scan data. Measurements were taken from the reconstituted drawings, and the anthropometric data were applied in the modification of the implant. This study is the first report on the application of Chinese anthropometric data on the design of a trauma implant. It is hoped that a larger scale of the study will provide a more comprehensive data base for wider application to orthopaedic implant design in the future.

Femoral shaft perforation at arthroplasty: to treat or not to treat

Femoral shaft perforation at total hip arthroplasty is a complication that is being noted more frequently, and it is often associated with femoral shaft fracture below the prosthesis. This study examines the anatomic and biomechanical effects of femoral shaft perforation at arthroplasty, and the effects of supporting the perforated bone with Partridge plates and bands. Two models, pig femora and Pedilen cylinders, were employed. Testing the bone models to failure in tensile mode showed that the perforations weakened the bone and that the Partridge plates and bands decreased the weakening effects of the perforation. The strengthening effect of the Partridge plates and bands on the bone with a perforation, allied with the presence of an internal splint in the event of a fracture through the perforation, suggests the benefit of using Partridge plates and bands if a cortical perforation is found at arthroplasty and revision is not feasible.