An ex vivo model using human osteoarthritic cartilage demonstrates the release of bioactive insulin-like growth factor-1 from a collagen-glycosaminoglycan scaffold.

Biomimetic scaffolds hold great promise for therapeutic repair of cartilage, but although most scaffolds are tested with cells in vitro, there are very few ex vivo models (EVMs) where adult cartilage and scaffolds are co-cultured to optimize their interaction prior to in vivo studies. This study describes a simple, non-compressive method that is applicable to mammalian or human cartilage and provides a reasonable throughput of samples. Rings of full-depth articular cartilage slices were derived from human donors undergoing knee replacement for osteoarthritis and a 3 mm core of a collagen/glycosaminoglycan biomimetic scaffold (Tigenix, UK) inserted to create the EVM. Adult osteoarthritis chondrocytes were seeded into the scaffold and cultures maintained for up to 30 days. Ex vivo models were stable throughout experiments, and cells remained viable. Chondrocytes seeded into the EVM attached throughout the scaffold and in contact with the cartilage explants. Cell migration and deposition of extracellular matrix proteins in the scaffold was enhanced by growth factors particularly if the scaffold was preloaded with growth factors. This study demonstrates that the EVM represents a suitable model that has potential for testing a range of therapeutic parameters such as numbers/types of cell, growth factors or therapeutic drugs before progressing to costly pre-clinical trials.

Mechanical properties of morcellised bone graft with the addition of hydroxyapatite.

Mixtures of morcellised bone graft (MBG) and hydroxyapatite (HA) are frequently used in revision arthroplasty surgery. However, the changes in the mechanical properties from adding HA to MBG are unknown. This study used a uniaxial compression test to replicate impaction bone grafting and subsequent early postoperative weightbearing to investigate the effect of adding different proportion of HA to MBG. To achieve this aim, human MBG was subjected to increasing impaction forces and the apparent stiffness and creep for each stress level determined. Subsequently, increasing proportions porous and non porous HA were added to the MBG. The major findings were that the apparent stiffness for MBG increased and the associated creep decreased both with the application of increasing stress and with the addition of increasing proportions of HA. In conclusion, greater proportions of HA in the graft mixture improved the mechanical response compared with MBG impacted under the same force. This improvement replicated the properties of pure MBG under high axial stress. This study indicates that graft mixtures of MBG and HA can be tailormade for patients. The need for less impaction force in MBG:HA mixtures to obtain the same properties as pure MBG may decrease the risk of intraoperative fracture.

Lateral epicondylitis: a review of pathology and management.

Lateral epicondylitis, or 'tennis elbow', is a common condition that usually affects patients between 35 and 55 years of age. It is generally self-limiting, but in some patients it may continue to cause persistent symptoms, which can be refractory to treatment. This review discusses the mechanism of disease, symptoms and signs, investigations, current management protocols and potential new treatments.

Synthetic collagen fascicles for the regeneration of tendon tissue.

The structure of an ideal scaffold for tendon regeneration must be designed to provide a mechanical, structural and chemotactic microenvironment for native cellular activity to synthesize functional (i.e. load bearing) tissue. Collagen fibre scaffolds for this application have shown some promise to date, although the microstructural control required to mimic the native tendon environment has yet to be achieved allowing for minimal control of critical in vivo properties such as degradation rate and mass transport. In this report we describe the fabrication of a novel multi-fibre collagen fascicle structure, based on type-I collagen with failure stress of 25-49 MPa, approximating the strength and structure of native tendon tissue. We demonstrate a microscopic fabrication process based on the automated assembly of type-I collagen fibres with the ability to produce a controllable fascicle-like, structural motif allowing variable numbers of fibres per fascicle. We have confirmed that the resulting post-fabrication type-I collagen structure retains the essential phase behaviour, alignment and spectral characteristics of aligned native type-I collagen. We have also shown that both ovine tendon fibroblasts and human white blood cells in whole blood readily infiltrate the matrix on a macroscopic scale and that these cells adhere to the fibre surface after seven days in culture. The study has indicated that the synthetic collagen fascicle system may be a suitable biomaterial scaffold to provide a rationally designed implantable matrix material to mediate tendon repair and regeneration.

Osteoinduction by combining bone morphogenetic protein (BMP)-2 with a bioactive novel nanocomposite.

OBJECTIVES: There is increasing application of bone morphogenetic proteins (BMPs) owing to their role in promoting fracture healing and bone fusion. However, an optimal delivery system has yet to be identified. The aims of this study were to synthesise bioactive BMP-2, combine it with a novel α-tricalcium phosphate/poly(D,L-lactide-co-glycolide) (α-TCP/PLGA) nanocomposite and study its release from the composite. METHODS: BMP-2 was synthesised using an Escherichia coli expression system and purified. In vitro bioactivity was confirmed using C2C12 cells and an alkaline phosphatase assay. The modified solution-evaporation method was used to fabricate α-TCP/PLGA nanocomposite and this was characterised using X-ray diffraction and scanning electron microscopy. Functionalisation of α-TCP/PLGA nanocomposite by adsorption of BMP-2 was performed and release of BMP-2 was characterised using an enzyme-linked immunosorbent assay (ELISA). RESULTS: Alkaline phosphatase activity of C2C12 cells was increased by the presence of all BMP-2/nanocomposite discs compared with the presence of a blank disc (p = 0.0022), and increased with increasing incubation concentrations of BMP-2, showing successful adsorption and bioactivity of BMP-2. A burst release profile was observed for BMP-2 from the nanocomposite. CONCLUSIONS: Functionalisation of α-TCP/PLGA with BMP-2 produced osteoinduction and was dose-dependent. This material therefore has potential application as an osteoinductive agent in regenerative medicine.

The effect of the addition of hydroxyapatite graft substitutes upon the hoop strain and subsequent subsidence of a femoral model during impaction bone grafting.

Impaction bone grafting using morcellised allograft can successfully restore bone stock in revision surgery. However, concerns exist regarding supply of bone and transmission of infection. Bone-graft extenders, such as tricalcium phosphate (TCP) and hydroxyapatite (HA), are used to minimise the use of donor bone. However, concerns exist around a reported increased risk of femoral fracture during impaction bone grafting with a 1:1 mixture of TCP/HA and morcellised bone graft (MBG) during impaction grafting in human cadaveric femora. Using a sawbones model, it was evaluated whether there was increased femoral cortical strain with a HA:MBG mixture during impaction grafting compared to MBG impacted at the same and a greater force. Subsequently the subsidence behaviour of the different graft mixes was compared by using a loaded femoral stem in an endurance test. It was demonstrated that the femora with the MBG:HA graft had greater cortical hoop stresses but improved subsidence behaviour compared to a graft composed of pure MBG impacted at the same force.

A new hip epiphyseal prosthesis: design revision driven by a validated numerical procedure.

An innovative epiphyseal device has been recently proposed claiming an effective bone-prosthesis load transfer and a nearly physiological bone stresses distribution. However preliminary experimental tests showed a 23% weakening of the femoral neck after implantation. Aim of this study was to revise the prosthesis geometry with the goal of enhancing the femoral neck strength after implantation, while maintaining unchanged the initial conceptual design. To this aim, the risk of femoral neck fractures, prosthesis fractures, aseptic loosening and excessive bone resorption were addressed through a validated finite element procedure following a systematic approach. The initial prosthesis geometry was revised to reduce each investigated failure risk below the threshold of acceptance (100%). The new geometry was re-assessed to verify the effectiveness of the revision. The first design was predicted to locally induce high bone strains and cement stresses, which translated in a risk of bone and cement failure exceeding the threshold of acceptance (>100%). The revised design preserved a good stability of the device, contemporary reducing the risk for bone (45%) and cement (60%) failure. If results will be confirmed by statistical and clinical experimentations, current clinical indications for hip epiphyseal devices might be extended.

Regeneration and repair of tendon and ligament tissue using collagen fibre biomaterials.

Collagen fibres are ubiquitous macromolecular assemblies in nature, providing the structures that support tensile mechanical loads within the human body. Aligned type I collagen fibres are the primary structural motif for tendon and ligament, and therefore biomaterials based on these structures are considered promising candidates for mediating regeneration of these tissues. However, despite considerable investigation, there remains no collagen-fibre-based biomaterial that has undergone clinical evaluation for this application. Recent research in this area has significantly enhanced our understanding of these complex and challenging biomaterials, and is reinvigorating interest in the development of such structures to recapitulate mechanical function. In this review we describe the progress to date towards a ligament or tendon regeneration template based on collagen fibre scaffolds. We highlight reports of particular relevance to the development of the underlying biomaterials science in this area. In addition, the potential for tailoring and manipulating the interactions between collagen fibres and biological systems, as hybrid biomaterial-biological ensembles, is discussed in the context of developing novel tissue engineering strategies for tendon and ligament.

The role of surface wettability and surface charge of electrosprayed nanoapatites on the behaviour of osteoblasts.

A new deposition method is presented, based on electrospraying, that can build bioceramic structures with desirable surface properties. This technology allows nanoapatite crystals, including hydroxyapatite (nHA), carbonate-substituted HA (nCHA) and silicon-substituted HA (nSiHA), to be electrosprayed on glass substrates. Human osteoblast cells cultured on nSiHA showed enhanced cell attachment, proliferation and protein expression, namely alkaline phosphatase, type 1 collagen and osteocalcin, as compared to nHA and nCHA. The modification of nanoapatite by the addition of silicon into the HA lattice structure renders the electrosprayed surface more hydrophilic and electronegatively charged.

Articular cartilage tissue engineering: today's research, tomorrow's practice?

Articular cartilage repair remains a challenge to surgeons and basic scientists. The field of tissue engineering allows the simultaneous use of material scaffolds, cells and signalling molecules to attempt to modulate the regenerative tissue. This review summarises the research that has been undertaken to date using this approach, with a particular emphasis on those techniques that have been introduced into clinical practice, via in vitro and preclinical studies.

The effects of silicate ions on human osteoblast adhesion, proliferation, and differentiation.

Silicon has been shown to have important effects on skeletal development and repair, and soluble silicate ions have been found to stimulate the expression of type-I collagen in osteoblast-like cell cultures. Furthermore, silicon has been incorporated into the hydroxyapatite lattice and enhanced metabolic activity of human osteosarcoma cells was observed when cells were cultured on this material. In vivo assessments have demonstrated enhanced bioactivity of silicon-substituted hydroxyapatite (Si-HA) over pure HA. However, detailed mechanisms for the stimulative effects of Si-HA have not been described. In this study, we found that silicon substitution into hydroxyapatite affects the adhesion of human osteoblast-like cells (HOBs) in culture, with 0.8 wt % silicon substitution being optimal. In addition, metabolic activity and proliferation of HOBs were increased by supplementation of the growth medium with 30 microM silicon. It was determined that this response may depend on the proportion of cells at different stages of differentiation within the cultures.

Stress shielding and stress concentration of contemporary epiphyseal hip prostheses.

After the first early failures, proximal femoral epiphyseal replacement is becoming popular again. Prosthesis-to-bone load transfer is critical for two reasons: stress shielding is suspected of being responsible for a number of failures of early epiphyseal prostheses; stress concentration is probably responsible of the relevant number of early femoral neck fractures in resurfaced patients. The scope of this work was to experimentally investigate the load transfer of a commercial epiphyseal prosthesis (Birmingham Hip Replacement (BHR)) and an innovative prototype proximal epiphyseal replacement. To investigate bone surface strain, ten cadaveric femurs were instrumented with 15 triaxial strain gauges. In addition the cement layer of the prototype was instrumented with embedded gauges to estimate the strain in the adjacent trabecular bone. Six different loading configurations were investigated, with and without muscles. For the BHR prosthesis, significant stress shielding was observed on the posterior side of the head-neck region (the strain was halved); a pronounced stress concentration was observed on the anterior surface (up to five times in some specimens); BHR was quite sensitive to the different loading configurations. For the prototype, the largest stress shielding was observed in the neck region (lower than the BHR; alteration less than 20 per cent); some stress concentration was observed at the head region, close to the rim of the prosthesis (alteration less than 20 per cent); the different loading configurations had similar effects. Such large alterations with respect to the pre-operative conditions were found only in regions where the strain level was low. Conversely, alterations were moderate where the strain was higher. Thus, prosthesis-to-bone load transfer of both devices has been elucidated; the prototype preserved a stress distribution closer to the physiological condition.

Assessment of the biocompatibility of photosensitive polyimide for implantable medical device use.

Polyimides have been widely used for biosensor encapsulation and more recently as substrates for neural implants. They have excellent thermal stability, high chemical resistance, and can be prepared as thin, flexible films. Photosensitive polyimides present similar physical properties to polyimides, and have the advantage that they can be photo-lithographically patterned. However, to date little data on their biocompatibility has been reported. Two commercially available polyimides (PI) and one photo-sensitive polyimide (PSPI) were evaluated in vitro using the ISO 10993 standard on biocompatibility. The materials were Dupont Kapton foil HN, HD Microsystem PI2611, and Fujifilm Durimide 7020 (PSPI). PI2611 and Durimide 7020 were spin-coated on silicon wafers, cured at temperatures ranging from 150 to 450 degrees C, and sterilized by autoclave. All materials were evaluated using a scanning electron microscope pre- and postcell culture. Cell viability was determined by an MTS assay. Their mechanical properties and stability during cell culture as a function of time and environment were investigated by nanoindentation. The MTS results show that PSPI is noncytotoxic compared with the negative control of polyethylene and the conventional PIs tested. Fibroblast adhesion, morphology, and spreading were good and better on the PSPI substrate than on the PI2611. Schwann cell appearance was similar on each of the PIs and the PSPI tested. The results suggest that PSPIs may have potential use for biological microsystem and neuroprosthetic applications.

Bone formation in a carbonate-substituted hydroxyapatite implant is inhibited by zoledronate: the importance of bioresorption to osteoconduction.

Carbonate-substituted hydroxyapatite (CHA) is more osteoconductive and more resorbable than hydroxyapatite (HA), but the underlying mode of its action is unclear. We hypothesised that increased resorption of the ceramic by osteoclasts might subsequently upregulate osteoblasts by a coupling mechanism, and sought to test this in a large animal model. Defects were created in both the lateral femoral condyles of 12 adult sheep. Six were implanted with CHA granules bilaterally, and six with HA. Six of the animals in each group received the bisphosphonate zoledronate (0.05 mg/kg), which inhibits the function of osteoclasts, intra-operatively. After six weeks bony ingrowth was greater in the CHA implants than in HA, but not in the animals given zoledronate. Functional osteoclasts are necessary for the enhanced osteoconduction seen in CHA compared with HA.

Deposition of nano-hydroxyapatite particles utilising direct and transitional electrohydrodynamic processes.

Electrohydrodynamic spraying is a well established process used to deposit, coat, analyse and synthesise materials within the biomedical remit. Recently, electrohydrodynamic printing has been developed to afford structures for potential applications in the biomedical and medical engineering fields. Both of these processes rely on the formation of an electrically-induced jet, however the resulting products can be made strikingly different and offer potential in broader applications. Here we show how spraying and printing are linked by elucidating the ease of transition between the processes. Changes in the deposition distance can result in either spray (>10 mm) or print formation (<3 mm), with an overlap of the two in between this range. For the optimal printing distance of 0.5 mm, gradual changes in the applied voltage (0-4.5 kV) encounters transitional printing modes (dripping, micro-dripping, rapid micro-dripping, unstable and stable jetting) which can be utilised for patterning. The results indicate the robustness of the electrohydrodynamic route in the nano-materials processing arena, with emphasis on biomedical materials.

In vitro evaluation of nanosized carbonate-substituted hydroxyapatite and its polyhydroxyethylmethacrylate nanocomposite.

Nanometer scale carbonate-substituted hydroxyapatite (nanoCHA) particles were prepared and examined using transmission electron microscopy, which revealed their polycrystalline nature with a rod-like morphology (20-30 nm in width and 50-80 nm in length). In vitro cytotoxicity study showed that there was some evidence of lactate dehydrogenase (LDH) release when macrophages were in contact with high concentrations of nanoCHA particles. The levels of LDH release decreased significantly with a reduction in nanoCHA concentration. A similar trend was observed for the inflammatory cytokine TNF-alpha. nanoCHA particles with high carbonate content induced a high level of TNF-alpha release. Biological testing using a human osteoblast (HOB) cell model found that HOB cells were able to grow and proliferate on a nanoCHA deposited surface. Well organized actin fibers were observed for HOB cells in contact with nanoCHA particles with low carbonate content and the cell proliferation rate was higher on these particles in comparison with those of high carbonate nanoCHA particles. Therefore, low carbonate nanoCHA particles were incorporated into poly-(2-hydroxyethylmethacrylate) matrix to make a nanocomposite. It was found that the nanoCHA composite was hydrophilic and became rubber-like after hydration. Both 20 wt % and 40 wt % composites were able to induce the formation of bone-like apatite after immersion in simulated body fluid. A high bioactivity of the composite was obtained with high loading of the nanoCHA filler. These results demonstrate the potential of formulating nanocomposites for biomedical applications.

Influence of nanohydroxyapatite patterns deposited by electrohydrodynamic spraying on osteoblast response.

Electrohydrodynamic spraying has been used to produce patterns of line width up to 100 microm in size on glass discs, using nanohydroxyapatite (nHA). A human osteoblast (HOB)-like cell model was then used to study the interaction between the HOB cells and nHA patterns in vitro. Growth of the cells was significantly increased (p < 0.05) on the nHA surfaces. In addition, HOBs attached and spread well, secreting extracellular matrix. It was found that a confluent, aligned cell layer was achieved on nHA patterns by day 9. Immunofluorescent staining indicated that these cells showed elongated nuclei, enhanced adhesion (vinculin adhesion plaques) and a well-aligned cytoskeleton (actin stress fibres). This work suggests that this type of spraying may provide a route for the production of nanoscale features on implants for biomedical applications.

Less invasive stabilisation system plating for distal femoral fractures.

PURPOSE: To review the outcome of less invasive stabilisation system (LISS) plating for complex distal femoral fractures. METHODS: Records of 6 men and 11 women who underwent LISS plating for complex distal femoral fractures from September 2001 to August 2005 were reviewed. One patient who died 12 months after surgery due to a cardiac problem was excluded. The mean age of the remaining patients was 61 years and the mean follow-up period was 12 months. Four patients, 3 of whom had open fractures, had sustained high-energy trauma. According to the AO classification, 8 fractures were type 33A and 9 type 33C. RESULTS: The mean time to union was 17 weeks. Two patients with non-union underwent a second LISS plating and bone grafting, resulting in a satisfactory final outcome. Delayed radiographic union was observed in one patient, but clinically he was asymptomatic and mobile. The fracture finally united at 9 months. CONCLUSION: LISS plating is useful in treating complex distal femoral fractures, resulting in reduced blood loss and low infection rates, while achieving early mobility due to primary stability of the construct.

Results of total hip arthroplasty in Gaucher's disease patients.

There is controversy regarding the success of total hip arthroplasty (THA) in patients with Gaucher's disease. We present a retrospective study of nine total hip replacements in six patients (four primary THAs and five revisions). Four were female and two were male. All patients were of white ethnic origin. Five hips have required revision surgery for loosened implants (four once only and one twice). The average age at the time of primary THA was 35.3 years (13-54). The average duration between primary THA and first revision was 11.4 years (6-19). The duration between first and second revision in one hip was six years. The follow-up ranged between 2.5 years to 19 years. One patient developed superficial infection postoperatively which settled with wound debridement and antibiotics. Excessive peri-operative blood loss was noted in three patients.

Biomechanics of the Birmingham hip resurfacing arthroplasty.

The effects of the method of fixation and interface conditions on the biomechanics of the femoral component of the Birmingham hip resurfacing arthroplasty were examined using a highly detailed three-dimensional computer model of the hip. Stresses and strains in the proximal femur were compared for the natural femur and for the femur resurfaced with the Birmingham hip resurfacing. A comparison of cemented versus uncemented fixation showed no advantage of either with regard to bone loading. When the Birmingham hip resurfacing femoral component was fixed to bone, proximal femoral stresses and strains were non-physiological. Bone resorption was predicted in the inferomedial and superolateral bone within the Birmingham hip resurfacing shell. Resorption was limited to the superolateral region when the stem was not fixed. The increased bone strain observed adjacent to the distal stem should stimulate an increase in bone density at that location. The remodelling of bone seen during revision of failed Birmingham hip resurfacing implants appears to be consistent with the predictions of our finite element analysis.