Total knee arthroplasty with a rotating hinge knee with carbon-fibre-reinforced (CFR)-PEEK as an alternative bushing material with enhanced creep, wear and fatigue behaviour has been clinically established [1-4]. The objective of our study was to compare results from in vitro biotribological characterisation to ex vivo findings on a retrievals. A modified in vitro wear simulation based on ISO 14243-1 was performed for 5 million cycles on rotating hinge knee (RHK) designs (EnduRo®) out of cobalt-chromium and ZrN-multilayer ceramic coating. The rotational & flexion axles-bushings and the flanges are made of CFR-PEEK with 30% polyacrylonitrile fibre content. Analysis of 12 retrieved EnduRo® RHK systems in cobalt-chromium and ZrN-multilayer in regard to loosening torques, microscopic surface analysis, distinction between different wear modes and classification with a modified HOOD-score has been performed. For the RHK design with the polyethylene gliding surface and bushings and flanges made out of CFR-PEEK, a cumulative volumetric wear was measured to be 12.9±3.95 mm. 3. in articulation to cobalt-chromium and 1.3±0.21 mm. 3. to ZrN-multilayer coating - a significant 9.9-fold decrease (p=0.0072). For the CFR-PEEK flexion bushing and flanges the volumetric wear rates were 2.3±0.48 mm. 3. /million cycles (cobalt-chromium) and 0.21±0.02 mm. 3. /million cycles (ZrN-multilayer) (p=0.0016). The 5 million cycles of in vitro wear testing reflect a mean in vivo service life of 2.9 years, which is in accordance to the time in vivo of 12–60 months of the retrieved RHK components [5]. The main wear modes were comparable between retrievals and in vitro specimens, whereby the size of affected area on the retrieved components showed a higher variation. For the EnduRo® RHK design the findings on retrieved implants demonstrate the high suitability of CFR-PEEK as a biomaterial for highly loaded bearings, such as RHK bushings and flanges in articulation to cobalt-chromium and to a ZrN-multilayer coating

Introduction. Trabecular Titanium is a biomaterial characterized by a regular three-dimensional hexagonal cell structure imitating trabecular bone morphology. Components are built via Electron Beam Melting technology in aone- step additive manufacturing process. This biomaterial combines the proven mechanical properties of Titanium with the elastic modulus provided by its cellular solid structure (Regis 2015 MRS Bulletin). Several in vitro studies reported promising outcomes on its osteoinductive and osteoconductive properties: Trabecular Titanium showed to significantly affect osteoblast attachment and proliferation while inhibiting osteoclastogenesis (Gastaldi 2010 J Biomed Mater Res A, Sollazzo 2011 ISRN Mater Sci); human adipose stem cells were able to adhere, proliferate and differentiate into an osteoblast-like phenotype in absence of osteogenic factors (Benazzo 2014 J Biomed Mater Res A). Furthermore, in vivo histological and histomorphometric analysis in a sheep model indicated that it provided bone in-growth in cancellous (+68%) and cortical bone (+87%) (Devine 2012 JBJS). A multicentre prospective study was performed to assess mid-term outcomes of acetabular cups in Trabecular Titanium after Total Hip Arthroplasty (THA). Methods. 89 patients (91 hips) underwent primary cementless THA. There were 46 (52%) men and 43 (48%) women, with a median (IQR) age and BMI of 67 (57–70) years and 26 (24–29) kg/m2, respectively. Diagnosis was mostly primary osteoarthritis in 80 (88%) cases. Radiographic and clinical evaluations (Harris Hip Score [HHS], SF-36) were performed preoperatively and at 7 days, 3, 6, 12, 24 and 60 months. Bone Mineral Density (BMD) was determined by dual-emission X-ray absorptiometry (DEXA) according to DeLee &Charnley 3 Regions of Interest (ROI) postoperatively at the same time-points using as baseline the measureat 1 week. Statistical analysis was carried out using Wilcoxon test. Results. Median (IQR) HHS and SF-36 improved significantly from 48 (39–61) and 49 (37–62) preoperatively to 99 (96–100) and 76 (60–85) at 60 mo. (p≤0.0001). Radiographic analysis showed evident signs of bone remodelling and biological fixation, with presence of superolateral and inferomedial bone buttress, and radial trabeculae in ROI I/II. All cups resulted radiographically stable without any radiolucent lines. The macro-porous structure of this biomaterial generates a high coefficient of friction (Marin 2012 Hip Int), promoting a firm mechanical interlocking at the implant-bone interface which could be already observed in the operating room. BMD initially declined from baseline at 7 days to 6 months. Then, BMD slightly increased or stabilized in all ROIs up to 24 months, while showing evidence of partial decline over time with increasing patient' age at 60 months, although without any clinical significance in terms of patients health status or implant stability. Statistical significant correlations in terms of bone remodeling were observed between groups of patients on the basis of gender and age (p≤0.05). No revision or implant failure was reported. Conclusions. All patients reported significant improvements in quality of life, pain relief and functional recovery. Radiographic evaluation confirmed good implant stability at 60 months. These outcomes corroborate the evidence reported on these cups by orthopaedic registries and literature (Perticarini 2015 BMC Musculoskelet Disord; Bistolfi 2014 Min Ortop)

Oxide ceramics, such as alumina and zirconia have been used extensively in arthroplasty bearings to address bearing wear and mitigate its delayed, undesirable consequences. In contrast to oxide ceramics that are well-known to orthopaedic surgeons, silicon nitride (Si. 3. N. 4. ) is a non-oxide ceramic that has been investigated extensively in very demanding industrial applications, such as precision bearings, cutting tools, turbo-machinery, and electronics. For the past four years, Si. 3. N. 4. has also been used as a biomaterial in the human body; specifically in spinal fusion surgery. As a implantable biomaterial, Si. 3. N. 4. has unique properties, such as high strength and fracture toughness, inherent chemical and phase stability, low wear, proven biocompatibility, excellent radiographic imaging, antibacterial advantages, and superior osteointegration. This property combination has proven beneficial and desirable in orthopaedic implants made for spinal fusion, spinal disc reconstruction, hip and knee arthroplasty, and other total joints (Fig. 1). The physical properties, shapes, sizes and surface features of Si. 3. N. 4. can be engineered for each application – ranging from dense, finely polished articulation components, to highly porous scaffolds that promote osteointegration. Both porous and polished surfaces can be incorporated in the same implant, opening a number of opportunities for arthroplasty implant design. Crack propagation modes for in situ toughened Si. 3. N. 4. differ favorably from those of conventional ceramics, rendering Si. 3. N. 4. extremely resistant to catastrophic failure in vivo (Fig. 2). Most significantly, our recent work has shown that Si. 3. N. 4. is resistant to bacterial biofilm formation, colonization and growth, when compared to medical-grade PEEK and titanium. These anti-infective characteristics are particularly valuable for in vivo implantation. We will present the unique properties and characteristics of Si. 3. N. 4. , and compare these to other ceramic and non-ceramic biomaterials. Si. 3. N. 4. was once used only in industrial applications, but early data show that this novel biomaterial is positively impacting orthopaedic care and will continue to do so into the future

Porous surfaces on orthopaedic implants have been shown to promote tissue ingrowth. This study evaluated biological fixation of novel additively manufactured porous implants with and without hydroxyapatite coatings in a canine transcortical model.

Laser rapid manufacturing (LRM) Ti6Al4V cylindrical implants were built with a random interconnected architecture mimicking cancellous bone (5.2 mm diameter, 10mm length, 50–60% porous, mean pore size 450μm). Three groups were investigated in this study: as-built with no coating (LRM), as-built coated with solution precipitated hydroxyapatite (LRM-PA), and as-built coated with a plasma sprayed hydroxyapatite (LRM-PSHA). Implants were press-fit into a 5mm unicortical, perpendicular drill hole in the femoral diaphysis of the left and right femurs in 12 canines. Right femora were harvested for histology (SEM, bone ingrowth into implant within cortical region) and left femora for mechanical push-out testing (shear strength of bone-implant interface) at 4 and 12 weeks (N=6, un-paired Student's t-test, p=0.05).

For mean bone ingrowth, there was no significant difference between groups at 4 weeks (LRM, LRM-PA, LRM-PSHA: 41.5+8.6%, 51+5.5% and 53.2+11%, respectively) or 12 weeks (LRM, LRM-PA, LRM-PSHA: 64.4+2.8%, 59.9+7.6%, 64.9+6.4%, respectively). LRM and LRM-PA implants had more bone ingrowth at 12 weeks than 4 weeks (p < 0 .05). Mean shear strength of all implants at 12 weeks (LRM, LRM-PA, LRM-PSHA: 39.9+3.6MPa, 33.7+4.6MPa, 36+4.1MPa respectively) were greater than at 4 weeks (LRM, LRM-PA, LRM-PSHA: 21.6+2.8MPa, 20.7+1.1MPa, 20.2+2.5MPa respectively) (p < 0 .05). No significant difference was observed between all groups at 4 or 12 weeks.

Overall, this canine study confirmed the suitability of this novel additive manufacturing porous material for biological fixation by bone ingrowth. All implants exhibited high bone ingrowth and mechanical shear strength in this canine model. No difference was observed between uncoated and hydroxyapatite coated implants.

Stem geometry is known to influence the outcome in THA; however it is unknown whether the material properties, stiffness in particular can influence the stem stability and outcome. The aim of this study was to measure the influence of stem material properties on micromotion and migration using Roentgen Stereophotogrammetric Analysis (RSA) system.

41 patients were implanted with a collarless polished tapered (CPT) femoral stem (Zimmer, Warsaw, Indiana), which was made of either cobalt-chromium (CoCr) (n=21) or stainless steel (n=20). RSA was used to measure dynamically inducible micromotion (DIMM: difference in stem position in going from double-leg stance (DLS) to single leg stance (SLS)), prosthesis bending (difference in the head-tip distance when going from DLS to SLS), and mean migration of the head, tip and the cement restrictor. DIMM and bending were measured at 3 months, migration at 6, 12 and 24 months. All analyses were carried out using SPSS for windows (v.15.0.0, Chicago. IL, USA). Results were reported as mean ± 95% confidence interval (CI) and regarded as significant when p < 0.05.

Preliminary analysis showed that total head DIMM was significantly (p = 0.02) greater for CoCr (0.97mm ± 0.6mm) than stainless steel (0.27mm ± 0.6mm). The mean stem bending for CoCr was 0.08mm (± 0.06mm) and for stainless steel 0.15mm (± 0.06mm) (p =0.77). Both implants heads migrated posteriorly, medially and distally. The mean subsidence for the cobalt-chromium and stainless steel stems was 1.02mm (± 0.19mm) (p < 0.001) and 1.12mm (± 0.34mm) (p=0.001) (p= 0.07) at 24 months.

It was interesting to note that the dynamically induced micromotion was greater for the stiffer stem, however there were no differences in terms of overall migration, indicating that survival (in terms of loosening) should be the similar for both steel and CoCr versions of this implant.

Purpose:

To examine the performance of a novel blood plasma-based bone putty for augmenting the treatment of open tibia fractures. The putty was manufactured from pooled blood plasma and contains a concentration of both plasma and platelet-derived regenerative factors. Based on clinical reports of the use of autologous platelet-rich plasma to treat injuries, we hypothesized that the putty would accelerate healing of fractures and surrounding soft tissues.

Aim. Bone and implant-associated infections caused by microorganisms that grow in biofilm are difficult to treat because of persistence and recurrence. Systemic administration of antibiotics is often inefficient because the poor vascularization of the site of infection. This issue has led to the development of biomaterials capable to locally deliver high doses of therapeutic agents to the injured bone with minimal systemic effects. In this context, calcium sulphate/hydroxyapatite (CS/HA) bone graft substitutes are widely used being safe, osteoconductive and resorbable biomaterials that can be easily enriched with consistent amounts of antibiotics. In this in vitro study, the capability of the eluted antibiotics to select the tested bacterial strains for antibiotic resistance was evaluated to confirm the safe use of the product. Method. S. aureus, S. epidermidis and P. aeruginosa isolated in our Institute from bone and joint infection with different resistance phenotypes were used. 6 × 2.5 mm CS/HA discs were generated by pouring the antibiotic loaded formulations in a mold and were used as a modified disk diffusion test. The resistance selection was evaluated by subculturing cells growing on the edge of the zone of inhibition (ZOI) for seven days. Minimum inhibitory concentrations (MICs) of gentamicin and vancomycin were determined by broth microdilution method before and after the selection of resistance assay. In addition, MICs were assessed after seven day passage on antibiotic free agar plates to evaluate if eventual decrease of antibiotic susceptibility was stable or only transient. Results. Commonly, no adaptation in presence of both CS/HA formulations was observed by analysing ZOI on agar medium. The kinetic of decrease of the ZOI was similar between the strains, with the exception of gentamicin resistant staphylococci in presence of gentamicin loaded CS/HA, which was faster with respect to the susceptible strains. Conclusions. The present study shows that elution of gentamicin and vancomycin from CS/HA bone graft substitutes did not induce a decrease in susceptibility to these antibiotics in an in vitro setting, suggesting the safe use of the product

Restoration a joint's articular surface following degenerative or traumatic pathology to the osteochondral unit pose a significant challenge. Recent advances have shown the utility of collagen-based scaffolds in the regeneration of osteochondral tissue. To provide these collagen scaffolds with the appropriate superstructure novel techniques in 3D printing have been investigated. This study investigates the use of polyɛ-caprolactone (PCL) collagen scaffolds in a porcine cadaveric model to establish the stability of the biomaterial once implanted. This study was performed in a porcine cadaveric knee model. 8mm defects were created in the medial femoral trochlea and repaired with a PCL collagen scaffold. Scaffolds were secured by one of three designs; Press Fit (PF), Press Fit with Rings (PFR), Press Fit with Fibrin Glue (PFFG). Mobilisation was simulated by mounting the pig legs on a continuous passive motion (CPM) machine for either 50 or 500 cycles. Biomechanical tensile testing was performed to examine the force required to displace the scaffold. 18 legs were used (6 PF, 6 PFR, 6 PFFG). Fixation remained intact in 17 of the cohort (94%). None of the PF or PFFG scaffolds displaced after CPM cycling. Mean peak forces required to displace the scaffold were highest in the PFFG group (3.173 Newtons, Standard deviation = 1.392N). The lowest peak forces were observed in the PFR group (0.871N, SD = 0.412N), while mean peak force observed in the PF group was 2.436N (SD = 0.768). There was a significant difference between PFFG and PFR (p = 0.005). There was no statistical significance in the relationship between the other groups. PCL reinforcement of collagen scaffolds provide an innovative solution for improving stiffness of the construct, allowing easier handling for the surgeon. Increasing the stiffness of the scaffold also allows press fit solutions for reliable fixation. Press fit PCL collagen scaffolds with and without fibrin glue provide dependable stability. Tensile testing provides an objective analysis of scaffold fixation. Further investigation of PCL collagen scaffolds in a live animal model to establish quality of osteochondral tissue regeneration are required

INTRODUCTION. Stimulation of angiogenesis via the delivery of growth factors (GFs) like vascular endothelial growth factor (VEGF) is a promising strategy for the treatment of avascular necrosis (AVN). Tyraminated poly-vinyl-alcohol hydrogels (PVA-Tyr), which have the ability to covalently incorporate GFs, were proposed as a platform for the controlled delivery of therapeutic levels VEGF to the necrotic areas[1]. Nevertheless, PVA hydrophilicity and bioinertness limits its integration with the host tissues. The aim of this study was to investigated the effectiveness of incorporating gelatin, an FDA-approved, non-immunogeneic biomaterial with biological recognition sites, as a strategy to facilitate blood vessels invasion of PVA-Tyr hydrogels and to restore the vascular supply to necrotic tissues. METHODS. Progressively higher gelatin concentrations (0.01–5wt%) were incorporated in the PVA-Tyr network. Hydrogel physico-chemical properties and endothelial cell attachment were evaluated. Afterwards, the capability of the released VEGF and gelatin to promote vascularization was evaluated via chorioallantoic membrane (CAM) assay. VEGF-loaded PVA-Tyr hydrogels with or without gelatin (n=7) were implanted in a subcutaneous mouse model for 3 weeks. Vascularization (CD31+ cells) and cell infiltration (H&E) were evaluated. Finally, AVN was induced in 6 weeks old male piglets as previously described [2]. A transphyseal hole (3mm) was drilled and PVA-Tyr hydrogels with 1% gelatin were delivered in the defects. Piglets were euthanized after 4 weeks and microCT analysis was performed. RESULTS. The incorporation of 1% gelatin significantly enhanced cell attachment without compromising hydrogels physical properties, degradation time, VEGF retention and release. Thus, this gelatin concentration was selected for further analysis. Additionally, the covalent incorporation of VEGF or gelatin to the PVA-Tyr network does not hamper their bioactivity, as both still promoted neo-angiogenesis in a CAM assay. Following subcutaneous implantation, the presence of gelatin did not increase the cellular infiltration in the PVA-Tyr hydrogels. Nevertheless, higher vascular infiltration was observed in the groups where either gelatin or VEGF were included. Additionally, preliminary microCT results indicated that the delivery of PVA-Tyr hydrogels containing 1% gelatin in an AVN model was effective in preventing the necrosis-associated resorption of the bone. DISCUSSION & CONCLUSIONS. These results indicated that the presence of either gelatin or VEGF was sufficient to promote vascular infiltration. Additionally, preliminary results suggested the suitability of the developed hydrogels to treat AVN

Aim. Antibiotic-loaded biomaterials are often used in dead space management after excision of infected bone. This study assessed the chronological progression of new bone formation in infected defects, filled only with an absorbable, osteoconductive bone void filler with Gentamicin (1). Method. 163 patients were treated for osteomyelitis or infected fractures with a single-stage excision, implantation of antibiotic carrier, stabilisation and wound closure. All had Cierny & Mader Type III (n=128) or Type IV (n=35) infection. No bone grafting was performed in any patient. Patients were followed up for a minimum of 12 months (mean 21.4 months; 12–56). Bone void filling was assessed on serial digitised, standardized radiographs taken immediately after surgery, at 6 weeks, 3, 6 and 12 months and then yearly. Data on defect size, location, degree of void filling, quality of the bone-biomaterial interface and material leakage were collected. Bone formation was calculated at final follow-up, as a percentage of initial defect volume, by determining the bone area on AP and lateral radiographs to the nearest 5%. Results. 138 patients had adequate radiographs for assessment. Infection was eradicated in 95.7%. 2.5% of patients suffered a fracture during follow-up. Overall, bone formation was good (mean 73.8% defect filling), with one quarter of patients having complete defect filling and 87% having more than 50% of the defect healed. Bone formed better in metaphyseal defects compared to diaphyseal defects (mean 79% filling vs 66%; p<0.02). Good interdigitation of the biomaterial with the host bone, seen on the initial radiograph, was associated with more bone formation (77% vs 69%; p=0.021). Leakage of the biomaterial out of the defect reduced mean bone formation from 77% to 62% (p=0.006). 38 cases had radiographs more than 2 years after implantation. In 24 (63.2%), bone formation continued to increase after the first year radiograph. Conclusion. This biomaterial was effective in allowing significant amounts of bone to form in the defect. This removed the need for bone grafting in this series, with a low risk of fracture or recurrent infection. However, bone formation is affected by the site of the lesion and the adequacy of filling at surgery. It is important to achieve good contact between the bone surface and the biomaterial at operation. Bone formation is slow and progresses for at least 2 years after implantation, in two thirds of patients

Aim. The use of medical devices has grown significantly over the last decades, and has become a major part of modern medicine and our daily life. Infection of implanted medical devices (biomaterials), like titanium orthopaedic implants, can have disastrous consequences, including removal of the device. For still not well understood reasons, the presence of a foreign body strongly increases susceptibility to infection. These so-called biomaterial-associated infections (BAI) are mainly caused by Staphylococcus aureus and Staphylococcus epidermidis. Formation of biofilms on the biomaterial surface is generally considered the main reason for these persistent infections, although bacteria may also enter the surrounding tissue and become internalized within host cells. To prevent biofilm formation using a non-antibiotic based strategy, we aimed to develop a novel permanently fixed antimicrobial coating for titanium devices based on stable immobilized quaternary ammonium compounds (QACs). Method. Medical grade titanium implants (10×4×1 mm) were dip-coated in a solution of 10% (w/v) hyperbranched polymer, subsequently in a solution of 30% (w/v) polyethyleneimine and 10 mM sodium iodide, using a dip-coater, followed by a washing step for 10 min in ethanol. The QAC-coating was characterized using water contact angle measurements, scanning electron microscopy, FTIR, AFM and XPS. The antimicrobial activity of the coating was evaluated against S. aureus strain JAR060131 and S. epidermidis strain ATCC 12228 using the JIS Z 2801:2000 surface microbicidal assay. Lastly, we assessed the in vivo antimicrobial activity in a mouse subcutaneous implant infection model with S. aureus administered locally on the QAC-coated implants prior to implantation to mimic contamination during surgery. Results. Detailed material characterization of the titanium samples showed the presence of a homogenous and stable coating layer at the titanium surface. Moreover, the coating successfully killed S. aureus and S. epidermidis in vitro. The QAC-coating strongly reduced S. aureus colonization of the implant surface as well as of the surrounding tissue, with no apparent macroscopic signs of toxicity or inflammation in the peri-implant tissue at 1 and 4 days after implantation. Conclusions. An antimicrobial coating with stable quaternary ammonium compounds on titanium has been developed which holds promise to prevent BAI. Non-antibiotic-based antimicrobial coatings have great significance in guiding the design of novel antimicrobial coatings in the present, post-antibiotic era

Aim. Chronic bone infections and infected fractures are often treated with excision of the dead bone and implantation of biomaterials which elute antibiotics. Gentamicin has been a preferred drug for local delivery, but this could induce renal dysfunction due to systemic toxicity. This is a particular concern in patients with pre-existing chronic renal disease treated with new antibiotic carriers which achieve very high peak levels of gentamicin in the first few days after surgery. Method. 163 patients (109 males; average age 51.6 years) with Cierny-Mader Type 3 or 4 chronic osteomyelitis had a single-stage operation with excision of the dead bone, filling of the osseous defect with a calcium sulphate-hydroxyapatite carrier, containing gentamicin and immediate soft tissue closure. 2. No patient was given systemic gentamicin or other renal toxic antibiotics. Mean carrier volume was 10.9mls (range 1–30mls) and mean gentamicin dosing was 190.75mg (maximum 525mg). Seven patients had pre-existing renal disease (4 diabetic nephropathy, 1 nephrotic syndrome, 1 renal transplant and 1 previous acute kidney injury). Serum creatinine levels were collected pre-operatively and during the first seven days post-operatively. Glomerular filtration rate (GFR) was calculated using the CKD-epi creatinine equation. Renal function was defined using the Chronic Kidney Disease (CKD) Staging system. Results. 155 cases had adequate data to allow calculation of pre- and post-operative GFR. Pre-operative CKD staging demonstrated 118 Class I (normal renal function), 30 Class II, 3 Class IIIa, 3 Class IIIb, and 1 Class V disease. Mean pre-operative GFR (99.7ml/min/1.73m. 2. , SD 21.0) was no different to post-operative GFR (103.2ml/min/1.73m. 2. , SD 21.3), p= 0.0861. Four cases had a >10% decline in GFR below normal, with only one case dropping a CKD stage, from I (normal) to II (mildly decreased). Only 1/7 cases with pre-existing renal disease had a GFR drop of >10% (from 11ml/min/1.73m. 2. to 8ml/min/1.73m. 2. ). 70/155 (45.2%) had a temporary GFR drop post-operatively, with the biggest drop occurring a mean 3.06 days following surgery (SD 2.1). No patient had clinical signs of new acute renal impairment post-operatively. Conclusions. Renal function is not significantly affected by local implantation of gentamicin up to 525mg. The presence of pre-existing renal disease is not a contraindication to local gentamicin therapy

Introduction. The complex cellular mechanisms of the aseptic loosening of total joint arthroplasties still remain not completely understood in detail. Especially the role of adherent endotoxins in this process remains unclear, as lipopolysaccharides (LPS) are known to be very potent modulators of the cell response on wear particle debris. Contributing factors on the LPS affinity of used orthopedic biomaterials as their surface roughness have to be investigated. The aim of this study was to evaluate the affinity of LPS on the surface roughness of different biomaterials in vitro. The hypothesis of the study was that rough surfaces bind more LPS than smooth surfaces. Materials and methods. Cubes with a side length from ultra-high-molecular-weight-polyethylene (UHMWPE), crosslinked polytethylene (XPE), carbon fibre reinforced poly-ether-ether-ketone (CFR-PEEK), titanium, titanium alloy, Polymethyl methacrylate (PMMA), implant steel (CoCr) and instrument steel (BC) were produced (figure 1). Cubes of each material have been produced with a rough and a smooth surface. Before the testings, all cubes and used materials were treated with E-Toxa-Clean(®) to eliminate pre-existing LPS on the used surfaces. The cubes were then fixed on the cap of a glass that was filled with a LPS solution with a concentration of 5 IE/ml. After 30 minutes the cube was removed and the LPS concentration in the supernatant was measured. The endotoxin content of each sample was evaluated by a Limulus Amoebocyte Lysate (LAL) - Test (Lonza, Verviers, Belgium). The detection level of endotoxin was set at < 0.005 EU/ml diluted 1/10. Results. All tested rough biomaterials showed a higher affinity to LPS compared to the smooth surfaces. Conclusion. The initial hypothesis could be confirmed. The results prove that rough and therefore larger surfaces bind more LPS than smooth surfaces. A rough surfaces correlates with a larger total surface of the used biomaterial. In this context protheses should be avoided that show a large rough surface, as these endoprostheses might bind more LPS and trigger an enhanced inflammatory reaction that results in an early aseptic loosening

Introduction. The treatment of chronic bone infection often involves excision of dead bone and implantation of biomaterials which elute antibiotics. Gentamicin is a preferred drug for local delivery, but its systemic use carries a well-established risk of nephrotoxicity. We aim to establish the risk of renal injury with local delivery in a ceramic carrier. Materials and Methods. 163 consecutive patients with Cierny-Mader Type 3 or 4 chronic osteomyelitis were treated with a single-stage operation which included filling of the osseous defect with a calcium sulphate-hydroxyapatite carrier containing gentamicin. The mean carrier volume used was 10.9mls, leading to a mean implanted gentamicin dose of 191.3mg (maximum 525mg). Serum creatinine levels were collected pre-operatively and during the first seven days post-operatively. Renal impairment was graded using the Chronic Kidney Disease (CKD) Staging system, and AKI was assessed using the RIFLE criteria. Results. 155 cases had adequate data to allow calculation of pre- and post-operative GFR. 7 patients had pre-existing renal disease. 70 patients (45.2%) had a temporary eGFR drop post-operatively, with the greatest decrease occurring a mean 3.06 days following surgery. Twenty cases had a >10% decline in eGFR, but 12 resolved within 7 days. 7 patients transiently fell into the “Risk” category according to RIFLE criteria, but no patient had a change consistent with “Injury”, “Failure” or “Loss” of renal function and none had clinical signs of new acute renal impairment post-operatively. Conclusions. The implantation of up to 525mg of gentamicin contained within Cerament G, as part of the surgical treatment of osteomyelitis, is safe and carries minimal risk of significant acute kidney injury. A small, transient increase in serum creatinine may be observed in the early post-operative period, and attention should be paid to limit patients exposure to other nephrotoxic agents. The majority of patients will return to their baseline renal function within 7 days following the operation. The presence of pre-existing renal disease is not a contraindication to local gentamicin therapy

Introduction. Titanium and its alloys are attractive biomaterials attributable to their desirable corrosion, mechanical, biocompatibility and osseointegration properties. Ti6Al4V alloy in particular remains a prominent biomaterial used in Total Hip Arthroplasty (THA) today. This is partly due to biocompatibility and stress shielding issues with CoCrMo alloys, resulting in its increasing side-lining from the THA construct. For several decades now, research efforts have been dedicated to understanding wear, corrosion and surface degradation processes in implant materials. Only recently have researchers shown interest in understanding the subsurface implications of fretting and the role it plays on implant fracture. The purpose of this study was to utilise advanced microscopy and spectroscopy techniques to characterise fretting-induced subsurface transformations in Ti6Al4V. This makes mapping specific regions that are most prone to wear and fatigue failures at the modular taper interface of THA probable. Thus, informing a proactive approach to component design and material selection. Method. A ball-on-flat configuration was utilised in this study to achieve a Hertzian point contact for a CoCrMo – Ti6Al4V material combination. Four fretting displacement amplitudes were assessed: ±10, ±25, ±50 and ±150 µm. An initial contact pressure of 1 GPa was used for all fretting tests in this study and each fretting test lasted 6000 cycles at a frequency of 1 Hz. The simulated physiological solution consisted of Foetal Bovine Serum (FBS) diluted to 25% with Phosphate Buffered Saline (PBS) and 0.03% Sodium Azide (SA) balance. The temperature was kept at ∼37°C. Subsurface transformations in the Ti6Al4V alloy was characterised using the Transmission Electron Microscopy (TEM) to obtain high resolution micrographs. The samples were prepared using a FIB-SEM. Bright-field, dark-field and selected area electron diffraction (SAED) patterns were all captured using a scanning TEM (STEM) and Energy Dispersed X-Ray spectroscopy (EDX) mapping was carried out. Results. At both ±10 and ±25 µm displacement, a stick fretting regime was realised. Subsurface transformation in the Ti6Al4V alloy was characterised as strain-induced orientation. At ±50 µm, a mixed fretting regime was realised, TEM and SAED micrographs as well as EDX spectroscopy identified complex but distinctive structures at the surface and subsurface of the Ti6Al4V alloy. This included a CoCrMo-rich fine particulate, mechanically mixed structure, an amorphous-transformed Ti6Al4V structure and a highly refined nano-crystalline Ti6Al4V structure. At ±150 µm, a full gross slip regime was realised and Ti6Al4V alloy was characterised mainly by subsurface cracks, formation and refinement of nano-crystalline structures. Conclusion. The degree of subsurface recrystallization within Ti6Al4V alloy was observed to be energy dependent. However, the manifestation of the dissipated energy was dependent on the contact condition. The interwoven relationship between energy dissipation, contact condition and mechanisms of clinical failure in Ti6Al4V was consolidated into a map (Figure 1). The map is intended to provide users with an indication of the failure modes to expect for an implant material subjected to specific tribocorrosion conditions. For any figures or tables, please contact the authors directly

Introduction. The osteogenic capability of any biomaterial is governed by a number of critical surface properties such as surface energy, surface potential, and topography. Prior work suggested that the Si-Y-O-N phase(s) present in the form of a thin (<150 nm), interrupted film at the surface of an annealed silicon nitride bioceramic may be responsible for an observed upregulation of osteoblastic activity due to passive surface properties and dissolution of chemical species. In this study high- resolution analytical electron microscopy was utilized to identify the Si-Y-O-N phase present on the annealed silicon nitride surface, and dissolution studies were employed to elucidate mechanisms of the material's favorable cell interactions. Materials and Methods. Si. 3. N. 4. discs (12.7 mm diameter × 1 mm thick) containing Y. 2. O. 3. and Al. 2. O. 3. sintering aids were processed using conventional techniques and subsequently subjected to annealing in a nitrogen atmosphere. Pre-cultured SaOS-2 osteosarcoma cells at a concentration of 5 × 10. 5. cells/ml were seeded onto sterile polished nitrogen-annealed Si. 3. N. 4. discs in an osteogenic medium consisting of DMEM supplemented with about 50 µg/mL ascorbic acid, 10 mM β-glycerol phosphate, 100 mM hydrocortisone, and 10% fetal bovine calf serum. The samples were incubated for up to 7 days at 37°C with two medium replenishments. Transmission electron microscopy (TEM) images were acquired from focused ion beam (FIB)-prepared samples using a Hitachi HF-3300 TEM (300 kV). Scanning transmission electron microscopy (STEM) images were recorded using a Nion UltraSTEM 100 (60 kV). STEM high-angle annular dark-field (HAADF) imaging and energy dispersive X-ray spectroscopy (EDS) analyses were performed on a JEOL JEM2200FS (200 kV) equipped with a third-order CEOS aberration corrector and a Bruker XFlash silicon drift detector. Results. A cross-section of the of the Si. 3. N. 4. /extracellular polymer (ECP) interface is illustrated in Fig. 1(a)∼(b) as a high- angle annular dark field (HAADF) STEM image (a) with and EDS map overlay (b) highlighting locations of Ca, Y, and Si. The underlying Si. 3. N. 4. microstructure is covered by a yttrium-rich intergranular phase (IGP) film. Deposition of cell-derived hydroxyapatite (HAp) occurred directly onto this IGP film. In Fig. 2, a bright field TEM image (electron diffraction pattern inset) shows the interface between the partially-crystalline HAp and the Y-Si-O-N phase, identified as monoclinic yttrium disilicate (i.e., m-Y. 2. Si. 2. O. 7. ) with a 2 atomic% N impurity, at teh atomic scale. Although rapid electron damage of the mineralized ECP was observed, EDS analyses suggested a Ca/P ratio of ∼1.43, along with the incorporation of Si. Conclusions. The osteogenic Si-Y-O-N phase was successfully identified as a minority concentration of Si. 3. N. 4. dissolved into a m-Y. 2. Si. 2. O. 7. matrix. Evidence of the release of (SiO. 4. ). 4−. tetrahedra from this phase into the local biological microenvironment and their incorporation into the cell-derived HAp layer was also observed. Identification of this phase paves the way for ongoing work to understand and optimize this novel biomaterial. For any figures or tables, please contact the authors directly

Introduction. Periprosthetic infections are leading causes of revision surgery resulting in significant increased patient comorbidities and costs. Considerable research has targeted development of biomaterials that may eliminate implant-related infections. 1. This in vitro study was developed to compare biofilm formation on three materials used in spinal fusion surgery – silicon nitride, PEEK, and titanium – using one gram-positive and one gram-negative bacterial species. Materials and Methods. Several surface treated silicon nitride (Si. 3. N. 4. , MC2. ®. , Amedica Corporation, Salt Lake City, UT), poly-ether-ether-ketone (PEEK, ASTM D6262), and medical grade titanium (Ti6Al4V, ASTM F136) discs Ø12.7 × 1mm were prepared or acquired for use in this well-plate study. Each group of discs (n=3) were ultrasonically cleaned, UV-sterilized, inoculated with 10. 5. Staphylococcus epidermidis (ATCC. ®. 25922™) or Escherichia coli (ATCC. ®. 14990™) and placed in a culture medium of phosphate buffered saline (PBS) containing 7% glucose and 10% human plasma on a shaking incubator at 37°C and 120 rpm for 24 or 48 hrs. Coupons were retrieved, rinsed in PBS to remove planktonic bacteria, placed in a centrifuge with fresh PBS, and vortexed. The bacterial solutions were serially diluted, plated, and incubated at 37°C for 24 to 48 hrs. Colony forming units (CFU/mm. 2. ) were counted using applicable dilution factors and surface areas. A two-tailed, heteroscedastic Student's t-test (95% confidence) was used to determine statistical significance. Results. Biofilm adhesion results are provided in Figures 1 and 2 for S. epi. and E. coli, respectively. For S. epi. at 24 hrs, biofilm growth on PEEK was about three orders of magnitude greater than on Ti6Al4V or any Si. 3. N. 4. material (all p<0.005). Ti6Al4V also had more bacteria than the Si. 3. N. 4. samples, but was only significant for as-fired and nitrogen-annealed treatments. Similar trends and significance for S. epi. were observed at 48 hrs. For E. coli, biofilm formation on PEEK was significantly greater than all other materials at both 24 and 48 hrs. Bacterial growth on Ti6Al4V was also statistically greater than all Si. 3. N. 4. conditions, with the possible exception of nitrogen-annealed Si. 3. N. 4. By 48 hrs, PEEK remained 2 orders of magnitude above Ti6Al4V, and 2.5–3 orders of magnitude greater than the Si. 3. N. 4. conditions. Ti6Al4V was also significantly greater than all of the Si. 3. N. 4. treatments at 48 hrs. Discussion. Si. 3. N. 4. , PEEK, and Ti6Al4V surfaces demonstrated significant differences in bacterial adhesion and proliferation for both gram-positive S. epi. and gram-negative E. coli, particularly at 48 hrs post-inoculation. The various Si. 3. N. 4. samples showed the most favorable bacterial resistance for both species tested. The exact mechanism of the bacteriostatic behavior of Si. 3. N. 4. is still under investigation; but it may result from chemical interaction with the material's surface to form peroxynitrite (a powerful oxidative agent). 2. Conclusion. Identifying biomaterial surfaces that resist biofilm adhesion is an important emerging strategy in addressing implant-related infections. Si. 3. N. 4. is a new biomaterial with the apparent potential to suppress biofilm formation

Millions of medical devices made of synthetic or modified natural materials all trigger a similar reaction—the foreign body reaction. Biocompatibility, for materials that pass routine cytoxicity assays, is largely associated with a mild foreign body reaction. I.e. a thin, avacular, collagenous, non-adherent foreign body capsule. The implant is incorporated into a dead-zone of acellular scar. The contemporary tissue engineering paradigm would suggest that synthetic polymers and scaffolds lacking cellular, biomolecule or biomimetic elements will give this same fibrotic, avascular healing reaction. In this talk, a synthetic biomaterial will be described that readily integrates into tissue and may stimulate spontaneous reconstruction of tissue. The material is fabricated by a process called sphere-templating and it can be made from many synthetic polymers including hydrogels, silicones and polyurethanes. All pores are identical in size and interconnected. Studies from our group have shown optimal healing (as suggested by extensive vascularity and minimal fibrosis) for spherical pores of 30–40 m size. The integrative healing noted is independent of biomaterial. Similar results are observed with sphere-templated silicone rubber and pHEMA hydrogel. In addition, surface chemical modification of the hydrogel with carbonyl diimidazole, or immobilisation on the hydrogel of collagen I or laminin did not change the healing response. Also, good healing results have been seen upon implantation in skin (subcutaneous, percutaneous), heart muscle, sclera, skeletal muscle, bone and vaginal wall. We consistently find the pore spaces heavily populated by monocytic cells that stain for macrophage cell surface markers. However, at long implantation times (16 or more weeks), the ability to stain for macrophage surface markers decreases. It could be possible that these cells populating the implants are differentiating into other tissues. Thus, such materials may represent a path to cell-free tissue engineering. Others have seen similar healing results, via completely different materials strategies, generally involving biological molecules. The in vivo results from our group and related results from other groups suggest we are on the cusp of a revolution in healing, biomaterials integration and tissue reconstruction. Also, the boundaries between biomaterials and tissue engineering continue to blur

Hemiarthroplasty is a common procedure that is an attractive alternative to total arthroplasty because it conserves natural tissue, allows for quicker recovery, and has a lower cost. One significant issue with hemiarthroplasties is that they lead to accelerated wear of the opposing native cartilage, likely due to the high stiffness of the implant. The purpose of this study was to investigate the range of currently available biomaterials for hemiarthroplasty applications. We employed a finite-element (FE) model of a radial head implant against the native capitellum as our joint model. The FE model was developed in ABAQUS v6.14 (Dassault Systèmes Simulia Corp., Providence, RI, USA). A solid axisymmetric concave implant with seven different materials and the native radial head were evaluated, six modelled as elastic materials with different Young's moduli (E) and Poisson's Ratios (ν), and one modelled as a Mooney-Rivlin hyperelastic material. The materials investigated were CoCr (E=230 GPa, ν = 0.3), PEEK (E=3.7 GPa, ν = 0.36), HDPE (E=2.7 GPa, ν = 0.42), UHMWPE (E=0.69 GPa, ν = 0.49), Bionate 75D (E=0.288 GPa, ν = 0.39), Bionate 55D (E=0.039 GPa, ν = 0.45), and Bionate 80A (modelled as a Mooney-Rivlin hyperelastic material). A load of 100 N was applied to the radius through the center of rotation representing a typical load through the radius. The variable of interest was articular contact stress on the capitellum. The CoCr implant had a maximum contact stress over 114% higher than the native radial head. By changing the material to lower the stiffness of the implant, the maximum contact stress was 24%, 70%, 105%, 111%, 113%, and 113% higher than the native radial head for Bionate 80A, Bionate 55D, Bionate 75D, UHMWPE, HDPE, and PEEK respectively. This work shows that lowering implant stiffness can reduce the contact stress on cartilage in hemiarthroplasty implants. By changing the material below a Young's modulus of ∼100 MPa elevated stresses on the capitellum can be markedly reduced and hence potentially reduce or prevent degenerative changes of the native articulating cartilage. Low stiffness implant materials are not a novel concept, but to date there have been few that investigate materials (such as Bionate) as a potential load bearing material for implant applications. Further work is required to assess the efficacy of these materials for articular bearing applications

Aim. There is an ongoing controversy whether the observed benefit of infection risk reduction by ALBC outweighs the risk of possible antimicrobial resistance development. Methods. The scientific & clinical literature in PubMed, Medline and Embase has been systematically reviewed with the keywords “antibiotic resistance”, “antibiotic loaded bone cement”, “local antibiotics”, “bacterial colonization” and “joint infection”. In total 28 relevant publications were found with the majority of them reporting laboratory results. Only 7 papers focused on clinical septic situations & patient data. Results. Although rare as consequence of the initially high drug concentrations in situ, experimental and clinical studies demonstrated survival of resistant bacteria on ALBC with subsequent bacterial re-colonisation of the biomaterial. This was most notable for coagulase-negative staphylococci (CoNS). Bacterial survival in presence of ALBC represents a selection process of already pre-existing high-level resistant mutants and not antibiotic resistance induction. The use of antibiotic combinations with gentamicin in bone cement is associated with a markedly lower risk of survival of resistant bacteria. This is particularly important in patients at high infection risks and in septic revision cases. There is no clinical evidence for a widespread increase of clinically important gentamicin resistancies in the orthopaedic ward because of routine use of ALBC. On an individual basis, the benefit of a lower infection probability with combined systemic & local antibiotic application should outweigh the risk of selecting pre-existing resistant bacteria. Each prevented infection case means that a complex and extended antibiotic therapy with risk of antibiotic resistance development over time has been avoided for a patient. In those cases where pre-existing resistant bacteria have survived the prophylactic exposure to antibiotics in bone cement, they remain in vast majority still susceptible to the clinically important antibiotics used for treatment of prosthetic joint infections. Conclusions. The benefit of a lower infection probability with ALBC should outweigh the risk of selecting resistant bacteria against the particular antibiotic used in bone cement. A trend towards broad resistance development which may complicate treatment of infection cases was not found