By means of plasma polymerization, positively charged, nanometre-thin coatings can be applied to implant surfaces. The aim of the present study was to quantify the adhesion of human bone cells in vitro and to evaluate the bone ongrowth in vivo, on titanium surfaces modified by plasma polymer coatings. Different implant surface configurations were examined: titanium alloy (Ti6Al4V) coated with plasma-polymerized allylamine (PPAAm) and plasma-polymerized ethylenediamine (PPEDA) versus uncoated. Shear stress on human osteoblast-like MG-63 cells was investigated in vitro using a spinning disc device. Furthermore, bone-to-implant contact (BIC) was evaluated in vivo. Custom-made conical titanium implants were inserted at the medial tibia of female Sprague-Dawley rats. After a follow-up of six weeks, the BIC was determined by means of histomorphometry. The quantification of cell adhesion showed a significantly higher shear stress for MG-63 cells on PPAAm and PPEDA compared to uncoated Ti6Al4V. Uncoated titanium alloyed implants showed the lowest BIC (40.4%). Implants with PPAAm coating revealed a clear but not significant increase of the BIC (58.5%) and implants with PPEDA a significantly increased BIC (63.7%). In conclusion, plasma polymer coatings demonstrate enhanced cell adhesion and bone ongrowth compared to uncoated titanium surfaces.

Purpose: The repair of large segmental bone defects caused by fracture, tumor or infection remains challenging in orthopedic surgery. The capability of two different bone scaffold materials, sintered tricalciumphosphate and a titanium alloy (Ti6Al4V), were determined by mechanical and biomechanical testing.Methods: All scaffolds were fabricated by means of additive manufacturing techniques with identical design and controlled pore geometry. Small-sized sintered TCP scaffolds (10 mm diameter, 21 mm length) were fabricated as dense and open-porous samples and tested in an axial loading procedure. Material properties for titanium alloy were determined by using both tensile (dense) and compressive test samples (open-porous). Furthermore, large-sized open-porous TCP and titanium alloy scaffolds (30 mm in height and diameter, 700 mu m pore size) were tested in a biomechanical setup simulating a large segmental bone defect using a composite femur stabilized with an osteosynthesis plate. Static physiologic loads (1.9 kN) were applied within these tests.Results: Ultimate compressive strength of the TCP samples was 11.2 +/- 0.7 MPa and 2.2 +/- 0.3 MPa, respectively, for the dense and the open-porous samples. Tensile strength and ultimate compressive strength was 909.8 +/- 4.9 MPa and 183.3 +/- 3.7 MPa, respectively, for the dense and the open-porous titanium alloy samples. Furthermore, the biomechanical results showed good mechanical stability for the titanium alloy scaffolds. TCP scaffolds failed at 30% of the maximum load.Conclusions: Based on recent data, the 3D printed TCP scaffolds tested cannot currently be recommended for high load-bearing situations. Scaffolds made of titanium could be optimized by adapting the biomechanical requirements.

Diagnosis of total hip replacement (THR) loosening using imaging often fails to provide reliable results. New implants instrumented with sensors shall conform to this challenge. Therefore, a novel concept of an in vivo sensor was tested. This simple mechano-acoustical sensor is integrated inside the total hip stem and enables detection of osseous fixation. The sensor is excited by an external coil and impinges inside the THR. The spring-back of the sensor can be detected by an extracorporeal coil, while the structure-borne sound is measured with a vibration sensor placed at the patient’s leg. Experiments of a THR with one integrated sensor showed the possibility to differentiate between well fixed and loosened implants. The presented in vivo sensor system has a promising potential to detect loosening and to analyze osseointegration.

New developments of antimicrobial implant surfaces doped with copper (Cu) ions may minimize the risk of implant-associated infections. However, experimental evaluation of the Cu release is influenced by various test parameters. The aim of our study was to evaluate the Cu release characteristics in vitro according to the storage fluid and surface roughness. Plasma immersion ion implantation of Cu (Cu-PIII) and pulsed magnetron sputtering process of a titanium copper film (Ti-Cu) were applied to titanium alloy (Ti6Al4V) samples with different surface finishing of the implant material (polished, hydroxyapatite and corundum blasted). The samples were submersed into either double-distilled water, human serum, or cell culture medium. Subsequently, the Cu concentration in the supernatant was measured using atomic absorption spectrometry. The test fluid as well as the surface roughness can alter the Cu release significantly, whereby the highest Cu release was determined for samples with corundum-blasted surfaces stored in cell medium.

The use of finite element analysis (FEA) has grown to a more and more important method in the field of biomedical engineering and biomechanics. Although increased computational performance allows new ways to generate more complex biomechanical models, in the area of orthopaedic surgery, solid modelling of screws and drill holes represent a limitation of their use for individual cases and an increase of computational costs. To cope with these requirements, different methods for numerical screw modelling have therefore been investigated to improve its application diversity. Exemplarily, fixation was performed for stabilization of a large segmental femoral bone defect by an osteosynthesis plate. Three different numerical modelling techniques for implant fixation were used in this study, i.e. without screw modelling, screws as solid elements as well as screws as structural elements. The latter one offers the possibility to implement automatically generated screws with variable geometry on arbitrary FE models. Structural screws were parametrically generated by a Python script for the automatic generation in the FE-software Abaqus/CAE on both a tetrahedral and a hexahedral meshed femur. Accuracy of the FE models was confirmed by experimental testing using a composite femur with a segmental defect and an identical osteosynthesis plate for primary stabilisation with titanium screws. Both deflection of the femoral head and the gap alteration were measured with an optical measuring system with an accuracy of approximately 3 µm. For both screw modelling techniques a sufficient correlation of approximately 95% between numerical and experimental analysis was found. Furthermore, using structural elements for screw modelling the computational time could be reduced by 85% using hexahedral elements instead of tetrahedral elements for femur meshing. The automatically generated screw modelling offers a realistic simulation of the osteosynthesis fixation with screws in the adjacent bone stock and can be used for further investigations.

Purpose. To compare the inner contour of the femoral component of 10 total knee replacement (TKR) designs for possible exchange in use.Methods. Inner contours of the femoral components of 10 cemented, cruciate-retaining TKR designs (e. motion, Genesis, Genia, Innex, LCS, Multigen Plus, NexGen, PFC, Scorpio, Vanguard) were scanned and reconstructed to 2-dimensional contours. Their cross-sections were compared by superimposition and aligning at the distal and anterior cuts. The patellar notch and outer contour were not analysed.Results. The maximum deviation was 5 mm in the posterior and posterior oblique cuts and 10 mm in the anterior oblique cut. Based on similarity of the inner contour, LCS and Innex was classified as group I, e. motion, Genesis, Scorpio, Vanguard, and Multigen Plus as group II, and Genia, NexGen, and PFC as group III. All 2 designs in group I were not compatible with the other 8 designs. Four of the 5 designs in group II showed good compatibility. All 3 designs in group III significantly differed in the posterior and oblique cuts.Conclusion. A standardised inner contour of the femoral component can increase compatibility of different TKR systems in revision surgery and reduces the extent of bone resection.

The bone mineral density (BMD) of retrieved cancellous bone samples is compared to the BMD measuredin vivoin the respective osteoarthritic patients. Furthermore, mechanical properties, in terms of structural modulus (Es) and ultimate compression strength (σmax) of the bone samples, are correlated to BMD data. Human femoral heads were retrieved from 13 osteoarthritic patients undergoing total hip replacement. Subsequently, the BMD of each bone sample was analysed using dual energy X-ray absorptiometry (DXA) as well as ashing. Furthermore, BMDs of the proximal femur were analysed preoperatively in the respective patients by DXA. BMDs of the femoral neck and head showed a wide variation, from1016±166 mg/cm2to1376±404 mg/cm2. BMDs of the bone samples measured by DXA and ashing yielded values of315±199 mg/cm2and347±113 mg/cm3, respectively.Esandσmaxamounted to232±151 N/mm2and6.4±3.7 N/mm2. Significant correlation was found between the DXA and ashing data on the bone samples and the DXA data from the patients at the femoral head (r=0.85and 0.79, resp.).Escorrelated significantly with BMD in the patients and bone samples as well as the ashing data (r=0.79,r=0.82, andr=0.8, resp.).

The objective of this study was to analyse retrieved human femoral bone samples using three different test methods, to elucidate the relationship between bone mineral density and mechanical properties. Human femoral heads were retrieved from 22 donors undergoing primary total hip replacement due to hip osteoarthritis and stored for a maximum of 24 hours postoperatively at + 6 °C to 8 °C.Analysis revealed an average structural modulus of 232±130 N/mm(2) and ultimate compression strength of 6.1±3.3 N/mm(2) with high standard deviations. Bone mineral densities of 385±133 mg/cm(2) and 353±172 mg/cm(3) were measured using thedual energy X-ray absorptiometry (DXA) and quantitative computed tomography (QCT), respectively. Ashing resulted in a bone mineral density of 323±97 mg/cm(3). In particular, significant linear correlations were found between DXA and ashing with r = 0.89 (p < 0.01, n = 22) and between structural modulus and ashing with r = 0.76 (p < 0.01, n = 22).Thus, we demonstrated a significant relationship between mechanical properties and bone density. The correlations found can help to determine the mechanical load capacity of individual patients undergoing surgical treatments by means of noninvasive bone density measurements.

Aim Design optimization and surface modifications of orthopedic implants are focused on adhesive properties depending on specific applications. To obtain an in vitro understanding of the adhesion interaction of bone cells on implant surfaces the time-dependent adhesion behavior of osteoblastic cells was studied. Materials and Methods MG-63 osteoblastic cells were seeded on discs of polished titanium alloy (Ti6Al4V) and allowed to adhere for various time periods (1 to 48 h). Using a spinning disc device and a confocal laser scanning microscope (LSM) the shear stress required to detach the bone cells from the substrate was determined. An approximation of the adhesion force was calculated from measurements of cell height and contact radius. Results Shear stress ranged from 40.4 N/m2 to 82.4 N/m2 showing an increase in cell adhesion reaching a maximum after 6 h before decreasing significantly. Using the cell height and contact radii, measured for the various time periods, the lowest adhesion force of 232 nN was approximated after 1 h cell adhesion and analogous to the adhesion strength measurements, the highest of 664 nN after 6 h. Generally, cell adhesion decreased at incubation times longer than 6 h before an increase after 48 h was observed once again. Conclusions differences in adhesion behavior over time indicate dynamic cell-substrate interactions because of cell migration and proliferation processes. The study stresses the importance of calculating the adhesion force rather than shear stress to gain more expressive data regarding cell adhesion.

Implant infections remain feared and severe complications after total joint arthroplasty. The incidence of multi-resistant pathogens, causing such infections, is rising continuously, and orthopaedic surgeons are confronted with an ever-changing resistance pattern. Anti-infectious surface coatings aim for a high local effective concentration and a low systemic toxicity at the same time. Antibacterial efficacy and biomechanical stability of a novel broad-spectrum anti-infectious coating is assessed in the present study. Antibacterial efficacy of a sol–gel derived titanium dioxide (TiO2) coating for metal implants with and without integrated copper ions as antibiotic agent was assessed against methicillin resistant Staphylococcus aureus (MRSA 27065). Both bacterial surface adhesion and growth of planktonic bacteria were assessed with bare and various TiO2-coated Ti6Al4V metal discs. Furthermore, bonding strength of the TiO2 surface coating, using standard testing procedures, as well as surface roughness were determined. We found a significant reduction of the bacterial growth rate for the coatings with integrated copper ions, with highest reduction rates observed for a fourfold copper TiO2-coating. Pure TiO2 without integrated copper ions did not reduce bacterial growth compared to uncoated Ti6Al4V. The coating was not detached from the substrate by standard adhesive failure testing, which indicated an excellent durability of the implant coating. The TiO2 coating with integrated copper ions could offer a new strategy for preventing implant-associated infections, with antibacterial properties not only against the most common bacteria causing implant infections but also against multiresistant strains such as MRSA.

The main reason for the revision of total hip replacements is aseptic loosening, caused by stress shielding and wear particle induced osteolysis. In order to detect an implant loosening early, the osseointegration of endoprosthetic implants must be measured exactly. Currently applied diagnostic methods, such as standard radiographs and clinical symptomatology, often result in an imprecise diagnosis. A novel radiation-free method to improve the diagnostic investigation of implant loosening is presented. The osseointegration of an implant can be identified using mechanical magnetic sensors (oscillators), which impinge on small membranes inside an implant component, e.g., the femoral hip stem. The maximum velocity after impingement of the oscillator depends on the osseointegration of the implant. Excitation of the oscillator is realized by a coil outside the human body. Another external coil is used to detect the velocity of the oscillator. To demonstrate the principle of the novel loosening sensor, an overdimensioned test device was designed to measure simulated loosening phases in the first experimental tests with different material layers. The overdimensioned test device of the loosening sensor showed significant differences in the various phases of fixation. Analysis of the membrane without any material layer in the case of advanced loosening resulted in a 23% higher maximum velocity compared to an attached artificial bone layer. Based on these preliminary results, the sensor system shows potential for the detection of implant loosening. Moreover, the proposed system could be used in experimental applications to determine the quality of bioactive coatings and new implant materials.

Currently applied diagnostic methods for loosening of total hip replacements often result in imprecise identification of implant fixation and in the worst case unnecessary revision surgery. Developed sensors integrated in implants require adequate energy supply, which in most cases is achieved by inductive coupling and complex data telemetry. In order to avoid a telemetric apparatus, we developed a passive concept of a novel in vivo method to improve diagnostic investigations of total hip replacement loosening. A mechano-acoustical sensor, attached on small membranes inside the femoral hip stem, is proposed and enables osseous anchorage detection. The sensor is excited and detected by extracorporeal coils. First functional models show significant differences between different material layers located at the membrane. The novel in vivo sensor system has a promising potential to detect implant loosening.

Introduction: Total knee replacement has become a common procedure with good clinical results. Today many different designs of the femoral component of bicondylar endoprostheses are offered by industry. The femoral components show similar designs however different angles and length of the cross sections are specific. Because of these design differences the preoperative planning and sparing bone resection are difficult at the revision surgery. The aim of this experimental study was to compare the design of femoral components at their cross section contours to find congruence and differences of common bicondylar endoprostheses to prove the possibility of design exchange during revision surgery. Material and method: Ten femoral components (e.motion ® , Genesis II, Genia ® , Innex ® , LCS ® , Multigen Plus, NexGen ® , P.F.C. ® , Scorpio ® , Vanguard ® ) of similar implant size were analysed with regard to their cross section design. Therefore the constructional properties of the inner surface (direction and length of cross sections) of the components were determined. The components were scanned with a three-dimensional laser scanner and were transferred to two dimensional CAD models to the lateral and frontal view in order to compare the inner contours. The contours of the cross sections were overlaid with congruence of the posterior and anterior cross section of all components at lateral view. Results: Four of the ten analysed femoral components showed good congruence of the cross sections. Here, only a few additional bone resections or extra bone cement have to be done at the diagonal cross sections to change the femoral design among each other. Four other components show wide differences between the inner contours in comparison to the first four components especially at their posterior and diagonal cross sections. Two components can not be compared with the others due to their diagonal distal cross section. Discussion: The numerical results shows good congruence of cross section contours of some analysed femoral components. Furthermore there were clear design differences which complicate the exchange of the femoral component at revision surgery. The use of an elementary inner contour of femoral components of bicondylar endoprostheses could be an advantage for revision arthroplasty in regard to bone sparing surgical treatment.

Aseptic loosening in total hip replacement is mainly caused by wear particles inducing inflammation and osteolysis. Wear can be a consequence of micromotions at the interface between implant and bone cement. Due to complex cellular interactions, different mediators (e.g. cytokines, proteinases) are released, which can promote osteolytic processes in the periprosthetic tissue followed by loosening of the implant. Furthermore, a reduced matrix synthesis and an induced apoptosis rate can be observed. The purpose of this study was to evaluate to what extent human primary osteoblasts exposed to wear particles are involved in the osteolysis. The viability, the secretion of collagen and collagenases and the variety of released cytokines after particle exposure was examined. Therefore, human osteoblasts were incubated with particles experimentally generated in the interface between hip stems with rough and smooth surface finishings as well as different material compositions (Ti-6Al-7Nb, Co-28Cr-6Mo and 316L) and bone cement mantle made of Palacos R containing zirconium oxide particles. Commercially pure titanium particles, titanium oxide, polymethylmethacrylate and particulate zirconium oxide were used as references. The results revealed distinct effects on the cytokine release of human osteoblasts towards particulate debris. Thereby, human osteoblasts released increased levels of interleukine (IL)-6 and IL-8 after treatment with metallic wear particles. The expression of VEGF was slightly induced by all particle entities at lower concentrations. Apoptotic rates were enhanced for osteoblasts exposed to all the tested particles. Furthermore, the de novo synthesis of type 1 collagen was reduced and the expression of the matrix metalloproteinase (MMP)-1 was considerably increased. However, wear particles of Co-28Cr-6Mo stems seemed to be more aggressive, whereas particles derived from stainless steel stems caused less adverse cellular reaction. Among the reference particles, which caused less altered reactions in the metabolism of osteoblasts in general, ZrO2 can be assumed as the material with the smallest cell biological effects.

Most revisions of total joint replacements are due to implant loosening, which is mainly caused by wear particles ("wear disease") and inadequate primary implant stability. The optimised integration of cementless total hip and knee endoprostheses into the bone stock is the most adequate approach to achieve secondary implant stability and to prevent implant loosening. Secondary stability is characterized by bone ingrowth of the implant and decreases the amount of relative implant motion between the implant and bone stock. It has also been suggested that prostheses which are fully occupied by bone cells are less susceptible to infection. The economic impact of implant loosening is immense, hence orthopaedic implant manufactures refine their products continuously.Many technical developments have improved the survival rate of endoprosthetic implants. Modem materials and surface modifications such as coatings help to reduce wear rates, promote cell ongrowth or prevent infections. The cell adhesion of bone cells onto implant surfaces has not been thoroughly investigated so far. However, different methods to measure cell adhesion have been described. Some workgroups investigate short-term adhesion or proliferation of bone cells on implant materials in-vitro, but little is known about the long-term adhesion. Proliferation or short-term adhesion cannot predict how strong the bonding between bone and implant will be. In most cases, cost intensive animal studies have to be performed in order to gain expressive data. Hence, it is important to assess the bone cell adhesion forces in an adequate experimental setup in-vitro.The exploration of bone cell adhesion on surfaces of orthopaedic implants encourages the development of bio-compatible, bio-active and anti-infectious surfaces. We have developed a test device, based on the spinning disc principle, which allows quantitative measurements of osteoblastic cells on implant surfaces. First results show differences in adhesion forces depending on the substrate. In future assessments different bio-active and anti-infectious surface modifications will be analyzed regarding bone cell adhesion prior to animal studies.

In total joint replacement much effort has been made to reduce implant loosening. We investigated different implant coatings (copper integrated titanium dioxide (TiO2–Cu), titanium nitride (TiN), plasma polymerized allylamine (PPAAm), and calcium phosphate (CaP)) regarding the adhesion strength and wear resistance. Standardized scratch and adhesive tests were applied. Abrasive wear was measured with artificial bone and bone cement using a special testing machine. All tested coatings have higher bonding strengths than the 22 N/mm2 required for medical implant surface coatings by ASTM standard 4711-F. Using bone cement, wear testing revealed higher wear rates in most cases. Polished surfaces reduce the amount of wear, whereas rough surfaces highly increase the wear rate due to three-body wear, especially ceramic surfaces. In general, the application of bone cement in conjunction with modified implant surfaces can lead to an increase in wear rate.

Aseptic loosening of total hip replacement is mainly caused by wear particles. Abrasive wear occurs at articulating surfaces or as a consequence of micro-motions at the interface between femoral stem and bone cement. Direct impact of wear particles on osteolysis, the remodeling of the bone stock and a directly affected function of osteoblasts was described. The present study examined the response of human osteoblasts exposed to different wear particles, which were generated in a test device providing oscillating micro-motions at the interface between femoral stem and standard bone cement. Characterization of released particles was performed by quantifying the size distribution and the metal content of the wear debris. Human osteoblasts were incubated with particles obtained from hip stems with different material compositions (Ti-6Al-7Nb and Co-28Cr-6Mo) and rough and smooth surface finishings combined with standard bone cement (Palacos(R) R) containing zirconium oxide particles. Commercially pure titanium particles (cp-Ti) and particulate zirconium oxide (ZrO(2)) were used for comparative analyses. The results revealed significant (p < 0.05) reduction of the cell viability after exposure to higher concentration of metallic particles, particularly from Co-based alloys. In contrast, ZrO(2) alone showed significantly less adverse effects on the cells. When increasing metallic particle concentrations massive inhibition was also observed in the release of cytokines including interleukine-6 (IL-6) and interleukine-8 (IL-8), but the expression of Procollagen I and the cell viability showed the highest reduction after exposure to Co-based alloy particles from rough stems.