Playing with Low Amounts of Expanded Graphite for Melt-Processed Polyamide and Copolyester Nanocomposites to Achieve Control of Mechanical, Tribological, Thermal and Dielectric Properties.

Polyamide 11 (PA11) and copolyester (TPC-E) were compounded through melt extrusion with low levels (below 10%) of expanded graphite (EG), aiming at the manufacturing of a thermally and electrically conductive composite resistant to friction and with acceptable mechanical properties. Thermal characterisation showed that the EG presence had no influence on the onset degradation temperature or melting temperature. While the specific density of the produced composite materials increased linearly with increasing levels of EG, the tensile modulus and flexural modulus showed a significant increase already at the introduction of 1 wt% EG. However, the elongation at break decreased significantly for higher loadings, which is typical for composite materials. We observed the increase in the dielectric and thermal conductivity, and the dissipated power displayed a much larger increase where high frequencies (e.g., 10 GHz) were taken into account. The tribological results showed significant changes at 4 wt% for the PA11 composite and 6 wt% for the TPC-E composite. Morphological analysis of the wear surfaces indicated that the main wear mechanism changed from abrasive wear to adhesive wear, which contributes to the enhanced wear resistance of the developed materials. Overall, we manufactured new composite materials with enhanced dielectric properties and superior wear resistance while maintaining good processability, specifically upon using 4-6 wt% of EG.

Accuracy of intraoperative bone registration and stereotactic boundary reconstruction during total knee arthroplasty surgery.

BACKGROUND: The intraoperative registration of the bones play a crucial role in image-based computer-assisted knee arthroplasty to achieve accurate implant placement and to create reliable stereotactic bone boundaries for robot-assisted surgical systems. METHOD: This study assessed the intraoperative registration accuracy on six intact fresh frozen cadavers. RESULTS: Rotational errors around the mechanical axis were the largest, with a standard deviation of 1.2° and outliers up to 3.7°. The mean translational errors were lower than 1 mm, with outliers up to 1.5 mm. These errors were amplified to 2 mm for the registration-based reconstruction of the posterior bone surface at the resection levels. CONCLUSION: Given the cumulative behaviour of surgical errors, registration errors can affect the final implant positioning. Furthermore, inaccuracies in the reconstructed bone boundary directly affect the virtual stereotactic boundaries used in robotic-assisted surgery and can result in an incomplete resection or inadvertent soft tissue damage.

Setting the Optimal Laser Power for Sustainable Powder Bed Fusion Processing of Elastomeric Polyesters: A Combined Experimental and Theoretical Study.

Additive manufacturing (AM) of polymeric materials offers many benefits, from rapid prototyping to the production of end-use material parts. Powder bed fusion (PBF), more specifically selective laser sintering (SLS), is a very promising AM technology. However, up until now, most SLS research has been directed toward polyamide powders. In addition, only basic models have been put forward that are less directed to the identification of the most suited operating conditions in a sustainable production context. In the present combined experimental and theoretical study, the impacts of several SLS processing parameters (e.g., laser power, part bed temperature, and layer thickness) are investigated for a thermoplastic elastomer polyester by means of colorimetric, morphological, physical, and mechanical analysis of the printed parts. It is shown that an optimal SLS processing window exists in which the printed polyester material presents a higher density and better mechanical properties as well as a low yellowing index, specifically upon using a laser power of 17-20 W. It is further highlighted that the current models are not accurate enough at predicting the laser power at which thermal degradation occurs. Updated and more fundamental equations are therefore proposed, and guidelines are formulated to better assess the laser power for degradation and the maximal temperature achieved during sintering. This is performed by employing the reflection and absorbance of the laser light and taking into account the particle size distribution of the powder material.

An improved method for assessing the technical accuracy of optical tracking systems for orthopaedic surgical navigation.

BACKGROUND: Optical tracking systems (OTSs) are essential components of many modern computer assisted orthopaedic surgery (CAOS) systems but patient movement is often neglected in the evaluation of the accuracy. The aim of this study was to develop a representative test to assess the accuracy of OTSs including patient movement and demonstrate the effect of pointer design and OTS choice. METHOD: A mobile phantom with dynamic reference base (DRB) attached was designed and constructed. The point registration trueness and precision were evaluated for measurements with both a static and moving phantom. RESULTS: The trueness of the total target registration error (TTRE) was 1.4 to 2.7 times worse with a moving phantom compared to a static phantom. CONCLUSION: The accuracy of OTSs for CAOS applications should be evaluated by measurements with a moving phantom as the evaluation of the TTRE with a static frame significantly underestimates the measurement error.

Abrasive Sensitivity of Martensitic and a Multi-Phase Steels under Different Abrasive Conditions.

The wear behaviour of two martensitic and one multiphase steel targeted for abrasion and erosion applications in agriculture and mining industry were investigated in three abrasive test systems with different complexity. Scratch tests were performed with different indenter radii, shapes, and loads. The material behaviour was also investigated in multi-asperity contact systems. Pin-on-disc tests were performed with various loads and abrasive particles, as well as abrasive slurry-pot tests with different sliding velocities, distances, and impact angles of the abrasive media were performed. Comparing the test systems, the tested materials ranked similarly based on their wear performance, however, in each configuration, the dominant variable of the wear mechanism differed. The significance and contributions of test paramecenterters, the material's mechanical properties (H, σM, σY, E, εεM, εεB, W, σc, Ec) and the dimensionless numbers formed from them were investigated on the wear behaviour and the surface deformation. Correlation between parameters was established by multiple linear regression models. The sensitivity of the tested materials to abrasion was evaluated taking into account the wide range of influencing parameters.

Soft-tissue penetration of the oscillating saw during tibial resection in total knee arthroplasty.

AIMS: Inadvertent soft tissue damage caused by the oscillating saw during total knee arthroplasty (TKA) occurs when the sawblade passes beyond the bony boundaries into the soft tissue. The primary objective of this study is to assess the risk of inadvertent soft tissue damage during jig-based TKA by evaluating the excursion of the oscillating saw past the bony boundaries. The second objective is the investigation of the relation between this excursion and the surgeon's experience level. METHODS: A conventional jig-based TKA procedure with medial parapatellar approach was performed on 12 cadaveric knees by three experienced surgeons and three residents. During the proximal tibial resection, the motion of the oscillating saw with respect to the tibia was recorded. The distance of the outer point of this cutting portion to the edge of the bone was defined as the excursion of the oscillating saw. The excursion of the sawblade was evaluated in six zones containing the following structures: medial collateral ligament (MCL), posteromedial corner (PMC), iliotibial band (ITB), lateral collateral ligament (LCL), popliteus tendon (PopT), and neurovascular bundle (NVB). RESULTS: The mean 75th percentile value of the excursion of all cases was mean 2.8 mm (SD 2.9) for the MCL zone, mean 4.8 mm (SD 5.9) for the PMC zone, mean 3.4 mm (SD 2.0) for the ITB zone, mean 6.3 mm (SD 4.8) for the LCL zone, mean 4.9 mm (SD 5.7) for the PopT zone, and mean 6.1 mm (SD 3.9) for the NVB zone. Experienced surgeons had a significantly lower excursion than residents. CONCLUSION: This study showed that the oscillating saw significantly passes the edge of the bone during the tibial resection in TKA, even in experienced hands. While reported neurovascular complications in TKA are rare, direct injury to the capsule and stabilizing structures around the knee is a consequence of the use of a hand-held oscillating saw when making the tibial cut. Cite this article: Bone Joint J 2020;102-B(10):1324-1330.

Thermal, Viscoelastic, Mechanical and Wear Behaviour of Nanoparticle Filled Polytetrafluoroethylene: A Comparison.

In this research work, unfilled and mono-filled polytetrafluoroethylene (PTFE) materials were developed and characterised by physical, thermal, viscoelastic, mechanical, and wear analysis. The applied fillers were graphene, alumina (Al2O3), boehmite alumina (BA80), and hydrotalcite (MG70) in 0.25/1/4/8 and 16 wt % filler content. All samples were produced by room temperature pressing-free sintering method. All of the fillers were blended with PTFE by intensive dry mechanical stirring; the efficiency of the blending was analysed by Energy-dispersive X-ray spectroscopy (EDS) method. Compared to neat PTFE, graphene in 4/8/16 wt % improved the thermal conductivity by ~29%/~84%/~157%, respectively. All fillers increased the storage, shear and tensile modulus and decreased the ductility. PTFE with 4 wt % Al2O3 content reached the lowest wear rate; the reduction was more than two orders of magnitude compared to the neat PTFE.

Fabrication of Microporous Coatings on Titanium Implants with Improved Mechanical, Antibacterial, and Cell-Interactive Properties.

The success of an orthopedic implant therapy depends on successful bone integration and the prevention of microbial infections. In this work, plasma electrolytic oxidation (PEO) was performed to deposit TiO2 coatings enriched with Ca, P, and Ag on titanium to improve its surface properties and antibacterial efficacy while maintaining normal biological functions and thus to enhance the performance of orthopedic implants. After PEO treatment, the surface of Ti was converted to anatase and rutile TiO2, hydroxyapatite, and calcium titanate phases. The presence of these crystalline phases was further increased with an increased Ag content in the coatings. The developed coatings also exhibited a more porous morphology with an improved surface wettability, roughness, microhardness, and frictional coefficient. In vitro antibacterial assays indicated that the Ag-doped coatings can significantly prevent the growth of both Staphylococcus aureus and Escherichia coli by releasing Ag+ ions, and the ability to prevent these bacteria was enhanced by increasing the Ag content in the coatings, resulting in a maximal 6-log reduction of E. coli and a maximal 5-log reduction of S. aureus after 24 h of incubation. Moreover, the in vitro cytocompatibility evaluation of the coatings showed that the osteoblast (MC3T3) cell integration on the PEO-based coatings was greatly improved compared to untreated Ti and no notable impact on their cytocompatibility was observed on increasing the amount of Ag in the coating. In conclusion, the coating with favorable physicochemical and mechanical properties along with controlled silver ion release can offer an excellent antibacterial performance and osteocompatibility and can thus become a prospective coating strategy to face current challenges in orthopedics.

Online Wear Detection Using High-Speed Imaging.

In this paper, the change detection of a fast turning specimen is studied at micro-level, whereas the images are acquired without stopping the rotation. In the beginning of the experiment, the imaging system is focused on the surface of the specimen. By starting the rotation of the specimen, the diameter of the specimen changes due to wear, which results in de-focusing of the imaging system. So the amount of blur in the images can be used as evidence of the wear phenomenon. Due to the properties of the microscope, the corners of the frames were dark and had to be cropped. So, each micrograph reflects only a small area of the surface. Nevertheless, techniques like stitching of multiple images can provide a significant surface area for micro-level investigation which increases the effectiveness of analyzing the material modification. Based on the results computer vision could detect a change of about 1.2 µm in the diameter of the specimen. More important is that we could follow the same locations of the surface in the microscopic images despite blurring, uneven illumination, change on the surface, and relatively a high-speed rotation.

The effect of trochlear dysplasia on patellofemoral biomechanics: a cadaveric study with simulated trochlear deformities.

BACKGROUND: Trochlear dysplasia appears in different geometrical variations. The Dejour classification is widely used to grade the severity of trochlear dysplasia and to decide on treatment. PURPOSE: To investigate the effect of trochlear dysplasia on patellofemoral biomechanics and to determine if different types of trochlear dysplasia have different effects on patellofemoral biomechanics. STUDY DESIGN: Controlled laboratory study. METHODS: Trochlear dysplasia was simulated in 4 cadaveric knees by replacing the native cadaveric trochlea with different types of custom-made trochlear implants, manufactured with 3-dimensional printing. For each knee, 5 trochlear implants were designed: 1 implant simulated the native trochlea (control condition), and 4 implants simulated 4 types of trochlear dysplasia. The knees were subjected to 3 biomechanical tests: a squat simulation, an open chain extension simulation, and a patellar stability test. The patellofemoral kinematics, contact area, contact pressure, and stability were compared between the control condition (replica implants) and the trochlear dysplastic condition and among the subgroups of trochlear dysplasia. RESULTS: The patellofemoral joint in the trochlear dysplastic group showed increased internal rotation, lateral tilt, and lateral translation; increased contact pressures; decreased contact areas; and decreased stability when compared with the control group. Within the trochlear dysplastic group, the implants graded as Dejour type D showed the largest deviations for the kinematical parameters, and the implants graded as Dejour types B and D showed the largest deviations for the patellofemoral contact areas and pressures. CONCLUSION: Patellofemoral kinematics, contact area, contact pressure, and stability are significantly affected by trochlear dysplasia. Of all types of trochlear dysplasia, the models characterized with a pronounced trochlear bump showed the largest deviations in patellofemoral biomechanics. CLINICAL RELEVANCE: Investigating the relationship between the shape of the trochlea and patellofemoral biomechanics can provide insight into the short-term effects (maltracking, increased pressures, and instability) and long-term effects (osteoarthritis) of different types of trochlear dysplasia. Furthermore, this investigation provides an empirical explanation for better treatment outcomes of trochleoplasty for Dejour types B and D dysplasia.

The use of rapid prototyped implants to simulate knee joint abnormalities for in vitro testing: a validation study with replica implants of the native trochlea.

To investigate the biomechanical effect of skeletal knee joint abnormalities, the authors propose to implant pathologically shaped rapid prototyped implants in cadaver knee specimens. This new method was validated by replacing the native trochlea by a replica implant on four cadaver knees with the aid of cadaver-specific guiding instruments. The accuracy of the guiding instruments was assessed by measuring the rotational errors of the cutting planes (on average 3.01° in extension and 1.18° in external/internal rotation). During a squat and open chain simulation, the patella showed small differences in its articulation with the native trochlea and the replica trochlea, which could partially be explained by the rotational errors of the implants. This study concludes that this method is valid to investigate the effect of knee joint abnormalities with a replica implant as a control condition to account for the influence of material properties and rotational errors of the implant.

Pilot validation study on a quasi-static weight-bearing knee rig.

This article presents a pilot study on a quasi-static knee rig designed to investigate the influence of pathologies and surgical interventions on the patellofemoral kinetics of cadaveric knees. The knee rig allows cadaveric knees to flex and extend under a simulated body weight by transmitting a force to the quadriceps tendon. During the squat simulation, the ground reaction force stays within physiological values. Before using this device to answer clinical questions, two knee specimens were tested to assess the repeatability of the rig. Four repeated flexion-extension cycles were performed under a simulated body weight of 700 N, with an isolated force on the quadriceps tendon up to 2700 N and with a ground reaction force close to 350 N. The resulting patellofemoral contact area shifted from distal to proximal during knee flexion. From 20 degrees to 60 degrees of knee flexion, the mean contact area and pressure increased from 80.2 +/- 3.3 to 349.5 +/- 10.1 mm2 and from 0.9 +/- 0.2 to 5.9 +/- 0.7 MPa, respectively. The transmitted force on the quadriceps tendon, the ground reaction force and the patellofemoral contact area and pressure were continuously measured and showed a relative variability of 1.6%, 2.4%, 2.8% and 3.2%, respectively. The presented knee rig shows a good repeatability that allows us to use this knee rig to quantify the influence of anatomical changes on the patellofemoral contact area and pressures during a squat simulation.

Patellofemoral contact pressures.

A test rig for studying the biomechanical behaviour of post-mortem human knees is built. For loading the quadriceps tendon a special clamping device is constructed, so the forces up to 3000 N could easily be transferred to the tendon. Several post-mortem human knees used in this study are tested to collect data about the general biomechanics of knee joint during squatting. The forces in the quadriceps tendon and in the tibia are measured continuously; the flexion angle is also measured. On this modular test rig, the contact pressures of the patellofemoral joint are measured as well. Therefore a thin pressure film is used. Not only are measured the contact pressures, but the changing contact area is also visualized and measured. The forces and rotations measured in the joint and in the contact area allowed us to obtain perfectly reproducible values as well as a positive relation between contact area, contact position and working direction of the quadriceps tendon.