Experimental Measurements of Mechanical Properties of PUR Foam Used for Testing Medical Devices and Instruments Depending on Temperature, Density and Strain Rate

Assessment of the tolerance angle for pedicle screw insertion

Cannulation process intervenes before implantation of pedicle screw and depends on the surgeon's experience. A reliable experimental protocol has been developed for the characterization of the slipping behavior of the surgical tool on the cortical shell simulated by synthetic materials. Three types of synthetic foam samples with three different densities were tested using an MTS Acumen 3 A/T electrodynamic device with a tri-axis 3 kN Kistler load cell mounted on a surgical tool, moving at a constant rotational speed of 10° mm-1 and performing a three-step cannulation test. Cannulation angle varied between 10° and 30°. Synthetic samples were scanned after each tests, and cannulation coefficient associated to each perforation section was computed. Reproducibility tests resulted in an ICC for Sawbone samples of 0.979 (p < 0.001) and of 0.909 (p < 0.001) for Creaplast and Sawbone samples. Cannulation coefficient and maximum force in Z-axis are found the best descriptors of the perforation. Angular threshold for perforation prediction was found to be 17.5° with an area under the curve of the Receiver Operating Characteristic of 89.5%. This protocol characterizes the cannulation process before pedicle screw insertion and identifies the perforation tool angle until which the surgical tool slips on the cortical shell depending on bone quality.

Effect of Liquid Glass-Modified Lignin Waste on the Flammability Properties of Biopolyurethane Foam Composites

Water-blown biopolyurethane (bioPUR) foams are flammable and emit toxic gases during combustion. Herein, a novel approach suggested by the current study is to use different amounts of lignin waste (LigW), which increases the thermal stability and delays the flame spread and sodium silicate (LG), which has foaming ability at high temperatures and acts as a protective layer during a fire. However, there have been no studies carried out to investigate the synergy between these two materials. Therefore, two different ratios, namely 1/1 and 1/2 of LigW/LG, were used to prepare bioPUR foam composites. The obtained bioPUR foam composites with a 1/2 ratio of LigW/LG exhibited inhibition of flame propagation during the ignitability test by 7 s, increased thermal stability at higher temperatures by 40 °C, reduced total smoke production by 17%, reduced carbon monoxide release by 22%, and increased compressive strength by a maximum of 123% and 36% and tensile strength by a maximum of 49% and 30% at 100 °C and 200 °C, respectively, compared to bioPUR foam composites with unmodified LigW. Additionally, thanks to the sufficient compatibility between the polymeric matrix and LigW/LG particles, bioPUR foam composites were characterised by unchanged or even improved physical and mechanical properties, as well as increased glass transition temperature by 16% compared to bioPUR foam composites with unmodified LigW particles, making them suitable for application as a thermal insulating layer in building envelopes.

Stiff skin, soft core: soft backings enhance the conformability and friction of fibre-reinforced adhesives

Biomimetic adhesives with a stiff fibre-reinforced base layer generate strong attachment, even without bioinspired micropatterning of the contact surface. However, current fibre-reinforced adhesive designs are still less versatile with respect to substrate variability than their biological counterparts. In this study, we enhance the comformability of a fibre-reinforced adhesive on curved substrates by adding bioinspired soft backings. We designed and fabricated soft backing variations (polyurethane foams and silicone hydroskeletons) with varying compressive stiffnesses that mimic the soft viscoelastic structures in the adhesive appendages of tree frogs, geckos and other animals. The backings were mounted on a smooth silicone layer enforced with a polyester mesh, and we experimentally investigated the contact area and friction performance of these adhesives on a curved substrate. The results show that the contact area and friction created by a fibre-reinforced adhesive with a soft backing in contact with a non-flat substrate scale inversely with backing stiffness. The integration of stiff fibre-reinforcement with a compressible backing represents an important step in bringing bioinspired adhesives out of the laboratory and into the real world, for example in soft robotic grippers. Moreover, our findings stimulate further research into the role of soft tissues in biological adhesive systems.

Heat Accumulation in Implant Inter-Osteotomy Areas-An Experimental In Vitro Study

To examine the influence of the distance between adjacent implant osteotomies on heat accumulation in the inter-osteotomy area, two experimental groups with 15 pairs of osteotomies in Type II polyurethane blocks were compared: 7 mm inter-osteotomy separations (Group A, n = 15) and 14 mm inter-osteotomy separations (Group B, n = 15). An infrared thermographic analysis of thermal changes in the inter-osteotomy area was completed. A one-way analysis of variance (ANOVA) and Fisher post-test were used to determine group differences. Higher temperatures were recorded in Group A at the coronal and middle levels compared to the apical level in both groups. The temperature reached max temperatures at T80s and T100s. In Group A, the threshold for thermal necrosis was exceeded. Meanwhile, Group B did not reach the threshold for thermal necrosis. Preparing adjacent implant osteotomies in dense bone with a 7 mm separation between their centers increases the temperature in the inter-osteotomy area, exceeding the threshold for bone thermal necrosis; meanwhile, increasing the distance between osteotomies reduces the thermal accumulation and the risk for thermal necrosis.

A Review of Research on the Effect of Temperature on the Properties of Polyurethane Foams

Temperature is one of the main factors affecting the properties of polyurethane foams, and there are large differences in the mechanical properties of polyurethane foams at different temperatures. To understand the effect of temperature on the mechanical properties of polyurethane foams and to provide a theoretical basis for the application of polyurethane foams in extreme environments, this paper systematically describes the research on the effect of mold temperature, raw material temperature, and environmental temperature on the microstructure and mechanical properties of polyurethane foams in the formation and service stages of rigid polyurethane foams by domestic and foreign scholars, and summarizes the effect of temperature on the mechanical properties of polyurethane foams and the mechanism of action. A review of the literature shows that the effect of different temperatures on the mechanical properties of polyurethane foams can be summarized. The literature review shows that there are certain changes in the foaming process, pore structure, and mechanical properties of polyurethane foams at different temperatures, and the increase in temperature generally leads to the increase in pore size, decrease in density, and decrease in mechanical properties of polyurethane foams.

Experimental Characterization and Numerical Modeling of the Corrosion Effect on the Mechanical Properties of the Biodegradable Magnesium Alloy WE43 for Orthopedic Applications

Computational modeling plays an important role in the design of orthopedic implants. In the case of biodegradable magnesium alloys, a modeling approach is required to predict the effects of degradation on the implant's capacity to provide the desired stabilization of fractured bones. In the present work, a numerical corrosion model is implemented to predict the effects of biodegradation on the structural integrity of temporary trauma implants. A non-local average pitting corrosion model is calibrated based on experimental data collected from in vitro degradation experiments and mechanical testing of magnesium WE43 alloy specimens at different degradation stages. The localized corrosion (pitting) model was implemented by developing a user material subroutine (VUMAT) with the program Abaqus^®/Explicit. In order to accurately capture both the linear mechanical reduction in specimen resistance, as well as the non-linear corrosion behavior of magnesium WE43 observed experimentally, the corrosion model was extended by employing a variable corrosion kinetic parameter, which is time-dependent. The corrosion model was applied to a validated case study involving the pull-out test of orthopedic screws and was able to capture the expected loss of screw pull-out force due to corrosion. The proposed numerical model proved to be an efficient tool in the evaluation of the structural integrity of biodegradable magnesium alloys and bone-implant assembly and can be used in future works in the design optimization and pre-validation of orthopedic implants.

The Use of Polyurethane Injection as a Geotechnical Seismic Isolation Method in Large-Scale Applications: A Numerical Study

This paper analyses the effect of polyurethane injections on the seismic surficial response of cohesionless soils. For this purpose, dynamic finite element numerical analyses were performed through GiD + OpenSees. Both the soil and the composite material, resulted after the expansion of the injected polyurethane, are modelled with a nonlinear hysteretic constitutive model. Based on the polyurethane percentage, a homogenisation of the characteristics was considered for the composite material: linear for density and damping, and exponential (experimentally calibrated) for the stiffness. An expansion coefficient quantifies how much the injected polyurethane expands: three expansion coefficients were considered, each of them related to a different polyurethane density. For the evaluation of the foam stiffness, a linear stiffness–density correlation was used, derived after impact tests. Results showed that polyurethane reduces the surficial accelerations proportionally to the ratio of its seismic impedance and volumetric percentage with respect to the soil seismic impedance and total volume. This is a preliminary indication for the design of polyurethane injections in cohesionless soils for seismic acceleration reduction.

Is Fracture Toughness of PUR Foams a Material Property? A Statistical Approach

The published data on the experimentally determined fracture toughness of foams are based on a small number of specimens, having a lack of statistical consistency. The paper proposes a statistical approach on the fracture toughness results of rigid polyurethane (PUR) foams of three different densities. Five types of fracture tests were considered. The results were statistically analyzed using six types of regressions and a meta-analysis to identify the factors influencing the fracture toughness. The statistical analysis indicates that the fracture toughness represents a material property because does not depend on the specimen type. The density plays a major role in the fracture toughness of PUR foams. The irregular shape of the cells induced small anisotropy for low-density foams (100 kg/m³ and 145 kg/m³). This effect could not be observed for the foam with 300 kg/m³ density, for which the cells have a more regular spherical shape. The statistical analysis indicates that the influence of the loading speed is very weak.