Unintended consequences: Assessing thermo-mechanical changes in vinyl nitrile foam due to micro-computed X-ray tomographic imaging.

Micro-computed X-ray tomography (µCT) is a volumetric imaging tool used to quantify the internal structure of materials. µCT imaging with mechanical testing (in situ µCT) helps visualize strain-induced structural changes and develop structure-property relationships. However, the effects on thermophysical properties of radiation exposure during in situ µCT imaging are seldom addressed, despite potential radiation sensitivity in elastomers. This work quantifies the radiation dosage effect on thermo-, chemical-, and mechanical-properties for a vinyl nitrile-based foam. Material properties were measured after (0, 1, 2, and 3) days at (8.1 ± 0.9) kGy/d. Morphological characteristics were investigated via scanning electron microscopy. Thermal transitions were assessed using differential scanning calorimetry. Viscoelasticity was measured with dynamic mechanical analysis over a range from -30 °C to 60 °C. Higher dose lead to stiffening and increased dissipation. Chemical structure was assessed with Fourier transform infrared spectroscopy and energy-dispersive X-ray spectroscopy. Soxhlet extraction was used to measure gel content. In summary, substantial changes occur in thermophysical properties, which may confound structure-property measurements. However, this also provides a modification pathway. Quantitation and calibration of the properties changes informed a finite element user material for material designers to explore tunablity and design optimization for impact protection engineers.

A materials data framework and dataset for elastomeric foam impact mitigating materials.

The availability of materials data for impact-mitigating materials has lagged behind applications-based data. For example, data describing on-field helmeted impacts are available, whereas material behaviors for the constituent impact-mitigating materials used in helmet designs lack open datasets. Here, we describe a new FAIR (findable, accessible, interoperable, reusable) data framework with structural and mechanical response data for one example elastic impact protection foam. The continuum-scale behavior of foams emerges from the interplay of polymer properties, internal gas, and geometric structure. This behavior is rate and temperature sensitive, therefore, describing structure-property characteristics requires data collected across several types of instruments. Data included are from structure imaging via micro-computed tomography, finite deformation mechanical measurements from universal test systems with full-field displacement and strain, and visco-thermo-elastic properties from dynamic mechanical analysis. These data facilitate modeling and design efforts in foam mechanics, e.g., homogenization, direct numerical simulation, or phenomenological fitting. The data framework is implemented using data services and software from the Materials Data Facility of the Center for Hierarchical Materials Design.

Epifluorescence-based three-dimensional traction force microscopy.

We introduce a novel method to compute three-dimensional (3D) displacements and both in-plane and out-of-plane tractions on nominally planar transparent materials using standard epifluorescence microscopy. Despite the importance of out-of-plane components to fully understanding cell behavior, epifluorescence images are generally not used for 3D traction force microscopy (TFM) experiments due to limitations in spatial resolution and measuring out-of-plane motion. To extend an epifluorescence-based technique to 3D, we employ a topology-based single particle tracking algorithm to reconstruct high spatial-frequency 3D motion fields from densely seeded single-particle layer images. Using an open-source finite element (FE) based solver, we then compute the 3D full-field stress and strain and surface traction fields. We demonstrate this technique by measuring tractions generated by both single human neutrophils and multicellular monolayers of Madin-Darby canine kidney cells, highlighting its acuity in reconstructing both individual and collective cellular tractions. In summary, this represents a new, easily accessible method for calculating fully three-dimensional displacement and 3D surface tractions at high spatial frequency from epifluorescence images. We released and support the complete technique as a free and open-source code package.

Rapid, topology-based particle tracking for high-resolution measurements of large complex 3D motion fields.

Spatiotemporal tracking of tracer particles or objects of interest can reveal localized behaviors in biological and physical systems. However, existing tracking algorithms are most effective for relatively low numbers of particles that undergo displacements smaller than their typical interparticle separation distance. Here, we demonstrate a single particle tracking algorithm to reconstruct large complex motion fields with large particle numbers, orders of magnitude larger than previously tractably resolvable, thus opening the door for attaining very high Nyquist spatial frequency motion recovery in the images. Our key innovations are feature vectors that encode nearest neighbor positions, a rigorous outlier removal scheme, and an iterative deformation warping scheme. We test this technique for its accuracy and computational efficacy using synthetically and experimentally generated 3D particle images, including non-affine deformation fields in soft materials, complex fluid flows, and cell-generated deformations. We augment this algorithm with additional particle information (e.g., color, size, or shape) to further enhance tracking accuracy for high gradient and large displacement fields. These applications demonstrate that this versatile technique can rapidly track unprecedented numbers of particles to resolve large and complex motion fields in 2D and 3D images, particularly when spatial correlations exist.

Winning the war on surgical site infection: evidence-based preoperative interventions for total joint arthroplasty.

Postoperative surgical site infections (SSIs) are the most common cause of expensive and debilitating revision surgeries. The Institute for Healthcare Improvement has introduced a three-intervention package, titled Project JOINTS, which attempts to control preoperative and perioperative factors contributing to postoperative SSI in patients undergoing total joint arthroplasty (TJA). The three interventions are preoperative screening for Staphylococcus aureus, decolonizing the skin and nares, and intraoperative administration of combined antimicrobial and alcohol agents to the skin. Canton-Potsdam Hospital was an early adopter of the Project JOINTS protocol, and this quality improvement project has demonstrated a reduced SSI rate throughout the two years of implementation. Before implementation, 596 TJAs were performed with an S aureus SSI rate of 1.8%. During Project JOINTS, 305 TJAs were conducted with a significantly (P = .050) lower S aureus SSI rate of 0.66%. Thus, Project JOINTS is effective at reducing the postoperative incidence of S aureus SSIs in patients undergoing TJA.

Synergistic effects between phosphonium-alkylphosphate ionic liquids and zinc dialkyldithiophosphate (ZDDP) as lubricant additives.

Unique synergistic effects between phosphonium-alkylphosphate ionic liquids (ILs) and zinc dialkyldithiophosphate (ZDDP) are discovered when used together as lubricant additives, resulting in significant friction and wear reduction along with distinct tribofilm composition and mechanical properties. The synergism is attributed to the remarkably 30-70× higher-than-nominal concentrations of hypothetical new compounds (via anion exchange between IL and ZDDP) on the fluid surface/interface.

Cervine tibia morphology and mechanical strength: a suitable tibia model?

Animal models for orthopaedic implant testing are well-established but morphologically dissimilar to human tibiae; notably, most are shorter. The purpose of this study was to quantitatively evaluate the morphology and mechanical properties of the cervine tibia, particularly with regard to its suitability for testing orthopaedic implants. Two endosteal and eleven periosteal measurements were made on 15 cervine tibiae. The mechanical strength in axial compression and torsion was measured using 11 tibiae. The cervine tibia is morphologically similar to the human tibia and more closely matches the length of the human tibia than current tibia models (ovine, porcine, and caprine). The distal epiphysis dimensions are notably different, but no more so than the current tibia models. The torsional stiffness of the cervine tibia is within the range of previously reported values for human tibiae. Furthermore, in many regions, cervine tibiae are abundant and locally available at a low cost. Given these mechanical and morphological data, coupled with potential cost savings if regionally available, the cervine tibia may be an appropriate model for orthopaedic implant testing.

Cyclic cryopreservation affects the nanoscale material properties of trabecular bone.

Tissues such as bone are often stored via freezing, or cryopreservation. During an experimental protocol, bone may be frozen and thawed a number of times. For whole bone, the mechanical properties (strength and modulus) do not significantly change throughout five freeze-thaw cycles. Material properties at the trabecular and lamellar scales are distinct from whole bone properties, thus the impact of freeze-thaw cycling at this scale is unknown. To address this, the effect of repeated freezing on viscoelastic material properties of trabecular bone was quantified via dynamic nanoindentation. Vertebrae from five cervine spines (1.5-year-old, male) were semi-randomly assigned, three-to-a-cycle, to 0-10 freeze-thaw cycles. After freeze-thaw cycling, the vertebrae were dissected, prepared and tested. ANOVA (factors cycle, frequency, and donor) on storage modulus, loss modulus, and loss tangent, were conducted. Results revealed significant changes between cycles for all material properties for most cycles, no significant difference across most of the dynamic range, and significant differences between some donors. Regression analysis showed a moderate positive correlation between cycles and material property for loss modulus and loss tangent, and weak negative correlation for storage modulus, all correlations were significant. These results indicate that not only is elasticity unpredictably altered, but also that damping and viscoelasticity tend to increase with additional freeze-thaw cycling.