Development, manufacturing, and preliminary validation of a reusable half-face respirator during the COVID-19 pandemic

Introduction

The COVID-19 pandemic has led to widespread shortages of N95 respirators and other personal protective equipment (PPE). An effective, reusable, locally-manufactured respirator can mitigate this problem. We describe the development, manufacture, and preliminary testing of an open-hardware-licensed device, the “simple silicone mask” (SSM).

Methods

A multidisciplinary team developed a reusable silicone half facepiece respirator over 9 prototype iterations. The manufacturing process consisted of 3D printing and silicone casting. Prototypes were assessed for comfort and breathability. Filtration was assessed by user seal checks and quantitative fit-testing according to CSA Z94.4–18.

Results

The respirator originally included a cartridge for holding filter material; this was modified to connect to standard heat-moisture exchange (HME) filters (N95 or greater) after the cartridge showed poor filtration performance due to flow acceleration around the filter edges, which was exacerbated by high filter resistance. All 8 HME-based iterations provided an adequate seal by user seal checks and achieved a pass rate of 87.5% (N = 8) on quantitative testing, with all failures occurring in the first iteration. The overall median fit-factor was 1662 (100 = pass). Estimated unit cost for a production run of 1000 using distributed manufacturing techniques is CAD $15 in materials and 20 minutes of labor.

Conclusion

Small-scale manufacturing of an effective, reusable N95 respirator during a pandemic is feasible and cost-effective. Required quantities of reusables are more predictable and less vulnerable to supply chain disruption than disposables. With further evaluation, such devices may be an alternative to disposable respirators during public health emergencies. The respirator described above is an investigational device and requires further evaluation and regulatory requirements before clinical deployment. The authors and affiliates do not endorse the use of this device at present.

An apparatus for rapid and nondestructive comparison of masks and respirators

The SARS-CoV-2 global pandemic has produced widespread shortages of certified air-filtering personal protection equipment and an acute need for rapid evaluation of breathability and filtration efficiency of proposed alternative solutions. Here, we describe experimental efforts to nondestructively quantify three vital characteristics of mask approaches: breathability, material filtration effectiveness, and sensitivity to fit. We focus on protection against aqueous aerosols >0.3 μm using off-the-shelf particle, flow, and pressure sensors, permitting rapid comparative evaluation of these three properties. We present and discuss both the pressure drop and the particle penetration as a function of flow to permit comparison of relative protection for a set of proposed filter and mask designs. The design considerations of the testing apparatus can be reproduced by university laboratories and medical facilities and used for rapid local quality control of respirator masks that are of uncertified origin, monitoring the long-term effects of various disinfection schemes and evaluating improvised products not designed or marketed for filtration.

Measurement of filtration efficiencies of healthcare and consumer materials using modified respirator fit tester setup

During the current SARS-CoV-2 pandemic there is unprecedented demand for personal protective equipment (PPE), especially N95 respirators and surgical masks. The ability of SARS-CoV-2 to be transmitted via respiratory droplets from asymptomatic individuals has necessitated increased usage of both N95 respirators in the healthcare setting and masks (both surgical and homemade) in public spaces. These precautions rely on two fundamental principles of transmission prevention: particle filtration and droplet containment. The former is the focus of NIOSH N95 testing guidelines, and the latter is an FDA guideline for respirators and surgical masks. While studies have investigated droplet containment to provide guidance for homemade mask production, limited work has been done to characterize the filtration efficiency (FE) of materials used in home mask making. In this work, we demonstrate the low-cost (<$300) conversion of standard equipment used to fit-test respirators in hospital and industrial settings into a setup that measures quantitative FEs of materials based on NIOSH N95 guidelines, and subsequently measure FEs of materials found in healthcare and consumer spaces. These materials demonstrate significant variability in filtration characteristics, even for visually similar materials. We demonstrate a FE of 96.49% and pressure drop of 25.4 mmH20 for a double-layer of sterilization wrap used in surgical suites and a FE of 90.37% for a combination of consumer-grade materials. The excellent filtration characteristics of the former demonstrate potential utility for emergent situations when N95 respirators are not available, while those of the latter demonstrate that a high FE can be achieved using publicly available materials.

An observational ergonomic tool for assessing the worn condition of slip-resistant shoes

Worn shoes are known to contribute to slip-and-fall risk, a common cause of workplace injuries. However, guidelines for replacing shoes are not well developed. Recent experiments and lubrication theory suggest that the size of the worn region is an important contributor to the shoe tread's ability to drain fluid and therefore the under-shoe friction. This study evaluated a simple test for comparing the size of the worn region relative to a common object (AAA and AA battery) as a means of determining shoe replacement. This study consisted of three components involving slip-resistant shoes: Experiment #1: a longitudinal, mechanical, accelerated wear experiment; Experiment #2: a longitudinal experiment where the same shoes were tested after each month of worker use; and Experiment #3: a cross-sectional experiment that exposed participants to a slippery condition, while donning their own worn shoes. The COF (Experiments #1 and #2); under-shoe fluid pressure (all experiments); and slip severity (Experiment #3) were compared across outcomes (fail/pass) of the battery tests. Larger fluid pressures, lower coefficient of friction, and more severe slips were observed for shoes that failed the battery tests compared with those passing the tests. This method offers promise for assessing loss in friction and an increase in slip risk for slip-resistant shoes.

Significant correlation of bone material strength index as measured by the OsteoProbe with Vickers and Rockwell hardness

The bone material strength index (BMSi), as measured by the OsteoProbe, is significantly correlated with Vickers hardness and Rockwell (RW) hardness measurements on conventional materials. The Vickers and RW measurements were carried out according to American Society for Testing and Materials standard test methods, and OsteoProbe measurements followed published standardized testing methods. The correlations between the BMSi and RW hardness, r = 0.93, and between the BMSi and Vickers hardness, r = 0.94, are comparable with the correlation between RW and Vickers hardness, r = 0.87. The correlation between the BMSi and RW is significant at p < 0.01, and the correlation between the BMSi and Vickers hardness is significant at p < 0.01. These results show that the indentation measurement performed by the OsteoProbe may be considered as a type of hardness measurement comparable to widely used conventional methods, with specific applications targeted by its portable and narrow design.

Single particles as resonators for thermomechanical analysis

Thermal methods are indispensable for the characterization of most materials. However, the existing methods require bulk amounts for analysis and give an averaged response of a material. This can be especially challenging in a biomedical setting, where only very limited amounts of material are initially available. Nano- and microelectromechanical systems (NEMS/MEMS) offer the possibility of conducting thermal analysis on small amounts of materials in the nano-microgram range, but cleanroom fabricated resonators are required. Here, we report the use of single drug and collagen particles as micro mechanical resonators, thereby eliminating the need for cleanroom fabrication. Furthermore, the proposed method reveals additional thermal transitions that are undetected by standard thermal methods and provide the possibility of understanding fundamental changes in the mechanical properties of the materials during thermal cycling. This method is applicable to a variety of different materials and opens the door to fundamental mechanistic insights.

Design and evaluation of a laboratory-based wheelchair castor testing protocol using community data

Wheelchair castors fail frequently causing physical, social and economic consequences for wheelchair users. These failures occur in spite of established wheelchair test methods and regulations, suggesting that the existing tests may not be sufficient to screen poorly designed castors. An expert stakeholder group, convened by the International Society of Wheelchair Professionals (ISWP), noted castor failures as a high priority and recommended that a new castor testing system should be developed. In a previous study, the effect of shock exposure on castor durability was studied. The current paper extends the previous work and focuses on the development of a castor testing protocol based on shock, corrosion and abrasion exposure data collected in the community. The testing protocol was applied to 8 different castor models tested under four conditions: shock, corrosion + shock, abrasion + shock and abrasion + corrosion + shock. For each model, a total of n = 8 samples were evaluated across the four conditions. Results demonstrate that corrosion and abrasion reduced castor durability between 13% to 100% depending on the model. Importantly, the inclusion of corrosion and abrasion resulted in changes in the failure modes for 75% of the tested models and two-thirds of the altered failure modes are associated with increased risk of injury for wheelchair users. These results suggest that corrosion and abrasion present in the community reduce castor durability, thus supporting their inclusion in the castor testing protocol and potentially other wheelchair standards.

Fully integrated fused quartz acoustic horns for structural health monitoring

Non-destructive acoustic structural sensing is an imperative technology, applicable to many different fields such as aerospace and civil engineering. To maintain a high sensitivity or to mitigate acoustic loss, it is important to increase the signal-to-noise ratio by improving coupling efficiency from acoustic sources to the object under test, such as an acoustic waveguide. Here, a fully integrated fused quartz horn design is combined with a fused quartz acoustic waveguide. The resulting system is intended to demonstrate a high accuracy low cost alternative to current sensing systems and the present article report on the viability of using a merged acoustic horn and waveguide.

Mechanical characterization of bone quality in distal femur fractures using pre-operative computed tomography scans

BACKGROUND

Mechanical testing of implant constructs designed to treat distal femur fractures has been hampered by a lack of clinical data on the biomechanical properties of the distal femur in patients who sustain these fractures. Therefore, the purpose of this study was to use quantitative computed tomography (qCT) to investigate the mechanical characteristics of fractured distal femurs to inform the selection of synthetic materials for biomechanical testing.

METHODS

Distal femur fractures treated at a Level I trauma center were retrospectively reviewed and 43 cases with preoperative CT scans were identified for analysis. Scans were segmented and each bone fragment was reconstructed as a 3D model. The Young's modulus of the distal femur was determined from voxel-based radiodensity.

FINDINGS

Median patient age was 72 years (IQR = 57-81), with 26% males and 74% females. Young's modulus in the distal femur was negatively correlated with patient age (R² = 0.50, p < 0.001). The distribution of patient-specific modulus values was also compared with the compressive modulus ranges for graded polyurethane foams according to ASTM F1839. Bone quality ranged from Grade 25 in younger individuals to Grade 5 in older individuals.

CONCLUSION

No single grade of synthetic polyurethane foam can be selected to model all clinically important scenarios for biomechanical testing of distal femur fracture fixation devices. Rather, this data can be used to select an appropriate material for a given clinical scenario. A Grade 25 foam is appropriate for implant longevity, whereas for implant stability, Grades 5-15 are more appropriate.

Creep experimental study on the lumbar intervertebral disk under vibration compression load

The intervertebral disk cushions the load generated by human activity and absorbs energy to keep the spine moving steadily. Vibration condition is one of the important causes of disk degeneration. Creep experiments using the sheep lumbar intervertebral disk were carried out under vibration compression. Regularities of the strain of the disk with time were obtained and compared with those of static load. The influence of vibration frequency and time on the creep properties of the intervertebral disk was analyzed. An intervertebral disk three-parameter solid creep constitutive model considering vibration factors was established and the parameters in the model were identified. The results show that the strain of the lumbar intervertebral disk exhibits an exponential relationship with time and is unrelated to static compression or vibration load. Under the same vibration amplitude, the creep increases with vibration frequency and the relationship between them is nonlinear. The vibration frequency has a significant effect on the strain. The creep rate decreases gradually with time and is obviously influenced by vibration frequency at low vibration amplitudes. The creep prediction results obtained using the constitutive model with the time-varying material parameters are in good agreement with the experimental results. The two elastic moduli in the model decrease with time and the viscosity coefficient increases with time.

Integrating structural heterogeneity, fiber orientation, and recruitment in multiscale ECM mechanics

Extracellular matrix (ECM) plays critical roles in establishing tissue structure-function relationships and controlling cell fate. However, the mechanisms by which ECM mechanics influence cell and tissue behavior remain to be elucidated since the events associated with this process span length scales from the tissue to molecular level. Entirely new methods are needed in order to better understand the multiscale mechanics of ECM. In this study, a multiscale experimental approach was established by integrating Optical Magnetic Twisting Cytometry (OMTC) with a biaxial tensile tester to study the microscopic (local) ECM mechanical properties under controlled tissue-level (global) loading. Adventitial layer of porcine thoracic artery was used as a collagen-based ECM. Multiphoton microscopy imaging was performed to capture the changes in ECM fiber structure during biaxial deformation. As visualized from multiphoton microscopy images, biaxial stretch induces gradual fiber straightening and the fiber families become evident at higher stretch levels. The OMTC measurements show that the local apparent storage and loss modulus increases with the global biaxial stretch, however there exists a complex interplay among local ECM mechanical properties, ECM structural heterogeneity, and fiber distribution and engagement. The phase lag does not change significantly with global biaxial stretch. Our results also show a much faster increase in global tissue tangent modulus compared to the local apparent complex modulus with biaxial stretch, indicating the scale dependency of ECM mechanics.

Array based real-time measurement of fluid viscosities and mass-densities to monitor biological filament formation

Liquid mass density and viscosity are fundamental characteristics of fluids. Their quantification by means of classical viscosity and density meters has several drawbacks: (i) the liquid-density and the viscosity cannot be measured simultaneously, (ii) sample volumes in the mL-range are consumed, (iii) the measurements cannot be multiplexed, and, (iv) the quantifications are time-consuming (minutes). Nano-mechanical transducers promise to overcome these limitations. We use fully clamped, gold coated silicon-nitride membranes with a thickness of 200 nm to measure liquid viscosity and density of samples of 1 μL volumes residing above the membrane in a miniature well. Photo-thermal actuation is used to excite the membrane, and an optical deflection system measures the response. From the response spectra, the eigenfrequency (f) and the quality (Q) factor are extracted and used to determine liquid density and viscosity by applying a three-point calibrated, simplified lumped model. We tested the system using calibrated solutions with viscosities in the range of 1-219 mPa s and mass densities between 998 kg m-3 and 1235 kg m-3. Real-time measurements were performed that characterize the polymerization of G-actin to F-actin filaments. The method presented promises to overcome the aforementioned limitations and thereby enables the real-time characterization of sub-μL sample volumes in a multiplexed manner.

A novel technique for in situ uniaxial tests of self-assembled soft biomaterials

We introduce a novel method to form 3D biomimetic tissues from a droplet of a cell-extracellular matrix (ECM) mixture on a sensor stage and to quantify tissue force and stiffness as a function of time under optical microscopes. This method exploits advances in micro-nano fabrication and capillarity for self-assembly and self-alignment of tissues on the stage. It allows simultaneous investigation of the microstructure of the tissue in situ while its mechanical response is quantified, thus linking tissue biophysics with physiology and revealing structural-functional properties of 3D tissues. We demonstrate the functionality of the stage by studying the mechanical behavior of different cell-collagen mixtures under mechanical, chemical and electrical stimulation. This includes force evolution in cell-free collagen during curing, myotubes differentiated from muscle cell-collagen/Matrigel ECM subjected to electrical stimulation, and fibroblast-collagen tissue subjected to cancer cell conditioned media (CM) and a Rho-kinase inhibitor, Y27632. Muscle contraction decreases with increasing frequency of electrical stimulation, and fibroblasts respond to CM by increasing contractility for a short time and completely relax in the presence of Y27632 but restore force with Y27632 washout.

Design and analysis of a burst strength device for testing vascular grafts

The design and analysis of a device to measure the burst strength (strength under a state of pure radial internal pressure) and compliance of vascular grafts and flexible pressurized tubes is presented. The device comprises three main sections, viz., a clean air-dry pressure controller, a test specimen holder, and automated software for control and data collection. Air pressure is controlled by means of a valve and a dedicated mechanism allowing reaching up to 120 psi in increments of 1 psi, and recording pressure changes with 0.04 psi resolution. The circumferential strain is determined by measuring the radial displacement of the vascular graft using an optical arrangement capable of determining a maximum radial displacement of 10 mm with 0.02 mm resolution. The instrument provides a low uncertainty in compliance (±0.32%/100 mm Hg^-1) and burst strength measurements. Due to its simplicity, the device can easily be reproduced in other laboratories contributing to a dedicated instrument with high resolution at low cost. The reliability of the apparatus is further confirmed by conducting finite element analysis, elasticity solutions for pressurized cylinders, and testing of small diameter vascular grafts made of a commercial aliphatic polyurethane tested under radial internal pressure.

Personalised 3D knee compliance from clinically viable knee laxity measurements: A proof of concept ex vivo experiment

Personalised information of knee mechanics is increasingly used for guiding knee reconstruction surgery. We explored use of uniaxial knee laxity tests mimicking Lachman and Pivot-shift tests for quantifying 3D knee compliance in healthy and injured knees. Two healthy knee specimens (males, 60 and 88 years of age) were tested. Six-degree-of-freedom tibiofemoral displacements were applied to each specimen at 5 intermediate angles between 0° and 90° knee flexion. The force response was recorded. Six-degree-of-freedom and uniaxial tests were repeated after sequential resection of the anterior cruciate, posterior cruciate and lateral collateral ligament. 3D knee compliance (C_6DOF) was calculated using the six-degrees-of-freedom measurements for both the healthy and ligament-deficient knees and validated using a leave-one-out cross-validation. 3D knee compliance (C_CT) was also calculated using uniaxial measurements for Lachman and Pivot-shift tests both conjointly and separately. C_6DOF and C_CT matrices were compared component-by-component and using principal axes decomposition. Bland-Altman plots, median and 40-60th percentile range were used as measurements of bias and dispersion. The error on tibiofemoral displacements predicted using C_6DOF was < 9.6% for every loading direction and after release of each ligament. Overall, there was good agreement between C_6DOF and C_CT components for both the component-by-component and principal component comparison. The dispersion of principal components (compliance coefficients, positions and pitches) based on both uniaxial tests was lower than that based on single uniaxial tests. Uniaxial tests may provide personalised information of 3D knee compliance.

Monitoring and Assessing the Degradation Rate of Magnesium-Based Artificial Bone In Vitro Using a Wireless Magnetoelastic Sensor

A magnetoelastic-based (MB) sensor was employed as a novel method to monitor and assess the degradation rate of magnesium-based artificial bone (MBAB) in vitro, which can be used as an implant to repair a bone defect, providing a quantitative method to depict the degradation rate of MBAB. MBABs were fabricated by the Pro/Engineering software and a precision machine tool using high-purity (HP) magnesium. The MB sensor was embedded in the neutral surface of MBAB by an unharmful quick adhesive, forming the MB sensor-embedded MBAB (EMBAB). The modified simulated body fluid (MSBF) media (PH = 7.4), mimicking the human internal environment, and the NaOH media (PH = 12), accelerating EMBAB’s degradation, were used to immerse the EMBAB for 15 days at 37 °C. The EMBAB was then tested daily on a self-developed experimental platform to monitor the relative output power under a 100 N external force. The results showed that the relative output power of the sensing coil gradually increased with the EMBAB’s degradation. The degradation rate of the EMBAB could be calculated on the basis of the changes of the relative output power caused by the MB sensor and of the degradation time. With the EMBAB’s degradation, an increasing strain directly worked on the MB sensor, significantly changing the value of the relative output power, which means that the EMBAB was characterized by a quick degradation rate. During the 15 days of the experiment, the degradation rates on the 7th and 15th days were 0.005 dbm/day and 0.02 dbm/day, and 0.02 dbm/day and 0.04 dbm/day in MSBF and alkaline media, respectively. Therefore, the MB sensor provides a wireless and passive method to monitor and assess the degradation rate of bone implants in vitro.

Noncontact Strain Monitoring of Osseointegrated Prostheses

The objective of this study was to develop a noncontact, noninvasive, imaging system for monitoring the strain and deformation states of osseointegrated prostheses. The proposed sensing methodology comprised of two parts. First, a passive thin film was designed such that its electrical permittivity increases in tandem with applied tensile loading and decreases while unloading. It was found that patterning the thin films could enhance their dielectric property's sensitivity to strain. The film can be deposited onto prosthesis surfaces as an external coating prior to implant. Second, an electrical capacitance tomography (ECT) measurement technique and reconstruction algorithm were implemented to capture strain-induced changes in the dielectric property of nanocomposite-coated prosthesis phantoms when subjected to different loading scenarios. The preliminary results showed that ECT, when coupled with strain-sensitive nanocomposites, could quantify the strain-induced changes in the dielectric property of thin film-coated prosthesis phantoms. The results suggested that ECT coupled with embedded thin films could serve as a new noncontact strain sensing method for scenarios when tethered strain sensors cannot be used or instrumented, especially in the case of osseointegrated prostheses.

Simulated cuspal deflection and flexural properties of high viscosity bulk-fill and conventional resin composites

OBJECTIVES

The purpose of this study was to investigate the simulated cuspal deflection and flexural properties of high viscosity bulk-fill and conventional resin composites.

METHODS

Seven high viscosity bulk-fill resin composites and eight conventional resin composites were used. Aluminum blocks (10 mm x 8 mm x 15 mm) with a mesio-occlusal-distal (MOD) cavity [4 (W) mm x 8 (L) mm x 4 (D) mm] were prepared and randomly divided into groups for different measurement techniques [micrometer vs CSLM] and further subdivided according to type of resin composite (high viscosity bulk-fill vs conventional resin composite). The simulated cuspal deflection resulting from the polymerization of resin composite bonded to a precisely machined MOD cavity within an aluminum block was measured with either a novel highly accurate submicron digimatic micrometer (MDH-25 M, Mitsutoyo, Tokyo, Japan) or a confocal laser scanning microscope (CLSM, VK-9710, Keyence, Tokyo, Japan) cuspal measurement method. In addition, flexural properties of tested resin composites were measured to investigate the relationship between simulated cuspal deflection and flexural properties. Scanning electron microscopy observation of tested resin composites was also conducted.

RESULTS

The simulated cuspal deflection of high viscosity bulk-fill resin composites was similar to that of conventional resin composites, regardless of measurement method. There were no statistically significant differences (p > 0.05) between the micrometer and CLSM cuspal measurement methods. There were statistically significant differences (p < 0.05) in flexural strength and elastic modulus depending on the material, regardless of the type of resin composite. Pearson correlation analysis did not show any statistically significant (p < 0.05) relationship between flexural properties and cuspal deflection.

CONCLUSIONS

The results of this study indicate that high viscosity bulk-fill resin composites show similar cuspal deflection with bulk-filling techniques, to those shown by conventional resin composites with incremental filling techniques. Simulated cuspal deflection can be measured using either a micrometer or CLSM, but this experiment failed to show any relationship between the flexural properties and simulated cuspal deflection of resin composites.

SIGNIFICANCE

High viscosity bulk-fill resin composites produce the same level of cuspal deflection as a conventional incrementally filled resin composite.

Utilization of a robotic mount to determine the force required to cut palatal tissue

Determination of the material properties of soft tissue is a growing area of interest that aids in the development of new surgical tools and surgical simulators. This study first aims to develop a robot-operated tissue testing system for determination of tissue cutting forces. Second, this system was used to ascertain the cutting properties of the hard and soft palate mucosa and soft palate musculature for the purpose of developing a robotic instrument for cleft palate surgery and a cleft-specific surgical simulator. The palate tissue was cut with a 15 blade mounted to the robot with varying angles (30°, 60°, 90°) and speeds (1.5, 2.5, 3.5 cm/s) of cutting to imitate typical operative tasks. The cutting force range for hard palate mucosa, soft palate mucosa and soft palate muscle were 0.98-3.30, 0.34-1.74 and 0.71-2.71 N, respectively. The break-in force of the cut (i.e. force required for the blade to penetrate the tissue) is significantly impacted by the angle of the blade relative to the tissue rather than the cutting speed. Furthermore, the total surface area of the tissue in contact with the blade during the cut has a significant impact on the total force expended on the tissue.

Juvenile bovine bone is an appropriate surrogate for normal and reduced density human bone in biomechanical testing: a validation study

Orthopaedic research necessitates accurate and reliable models of human bone to enable biomechanical discoveries and translation into clinical scenarios. Juvenile bovine bone is postulated to be a potential model of normal human bone given its dimensions and comparatively reduced ethical restrictions. Demineralisation techniques can reduce bone density and alter bone properties, and methods to model osteoporotic bone using demineralised juvenile bovine bone are investigated. Juvenile bovine long bones were quantitatively CT scanned to assess bone density. Demineralisation using hydrochloric acid (0.6, 1.2 and 2.4 M) was performed to create different bone density models which underwent biomechanical validation for normal and osteoporotic bone models. All long bones were found to have comparable features to normal human bone including bone density (1.96 ± 0.08 gcm-3), screw insertion torque and pullout strength. Demineralisation significantly reduced bone density and pullout strength for all types, with 0.6 M hydrochloric acid creating reductions of 25% and 71% respectively. Juvenile bovine bone is inexpensive, easy to source and not subject to extensive ethical procedures. This study establishes for the first time, the use of its long bones as surrogates for both normal and osteoporotic human specimens and offers preliminary validation for its use in biomechanical testing.

Open-source micro-tensile testers via additive manufacturing for the mechanical characterization of thin films and papers

The cost of specialized scientific equipment can be high and with limited funding resources, researchers and students are often unable to access or purchase the ideal equipment for their projects. In the fields of materials science and mechanical engineering, fundamental equipment such as tensile testing devices can cost tens to hundreds of thousands of dollars. While a research lab often has access to a large-scale testing machine suitable for conventional samples, loading devices for meso- and micro-scale samples for in-situ testing with the myriad of microscopy tools are often hard to source and cost prohibitive. Open-source software has allowed for great strides in the reduction of costs associated with software development and open-source hardware and additive manufacturing have the potential to similarly reduce the costs of scientific equipment and increase the accessibility of scientific research. To investigate the feasibility of open-source hardware, a micro-tensile tester was designed with a freely accessible computer-aided design package and manufactured with a desktop 3D-printer and off-the-shelf components. To our knowledge this is one of the first demonstrations of a tensile tester with additively manufactured components for scientific research. The capabilities of the tensile tester were demonstrated by investigating the mechanical properties of Graphene Oxide (GO) paper and thin films. A 3D printed tensile tester was successfully used in conjunction with an atomic force microscope to provide one of the first quantitative measurements of GO thin film buckling under compression. The tensile tester was also used in conjunction with an atomic force microscope to observe the change in surface topology of a GO paper in response to increasing tensile strain. No significant change in surface topology was observed in contrast to prior hypotheses from the literature. Based on this result obtained with the new open source tensile stage we propose an alternative hypothesis we term ‘superlamellae consolidation’ to explain the initial deformation of GO paper. The additively manufactured tensile tester tested represents cost savings of >99% compared to commercial solutions in its class and offers simple customization. However, continued development is needed for the tensile tester presented here to approach the technical specifications achievable with commercial solutions.

Measuring relative positions and orientations of the tibia with respect to the femur using one-channel 3D-tracked A-mode ultrasound tracking system: A cadaveric study

The purpose of this study is to investigate the technical feasibility of measuring relative positions and orientations of the tibia with respect to the femur in an in-vitro experiment by using a 3D-tracked A-mode ultrasound system and to determine its accuracy of angular and translational measurements. As A-mode ultrasound is capable of detecting bone surface through soft tissue in a non-invasive manner, the combination of a single A-mode ultrasound transducer with an optical motion tracking system provides the possibility for digitizing the 3D locations of bony points at different anatomical regions on the thigh and the shank. After measuring bony points over a large area of both the femur and tibia, the bone models of the femur and tibia that were segmented from CT or MRI images were registered to the corresponding bony points. Then the relative position of the tibia with respect to the femur could be obtained and the angular and translational components could also be measured. A cadaveric experiment was conducted to assess its accuracy compared to the reference measurement obtained by optical markers fixed to intra-cortical bone pins placed in the femur and tibia. The results showed that the ultrasound system could achieve 0.49 ± 0.83°, 0.85 ± 1.86° and 1.85 ± 2.78° (mean ± standard deviation) errors for Flexion-Extension, Adduction-Abduction and External-Internal rotations, respectively, and -2.22 ± 3.62 mm, -2.80 ± 2.35 mm and -1.44 ± 2.90 mm errors for Anterior-Posterior, Proximal-Distal and Lateral-Medial translations, respectively. It was concluded that this technique is feasible and facilitates the integration of arrays of A-mode ultrasound transducers with an optical motion tracking system for non-invasive dynamic tibiofemoral kinematics measurement.

A Novel Small-Specimen Planar Biaxial Testing System With Full In-Plane Deformation Control

Simulations of soft tissues require accurate and robust constitutive models, whose form is derived from carefully designed experimental studies. For such investigations of membranes or thin specimens, planar biaxial systems have been used extensively. Yet, all such systems remain limited in their ability to: (1) fully prescribe in-plane deformation gradient tensor F2D, (2) ensure homogeneity of the applied deformation, and (3) be able to accommodate sufficiently small specimens to ensure a reasonable degree of material homogeneity. To address these issues, we have developed a novel planar biaxial testing device that overcomes these difficulties and is capable of full control of the in-plane deformation gradient tensor F2D and of testing specimens as small as ∼4 mm × ∼4 mm. Individual actuation of the specimen attachment points, combined with a robust real-time feedback control, enabled the device to enforce any arbitrary F2D with a high degree of accuracy and homogeneity. Results from extensive device validation trials and example tissues illustrated the ability of the device to perform as designed and gather data needed for developing and validating constitutive models. Examples included the murine aortic tissues, allowing for investigators to take advantage of the genetic manipulation of murine disease models. These capabilities highlight the potential of the device to serve as a platform for informing and verifying the results of inverse models and for conducting robust, controlled investigation into the biomechanics of very local behaviors of soft tissues and membrane biomaterials.

A study of the reproducibility and reliability of the musculo-articular stiffness of the ankle joint

The objective of this work was to evaluate the reproducibility, reliability and usefulness of the musculo-articular stiffness (MAS) of the ankle joint, measuring it by the free vibration technique. Seventeen (nine males and eight females) healthy university students were included in the study. Force (f), MAS (k) and unitary MAS (k_u) (defined as the ratio between the value of stiffness k obtained in the test (absolute terms) and the value of force (f)) were obtained. A test-retest protocol was designed and performed on the same day to determine the short-term reproducibility of f, k and k_u. Short-term reproducibility of k and k_u on 1 day in absolute terms (< 7% Coefficient of Variation (CV)) and relative reproducibility (Intraclass Correlation Coefficient (ICC) and Pearson ≥ 0.97) for both feet were obtained. The reliability of k and k_u in absol_ute terms (< 9% CV) and in relative terms (ICC and Pearson ≥0.93) based on repeating the protocol for 1 week was analysed for both feet. To analyse the usefulness, the Effect Size (ES) ratio = "Trivial" for all variables (for 1 day and 1 week) and the Smallest Worthwhile Change (SWC) ratio (Typical Error (TE)< SWC) = "GOOD" for k and k_u (1 day and 1 week) were considered. The Minimal Difference needed to be considered "real" (MD) for k_u ≅ 3.5% (1 day); k_u≅ 8.5% (1 week) (p < 0.05) was obtained. The statistical analysis carried out displayed the high reproducibility, reliability and usefulness of the MAS test, which was more consistent with k_u than k. Therefore, the unitary stiffness (k_u) proven to be representative of the mechanical response of the ankle joint obtained by free vibration techniques, which allows comparison between different subjects.

The effect of abrading and cutting instruments on machinability of dental ceramics

The aim was to investigate the effect of machining instruments on machinability of dental ceramics. Four dental ceramics, including two zirconia ceramics were machined by three types (SiC, diamond vitrified, and diamond sintered) of wheels with a hand-piece engine and two types (diamond and carbide) of burs with a high-speed air turbine. The machining conditions used were abrading speeds of 10,000 and 15,000 r.p.m. with abrading force of 100 gf for the hand-piece engine, and a pressure of 200 kPa and a cutting force of 80 gf for the air-turbine hand-piece. The machinability efficiency was evaluated by volume losses after machining the ceramics. A high-abrading speed had high-abrading efficiency (high-volume loss) compared to low-abrading speed in all abrading instruments used. The diamond vitrified wheels demonstrated higher volume loss for two zirconia ceramics than those of SiC and diamond sintered wheels. When the high-speed air-turbine instruments were used, the diamond points showed higher volume losses compared to the carbide burs for one ceramic and two zirconia ceramics with high-mechanical properties. The results of this study indicated that the machinability of dental ceramics depends on the mechanical and physical properties of dental ceramics and machining instruments. The abrading wheels show autogenous action of abrasive grains, in which ground abrasive grains drop out from the binder during abrasion, then the binder follow to wear out, subsequently new abrasive grains come out onto the instrument surface (autogenous action) and increase the grinding amount (volume loss) of grinding materials.

Real-time synchronous measurement of curing characteristics and polymerization stress in bone cements with a cantilever-beam based instrument

An instrumentation capable of simultaneously determining degree of conversion (DC), polymerization stress (PS), and polymerization exotherm (PE) in real time was introduced to self-curing bone cements. This comprises the combination of an in situ high-speed near-infrared spectrometer, a cantilever-beam instrument with compliance-variable feature, and a microprobe thermocouple. Two polymethylmethacrylate-based commercial bone cements, containing essentially the same raw materials but differ in their viscosity for orthopedic applications, were used to demonstrate the applicability of the instrumentation. The results show that for both the cements studied the final DC was marginally different, the final PS was different at the low compliance, the peak of the PE was similar, and their polymerization rates were significantly different. Systematic variation of instrumental compliance for testing reveals differences in the characteristics of PS profiles of both the cements. This emphasizes the importance of instrumental compliance in obtaining an accurate understanding of PS evaluation. Finally, the key advantage for the simultaneous measurements is that these polymerization properties can be correlated directly, thus providing higher measurement confidence and enables a more in-depth understanding of the network formation process.

Design, optimisation and testing of a compact, inexpensive elastic element for series elastic actuators

This paper presents the development of a compact torsion spring for use as an elastic element in a lightweight series elastic actuator for an active orthosis. This orthosis is going to be utilised as an assistive device for motorically impaired stroke-patients. In the design a two-step optimisation strategy was implemented to meet all requirements for the torsion spring. The first step was to identify a promising topology for the element. In the second step, the shape was optimised based on a finite element model using two different optimisation methods in order to minimise the von Mises equivalent stresses. Four promising variants of the identified topology were extracted from these calculations, one of which was then chosen as the final design. A prototype was manufactured by a laser cutting process, which is a new procedure in the context of elastic elements for series elastic actuators. The calculation results were validated successfully by measurement of the spring properties of this prototype.

Multimodal Measurements of Single-Molecule Dynamics Using FluoRBT

Single-molecule methods provide direct measurements of macromolecular dynamics, but are limited by the number of degrees of freedom that can be followed at one time. High-resolution rotor bead tracking (RBT) measures DNA torque, twist, and extension, and can be used to characterize the structural dynamics of DNA and diverse nucleoprotein complexes. Here, we extend RBT to enable simultaneous monitoring of additional degrees of freedom. Fluorescence-RBT (FluoRBT) combines magnetic tweezers, infrared evanescent scattering, and single-molecule FRET imaging, providing real-time multiparameter measurements of complex molecular processes. We demonstrate the capabilities of FluoRBT by conducting simultaneous measurements of extension and FRET during opening and closing of a DNA hairpin under tension, and by observing simultaneous changes in FRET and torque during a transition between right-handed B-form and left-handed Z-form DNA under controlled supercoiling. We discover unanticipated continuous changes in FRET with applied torque, and also show how FluoRBT can facilitate high-resolution FRET measurements of molecular states, by using a mechanical signal as an independent temporal reference for aligning and averaging noisy fluorescence data. By combining mechanical measurements of global DNA deformations with FRET measurements of local conformational changes, FluoRBT will enable multidimensional investigations of systems ranging from DNA structures to large macromolecular machines.

Characterization of Effective Orifice Areas of Mitral Prosthetic Heart Valves: An In-Vitro Study

BACKGROUND

Reference values of hemodynamic parameters for the assessment of prosthetic heart valves are necessary, and ideally need to be provided by entities independent of the valve manufacturers. Thus, the study aim was to provide, in vitro, normal reference values of the effective orifice area (EOA) for different models and sizes of mitral prosthetic valve, and to assess the determinants of EOA and mean transvalvular pressure gradient (mTPG).

METHODS

Four models of mechanical prostheses were tested (one mono-leaflet, three bi-leaflet) and four models of bioprostheses (two bovine pericardial, two porcine) on a double-activation pulsed duplicator that was specifically designed and optimized for assessing the hemodynamic performance of mitral prosthetic valves. The hemodynamic conditions were standardized and included for bioprostheses: two mitral flow volumes, three mean aortic pressures, two heart rates, and three E/A ratios. The EOAs were measured with Doppler echocardiography, using the same method (continuity equation) as was used in the clinical setting. Overestimation in term of EOA was defined according to guidelines as >0.25 cm2.

RESULTS

EOA reference values were recorded. For mono-leaflet prostheses (Medtronic Hall 7700, size 25 to 31 mm) 2.29 and 3.49; for bi-leaflet prostheses (St. Jude Medical Master and Master HP, sizes 25 to 33 mm and On-X valve, sizes 27-29 mm) 1.34 and 4.74 cm2; for porcine bioprostheses (Medtronic Mosaic CINCH, sizes 25 to 31 mm and St. Jude Epic 100, sizes 25 to 33 mm) 1.35 and 3.56 cm2; for bovine pericardial bioprosthetic valves (Edwards Perimount 6900P and Magna Ease 7300, sizes 25 to 33 mm) 1.67 and 2.36 cm2. There were some discrepancies between the normal reference EOAs measured compared to those provided by the prosthesis manufacturers, or in published reports. The bioprosthetic EOAs were shown to be smaller than the manufacturers' values in 32% of valves (by an average of 0.57 ± 0.28 cm2) versus in 7% of valves when compared to values reported elsewhere (by an average of 0.43 ± 0.17 cm2). The relationship between EOA and internal orifice area (IOA) varied according to the type of prosthesis. The EOA was close to the IOA in mechanical valves (regression slopes 0.87-0.99) but was much smaller than the IOA in bioprosthetic valves (slopes 0.25-0.30). The EOA was influenced by prosthesis diameter, prosthesis stent diameter and height, while the mTPG was influenced by EOA and heart rate.

CONCLUSIONS

The present study has provided normal reference values of EOAs for several frequently used mitral prostheses. This information may be helpful for identifying and quantifying prosthetic valve dysfunction and prosthesis-patient mismatch.

A novel miniature in-line load-cell to measure in-situ tensile forces in the tibialis anterior tendon of rats

Direct measurements of muscular forces usually require a substantial rearrangement of the biomechanical system. To circumvent this problem, various indirect techniques have been used in the past. We introduce a novel direct method, using a lightweight (~0.5 g) miniature (3 x 3 x 7 mm) in-line load-cell to measure tension in the tibialis anterior tendon of rats. A linear motor was used to produce force-profiles to assess linearity, step-response, hysteresis and frequency behavior under controlled conditions. Sensor responses to a series of rectangular force-pulses correlated linearly (R² = 0.999) within the range of 0–20 N. The maximal relative error at full scale (20 N) was 0.07% of the average measured signal. The standard deviation of the mean response to repeated 20 N force pulses was ± 0.04% of the mean response. The step-response of the load-cell showed the behavior of a PD2T2-element in control-engineering terminology. The maximal hysteretic error was 5.4% of the full-scale signal. Sinusoidal signals were attenuated maximally (-4 dB) at 200 Hz, within a measured range of 0.01–200 Hz. When measuring muscular forces this should be of minor concern as the fusion-frequency of muscles is generally much lower. The newly developed load-cell measured tensile forces of up to 20 N, without inelastic deformation of the sensor. It qualifies for various applications in which it is of interest directly to measure forces within a particular tendon causing only minimal disturbance to the biomechanical system.

Biodegradability and platelets adhesion assessment of magnesium-based alloys using a microfluidic system

Magnesium (Mg)-based stents are extensively explored to alleviate atherosclerosis due to their biodegradability and relative hemocompatibility. To ensure the quality, safety and cost-efficacy of bioresorbable scaffolds and full utilization of the material tunability afforded by alloying, it is critical to access degradability and thrombosis potential of Mg-based alloys using improved in vitro models that mimic as closely as possible the in vivo microenvironment. In this study, we investigated biodegradation and initial thrombogenic behavior of Mg-based alloys at the interface between Mg alloys' surface and simulated physiological environment using a microfluidic system. The degradation properties of Mg-based alloys WE43, AZ31, ZWEK-L, and ZWEK-C were evaluated in complete culture medium and their thrombosis potentials in platelet rich plasma, respectively. The results show that 1) physiological shear stress increased the corrosion rate and decreased platelets adhesion rate as compared to static immersion; 2) secondary phases and impurities in material composition induced galvanic corrosion, resulting in higher corrosion resistance and platelet adhesion rate; 3) Mg-based alloys with higher corrosion rate showed higher platelets adhesion rate. We conclude that a microfluidic-based in vitro system allows evaluation of biodegradation behaviors and platelets responses of Mg-based alloys under specific shear stress, and degradability is related to platelets adhesion.

Flow and fracture behavior of aluminum alloy 6082-T6 at different tensile strain rates and triaxialities

This study aims to investigate the flow and fracture behavior of aluminum alloy 6082-T6 (AA6082-T6) at different strain rates and triaxialities. Two groups of Charpy impact tests were carried out to further investigate its dynamic impact fracture property. A series of tensile tests and numerical simulations based on finite element analysis (FEA) were performed. Experimental data on smooth specimens under various strain rates ranging from 0.0001~3400 s-1 shows that AA6082-T6 is rather insensitive to strain rates in general. However, clear rate sensitivity was observed in the range of 0.001~1 s-1 while such a characteristic is counteracted by the adiabatic heating of specimens under high strain rates. A Johnson-Cook constitutive model was proposed based on tensile tests at different strain rates. In this study, the average stress triaxiality and equivalent plastic strain at facture obtained from numerical simulations were used for the calibration of J-C fracture model. Both of the J-C constitutive model and fracture model were employed in numerical simulations and the results was compared with experimental results. The calibrated J-C fracture model exhibits higher accuracy than the J-C fracture model obtained by the common method in predicting the fracture behavior of AA6082-T6. Finally, the Scanning Electron Microscope (SEM) of fractured specimens with different initial stress triaxialities were analyzed. The magnified fractographs indicate that high initial stress triaxiality likely results in dimple fracture.

Automated transepithelial electrical resistance measurements of the EpiDerm reconstructed human epidermis model

Understanding the effect of exogenous substances on human skin is critical for toxicology assessment. To address this, numerous artificial models of the topmost layer of human skin, so-called reconstructed human epidermis (RhE), have been created in an attempt to produce a clear analogue for testing. Unfortunately, current testing modalities still rely on endpoint assays and are not capable of monitoring time-resolved changes in barrier function without using numerous redundant samples. In this work, a novel, time-resolved approach is realized by monitoring the transepithelial electrical resistance (TEER) of MatTek EpiDerm® reconstructed human epidermis model, utilizing an automated protocol with the Intelligent Mobile Lab for in vitro diagnostics (IMOLA-IVD).

Immunoaffinity based methods are superior to kits for purification of prostate derived extracellular vesicles from plasma samples

BACKGROUND

The ability to isolate extracellular vesicles (EVs) such as exosomes or microparticles is an important method that is currently not standardized. While commercially available kits offer purification of EVs from biofluids, such purified EV samples will also contain non-EV entities such as soluble protein and nucleic acids that could confound subsequent experimentation. Ideally, only EVs would be isolated and no soluble protein would be present in the final EV preparation.

METHODS

We compared commercially available EV isolation kits with immunoaffinity purification techniques and evaluated our final EV preparations using atomic force microscopy (AFM) and nanoscale flow cytometry (NFC). AFM is the only modality capable of detecting distinguishing soluble protein from EVs which is important for downstream proteomics approaches. NFC is the only technique capable of quantitating the proportion of target EVs to non-target EVs in the final EV preparation.

RESULTS

To determine enrichment of prostate derived EVs relative to non-target MPs, anti-PSMA (Prostate Specific Membrane Antigen) antibodies were used in NFC. Antibody-based immunoaffinity purification generated the highest quality of prostate derived EV preparations due to the lack of protein and RNA present in the samples. All kits produced poor purity EV preparations that failed to deplete the sample of plasma protein.

CONCLUSIONS

While attractive due to their ease of use, EV purification kits do not provide substantial improvements in isolation of EVs from biofluids such as plasma. Immunoaffinity approaches are more efficient and economical and will also eliminate a significant portion of plasma proteins which is necessary for downstream approaches.

Bonding Efficacy and Fracture Pattern of Adhesives Submitted to Mechanical Aging with the Rub&Roll Device

PURPOSE

To evaluate the effect of water storage and cyclic loading on the microtensile bond strength (μTBS) and fracture pattern of adhesives to dentin.

MATERIALS AND METHODS

Midcoronal dentin surfaces (n = 36) were prepared and composite restorations were built up using two adhesives (self-etch and etch-and-rinse). The specimens were randomly divided into 3 groups according to the aging conditions (n = 6): 1.

CONTROL

storage in water for 24 h (CO); 2. water storage: storage in water for 6 months (WS); 3. mechanical loading: 750,000 mechanical cycles (ML) using the Rub&Roll loading device. Specimens were sections into beams and the μTBS was tested. Fracture patterns were analyzed using stereomicroscopy and fractographic analysis was performed using SEM. μTBS data (n = 53-72 specimens) were subjected to two-way ANOVA and Tukey's post-hoc test. The chi-squared test was used to compare the distribution of failure modes (p < 0.05).

RESULTS

Aging conditions and adhesives significantly affected μTBS (p < 0.01). The CO group showed no difference between materials and had highest μTBS. After WS, the self-etch adhesive showed higher μTBS than did the etchand- rinse adhesive. ML resulted in lower μTBS for both adhesives. Materials (p < 0.01) and aging (p < 0.01) significantly influenced the distribution of failure modes. SEM analysis showed that specimens submitted to WS or ML showed features of degradation and fatigue at the fractured interface, depending on the adhesive.

CONCLUSION

Mechanical loading had a negative effect on the bonding efficacy of both adhesives and influenced the fracture pattern, with specimens presenting a different fracture surface from that observed in water-stored specimens.

Deposition of phosphate coatings on titanium within scaffold structure

PURPOSE

Existing knowledge about the appearance, thickness, and chemical composition of phosphate coatings on titanium inside porous structures is insufficient. Such knowledge is important for the design and fabrication of porous implants.

METHODS

Metallic scaffolds were fabricated by selective laser melting of 316L stainless steel powder. Phosphate coatings were deposited on Ti sensors placed either outside the scaffolds or in the holes in the scaffolds. The electrochemically-assisted cathodic deposition of phosphate coatings was performed under galvanostatic conditions in an electrolyte containing the calcium and phosphate ions. The phosphate deposits were microscopically investigated; this included the performance of mass weight measurements and chemical analyses of the content of Ca2+ and  24 PO ions after the dissolution of deposits.

RESULTS

The thicknesses of the calcium phosphate coatings were about 140 and 200 nm for isolated titanium sensors and 170 and 300 nm for titanium sensors placed inside pores. Deposition of calcium phosphate occurred inside the pores up to 150 mm below the scaffold surface. The deposits were rich in Ca, with a Ca/P ratio ranging from 2 to 2.5.

CONCLUSIONS

Calcium phosphate coatings can be successfully deposited on a Ti surface inside a model scaffold. An increase in cathodic current results in an increase in coating thickness. Any decrease in the cathodic current inside the porous structure is slight. The calcium phosphate inside the pores has a much higher Ca/P ratio than that of stoichiometric HAp, likely due to a gradual increase in Ca fraction with distance from the surface.

Drilling resistance: A method to investigate bone quality

PURPOSE

Bone drilling is a major part of orthopaedic surgery performed during the internal fixation of fractured bones. At present, information related to drilling force, drilling torque, rate of drill-bit penetration and drill-bit rotational speed is not available to orthopaedic surgeons, clinicians and researchers as bone drilling is performed manually.

METHODS

This study demonstrates that bone drilling force data if recorded in-vivo, during the repair of bone fractures, can provide information about the quality of the bone. To understand the variability and anisotropic behaviour of cortical bone tissue, specimens cut from three anatomic positions of pig and bovine were investigated at the same drilling speed and feed rate.

RESULTS

The experimental results showed that the drilling force does not only vary from one animal bone to another, but also vary within the same bone due to its changing microstructure. Drilling force does not give a direct indication of bone quality; therefore it has been correlated with screw pull-out force to provide a realistic estimation of the bone quality. A significantly high value of correlation (r2 = 0.93 for pig bones and r2 = 0.88 for bovine bones) between maximum drilling force and normalised screw pull-out strength was found.

CONCLUSIONS

The results show that drilling data can be used to indicate bone quality during orthopaedic surgery.

The Influence of Specimen Attachment and Dimension on Microtensile Strength

The higher microtensile bond strength values found for specimens with a smaller cross-sectional area are often explained by the lower occurrence of internal defects and surface flaws. We hypothesized that this aberrant behavior is mainly caused by the lateral way of attachment of the specimens to the testing device, which makes the strength dependent on the thickness. This study showed that composite bars of 1×1×10, 1×2×10, and 1×3×10mm attached at their 1-mm-wide side (situation A) fractured at loads of the same magnitude, as a result of which the microtensile strength (μTS), calculated as F/A (force at fracture/cross-sectional area), significantly increased for specimens with decreasing thickness. Attachment at the 1-, 2-, or 3-mm-wide side (situation B) resulted in equal μTS values (P > 0.05). Finite element analysis showed different stress patterns for situation A, but comparable patterns for situation B. Both situations showed the same maximum stress at fracture.

A Shearing-Stretching Device That Can Apply Physiological Fluid Shear Stress and Cyclic Stretch Concurrently to Endothelial Cells

Endothelial cell (EC) morphology and functions can be highly impacted by the mechanical stresses that the cells experience in vivo. In most areas in the vasculature, ECs are continuously exposed to unsteady blood flow-induced shear stress and vasodilation-contraction-induced tensile stress/strain simultaneously. Investigations on how ECs respond to combined shear stress and tensile strain will help us to better understand how an altered mechanical environment affects EC mechanotransduction, dysfunction, and associated cardiovascular disease development. In the present study, a programmable shearing and stretching device that can apply dynamic fluid shear stress and cyclic tensile strain simultaneously to cultured ECs was developed. Flow and stress/strain conditions in the device were simulated using a fluid structure interaction (FSI) model. To characterize the performance of this device and the effect of combined shear stress-tensile strain on EC morphology, human coronary artery ECs (HCAECs) were exposed to concurrent shear stress and cyclic tensile strain in the device. Changes in EC morphology were evaluated through cell elongation, cell alignment, and cell junctional actin accumulation. Results obtained from the numerical simulation indicated that in the "in-plane" area of the device, both fluid shear stress and biaxial tensile strain were uniform. Results obtained from the in vitro experiments demonstrated that shear stress, alone or combined with cyclic tensile strain, induced significant cell elongation. While biaxial tensile strain alone did not induce any appreciable change in EC elongation. Fluid shear stress and cyclic tensile strain had different effects on EC actin filament alignment and accumulation. By combining various fluid shear stress and cyclic tensile strain conditions, this device can provide a physiologically relevant mechanical environment to study EC responses to physiological and pathological mechanical stimulation.

Effect of various testing conditions on results for a handheld reference point indentation instrument in horses

OBJECTIVE

To compare results obtained with a handheld reference point indentation instrument for bone material strength index (BMSi) measurements in the equine third metacarpal bone for various testing conditions.

SAMPLE

24 third metacarpal bones.

PROCEDURES

Third metacarpal bones from both forelimbs of 12 horses were obtained. The dorsal surface of each bone was divided into 6 testing regions. In vivo and ex vivo measurements of BMSi were obtained through the skin and on exposed bone, respectively, to determine effects of each testing condition. Difference plots were used to assess agreement between BMSi obtained for various conditions. Linear regression analysis was used to assess effects of age, sex, and body weight on BMSi. A mixed-model ANOVA was used to assess effects of age, sex, limb, bone region, and testing condition on BMSi values.

RESULTS

Indentation measurements were performed on standing sedated and recumbent anesthetized horses and on cadaveric bone. Regional differences in BMSi values were detected in adult horses. A significant linear relationship (r(2) = 0.71) was found between body weight and BMSi values. There was no difference between in vivo and ex vivo BMSi values. A small constant bias was detected between BMSi obtained through the skin, compared with values obtained directly on bone.

CONCLUSIONS AND CLINICAL RELEVANCE

Reference point indentation can be used for in vivo assessment of the resistance of bone tissue to microfracture in horses. Testing through the skin should account for a small constant bias, compared with results for testing directly on exposed bone.

Inspection of thick welded joints using laser-ultrasonic SAFT

The detection of defects in thick butt joints in the early phase of multi-pass arc welding would be very valuable to reduce cost and time in the necessity of reworking. As a non-contact method, the laser-ultrasonic technique (LUT) has the potential for the automated inspection of welds, ultimately online during manufacturing. In this study, testing has been carried out using LUT combined with the synthetic aperture focusing technique (SAFT) on 25 and 50mm thick butt welded joints of steel both completed and partially welded. EDM slits of 2 or 3mm height were inserted at different depths in the multi-pass welding process to simulate a lack of fusion. Line scans transverse to the weld are performed with the generation and detection laser spots superimposed directly on the surface of the weld bead. A CCD line camera is used to simultaneously acquire the surface profile for correction in the SAFT processing. All artificial defects but also real defects are visualized in the investigated thick butt weld specimens, either completed or partially welded after a given number of passes. The results obtained clearly show the potential of using the LUT with SAFT for the automated inspection of arc welds or hybrid laser-arc welds during manufacturing.

Intracranial Aneurysm Model for Detachable Coil Testing

Intracranial aneurysm is major vascular disease which is life-threatening and challenging treatment. Detachable coil is one of the standard treatments. Because of little knowledge about it, the detachable coils were evaluated by various methods. Animal aneurysm models were also used to test this equipment. In the present study, sidewall aneurysms were created on common carotid arteries of Landrace-Yorkshire-Durocswine. External jugular vein grafts were used as aneurysm sac. End-to-side anastomosis was done. Ten aneurysms were created successfully in 5 swine. There is no perioperative death. This animal aneurysm model is appropriated for coil testing especially in the histopathology aspect.

Using a Dental Student Exercise on Shear Bond Testing to Both Provide Skills Practice and Demonstrate a Research Process

This article describes an exercise with junior dental students at the University of the Pacific Arthur A. Dugoni School of Dentistry designed in part to serve the requirement for dental accreditation Standard 6-3 ("Dental education programs must provide opportunities, encourage, and support student participation in research and other scholarly activities mentored by faculty"). The exercise has been conducted for seven years and has been found to provide a distinctive and important experience to the education of these dental students. The exercise has three aims. First, it is an exercise in which students practice their skills with dental bonding; second, it serves as a tool to give immediate feedback on these skills that is otherwise not possible in a real patient situation; and third, it demonstrates to the students how data from the exercise with the students as subjects can be used in a research study. The project thus serves as an innovative way to use a skill-building exercise to educate students about research at the same time.

Design, fabrication and characterization of a pure uniaxial microloading system for biologic testing

The field of mechanobiology aims to understand the role the mechanical environment plays in directing cell and tissue development, function and disease. The empirical aspect of the field requires the development of accurate, reproducible and reliable loading platforms that can apply microprecision mechanical load. In this study we designed, fabricated and characterized a pure uniaxial loading platform capable of testing small synthetic and organic specimens along a horizontal axis. The major motivation for platform development was in stimulating bone cells seeded on elastomeric substrates and soft tissue loading. The biological uses required the development of culturing fixtures and environmental chamber. The device utilizes commercial microactuators, load cells and a rail/carriage block system. Following fabrication, acceptable performance was verified by suture tensile testing.

Right-Left Differences in Knee Extension Stiffness for the Normal Rat Knee: In Vitro Measurements Using a New Testing Apparatus

Knee stiffness following joint injury or immobilization is a common clinical problem, and the rat has been used as a model for studies related to joint stiffness and limitation of motion. Knee stiffness measurements have been reported for the anesthetized rat, but it is difficult to separate the contributions of muscular and ligamentous restraints to the recorded values. in vitro testing of isolated rat knees devoid of musculature allows measurement of joint structural properties alone. In order to measure the effects of therapeutic or surgical interventions designed to alter joint stiffness, the opposite extremity is often used as a control. However, right-left stiffness differences for the normal rat knee have not been reported in the literature. If stiffness changes observed for a treatment group are within the normal right-left variation, validity of the results could be questioned. The objectives of this study were to utilize a new testing apparatus to measure right-left stiffness differences during knee extension in a population of normal rat knees and to document repeatability of the stiffness measurements on successive testing days. Moment versus rotation curves were recorded for 15 right-left pairs of normal rat knees on three consecutive days, with overnight specimen storage in a refrigerator. Each knee was subjected to ten loading-unloading cycles, with the last loading curve used for analysis. Angular rotation (AR), defined here as the change in flexion-extension angle from a specified applied joint moment, is commonly used as a measure of overall joint stiffness. For these tests, ARs were measured from the recorded test curves with a maximum applied extension moment of 100 g cm. Mean rotations for testing days 2 and 3 were 0.81-1.25 deg lower (p < 0.001) than for day 1, but were not significantly different from each other. For each testing day, mean rotations for right knees were 1.12-1.30 deg greater (p < 0.001) than left knees. These right-left stiffness differences should be considered when interpreting the results of knee treatment studies designed to alter knee stiffness when using the opposite extremity as a control.

[Estimations of mechanical properties of bones using nanoindentation]

Nanoindentation has been applied in recent years to measure the mechanical properties of bone tissues at a microscopic scale, overcoming the limitations of traditional mechanical testing techniques for small samples. This method is precise and accurate and appears well suited for measuring mechanical properties in bone. Dynamic nanoindentation is also a promising method of measuring the viscoelastic properties of bone tissues at smaller length and load scales than allowed by other testing methods, thus allowing individual constituents and local regions of inhomogeneous tissues to be characterized individually. This article describes our nanoindentation studies of bone tissues with recent studies.

Characterisation of CIME, an experimental chamber for simulating interactions between materials of the cultural heritage and the environment

An approach consisting in combining in situ and laboratory experiments is often favoured for investigating the mechanisms involved in the weathering of the materials of the cultural heritage. However, the realistic simulation in the laboratory of the environmental conditions ruling the interactions of atmospheric compounds with materials is a very complex task. The aim of this work is to characterise CIME, a new chamber specially built to simulate the interactions between materials of the cultural heritage and the environment. The originality of this instrument is that beside the usual climatic parameters (temperature, relative humidity, solar radiation) and gaseous pollutants, it also allows the controlled injection of different types of particulate matter such as terrigenous, marine and anthropogenic. Therefore, varied realistic atmospheric environments (marine or urban) can be easily simulated within CIME. In addition to the technical description of CIME, this paper shows the first results obtained by the impact of gaseous pollutants on non-durable glass, bronze and limestone. The first experiments for the deposition of different particles (calcite, clays, soot and halite) are also presented.

Study of the measurement for the diffusion coefficient by digital holographic interferometry

In the measurement of the diffusion coefficient by digital holographic interferometry, the conformity between the experiment and the ideal physical model is lacking analysis. Two data processing methods are put forward to overcome this problem. By these methods, it is found that there is obvious asymmetry in the experiment and the asymmetry is becoming smaller with time. Besides, the initial time for diffusion cannot be treated as a constant throughout the whole experiment. This means that there is a difference between the experiment and the physical model. With these methods, the diffusion coefficient of KCl in water at 0.33  mol/L and 25°C is measured. When the asymmetry is ignored, the result is 1.839×10(-9)  m2/s, which is in good agreement with the data in the literature. Because the asymmetry is becoming smaller with time, the experimental data in the latter time period conforms to the ideal physical model. With this idea, a more accurate diffusion coefficient is 2.003×10(-9)  m2/s, which is about 10% larger than the data in the literature.

Nanomechanical properties of human skin and introduction of a novel hair indenter

The mechanical resistance of the stratum corneum, the outermost layer of skin, to deformation has been evaluated at different length scales using Atomic Force Microscopy. Nanomechanical surface mapping was first conducted using a sharp silicon tip and revealed that Young׳s modulus of the stratum corneum varied over the surface with a mean value of about 0.4GPa. Force indentation measurements showed permanent deformation of the skin surface only at high applied loads (above 4µN). The latter effect was further demonstrated using nanomechanical imaging in which the obtained depth profiles clearly illustrate the effects of increased normal force on the elastic/plastic surface deformation. Force measurements utilizing the single hair fiber probe supported the nanoindentation results of the stratum corneum being highly elastic at the nanoscale, but revealed that the lateral scale of the deformation determines the effective elastic modulus.This result resolves the fact that the reported values in the literature vary greatly and will help to understand the biophysics of the interaction of razor cut hairs that curl back during growth and interact with the skin.

Static and dynamic fatigue behavior of topology designed and conventional 3D printed bioresorbable PCL cervical interbody fusion devices

Recently, as an alternative to metal spinal fusion cages, 3D printed bioresorbable materials have been explored; however, the static and fatigue properties of these novel cages are not well known. Unfortunately, current ASTM testing standards used to determine these properties were designed prior to the advent of bioresorbable materials for cages. Therefore, the applicability of these standards for bioresorbable materials is unknown. In this study, an image-based topology and a conventional 3D printed bioresorbable poly(ε)-caprolactone (PCL) cervical cage design were tested in compression, compression-shear, and torsion, to establish their static and fatigue properties. Difficulties were in fact identified in establishing failure criteria and in particular determining compressive failure load. Given these limitations, under static loads, both designs withstood loads of over 650 N in compression, 395 N in compression-shear, and 0.25 Nm in torsion, prior to yielding. Under dynamic testing, both designs withstood 5 million (5M) cycles of compression at 125% of their respective yield forces. Geometry significantly affected both the static and fatigue properties of the cages. The measured compressive yield loads fall within the reported physiological ranges; consequently, these PCL bioresorbable cages would likely require supplemental fixation. Most importantly, supplemental testing methods may be necessary beyond the current ASTM standards, to provide more accurate and reliable results, ultimately improving preclinical evaluation of these devices.