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Research Papers

ASME J of Medical Diagnostics. 2019;2(3):031001-031001-7. doi:10.1115/1.4042926.

A bending test scheme for accurately determining the structural elasticity of human nails is reported. The structural elasticity expresses the deformability of a multilayered material for bending, and it is the flexural rigidity without depending on the external dimensions. The human nail samples used in this study were prepared from the free ends of the nails and are, therefore, curved, so the equation to determine the structural elasticity was derived from elastic, curved beam theory. The structural elasticity of the nail samples determined by the bending tests was found to be 2.19 GPa, and this value decreased by about 50% when nail polish was put on the nails. Lower value of the Young's modulus of the nail polish was found to cause decrease in the structural elasticity of the sample. Moreover, we also measured the structural elasticity of samples of hair prepared from the same person by the bending tests. Surprisingly, the structural elasticity of the hair (4.37 GPa) was found to be twice that of the nails.

Commentary by Dr. Valentin Fuster
ASME J of Medical Diagnostics. 2019;2(3):031002-031002-9. doi:10.1115/1.4042874.

Convection-enhanced delivery (CED) is an investigational therapy developed to circumvent the limitations of drug delivery to the brain. Catheters are used in CED to locally infuse therapeutic agents into brain tissue. CED has demonstrated clinical utility for treatment of malignant brain tumors; however, CED has been limited by lack of CED-specific catheters. Therefore, we developed a multiport, arborizing catheter to maximize drug distribution for CED. Using a multiphasic finite element (FE) framework, we parametrically determined the influence of design variables of the catheter on the dispersal volume of the infusion. We predicted dispersal volume of a solute infused in a permeable hyperelastic solid matrix, as a function of separation distance (ranging from 0.5 to 2.0 cm) of imbedded infusion cavities that represented individual ports in a multiport catheter. To validate the model, we compared FE solutions of pressure-controlled infusions to experimental data of indigo carmine dye infused in agarose tissue phantoms. The Tc50, defined as the infusion time required for the normalized solute concentration between two sources to equal 50% of the prescribed concentration, was determined for simulations with infusion pressures ranging from 1 to 4 kPa. In our validated model, we demonstrate that multiple ports increase dispersal volume with increasing port distance but are associated with a significant increase in infusion time. Tc50 increases approximately tenfold when doubling the port distance. Increasing the infusion flow rate (from 0.7 μL/min to 8.48 μL/min) can mitigate the increased infusion time. In conclusion, a compromise of port distance and flow rate could improve infusion duration and dispersal volume.

Commentary by Dr. Valentin Fuster
ASME J of Medical Diagnostics. 2019;2(3):031003-031003-8. doi:10.1115/1.4043403.

The global prevalence of asthma and chronic obstructive pulmonary disease (COPD) is on the order of hundreds of millions of individuals. The most common treatment approach is to take a self-administered inhaled medication. This study focuses on pressurized metered-dose inhalers (MDIs) where, unfortunately, rates of mishandling and misuse are extremely high and lead to improper treatment. One significant challenge results from the timing miscoordination of the medicine dispersion and inhalation breath. To address this, this study demonstrates the feasibility of automating the timing of the medicine dispersion by integrating a shape memory alloy (SMA) actuator and a differential pressure sensor into the casing of a traditional MDI. The approach is to measure the vacuum pressure created by an inspiratory breath, evaluate criteria indicating an acceptable breath, and if those criteria are met, heat the SMA actuator to depress the cartridge and disperse medicine. To meet actuation requirements and reliably depress the inhaler cartridge, two concepts for configuring an SMA wire were designed and compared with respect to complexity, actuation timing, and energy consumption. The proposed concept was able to disperse medicine in 263 ms, averaged over 100 actuations on a single battery charge, facilitating the early dispersion of medicine during an inhalation breath. By describing the design process of an SMA-actuated MDI that does not result in a significant increase of its weight or size, this study provides a practical technological approach for reducing the improper treatment of asthma and COPD due to timing miscoordination.

Commentary by Dr. Valentin Fuster
ASME J of Medical Diagnostics. 2019;2(3):031004-031004-7. doi:10.1115/1.4043537.

Chronic exertional compartment syndrome (CECS) is an exercise-induced condition, in which high pressure develops in one or several lower leg compartments, resulting in pain, numbness, and temporary muscle paresis. Diagnosis of CECS is assisted by measurements of intracompartment pressures (ICP) at rest, 1-min and 5-min after cessation of running exercise (Pedowitz criteria). ICP is measured via needle manometry, which is an invasive procedure. We have recently shown that intramuscular pressure is correlated to shear modulus measured via shear wave elastography (SWE) (Spearman's correlation coefficient = 0.99). The objectives of this study were to quantify temporal changes in shear modulus of muscle in lower leg compartments of healthy individuals before and after running exercise, and to evaluate a Pedowitz-like criterion for diagnosis of CECS using muscle shear modulus as biomarker. Specifically, the shear modulus of the tibialis anterior (TA) and peroneus longus (PL) was measured at time intervals of 1 min for 10 min after cessation of exercise. The shear modulus of the TA, PL, Soleus and Tibialis posterior were also measured bilaterally before, and at 1- and 5-min after exercise in a procedure that resembles the Pedowitz test for ICP. The shear modulus of all compartments increased significantly in both legs 1-min postexercise and gradually decreased to prerunning values. 50% of such decrease occurred at between 3 and 5 min after cessation of exercise. Additionally, the change in shear modulus followed a similar pattern than ICP in the Pedowitz-like protocol. Therefore, SWE has the potential to diagnose CECS noninvasively.

Commentary by Dr. Valentin Fuster

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