Effects of Light Attenuation on Local and Bulk Mechanical Properties of Photopolymerized PEG Hydrogels

Cell experiments investigating cell behavior as a function of material stiffness are often carried out on the surface of hydrogels. An assumption that the bulk hydrogel mechanical properties represent the surface properties is often employed but in many cases is not valid. In photo-initiated radical polymerization, photons are absorbed by initiator chromophores generating high energy electrons. As photons progress through the prepolymer solution, the intensity of light that reaches the distal end of the solution is decreased through this attenuation. This work aims to determine whether light attenuation plays a significant role in local stiffness within a poly(ethylene glycol) diacrylate (PEGDA) hydrogel, compared to its bulk stiffness. Differences in bulk properties were tested by varying the polymerization parameters of hydrogel cylindrical plugs, including sample thickness (0.7mm – 1.2mm), photoinitiator type (EosinY vs LAP), PEGDA weight percent, and exposure time. Mechanical loading data of the plugs was analyzed to reveal the relationships between the physical properties (e.g. thickness, surface area, volume) and chemical properties (e.g. monomer and initiator concentrations, exposure settings). Preliminary data suggests that an appreciable difference in physical properties exists between gels of differing thickness (1.0mm vs 0.3mm based on gel point). The goals of this work are to quantify the extent of this difference based on sample thickness, and to compare the bulk stiffness data with local surface stiffness measurements obtained using an AFM nano-indentation technique and determine whether changes in bulk properties carry over to changes in surface properties

Understanding the Effect of Body Weight on Muscle Activity During Unilateral Hopping

Running can be described as a series of bilateral single-legged jumps and landings. Interestingly, single-legged jumps and landings are qualitatively more difficult unilaterally than bilaterally known as bilateral deficit syndrome (BDS). For example, one leg will produce less mechanical energy while jump squatting unilaterally than it would produce if both legs worked synchronously. The analysis of dynamic conditions under different levels of body weight support of the hopping movement may prove useful to understanding the bilateral deficit. Purpose: To compare muscle activity of the lower extremity during single-legged hopping at different levels of body weight support. Methods: The research study was recently approved by the Institutional Review Board and data collection has begun. Therefore, no data are presented in the abstract at this time. Subjects will be equipped with electromyography (EMG) leads to measure muscle activity of the rectus femoris, semitendinosus, medial gastrocnemius, and tibialis anterior. Subjects will be asked to perform 5 trials of hopping forwards at a preferred speed (PS) for 1 minute at varying levels of body weight (80%, 70%, 60%, 50%, 40%). EMG data of all four muscles will be compared across the separate body weight control conditions

Pediatric Artificial Lung: Improving a Large Animal Model of ESLF

Undergraduate Research Opportunity Program (UROP)http://deepblue.lib.umich.edu/bitstream/2027.42/116115/1/Pediatric_Artificial_Lung_Improving_Large_Animal_Model_ESLF.pd

Dynamic Modeling of Fluid Flow within Three-Dimensional Perfusion Bioreactor

Three-dimensional perfusion bioreactors have been shown to enhance cell viability and function through improved nutrient exchange. However, the ideal bioreactor scaffold geometry is still unknown. The focus of this study is to use computational fluid flow studies to inform bioreactor design. Specifically, we will model the effect of bioreactor design on fluid shear stress and then correlate these values with stem cell viability in the bioreactor. Previous studies have shown that the maximum shear stress level for the viability of human mesenchymal stem cells (hMSCs) is 0.3 dynes/cm2. Two distinct Computer Aided Design models were created consisting of parallel planes of pillars (0.5 mm diameter, 2 mm height) in a linear array with 1 mm center to center spacing. One design consists of seven horizontal layers inserted into a 3D printed housing while the other consists of five layers encapsulated by a cylinder matching the inner diameter of silicon tubing (0.5 in). For in vitro testing, both scaffold designs were created by 3D printing and were coated with collagen to facilitate hMSC adhesion. To quantify results, hMSCs were harvested from the scaffolds for analyses by picogreen DNA quantification for total DNA and cell viability, and immunohistochemical markers for stem cell population maintenance. In the effort to establish a predictive model, we will compare the flow simulation results to the degree of cell proliferation in the bioreactor experiment. The significance of cell proliferation will indicate further improvements on the bioreactor design

Hygrothermal performance of wood-hemp insulation in timber frame wall panels with and without a vapour barrier

An in situ experiment on a full-scale timber frame test building was carried out to study the hygrothermal performance of wood-hemp composite insulation in timber frame wall panels with and without a vapour barrier. The heat transfer properties and the likelihood of mould growth and condensation in the panels were compared. Step changes in the internal relative humidity were performed to explore the effects of high, normal and low internal moisture loads on the wall panels. No significant difference in the average equivalent thermal transmittance (U-values) between the panels with and without a vapour barrier was observed. The average equivalent U-values of the panels were close to the U-values calculated from the manufacturers’ declared thermal conductivity values of the insulation. The likelihood of condensation was higher at the interface of the wood-hemp insulation and the oriented strand board (OSB) in the panel without a vapour barrier. In terms of the parametric assessment of the mould germination potential, the relative humidity, the temperature and the exposure conditions in the insulation-OSB interfaces of the panel without a vapour barrier were found to be more favourable to the germination of mould spores. Nonetheless, when the insulations were dismantled, no mould was visually detected

Patient-Specific Prosthetic Fingers by Remote Collaboration - A Case Study

The concealment of amputation through prosthesis usage can shield an amputee from social stigma and help improve the emotional healing process especially at the early stages of hand or finger loss. However, the traditional techniques in prosthesis fabrication defy this as the patients need numerous visits to the clinics for measurements, fitting and follow-ups. This paper presents a method for constructing a prosthetic finger through online collaboration with the designer. The main input from the amputee comes from the Computer Tomography (CT) data in the region of the affected and the non-affected fingers. These data are sent over the internet and the prosthesis is constructed using visualization, computer-aided design and manufacturing tools. The finished product is then shipped to the patient. A case study with a single patient having an amputated ring finger at the proximal interphalangeal joint shows that the proposed method has a potential to address the patient's psychosocial concerns and minimize the exposure of the finger loss to the public.Comment: Open Access articl