C.P. Stephens

Cell proliferation, viability, and in vitro differentiation of equine mesenchymal stem cells seeded on bacterial cellulose hydrogel scaffolds.

The culture of multipotent mesenchymal stem cells on natural biopolymers holds great promise for treatments of connective tissue disorders such as osteoarthritis. The safety and performance of such therapies relies on the systematic in vitro evaluation of the developed stem cell-biomaterial constructs prior to in vivo implantation. This study evaluates bacterial cellulose (BC), a biocompatible natural polymer, as a scaffold for equine-derived bone marrow mesenchymal stem cells (EqMSCs) for application in bone and cartilage tissue engineering. An equine model was chosen due to similarities in size, load and types of joint injuries suffered by horses and humans. Lyophilized and critical point dried BC hydrogel scaffolds were characterized using scanning electron microscopy (SEM) to confirm nanostructure morphology which demonstrated that critical point drying induces fibre bundling unlike lyophilisation. EqMSCs positively expressed the undifferentiated pluripotent mesenchymal stem cell surface markers CD44 and CD90. The BC scaffolds were shown to be cytocompatible, supporting cellular adhesion and proliferation, and allowed for osteogenic and chondrogenic differentiation of EqMSCs. The cells seeded on the BC hydrogel were shown to be viable and metabolically active. These findings demonstrate that the combination of a BC hydrogel and EqMSCs are promising constructs for musculoskeletal tissue engineering applications.

A low power wireless apnea detection system based on pyroelectric sensor

The paper presents a fully integrated system for apnea detection. Apnea has been one of the leading causes of death in the USA and it is even more critical for premature neonatal infants. A prototype device with the pyroelectric sensor and a wireless telemetry designed in 0.5 μm CMOS process is presented which overcomes the complexity of the point of care diagnosis of sleeping disorders.

Fabricating neuromast-inspired gel structures for membrane-based hair cell sensing

Recent research has shown that a new class of mechanical sensor, assembled from biomolecules and which features an artificial cell membrane as the sensing element, can be used to mimic basic hair cell mechanotransduction in vertebrates. The work presented in this paper is motivated by the need to increase sensor performance and stability by refining the methods used to fabricate and connect lipid-encapsulated hydrogels. Inspired by superficial neuromasts found on fish, three hydrogel materials are compared for their ability to be readily shaped into neuromast-inspired geometries and enable lipid bilayer formation using self-assembly at an oil/water interface. Agarose, polyethylene glycol (PEG, 6kg/mole), and hydroxyethyl methacrylate (HEMA) gel materials are compared. The results of this initial study determined that UV-curable gel materials such as PEG and HEMA enable more accurate shaping of the gel-needed for developing a sensor that uses a gel material both for mechanical support and membrane formation-compared to agarose. However, the lower hydrophobicity of agarose and PEG materials provide a more fluid, water-like environment for membrane formation-unlike HEMA. In working toward a neuromast-inspired design, a final experiment demonstrates that a bilayer can also be formed directly between two lipid-covered PEG surfaces. These initial results suggest that candidate gel materials with a low hydrophobicity, high fluidity, and a low modulus can be used to provide membrane support.

Spectroscopic Investigations on the Effect of Proton Bombardment of Polyimide

The effect of the radiation component of the space environment on polyimide films is reviewed. Experimental data obtained by electron spin resonance and dynamical mechanical analysis proved that the ionizing radiation generates free radicals with a long lifetime through a dominant chain scission mechanism. The radiation-induced shift of the glass transition of polyimide towards lower values confirms the decrease of the average molecular mass of the polymer during irradiation. The importance of polyimide for space exploration is critically analyzed.