Design, Fabrication, Structure Optimization and Pressure Sensing Demonstration of COC Piezoelectret Sensor and Sensor Array.

This study reported on the design and fabrication of a pseudo-piezoelectric material (piezoelectret) from cyclic olefin copolymer (COC) based on a micropillar structure. The fabrication feasibility of such structure was explored and piezoelectret with the good piezoelectric activity (characterized by quasi-static piezoelectric coefficient d33) was demonstrated. Response surface method with a central composite design was employed to investigate the effects of the structure parameter on the piezoelectric coefficient d33. An optimal structure design was obtained and was validated by experiments. With the optimal design, d33 can reach an exceptional high value of ~9000 pC/N under low pressure. The charging process and the electrical and electromechanical characteristics were further investigated by experimentation and modeling. We further demonstrated the scalability of the fabrication process and demonstrated the application of these sensors in position specific pressure sensing (pressure mapping).

Additively manufactured biomorphic cellular structures inspired by wood microstructure.

Biological cellular materials are an important area of research in Additive manufacturing due to their intricate lightweight designs and forms with high energy absorption characteristics under compressive loading. In this study, we utilize the capability of Additive Manufacturing (AM) technology, experimental testing, and Finite Element Analysis (FEA) to design and investigate the mechanical behavior and energy absorption capabilities of novel Biomorphic Cellular Structures (BCS) inspired by the microstructure of cedar, oak, and palm wood. A comparative study of the elastic properties of the biomorphic cellular structures is carried out. The deformation and failure modes of the different cells were studied, and their performance was also discussed. Nonlinear finite element numerical simulation conducted has shown high accuracy in the prediction of deformation of the samples manufactured using additive manufacturing. The results show that cedar-bcs provides the best mechanical performance compared to the other two biomorphic cellular structures which could be as a result of its more vertical cell wall orientation, nevertheless, the palm-bcs showed a step-wise deformation and improved collapse stress. The obtained results suggest that the unique opportunities offered by the proposed experimental method, in combination with computational models, could serve to provide novel important information for the rational design of additively manufactured porous biomorphic materials.

Evaluation of the inter-particle interference of cellulose and lignin in lignocellulosic materials.

The inter-particle interference of lignocellulosic materials describes the order of the macromolecules at a larger size scale, which can give information about the pore structure, and interface of cellulose and lignin. The pore structure and interface influence the rate of enzymatic hydrolysis and thermal decomposition in cellulosic ethanol manufacturing. In this study, the inter-particle interference of cellulose and lignin of three major categories of lignocellulosic materials: wood-based (cedar and oak), energy crop (bamboo), and agricultural or forestry waste (palm) were evaluated. Scanning electron microscopy (SEM) reveals morphological irregularities in the case of bamboo and palm, which may form nucleation sites for faster accessibility to enzyme molecules. Small-angle X-ray scattering (SAXS) shows increased power-law exponent for palm, suggesting a less clustered structure, which was consistent with the rough surface morphology as detected by the SEM. Differential Scanning Calorimetry (DSC) showed a higher temperature maximum for cedar and oak, which is indicative of higher intermolecular forces within their organic compounds, and could result in slower disintegration of the macromolecules during biochemical processing. This study will help to estimate the activity of the macromolecules and absorption capacity of lignocellulosic materials during biochemical processing.

Investigation of molecular and supramolecular assemblies of cellulose and lignin of lignocellulosic materials by spectroscopy and thermal analysis.

The study of lignocellulosic materials calls for understanding the structure, and function of different cellulosic materials from diverse sources to scale-up cellulosic ethanol production. For the first time, a systematic assessment of the molecular and supramolecular structure highlighting the similarities and dissimilarities of three major categories of lignocellulosic materials: wood-based (cedar and oak), energy crop (bamboo), and agricultural or forestry waste (palm) are reported. The cellulose, hemicellulose, and lignin constituents were compared for their suitability in cellulosic ethanol production. FTIR showed structural variations within the functional groups with notable OH group in the palm and CC group in cedar. From the X-ray scattering, bamboo exhibited the highest crystallinity (49.5%), and palm showed the lowest crystallinity (22.6%) and crystallite size (2.6 nm). TGA revealed high cellulose amount and stable structure for cedar and oak, and the most unstable structure in the palm, which indicates a better cellulose/hemicellulose accessibility and biodegradability for enzymatic or chemical action in the palm. This comparative assessment can greatly facilitate material selection and component mixture, for developing an efficient and cost-effective biochemical process in ethanol manufacturing.

Vascular differentiation from pluripotent stem cells in 3-D auxetic scaffolds.

Auxetic scaffolds, that is, scaffolds that can display negative Poisson's ratio, have unique physical properties and can expand transversally when axially strained or contract under compression. Auxetic materials have been used for bioprostheses and artery stents due to the enhanced compressive strength and shear stiffness. In vascular tissue engineering, auxetic scaffolds allow the widening of blood vessels when blood flows through (creating compressive stress) to prevent the blockage. However, the influence of auxetic materials on the cellular fate decision in local environment is unclear. In this study, auxetic polyurethane foams were used to support vascular differentiation from pluripotent stem cells. The expression of alkaline phosphatase, Oct-4, and Nanog was lower after 4 days of differentiation for the cells grown in auxetic scaffolds. Higher expression of vascular markers CD31 and VE-cadherin was observed for the cells from auxetic scaffolds compared with those from the scaffolds before auxetic conversion. Little influence on the expression of cardiac marker α-actinin was observed. The vascular cells secreted extracellular matrix proteins vitronectin and laminin and expressed membrane-bound matrix metalloproteinase 9. The examination of Yes-associated protein expression indicated more cytoplasmic retention in the cells from auxetic scaffolds compared with those from regular scaffolds, suggesting that the auxetic scaffolds may affect cellular contraction. This study demonstrates a novel 3-D culture based on auxetic scaffolds for vascular differentiation and provides a platform to study the influence of biophysical microenvironments on differentiation of pluripotent stem cells. The outcome of this study has implications for regenerative medicine and drug discovery.