Unoccupied space and short-range order characterization in polymers under heat treatment

Large scale molecular dynamics simulations on polyvinyl alcohol were used to investigate the distribution of unoccupied space under different heat treatments. Representative volume elements consisting of 3600 chains of 300 monomers were equilibrated at melt state and cooled by different cooling rates. The positions of center of mass of the monomers were extracted and a series of spatial analysis were conducted to estimate the distribution of free volume or unoccupied space by Voronoi tessellation algorithm. An open-source software was employed which incorporates both compilers of Matlab and C programing languages to reduce the computational costs associated with Voronoi calculations and statistical analysis. The results confirmed that low free volume content is achievable through annealing while high free volume content is achievable through quenching samples at high cooling rates. An appreciable degree of short-range order in the packing of chains is revealed in annealed samples.Comment: 8 page

Permeability mapping of gelatin methacryloyl hydrogels

We report the development of an efficient, customized spherical indentation-based testing method to systematically estimate the hydraulic permeability of gelatin methacryloyl (GelMA) hydrogels fabricated in a wide range of mass concentrations and photocrosslinking conditions. Numerical simulations and Biot's theory of poroelasticity were implemented to calibrate our experimental data. We correlated elastic moduli and permeability coefficients with different GelMA concentrations and crosslinking densities. Our model could also predict drug release rates from the GelMA hydrogels and diffusion of biomolecules into the three-dimensional GelMA hydrogels. The results potentially provide a design map for choosing desired GelMA-based hydrogels for use in drug delivery, tissue engineering, and regenerative medicine, which may be further expanded to predicting the permeability behaviors of various other hydrogel types

Ink Formulation and Selection for Biological Applications of Two-Photon Polymerization

Two-photon polymerization (TPP) uses nonlinear light interactions in photo-cross-linkable precursors to create high-resolution (∼100 nm) structures and high dimensional fidelity. Using a near-infrared light source in TPP results in less scattering and a higher penetration depth, making it attractive for creating biological models and tissue scaffolds. Due to unmatched flexibility and spatial resolution, they range from microvascular constructs to microneedles and stents. This review reviews the working principles and current inks used for TPP-printed constructs. We discuss the advantages of TPP over conventional additive manufacturing methods for tissue engineering, vascularized models, and other biomedical applications. This review provides a short recipe for selecting inks and photoinitiators for a desired structure