Microphase Separation in Sulfonated Block Copolymers Studied by Monte-Carlo Simulations

The underpinnings of microphase separation in symmetric poly(styrenesulfonate-block-methylbutylene) (PSS-PMB) copolymer melts were examined by Monte Carlo lattice simulations. The main challenge is understanding the effect of ion pairs in the PSS block on thermodynamics. We assume that experimentally determined Flory-Huggins interaction parameters are adequate for describing intermonomer interactions. Our model does not account for either electrostatic or dipolar interactions. This enables comparisons between simulated and experimentally observed microphases reported by Park and Balsara [Macromolecules 2008, 41, 3678] without resorting to any adjustable parameters. The PSS block in both experiments and theory is partially sulfonated. We quantified the effect of sequence distribution on phase behavior by using alternating and blocky PSS chains in the simulations. Depending on temperature and sequence distribution, simulations show performed lamellae, gyroid, and hexagonally packed cylinders in addition to the lamellar phase found in simple symmetric block copolymers that do not contain ions. This is driven by extremely repulsive interactions between styrenesulfonate monomers and the uncharged species in the melts. The symmetry of the microphases and the locations of the order-disorder and order-order phase transitions are in qualitative agreement with experimental observations.X112927sciescopu

Improved human bone marrow mesenchymal stem cell osteogenesis in 3D bioprinted tissue scaffolds with low intensity pulsed ultrasound stimulation

3D printing and ultrasound techniques are showing great promise in the evolution of human musculoskeletal tissue repair and regeneration medicine. The uniqueness of the present study was to combine low intensity pulsed ultrasound (LIPUS) and advanced 3D printing techniques to synergistically improve growth and osteogenic differentiation of human mesenchymal stem cells (MSC). Specifically, polyethylene glycol diacrylate bioinks containing cell adhesive Arginine-Glycine-Aspartic acid-Serene (RGDS) peptide and/or nanocrystalline hydroxyapatite (nHA) were used to fabricate 3D scaffolds with different geometric patterns via novel table-top stereolithography 3D printer. The resultant scaffolds provide a highly porous and interconnected 3D environment to support cell proliferation. Scaffolds with small square pores were determined to be the optimal geometric pattern for MSC attachment and growth. The optimal LIPUS working parameters were determined to be 1.5 MHz, 20% duty cycle with 150 mW/cm2 intensity. Results demonstrated that RGDS peptide and nHA containing 3D printed scaffolds under LIPUS treatment can greatly promote MSC proliferation, alkaline phosphatase activity, calcium deposition and total protein content. These results illustrate the effectiveness of the combination of LIPUS and biomimetic 3D printing scaffolds as a valuable combinatorial tool for improved MSC function, thus make them promising for future clinical and various regenerative medicine application. © The Author(s) 2016