Sarah Brosnan, a research associate in the Ashby Group, has received a post-doctoral NSF fellowship in biology to work with Professor Markus Antonietti at the Max Planck Institute for Colloids and Interfaces in Potsdam, Germany.
Sarah's research has led to the development of the first example of shape memory polymer particles that can have any starting shape, have a large variety of temporary shapes, return to the original shape at biologically reasonable and tunable temperatures, display no cytotoxicity, and have a surface chemistry that can be trivially modified.
Materials capable of dynamically controlling surface chemistry and topography are highly desirable. Sarah Brosnan, Andrew Brown and Professor Valerie Ashby, as published in JACS, have designed a system that is uniquely able to remotely control the presented functionality and geometry at a given time by using a functionalizable shape memory material.
The group accomplished this by incorporating controlled amounts of an azide-containing monomer into a shape memory polymeric material. These materials are capable of physically changing surface geometry over a broad range of length scales from >1 mm to 100 nm. Using copper-assisted click chemistry, they can be functionalized with a variety of molecules to yield different surfaces. Combining these features gave materials that can change both the presented geometry and functionality at tunable transition temperatures.
Sarah Brosnan, a graduate student in the Ashby Group, was selected as one of three winners at the 2012 World Polymer Congress poster competition. Sarah was chosen from a field of over 400 competitors from all over the world.
Sarah's poster, titled "Monodisperse Shape-Specific Shape Memory Particles," explains how the size, shape, and surface characteristics of micro- and nanoparticles are of critical importance for determining their ultimate distribution throughout the body, their delivery, and bioactivity. These properties are particularly important for nano-based medicine, therapeutics, and bio-imaging applications. Micro- and nano-sized polymer particles that are capable of changing from a selected shape to another on demand have been elusive. In all previous attempts, the particles change shape, but require one of the shapes to be a sphere and often offer little to no control over the final or original shape.
Sarah's research has led to the development of the first example of shape memory polymer particles that can have any starting shape, have a large variety of temporary shapes, return to the original shape at biologically reasonable and tunable temperatures, display no cytotoxicity, and have a surface chemistry that can be trivially modified.
Surface topography is a key regulator of many cellular phenomena including development, gene expression, proliferation, and stem cell fate. Efforts to investigate cell-topography interactions have traditionally relied upon static synthetic topographies that aim to emulate the extracellular matrix. While fixed topographies have generated a great deal of information, the suitability of these materials for in vitro cell-substrate analysis is ultimately limited by their static design. The Ashby Group has developed a shape memory polymer (SMP) cell culture platform that is capable of probing cell-topography interactions in a more biomimetic context. Published in Advanced Materials, their work describes the synthesis and application of thermally-responsive poly(ε-caprolactone) SMP micro-arrays to dynamic cell culture.
Favorable thermal, mechanical, and shape memory properties were achieved by manipulating the molecular weight and architecture of the network prepolymers. A soft replica fabrication method facilitated the preparation of the SMP surfaces with exceptional feature size and shape specificity. Oxygen plasma-fibronectin modified SMP surfaces supported human mesenchymal stem cell (hMSC) culture with good attachment efficiency, normal cell morphology, and minimal cytotoxicity. hMSC morphology changed from highly aligned to stellate shaped in response to a surface transformation between a 3 x 5 µm channel array and a planar surface at 37℃. This on-demand, surface directed change in cell morphology offers a novel means to investigate the effect of dynamic topography on cellular behavior.
Published in Macromolecules, Jason Rochette in the Ashby Group describes how the synthesis of a library of poly(ester urethane)s (PEUs) containing pendant photoresponsive moieties afforded through the incorporation of one of two novel bifunctional monomers resulted in degradable materials with a range of tunable thermal and mechanical properties.
Examination of these materials under physiological conditions displayed tunable degradation with rates faster than PCL-based materials, and initial biocompatibility studies exhibited negligible cytotoxicity for HeLa cells based on results of ATP assay. The ability to tune thermal properties also allowed specific polymer compositions to boast transition temperatures within a range of applicable temperature for thermal shape memory.
Twenty-four instructors in 18 different departments or schools, many in the College of Arts and Sciences, received 2013 University Teaching Awards at the University of North Carolina at Chapel Hill. Winners of the award, the highest campus-wide recognition for teaching excellence, were recognized during halftime of the Carolina – Virginia Tech men's basketball game on February 2nd.
Valerie Sheares Ashby, Professor and Chair of the Department of Chemistry won the prestigious Johnston Teaching Excellence Award for excellence in undergraduate teaching. A banquet will be held at the Carolina Club in April to present the awards and further honor the winners.
Hayden Black, a researcher in the Ashby Group, reports in Organic Letters the synthesis and semiconducting properties of two fused thienoacene compounds with 2-dimensional ring connectivity.
These new semiconductors show exceptional π-π stacking in the solid state and crystallize into 1-D microcrystals from the vapor phase. Field effect transistors were fabricated, showing hole mobilities greater than 10-3 cm2/V s for both compounds and On/Off current ratios greater than 105.
As reported in Macromolecules, the Ashby Group reports a new class of thermoplastic poly(ester urethane)s containing novel soft segments are prepared using a one-step synthesis. Amorphous polyester prepolymers ( <Mn>) = 1.5 × 103−3.4 × 103 g/mol) were incorporated as soft segments in poly(ester urethane)s using an aromatic diisocyanate, 4,4'-methylenebis(phenylisocyanate), but with no chain extension. These completely amorphous materials had a wide range of mechanical properties E = 0.86−29.3 MPa; γmax = 2106%, and they possessed linear degradation profiles.
A combination of contact angle studies, water uptake studies, and XPS analysis showed that these materials exhibited a surface segregation phenomenon upon contact with water. Kinetic analyses showed that three of the materials are among the fastest degrading poly(ester urethane)s reported in the literature to date. Initial cytotoxicity testing by minimum essential medium tests showed that only one of the nine new materials gave a cytotoxic response. Two separate sterilization methods did not elicit a cytotoxic response in the poly(ester urethane)s even after a 1 week incubation period.