2022 Nelson W. Taylor Lecture in Materials

11:25 a.m. Keynote Speaker: Michael Rubinstein

Aleksandar S. Vesic Distinguished Professor, Professor of  Mechanical Engineering and Materials Science, Biomedical Engineering, Chemistry, and Physics at Duke University.

“A-B associating polymer solutions and gels”

Polymer associations due to the formation of reversible bonds between different groups (A-B type) are qualitatively different from pairwise associations of the same groups (A-A type). The degree of conversion for A-B associations is lower than for A-A associations and depends on the stoichiometry of the associating groups. We predict re-entrant sol-gel-sol transitions for solutions of A-B associating polymers as functions of stoichiometry. Both A-B gelation and phase separation are suppressed relative to A-A solutions with phase diagrams for both dependent on solvent quality. Chemical incompatibility between A and B polymers results in competition between A-B association-induced attractive phase separation and incompatibility-driven repulsive phase separation. An example of A-B associating solutions is a coacervate of oppositely charged polyelectrolytes. Weak associations between oppositely charged polyelectrolytes (less than thermal energy kT per charge) with asymmetry of the polyanion and polycation line charge densities form double-semidilute solutions. Dynamics of higher charged polymers in these asymmetric coacervates are slower due to dynamic coupling between polyanions and polycations including reptation of higher charged polyelectrolytes along the confining tubes of lower charged polyelectrolytes. Strong associations with binding energy higher than thermal energy kT form reversible gels and, in the case of asymmetry of charge line density, these networks have bottlebrush or star-brush symmetry and unusual properties.

8:30 a.m. Enrique Gomez

Professor, Chemical Engineering and Materials Science and Engineering, Penn State

“Nanoscale control of density variations is crucial to optimize polymer membranes for water purification”

Reverse osmosis modules comprised of composite polymer membranes represent a leading technology in desalination and purification of brackish water. Nanoporous polymeric membranes are key for prefiltering of such reverse osmosis systems, as well as for purification of biopharmaceutical products, such as monoclonal antibodies. The field has relied on intricate control of membrane properties through systematic perturbations to membrane chemistries and processing, yet many fundamental questions remain on the mechanisms that govern water transport and separations. We have leveraged advances in multi-modal electron microscopy to generate new insights on membrane structure and function. For example, we have combined the focused ion beam with scanning electron microscopy through serial sectioning to reconstruct a 3D representation of ultrafiltration membranes using for virus removal from biopharmaceutical streams. In addition, we have combined energy-filtered transmission electron microscopy with electron tomography from scanning transmission electron microscopy images to map the variation in density of polyamide films used in reverse osmosis membranes. Quantitative analyses of imaging products are key to extract mechanistic details that govern water transport and separations. Furthermore, we image membranes challenged with model and common foulants, to ascertain initial conditions and mechanisms for degradation of filtration performance.

9: 25 a.m. Robert Hickey

Assistant Professor, Materials Science and Engineering, Penn State

“Hierarchically ordered block copolymer materials via nonequilibrium processing”

The diversity and vastness in the types of properties of living systems, including enhanced mechanical properties of skin and bone, or responsive optical properties derived from structural coloration, are a result of the multiscale, hierarchical structure of the materials. The field of materials chemistry has leveraged equilibrium concepts to create complex materials seen in nature, yet achieving the remarkable properties present in living systems requires moving beyond this formalism by utilizing nonequilibrium processes to create new and exciting materials. Here, the presentation will describe a new method to create hierarchically ordered, physically crosslinked hydrogels, and recent developments in further processing the hydrogel materials to create linear and rotary actuators. Specifically, we have explored a modified nonsolvent-induced phase separation method termed rapid injection processing to produce hierarchically ordered hydrogels with structures and mechanical properties resembling those of living biomaterials. The hydrogel fabrication process entails injecting a triblock copolymer, such as poly(styrene)-poly(ethylene oxide)-poly(styrene) (SOS), solution into a coagulating liquid (i.e., water), driving the hydrophobic polymer domains to organize at the nano and microscale and forming bulk hydrogels. We have established a universal and quantitative method for fabricating and controlling physically crosslinked hydrogels exhibiting hierarchical ordering by controlling the initial pre-injection triblock copolymer solution concentration and water-miscible organic solvent. Additionally, water-swollen hydrogel materials are easily processed to create high-performance linear and rotary actuators via strain-programmed hydrogel crystallization. The crystallized fibers display enhanced mechanical properties due to the aligned alternating amorphous and crystalline domains, and actuation is triggered using either water or heat. The work presented here highlights that by harnessing nonequilibrium methods, it is possible to create materials with tunable physical properties via controlling the structure from the nanometer to the micrometer.

10:25 a.m. Hee Jeung Oh

Assistant Professor, Chemical Engineering, Penn State

“3D printed biosponge polymers for capturing drugs before they spread through the body”

Due to longer life expectancies, the prevalence of age-related diseases is increasing rapidly, and the need for developing biomedical devices that can solve big health problems is similarly greater. Inspired by adsorption columns, which are routinely used in industry to remove pollutants from chemical streams, this research describes the design of biosponge polymers for capturing unwanted toxins in the body. One significant benefit of using polymer membranes is their tunable binding affinity to target molecules using specific chemical, physical, or biological features. One example is using properly designed biosponge polymers to remove cancer chemotherapy drugs that are not taken up by the target tumor during chemotherapy to reduce the drugs’ toxic side effects.
Cancer is becoming the leading cause of death in most developed nations. Despite efforts to develop targeted and personalized cancer therapeutics, dosing of the cancer chemotherapeutics is limited by toxic side effects. During intra-arterial chemotherapy infusion to a target organ, typically, more than 50-90% of the injected drug is not trapped in the target organ and bypasses the tumor to general circulation, causing toxicities in distant locations.
In the context of reducing the toxicity of chemotherapy, we have designed, built, and deployed porous biosponge polymer adsorbers for capturing chemotherapy drugs before they spread through the body. The porosity was obtained by 3D printing of lattice structures. The surface of porous cylinders was coated with an ion-containing nanostructured block polymer which is responsible for capturing doxorubicin, a widely used chemotherapy drug with significant toxic side effects. Using a swine model, our initial design enables the capture of 69 % of the administered drug without any adverse effects. Additional improvement may be obtained by changing the chemical composition of the selective membrane layer and controlling the lattice structure and size with elastomers.