Thank you!

The 2021 Virtual MRS Spring Meeting & Exhibit came to conclusion on Friday, April 23. Due to the COVID-19 pandemic, special efforts were made by volunteers and participants to ensure a successful virtual Meeting!

Meeting content will be available to registered participants through May 31, 2021.

Our congratulations go to the 2021 Spring Meeting Chairs Linyou Cao, Seung Min Han, Lena Kourkoutis, Andreas Lendlein, and Xiaolin Li for putting together an excellent technical program along with various special events. MRS would also like to thank all the Symposium Organizers and Session Chairs for their part in the success of this Meeting. A thank you goes to the Exhibitors, Symposium Support, and to the sponsors of the Meeting and of the special events and activities.

Contributors to news on the 2021 Virtual MRS Spring Meeting & Exhibit include Meeting Scene reporters Arun Kumar, Jessalyn Hui Ying Low, Judy Meiksin, and Victor A. Rodriguez-Toro; bloggers Essraa Ahmed and Sebastián Suárez Schmidt; and graphic artist Stephanie Gabborin; with newsletter production by Jason Zimmerman.

Thank you for subscribing to the MRS Meeting Scene newsletters We hope you enjoyed reading them and continue your subscription as we launch into the 2021 MRS Fall Meeting & Exhibit – A Hybrid Event - the conversation already started at #f21mrs! We welcome your comments and feedback.

Symposium SM04/SM01: Beyond Nano-Challenges and Opportunities in Drug Delivery / Materials Modulating Stem Cells and Immune Response

Annemiek Uvyn, Ghent University

Tagging the Cancer Cell Surface for Innate Immune Recognition and Destruction by Bifunctional Multivalent Antibody-Recruiting Polymers

Written by Jessalyn Hui Ying Low

Monoclonal antibody (mAb) therapies are immunotherapies commonly used in cancer treatment to kill cancer cells, but have several limitations such as high production costs and possible severe side effects. “Instead of delivering mAB, synthetic compounds that can deliver endogenous antibodies to the cancer cell surface could be a viable alternative,” says Annemiek Uvyn, where Uvyn describes in this talk how antibody-recruiting polymers could be designed for this purpose.

Uvyn explains that these antibody-recruiting polymers are functionalized with two key classes of motifs—cell-binding motifs to bind to the cancer cell, as well as antibody-recruiting motifs to bind to the endogenous antibodies. Cell-binding motifs can be in the form of lipid motifs, for anchoring to the phospholipid bilayer of the cell membrane via hydrophobic interaction, or cyclooctyne motifs, for click coupling to azides introduced in the glycocalyx of cancer cells. As for antibody-recruiting motifs, haptens like dinitrophenyl (DNP) are used. It was also demonstrated that the more DNP units there are on the polymer backbone, the greater the binding avidity of antibodies.

With these antibody-recruiting polymers, it was validated successfully in vitro the ability for high avidity antibody binding and recruitment of antibodies to the cancer cells. More importantly, functional assay studies successfully showed that these lipid-polyDNP antibody-recruiting polymers could induce cancer cell killing via phagocytosis by macrophages, which was in fact achieved to a similar extent as that of cetuximab, a mAb. This highlights the potential of using these antibody-recruiting polymers for immunotherapies, to induce innate immune effector killing of cancer cells.

Symposium SM13: Advances in Membrane and Water Treatment Materials for Sustainable Environmental Remediation

Niraj Ashutosh Vidwans, Texas A&M University

Strategies for the Scale-up of the Photocatalysis Process for Disinfecting Large Quantities of Water

Written by Arun Kumar

Current water disinfection methods are limited by the release of harmful by-products, waste produce, and incomplete pathogen deactivation. In this regard, the photocatalytic disinfection method using titanium oxide (TiO₂) can be a better alternative for the process says Niraj Vidwans from Texas A&M University. TiO₂ can efficiently generate reactive oxygen species when exposed to ultraviolet-A light that can in turn showcase excellent antimicrobial activity and contaminant removal from the water. TiO₂ aeroxide P25 nanoparticles are a standard catalyst for the photocatalytic process, but they are often hard to remove from the water after disinfection. So the research group prefers the use of porous TiO₂ nanowires for the photocatalysis process. Initial experimentation shows that ultraviolet light-A combined with the nanowires were able to disinfect E. coli bacteria by four orders exhibiting good catalytic activity. Several flow pattern changes and chemical composition changes in the TiO₂ nanowires make them compatible for disinfection applications in different water sources. Following the optimization strategies, a bench-scale up setup was used to measure the efficiency of their process in a flow photocatalytic bioreactor. The team also demonstrates that the photocatalyst can be recovered and reused for photoreaction. Vidwans envisions developing a protocol to expand the flow reactor into a continuous-mode flow reactor for photocatalytic disinfection. The high specific surface area obtained when TiO₂ is made in nanocrystalline form (nanoparticles and nanowires) aids in engineering efficient water remediation processes.

Symposium SM05: Progress in Multimaterials and Multiphase-Based Multifunctional Materials

Jacques Lux, UT Southwestern

Late News: Microbubbles Cloaked with Hydrogels as pH-Activatable Ultrasound Contrast Agents

Written by Jessalyn Hui Ying Low

Ultrasound imaging make use of microbubbles (MBs) as contrast agents, and can be used to detect deep vein thrombosis (DVT). However, it is difficult to distinguish acute DVT from chronic DVT, where acute DVT requires aggressive treatment with anticoagulants and can result in internal bleeding. In this talk, Jacques Lux shares how thrombin-specific ultrasound contrast agents can be designed to detect acute DVT through thrombin activity, which is indicative of active thrombosis.

Lux explains that this is achieved by conjugating activatable cell penetrating peptides (ACPPs) to the surface of the MB. In the presence of thrombin, ACPPs will be cleaved causing the MB surface to become positively charged, thus adhering to negatively charged surfaces like fibrin. This allows the microbubbles to be accumulated into clots, exhibiting an increased signal under ultrasound.

To further increase the specificity of these microbubbles to the biomarker of interest (thrombin in this case, but proof of concept done with pH), a hydrogel cloak is added, which contains hyaluronic acid (HA) and a pH-sensitive crosslinker. This serves the purpose of stiffening the MB shell and silencing the harmonic signal in the absence of the biomarker. On the other hand, in the presence of the biomarker, biodegradable crosslinkers in the hydrogel will be cleaved to allow for oscillation of the MB and production of harmonic signal that is specific to the biomarker. It was demonstrated successfully that in acidic pH, harmonic signal was turned on, but not in neutral pH. By extending these hydrogel cloaks to the usage of thrombin-sensitive crosslinkers, these MBs show great potential in exhibiting specificity to thrombin which can be used to detect acute DVT via ultrasound imaging.

Symposium SM04: Beyond Nano–Challenges and Opportunities in Drug Delivery

Juliane Nguyen, University of North Carolina-Chapel Hill

Developing Therapeutic Materials to Redirect Cellular Chatter

Written by Arun Kumar

Cellular communication takes place when soluble proteins such as chemokines, cytokines, or exosomes are exchanged between cells. Exosomes are tiny vesicles secreted by cells containing proteins, nucleic acids, lipid profiles, or other molecules. Recently, exosome communication has brought light to interesting functionality in the growth and repair of cardiac tissue. Juliane Nguyen presents that the exosomes secreted by damaged cardiac tissues can recruit mesenchymal stem cells (MSCs) from the bone marrow and have a regenerative and angiogenetic effect at the damage site. Looking closely at the content of exosomes, the group was able to associate the activity of a microRNA, miR-101 isolated from the exosomes to the regenerative pathways such as angiogenesis and anti-apoptotic signaling. Mice suffering from myocardial infarction treated with miR-101 loaded MSCs displayed reduced fibrosis and improved cardiac function. The next question the research group wanted to answer was how to upscale the exosome production from the cells and use it as a therapeutic intervention. Small molecules like N-Methyldopamine and Norepinephrine were found to regulate protein targets that significantly promoted exosome production and increased the exosomes secreted per cell without affecting the protein composition within them. With an improved exosome secreted, the group is focusing on using RNA-based materials to modulate the cellular communication and target miRNA to a specific cellular location to promote therapeutic outcomes.

Symposium X: Frontiers of Materials Research

Iuliana P. Radu, imec
How New and Old Materials Research and Know-How Extend the Increase in Computation Power

Written by Sophia Chen

Iuliana Radu of the Interuniversity Microelectronics Centre (imec), an institute dedicated to the research and development of nanoelectronics in Belgium, delivered a Symposium X lecture on Friday. Radu, a physicist by training, discussed how materials science can further increase computational power.

We currently live in an era where “the data center is the programming unit,” said Radu. People no longer store most of their data locally, instead piping it to a data center and processing it offsite. This has motivated the need for more powerful computation.

At imec, Radu and her colleagues develop the next generation of computers, where one approach is to shrink the transistor further. While researchers are studying a variety of materials and strategies for this, Radu’s presentation focused on a class of materials known as transition metal dichalcogenides. As a two-dimensional material—in other words, when the material occurs as a single atomic layer—transition metal dichalcogenides can make transistors smaller by shortening its so-called gate length, compared to when they are made from silicon.  One example of such a material is tungsten disulfide, which Radu has studied.

Radu described the current research on integrating these materials in transistors. One challenge is depositing them in stacked nanosheets on a substrate in a scalable process. Researchers are also studying the defects that occur in these materials.

In addition, researchers are considering how materials science can benefit future quantum computers. Radu anticipates this new type of computer, based not on transistors but on components known as quantum bits, or qubits, to be a paradigm shift for the field of computation, as they are capable of performing very different algorithms than classical computers.

Radu discussed two materials for making qubits—semiconductors and superconductors. Both types of qubit function at low temperatures near absolute zero, and the classical electronics that control the qubit will require materials that can function at these low temperatures.

Symposium X—Frontiers of Materials Research features lectures aimed at a broad audience to provide meeting attendees with an overview of leading-edge topics.

Symposium EL02: Fundamentals of Halide Semiconductors for Optoelectronics

Vincenzo Pecunia, Soochow University

Lead-Free Perovskite-Inspired Semiconductors for Indoor Photovoltaics

Written by Victor A. Rodriguez-Toro

Vicenzo Pecunia and collaborators highlight a prediction in which we should expect one trillion of Internet-of-things (IoT) devices by 2035. The use of ambient energy harvesters can enable the success of this technology, including indoor photovoltaics (IPV). Perovskite photovoltaics (PPV) has emerged as an attractive energy harvester because its power conversion efficiency (PCE) is higher (e.g., amorphous hydrogenated silicon) or comparable (crystalline) to industry-standard IPV technologies. However, the toxicity of some types of perovskites (e.g., lead-based ones) has motivated researchers to find safer materials which preserve their outstanding optoelectronics properties. Perovskite-inspired systems based on antimony or Sb (i.e., Cs₃Sb₂Cl_xI_0-x) and bismuth or Bi (i.e., BiOI) were found to have a PCE of 4–5% when tested under indoor illumination conditions (fluorescent and white light LED). Furthermore, it is shown to be the first-known demonstration of printed electronics (~10,000 thin-film transistors) powered by IPV processed from solution.

Symposium SM04: Beyond Nano-Challenges and Opportunities in Drug Delivery

Anna Salvati, Groningen Research Institute of Pharmacy

Late News: Dissecting How Cells Internalize and Process Nano-Sized Drug Carriers for Nanomedicine Applications

Written by Jessalyn Hui Ying Low

For intracellular delivery of nanomedicines, nanomedicines have to first interact with the cell membrane and be recognized, after which they can be internalized by cells via a variety of cellular pathways. In this talk, Anna Salvati explains the research work done to understand deeper such interactions, in particularly how corona molecules can affect internalization of drugs. “By understanding these interactions better, we can design nanomedicines to achieve the desired outcomes at cell level and control these interactions,” says Salvati.

Salvati explains that when in a biological environment, formation of a corona occurs on the nanocarriers due to adsorption of surrounding biomolecules. This corona can in fact be recognized by cell receptors, mediating the interaction between the cells and nanoparticles. It was found that for the same nanoparticle, but with different corona compositions, the internalization pathway of the nanoparticle is also different, implying that different corona compositions are recognized differently by cell receptors. Salvati also highlights that even if a specific receptor is targeted, cells can internalize the nanoparticles via a different pathway as compared to the endogenous ligands. In addition, by changing the compositions of liposomes, it was shown how the corona composition can be tuned, and how this in turn affects the kinetics and mechanisms of uptake by the cell.

To understand better the mechanisms of internalization, it is also important to have better models beyond conventional in vitro cell cultures, as Salvati shares. One of such models the research group has developed are in vitro endothelial cell barriers, to mimic the barriers that nanomedicines face in vivo. It was found that when cells developed into a barrier, endocytic markers were expressed to different levels, and had a lower nanoparticle uptake as compared to standard cell cultures, indicating that such organization of the cells influences how nanoparticles are processed. Another model is a precision-cut tissue slices ex vivo model, where it was shown that precision-cut liver slices reproduced the preferential accumulation of nanoparticles by Kupffer cells as observed in vivo. This highlights how these models can be leveraged to better understand cellular internalization of nanomedicines occurring in vivo and optimize the design of nanomedicines.

Symposium SM09: Peptide and Protein Design for Responsive Materials

Minkyu Kim, University of Arizona

Late News: Artificial Protein Design Rules to Harness Protein Tertiary Structures for Polymeric Materials with Exotic Mechanical Behaviors

Written by Jessalyn Hui Ying Low

Erythrocytes carry oxygen throughout the body and are required to pass through narrow biological barriers like splenic slits. As such, they exhibit unique mechanical properties including reversible deformability and fatigue resistance, owing to the proteins found in their cytoskeleton, specifically ankyrin proteins. “If erythrocyte mimetic materials are available, that would be a breakthrough in drug delivery system fields for better biodistribution and long-term circulation of delivered pharmaceuticals, which cannot be achieved by most of current drug delivery systems,” says Minkyu Kim. In this talk, Kim shares how by designing polymer networks incorporated with protein structure, erythrocyte cytoskeleton mimicking materials can be built.

One of the key challenges in designing these polymer networks is the presence of topological defects such as molecular entanglements and loops, which could negatively affect mechanical properties. This is unlike in erythrocyte cytoskeleton, which have rod-like strands instead of coil-like strands. Therefore, by controlling strand rigidity, it is possible to reduce topological defects in the hydrogel’s polymer network.

When rod-like synthetic ankyrin protein strands were inserted into the hydrogel, it was found that the gel elastic modulus (G’) and gel relaxation time (λ_R) were close to tripled. This indicates the reduced topological defects in the network, likely due to the strain rigidity. This rigidity, however, also increased dangling chains, which could be decreased by inducing additional flexibility in the network. As such, flexible coil-like nonstructured protein strands were introduced, where strand flexibility could be controlled by rod:coil length ratio. It was found that at optimal rod:coil length ratio, λ_R was improved, implying that junction stability in the polymer network is enhanced, likely due to controlled mobility of the crosslinkers. Moreover, stability can be further improved when coupled with an asymmetric rod-coil protein design at the optimal rod:coil ratio, which may be due to reduced steric hindrance of rod-like proteins.  

Kim also reports that work is currently done to further develop these cytoskeleton-mimetic materials, in particular establishing selection criteria for crosslinkers such as crosslinking specificity and strength. With these design principles, it opens up new avenues for the development of soft materials with reduced network defects, with applications in tissue engineering and drug delivery systems.

Symposium EL02: Fundamentals of Halide Semiconductors for Optoelectronics

Ruth Shinar, Iowa State University

Tunable Perovskite-Based Photodetectors in Optical Sensing

Written by Victor A. Rodriguez-Toro

Compact spectroscopic platforms for (bio)chemical sensing have been proposed in the past. Typically, it consists of a light source in the visible range that sends an optical pulse to photoexcite a phosphorescent dye, which is embedded in a thin film like polystyrene (PS). Once the visible light is turned off (end of the optical pulse), a signal of photoluminescence (at longer wavelength than the light source) is emitted from the dye and sensed by a photodetector (PD). Characteristics of the emitted signal (amplitude and decay time) depend on the interaction of the dye with the analyte (e.g., oxygen) to detect. As the analyte concentration increases, the amplitude of the photoluminescence signal is lower, and the decay time is shorter. Therefore, two measurement modes to determine the analyte concentration can be established by monitoring (1) the optical intensity or (2) decay time. The latter constrains the response time of the light source and the PD to be in the order of 1 ms. Furthermore, it is desirable that the PD to have a low external quantum efficiency (EQE) at the wavelengths of the light source, but a high EQE at the wavelengths of the emitted signal of photoluminescence. 

Shinar and co-workers present the assessment of various photodetection technologies. First, inorganic PDs based on inorganic materials such as amorphous silicon are evaluated making evident their long response time (~250 ms) and the need for external filters. Second, organic photodetectors (OPDs) based on the polymer P3HT and the acceptor PCBM were evaluated showing low EQE in the region of interest for detection.

Finally, perovskite photodetectors (PPDs) were evaluated showing a high EQE, fast response times, and the ability to have systems with broadband and narrowband photodetection sensitivity.