Next-generation electronics will autonomously respond to local stimuli and be seamlessly integrated with the human body, opening doors for remarkable opportunities in environmental monitoring, advanced consumer products, and health diagnostics for personalized therapy. The underpinnings of such electronics is the development of new electronic materials with a wide suite of functional properties beyond our current toolkit. Team Tran will leverage the rich palette of polymer chemistry to design new materials encoded with information for self-assembly, degradability, and electronic transport.
SEQUENCE CONTROL + RECOGNITION
The presentation of bioactive moieties in terms of multivalency, ligand density, and architecture plays a central role in biological recognition processes, including cellular adhesion and pathogen binding. Recapitulating these precise molecular recognition motifs in synthetic polymer platforms for transduction into electronic signals will enable new tools for interrogating and driving biological systems. Combining the attributes of molecular recognition and electronic sensors has been a challenge. The importance of multivalent interactions for enhanced binding avidity has inspired well-defined synthetic mimics; however, read-outs have been mostly limited to exogenous fluorescence. Alternatively, graphene, carbon nanotubes, and their derivatives are ubiquitous signal transduction elements. However, the molecular recognition motifs are randomly inserted via covalent bonding at defect sites or by non-specific physical adsorption, leading to limited sensitivity and reproducibility. Our research program will develop sequence-controlled electron-conducting polypeptoids that self-assemble into two-dimensional (2D) nanosheets to bridge the synthetic divide between molecular recognition and electronic sensors.
SOFT + COMPATIBLE
Advances in implantable bioelectronics are changing our understanding and treatment of neurological disorders. For example, commercial ventures like Neuralink are realizing ultra-high bandwidth brain-machine interfaces with fiber-like flexible probes. For chronic implantation needed for lifelong disorders, it is important to consider strategies to mitigate immunological responses that lead to the failure of an implanted device. An approach to improve tissue compatibility is to reduce the mechanical rigidity of devices by using low bending stiffness architectures or lower-modulus materials, but this still has not matched the moduli of tissue. Although they exhibit a good mechanical match to tissue, hydrogels contain water that complicates electronic performance and device fabrication. Alternatively, chemical strategies to avoid device failure center on using materials that are non-fouling or effectively mimic the natural milieu. For example, in non-fouling materials, there is no initial non-specific protein adsorption; this avoids the cascade of immunological events that leads to fibrotic capsule formation and device failure. Currently, an integrated materials platform that exploits both mechanical and chemical approaches does not exist. We work to establish a platform of functionalized bottlebrush elastomers for developing bioelectronics with tissue-matched stiffnesses. Due to the densely grafted side chains and decreased physical interactions between chains, bottlebrush polymers circumvent the lower limit in modulus set by the presence of entanglements in conventional linear systems. Upon cross-linking, the solvent-free bottlebrush elastomers exhibit unprecedented low moduli, around 1 kPa, that can match soft biological tissue.
BIODEGRADABLE + RECYCLABLE
Biodegradable electronics will reduce our environmental footprint and challenges in health monitoring, disease treatment, and sustainability. For instance, a biodegradable, flexible, passive arterial pulse sensor can wirelessly monitor blood flow for post-anastomosis surgery. Importantly, the degradation by-products must be non-toxic and bioresorbable such that negligible or even positive impact is observed. The next stage to advance such electronics is the development of new biodegradable electronic materials, particularly semiconductors which are active materials needed to fabricate transistors. However, there are limited reports of biodegradable electron-conducting polymers due to the inherent resistance of most charge-conducting chemistries to hydrolytic cleavage. Most reports are composites of non-degradable materials, for which the toxicity is undefined, or high molecular weight polymers, which present challenges in filtration by the kidneys and resulting accumulation in the circulatory system. To circumvent these issues, we develop electron-conducting polymers that, when in biofluids and water, degrade into derivatives of natural compounds. We look to Nature for inspiration because Nature provides a wealth of π-conjugated molecules that are potential precursors for electron-conducting polymers, such as melanin, 𝛽-carotene, and indigo.
AUTOMATED + ACCELERATED
Throughout all the research directions, we are interested in automation and using AI to help accelerate our research. Automation offers the opportunity for reproducible and batch sample preparation, synthesis, and characterization. While some automated instruments are commercially available, we will custom build components and integrate systems to ultimately develop self-driving labs. In self-driving labs, there is autonomated synthesis and characterization as well as AI-driven decision making. These autonomous and iterative cycles can reduce material discovery and costs by ten-fold. However, substantial efforts are needed to create the initial integrated infrastructure and analysis of characterization data for autonomous feedback. To learn more about this area of research, check out the Acceleration Consortium.
POLYMER CHEMISTS <> MOLECULAR ARCHITECTS
Designing bio-integrated electronics for resilience starts at the molecular level, whereby “molecular architecture” dictates function. The ability to predict how variations in molecular level features translate to bulk polymer properties is critical for realizing large-scale bulk applications and opening avenues for niche applications. Similar to architectural resilient design principles, there are analogous principles for materials used in bio-integrated electronics, including strategies to address mechanical mismatch, fouling, improper adhesion, and degradation within biological systems.
OUR INSTRUMENTATIONS
I am pretty happy with most of my equipment, as it is a balance between price and availability. One of my favorite instruments is the automated recycling GPC— something I did not have in my PhD and postdoc. It is awesome! I also think the Vigor glove boxes are just as good (so far!), and much more competitive price wise. I also quite like the Gyros PurePep for our solid-phase synthesis. A bit expensive but maybe we will get more reactors in the future for the space. It is particularly good for programming of peptoids. I really avoided getting a UV-Vis but it was essential for our time studies, so we thank Agilent for the discount through the award. We got a Teledyne ISCO flash, which I normally like, but I got a demo unit that is sub-par (weaker pump, cannot do very large columns; lacking a setting so the nozzle leaks upon disconnecting). In retrospect, I wonder if we should’ve stuck with the classic Biotage for microwave reactions. I liked the automation feature in CEM, but we noticed the seal is not as robust and had a hardware failure within two years (and no way we can fix it ourselves). For a lab with high throughput, the automation may be useful.
Happy to chat with anyone who wants more details on these instruments!
to be purchased/moved soon:
2-port glove box
6 port-glove box
High temperature GPC
Room temperature GPC
Keithley 4200 and probe station