Introduction to responsive materials for healthcare diagnostics

Marek W. Urban

Marek W. Urban is the J. E. Sirrine Foundation Endowed Chair and Professor of Materials Science and Engineering and Chemistry (courtesy) Departments at Clemson University. Prior to joining Clemson University, he was a professor, department chair, and director of polymer science programs at NDSU and USM, where he also directed the Materials Research Science and Engineering (MRSEC) as well as Industry/University Cooperative Research (I/U CRC) Centers funded by the National Science Foundation. He is the author of about 500 research publications and 12 patents, author of four and editor of seven books. His research on self-healing polymers and antimicrobial polymer surfaces has been featured by numerous media. He is a Fellow of American Chemical Society (ACS) PMSE Division, the Royal Society of Chemistry (RSC), American Institute of Chemists (AIC), and the American Association for Advancement of Science (AAAS). His research group’s current research efforts focus on the development of polymeric materials and interfaces with ‘living-like’ functions, self-healing commodity polymers, new generations of stimuli-responsive materials with adaptable, sensing, and signaling functions as well as spectroscopic imaging methods enabling molecular detection of stimuli-responsiveness.

Over the last several decades polymeric materials became integral components in many healthcare applications. But it was not until the turn of the 21st century when controllable polymerization processes enabled the placement of monomeric units in a desirable order of sequences, resulting in macromolecules composed of repeating units capable of responding to external physical, chemical, or biological changes. This formulated the principles governing the design of modern stimuli-responsive polymers. Of particular interest and timely in view of the Covid-19 pandemic is the development of macromolecular ‘switching’ devices responding to an environmental stimulus indicative of disease leading to a successful diagnosis of underlying medical conditions. The common devices used in healthcare diagnostics are sensors and probes. Sensors are devices which respond to an external stimulus and diagnose reversible processes, but sensors become probes if the measured processes are not reversible requiring probe regeneration to make another test. There are many diagnostic probes and sensors which utilize stimuli-responsive polymers that respond to an array of physical (temperature, light, electric or magnetic fields, plasmons), chemical (pH, solvent polarity, ion types and their strength, chemical agents), or biological (enzymes, ligands, or biological agents, such as antibody-, aptamer-, peptide-based) stimuli. Particularly useful are biosensors responsive to pH changes because local pH gradients are often associated with a broad variety of diseases (DOI: 10.1039/D0TB00344A). On the other hand, supramolecular interactions due to strong streptavidin–biotin bonding affinity formulated an assay platform using birefringence as the visual signal output of binding (DOI: 10.1039/D0TB00355G). Taking advantage of the durability and stimuli-responsiveness of liquid crystal elastomers (LCEs) implantable electronic sensors and probes became feasible (DOI: 10.1039/D0TB00471E). In essence, attractive combination of various stimuli and responses combined with additive manufacturing capabilities granted the development of novel probes and sensing devices, unlocking new venues for noninvasive diagnostics.

In modern health diagnostics it is also essential to achieve high sensitivity because many drugs exhibit narrow therapeutic index and small concentration changes may lead to adverse reactions or therapeutic failure (DOI: 10.1039/D0TB00354A). A technological step forward is the development of ‘lab-on-a-chip’ devices which not only miniaturized medical biosensors, but reduced costs and time while achieving unprecedented sensitivity and specificity. Along the same lines, the development of instrument-free point-of-care devices for detection of antibiotic resistance for rapid diagnosis of drug resistance offers a simple paper-based diagnostic tool. While these new developments are critical in healthcare diagnostics, long time serving medical community magnetic resonance imaging (MRI) stimulus-responsive polymers now serve as carriers capable of selectively activating contrast agents in pathological tissues (DOI: 10.1039/D0TB00366B), where the local pH environment and ion concentrations are different from normal tissues. In essence, improved efficacy of existing imaging techniques, molecular recognition-based separation and purification of biomolecules, or drug delivery systems are becoming widely available due to stimuli-responsive polymers. These developments are possible because of controlled polymerization, advanced polymer processing, and the capability of additive manufacturing, thus providing an outstanding opportunity for creating the device-level healthcare products through nano–micro–macro scaling. Future breakthroughs in health diagnostics may include polymers capable of self-healing,¹ signaling, or communications with macroscale properties exquisitely sensitive to molecular features of the surroundings with predictable anabolic and catabolic activities as well as the ability to disintegrate in a controlled manner.

There are numerous specialized topic areas in responsive polymeric materials utilized in healthcare diagnostics that were not included here due to space limitations. This themed issue aims to cover selected recent advances and applications of responsive polymers in healthcare diagnostics. The guest editors are thankful to all authors for delivering the high-quality contributions without whom this issue would not be possible. Furthermore, co-editor of this issue, Dr Gemma Davies, who spearheaded the entire project is thanked for her tireless efforts in bringing this issue to fruition. Finally, the entire editorial staff from Journal of Materials Chemistry B is thanked for their continued support and dedication during the production of this themed issue.

References

1. S. Wang and M. W. Urban, Self-healing polymers, Nat. Rev. Mater., 2020 DOI:10.1038/s41578-020-0202-4.

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