(6hy) Designing Polymers As Molecular Recognition Agents for Diagnostic Biosensing and Imaging

In most diagnostic tests, whether biosensor or imaging based, biomolecules are used for molecular recognition of biomarkers. While antibodies and enzymes exhibit unparalleled specificity, they are expensive and thermally unstable, requiring cold-chain methods for transportation and storage. As the healthcare field move towards point-of-care testing and personalized diagnostics, there is a need to make diagnostic tests more affordable and environmentally robust. To this end, I am interested in engineering polymers capable of molecular recognition. During my PhD, I designed and tested different strategies for synthesizing hydrogel particles capable of protein biomarker detection (“Investigation of Micro- and Nanoscale Hydrogels as Protein Receptors for Use in Diagnostic Biosensors”, advisor Nicholas Peppas). I then chose to pursue a postdoctoral position under the advisement of Christopher Bowman to learn how to synthesize tandem repeat “click” nucleic acids for use in disease diagnosis and medical imaging.

As a faculty candidate, I aim to apply my knowledge and previous research experience in polymer chemistry, biophysical methods, and nanotechnology to continue advancing the field of polymer-based diagnostics. The multidisciplinary nature of this type of research aligns with my interests across the fields of chemistry, materials science, nanotechnology, and statistics. Future directions that excite me include, but are not limited to, the following:

• Differential sensing using cross-reactive polymers. I began investigating this relatively unexplored field during my PhD. By applying multivariate statistical methods, signal patterns generated from the cross-reactive polymers could be linked to disease-related changes in biomarker levels in human tears. By further tuning polymer chemistry and architecture, I expect that a wide-range of cross-reactive receptors for different biomarker panels could be designed.
• Dynamic covalent chemistry for template-directed polymer synthesis. Dynamic covalent chemistry is emerging as a powerful tool for manipulating material properties. In parallel to the first direction (i.e., differential sensing), I am excited to explore dynamic covalent chemistry approaches to improve selectivity of artificial molecular recognition agents.
• Applications of click nucleic acids in diagnostic imaging. The click nucleic acids (CNAs) being developed in the Bowman Laboratory are an emerging class of synthetic nucleic acids. Unlike DNA and peptide nucleic acids, tandem repeat sequences of CNAs can be efficiently and affordably synthesized. As such, CNAs will have great utility in imaging and detection of disease-associated, polymorphic tandem repeat sequences.

Teaching Interests:

With a B.S. in Materials Science and Engineering and a Ph.D. in Biomedical Engineering, I am well-suited to teach courses covering a range of chemical and biological engineering topics. I am particularly interested in teaching courses covering topics such as biophysical methods, biomaterials and biotechnology, polymer science, nanotechnology, and statistical analysis for engineers, as these are the topics I am most intimately familiar with given my research experiences. In addition to leading lectures, I would be interested in leading laboratory courses, including designing new experiments to help students better grasp complex topics.

Regardless of the topic, my approach to teaching will be centered around designing problem sets that, while challenging, will ultimately lead to a better understanding of the topics covered in class. While at the time I may have said otherwise, working tirelessly through problem sets with my peers were some of my favorite memories from my undergraduate education. I learned so much through these problem sets, not only about the concepts covered in class, but also about the importance of teamwork and learning new strategies for problem solving.

Research Experience:

Based on my undergraduate research experiences, I entered the Biomedical Engineering graduate program at University of Texas at Austin with a strong interest in polymer chemistry and nanomaterials. The objective of my dissertation research in the Peppas Laboratory was to develop a low-cost, non-invasive screening test for Sjögren’s syndrome (SS), an autoimmune disease that primarily affects the exocrine system. My hypothesis was that, by using polymers as molecular recognition agents and nanomaterials for signal transduction, it would be possible to develop an inexpensive biosensor for detecting concentration changes of SS protein biomarkers. During the first three years of my PhD, the synthetic receptors I focused on were molecularly imprinted polymers (MIPs). MIPs are made by incubating a template molecule, such as a protein biomarker, with monomers that form favorable non-covalent interactions with the template. I worked on developing MIPs for lysozyme, a biomarker of SS, with an emphasis on characterizing the selectivity of the MIPs for lysozyme. I found that MIPs had higher adsorption capacity for proteins than non-imprinted polymers (NIPs), but the imprinting process did not improve selectivity for lysozyme. Additionally, the data showed that the MIPs and NIPs were cross-reactive (i.e., semi-selective) for proteins that had similar charges as lysozyme.

Given the added time and cost associated with synthesizing MIPs without improvement of selectivity, I transitioned my research to embrace the cross-reactivity of charge-containing hydrogels. Specifically, I shifted from the idea of developing a biosensor using highly selective molecular recognition agents to the idea of using differential sensor arrays. In this new approach, addition of an analyte solution or mixture to a set of cross-reactive receptors produces a signal pattern that corresponds to the binding affinity of different receptors for different analytes. The cross-reactive receptors I developed were poly(N-isopropylacrylamide) (poly(NIPAM)) nanogels with different ionic functional groups. These studies demonstrated that by using turbidity changes as input for multivariate analysis, it was possible to differentiate eleven proteins and detect clinically relevant changes in lysozyme concentration with as few as two nanogels. The last major thrust of my dissertation research was to synthesize these poly(NIPAM) nanogels on the surface of gold nanomaterials for use in a localized surface plasmon resonance (LSPR)-based biosensor. Varying the concentration of two SS biomarkers, lysozyme and lactoferrin, in human tears led to concentration-dependent shifts in the LSPR wavelength of poly(NIPAM-co-MAA) coated AuNSs.

After completing my PhD, I still had a strong interest in biosensing using synthetic polymers for molecular recognition. To this end, I joined the laboratory of Dr. Christopher Bowman at University of Colorado Boulder, where I am working on characterizing and applying “click” nucleic acids (CNAs) for biosensing applications. In addition to characterizing CNA-DNA binding, I am working towards applying the CNAs as diagnostic imaging probes.

Publications:

1. H.R. Culver, I. Sharma, M.E. Wechsler, E.V. Anslyn, N.A. Peppas, “Charged poly(N-isopropylacrylamide) nanogels for use as differential protein receptors in a turbidimetric sensor array,” Analyst 2017, 142, 3183-3193.
2. H.R Culver, N.A. Peppas, “Protein-imprinted polymers: The shape of things to come?” Chem. Mater. 2017, 29, 5753-5761.
3. H.R. Culver, J.R. Clegg, N.A. Peppas, “Analyte-responsive hydrogels: Intelligent materials for biosensing and drug delivery,” Acc. Chem. Res. 2017, 50 (2), 170-178.
4. H.R. Culver, S.D. Steichen, N.A. Peppas, “A closer look at the impact of molecular imprinting on adsorption capacity and selectivity for protein templates,” Biomacromolecules 2016, 17 (12), 4045-4053.
5. H.R. Culver, S.D. Steichen, M. Herrera-Alonso, N.A. Peppas, “A versatile route to colloidal stability and surface functionalization of hydrophobic nanomaterials,” Langmuir 2016, 32, 5629-5636.
6. J.L. Santos, Y. Li, H.R. Culver, M.S. Yu, M. Herrera-Alonso, “Targeting denatured collagen through collagen mimetic peptide decorated conducting polymer nanoparticles,” Chem. Commun. 2014, 50, 15045-15048.
7. H.R. Culver, A.M. Daily, A. Khademhosseini, N.A. Peppas, “Intelligent recognitive systems in nanomedicine,” Curr. Opin. Chem. Eng. 2014, 4, 105–113.

Proposal writing experience:

Fellowships:

• NSF Graduate Research Fellowship (funded)
• NSF Graduate Opportunities Worldwide Fellowship (funded)
• USAID Development Research and Innovation Fellowship (funded)
• F32 NS106791 (not discussed)
• F32 GM130082 (scored, not funded – currently in revision)

Grants (Assisted PIs):

• NIH R01 EB019472 (scored, not funded)
• NIH R01 EB022025 (original scored, not funded; resubmission funded)
• NIH R21 NS107984 (scored, not funded)
• DARPA proposal in response to Broad Agency Announcement #HR001118S0034 (under review)

Awards:

• Donald D. Harrington Dissertation Fellowship
• Philanthropic Educational Organization Scholar Award
• Thrust 2000 – O.L. Chenoweth Endowed Graduate in Engineering Fellowship
• BMES Innovation and Career Development Award
• The Materials Science and Engineering Achievement Award, Johns Hopkins University