Areas of Expertise (5)
Biomimetic and Bio-inspired Materials
Nanostructured Soft Matter
Biomolecular Engineering and Self-assembly
Drug delivery and Nanomedicine
Sustainable Materials and Plastic Upcycling
R. Helen Zha, an assistant professor of chemical and biological engineering at Rensselaer Polytechnic Institute, focuses her research on developing bio-inspired materials for applications in human healthcare and sustainability. She earned her bachelors of science at MIT in Materials Science & Engineering with a focus on polymeric materials, before receiving her Ph.D. from Northwestern University. While at Northwestern, Zha worked as an NSF Graduate Research Fellow on self-assembling peptide-based materials. As a postdoctoral researcher at Eindhoven University of Technology in the Netherlands, Zha developed supramolecular materials with highly ordered nanostructures and photoswitchable properties. Following her work at Eindhoven, she moved to UC Berkeley where she worked as a postdoctoral researcher on bio-inspired antimicrobial coatings.
Massachusetts Institute of Technology: B.Sc., Materials Science & Engineering with a focus on polymeric materials 2007
Northwestern University: Ph.D. 2003
Eindhoven University of Technology in the Netherlands: Postdoctoral Researcher 2016
UC Berkeley: Postdoctoral Researcher 2017
Media Appearances (2)
RPI researchers working to develop virus-killing masks
While efforts are underway by many groups to develop an easy and effective method to sanitize the N-95 masks used by health care providers and first responders, a team at RPI is taking another approach. What if you could coat the masks with an anti-viral material - something that would kill the virus on contact?
Research Turns Plastic Waste into Biodegradable Silk
Plastics Today online
Solutions to big problems can spring from little things. In research at Rensselaer Polytechnic Institute in Troy, NY, a microorganism that digests common petroleum-based plastic waste and yields a biodegradable plastic alternative represents a new solution to an on-going problem.
Rapid Synthesis of Silk-Like Polymers Facilitated by Microwave Irradiation and Click ChemistryBiomacromolecules
Amrita Sarkar, Cody Edson, Ding Tian, Tanner D. Fink, Katherine Cianciotti, Richard A. Gross, Chulsung Bae, and R. Helen Zha
Silk is a natural fiber that surpasses most man-made polymers in its combination of strength and toughness. Silk fibroin, the primary protein component of silk, can be synthetically mimicked by a linear copolymer with alternating rigid and soft segments. Strategies for chemical synthesis of such silk-like polymers have persistently resulted in poor sequence control, long reaction times, and low molecular weights. Here, we present a two-stage approach for rapidly synthesizing silk-like polymers with precisely defined rigid blocks. This approach utilizes solid-phase peptide synthesis to create uniform oligoalanine “prepolymers”, followed by microwave-assisted step-growth polymerization with bifunctional poly(ethylene glycol). Multiple coupling chemistries and reaction conditions were explored, with microwave-assisted click chemistry yielding polymers with Mw ∼ 14 kg/mol in less than 20 min. These polymers formed antiparallel β-sheets and nanofibers, which is consistent with the structure of natural silk fibroin. Thus, our strategy demonstrates a promising modular approach for synthesizing silk-like polymers.
Coating Topologically Complex Electrospun Fibers with Nanothin Silk Fibroin Enhances Neurite Outgrowth in VitroACS Biomaterials Science & Engineering
Alexis Ziemba, Tanner Fink, Mary Clare Crochiere, Devan Puhl, Samichya Sapkota, Ryan Gilbert, R. Helen Zha.
Electrospun poly-l-lactic acid (PLLA) fibers are commonly used for tissue engineering applications because of their uniform morphology, and their efficacy can be further enhanced via surface modification. In this study, we aimed to increase neurite outgrowth along electrospun fibers by coating with silk fibroin (SF), a bioinert protein derived from Bombyx mori cocoon threads, shown to be neurocompatible. Aligned PLLA fibers were electrospun with smooth, pitted, and divoted surface nanotopographies and coated with SF by immersion in coating solution for either 12 or 24 h. Specifically, thin-film coatings of SF were generated by leveraging the controlled self-assembly of SF in aqueous conditions that promote β-sheet assembly. For both 12- and 24-h coatings, Congo Red staining for β-sheet structures confirmed the presence of SF coatings on PLLA fibers. Confocal imaging of fluorescein-labeled SF further demonstrated a homogeneous coating formation on PLLA fibers. No change in the water contact angle of the surfaces was observed after coating; however, an increase in the isoelectric point (pI) to values comparable with the theoretical pI of SF was seen. Notably, there was a significant trend of increased dorsal root ganglia (DRG) adhesion on scaffolds coated with SF, as well as greater neurite outgrowth on pitted and divoted fibers that had been coated with SF. Ultimately, this work demonstrated that thin-film SF coatings formed by self-assembly uniformly coat electrospun fibers, providing a new strategy to increase the neuroregenerative capacity of electrospun scaffolds. To our knowledge, this is the first instance of biomedical modification of topologically complex substrates using noncovalent methods.
Chemical Synthesis of Silk-Mimetic PolymersMaterials
Amrita Sarkar, Alexander J. Connor, Mattheos Koffas, R. Helen Zha
Silk is a naturally occurring high-performance material that can surpass man-made polymers in toughness and strength. The remarkable mechanical properties of silk result from the primary sequence of silk fibroin, which bears semblance to a linear segmented copolymer with alternating rigid (“crystalline”) and flexible (“amorphous”) blocks. Silk-mimetic polymers are therefore of great emerging interest, as they can potentially exhibit the advantageous features of natural silk while possessing synthetic flexibility as well as non-natural compositions. This review describes the relationships between primary sequence and material properties in natural silk fibroin and furthermore discusses chemical approaches towards the synthesis of silk-mimetic polymers. In particular, step-growth polymerization, controlled radical polymerization, and copolymerization with naturally derived silk fibroin are presented as strategies for synthesizing silk-mimetic polymers with varying molecular weights and degrees of sequence control. Strategies for improving macromolecular solubility during polymerization are also highlighted. Lastly, the relationships between synthetic approach, supramolecular structure, and bulk material properties are explored in this review, with the aim of providing an informative perspective on the challenges facing chemical synthesis of silk-mimetic polymers with desirable properties.
Universal nanothin silk coatings via controlled spidroin self-assemblyBiomaterials Science
R. Helen Zha, Peyman Delparastan, Tanner D. Fink, Joschka Bauer, Thomas Scheibel, and Phillip B. Messersmith
Robust, biocompatible, and facile coatings are promising for improving the in vivo performance of medical implants and devices. Here, we demonstrate the formation of nanothin silk coatings by leveraging the biomimetic self-assembly of eADF4(C16), an amphiphilic recombinant protein based on the Araneus diadematus dragline spidroin ADF4. These coatings result from concurrent adsorption and supramolecular assembly of eADF4(C16) induced by KH2PO4, thereby providing a mild one-pot coating strategy in which the coating rate can be controlled by protein and KH2PO4 concentration. The thickness of the coatings ranges from 2–30 nm depending on the time immersed in the aqueous coating solution. Coatings can be formed on hydrophobic and hydrophilic substrates regardless of surface chemistry and without requiring specialized surface activation. Moreover, coatings appear to be stable through vigorous rinsing and prolonged agitation in water. Grazing incidence wide angle X-ray scattering, single-molecule force spectroscopy, and Congo red staining techniques confirm the formation of β-sheet nanocrystals within the eADF4(C16) coating, which contributes to the cohesive and adhesive stability of the material. Coatings are exceptionally smooth in the dry state and are hydrophilic regardless of substrate hydrophobicity. Under aqueous conditions, nanothin silk coatings exhibit the properties of a hydrogel material.
Silk and Silk‐Like Supramolecular MaterialsMacromolecular Rapid Communications
Tanner D. Fink R. Helen Zha
Silk is a source of marvel for centuries as one of nature's high‐performance materials. More recently, chemical and structural analysis techniques have helped explore the relationship between silk's properties and its hierarchical structure. Furthermore, recombinant protein engineering as well as polymer and organic synthesis techniques have enabled the production of silk‐like materials. It has become apparent that silk is a supramolecular polymer with many of the properties exhibited by well‐known synthetic supramolecular materials, such as block copolymers, liquid crystals, thermoplastic elastomers, and self‐assembling peptides. In this review, the hierarchical structure and supramolecular assembly of silk are discussed in comparison to these synthetic supramolecular systems. By focusing on the connections between chemical structure, nanoscale molecular organization, and material properties, the aim is to provide perspectives on the rational design of advanced soft matter to supramolecular chemists and molecular engineers who look to nature for inspiration.