STEP: Spinneret based Tunable Engineering Parameters

Amrinder Nain, Engr

Department of Mechanical Engineering
237 Kelly Hall - 0194
Blacksburg, VA 24061

Dr. Amrinder S. Nain

Associate Professor


Current Lab Members:

Abinash Padhi (PhD Candidate)

Aniket Jana (PhD Candidate)

Apratim Mukherjee (PhD Candidate)

Alex Hall (Masters Student)

Jugroop Singh (Masters Student)

Christopher Delaughter (Undergrad)

Matthew Apperson (Undergrad)


Puja Sharma

Amritpal Gill

Brian Koons

Sean Meehan

Kevin Sheets

Ji Wang


The Spinneret based Tunable Engineering Parameters (STEP) Laboratory was founded by Dr. Amrinder S Nain in 2009. Our lab specializes in manufacturing of mechanistically tunable polymeric nanofibers using a non-electrospinning technology and investigating the interactions of biological systems with various polymeric nanofibers. Our lab takes an interdisciplinary approach to research by working together with the departments of Mechanical Engineering and Biomedical Engineering and Mechanics, and the Macromolecules and Interfaces Institute at Virginia Tech.

Our current research endeavors include studies of cancer cell protrusion, single and collective cell migration, apoptosis dynamics of mesenchymal stem cells (MSCs), formation of cancer leader cells and active inside-out and outside-in nanoscale force measurements of cells.

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Research Topics

  • Fiber Manufacturing

    Spinneret-based Tunable Engineered Parameters (STEP) Technique

    The Spinneret based Tunable Engineering Parameters (STEP) is a dry spinning technique that allows the deposition of nano-micron sized diameter fibers with user defined control of diameter, spacing, and deposition angle.  Using the STEP technique, various polymers (polystyrene, polyurethane, poly (methyl methacrylate), poly (lactic-co-glycolic acid) can be deposited over a substrate to form highly aligned nanofibers with desired parameters. These fiber composites provide a unique platform for a wide range of biomedical applications such as studies of single cell behavior, tissue engineering, anti-bacterial surface designs, and wound healing.

    By using Spinneret based Tunable Engineered Parameters (STEP) technique, fibers of diameters ranging from less than 100 nm to 1.5 µm can be deposited. These nanofibers have superior spinnability and can be manufactured in either a single array of parallel and highly aligned fibers, in cross-hatch patterns of orthogonal fibers or in multilayer assemble of more than one layer of fibers.

    Our ability to precisely vary parameters like diameter, fiber spacing and length introduces desired changes in mechanical properties (such as structural stiffness) of the fibers. This can be utilized to study the response of single cells as the mechanical properties of their microenvironment change. Control of fiber spacing has also been deemed useful in the study of designing anti-bacterial surfaces and hydrophobic materials.

  • Advanced Materials

    Micro/Nano Composite Fibers

    Infusion of nano materials in polymer composites opens a new door to the composites industry. With the vision to make stiffer composite structures by adding nanoparticles in polymers, several approaches were followed to functionalize nanoparticles and later add these particles to a different polymer system. This was done to improve the interfacial attraction of nanoparticles in the polymer matrix. However, creating a material with superior mechanical property with homogenous nanoparticle dispersion throughout the polymer matrix is a great challenge Therefore, our group investigates different solution schemes to get a uniform nanoparticle-reinforced matrix of polymer nanofibers.

    A potential application of such nanoparticle – polymer fiber composites is in the design of armor vests. Incorporating segments of stiffer composites nanoparticle-fibers scaffolds in the vest can potentially improve the functionality of these vests by offering protection against ballistic properties of projectiles.

    Fiber Characterization

    Nanofiber characterization is essential for exploring the potential applications of our nanofibers in the fields of biomedical, electronic, and electromechanical devices. Characterization of these structures poses special challenges when compared to standard tensile or bending tests due to manipulation difficulties and unattainable boundary conditions. Our group is exploring new approaches to attain fixed boundary conditions by using the STEP technique. Using high spatial resolution and force-sensing capabilities provided by the AFM and Nanoindenter, we have, and continue to explore a wide spectrum of mechanical properties including elastic modulus, ultimate strength, and failure.

  • Biomedical

    Cellular Dynamics

    One of the major objectives of our lab is to study the influence of mechanical and geometrical properties of nanofibers on single cell dynamics. Cells are surrounded by extracellular matrix (ECM) inside the body. The ECM is composed of nano-micro fibrous proteins, non-fibrous proteins, proteoglycans and various cytokines. It continuously provides biochemical and biophysical cues to cells. Changes in ECM can influence cell differentiation, behavior and migration. Furthermore, mechanical changes in the ECM have been attributed to diseases like cancer and wound ulcers. Therefore obtaining a better understanding of single cell interactions with its immediate microenvironment has powerful implications in fields like tissue engineering and oncology.

    Our lab focuses in understanding the biophysical reactions of single cells as they interact with the mechanically characterized STEP nanofibers. The fibers that are in the nano-sub micrometer range closely represent the dimensionality of the fibrous ECM in vivo. STEP enables the fine tuning of the mechanical and geometrical properties of these fibers which can be used to study single and collective cell behavior using time lapse video microscopy and immunofluorescence.

    Cancer Cell Behavior

    Cancer causes over a $100 billion in health and morbidity costs annually, and is the second leading cause of death in the U.S. The extracellular matrix (ECM) that surrounds cancer cells plays an essential role in the behavior of cancer cells and progression of cancer. However, platforms that closely represent the ECM are limited, compromising our ability to perform realistic in vitro experiments. Furthermore, the past few decades have been devoted mostly to understand the biochemical and genetic aspects of cancer, and the understanding of cancer biophysics in still in its infancy.  The STEP technique enables the manufacturing of mechanistically tunable polymeric nanofibers that closely represent the dimensionality of fibrous proteins in the ECM. The migratory, genetic and protein expression of various cancer cells in response to changes in the mechanical and geometric properties of the nanofibers can be investigated. Currently, we are using highly metastatic cancer cell lines DBTRG-05MG, MDA-MB-231 and PC-3 (glioblastoma, breast cancer, and prostate cancer respectively) to investigate the cell protrusion dynamics, leader cell migration, and inside-out and outside-in cell forces. We intend to underscore the less probed field of cancer biophysics, and emphasize the fact that cancer should be viewed as a system that encompasses not only the biochemical, but also the biophysical aspects of a tumor.

    Hepatic Tissue Engineering

    Liver is a multifunctional organ and plays a vital role in homeostasis, drug metabolism and toxicity control. It detoxifies toxic elements and maintains homeostasis by regulating proteins, lipids and carbohydrates in our body. Therefore, its failure is often times catastrophic and fatal. Current treatments for acute liver failure are limited to liver transplantation involving a donor. Due to limited availability of healthy liver donors, the prognosis of liver failure is compromised. Therefore, hepatic tissue engineering opens a promising alternative avenue towards the treatment of liver failure. Providing long term functional maintenance of a large number of hepatocytes that represent a ‘significant liver mass’ in a true 3D environment is challenging using existing platforms used for  hepatic engineering. . Using the STEP platform, we have recently demonstrated that primary hepatocytes are able to maintain their differentiated state when cultured on suspended cross-hatched pattern of polymeric nanofibers. Compared to other culturing methods where cells are either placed in suspension or attached to flat substrates, the STEP platform provides a 3D nanofiber assembly that allows the cells to attach onto suspended nanofibers.  We have observed that the hepatocytes conform to the 3D environment by wrapping around the fibers over time. These hepatocytes form suspended acrobatic monolayers, are have been observed to maintain their differentiated state and function over significant amount of time.

    Aortic Aneurysm

    Aortic aneurisms, or aortic dissections, are potentially fatal ruptures of the aorta that arise from a gradual loss of elasticity within endothelial cells over time. Our lab is studying the general behavior of both normal and compromised cells on various geometries in the hopes of detecting differing patterns between the two cell types


  1. Methods, Apparatuses and Systems for Fabrication of Polymeric Nano- and Micro-fibers with controlled Diameter and Orientation, Issued.
  2. Control of Cell Behavior by Aligned Micro/Nanofibrous Biomaterial Scaffolds Fabricated by Spinneret-Based Tunable Engineered Parameters (STEP) Technique, Issued.
  3. Methods, Apparatuses and Systems for Fabrication of Polymeric Nano- and Micro-Fibers in Aligned Configurations, Issued.

Selected Publications:

Mukherjee, A., Koons, B., Sharma, P., Ye, Z., Behkam, B., and Nain, A.S., “Cancer Protrusions on a Tightrope: Nanofiber Curvature Constrast Quantitates Single Protrusion Dynamics.” ACS Nano, Accepted for Publication on 11/15/2017

Sharma, P., Ng, C., Jana, A., Padhi, A., Szymanski, P., Lee, J.S.H., Behkam, B., Nain, A.S.N., “Aligned Fibers Direct Collective Cell Migration to Engineer Closing and Nonclosing Wound Gaps.” MBoC28 (19), 2017

Hall, A., Chan, P., Sheets, K., Apperson, M., Delaughter, C., Gleason, T.G., Phillippi, J.A., and Nain, A.S., “Nanonet Force Microscopy for Measuring Forces in Single Smooth Muscle Cells of Human Aorta”, MBoC28 (25), 2017

Sheets, K., Wang, J., Zhao, W., Kapania, R., and Nain, A.S., “Nanonet Force Microscopy for Measuring Cell Forces”, 111 (1), pp. 197-207, 2016

Meehan, S., and Nain, A.S., “Role of Suspended Fiber Structural Stiffness and Curvature on Single-Cell Migration, Nucleus Shape, and Focal-Adhesion-Cluster Length.”, 107 (11), pp. 2604-2611, 2014

Sharma, P., Kim, A., Gill, A., Wang, J., Sheets, K., Behkam, B., and Nain, A.S., “Aligned and Suspended Fiber Force Probes for Drug Testing at Single Cell Resolution.”, Biofabrication(4), pp. 1-10, 2014

Wang, J., and Nain, A.S., “Suspended Micro/Nanofiber Hierarchical Biological Scaffolds Fabricated Using Non-Electrospinning STEP Technique”, Langmuir30 (45), pp. 13641-13649., 2014

Sheets, K., Wunsch, S., Ng, C., and Nain, A.S., “Shape-dependent Cell Migration and Focal Adhesion Organization on Suspended and Aligned Nanofiber Scaffolds”, Acta Biomaterialia9(7), pp. 7169-7177, 2013

Sheets, K., Wang, J., Meehan, S., Sharma, P., Ng, C., Khan, M., Koons, B., Behkam, B., and Nain, A.S., “Cell Fiber Interactions on Aligned and Suspended Nanofiber Scaffolds.”, Journal of Biomaterials and Tissue Eng.(4), pp. 353-368, 2013

Sharma, P., Sheets, K., Elankumaran, S., and Nain, A.S., “The Mechanistic Influence of Aligned Nanofibers on Cell Shape, Migration and Blebbing Dynamics of Glioma Cells.” Integr. Biol., 5, pp. 1036-1044, 2013

Nain, A.S., Sitti, M., Jacobson, A., Kowalewski, T., and Amon, C., “Dry Spinning Based Spinneret Tunable Engineering Parameters (STEP) Technique for Controlled and Aligned Deposition of Polymeric Nanofibers.” Macr. Rapid Comm.30, pp. 1406-1412, 2009

Laboratory address and students offices:

Department of Mechanical Engineering
430 Kelly Hall
Blacksburg, VA 24061

Department of Mechanical Engineering
College of Engineering, Virginia Tech
635 Prices Fork Road, Blacksburg, VA 24061