Department of Materials Science and Engineering (MSE)

Permanent URI for this community

https://hdl.handle.net/10919/24369
The mission of the Materials Science and Engineering (MSE) Department at Virginia Tech is to lead the multidisciplinary efforts of the College of Engineering, the University, and the Commonwealth in the field of Materials Science and Engineering through our programs of undergraduate and graduate education, research, and continuing education. In service to our many constituencies, we are committed to the excellence of the contributions of faculty members, staff, and students, as judged by the principles and philosophies to which we aspire.

Browse

Browsing Department of Materials Science and Engineering (MSE) by Department "Chemical Engineering"

Now showing 1 - 6 of 6
  • Thumbnail Image
    Bioactive Cellulose Nanocrystal-Poly(epsilon-Caprolactone) Nanocomposites for Bone Tissue Engineering Applications
    Hong, Jung Ki; Cooke, Shelley L.; Whittington, Abby R.; Roman, Maren (2021-02-25)
    3D-printed bone scaffolds hold great promise for the individualized treatment of critical-size bone defects. Among the resorbable polymers available for use as 3D-printable scaffold materials, poly(epsilon-caprolactone) (PCL) has many benefits. However, its relatively low stiffness and lack of bioactivity limit its use in load-bearing bone scaffolds. This study tests the hypothesis that surface-oxidized cellulose nanocrystals (SO-CNCs), decorated with carboxyl groups, can act as multi-functional scaffold additives that (1) improve the mechanical properties of PCL and (2) induce biomineral formation upon PCL resorption. To this end, an in vitro biomineralization study was performed to assess the ability of SO-CNCs to induce the formation of calcium phosphate minerals. In addition, PCL nanocomposites containing different amounts of SO-CNCs (1, 2, 3, 5, and 10 wt%) were prepared using melt compounding extrusion and characterized in terms of Young's modulus, ultimate tensile strength, crystallinity, thermal transitions, and water contact angle. Neither sulfuric acid-hydrolyzed CNCs (SH-CNCs) nor SO-CNCs were toxic to MC3T3 preosteoblasts during a 24 h exposure at concentrations ranging from 0.25 to 3.0 mg/mL. SO-CNCs were more effective at inducing mineral formation than SH-CNCs in simulated body fluid (1x). An SO-CNC content of 10 wt% in the PCL matrix caused a more than 2-fold increase in Young's modulus (stiffness) and a more than 60% increase in ultimate tensile strength. The matrix glass transition and melting temperatures were not affected by the SO-CNCs but the crystallization temperature increased by about 5.5 degrees C upon addition of 10 wt% SO-CNCs, the matrix crystallinity decreased from about 43 to about 40%, and the water contact angle decreased from 87 to 82.6 degrees. The abilities of SO-CNCs to induce calcium phosphate mineral formation and increase the Young's modulus of PCL render them attractive for applications as multi-functional nanoscale additives in PCL-based bone scaffolds.
  • Thumbnail Image
    Fabrication and Characterization of Three Dimensional Electrospun Cortical Bone Scaffolds
    Andric, Tea; Taylor, Brittany L.; Degen, Katherine E.; Whittington, Abby R.; Freeman, Joseph W. (De Gruyter Open, 2014)
    Bone is a composite tissue composed of an organic matrix, inorganic mineral matrix and water. Structurally, bone is organized into two distinct types: trabecular (or cancellous) and cortical (or compact) bone. Cortical bone is highly organized, dense and composed of tightly packed units or osteons whereas trabecular bone is highly porous and usually found within the confines of cortical bone. Osteons, the subunits of cortical bone, consist of concentric layers of mineralized collagen fibers. While many scaffold fabrication techniques have sought to replicate the structure and organization of trabecular bone, very little research focuses on mimicking the organization of native cortical bone. In this study we fabricated three-dimensional electrospun cortical scaffolds by heat sintering individual osteon-like scaffolds. The scaffolds contained a system of channels running parallel to the length of the scaffolds, as found naturally in the haversian systems of bone tissue. The purpose of the studies discussed in this paper was to develop a mechanically enhanced biomimetic electrospun cortical scaffold. To that end we investigated the appropriate mineralization and cross-linking methods for these structures and to evaluate the mechanical properties of scaffolds with varying fiber angles. Cross-linking the gelatin in the scaffolds prior to the mineralization of the scaffolds proved to help prevent channels of the osteons from collapsing during fabrication. Premineralization, before larger scaffold formation and mineralization, increased mineral deposition between the electrospun layers of the scaffolds. A combination of cross-linking and premineralization significantly increased the compressive moduli of the individual scaffolds. Furthermore, scaffolds with fibers orientation ranging between 15° and 45° yielded the highest compressive moduli and yield strength.
  • Thumbnail Image
    Functionalized Cellulose Nanocrystal Nanocomposite Membranes with Controlled Interfacial Transport for Improved Reverse Osmosis Performance
    Smith, Ethan D.; Hendren, Keith D.; Haag, James; Foster, Earl Johan; Martin, Stephen M. (MDPI, 2019-01-20)
    Thin-film nanocomposite membranes (TFNs) are a recent class of materials that use nanoparticles to provide improvements over traditional thin-film composite (TFC) reverse osmosis membranes by addressing various design challenges, e.g., low flux for brackish water sources, biofouling, etc. In this study, TFNs were produced using as-received cellulose nanocrystals (CNCs) and 2,2,6,6-Tetramethylpiperidine-1-oxyl (TEMPO)-oxidized cellulose nanocrystals (TOCNs) as nanoparticle additives. Cellulose nanocrystals are broadly interesting due to their high aspect ratios, low cost, sustainability, and potential for surface modification. Two methods of membrane fabrication were used in order to study the effects of nanoparticle dispersion on membrane flux and salt rejection: a vacuum filtration method and a monomer dispersion method. In both cases, various quantities of CNCs and TOCNs were incorporated into a polyamide TFC membrane via in-situ interfacial polymerization. The flux and rejection performance of the resulting membranes was evaluated, and the membranes were characterized via attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), transmission electron microscopy (TEM), and atomic force microscopy (AFM). The vacuum filtration method resulted in inconsistent TFN formation with poor nanocrystal dispersion in the polymer. In contrast, the dispersion method resulted in more consistent TFN formation with improvements in both water flux and salt rejection observed. The best improvement was obtained via the monomer dispersion method at 0.5 wt% TOCN loading resulting in a 260% increase in water flux and an increase in salt rejection to 98.98 ± 0.41% compared to 97.53 ± 0.31% for the plain polyamide membrane. The increased flux is attributed to the formation of nanochannels at the interface between the high aspect ratio nanocrystals and the polyamide matrix. These nanochannels serve as rapid transport pathways through the membrane, and can be used to tune selectivity via control of particle/polymer interactions.
  • Thumbnail Image
    Gradient Poly(ethylene glycol) Diacrylate and Cellulose Nanocrystals Tissue Engineering Composite Scaffolds via Extrusion Bioprinting
    Frost, Brody A.; Sutliff, Bradley P.; Thayer, Patrick; Bortner, Michael J.; Foster, Earl Johan (2019-10-18)
    Bioprinting has advanced drastically in the last decade, leading to many new biomedical applications for tissue engineering and regenerative medicine. However, there are still a myriad of challenges to overcome, with vast amounts of research going into bioprinter technology, biomaterials, cell sources, vascularization, innervation, maturation, and complex 4D functionalization. Currently, stereolithographic bioprinting is the primary technique for polymer resin bioinks. However, it lacks the ability to print multiple cell types and multiple materials, control directionality of materials, and place fillers, cells, and other biological components in specific locations among the scaffolds. This study sought to create bioinks from a typical polymer resin, poly(ethylene glycol) diacrylate (PEGDA), for use in extrusion bioprinting to fabricate gradient scaffolds for complex tissue engineering applications. Bioinks were created by adding cellulose nanocrystals (CNCs) into the PEGDA resin at ratios from 95/5 to 60/40 w/w PEGDA/CNCs, in order to reach the viscosities needed for extrusion printing. The bioinks were cast, as well as printed into single-material and multiple-material (gradient) scaffolds using a CELLINK BIOX printer, and crosslinked using lithium phenyl-2,4,6-trimethylbenzoylphosphinate as the photoinitiator. Thermal and mechanical characterizations were performed on the bioinks and scaffolds using thermogravimetric analysis, rheology, and dynamic mechanical analysis. The 95/5 w/w composition lacked the required viscosity to print, while the 60/40 w/w composition displayed extreme brittleness after crosslinking, making both CNC compositions non-ideal. Therefore, only the bioink compositions of 90/10, 80/20, and 70/30 w/w were used to produce gradient scaffolds. The gradient scaffolds were printed successfully and embodied unique mechanical properties, utilizing the benefits of each composition to increase mechanical properties of the scaffold as a whole. The bioinks and gradient scaffolds successfully demonstrated tunability of their mechanical properties by varying CNC content within the bioink composition and the compositions used in the gradient scaffolds. Although stereolithographic bioprinting currently dominates the printing of PEGDA resins, extrusion bioprinting will allow for controlled directionality, cell placement, and increased complexity of materials and cell types, improving the reliability and functionality of the scaffolds for tissue engineering applications.
  • Thumbnail Image
    Investigation into Polyurethane at Varying Dose Rates of Ionizing Radiation for Clinical Application
    Cooke, Shelley L.; Whittington, Abby R. (Hindawi, 2018-10-01)
    Polyurethanes (PUs) are commonly used materials for medical devices. These devices are exposed repeatedly to radiation when patients undergo radiotherapy treatments. It has been found that peripherally inserted central catheters (PICCs) and central venous catheters (CVCs) fail at an increased rate (14.7% and 8.8%, respectively) when radiated. Currently, little research is available on increased failure seen in conjunction with radiation, but complex in vivo environments within a human patient make it difficult to isolate effects of individual variables. This research investigated effects of radiation in an aqueous environment to determine whether radiation combined with a mimicked in vivo environment is sufficient to change PU devices. The following dose rates were used in this study: 3.2 Gy·min−1, 4.5 Gy·min−1, 44 Gy·min−1, and 833 Gy·min−1. Samples were characterized in four main ways: cellular response, physical changes, chemical changes, and mechanical changes. Results reveal normal cellular response at all dose rates, indicating dose rate does not alter cellular adhesion or proliferation, and biocompatibility of the material is not being altered. Results from physical, chemical, and mechanical effects confirm that varying dose rates alone do not initiate material changes, which negates the hypothesis that varying dose rates of radiation contribute to the complications in PICC and CVCs.
  • Thumbnail Image
    Using startup of steady shear flow in a sliding plate rheometer to determine material parameters for the purpose of predicting long fiber orientation
    Ortman, Kevin; Baird, Donald G.; Wapperom, Peter; Whittington, Abby R. (AIP Publishing, 2012-07-01)
    The properties of long glass fiber reinforced parts, such as those manufactured by means of injection molding and compression molding, are highly dependent on the fiber orientation generated during processing. A sliding plate rheometer was used to understand the transient stress and orientation development of concentrated long glass fibers during the startup of steady shear flow. An orientation model and stress tensor combination, based on semiflexible fibers, was assessed in its ability to predict fiber orientation when using model parameters obtained from the fits of the stress responses. Specifically, samples of different initial fiber orientations was subjected to the startup of steady shear flow, and an orientation model based on bead and rod theory was coupled with a derived stress tensor that accounts for the semiflexibility of the fibers to obtain the corresponding model parameters. The results showed the semiflexible orientation model and stress tensor combination, overall, provided improved rheological results as compared to the Folgar-Tucker model when coupled with the stress tensor of Lipscomb et al. [J. Non-Newtonian Fluid Mech. 26, 297-325 (1988)]. Furthermore, it was found that both stress tensors required empirical modification to accurately fit the measured data. Finally, orientation models provided encouraging results when predicting the transient fiber orientation for all initial fiber orientations explored. (C) 2012 The Society of Rheology. [http://dx.doi.org/10.1122/1.4717496]