Browsing by Author "Frost, Brody A."
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- Gradient Poly(ethylene glycol) Diacrylate and Cellulose Nanocrystals Tissue Engineering Composite Scaffolds via Extrusion BioprintingFrost, 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.
- Isolation of Thermally Stable Cellulose Nanocrystals from Spent Coffee Grounds via Phosphoric Acid HydrolysisFrost, Brody A.; Foster, Earl Johan (2020-02-01)As the world's population exponentially grows, so does the need for the production of food, with cereal production growing annually from an estimated 1.0 billion to 2.5 billion tons within the last few decades. This rapid growth in food production results in an ever increasing amount of agricultural wastes, of which already occupies nearly 50% of the total landfill area. For example, is the billions of dry tons of cellulose-containing spent coffee grounds disposed in landfills annually. This paper seeks to provide a method for isolating cellulose nanocrystals (CNCs) from spent coffee grounds, in order to recycle and utilize the cellulosic waste material which would otherwise have no applications. CNCs have already been shown to have vast applications in the polymer engineering field, mainly utilized for their high strength to weight ratio for reinforcement of polymer-based nanocomposites. A successful method of purifying and hydrolyzing the spent coffee grounds in order to isolate usable CNCs was established. The CNCs were then characterized using current techniques to determine important chemical and physical properties. A few crucial properties determined were aspect ratio of 12 +/- 3, crystallinity of 74.2%, surface charge density of (48.4 +/- 6.2) mM/kg cellulose, and the ability to successfully reinforce a polymer based nanocomposite. These characteristics compare well to other literature data and common commercial sources of CNCs.
- Materials for the Spine: Anatomy, Problems, and SolutionsFrost, Brody A.; Camarero-Espinosa, Sandra; Foster, Earl Johan (MDPI, 2019-01-14)Disc degeneration affects 12% to 35% of a given population, based on genetics, age, gender, and other environmental factors, and usually occurs in the lumbar spine due to heavier loads and more strenuous motions. Degeneration of the extracellular matrix (ECM) within reduces mechanical integrity, shock absorption, and swelling capabilities of the intervertebral disc. When severe enough, the disc can bulge and eventually herniate, leading to pressure build up on the spinal cord. This can cause immense lower back pain in individuals, leading to total medical costs exceeding $100 billion. Current treatment options include both invasive and noninvasive methods, with spinal fusion surgery and total disc replacement (TDR) being the most common invasive procedures. Although these treatments cause pain relief for the majority of patients, multiple challenges arise for each. Therefore, newer tissue engineering methods are being researched to solve the ever-growing problem. This review spans the anatomy of the spine, with an emphasis on the functions and biological aspects of the intervertebral discs, as well as the problems, associated solutions, and future research in the field.
- Polymer Composite Spinal Disc ImplantsFrost, Brody A. (Virginia Tech, 2017)The goal of this research study was to create an artificial annulus fibrosus similar to that of the natural intervertebral disc, as well as find preliminary results for vertebral endplate connection and nucleus pulposus internal pressure, for the correction of disc degeneration in the spine. The three-part composite samples needed to demonstrate good shock absorption and load distribution while maintaining strength and flexibility, and removing the need for metal in the body, something of which no current total disc replacement or spinal fusion surgery can offer. For this study, the spinal disc was separated into its three different components, the annulus fibrosus, the nucleus pulposus, and the vertebral endplates, each playing a vital role in the function of the disc. Two low-cost materials were selected, a Covestro polyurethane and cellulose nanocrystals, for the purpose of creating a polymer composite spinal disc implant. A methodology was established for creating the cast composite material for use as an annulus fibrosus, while also investigating its mechanical properties. The same composite material was used to acquire preliminary results for vertebral endplate connection to the synthesized annulus, however no additional material was used to determine or mimic the mechanical properties of these endplates, due to time constraints. Also because of time constraints, the nucleus used in this study was only comprised of water with no other additives for preliminary testing since the natural nucleus is comprised of about 80-90% water. These properties were then compared to the mechanical properties of the natural disc, so that they could be finely tuned to emulate the natural disc. It is shown in this study that the composite material, when swelled in water, was able to mimic the annulus fibrosus in tensile strength and modulus, however showed higher compressive strength and modulus than ideal. The samples also did not undergo any permanent deformation within the realm of force actually introduced to the natural disc. The vertebral endplates showed decent adhesion to the synthesized annulus, however there were slight defects that became failure concentrators during compression testing. The nucleus showed promising results maintaining good internal pressure to the system causing better compressive load distribution, with barreling of the samples.