Browsing by Subject "Scaffolds"
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Item Chemically modified hyaluronic acid biomaterials for cell culture and tissue engineering(2016-12) Joaquin, Alysa Marie; Zoldan, Janeta; Suggs, LauraThe fate and behavior of cells is strongly dependent on the cell microenvironment, and this knowledge has been applied to the design of biomaterials to influence cell growth, morphology, and differentiation. However, a dearth of research specifically focused on the effects of material hydrophobicity on cell behavior indicates that this easily controllable material property is being overlooked. The field of tissue engineering has a need for cost-efficient, scalable methods to both increase stem cell stocks and control cell behavior, and hydrophobic biomaterials may be a robust solution to these needs. To evaluate the utility of hydrophobicity in controlling cell behavior, hyaluronic acid was modified with amines representing a wide range of hydrophobicity, resulting in twelve new materials. Both mouse embryonic stem cells (mESCs) and fibroblasts were cultured on these materials to evaluate the differences in pluripotent and differentiated cell behavior in response to hydrophobic materials. The viability of cells cultured on these materials was tested as an indicator of biocompatibility, and cell morphology and spreading area was evaluated to relate cell behavior to biomaterial hydrophobicity. Eight of the twelve materials proved to be biocompatible, and hydrophobic materials inhibited cell spreading; fibroblasts cultured on modified HA hydrogels grew in populations of both compact cell clusters and elongated, multi-polar morphologies, and cell spreading area increased as hydrophobicity decreased. Similarly, mESC spreading area increased with decreasing hydrophobicity; mESCs grown on the least hydrophobic HA hydrogels also multi-polar spreading, while mESCs cultured on the more hydrophobic materials grew exclusively in compact cell clusters. As the morphology of cells is often indicative of cell fate, and as hydrophobic materials tended to inhibit cell spreading, we expected that mESCs cultured on hydrophobic materials would maintain pluripotency. To this end, hybrid scaffolds composed of modified HA and gelatin were developed as a platform for stem cell pluripotency maintenance. The mESCs seeded into these scaffolds had a higher expression of the pluripotency marker SSEA-1 compared to control mESCs grown in complete medium after 24 hours, indicating that hydrophobicity is an important material property to consider in stem cell culture.Item The effects of problem-based learning scaffolds on cognitive load, problem-solving, and student performance within a multimedia-enhanced learning environment(2014-05) Horton, Lucas Robert; Liu, Min, Ed. D.Learners who are novice problem solvers often encounter difficulty when solving complex problems. One explanation for this difficulty is that the cognitive requirements of problem-solving are sufficiently high that learners easily become overwhelmed and frustrated, leading to a state known as cognitive overload in which learning is obstructed. Cognitive Load Theory is concerned with the design of instructional approaches intended to manage the cognitive load required for thinking and problem-solving tasks. Scaffolds are any kind of support that facilitates the accomplishment of a difficult task that a learner would not be able to accomplish on their own. They are potential mechanisms to support students in negotiating the potentially high cognitive load required by complex problem-solving. The purpose of this study was to examine the effects of technology-based scaffolds within a problem-based learning environment known as Alien Rescue. The study investigated the impact of scaffolds on cognitive load, problem-solving behaviors, science knowledge, and student perceptions of the learning environment. Participants for this study included sixth grade students from a suburban middle school in the southwestern United States. Student classes were assigned to one of three treatment conditions: (a) a problem constraint condition in which students were guided through a problem-solving process similar to that of an expert, (b) a prompt condition in which students were provided with guiding messages during problem-solving, and (c) a control condition with no scaffolding. All conditions participated in the use of Alien Rescue for three weeks. Measures including a self-report measure of mental effort, calculated instructional efficiency scores, problem solution scores, student activity logs, and science knowledge test performance were used to evaluate students' cognitive load, problem-solving performance, problem-solving strategies, and learning gains. An open-ended questionnaire and student interviews were used to gather data on students' perceptions of the program. Results of the study indicate statistically significant differences between treatment conditions with respect to problem-solving efficiency, student problem-solving behaviors, and scientific knowledge gain. Additionally, qualitative findings highlight problematic aspects of the highly structured condition as implemented within the classroom context while also identifying components of the learning environment that were perceived as helpful and useful to participants. Teacher interviews also provided insight into classroom implementation of the program and opportunities to further enhance scaffolds to support student learning. Implications of the study from research, instructional design, and technology perspectives are discussed along with a treatment of study limitations and opportunities for further research in this area.Item Inorganic-Organic Shape Memory Polymers and Foams for Bone Defect Repairs(2013-04-16) Zhang, DaweiThe ultimate goal of this research was to develop a ?self-fitting? shape memory polymer (SMP) scaffold for the repair of craniomaxillofacial (CMF) bone defects. CMF defects may be caused by trauma, tumor removal or congenital abnormalities and represent a major class of bone defects. Their repair with autografts is limited by availability, donor site morbidity and complex surgical procedures. In addition, shaping and positioning of these rigid grafts into irregular defects is difficult. Herein, we have developed SMP scaffolds which soften at T > ~56 ?C, allowing them to conformally fit into a bone defect. Upon cooling to body temperature, the scaffold becomes rigid and mechanically locks in place. This research was comprised of four major studies. In the first study, photocrosslinkable acrylated (AcO) SMP macromers containing a poly(?-caprolactone) (PCL) segment and polydimethylsiloxane (PDMS) segments were synthesized with the general formula: AcO-PCL40-block-PDMSm-block-PCL40-OAc. By varying the PDMS segment length (m), solid SMPs with highly tunable mechanical properties and excellent shape memory abilities were prepared. In the second study, porous SMP scaffolds were fabricated based on AcO-PCL40-block-PDMS37-block-PCL40-OAc via a revised solvent casting particulate leaching (SCPL) method. By tailoring scaffold parameters including salt fusion, macromer concentration and salt size, scaffold properties (e.g. pore features, compressive modulus and shape memory behavior) were tuned. In the third study, porous SMP scaffolds were produced from macromers with variable PDMS segment lengths (m = 0 ? 130) via an optimized SCPL method. The impact on pore features, thermal, mechanical, and shape memory properties as well as degradation rates were investigated. In the final study, a bioactive polydopamine coating was applied onto pore surfaces of the SMP scaffold prepared from PCL diacrylate. The thin coating did not affect intrinsic bulk properties of the scaffold. However, the coating significantly increased its bioactivity, giving rise to the formation of ?bone-bonding? hydroxyapatite (HAp) when exposed to simulated body fluid (SBF). It was also shown that the coating largely enhanced the scaffold?s capacities to support osteoblasts adhesion, proliferation and osteogenesis. Thus, the polydopamine coating should enhance the performance of the ?self-fitting? SMP scaffolds for the repair of bone defects.Item Microscale modeling of layered fibrous networks with applications to biomaterials for tissue engineering(2015-08) Carleton, James Brian; Rodin, G. J. (Gregory J.); Sacks, Michael S.; Gonzalez, Oscar; van de Geijn, Robert; Mear, MarkMany important biomaterials are composed of multiple layers of networked fibers. A prime example is in the field of tissue engineering, in which damaged or diseased native tissues are replaced by artificial tissues that are grown on fibrous polymer networks. For load bearing tissues, it is critical that the mechanical behavior of the engineered tissue be similar to the behavior of the native tissue that it will replace. In the case of soft tissues such as heart valves, the macroscale mechanical behavior is highly anisotropic and nonlinear. This behavior is a result of complex deformations of the collagen and elastin fibers that form the extracellular matrix (ECM). The microstructure of engineered tissues must be properly designed to reproduce this unique macroscopic behavior. While there is a growing interest in modeling and simulation of the mechanical response of this class of biomaterials, a theoretical foundation for such simulations has yet to be firmly established. This work introduces a method for modeling materials that have a layered, fibrous network microstructure. Methods for characterizing the complex network geometry are first established. Then an algorithm is developed for generating realistic network geometry that is a good representation of electrospun tissue scaffolds, which serve as the primary synthetic structure on which engineered tissues are grown. The level of fidelity to the real geometry is a significant improvement on previous representations. This improvement is important, since the scaffold geometry has a strong influence over the macroscopic mechanical behavior of the tissue, cell proliferation and attachment, nutrient and waste flows, and extracellular matrix (ECM) generation. Because of the importance of scaffolds in tissue formation and function, this work focuses on characterizing scaffold network geometry and elucidating the impact of geometry on macroscale mechanics. Simulation plays an important role in developing a detailed understanding of scaffold mechanics. In this work, Cosserat rod theory is used to model individual fibers, which are connected to form a network that is treated as a representative volume element (RVE) of the material. The continuum theory is the basis for a finite element discretization. The nonlinear equations are solved using Newton's method in a parallel implementation that is capable of accurately capturing the large, three-dimensional fiber rotations and large fiber stretches that result from the large macroscopic deformations experienced by these biomaterials in their natural environment. Comparisons of simulation results with existing analytical models of soft tissues show that these models can predict the behavior of scaffold networks with reasonable accuracy, despite the significant differences between soft tissue and scaffold network microstructural geometry. The simulations also reveal how macroscale loading is related to the microscale fiber deformations and the load distribution among the fibers. The effects of different characteristics of the microstructural geometry on macroscopic behavior are explored, and the implications for the design of scaffolds that produce the desired macroscopic behavior are discussed. Overall, the improved modeling of electrospun scaffolds presented in this work is an important step toward designing more functional engineered tissues.