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 Computational Design, Freeform Fabrication and Testing of Nylon-6 Tissue Engineering Scaffolds(2002) Das, Suman; Hollister, Scott J.; Flanagan, Colleen; Adewunmi, Adebisi; Bark, Karlin; Chen, Cindy; Ramaswamy, Krishnan; Rose, Daniel; Widjaja, ErwinApproximately 100,000 people in the US alone suffer from TMJ disease to the extent that surgical reconstruction is needed. In order to reconstruct a whole joint such as the TMJ, advanced, novel fabrication methods are needed to build complex, threedimensional scaffolds incorporating multiple, functionally graded biomaterials and porosity that will enable the simultaneous growth of multiple tissues including blood vessels. The aim of this research is to develop, demonstrate and characterize techniques for fabricating such scaffolds by combining solid freeform fabrication and computational design methods. When fully developed, such techniques are expected to enable the fabrication of tissue engineering scaffolds endowed with functionally graded material composition and porosity exhibiting sharp or smooth gradients. As a first step towards realizing this goal, we have designed and fabricated scaffolds with various architectures in Nylon-6, a biocompatible polymer using selective laser sintering. Results of biocompatibility, mechanical testing and implantation are presented.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 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.Item Rapid Prototyping of 3D Scaffolds for Tissue Engineering Using a Four-Axis Multiple-Dispenser Robotic System(2003) Geng, L.; Wong, Y.S.; Hutmacher, D.W.; Feng, W.; Loh, H.T.; Fuh, J.Y.H.A desktop rapid prototyping (RP) system has been developed to fabricate scaffolds for tissue engineering (TE) applications. The system is a computer-controlled four-axis machine with a multiple-dispenser head. This paper presents the scaffold fabrication process to build free-form scaffolds from relevant features extracted from given CT-scan images for TE applications. This involves obtaining the required geometric data for the scaffold in the form of a solid model from CT-scan images. The extracted scaffold model is then sliced into consecutive two-dimensional (2D) layers to generate appropriately formatted data for the desktop RP system to fabricate the scaffolds. The basic material processing involves the sequential dispensing of two or more materials to form a strand. The four-axis system enables strands to be laid in a different direction at each layer to form suitable interlacing 3D free-form scaffold structures. The multipledispenser head also allows the introduction of living cells and additional materials during the scaffold building. The building of the scaffolds with the desktop RP system is described based on the sequential dispensing of chitosan dissolved in acetic acid and sodium hydroxide solution. Neutralization of the acetic acid by the sodium hydroxide results in a precipitate to form a gellike chitosan strand.