Mass transport within collagen-based matrices is critical to tissue development, repair, and pathogenesis as well as the design of next generation tissue engineering strategies. This work shows how collagen precursors, specified by intermolecular cross-link composition, provide independent control of collagen matrix mechanical and transport properties. Collagen matrices were prepared from tissue-extracted monomers or oligomers. Viscoelastic behavior was measured in oscillatory shear and unconfined compression. Matrix permeability and diffusivity were measured using gravity-driven permeametry and integrated optical imaging, respectively. Both collagen types showed an increase in stiffness and permeability hindrance with increasing collagen concentration (fibril density); however, different physical property-concentration relationships were noted. Diffusivity wasn’t affected by concentration for either collagen type over the range tested. In general, oligomer matrices exhibited a substantial increase in stiffness and only a modest decrease in transport properties when compared to monomer matrices prepared at the same concentration. The observed differences in viscoelastic and transport properties were largely attributed to increased levels of interfibril branching within oligomer matrices. The ability to relate physical properties to relevant microstructure parameters, including fibril density and interfibril branching, is expected to advance the understanding of cell-matrix signaling as well as facilitate model-based prediction and design of matrix-based therapeutic strategies.

We present proof-of-concept studies that display the potential for using a glucose-sensitive hydrogel as a continuous glucose sensor. A study to characterize the swelling ratio of the hydrogel at normal physiological and pathological hyperglycemic glucose levels was performed. The hydrogel exposed to the hyperglycemic glucose solution had a higher equilibrium swelling ratio than the hydrogel exposed to the normal glucose concentration solution. The diffusivity of a small molecule, fluorescein isothiocyanate (FITC), through a hydrogel exposed to a hyperglycemic solution was determined using fluorescence recovery after photobleaching (FRAP). The diffusivity was found to be 4.2 × 10(-14) m(2)/s, a value approximately four orders of magnitude smaller than the diffusivity of FITC in glucose solution. The permeability of the hydrogel after equilibration in a hyperglycemic solution was found to be 5.1 × 10(-17) m(2), in the range of 2-4% agarose gels.

Expansive soil formations can be found throughout the United States. When subjected to wetting, these formations have the potential to swell and exert large uplift forces on buildings and foundations. Lightly loaded structures, such as single family residences founded in areas of expansive soils, can be significantly damaged due to uplift movement from swelling actions. Designing an economical deep foundation that can resist uplift forces is critical to prevent damage to these structures. The current solutions to control uplift due to swelling soils, such as over-excavation and replacement of the expansive material or the use of drilled shafts can be costly. Piles made from recycled polymer materials could provide a solution. Due to a lower coefficient of friction along the interface of the soil-pile interface compared to traditional pile materials, solid recycled plastic piles can allow expansive soils to move nearly independently from the pile when wetted. This results in a much smaller magnitude of uplift force being transferred to the structure, which minimizes the risk of significant structural damage from excessive movements. This paper presents the results of research conducted on the use of recycled plastic piles in an expansive shale environment. The preliminary phase of the project involved the installation of six recycled plastic piles at a test site on the South Dakota School of Mines and Technology campus. Two of the piles were subjected to a full-scale compression load test in order to determine ultimate capacity. The remaining four piles were subjected to long-term monitoring of uplift movement during the course of the project. A concrete anchor was also installed at the test site for uplift monitoring. Data gathered during the field and laboratory testing was utilized in a non-linear soilstructure interaction model to predict the displacement behavior and internal stresses within a plastic pile and concrete anchor subjected to uplift forces from the swelling shale. While more research is needed to further understand the application for recycled plastic piles, the results from this research indicate that their use is a viable alternative for support of lightly loaded structures in expansive soil environments.

3638 Poster Board III-574 Previously we reported the impact of hematopoietic niche (HN) elements, calvaria-derived osteoblasts (OB) and bone marrow derived stromal cells (SC), on murine hematopoietic stem cells (HSC, defined as Lin-sca1+c-kit+ or LSK) cultured in a conventional two-dimensional (2D) format. Interestingly, we found that OB maintained the functional properties of LSK cells including their long-term marrow repopulating potential significantly better than SC thus corroborating the importance of OB in the overall competence of the HN. We also reported that this stem cell function-enhancing activity is induced by the up regulation of Notch-mediated signaling between HSC and OB. However, which specific lineage or developmental stage of OB enhances HSC function is still unknown. In the present study, we evaluated the interactions between HSC and OB at various stages of development. We also examined the impact of physical parameters of the extra cellular matrix, such as stiffness/storage modulus using a more physiologically relevant 3D context consisting of collagen-fibril matrices in which the fibril density and shear storage modulus was systematically varied. OB were harvested from murine calvaria and used directly (fresh OB) or were cultured for 1, 2, or 3 weeks in basic or complete medium (supplemented with ascorbic acid and β-glycerophosphate). A total of 1000 LSK cells were co-cultured for 1 week with either fresh OB or OB cultured for 1, 2, or 3 weeks. Cultures were examined for hematopoietic cell number increase, colony forming unit (CFU) expansion, LSK phenotype, and plating efficiency. In addition, OB function was analyzed by measuring alkaline phosphatase activity and calcium deposition/mineralization. Surprisingly, total hematopoietic cell number on day7 was significantly higher in cultures containing fresh OB (34.5±3.3×105) compared to OB cultured for 1 week (12.4±4.0 ×105, p=0.05), 2 weeks (9.8±4.6 ×105, p=0.03), or 3 weeks (7.8±3.4 ×105, p=0.02). Total CFU fold expansion was also significantly elevated in fresh OB co-cultures (149.6±45.7) vs OB cultured for 1 week (62.4±18.7, p=0.04), 2 weeks (51.0±14.5, p=0.01), or 3 weeks (52.4±23, p=0.03). The percentage of Lin-Sca1+ cells was also significantly higher in co-cultures of fresh OB (29.5±3.6%) vs OB cultured for 1 week (5.3±0.9, p=0.02), 2 weeks (0.9±0.2, p=0.008), or 3 weeks (1.0±0.2, p=0.008). Interestingly, alkaline phosphatase activity and calcium deposition were inversely associated with all hematopoietic properties examined. In order to examine the significance of 3D spatial and physical properties of the extra cellular matrix microenvironment, which is absent in traditional culture systems, LSK cells were cultured in both the presence and absence of calvariae-derived OB within 3D engineered collagen type I matrix constructs in an effort to recreate the in vivo niche conditions. Matrix parameters, including collagen fibril density (9-20%) and shear storage modulus (50-800 Pa, G') were systematically varied and quantified. LSK proliferated most rapidly when co-cultured with OB in low fibril density/G' (50 Pa) collagen type I matrices (836.8±74 fold-increase) compared to 200Pa (172.3±26, p=0.007) or 800Pa (128.4±27, p=0.006). Proliferation of LSK cells in matrices not containing OB was minimal. Interestingly, the clonogenicity of cells harvested from 800Pa matrices was nearly 3-fold and 1.5-fold higher than that for cells from 50Pa and 200Pa matrices, respectively. Furthermore, 800Pa matrices maintained the highest percentage of Lin-Sca1+ cells for 7days (15.9±7.3) compared to 200Pa (9.3±3.5) and 50Pa (6.9±1.5) matrices. These data illustrate that collagen matrices with relatively high fibril density/G' suppressed rapid proliferation and expansion and maintained progenitor cell function. Alternatively, low stiffness matrices promoted cell expansion at the apparent expense of differentiation and loss of clonogenic potential of progenitor cells. Collectively these results demonstrate that early stage OB maintains HSC function significantly better than later stage OB. Furthermore, physical properties such as fibril density and shear storage modulus (stiffness) of the surrounding collagen fibril matrix also play a critical role in HSC proliferation and maintenance of stem cell pool. Disclosures: No relevant conflicts of interest to declare.