Kristin J Dills

California State Polytechnic University, Pomona, Pomona, CA, United States

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Publications (3)4.18 Total impact

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    ABSTRACT: In vitro cultures with insulin-like growth factor-1 (IGF-1) and transforming growth factor-β1 (TGF-β1) have previously been shown to differentially modulate the growth of immature bovine articular cartilage. IGF-1 stimulates expansive growth yet decreases compressive moduli and increases compressive Poisson's ratios, whereas TGF-β1 maintains tissue size, increases compressive moduli, and decreases compressive Poisson's ratios. The current study's hypothesis was that sequential application of IGF-1 and TGF-β1 during in vitro culture produces geometric and compressive mechanical properties that lie between extreme values produced when using either growth factor alone. Immature bovine articular cartilage specimens were harvested and either untreated (D0, i.e., day zero) or cultured in vitro for either 6 days with IGF-1 (D6 IGF), 12 days with IGF-1 (D12 IGF), or 6 days with IGF-1 followed by 6 days with TGF-β1 (D12 SEQ, i.e., sequential). Following treatment, all specimens were tested for geometric, biochemical, and compressive mechanical properties. Relative to D0, D12 SEQ treatment enhanced volumetric growth, but to a lower value than that for D12 IGF. Furthermore, D12 SEQ treatment maintained compressive moduli and Poisson's ratios at values higher and lower, respectively, than those for D12 IGF. Considering the previously described effects of 12 days of treatment with TGF-β1 alone, D12 SEQ induced both growth and mechanical property changes between those produced with either IGF-1 or TGF-β1 alone. The results suggest that it may be possible to vary the durations of select growth factors, including IGF-1 and TGF-β1, to more precisely modulate the geometric, biochemical, and mechanical properties of immature cartilage graft tissue in clinical repair strategies.
    Journal of Biomechanical Engineering 03/2012; 134(3):031001. · 1.52 Impact Factor
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    ABSTRACT: Mechanisms of articular cartilage growth and maturation have been elucidated by studying composition-function dynamics during in vivo development and in vitro culture with stimuli such as insulin-like growth factor-1 (IGF-1) and transforming growth factor-beta 1 (TGF-beta1). This study tested the hypothesis that IGF-1 and TGF-beta1 regulate immature cartilage compressive moduli and Poisson's ratios in a manner consistent with known effects on tensile properties. Bovine calf articular cartilage from superficial-articular (S) and middle-growth (M) regions were analyzed fresh or following culture in medium with IGF-1 or TGF-beta1. Mechanical properties in confined (CC) and unconfined (UCC) compression, cartilage matrix composition, and explant size were assessed. Culture with IGF-1 resulted in softening in CC and UCC, increased Poisson's ratios, substantially increased tissue volume, and accumulation of glycosaminoglycan (GAG) and collagen (COL). Culture with TGF-beta1 promoted maturational changes in the S layer, including stiffening in CC and UCC and increased concentrations of GAG, COL, and pyridinoline crosslinks (PYR), but little growth. Culture of M layer explants with TGF-beta1 was nearly homeostatic. Across treatment groups, compressive moduli in CC and UCC were positively related to GAG, COL, and PYR concentrations, while Poisson's ratios were negatively related to concentrations of these matrix components. Thus, IGF-1 and TGF-beta1 differentially regulate the compressive mechanical properties and size of immature articular cartilage in vitro. Prescribing tissue growth, maturation, or homeostasis by controlling the in vitro biochemical environment with such growth factors may have applications in cartilage repair and tissue engineering.
    Journal of biomechanics 09/2010; 43(13):2501-7. · 2.66 Impact Factor
  • Zack Blois, Robia Choi, Kristin Dills
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    ABSTRACT: The Mobility Aid project was proposed by Theresa Mortilla and Idee Shapiro. The goal of the project was to design and build a device that can quickly and easily transform between a mobility walker and an electric scooter to allow for more freedom of mobility. The inspiration for this project arose from the fact that Theresa suffers from multiple sclerosis in her legs and can only walk for about thirty minutes at a time until she gets too fatigued and must sit down and rest. This device would provide her with the ability to continue moving while giving her legs their needed rest.While this was a very exciting and life-changing project, the project requirements presented many obstacles and design challenges to overcome. The device must be lightweight so that Theresa can push it easily as a walker, but it must be structural enough to support all of the forces while used as a scooter. It must also be simple and easy to use as Theresa will most likely be fatigued when she has to transform the device. These were just a few of the design considerations faced in this project.After much research and many different design iterations, a final design was reached. It consists of a four-wheel device with an aluminum frame, has a rigid folding seat, and has interchangeable handlebars.As expected, during the building phase there were many little flaws that slowed down construction. These provided unnecessary roadblocks but were overcome with collaboration between group members and assistance from outside sources.
    Mechanical Engineering.