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2. Templated synthesis of tailored clays to yield increased pore volumes for sorption and exchange

Author

Powell, Katherine M.

Subjects
549.6
Abstract

The study aimed to enhance the textural properties of the synthetic hectorite clay Laponite RD. In the early 1990s Mobil Research and Development Corporation produced the first ordered mesoporous molecular sieves. This family of materials, M41S, were fabricated via liquid crystal templating (LCT), a technique involving the condensation and hydrolysis of a silica source around an organic template. As clays are primarily silicates, the question arises "Why not apply the same principles to enhance porosity characteristics of other silicates such as clays?" Optimization of reagent concentrations, template choice, synthesis protocol and template removal strategy led to a maximum total pore volume of 0.95 cm3 g-1. This was achieved through templating Laponite RD with the neutral surfactant polyoxyethylene (20) sorbitan trioleate (Tween 85). This more than trebled the original total pore volume of Laponite RD, 0.27 cm3 g-1. An increase in modal pore diameter was also observed after use of this template; from 36.6 A to 52.3 A. Synthesis of Laponite-like compounds within the laboratory led to enhancement of porosity characteristics without templating; a total pore volume of 0.44 cm3 g-1 was observed for this synthetic hectorite (KP). Use of a template further enhanced the porosity characteristics of these samples. The cationic surfactant CTMA+ (used in the original Mobil synthesis) led to a total pore volume of 0.60 cm3 g-1 for modified hectorite KP. A similar result, 0.65 cm3 g-1, was achieved through templating Laponite RD with this same surfactant. Sorption and exchange properties of the newly modified hectorites were assessed by simple equilibrium batch testing methods using both single metal and multi-metal solutions. Hectorite KP samples removed a greater percentage of metal ions from aqueous solution than its Laponite RD analogues. For 5 mg dm-3 single element solutions CTMA+ modified hectorite removed > 95% of all eight metals tested. For solutions containing higher concentrations of ions the removal efficiency of all tested clays were reduced due to greater competition between ions. Partial interlayer collapse was observed during powder XRD studies, due to the acidic nature of the metal ion solutions.

Published
2005

6. Design of a multifunctional compliant instrument for minimally invasive surgery

Author

Frecker, Mary I., Powell, Katherine M., and Haluck, Randy

Subjects
Surgical equipment and supplies -- Design and construction, Surgical equipment and supplies -- Mechanical properties, Medical equipment -- Design and construction, Medical equipment -- Mechanical properties, Physiological apparatus -- Design and construction, Physiological apparatus -- Mechanical properties, Engineering and manufacturing industries, Science and technology
Abstract

A new multifunctional compliant instrument has been designed for use in minimally invasive surgery. The instrument combines scissors and forceps into a single multifunctional device. The main advantage of using multifunctional instruments for minimally invasive surgery is that instrument exchanges can be reduced, thus reducing procedure time and risk of inadvertent tissue injury during instrument exchanges. In this paper, the length, width, and thickness of the multifunctional compliant mechanism tool tip is optimized to maximize the jaw opening and the grasping force. The optimized design is then modeled to simulate the stresses encountered in the scissors mode. A 5.0 mm diameter stainless steel prototype is fabricated using electro-discharge machining and is shown to grasp and cut successfully. [DOI: 10.1115/1.2056560] Keywords: Minimally Invasive Surgery, Multifunctional Instrument, Compliant Mechanism

Published
2005

8. Effects of Raloxifene and tibial loading on bone mass and mechanics in male and female mice.

Author

Berman, Alycia G., Damrath, John G., Hatch, Jennifer, Pulliam, Alexis N., Powell, Katherine M., Hinton, Madicyn, and Wallace, Joseph M.

Subjects
BONE mechanics, SELECTIVE estrogen receptor modulators, RALOXIFENE, BONE density, BONE growth, CANCELLOUS bone
Abstract

Purpose: Raloxifene (RAL) is a selective estrogen receptor modulator (SERM) that has previously been shown to cause acellular benefits to bone tissue. Due to these improvements, RAL was combined with targeted tibial loading to assess if RAL treatment during periods of active bone formation would allow for further mechanical enhancements. Methods: Structural, mechanical, and microstructural effects were assessed in bone from C57BL/6 mice that were treated with RAL (0.5 mg/kg), tibial loading, or both for 6 weeks, beginning at 10 weeks of age. Results:Ex vivo microcomputed tomography (CT) images indicated RAL and loading work together to improve bone mass and architecture, especially within the cancellous region of males. Increases in cancellous bone volume fraction were heavily driven by increases in trabecular thickness, though there were some effects on trabecular spacing and number. In the cortical regions, RAL and loading both increased cross-sectional area, cortical area, and cortical thickness. Whole-bone mechanical testing primarily indicated the effects of loading. Further characterization through Raman spectroscopy and nanoindentation showed load-based changes in mineralization and micromechanics, while both loading and RAL caused changes in the secondary collagen structure. In contrast to males, in females, there were large load-based effects in the cancellous and cortical regions, resulting in increased whole-bone mechanical properties. RAL had less of an effect on cancellous and cortical architecture, though some effects were still present. Conclusion: RAL and loading work together to impact bone architecture and mechanical integrity, leading to greater improvements than either treatment individually. [ABSTRACT FROM AUTHOR]

Published
2022
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9. The Effects of Zoledronate and Raloxifene Combination Therapy on Diseased Mouse Bone

Author

Powell, Katherine M

Subjects
Biomedical engineering not elsewhere classified
Abstract

Current interventions used to reduce skeletal fragility are insufficient at enhancing bone across multiple hierarchical levels. Bisphosphonates, such as Zoledronate (ZOL), treat a variety of bone disorders by increasing bone mass and bone mineral density to decrease fracture risk. Despite the mass-based improvements, bisphosphonate use has been shown to compromise bone quality. Alternatively, Raloxifene (RAL) has recently been demonstrated to improve tissue quality and overall mechanical properties by binding to collagen and increasing tissue hydration in a cell-independent manner. We hypothesized that a combination of RAL and ZOL would improve mechanical and material properties of bone more than either monotherapy alone by enhancing both quantity and quality of bone. In this study, wildtype (WT) and heterozygous (OIM+/-) male mice from the Osteogenesis Imperfecta (OI) murine model were treated with either RAL, ZOL, or RAL and ZOL from 8 weeks to 16 weeks of age. Combination treatment resulted in higher trabecular architecture, cortical mechanical properties, and cortical fracture toughness in diseased mouse bone. Two fracture toughness properties, direct measures of the tissue’s ability to resist the initiation and propagation of a crack, were significantly improved with combination treatment in OIM+/- compared to control. There was no significant effect on fracture toughness with either monotherapy alone in either genotype. Following the mass-based effects of ZOL, bone volume fraction was significantly higher with combination treatment in both genotypes. Similar results were seen in trabecular number. Combination treatment resulted in higher ultimate stress in both genotypes, with RAL additionally increasing ultimate stress in OIM+/-. RAL and combination treatment in OIM+/- also produced a higher resilience compared to the control. Given no significant changes in cortical geometry, these mechanical alterations were likely driven by the quality-based effects of RAL. In conclusion, this study demonstrates the beneficial effects of using combination therapy to increase bone mass while simultaneously improving tissue quality, especially to enhance the mechanical integrity of diseased bone. Combination therapies could be a future mechanism to improve bone health and combat skeletal fragility on multiple hierarchical levels.

Published
2019
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