Development and Applications of Advanced Ultrasound Techniques for Characterization and Stimulation of Engineered Tissues

Mechanobiology is central in the development, pathology, and regeneration of musculoskeletal tissues, in which mechanical factors play important roles. Therefore, there is a need for methods to characterize the composition and mechanical properties of developing musculoskeletal tissues over time. Ultrasound elastographic techniques have been developed for noninvasive imaging of spatial heterogeneity in tissue stiffness. However, their application for quantitative assessment of tissue mechanical properties, especially viscoelastic properties, has not been exploited. Additionally, ultrasound energy may be used to apply mechanical stimulation to engineered constructs at the microscale, and thereby to enhance tissue regeneration. We have developed a multimode ultrasound viscoelastography (MUVE) system for assessing microscale mechanical properties of engineered hydrogels. MUVE uses focused ultrasound pulses to apply acoustic radiation force (ARF) to deform samples, while concurrently measuring sample dimensions using coaxial high frequency ultrasound imaging. We used MUVE to perform creep tests on agarose, collagen, and fibrin hydrogels of defined concentrations, as well as to monitor the mechanical properties of cell-seeded constructs over time. Local and bulk viscoelastic properties were extracted from strain-time curves through fitting of relevant constitutive models, showing clear differences between concentrations and materials. In particular, we showed that MUVE is capable of mapping heterogeneity of samples in 3D. Using inclusion of dense agarose microbeads within agarose, collagen and fibrin hydrogels, we determined the spatial resolution of MUVE to be approximately 200 μm in both the lateral and axial directions. Comparison of MUVE to nanoindentation and shear rheometry showed that our ultrasound-based technique was superior in generating consistent, microscale data, particularly for very soft materials. We have also adapted MUVE to generate localized cyclic compression, as a means to mechanically stimulate engineered tissue constructs at the microscale. Selected treatment protocols were shown to enhance the osteogenic differentiation of human mesenchymal stem cells in collagen-fibrin hydrogels. Constructs treated at 1 Hz at an acoustic pressure of 0.7 MPa for 30 minutes per day showed accelerated osteogenesis and increased mineralization by 10 to 30 percent, relative to unstimulated controls. In separate experiments, the ultrasound pulse intensity was increased over time to compensate for changes in matrix properties over time, and a 35 percent increase in mineralization was achieved. We also extended the application of a previously-developed spectral ultrasound imaging (SUSI) technique to an animal model for early detection of heterotopic ossification (HO). The quantitative information on acoustic scatterer size and concentration derived from SUSI was used to differentiate tissue composition in a burn/tenotomy mice model from the control model. Importantly, HO foci were detected as early as one week after injury using SUSI, which is 3-5 weeks earlier than when using conventional micro-computed tomography. Taken together, these results demonstrate that ultrasound-based techniques can non-invasively and quantitatively characterize viscoelastic properties of soft materials in 3D, as well as their composition over time. Ultrasound pulses can also be used to stimulate engineered constructs to promote musculoskeletal tissue formation. MUVE, SUSI, and ultrasound stimulation can be combined into an integrated system to investigate the roles of matrix composition, static mechanical environment, and dynamic mechanical stimuli in tissue regeneration, as well as the interactions of these factors and their evolution over time. Ultrasound-based techniques therefore have promising potential in noninvasively characterizing the composition and biomechanics, as well as providing mechanical intervention in native and engineered tissues as they develop over time.PHDBiomedical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/144116/1/xho_1.pd

Glassy Materials Based Microdevices

Microtechnology has changed our world since the last century, when silicon microelectronics revolutionized sensor, control and communication areas, with applications extending from domotics to automotive, and from security to biomedicine. The present century, however, is also seeing an accelerating pace of innovation in glassy materials; as an example, glass-ceramics, which successfully combine the properties of an amorphous matrix with those of micro- or nano-crystals, offer a very high flexibility of design to chemists, physicists and engineers, who can conceive and implement advanced microdevices. In a very similar way, the synthesis of glassy polymers in a very wide range of chemical structures offers unprecedented potential of applications. The contemporary availability of microfabrication technologies, such as direct laser writing or 3D printing, which add to the most common processes (deposition, lithography and etching), facilitates the development of novel or advanced microdevices based on glassy materials. Biochemical and biomedical sensors, especially with the lab-on-a-chip target, are one of the most evident proofs of the success of this material platform. Other applications have also emerged in environment, food, and chemical industries. The present Special Issue of Micromachines aims at reviewing the current state-of-the-art and presenting perspectives of further development. Contributions related to the technologies, glassy materials, design and fabrication processes, characterization, and, eventually, applications are welcome

The NASA SBIR product catalog

The purpose of this catalog is to assist small business firms in making the community aware of products emerging from their efforts in the Small Business Innovation Research (SBIR) program. It contains descriptions of some products that have advanced into Phase 3 and others that are identified as prospective products. Both lists of products in this catalog are based on information supplied by NASA SBIR contractors in responding to an invitation to be represented in this document. Generally, all products suggested by the small firms were included in order to meet the goals of information exchange for SBIR results. Of the 444 SBIR contractors NASA queried, 137 provided information on 219 products. The catalog presents the product information in the technology areas listed in the table of contents. Within each area, the products are listed in alphabetical order by product name and are given identifying numbers. Also included is an alphabetical listing of the companies that have products described. This listing cross-references the product list and provides information on the business activity of each firm. In addition, there are three indexes: one a list of firms by states, one that lists the products according to NASA Centers that managed the SBIR projects, and one that lists the products by the relevant Technical Topics utilized in NASA's annual program solicitation under which each SBIR project was selected

Optimization in the design of a 12 gigahertz low cost ground receiving system for broadcast satellites. Volume 2: Antenna system and interference

The antenna characteristics are analyzed of a low cost mass-producible ground station to be used in broadcast satellite systems. It is found that a prime focus antenna is sufficient for a low-cost but not a low noise system. For the antenna feed waveguide systems are the best choice for the 12 GHz band, while printed-element systems are recommended for the 2.6 GHz band. Zoned reflectors are analyzed and appear to be attractive from the standpoint of cost. However, these reflectors suffer a gain reduction of about one db and a possible increase in sidelobe levels. The off-axis gain of a non-auto-tracking station can be optimized by establishing a special illumination function at the reflector aperture. A step-feed tracking system is proposed to provide automatic procedures for searching for peak signal from a geostationary satellite. This system uses integrated circuitry and therefore results in cost saving under mass production. It is estimated that a complete step-track system would cost only $512 for a production quantity of 1000 units per year

Field Programmable Gate Arrays (FPGAs) II

This Edited Volume Field Programmable Gate Arrays (FPGAs) II is a collection of reviewed and relevant research chapters, offering a comprehensive overview of recent developments in the field of Computer and Information Science. The book comprises single chapters authored by various researchers and edited by an expert active in the Computer and Information Science research area. All chapters are complete in itself but united under a common research study topic. This publication aims at providing a thorough overview of the latest research efforts by international authors on Computer and Information Science, and open new possible research paths for further novel developments

LASER Tech Briefs, Spring 1994

Topics in this Laser Tech Brief include: Electronic Components and Circuits. Electronic Systems, Physical Sciences, Materials, Mechanics, Fabrication Technology, and books and reports

NASA/ASEE Summer Faculty Fellowship Program

This document is a collection of technical reports on research conducted by the participants in the 1992 NASA/ASEE Summer Faculty Fellowship Program at Kennedy Space Center (KSC). This was the eighth year that a NASA/ASEE program has been conducted at KSC. The 1992 program was administered by the University of Central Florida in cooperation with KSC. The program was operated under the auspices of the American Society for Engineering Education (ASEE) with sponsorship and funding from the Office of Educational Affairs, NASA Headquarters, Washington, D.C. The KSC program was one of nine such Aeronautics and Space Research Programs funded by NASA Headquarters in 1992. The basic common objectives are to further the professional knowledge, to stimulate an exchange of ideas, to enrich and refresh the research and teaching activities, and to contribute to the research objectives of the NASA centers

NASA Tech Briefs, December 1999

Topics include: Imaging/Videos/Cameras; Electronic Components and Circuits; Electronic Systems; Physical Sciences; Materials; Computer Programs; Mechanics; Machinery/Automation; Books and Reports