Characterization of the vocal fold lamina propria towards voice restoration

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2004.Includes bibliographical references.During normal speech, human vocal folds sustain greater than 100 high impact collisions each second. When the pliability of this complex biomechanical system is reduced by scarring, voice quality may be compromised. Currently, little can be done to treat patients affected with voice loss or chronic voice impairment due to scarring. Because of the size of the patient population suffering from voice impairment secondary to scarring, alternate treatment methods are currently being actively investigated. An implant-based approach is one strategy for treating lamina propria scarring. To rationally design an implant material for this purpose, it is important to have a more complete understanding of lamina propria biochemistry and microstructure than is currently in literature. This dissertation presents the following critical insights into normal human lamina propria biochemical structure: 1.) quantitative analysis of collagen, elastin, hyaluronan, and proteoglycan presence; 2.) quantitative examination of the spatial distributions of collagen, elastin, and hyaluronan, and qualitative investigation of the spatial distributions of specific proteoglycan types; and 3.) assessment of total cellularity and spatial variations in extracellular matrix turnover. Similar analyses have been carried out on the vocal fold lamina propria of normal dog, pig, and ferret towards identifying an appropriate animal model for implant trials.by Mariah Somer Hahn.Ph.D

Phase-referenced interferometer with subwavelength and subhertz sensitivity applied to the study of cell membrane dynamics

We report a highly sensitive means of measuring cellular dynamics with a novel interferometer that can measure motional phase changes. The system is based on a modified Michelson interferometer with a composite laser beam of 1550-nm low-coherence light and 775-nm CW light. The sample is prepared on a coverslip that is highly reflective at 775nm. By referencing the heterodyne phase of the 1550-nm light reflected from the sample to that of the 775-nm light reflected from the coverslip, small motions in the sample are detected, and motional artifacts from vibrations in the interferometer are completely eliminated. We demonstrate that the system is sensitive to motions as small as 3.6nm and velocities as small as 1nm/s. Using the instrument, we study transient volume changes of a few (approximately three) cells in a monolayer immersed in weakly hypotonic and hypertonic solutions

Micropatterning of Poly (N-isopropylacrylamide) (PNIPAAm) Hydrogels: Effects on Thermosensitivity and Cell Release Behavior

The thermally driven, reversible change in the surface properties of poly (N-isopropylacrylamide) (PNIPAAm) hydrogels from a hydrophilic (water-swollen) state to a hydrophobic (deswollen) state when heated above the volume phase transition temperature (VPTT, ~35 oC) makes them useful in inducing controlled cell release. To improve the kinetics of swelling and deswelling, we have prepared microstructured (i.e., micropillared) thermoresponsive surfaces comprising pure PNIPAAm hydrogel and nanocomposite PNIPAAm hydrogel embedded with polysiloxane colloidal nanoparticles (~220 nm diameter, 1 wt%) via photopolymerization. The thermosensitivity (i.e., degree and rate of swelling/deswelling) of these surfaces and how it can be regulated using different micropillar sizes and densities were characterized by measuring the dynamic size changes in micropillar dimensions in response to thermal activation. Our results show that the dynamic thermal response rate can be increased by more than twofold when the micropillar size is reduced from 200 to 100 μm. The temperature-controlled cell release behaviors of pure PNIPAAm and nanocomposite PNIPAAm micropatterned surfaces were successfully characterized using mesenchymal progenitor cells (10T1/2). This study demonstrates that the thermosensitivity of PNIPAAm surfaces can be regulated by introducing micropillars of different sizes and densities, while maintaining good temperature-controlled cell release behavior

Mechanical Characterization of Hybrid Vesicles Based on Linear Poly(Dimethylsiloxane-b-Ethylene Oxide) and Poly(Butadiene-b-Ethylene Oxide) Block Copolymers

Poly(dimethylsiloxane-ethylene oxide) (PDMS-PEO) and poly(butadiene-b-ethylene oxide) (PBd-PEO) are two block copolymers which separately form vesicles with disparate membrane permeabilities and fluidities. Thus, hybrid vesicles formed from both PDMS-PEO and PBd-PEO may ultimately allow for systematic, application-specific tuning of vesicle membrane fluidity and permeability. However, given the relatively low strength previously noted for comb-type PDMS-PEO vesicles, the mechanical robustness of the resulting hybrid vesicles must first be confirmed. Toward this end, we have characterized the mechanical behavior of vesicles formed from mixtures of linear PDMS-PEO and linear PBd-PEO using micropipette aspiration. Tension versus strain plots of pure PDMS12-PEO46 vesicles revealed a non-linear response in the high tension regime, in contrast to the approximately linear response of pure PBd33-PEO20 vesicles. Remarkably, the area expansion modulus, critical tension, and cohesive energy density of PDMS12-PEO46 vesicles were each significantly greater than for PBd33-PEO20 vesicles, although critical strain was not significantly different between these vesicle types. PDMS12-PEO46/PBd33-PEO20 hybrid vesicles generally displayed graded responses in between that of the pure component vesicles. Thus, the PDMS12-PEO46/PBd33-PEO20 hybrid vesicles retained or exceeded the strength and toughness characteristic of pure PBd-PEO vesicles, indicating that future assessment of the membrane permeability and fluidity of these hybrid vesicles may be warranted

Implant-based repair of osteochondral defects

The present invention is directed to a unique technology for preparing a growth-factor free, cylindrical, hydrogel implant that has multiple (three or more) longitudinal hydrogel zones with varying chemical and physical properties. The implant may be wholly made of hydrogels or the hydrogels may be associated with cells, such as mesenchymal stem cells (MSCs).U

Implant-based repair of osteochondral defects

The present invention is directed to a unique technology for preparing a growth-factor free, cylindrical, hydrogel implant that has multiple (three or more) longitudinal hydrogel zones with varying chemical and physical properties. The implant may be wholly made of hydrogels or the hydrogels may be associated with cells, such as mesenchymal stem cells (MSCs).U

An Improved Correlation to Predict Molecular Weight Between Crosslinks Based on Equilibrium Degree of Swelling of Hydrogel Networks

Accurate characterization of hydrogel diffusional properties is of substantial importance for a range of biotechnological applications. The diffusional capacity of hydrogels has commonly been estimated using the average molecular weight between crosslinks (Mc), which is calculated based on the equilibrium degree of swelling. However, the existing correlation linking Mc and equilibrium swelling fails to accurately reflect the diffusional properties of highly crosslinked hydrogel networks. Also, as demonstrated herein, the current model fails to accurately predict the diffusional properties of hydrogels when polymer concentration and molecular weight are varied simultaneously. To address these limitations, we evaluated the diffusional properties of 48 distinct hydrogel formulations using two different photoinitiator systems, employing molecular size exclusion as an alternative methodology to calculate average hydrogel mesh size. The resulting data were then utilized to develop a revised correlation between Mc and hydrogel equilibrium swelling that substantially reduces the limitations associated with the current correlation

Designer collagens and use thereof

The present invention identified a recombinant synthetic collagen containing a triple helical backbone protein produced in a prokaryotic expression system where the protein contains at least one ‘inserted’ biologically active sequence(s).U