Thesis (Ph.D.)--Ohio University, November, 2005. / Title from PDF t.p. Includes bibliographical references (p. 165-167)

<p>Sight-threatening diseases, such as age-related macular degeneration (AMD), affect the tissues of the posterior segment of the eye. Though modern classes of biomolecular based drugs are therapeutically useful, drug targeting for prolonged bioavailability to pathological sites within the eye is challenging. Current delivery approaches are invasive and lack control over drug release rates and tissue-specific localization. In this thesis, a device using microneedles embedded in a flexible platform was developed that could potentially overcome these challenges.</p> <p>New methods for microneedle fabrication were developed by co-opting simple chemical etch methods commonly used for optical probe fabrication as an alternative to current complex and expensive photolithographic technologies to produce out-of-plane, high aspect ratio microneedles which are often constrained materially to silicon and metal. Microneedles with repeatable tip and taper sizes were obtained using hydrofluoric acid, an organic phase and fused-silica capillary tubing. Microneedles with 10 um tips were made using single and batch mode methods and were then integrated into poly (dimethylsiloxane) (PDMS) for alignment using low cost micromolding approaches offering the same degree of accuracy provided by conventional photolithography<strong>. </strong></p> <p>Single microneedle-based devices successfully delivered rhodamine intrasclerally, intravitreally, suprachoroidally and to the retina. This is the first demonstration of active delivery to specific spatial regions within the posterior eye at controllable rates using a non-implantable, biocompatible device – with minimal fabrication facilities, equipment and cost. The fabricated device demonstrated a new hybrid approach of coupling a rigid microneedle with a soft and pliable substrate that could conform to biological tissues.</p> / Doctor of Philosophy (PhD)

Stenting remains a common treatment option for atherosclerotic arteries. The main drawback of early stent platforms was restenosis, which has been combated by drug eluting stents; however, these stents have suffered from a higher incidence of late stage thrombosis. To address current stenting limitations, the major research focuses have been the development of the next generation of drug eluting stents and first generation bioabsorbable stents. The main objective of this dissertation was the design and development of a new class of bioabsorbable stent composed of elastin mimetic protein polymers. The first phase explored different stent design schemes and fabrication strategies. Successfully fabricated stents were then mechanically tested to ensure they possessed sufficient mechanical strength. Additionally, described herein is the potential to modulate the properties of the elastin mimetics through different crosslinking strategies. We have demonstrated that chemical crosslinking allows for the tailoring of the physical, mechanical, drug delivery, and endothelialization properties of these materials. The potential for drug delivery from this elastin mimetic stent was benchmarked as was the potential to endothelialize these stents. Furthermore, we developed the necessary delivery systems to allow for deployment in the rat aorta model.

Microneedles have been developed as a minimally invasive alternative to painful hypodermic needles to deliver modern biotherapeutics. Previously, several in-vitro and in-vivo animal studies have been conducted to show that microneedles increase skin permeability to a wide range of molecules that cannot cross the skin using conventional transdermal patches due to the skin's stratum corneum barrier. However, only a limited number of studies have been performed to study microneedle-based drug delivery in human subjects. Therefore, the objective of this study was to perform the first-in-humans microneedle studies to: a) characterize skin repair responses to solid microneedle insertion to determine the extent of increased skin permeability coupled with predictions of pharmacokinetics of drug delivered through premeabilized skin, b) determine the effect of hollow microneedle-based infusion parameters on flow conductivity of skin and pain and thereby identify barriers to fluid flow into the skin from hollow microneedles, c) assess the safety and efficacy of systemic therapeutic effects through measurement of pharmacokinetic parameters, pain and irritation for microneedle-based insulin delivery in type 1 diabetes subjects, and d) assess the safety and efficacy of local therapeutic effects though delivery of lidocaine to the skin. Results showed for the first time that solid microneedle-treated skin reseals rapidly (< 2 h) in the absence of occlusion whereas occluded skin reseals slowly (3-40 h) depending on microneedle geometry as determined by skin impedance measurements. Increased microneedle length, number, and cross-sectional area led to slower recovery kinetics in the presence of occlusion. This thesis also demonstrated that the flow conductivity of skin decreased as fluid was infused to the dermis through hollow microneedles due to the dense structure of the dermis. Microneedle retraction, low flow rates, and the addition of hyaluronidase helped increase flow conductivity. Microneedles were able to deliver 800 µl of saline to the dermis without causing significant pain. Further, microneedle-based insulin delivery in type 1 diabetes subjects revealed that microneedles provided faster pharmacokinetics and improved glycaemic control than conventional subcutaneous catheters. Lastly, microneedle-based lidocaine injection demonstrated that microneedles were less painful, as effective, and more preferred than hypodermic needles in anesthetizing clinically relevant areas.

Accessing the inner ear presents a significant challenge for the diagnosis and treatment of inner ear diseases. Many existing techniques to access the inner ear are invasive and can cause permanent damage to the cochlea. Recently, a novel microneedle has been fabricated to perforate the round window membrane (RWM) – a membrane sealing one of the two openings in the cochlea. These perforations enhance drug delivery into the inner ear, potentially improving the efficacy of therapeutics. Furthermore, they allow for the aspiration of perilymph samples, which is essential for diagnosing inner ear diseases. However, owing to limited knowledge about the mechanical properties of the RWM, certain technical aspects remain unexplored. Specifically, the interaction between the RWM and the microneedle during perforation is yet to be examined. This investigation is pivotal for the optimal design of microneedles — those robust enough to perforate RWMs yet delicate enough to minimize damage. In this thesis, we conduct a thorough examination of the guinea pig RWM, encompassing its geometry and its mechanical responses to pressures from the middle ear and inner ear. Additionally, we also formulate a comprehensive constitutive law for the guinea pig RWM. Our exploration begins with the creation of a U-Net model tailored to automatically segment the RWM. Despite the presence of other structures in the same image—such as bone, the basilar membrane, and ambient noise—the model proved invaluable for efficiently and automatically segmenting the RWM. To enhance accuracy, post-processing techniques like connected component analysis and majority voting were incorporated. Using this 3D model, we proceeded to study the RWM’s geometry. Recognizing the shrinkage observed in fixed RWMs, we integrated fresh RWM data to estimate the shrinkage ratio. Subsequently, we analyzed both the overall RWM thickness and that of the middle connective tissue layer—crucial metrics for future RWM modeling. Next, we proposed a method to evaluate the in-plane deformation of the RWM due to applied pressure. This involved using a bulge test system to pressurize and deform the RWM, combined with confocal microscopy to track stained nuclei or pre-introduced fluorescent beads on the RWM. We then utilized the coherent point drift (CPD) algorithm to measure the displacement of beads and nuclei. Results indicated that both markers could be successfully used to measure the RWM’s displacement. Further analysis revealed the in-plane Lagrangian strain of the RWM, with a significant observation being that the direction of maximum in-plane Lagrangian strain is perpendicular to the fiber direction. This underscores the crucial role of collagen fibers in determining the RWM’s mechanical properties. To conclude our study, we devised a constitutive law for the RWM, conceptualizing it as a combination of the ground substance and a family of dispersed fibers. This model was integrated into a FEBioStudio plugin, facilitating simulations of the RWM’s mechanical reactions to different pressures. Although our simulations closely aligned with experimental findings, some discrepancies were noted, likely stemming from an incomplete understanding of fiber dispersions. Nevertheless, our constitutive law reinforces the notion that fibers primarily govern the RWM’s mechanical characteristics.

The major hurdle in the development of transdermal route as a versatile drug delivery method is the formidable transport barrier provided by the stratum corneum. Despite decades of research to overcome the stratum corneum barrier, limited success has been achieved. The objectives of this research were to develop and characterize two different strategies to overcome the stratum corneum barrier for transdermal delivery of biopharmaceuticals and vaccines. In the first strategy, coated microneedles (sharp-tipped, micron-sized structures) were developed to enable delivery of drugs directly into the skin by bypassing the stratum corneum barrier. In the second strategy, instead of bypassing the barrier, microdermabrasion was used to selectively abrade stratum corneum with sharp microparticles for topical drug application. Coated microneedles For developing painless microneedles, the first detailed study was performed to characterize the effect of microneedle geometry on pain caused by microneedle insertions in human volunteers. This study demonstrated that microneedles are significantly less painful than a 26-gage hypodermic needle and that decreasing microneedle length and numbers reduces pain. Next, the first in-depth study of microneedle coating methods and formulations was performed to (i) develop a novel micron-scale dip-coating process, (ii) test the breadth of compounds that can be coated onto microneedles, and (iii) develop a rational basis to design novel coating formulations based on the physics of dip-coating. Finally, a plasmid DNA-vaccine was coated onto microneedles to immunize mice, to provide the first evidence that microneedle-based skin immunization can generate a robust in vivo antigen-specific cytotoxic-T-lymphocyte response using similar, or lower, DNA doses on microneedles as when using the gene gun or intramuscular injection. Microdermabrasion We demonstrated for the first time that microdermabrasion in monkeys and humans can selectively, yet completely remove the stratum corneum layer. Using a mobile mode of microdermabrasion, an increase in the number of treatment passes led to greater tissue removal. Furthermore, topical application of Modified Vaccinia Ankara virus after microdermabrasion induced virus-specific antibodies in monkeys. In conclusion, both coated microneedles and microdermabrasion were developed to enable delivery of biomolecules into the skin, indicating their potential for transdermal delivery of a wide range of biopharmaceuticals and vaccines.