Degree Type

Dissertation

Date of Award

2019

Degree Name

Doctor of Philosophy

Department

Mechanical Engineering

Major

Mechanical Engineering

First Advisor

Nicole N. Hashemi

Abstract

Traumatic brain injuries (TBIs) are a highly complex injury that is heavily studied in modern research. An aspect of TBIs that has been almost entirely overlooked is the existence of cavitation in the brain during a high impact injury. The presence of cavitation in the brain is a recent theory and is feared to cause detrimental damages on brain tissue. The following chapters aim to investigate this phenomena by first engineering an apparats that simulates controlled cavitation for TBI applications. The apparatus that is used in this study involves acoustical techniques to cause microbubbles (MBs) to oscillate and fragment under resonant conditions, detailed in Chapter 2. MBs are created by using a syringe to push air through capillary tubing, resulting in MBs ranging from 50-100 μm. The MBs exit at a consistent rate and arbitrary amounts are adhered to an analyt sample prior to inducing acoustical cavitation. This method is advantageous and novel because it allows for arbitrary amounts of cavitation, the size of the created MBs is similar to that of what is thought to exist in vivo, and it is cost-effective.

Using this developed apparatus, there are a variety of studies that have novel potential. Chapter 3 highlights the response the soft polymers have to surrounding cavitation. Using 3D confocal microscopy and interferometry techniques, it is apparent that the soft polymer surface is visually damaged after cavitation exposure. Further roughness calculations demonstrate distinct alterations in the overall roughness and skewness of the surface for experimental samples. Although these soft polymers do not entirely replicate the response to cavitation of the human brain, they provide insight on how alarming inter-cranial actually is and motivate future studies.

Reactive astrocytes are known to have a large role in the response of the brain after a TBI. Introducing astrocytes in the developed apparatus is made possible by sterilizing all the components and using phosphate buffered saline (PBS) as the cavitation medium. Culturing astrocytes on biocompatible microfibers allows for the investigation of a finite amount of cells. Chapter 4 illustrates a distinct morphological change that the astrocytes undergo after experiencing cavitation. Over 48 hours different stages of morphology are represented. Chapter 4 also elucidates genetic changes that astrocytes undergo immediately after cavitation, via quantitative polymerase chain reaction (qPCR) techniques. Results show alarming upregulation in various genes that are known to be upregulated in other neurodegenerative diseases. These findings add additional concern for the damages that cavitation causes on nearby cranial anatomy. These results also inspired an additional genetic study to characterize the longitudinal gene expression trend from 0-48 hours post-cavitation, summarized in Chapter 5. This was primarily an exploratory study to help further investigate the morphological changes that were found in Chapter 4. In the ten genes that were studied, there was no consistent trend in gene expression from multiple genes to the next. Future studies aim to include RNA sequencing to obtain a complete summary on the expression changes in the entire genome.

Taken together, the following chapters summarize the engineering of an applied apparatus that simulates controlled cavitation in vitro. Introducing soft polymers in this apparatus yields distinct surface alterations. This apparatus is biocompatible and used to study morphological and genetic changes in astrocytes. These results are novel and help legitimize the concerning detriments that cavitation has inside the human skull. Future studies aim to build on this foundation and continue to bolster the current understanding, therapeutics, and preventative techniques in TBIs.

Copyright Owner

Alex Wrede

Language

en

File Format

application/pdf

File Size

87 pages

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