Chemical and Biological Engineering ETDs

Publication Date

8-28-2012

Abstract

An estimated 19,000 deaths and $3-4 billion in health care costs per year in the U.S. are attributed to methicillin-resistant Staphylococcus aureus (MRSA) infections. Certain cationic phenylene ethynylene (CPE)-based polymers (PPEs) and oligomers (OPEs) have been demonstrated to exhibit dark and light-activated antimicrobial activity. Envisioned applications of these CPEs include the fabrication of antimicrobial surfaces to reduce or prevent the spread of potentially untreatable strains of bacteria. Until recently, it was unknown if the polymers or oligomers would exhibit similar biocidal activity toward mammalian cells. This work examines the toxicity of CPEs to mammalian cells at three levels: cytoxicity testing of cell monolayers, skin irritation testing of tissues, and intracellular co-localization. Eight CPEs, two PPEs and six OPEs, were selected for these studies based on biocidal activity and diversity of repeat unit number and functional groups. In the cytotoxicity studies, two cell types were exposed to eight CPEs at concentrations from 1-100 μg/mL for 24 hours. As expected, concentration plays the largest role in determining viability. At intermediate concentrations (~5-10 μg/mL ), the interplay between light and the light-activated compounds is very important. To mimic skin exposure in vitro, eight CPEs and two types of electrospun mats were selected for skin irritation testing using tissues derived from human epidermal keratinocytes. PPE-DABCO and PPE-Th were non-irritants up to the highest tested concentrations, 924 μg/mL and 100 μg/mL, respectively. The lack of skin irritation for all substances, as measured by two endpoints, alleviates initial safety concerns for products based on these polymers and oligomers, both in solution and as electrospun mats. In the localization studies, three compounds (one polymer and two oligomers) were included in growth media above epithelial cell monolayers for 1-4 hours, stained to localize the nearest membrane or organelle, and viewed using fluorescence microscopy. The three compounds were successfully localized to two distinct locations within the cell, indicating that at least two modes of action are possible for these compounds. In all cases, the addition of light changed the effects of the compounds on the mammalian cells. The modes of action of these compounds appear to be governed primarily by length. For applications below cytotoxic concentrations, these compounds are safe for mammalian cells. The concentrations at which the longer S-OPEs and the DABCO-containing compounds are cytotoxic are much higher than for the shortest S-OPE, PPE-Th, and the remaining two EO-OPEs, thus these compounds have the widest range of concentrations available for potential applications. Although the more aggressive EO-OPEs may find limited applicability for antimicrobial agents, they may find promise for other applications, such as live-cell imaging, intracellular drug delivery, and as anti-cancer agents.

Keywords

antimicrobial, polymer, in vitro, cytotoxicity, cell, skin, irritation, oligomer, electrolyte, phenylene ethynylene, conjugated, antibacterial, biocide; Antimicrobial polymers--Toxicity., Microbial sensitivity tests.

Document Type

Dissertation

Language

English

Degree Name

Chemical Engineering

Level of Degree

Doctoral

Department Name

Chemical and Biological Engineering

First Committee Member (Chair)

Whitten, David G.

Second Committee Member

Lidke, Diane S.

Third Committee Member

Evans, Deborah G.

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