No abstract

Polyelectrolyte complexation, with and without additional salts such as NaCl, has been of long-standing interest across such areas as polyelectrolyte blends, layer-by-layer (LbL) thin films, and coacervates. To better understand how to control complexation strength, we study polyanionic microgels involving sulfonic or carboxylic acids that interact with colistin, a small multivalent cationic (+5) macroion. Complexation causes microgel deswelling, which can be followed by in situ optical microscopy. The release of complexed colistin causes microgel swelling and is triggered by threshold levels of NaCl in the surrounding buffer. Differences in these thresholds together with differences in the Na+ doping of complexed microgels indicate that colistin complexation is stronger with poly­(styrene sulfonate) (PSS) than it is with poly­(acrylic acid) (PAA). Coarse-grained molecular dynamics simulations show that the free-energy decrease accompanying colistin-PSS complexation is significantly greater than that for colistin-PAA complexation. These simulations furthermore indicate that pendant aromatic groups in PSS play an important steric role as a spacer that creates polyanion conformations that maximize opportunities for both Coulombic and nonbonded Lennard-Jones interactions with colistin.

Bacterial contamination of an exposed implantable medical device by the atmosphere of an operating room (OR) is increasingly implicated as a cause of device‐associated infection. Here, OR contamination is modeled in vitro using an aerosolizing system to spray small quantities of staphylococci onto titanium rods. Contaminated rods always manifest culturable bacteria. Self‐assembly is used to create a self‐defensive Ti surface that substantially enhances the rod's resistance to such contamination. Poly(acrylic acid) microgels are electrostatically deposited onto small Ti rods and subsequently loaded by complexation with a cationic antimicrobial peptoid (TM1). The microgels are visualized in situ by optical microscopy, and changes in microgel diameter indicate the loading state. These measurements show that TM1 can be quickly loaded from low‐ionic‐strength buffer and subsequently remained sequestered within the microgels for up to 4 weeks when soaked in phosphate buffered saline. TM1‐loaded microgel‐modified Ti surfaces are contaminated with aerosolized staphylococci, and subsequent assays indicate few or no culturable bacteria. In the absence of nutrients to enable metabolism, this finding suggests that bacteria trigger local TM1 release by contact transfer. The modified surfaces exhibit good in vitro cytocompatibility as manifested by the adhesion, spreading, and metabolic activity of human fetal osteoblasts.

Infection associated with tissue‐contacting biomedical devices is a compelling clinical problem initiated by the microbial colonization of the device surface. Among the possible sources of contaminating bacteria is the operating room (OR) itself, where viable bacteria in the atmosphere can sediment onto a device surface intraoperatively. We have developed an aerosolizing system that can reproducibly spray small quantities of aerosolized bacteria onto a surface to mimic OR contamination. This paper describes the design of the system and characterizes key aspects associated with its operation. The area density of sprayed bacteria is on the order of 102/cm2. Using titanium (Ti) alloy coupons as test substrates contaminated by staphylococci, we quantify the fraction of bacteria that are well adhered to the substrate, those that can be removed by sonication, and those that are not recovered after spraying. Despite the relatively low levels of surface contamination, we furthermore show that such a model is able to demonstrate a statistically significant reduction in colonization of Ti coupons modified by antimicrobial quaternary ammonium compounds relative to unmodified controls.