(154f) Effect of Poly-L-Lysine Molecular Weight on Antibacterial Activity of Polyelectrolyte Multilayer Coated Surfaces

Over 60% of hospital-acquired infections are device related. There is a need for device

coatings that can inhibit bacteria attachment, preventing biofilms, while also killing

planktonic bacteria. Small molecule antimicrobials embedded in such coatings can have

uncontrolled release increasing the likelihood of drug resistance, increased localized toxicity,

lack of stability, and loss of activity in the case of covalent attachment. Purely polymeric

coatings can overcome many of these complications. We have developed such coatings using

layer-by-layer self-assembly of hyaluronic acid (HA) and poly-L-lysine (PLL), a polycation,

which plays both a structural and functional role due to its intrinsic antibacterial properties.

An increased understanding of polymer physiochemical properties can improve their use in

functional materials. We investigated the effect of PLL molecular weight (MW) on the

antibacterial efficacy of (PLL/HA) films, finding that MW influences release-based killing

while film hydrophilicity for all PLL MWs examined imparts resistance to bacterial adhesion.

(PLL/HA) films were assembled containing 50 bilayers and denoted PLLⁿ, where n

represents the number of repeat units in the PLL utilized in a given architecture. Films

containing PLL with 30, 100, or 400 repeat units (6.3 kDa, 21 kDa, and 84 kDa, respectively)

were investigated. These films were exposed to Staphylococcus aureus in the exponential

growth phase. LIVE/DEAD staining and incubation on agar showed a significant reduction in

bacteria attachment on all coatings compared with uncoated substrates. We hypothesize that

this effect is related to the hydrophilicity of the films as evidenced by the large increase in

film thickness upon dry film hydration in phosphate buffered saline (775%, 670%, and 266%

for PLL⁴⁰⁰, PLL¹⁰⁰, and PLL³⁰, respectively). Upon repeated exposure to fresh bacteria

inoculum, PLL⁴⁰⁰ films lost bacterial growth inhibition activity rapidly (after 1 day), while

PLL³⁰ and PLL¹⁰⁰ were effective for 4 days and approximately 10 days, respectively. We

found that PLL concentrations were at or above the minimum inhibitory concentration of

PLL for each MW against S. aureus only while films were effective, suggesting that growth

inhibition occurs due to released PLL. Higher amounts of lower MW PLL were released into

the media daily compared to larger MW PLL, likely related to a higher PLL mobility in films

at lower MWs. Confocal imaging of films incubated with fluorescein labeled PLL confirmed

that PLL mobility in the films decreased with increasing MW. PLL MW also influenced the

thickness and stability of the films. PLL³⁰ films (1.2 ± 0.2 μm thick) underwent complete

dissolution by day 5, while PLL¹⁰⁰ coatings (3.6 ± 0.1 μm thick) underwent disruption more

slowly with considerable loss of film starting near day 10. This difference in stability

contributed to the longer-term efficacy of PLL¹⁰⁰ compared to PLL³⁰. Thus, we have

demonstrated that PLL MW plays a critical role in dictating coating bacterial inhibition and

long-term efficacy. The PLL films developed in this work may be tuned appropriately by

varying PLL MW to prevent and treat device-associated infections.