Caspofungin on ARGET-ATRP grafted PHEMA polymers: Enhancement and selectivity of prevention of attachment of Candida albicans

Abstract

There is a need for coatings for biomedical devices and implants that can prevent the attachment of fungal pathogens while allowing human cells and tissue to appose without cytotoxicity. Here, the authors study whether a poly(2-hydroxyethylmethacrylate) (PHEMA) coating can suppress attachment and biofilm formation by Candida albicans and whether caspofungin terminally attached to surface-tethered polymeric linkers can provide additional benefits. The multistep coating scheme first involved the plasma polymerization of ethanol, followed by the attachment of α-bromoisobutyryl bromide (BiBB) onto surface hydroxyl groups of the plasma polymer layer. Polymer chains were grafted using surface initiated activators regenerated by electron transfer atom transfer radical polymerization with 2-hydroxyethylmethacrylate, yielding PHEMA layers with a dry thickness of up to 89 nm in 2 h. Hydroxyl groups of PHEMA were oxidized to aldehydes using the Albright-Goldman reaction, and caspofungin was covalently immobilized onto them using reductive amination. While the PHEMA layer by itself reduced the growth of C. albicans biofilms by log 1.4, the addition of caspofungin resulted in a marked further reduction by >4 log units to below the threshold of the test. The authors have confirmed that the predominant mechanism of action is caused by antifungal drug molecules that are covalently attached to the surface, rather than out-diffusing from the coating. The authors confirm the selectivity of surface-attached caspofungin in eliminating fungal, not mammalian cells by showing no measurable toxicity toward the myeloid leukaemia suspension cell line KG-1a.

An Acid Test: Facile SI‐ARGET‐ATRP of Methacrylic Acid

“…Accordingly, we have investigated SI‐ATRP of PMAA. In contrast to the facile nature of SI‐ATRP of HEMA, however, we have found SI‐ATRP of MAA to be challenging, in accord with previous reports of ATRP of MAA as discussed above. Moreover, for ease of scale‐up to commercial applications, we wished to develop a facile method that could be used without specialist techniques such as air exclusion.…”

“…Polymer‐grafted substrates have been explored for their use as conjugation platforms, providing a well‐defined polymeric scaffold onto (and into) which biomolecules can be conjugated . We have been exploring substrate independent ATRP as a way of decorating medical device surfaces with bioactive compounds such as those that combat infections . Plasma polymerization is a versatile and scalable technology for preparing substrates for SI‐ATRP grafting; it can be used on medically‐relevant plastics and polymers in two or even one processing step .…”

“…To this solution, 1.4 mL of MAA (16 mmol) was added. Finally, 1.6 mL of the copper/ligand solution (consisting of 3.6 mg mL −1 CuCl 2 ·2H 2 O (0.02 mmol/ 0.02 m ) and 0.01 mL mL −1 PMDETA (0.05 mmol/0.05 m ) in 1:1 EtOH/H 2 O) was added (same copper/ligand solution as used in our previous publication) . The resulting solution totaled 16 mL, from which 1 mL was pipetted into each of the wells (24‐well plate) containing one initiator‐functionalized sample and allowed to react for 1h.…”

“…To prepare the substrate surface, we covalently immobilized the well‐known ATRP initiator α‐bromoisobutyryl bromide (BiBB) onto the surface of a thin ethanol plasma polymer interlayer, analogous to previous work on SI‐ARGET ATRP of hydroxyethylmethacrylate (HEMA) ( Scheme ) . By changing the reaction parameters such as solvent, monomer, and catalyst concentration, as well as the addition of acid and salts to the reaction, we have determined the “sweet spot” at which SI‐ARGET‐ATRP of PMAA proceeds reliably under ambient air conditions and with good control.…”

Editorial: In Focus Issue on Bacterial-Surface Interactions

“…Critically, the presence of these agents was shown to not affect mammalian cells, suggesting that these films could be suitable for antifungal medical device coatings. 1 The creation of antimicrobial systems from different metallic micro-and nanomaterials were explored in two studies that investigated both the efficacy and the mechanisms of anti-microbial action. Interestingly, the emphasis on high volume applications in each case presented specific challenges, with Tanasic et al 2 focusing on the properties of additives for surface paints and coatings in hospitals while Heiss et al 3 focused on the stability and long term activity of AgRu coatings on microparticles for water purification systems.…”