Polyurethane-coated silica particles with broad-spectrum antibacterial properties

Abstract

Antimicrobial polymer-coated silica particles were synthesized using a "grafting to" approach. A number of polyurethanes (PU) and poly(ethylene glycol)-containing polyurethanes (PU-PEG) with and without free isocyanate end groups were synthesized by metal-free organocatalytic polymerization of isophorone diisocyanate and N-methyldiethanolamine in the absence or presence of PEG diol using 1,8-diazabicyclo-[5.4.0]undec-7-ene as the catalyst, followed by covalent grafting onto primary amine, propyl chloride or benzyl chloride-functionalized silica particles via both surface-to-end-group ( primary amine to isocyanate) and surface-to-backbone ( propyl chloride or benzyl chloride to tertiary amine in PU and PU-PEG backbones, which generated quaternary ammoniums) attachment modes, resulting in various structures of the polymer-grafted surface. The free tertiary amine groups in the polymer coatings were quaternized using benzyl bromide or methyl iodide to impart antibacterial function. The samples were characterized by X-ray photoelectron spectroscopy (XPS), while their antibacterial efficacies and killing kinetics against Gram-positive S. aureus and Gram-negative E. coli were investigated. XPS spectra showed that the attachment mode on different types of surface-functionalized silica particles resulted in various degrees of polymer conjugation and subsequently led to varying antibacterial efficacies. The surface-to-end-group attachment mode after post-quaternization, in particular, produced PU-PEG-coated silica particles with excellent antibacterial potency against S. aureus and E. coli at a low particle concentration of 10 and 40 mg mL −1 , respectively. By using the same batch of particles in repeated applications, it was found that the antibacterial effectiveness was maintained, and the surface-grafted polymer was stable. Overall, these polymer-coated silica particles have good potential for practical antibacterial applications.

Update and challenges in organo-mediated polymerization reactions

“…[154] There are also some examples of step-growth polymerization reactions utilizing guanidines as organocatalysts. [20,155] A series of cyclic guanidines was thus shown to trigger the polyaddition of oligomeric diols (PEO-600 and PTMO-650) and IPDI, in bulk at 60 °C (Scheme 47), affording PUs with Mn = 21,700 -39,800 g.mol -1 (Đ = 1.33-1.89). [20] In contrast to NHC catalysis, [120] where traces of uretdione (dimer) and isocyanurate (trimer) were detected (see Scheme 33), the guanidine catalysis proceeded without any detectable side events, demonstrating the high selectivity of these catalysts for this reaction.…”

“…Guanidine catalyzed-synthesis of PUs from IPDI and PEO. [20] The effectiveness of DBU for synthesizing PUs was further demonstrated with the work of Hedrick, Yang et al, where PUs based on the polyaddition of methyldiethanolamine and IPDI, in presence or not of PEO, were prepared in dichloromethane at r.t. [155] Those polymers were next used to decorate silica nanoparticles, following a « grafting onto » approach. Upon quaternization of the amino groups in the main chain polymer, an antibacterial poly(ammonium)type coating was generated.…”

Tuning the Selectivity of Biodegradable Antimicrobial Cationic Polycarbonates by Exchanging the Counter‐Anion

“…More recently, researchers have been able to synthesize polymers that are able to mimic the cationic and amphiphilic structure of AMPs . Thus, different polycations including polymethacrylates, polynorbornenes, polyamides, polyurethanes, polyesters, and polycarbonates have shown to be efficient against antibiotic‐resistant bacteria. These synthetic polymers are able to overcome some of the drawbacks of AMPs such as their proteolytic stability and cost without marginalizing their ability to kill bacteria .…”

Thermoresponsive Random Poly(ether urethanes) with Tailorable LCSTs for Anticancer Drug Delivery

“…Generally, this is circumvented by the use of harsher polymerization conditions or higher catalyst loadings to obtain high‐molecular‐weight products . With the discovery of various organocatalysts that can serve as effective alternatives to tin‐based catalysts, new opportunities for the preparation of PUs for biomedical applications have emerged …”