Surface Density Variation within Cyclic Polymer Brushes Reveals Topology Effects on Their Nanotribological and Biopassive Properties

Dong

Macromol. Rapid Commun.

et al. 2019

little is known about the effects of PIL topology on bactericidal properties.Due to the absence of chain ends and steric constraints, cyclic polymers are one of the most intriguing nonlinear polymer topologies because they exhibit distinct properties in comparison with their linear counterparts. [9] For instance, Grayson and coworkers demonstrated that cyclic poly(ethylene imine) (PEI) exhibits a higher transfection efficiency when compared to its linear PEI analog in addition to reduced toxicity relative to the branched PEI "goldstandard" control. [10] Recent studies have also suggested that a cyclic hydrophilic moiety offers greater stability for selfassembled micelles than a linear analog. [11] In particular, the Benetti group studied how the topology effects typically displayed by cyclic poly(2-ethyl-2-oxazoline) (PEOXA) in solution manifested for brush assemblies generated on surfaces. It was demonstrated that the topological effects of the brush assemblies imparted by the cyclic polymer architecture translated into an enhancement of the brush properties, such as steric stabilization of surfaces, antifouling and lubricating behavior. [12] Inspired by these advances, in this study, we focused on the preparation of cyclic PIL brushes by the "grafting to" technique and systematically compared the bactericidal activity of linear brush analogs. In particular, the objective of this work was to explore whether the cyclic PIL architecture would impart PILs with enhanced properties in bactericidal activity, thus expanding the design possibilities for the development of excellent antibacterial surfaces.Herein, well-defined linear PIL adsorbates, in which the tertbutyldimethylsilyl ether and sulfonyl fluoride groups are at the α and ω positions of the polymer chains, were synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization using a heterodifunctional trithiocarbonate RAFT agent (Scheme 1). Cyclic PIL adsorbates were then conveniently obtained by intramolecular sulfur(VI)-fluoride exchange (SuFEx) click cyclization of the linear PILs in air at room temperature. In particular, both linear and cyclic PILs contain catechol groups that allow them to be efficiently grafted onto gold surfaces. [13] Subsequently, the morphologies of cyclic PIL brushes were characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The topological effects of cyclic PIL brushes on bactericidal activity were evaluated using the most common catheter-associated urinary tract infection pathogen-Escherichia coli [14] -and compared with those of the respective linear precursor.In addition to extensive studies of conventional linear poly(ionic liquids) (PILs), exploration of the effects of PIL topology, especially cyclic architecture, on bactericidal properties will expand the design possibilities for the development of excellent antibacterial surfaces. Herein, the preparation of antibacterial surfaces based on cyclic PIL brushes is reported for the first time and how the cyclic PIL architec...

Section: Methodsmentioning

confidence: 85%

Section: Methodsmentioning

confidence: 99%

Enhancement of Bactericidal Activity via Cyclic Poly(cationic liquid) Brushes

Dong

Macromol. Rapid Commun.

et al. 2019

“…In particular, cyclic PAOXA adsorbates are characterized by reduced molecular dimensions with respect to their linear counterparts of comparable molecular weight, [55,56] and thus can form denser brush layers when assembled on solid surfaces from diluted solutions. [57][58][59][60] In addition, due to the constraints introduced during their cyclization, [61] cyclic PAOXA grafts generate films that provide an augmented steric stabilization of the surface, when compared to linear-brush analogues (Figure 6a). [59,62] Hence, the unique properties and intrinsic structure of cyclic brushes enabled the fabrication of PAOXA surfaces with significantly enhanced biopassivity with respect to that typically displayed by linear PAOXA-based analogues.…”

Section: Topology Of Paoxas At Surfacesmentioning

confidence: 99%

Fabrication of Biopassive Surfaces Using Poly(2‐alkyl‐2‐oxazoline)s: Recent Progresses and Applications

Trachsel

Romio

Ramakrishna

et al. 2020

Adv Materials Inter

Self Cite

monomer composition enables to obtain hydrophilic and bioinert and/or amphiphilic PAOXA species displaying thermoresponsive properties. [6] Simultaneously, careful choice of initiator and/or terminator agents gives access to end-functional or heterobifunctional polymers, which can be directly applied for surface modification, or used as building blocks to yield structurally more complex adsorbates targeting specific substrates or generating well-defined polymer architectures at the interface. [7-9] Among the most recent studies focusing on the fabrication of biopassive PAOXA films, most of them involved grafting of pre-synthesized adsorbates by exploiting functional anchors that are specific for the target substrate to passivate. In other works, the growth of a PAOXAbased film was triggered from the substrate itself, through surface-initiated CROP (SI-CROP), while interest has been rising in applying plasma polymerization of 2-oxazolines to generate robustly attached coatings on an array of different supports. Through these strategies, and with the general objective of suppressing nonspecific interaction with biological entities, a broad range of biomaterials, ranging from inorganic supports, plastics and nanomaterials of diverse composition have been successfully functionalized with PAOXAs. While during the first decade of 2000s efforts were spent in dissecting the fundamental properties of PAOXAs assemblies on surfaces, [3,10,11] during the past five years their application in different coating formulations for biomaterials has been progressively expanding, and at least some of them are probably mature for a direct involvement of industry. In this progress report, we critically review the most recent studies focusing on the fabrication of PAOXA coatings, especially concentrating on the generation of bioinert surfaces, which probably represents their most appealing and technologically relevant application. 2. Composition of Bioinert PAOXA-Based Surfaces Among the different PAOXA species that were applied on surfaces to generate coatings, hydrophilic poly(2-methyl-2-oxazoline) (PMOXA) and poly(2-ethyl-2-oxazoline) (PEOXA) showed the most pronounced inertness towards nonspecific interactions with serum proteins, cells and bacteria. A recent study by Morgese et al. identified the superior biopassivity of linear Poly(2-alkyl-2-oxazoline)s (PAOXAs) are emerging among the most promising nonionic alternatives to poly(ethylene glycol)s (PEGs), specifically in the modification and functionalization of biomaterials. Due to their chemical tailorability and robustness, coupled to their relatively easy synthesis, PAOXAs are increasingly applied as adsorbates to generate bioinert surfaces that prevent nonspecific contamination by proteins, cells and bacteria. Passivation of medical devices, sensors and cell-sensitive platforms with PAOXAs enables a nearly quantitative suppression of nonspecific biological contamination, while biopassivity is maintained over longer incubation times than those recorded for more degradable PEG-b...

“…[57 -59] Similarly to their PEG-based analogues, poly(2ethyl-2-oxazoline) (PEOXA) brushes assembled on TiO 2 surfaces ( Figure 4) show a lubricious character that is strictly correlated with their surface coverage (expressed as grafting density, Σ, in Figure 4). [60,61] The characterization of the nanotribological properties of PEOXA brushes by lateral force microscopy (LFM) [62] has further highlighted the effect of chain interdigitation in determining friction between brushbearing surfaces. As shown in the friction force-vs.applied load (F f L) profiles reported in Figure 4,b, when PEOXA brushes are sheared against an identical brush countersurface, friction is generally lower for all grafting densities investigated, compared to the case where the same brushes are slid past a bare TiO 2 surface.…”

Section: Alternatives To Peg Brushesmentioning

confidence: 99%

“…This phenomenon was due to the absence of linear chain ends within cyclic brushes, which hinders interpenetration between opposing grafts [81] and markedly reduces dissipative forces that are typically responsible for the increment in friction observed between linear brushes at relatively high applied loads. [60,61]…”

Section: Effect Of Brush Architecture On Protein Resistance and Lubrimentioning

confidence: 99%

Using Polymers to Impart Lubricity and Biopassivity to Surfaces: Are These Properties Linked?

Benetti

Spencer

2019

Helvetica Chimica Acta

Self Cite

Polymer brushes have been widely applied for the reduction of both friction and non‐specific protein adsorption. In many (but not all) applications, such as contact lenses or medical devices, this combination of properties is highly desirable. Indeed, for many polymer‐brush systems, lubricity and resistance to biofouling appear to go hand in hand, with modifications of brush architecture, for example, leading to a similar degree of enhancement (or degradation) in both properties. In the case of poly(ethylene glycol) (PEG) brushes, this has been widely demonstrated. There are, however, examples where this behavior breaks down. In systems where linear brushes are covalently crosslinked during surface‐initiated polymerization (SIP), for example, the presence and the chemical nature of links between grafted chains might or might not influence biopassivity of the films, while it always causes an increment in friction. Furthermore, when the grafted‐chain topology is shifted from linear to cyclic, chemically identical brushes show a substantial improvement in lubrication, whereas their protein resistance remains unaltered. Architectural control of polymer brush films can provide another degree of freedom in the design of lubricious and biopassive coatings, leading to new combinations of surface properties and their independent modulation.