Topology Effects on the Structural and Physicochemical Properties of Polymer Brushes

Abstract

The application of polymer “brushes”, with their unique physicochemical properties, has led to a radical change in the way we functionalize biomaterials or formulate hybrids; however, their attractive traits can be largely surpassed by applying different polymer topologies, beyond the simple linear chain. Cyclic and loop brushes provide enhanced steric stabilization, improved biopassivity, and lubrication compared to their linear analogues. Focusing on poly­(2-ethyl-2-oxazoline) (PEOXA), an emerging polymer in nanobiotechnology, we systematically investigate how topology effects determine the structure of PEOXA brushes and to what extent technologically relevant properties such as protein resistance, nanomechanics, and nanotribology can be tuned by varying brush topology. The highly compact structure of cyclic PEOXA brushes confers an augmented entropic barrier to the surface, efficiently hindering unspecific interactions with biomolecules. Moreover, the intrinsic absence of chain ends at the cyclic-brush interface prevents interdigitation when two identical polymer layers are sheared against each other, dramatically reducing friction. Loop PEOXA brushes present structural and interfacial characteristics that are intermediate between those of linear and cyclic brushes, which can be precisely tuned by varying the relative concentration of loops and tails within the assembly. Such topological control allows biopassivity to be progressively increased and friction to be tuned.

Cyclic Polymer Grafts That Lubricate and Protect Damaged Cartilage

“…These results further corroborated the improvement in antifouling properties by cyclic PEOXAb rushes assembled on flat TiO 2 surfaces,w hich was ascribed to their higher grafting density coupled with their less compressible character when proteins approach the functionalized surface. [22,29] In the present system, we demonstrate that cyclic PMOXA brushes fabricated via copolymer chemisorption on cartilage surfaces also showed this distinctive topology effect, reducing protein contamination on the complex and rough surface of acollagenous tissue.…”

“…Moreover,r eplacing LPMOXA with CPMOXA for a = 0.1 and 0.3 determined asubstantial and statistically relevant decrease in the measured m at the highest applied pressures tested. Thea bsence of chain ends by CPMOXA prevented interdigitation under load [22,29,30] and ensured the constant presence of afluid film between the sheared brush interfaces.…”

Cyclic Polymer Grafts That Lubricate and Protect Damaged Cartilage

“…The replacement of L PMOXA with C PMOXA grafts determined a significant decrease in the physisorbed biofilm thickness (Supporting Information, Figure S11). These results further corroborated the improvement in antifouling properties by cyclic PEOXA brushes assembled on flat TiO 2 surfaces, which was ascribed to their higher grafting density coupled with their less compressible character when proteins approach the functionalized surface . In the present system, we demonstrate that cyclic PMOXA brushes fabricated via copolymer chemisorption on cartilage surfaces also showed this distinctive topology effect, reducing protein contamination on the complex and rough surface of a collagenous tissue.…”

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

“…[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.…”

“…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]…”