Temperature- and pH-Responsive Schizophrenic Copolymer Brush Coatings with Enhanced Temperature Response in Pure Water

Abstract

Novel brush coatings were fabricated with glass surface-grafted chains copolymerized using surface-initiated atom transfer radical polymerization (SI-ATRP) from 2-(2-methoxyethoxy)ethyl methacrylate (OEGMA188) and acrylamide (AAm), taken in different proportions. P(OEGMA188-co-AAm) brushes with AAm mole fraction >44% (determined with XPS and TOF-SIMS spectroscopy) and nearly constant with the depth copolymer composition (TOF-SIMS profiling) exhibit unusual temperature-induced transformations: The contact angle of water droplets on P(OEGMA188-co-AAm) coatings increases by ∼45° with temperature, compared to 17–18° for POEGMA188 and PAAm. The thickness of coatings immersed in water and the morphology of coatings imaged in air show a temperature response for POEGMA188 (using reflectance spectroscopy and AFM, respectively), but this response is weak for P(OEGMA188-co-AAm) and absent for PAAm. This suggests mechanisms more complex than a simple transition between hydrated loose coils and hydrophobic collapsed chains. For POEGMA188, the hydrogen bonds between the ether oxygens of poly(ethylene glycol) and water hydrogens are formed below the transition temperature T c and disrupted above T c when polymer–polymer interactions are favored. Different hydrogen bond structures of PAAm include free amide groups, cis-trans-multimers, and trans-multimers of amide groups. Here, hydrogen bonds between free amide groups and water dominate at T < T c but structures favored at T > T c, such as cis-trans-multimers and trans-multimers of amide groups, can still be hydrated. The enhanced temperature-dependent response of wettability for P(OEGMA188-co-AAm) with a high mole fraction of AAm suggests the formation at T c of more hydrophobic structures, realized by hydrogen bonding between the ether oxygens of OEGMA188 and the amide fragments of AAm, where water molecules are caged. Furthermore, P(OEGMA188-co-AAm) coatings immersed in pH buffer solutions exhibit a ‘schizophrenic’ behavior in wettability, with transitions that mimic LCST and UCST for pH = 3, LCST for pH = 5 and 7, and any transition blocked for pH = 9.

Thermoresponsive Smart Copolymer Coatings Based on P(NIPAM-co-HEMA) and P(OEGMA-co-HEMA) Brushes for Regenerative Medicine

“…At lower grafting densities, surface-tethered polymer chains can adopt various other conformations, which are referred to as mushroom or pancake . In our former works, − a fabrication method of temperature-responsive coatings using graft polymerization “from the surface” of oligoperoxide or atom transfer radical polymerization (ATRP) initiator, grafted to a native glass surface functionalized with (3-aminopropyl)­triethoxysilane (APTES), was developed. In particular, there is an increased interest in surfaces modified with temperature-responsive grafted polymer brushes, which can change their affinity toward proteins and cells under external stimuli and therefore have potential applications in biology and medicine.…”

Switching it Up: The Promise of Stimuli‐Responsive Polymer Systems in Biomedical Science

“…The LCST value of polymer systems depends on numerous different factors, for example, molecular weight of the polymers, embedded inorganic particles, organic or inorganic ions, buffer solutions, etc.. [25][26] The intensity of the temperature-induced response of polymer systems is an important factor in these polymer systems; a strong enhancement of the response was shown when combining several monomers. [27] In particular, poly(di-(ethylene glycol)methyl ether methacrylate)-co-acrylamide) coatings showed temperature-and pH-responsive schizophrenic behavior with enhanced temperature response in pure water. [27] On the other hand, some temperature-responsive polymers exhibit an UCST phase transition, where the polymer chains become soluble on heating due to decreased hydrophobic interactions (Figure 2e).…”

“…[27] In particular, poly(di-(ethylene glycol)methyl ether methacrylate)-co-acrylamide) coatings showed temperature-and pH-responsive schizophrenic behavior with enhanced temperature response in pure water. [27] On the other hand, some temperature-responsive polymers exhibit an UCST phase transition, where the polymer chains become soluble on heating due to decreased hydrophobic interactions (Figure 2e). The UCST is the critical temperature above which the components of a mixture are miscible in all proportions.…”

“…The intensity of the temperature‐induced response of polymer systems is an important factor in these polymer systems; a strong enhancement of the response was shown when combining several monomers [27] . In particular, poly(di(ethylene glycol)methyl ether methacrylate)‐ co ‐acrylamide) coatings showed temperature‐ and pH‐responsive schizophrenic behavior with enhanced temperature response in pure water [27] …”

Synthesis, Characterization, Conformation in Solution, and Thermoresponsiveness of Polymer Brushes of methoxy[oligo (propylene glycol)-block-oligo(ethylene glycol)]methacrylate and N-[3-(dimethylamino)propyl]methacrylamide Obtained via RAFT Polymerization

“…Amphiphilic (co)polymers methoxiolygoethylenglycolmethacrylate (MOEGM) have good biocompatibility and low toxicity, are susceptible to biodegradation, and have low critical solution temperature, which is close to human body temperature. In [ 21 ], a series of novel temperature-responsive copolymer brushes with P-(2-(2-methoxyethoxy)ethyl methacrylate)- co -acrylamide) (P-(OEGMA188- co -AAm)) chains grafted from glass surfaces functionalized with (3-aminopropyl)triethoxysilane followed by the ATRP initiator were synthesized. P(OEGMA188- co -AAm) with a high mole fraction of AAm demonstrates “schizophrenic” behavior in wettability after immersion in pH buffer solutions, with transitions that mimic LCST and UCST for pH = 3, LCST for pH = 5 and 7, and temperature-induced transitions blocked for pH = 9.…”