Characterization of Thermoresponsive Poly-N-Vinylcaprolactam Polymers for Biological Applications.

Michele Dal Bo,Giorgio Eisele,Ivan Donati,Lorenzo Marsili,Federico Berti,Giuseppe Toffoli

doi:10.3390/polym13162639

Abstract

Poly-N-Vinylcaprolactam (PNVCL) is a thermoresponsive polymer that exhibits lower critical solution temperature (LCST) between 25 and 50 °C. Due to its alleged biocompatibility, this polymer is becoming popular for biomedical and environmental applications. PNVCL with carboxyl terminations has been widely used for the preparation of thermoresponsive copolymers, micro- and nanogels for drug delivery and oncological therapies. However, the fabrication of such specific targeting devices needs standardized and reproducible preparation methods. This requires a deep understanding of how the miscibility behavior of the polymer is affected by its structural properties and the solution environment. In this work, PNVCL-COOH polymers were prepared via free radical polymerization (FRP) in order to exhibit LCST between 33 and 42 °C. The structural properties were investigated with NMR, FT-IR and conductimetric titration and the LCST was calculated via UV-VIS and DLS. The LCST is influenced by the molecular mass, as shown by both DLS and viscosimetric values. Finally, the behavior of the polymer was described as function of its concentration and in presence of different biologically relevant environments, such as aqueous buffers, NaCl solutions and human plasma.

Highlights

Thermoresponsive polymers are characterized by a drastic and discontinuous change of their physical properties with temperature
The aim of this work is to rationalize this concept, as we considered the polymerization of different PNVCL polymers with carboxyl terminations (PNVCL-COOH) that exhibit different lower critical solution temperature (LCST) according to their different molecular mass, their concentration and the solution environment
The initial results ruled out the possibility that PNVCL-COOH was able to precipitate in diethyl ether in the conditions described by the original procedure

Summary

Introduction

Thermoresponsive polymers are characterized by a drastic and discontinuous change of their physical properties with temperature. The critical solution temperature can correspond to the minimum or the maximum of the binodal curve. LCST-type polymers are solvated in water through hydrogen bonding and polar interactions [5] Their biological interest relies on the presence of a desirable sharp transition in aqueous systems [2]. Their utilization in the biological field requires that the LCST in aqueous solution is close to the normal human physiological temperature, which is usually comprehended between 36.5 and 37.5 ◦ C, but can oscillate in a wider range between 33.2 and 38.2 ◦ C [6]

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