Affinity of amine-functionalized plasma polymers with ionic solutions similar to those in the human body

Abstract

This work presents a study on the synthesis and on the interaction of allylamine, pyrrole and ethylenglycol polymerized by plasma with solutions of ionic composition similar to those in the nervous system. These polymers are attractive substrates to interact with the ionic pulses of the spinal cord due to their electrical and biocompatible characteristics. The ionic solutions were prepared with aqueous combinations of NaCl, MgSO₄, KH₂PO₄, KCl, CaCl₂, and NHCO₃. The polymers were prepared as thin films on glass substrates. The results indicated that some of the most important physical characteristics in the hydrophilicity of the polymers, roughness, porosity and functional groups, can be controlled with the energy of polymerization. The interaction between polymers and solutions was studied measuring the contact angle at the solid–liquid interface and the electrical conductivity of the polymers wet with these solutions. The contact angles were between 8° and 38°, and the electrical conductivity was in the 10⁻⁸ to 10⁻⁹ S/cm interval. The general tendencies indicate that the amine-functionalized polymers of this work are good materials to interact with the spinal cord system.

Introduction

Plasma processes allow the use of a great variety of materials in biological applications due to the functional groups with NH, CN, CO and OH bonds, common in the human body, which can be added to almost any material to enhance the biocompatible superficial properties [1], [2]. Compounds with some of these groups are: pyrrole (C₄H₄NH), allylamine (CH₂ = CHCH₂NH₂) and ethylenglycol (OHCH₂CH₂OH), whose chemical functionality influences the protein absorption, adhesion of cells and provides sites for immobilization of biomolecules [3]. Polypyrrole provides advantages in flexibility and biodegradability [4] and has been also used in studies of artificial muscles, due to its ability to change its volume under electrochemical stimulation [5], [6].

Polymers derived from these compounds are considered attractive substrates for implants in the nervous system, because their electrical characteristics can be used to interact with the ions of K⁺, Na⁺ or Ca²⁺ of this system. Additionally, as the human body contains approximately 60% of weight in electrolytic solutions, the chemical and electrical interaction at the solid–liquid interface can influence the reproduction of cells on materials implanted in biological systems and therefore on the regeneration of damaged tissues.

For that reason, the aim of this work is to study the interaction of amine-functionalized plasma polymers polypyrrole (PPy), polypyrrole doped with iodine (PPy/I), polyallylamine (PAl) and polyethylenglycol (PEG) with solutions of salt concentrations similar to those in the spinal cord. Polymers formed with pyrrole have heterocyclic segments, while ethylenglycol and allylamine form chains with aliphatic linear arrangements. The objective involves the chemical and electrical interactions, which are related with the H-bonding and the ionic or polar activity between both phases. These polymers and some of their copolymers are being studied in the reconnection between neuronal cells after a severe lesion in the spinal cord [7].