This review surveys methods for the fabrication, by plasma surface treatments or plasma polymerization, of polymeric surfaces and thin plasma polymer coatings that contain reactive chemical groups useful for the subsequent covalent immobilization, by solution chemical reactions or vapor phase grafting, of molecules or polymers that can exert bio-specific interfacial responses. Surfaces containing amine, carboxy, hydroxy, and aldehyde groups are the subject of this review. Aminated surfaces have been fabricated using various plasma vapors or mixtures and have found wide use for bio-interface applications. However, in many cases the amine surfaces have a rather limited shelf life, with post-plasma oxidation reactions and surface adaptation leading to the disappearance of amine groups from the surface. Aging is a widespread phenomenon that often has not been recognized, particularly in some of the earlier studies on the use of plasma-fabricated surfaces for bio-interfacial applications, and can markedly alter the surface chemistry. Plasma-fabricated surfaces that contain carboxy groups have also been well documented. Fewer reports exist on hydroxy and aldehyde surfaces prepared by plasma methods. Hydroxy surfaces can be prepared by water plasma treatment or the plasma polymerization of alkyl alcohol vapors. Water plasma treatment on many polymer substrates suffers from aging, with surface adaptation leading to the movement of surface modification effects into the polymer. Both hydroxy and aldehyde surfaces have been used for the covalent immobilization of biologically active molecules. Aging effects are less well documented than for amine surfaces. This review also surveys studies using such surfaces for cell colonization assays. Generally, these surface chemistries show good ability to support cell colonization, though the effectiveness seems to depend on the process vapor and the plasma conditions. Carboxylate co-polymer surfaces have shown excellent ability to support the colonization of some human cell lines of clinical interest. Immobilization of proteins onto plasma-carboxylated surfaces is also well established.

Plasma Methods for the Generation of Chemically Reactive Surfaces for Biomolecule Immobilization and Cell Colonization ‐ A Review

A technique to immobilize bioactive proteins, including bone morphogenetic protein-4 (BMP-4), on titanium alloy.

The aim of this review is to describe how biomaterial engineering processes, particularly in the field of polymer modifications for enhanced blood-compatibility, can take advantage of low-pressure plasma techniques. It will also be emphasized how a diagnostic approach on both plasma and surface reactions can lead to understand and control the chemistry of plasma processes.

Plasma treatments and plasma deposition of polymers for biomedical applications

Introduction of functional groups onto the surface of polyethylene for protein immobilization

Thermo-responsive PNiPAAm-g-PEG films for controlled cell detachment.

In order to introduce amine groups on poly(ethylene) (PE) surfaces, PE surfaces were preadsorbed with decylamine hydrochloride (DA.HCl) and subsequently treated with an argon plasma. It was shown by XPS (X-ray Photoelectron Spectroscopy), that approximately half of the preadsorbed (mono)layer was immobilized and that a substantial part (60-70%) of the incorporated nitrogen containing groups were amine groups. The availability of the surface amine groups for reactions was investigated by applying a gas phase reaction with 4-trifluoromethylbenzaldehyde and by a reductive methylation reaction in aqueous solution with 14C formaldehyde. A maximal number of reactive amine groups was found after a plasma treatment time of 2 s. The reductive methylation reaction was used to estimate the surface concentration of amine groups resulting in a typical surface concentration of 1 x 10-6 mol/m2 after a plasma treatment time of 2 s.

A.P. Pijpers

Papers

Introduction of amine groups on poly(ethylene) by plasma immobilization of a preadsorbed layer of decylamine hydrochloride