Defining plasma polymerization: new insight into what we should be measuring

Plasma-Functionalised Dressings for Enhanced Wound Healing

Fundamental knowledge about cell-surface interactions can be applied in the development of wound dressings and scaffolds to encourage wounds to heal. As surfaces produced with acid-functionalised monomers encourage keratinocyte adhesion, proliferation and migration, whilst amine functionalisation enhances fibroblast proliferation and migration in vitro, standard care wound dressings were plasma-coated with either acrylic acid or allylamine and applied to 6 mm excisional wounds on the backs of mice to test their effectiveness in vivo. At day 3, the rate of wound healing was increased in mice treated with dressings that were plasma-coated with allylamine compared to uncoated dressings, with a significantly reduced wound area. However, healing may be impaired following prolonged treatment with allylamine-functionalised dressings, with delayed re-epithelialisation and increased cellularisation of the wound site at later timepoints. Acrylic acid functionalisation, however, offered no early improvement in wound healing, but wounds treated with these dressings displayed increased collagen deposition at day 7 post wounding. These results suggest that plasma polymerisation may allow for the development of new dressings which can enhance wound closure by directing cell behaviour, but that the application of these dressings may require a timed approach to enhance specific phases of the wound healing response.

Particle aggregates formed during furfuryl methacrylate plasma polymerization affect human mesenchymal stem cell behaviour

Human Mesenchymal Stem cells (hMSCs) are becoming a major focus in biomedical fields. Application of in vitro expanded hMSCs to treat numerous ailments has led to a commercial emphasis on improving hMSC growth ex vivo. Production of substrate independent, novel thin films is one potential tool for production of commercial viable hMSC expansion. Plasma polymerization allow controlled chemical optimisation of large scale surface areas in a substrate independent manner. Previous study shown that plasma polymerized Furfuryl Methacrylate (ppFMA) surfaces allowed primary fibroblast cells adhesion and proliferation. However, under some deposition conditions, particle aggregates formation was observed. These aggregates had the effect of disrupting cell attachment, despite being chemically indistinguishable from the underlying surface. Herein, hMSCs were cultured on ppFMA surfaces to determine their suitability for stem cell culture and observe the effect of particle aggregates on hMSC attachment and growth. Both metabolic and DNA quantification assays showed that surfaces with particle aggregates had lower numbers of attached cells and slower growth. Uniform surfaces without aggregates showed higher cell attachment and growth levels, which were comparable to Thermanox. Phenotypic analysis showed that there was no change to hMSCs phenotype after 7 & 14days of culture on uniform ppFMA surface. Further investigation using time-lapse image analysis indicated that particle aggregates reduced cell attachment by presenting a physically weak boundary layer, which was damaged by intracellular tension during cell spreading. ppFMA surface can provide a stable substrate independent hMSCs expansion interface that could be applied to larger scale bioreactors, beads or scaffolds.

Haptotatic Plasma Polymerized Surfaces for Rapid Tissue Regeneration and Wound Healing

Skin has a remarkable capacity for regeneration; however, with an ever aging population, there is a growing burden to the healthcare system from chronic wounds. Novel therapies are required to address the problems associated with nonhealing chronic wounds. Novel wound dressings that can encourage increased reepithelialization could help to reduce the burden of chronic wounds. A suite of chemically defined surfaces have been produced using plasma polymerization, and the ability of these surfaces to support the growth of primary human skin cells has been assessed. Additionally, the ability of these surfaces to modulate cell migration and morphology has also been investigated. Keratinocytes and endothelial cells were extremely sensitive to surface chemistry showing increased viability and migration with an increased number of carboxylic acid functional groups. Fibroblasts proved to be more tolerant to changes in surface chemistry; however, these cells migrated fastest over amine-functionalized surfaces. The novel combination of comprehensive chemical characterization coupled with the focus on cell migration provides a unique insight into how a material's physicochemical properties affect cell migration.

Furfuryl methacrylate plasma polymers for biomedical applications

Furfuryl methacrylate (FMA) is a promising precursor for producing polymers for biomedical and cell therapy applications. Herein, FMA plasma polymer coatings were prepared with different powers, deposition times, and flow rates. The plasma polymer coatings were characterized using atomic force microscopy (AFM), scanning electron microscopy (SEM), x-ray photoelectron spectroscopy (XPS), and time-of-flight secondary ion mass spectrometry (ToF-SIMS). The results from AFM and SEM show the early growth of the coatings and the existence of particle aggregates on the surfaces. XPS results indicated no measureable chemical differences between the deposited films produced under different power and flow rate conditions. ToF-SIMS analysis demonstrated differing amounts of C5H5O (81 m/z) and C10H9O2 (161 m/z) species in the coatings which are related to the furan ring structure. Through judicious choice of plasma polymerization parameters, the quantity of the particle aggregates was reduced, and the fabricated plasma polymer coatings were chemically uniform and smooth. Primary human fibroblasts were cultured on FMA plasma polymer surfaces to determine the effect of surface chemical composition and the presence of particle aggregates on cell culture. Particle aggregates were shown to inhibit fibroblast attachment and proliferation.

Free-Radical-Induced Grafting from Plasma Polymer Surfaces

With the advances in science and engineering in the second part of the 20th century, emerging plasma-based technologies continuously find increasing applications in the domain of polymer chemistry, among others. Plasma technologies are predominantly used in two different ways: for the treatment of polymer substrates by a reactive or inert gas aiming at a specific surface functionalization or for the synthesis of a plasma polymer with a unique set of properties from an organic or mixed organic-inorganic precursor. Plasma polymer films (PPFs), often deposited by plasma-enhanced chemical vapor deposition (PECVD), currently attract a great deal of attention. Such films are widely used in various fields for the coating of solid substrates, including membranes, semiconductors, metals, textiles, and polymers, because of a combination of interesting properties such as excellent adhesion, highly cross-linked structures, and the possibility of tuning properties by simply varying the precursor and/or the synthesis parameters. Among the many appealing features of plasma-synthesized and -treated polymers, a highly reactive surface, rich in free radicals arising from deposition/treatment specifics, offers a particular advantage. When handled carefully, these reactive free radicals open doors to the controllable surface functionalization of materials without affecting their bulk properties. The goal of this review is to illustrate the increasing application of plasma-based technologies for tuning the surface properties of polymers, principally through free-radical chemistry.

Photo-doping of plasma-deposited polyaniline (PAni)

Although polyaniline (PAni) has been studied extensively in the past, little work has been done on producing films of this material via plasma deposition.

Chemical and physical processes in the retention of functional groups in plasma polymers studied by plasma phase mass spectroscopy

Retention of functional groups in plasma polymers depend on plasma chemistry and physical surface processes.

Role of Cellulose Nanocrystals on the Microstructure of Maleic Anhydride Plasma Polymer Thin Films

Recently, it was shown that the microstructure of a maleic anhydride plasma polymer (MAPP) could be tailored ab initio by adjusting the plasma process parameters. In this work, we aim to investigate the ability of cellulose nanocrystals (CNCs) to induce topographical structuration. Thus, a new approach was designed based on the deposition of MAPP on CNCs model surfaces. The nanocellulosic surfaces were produced by spin-coating the CNC suspension on a silicon wafer substrate and on a hydrophobic silicon wafer substrate patterned with circular hydrophilic microsized domains (diameter of 86.9 ± 4.9 μm), resulting in different degrees of CNC aggregation. By depositing the MAPP over these surfaces, it was possible to observe that the surface fraction of nanostructures increased from 20% to 35%. This observation suggests that CNCs can act as nucleation points resulting in more structures, although a critical density of the CNCs is required.

Development of a surface to increase retinal pigment epithelial cell (ARPE-19) proliferation under reduced serum conditions

Age related macular degeneration of the eye is brought about by damage to the retinal pigment epithelium (RPE) and is a major cause of adult blindness. One potential treatment method is transplantation of RPE cells grown in vitro. Maintaining RPE cell viability and physiological function in vitro is a challenge, and this must also be achieved using materials that can be subsequently used to deliver an intact cell sheet into the eye. In this paper, plasma polymerisation has been used to develop a chemically modified surface for maintaining RPE cells in vitro. Multiwell plates modified with a plasma copolymer of allylamine and octadiene maintained RPE cell growth at a level similar to that of TCPS. However, the addition of bound glycosaminoglycans (GAGs) to the plasma polymerised surface significantly enhanced RPE proliferation. Simply adding GAG to the culture media had no positive effect. It is shown that a combination of plasma polymer and GAG is a promising method for developing suitable surfaces for cell growth and delivery, that can be applied to any substrate material.

Development of a surface to enhance the effectiveness of fibroblast growth factor 2 (FGF-2)

Growth factors (GFs) play an important role in biological processes such as cell proliferation, differentiation and angiogenesis. GFs are known to bind to glycosaminoglycans (GAGs) in the extracellular matrix, aiding projection from degradation and pooling the GFs for quick response to biological stimuli in vivo. GFs are typically expensive and have a relatively short half-life in culture media, requiring regular replenishment. Here the cooperative binding of GF to a plasma polymerised surface decorated with heparin, and the subsequent culture of primary human dermal fibroblasts (HDFs) is investigated. A simple one-step technique suitable for coating a wide range of different substrates was utilised. Substrates such as culture-ware, scaffolds, bandages and devices for implantation could be coated. The modified surface was compared to standard culture techniques of addition of GF to the media. Results demonstrate that surface bound heparin and FGF-2 have a greater effect on cell proliferation especially at reduced serum concentrations. With performance equivalent to supplementing the media achieved at as little as 1% total FGF-2 added. The protective cooperative effect of FGF-2-GAG bound to modified surface at the interface could lead to reduced costs by reduction of FGF-2 required. Furthermore, for applications such as chronic non-healing wounds, bandages can be produced modified by plasma and decorated with GAGs that could utilise and protect important GFs. This would effectively re-introduce important biomolecules which are protected by GAG binding into a harsh environment.