AVS2016 Session PB+BI+PS-MoA: Plasma Processing of Biomaterials

In this work, the antimicrobial non-woven fabrics were prepared with the use of atmospheric pressure plasma deposition.Atmospheric pressure DC jet operating in N₂ at current density of 6 mA/cm² and voltage of 15 kV is used as a source of non-thermal plasma for engineering of the antibacterial nano-composites on surface of polymeric polyethylene terephthalate (PET) meshes. Nano-particles of Ag, Cu and ZnO are tested as antimicrobial agents through incorporation in to the structure of the plasma deposited composite film. The deposition process is carried out in three steps process. The fabric is first pretreated by depositing a first layer (250 nm - 500 nm) of organosilicon thin film using an atmospheric pressure plasma system, then nano-particles are incorporated by a dipping-dry, and finally the nano-particles are covered by a second organosilicon layer of 10-50 nm thickness. Top layer in the composite coating of “sandwich-like structure” with variable thickness is used for precise control of metal ions release and so to tune antimicrobial efficiency of the material. The deposition process and surface chemistry of the coatings are studied by emission spectroscopy, and surface analysis techniques: XPS, AFM and SEM. The antimicrobial activity of the treated fabrics is also tested against Pseudomonas aeruginosa and Staphylococcus aureus. It is revealed that thickness of top (barrier) layer plays a key role in release of metal ions and negligible small antibacterial activity is observed if barrier thickness exceeds 50 nm. Tests with S. aureus show that the highest 98% bacterial reduction is achieved with Cu NPs whereas Ag NPs are much less effective and can provide only 79% reduction. In contrast, the fabric antibacterial efficiency against of Pseudomonas aeruginosa is very low for both Cu and ZnO nanoparticles in spite of the load and only Ag NPs are proved to be effective (2 orders reduction) against of P. Aeruginosa. The results clearly indicate that plasma of atmospheric pressure can be used as effective tool for immobilization of nano-particles in composite coatings. Control of antibacterial activity can be achieved through variation of deposition parameters and a type of incorporate nanoparticles. The approach might present a new route to preparation of effective antimicrobial materials against of certain class of bacteria.

This work is partially supported by the M.Era-Net project “PlasmaTex”.

In this talk, different nonequilibrium atmospheric pressure plasmas used for biomedical applications such as planar DBD, single and double barrier DBD plasma jets, and transported discharges in tubes will be discussed. Indeed in the case of the latter, deposition and surface treatment, by means of a He cold transported discharge in tubes as long as 200 cm and tube inner diameters ranging from 1 to 20 mm, can present a great potential for surface modification of polymers used as biomaterials. We have, as well as several research groups, succeeded to retain the precursor moieties to obtain PEG like polymers which present interesting antifouling properties by using planar DBD and jets. However for particular plasma applications such as making a Drug Delivery System (DDS) based on several polymer or copolymer layers, encapsulating the drug, it is more reasonable to use a low pressure plasma which can give rise to dense crosslinked barrier films. The latter are less flexible and develop microcracks due to swelling and curvature of the host biocompatible and biodegradable substrate. In order to obtain good cohesive coatings with excellent barrier and mechanical properties, it is very important to deposit layers presenting a vertical chemical gradient, where stress is gradually distributed over the rigid and flexible zones of the DDS, which is more easily deposited in low pressure plasmas. Our recent results in copolymerizing amphiphilic precursors for the use of cell adhesive or nonadhesive surfaces will be presented. Such copolymers can be also used as biodegradable multi-layer copolymers for drug delivery applications. Human ovarian carcinoma cell lines (NIH:OVCAR‑3) were used for in vitro measurements of cell interactions with the surface of fabricated DDS. Proposed model of DDS on collagen films prevents migration, adhesion and growth of cancer cells on its surface, and by tuning the thickness of the dense barrier films, encapsulating the drug, it is possible to control the drug release kinetics and to improve the therapeutic effect. In vivo experiments were carried out by injecting OVCAR3 cells in mice lymph nodes to develop a tumor, followed by implantation of the DDS membranes to evaluate the feasibility of the proposed model.

The interaction of plasma with biomolecules is generally viewed as being a simple degradation reaction in which the plasma denatures any biologic material it encounters. Using a combination of heat, UV, free radicals, electrons and ions from the plasma, it is possible to cut, oxidise, burn and even ablate biological materials and this has established plasma sterilisation as a trusted technique in science, medicine and engineering.

However, recent research in our labs has shown that it is possible to minimise these effects and to instead use the plasma to cross-link biologic materials with retention of the biological properties of the precursor materials. Using low levels of applied plasma power, it is possible to produce low energy helium and argon plasma discharges. When biomolecules are nebulised into such a low temperature plasma, the materials are activated without losing their chemical structure. This activation can then effectively cross-link or coagulate the biomolecule without significant degradation. In addition, the plasma can activate substrates and effectively bind the biomolecules to the substrate as a thin nano-scale coating.

The result is a one-step process capable of modifying the surface of medical devices, research and diagnostic lab ware, implants and even living tissue. Tailored biological surfaces can be grown in situ over large areas using established equipment systems. The mechanisms used to control such reactions and to move the plasma from degradation to cross-linking modes are now being established and will be discussed. Examples of protein and polysaccharide coatings produced to date will also be presented.

Polymeric biomaterials are widely used in medical applications such as wound healing, drug release, and blood dialysis. For example, Tygon® and similar thermoplastics are chosen for these applications because of excellent mechanical strength and flexibility but often suffer from bacterial attachment and proliferation that ultimately leads to infection and fouling of the biomedical device. Biocidal agents can be incorporated into the polymer to actively eradicate bacteria, but it is difficult to ensure that biocidal action is localized at the material-biological interface. As a result, changing the surface properties of the polymer ensures a second mechanism by which to discourage bacterial attachment and growth. Plasmas are frequently used to alter the surfaces of biomaterials, most often by surface modification or deposition of a film to discourage bacterial attachment, while retaining the bulk properties critical to device performance. Specifically, H₂O (v) plasma treatment can enhance the compatibility of biomaterials by increasing hydrophilicity and altering surface chemistry; here, we demonstrate the use of this treatment method specifically for antibacterial materials. First, we have used H₂O (v) plasmas to tune the release of an antibacterial agent (NO) from drug-releasing polymers. Composition of treated drug-releasing polymers measured via X-ray photoelectron spectroscopy demonstrates a 100% increase in oxygen content and an associated increase in wettability, as observed via water contact angle goniometry. Compared to the untreated polymer, H₂O (v) plasma treated polymers had a delayed, but equally dramatic 8-log reduction in growth of both gram-negative Escherichia coli and gram-positive Staphylococcus aureus. Second, in a related study, we utilized plasma-enhanced chemical vapor deposition to deposit a film of 1,8-cineole, an antibacterial constituent of tea tree oil. Bacterial attachment and biofilm formation assays reveal significantly reduced growth of both bacterial strains on plasma polymerized cineole films. H₂O (v) plasma treatment of these materials will also be discussed. Furthermore, optical emission spectroscopy allows correlation of gas phase excited state species in our plasmas under various plasma conditions to the resulting 1,8-cineole film surface properties, thereby allowing for fine-tuning of film surface properties for deposition onto biomedically-relevant polymer structures such as 3D polycaprolactone scaffolds. Collectively, our studies of plasma processing of antibacterial materials demonstrate this technique is a valuable tool in the production of next generation biomedical devices.

Polystyrene is one of the most widely used cell-culture plate materials. Amino and/or carboxyl coated cell culture plates are commercially available and such surface functionalizations are known to contribute effectively to the control of growth and differentiation of various stem cells. Plasma-enhanced chemical vapor deposition (PECVD) or plasma ion implantation may be used to functionalize polystyrene surfaces of cell culture dishes. The goal of this research is to understand how such surface functionalizations are affected by plasma conditions. In this study, we have used molecular dynamics (MD) simulation to understand how incident ions and free radicals affect the formation of amines and carboxyl groups. The simulation is based on interatomic reactive potential functions developed in-house based on quantum mechanical calculations. Results of MD simulations under the conditions similar to PE-CVD by ammonia (NH3), cyclopropylamine (CPA), or N2/CH3OH plasmas or ion implantation by NH3, N2/H2, or N2/CH3OH plasmas suggest that, with energetic ion bombardment, functional groups such as primary amines are less likely to form and nitridation of the surface tends to occur. Some simulation results have been compared with experimental data obtained from parallel-plate discharges with an inverter power supply at a relatively high gas pressure of 250 - 2,500 Pa and found to be in good quantitative agreement.