AVS2009 Session BI-TuA: Biofouling

The present contribution describes a novel set of hydrogel coatings prepared by self-initiated photografting and photopolymerization (SIPGP). The method is based on UV free radical polymerization of methacrylate and acrylate monomers into 0-200 nm thick coatings on top of virtually any organic/polymeric substrate. The vast majority of the coatings are based on different mixtures of PEG containing methacrylates. These hydrogels display excellent protein rejecting properties in simple single component solutions and mixtures, as well as in serum and plasma [1]. Recent studies on platelet adsorption looks also were promising. The UV fabrication technology is also compatible with patterning on the micrometer length scale, thus providing an attractive platform for biochip development and microarraying [2]. The preparation of gradients is also discussed for tuning the physio/chemical properties of the hydrogel coatings [3]. A novel set of charged balanced hydrogel gradients have been prepared for studies of protein adsorption from protein mixtures and plasma with encouraging results [4]. Finally we describe an approach for array fabrication of nanobrushes/bushes on a pre-patterned template generated by Dip Pen Nanolithography (DPN).

1. A. Larsson, T. Ekblad, O. Andersson, B. Liedberg, Biomacromolecules, 8, 287-295 (2007).

2. A. Larsson, C-.X. Du, B. Liedberg, Biomacromolecules, 8, 3511 (2007).

3. A. Larsson, B. Liedberg, Langmuir, 23, 11319 (2007).

4. T. Ekblad, O. Andersson, F.-I. Tai, T. Ederth, B. Liedberg. Langmuir, 25, 3755 (2009).

Nosocomial (hospital-acquired) infections are the fourth leading cause of death in the U.S. with >2 million cases annually (or ~10% of American hospital patients). About 60-70% of all such infections are associated with an implanted medical device causing >$4.5 billion medical costs in 2002 and ~99,000 deaths annually. Over 65% of hospital-acquired infections are associated with implants or indwelling medical devices, with the case-to-fatality ratio between 5-50%. It is estimated that over 5 million artificial or prosthetic devices are implanted per annum in the U.S. alone. Microbial infections have been observed on most biomedical devices, including: prosthetic heart valves, orthopedic implants, intravascular catheters, artificial hearts, left ventricular assist devices, cardiac pacemakers, vascular prostheses, cerebrospinal fluid shunts, urinary catheters, ocular prostheses and contact lenses, and intrauterine contraceptive devices.

Traditional strategies to control medical device-based biofilm infections are based on the use of compounds that kill or inhibit the growth of freely suspended bacteria. However, “biofilm-bound” bacteria tend to be significantly less responsive to antibiotics and antimicrobial stressors than planktonic organisms of the same species. In fact, studies have shown that sub-lethal doses of antibiotics can exacerbate biofilm formation. Consequently, systemic antibiotic treatment typically fails to clear a biofilm infection and inevitably requires removal of the device. Moreover, the risk of antibiotic resistance development is drastically increased under the current standard use of systemic antibiotic treatment of medical-device infections.

Here novel non-antibiotic based concepts in biomaterials design (novel stealth surfaces or biomaterials that biologically prevent bacterial colonization) will be presented.

Competitive protein adsorption from human serum and protein mixtures onto unmodified and plasma polymerised polymer surfaces has been investigated using radioactive multi-labelling. By using several different isotopes it is possible to monitor several proteins simultaneously and thereby analyse the interaction between the different proteins during adsorption processes.

The outcome of competitive protein adsorption depends on both surface and protein characteristics, as well as parameters such as protein concentration and adsorption sequence. In this study surface characteristics of polymer surfaces have been modified by using plasma polymerisation where the polymer surface becomes more hydrophilic. Modified surfaces show non-fouling characteristics and have shown to be stable in buffer solutions for at least 24 hours. By changing the sequence of proteins introduced to a surface, different outcome from an adsorption series with the same proteins can be observed and by changing the internal ratio between different proteins concentration, different proteins will dominate the surface during adsorption.

Even though some polymer surfaces show protein monolayer adsorption behaviour and quite low amount of proteins adsorbed, other surfaces loose there resistance to protein adsorption as the protein concentration increases, and on hydrophobic polymer surface one can even see a very thick and cross linked protein multilayer formed. The tendency for protein multilayer formation is also influenced by other proteins present during adsorption and protein characteristics, where some proteins seem to be more fragile during adsorption to hydrophobic polymer surfaces than others.

The objective of the study is two-fold; to investigate basic processes and concepts during competitive protein adsorption and to contribute to development of polymer based biomaterials for use in contact with whole blood.