Surface and Interfacial Polymer Science

Simple click reactions on polymer surfaces leading to antimicrobial behavior

In this study we developed simple reactions that combined microwave plasma reactions in the presence of maleic anhydride with alkyne click chemistries to achieve a platform for unlimited possibilities for further surface modifications of aliphatic polymer surfaces. Using this approach, we covalently attached ampicillin (AMP) to polyethylene (PE) and polypropylene (PP) substrates. As a result, high efficacy against microbial film formation, manifested by efficient antimicrobial activity against S. aureus with a 97–99.8% decrease of bacterial growth, was achieved. This simple and clean process allows functionalization of any polymeric substrate without adverse effects on bulk polymer properties.

Covalent attachment of multilayers (CAM)

These studies show covalent attachment of multilayers (CAM) to chemically alter surfaces to achieve pH switchable antimicrobial and anticoagulant properties. Polyethylene (PE), poly(tetrafluoroethylene) (PTFE), and silicon (Si) surfaces were functionalized by tethering pH-responsive “switching” polyelectrolytes consisting of poly(2-vinyl pyridine) (P2VP) and poly(acrylic acid) (PAA) terminated with NH2 and COOH groups, respectively. At pH < 2.3, the P2VP segments are protonated and expended, but at pH > 5.5, they collapse while the PAA segments are expanded. The presence of terminal NH2 or COOH moieties on P2VP and PAA, respectively, facilitated the opportunity for covalently bonding ampicillin (AMP) and heparin (HEP) to both polyelectrolyte chains. Such surfaces, when exposed to S. aureus, inhibit the growth of microbial films (AMP) as well as anticoagulant properties (HEP).

Phage-Bacterium War on Polymeric Surfaces

These studies illustrate synthetic paths to covalently attach T1 and Φ11 bacteriophages (phages) to inert polymeric surfaces while maintaining the bacteriophage’s biological activities capable of killing deadly human pathogens. The first step involved the formation of acid (COOH) groups on polyethylene (PE) and polytetrafluoroethylene (PTFE) surfaces using microwave plasma reactions in the presence of maleic anhydride, followed by covalent attachment of T1 and Φ11 species via primary amine groups. The phages effectively retain their biological activity manifested by a rapid infection with their own DNA and effective destruction of Escherichia coli and Staphylococcus aureus human pathogens. These studies show that simultaneous covalent attachment of two biologically active phages effectively destroy both bacterial colonies and eliminate biofilm formation, thus offering an opportunity for an effective combat against multibacterial colonies as well as surface detections of other pathogens.

Micro-patterning of streptavidin–biotin-ampicillin/heparin on poly(tetrafluoroethylene) (PTFE) surfaces

In an effort to simultaneously inhibit formation of microbial films and surface blood coagulation multifunctional assemblies containing streptavidin (STR)–biotin bioconjugates were developed on poly(tetrafluoroethylene) (PTFE) surfaces. Using STR conjugated to a biotin-functionalized PTFE surface, spatially controlled micro-patterning was produced by grafting biotinylated polyethylene glycol (B-PEG) to COOH modified PTFE (MA-PTFE), followed by inkjet micro-printing of biotinylated ampicillin (B-AM) and biotinylated heparin (B-HP) molecules. These surfaces exhibit simultaneous antimicrobial and anticoagulant attributes manifested by “zone of inhibition” and anticoagulant measurements. Quantitative spectroscopic analysis revealed that the required surface density of COOH groups on PTFE is 2.94 × 10−7 g cm−2, and B-PEG and STR densities of 9.2 × 10−8 g cm−2 and 3.5 × 10−8 g cm−2, respectively, are sufficient to achieve simultaneous antimicrobial and anticoagulant responses. These studies also showed that the force required to remove STR–biotin conjugates attached to PTFE surfaces measured by atomic force microscopy is approximately 1090 pN, thus providing desirable surface mechanical stability.

Bioactive Polymeric Surfaces

Highly controllable microwave plasma reactions on surfaces of polymeric materials offer a platform of covalent bonding of acid groups via reactions and hydrolysis of maleic anhydride. Such functional groups can be further used for surface reactions leading to stimuli-responsive polymeric surfaces that are biologically active or may exhibit antibacterial, antithrombotic, or antifouling attributes. This process can be applied to almost any thermoplastic polymer. Several examples below show covalent attachment of various antibiotic molecules that, through a molecular spacer (PEG), exhibit antimicrobial properties.

Covalent Attachment of Multilayers on Poly(tetrafluoroethylene) Surfaces

These studies demonstrate a new approach of producing multifunctionalized coatings on poly(tetrafluoroethylene) (PTFE) surfaces by covalent attachments of multilayers (CAM) of heparin (HP) and poly(ethylene glycol) (PEG). This process can be universally applied to other covalently bonded species and was facilitated by microwave plasma reactions in the presence of maleic anhydride which, upon ring-opening and hydrolysis, provided covalent attachment of COOH groups to PTFE. These studies showed that alternating layers of PEG and HP can be covalently attached to COOH-PTFE surfaces, and the volume concentration and surface density of PEG and HP on the PTFE surface achieved by the CAM were 7.02–6.04 × 10–3 g/cm3 (2.1–1.8 × 10–7 g/cm2) and 9.3–8.7 × 10–3 g/cm3 (2.8–2.6 × 10–7 g/cm2), respectively. The CAM process may serve numerous applications when the covalent modification of inert polymeric substrates is required and particularly where the presence of bioactive species for biocompatibility enhancement is desirable.