A two-step bioluminescence assay for optimizing antibacterial coating of hollow-fiber membranes with polydopamine in an integrative approach.

Pure-water filtration membranes are often fouled by bacterial biofilms. Antibacterial coatings for preventing biofilm formation on such membranes should not rely on leaching of inhibiting compounds but should only be effective on surface contact. Certified assays for antibacterial coatings do not sufficiently exclude leaching effects and involve nutrient-rich cultivation media that do not correspond to conditions in pure-water systems. In this study, a two-step bioluminescence assay was developed for optimizing an antibacterial coating of PES/PVP ultrafiltration hollow-fiber membranes with a polydopamine as a sustainable, bio-inspired material for preventing bacterial biofilm formation. In the first step, leaching of the antimicrobial coating was analyzed by a bioluminescence assay with supernatants generated by washing coated membranes. In the second step, bioluminescence of bacterial biofilms on coated and uncoated membranes was measured using a nutrient-poor medium resembling site-specific conditions. Based on this bioluminescence assay, an optimized protocol for the coating process could be established by acidic polymerization of dopamine using 2 g/L sodium periodate and 4 g/L dopamine at 40 °C for 20 min reaction time. With coatings produced in this way, bioluminescence was reduced on coated membranes only while the corresponding supernatants exhibited no inhibitory effects.

Functional Nanomaterials and 3D-Printable Nanocomposite Hydrogels for Enhanced Cell Proliferation and for the Reduction of Bacterial Biofilm Formation.

Biomaterial-associated infections are a major cause of biomaterial implant failure. To prevent the initial attachment of bacteria to the implant surface, researchers have investigated various surface modification methods. However, most of these approaches also prevent the attachment, spread, and growth of mammalian cells, resulting in tissue integration failure. Therefore, the success of biomaterial implants requires an optimal balance between tissue integration (cell adhesion to biomaterial implants) and inhibition of bacterial colonization. In this regard, we synthesize bifunctional nanomaterials by functionalizing the pores and outer surfaces of periodic mesoporous organosilica (PMO) with antibacterial tetracycline (Tet) and antibacterial and cell-adhesive bipolymer poly-d-lysine (PDL), respectively. Then, the fabricated TetPMO-PDL nanomaterials are incorporated into alginate-based hydrogels to create injectable and 3D-printable nanocomposite (NC) hydrogels (AlgL-TetPMO-PDL). These bifunctional nanomaterial and 3D-printable NC hydrogel show pH-dependent release of Tet over 7 days. They also enhance the proliferation of eukaryotic cells (fibroblasts). TetPMO-PDL is inactive in reducing Pseudomonas aeruginosa, Staphylococcus aureus, and Enterococcus faecalis biofilms. However, AlgL-TetPMO-PDL shows significant antibiofilm activity against P. aeruginosa. These results suggest that the incorporation of TetPMO-PDL into AlgL may have a synergistic effect on the inhibition of the Gram-negative bacterial (P. aeruginosa) biofilm, while this has no effect on the reduction of the Gram-positive bacterial (S. aureus and E. faecalis) biofilm.

Bifunctional nanomaterials for simultaneously improving cell adhesion and affecting bacterial biofilm formation on silicon-based surfaces.

In the biomedical field, silicon-based materials are widely used as implants, biomedical devices, and drug delivery systems. Although these materials show promise for implant technologies and clinical applications, many of them fail to simultaneously possess key properties, such as mechanical stability, biostability, stretchability, cell adhesiveness, biofilm inhibition, and drug delivery ability. Therefore, there is considerable need for the development and improvement of new biomaterials with improved properties. In this context, we describe the synthesis of a new hybrid nanocomposite material that is prepared by incorporating bifunctional nanomaterials onto glass and polydimethylsiloxane surfaces. The results show that our hybrid nanocomposite material is elastic, stretchable, injectable, biostable, has pH-controlled drug delivery ability, and display improved cell adhesion and proliferation and, at the same time, impacted bacterial biofilm formation on the respective surfaces.

Genetic and physiological analysis of biofilm formation on different plastic surfaces by Sphingomonas sp. strain S2M10 reveals an essential function of sphingan biosynthesis.

Alphaproteobacteria belonging to the group of the sphingomonads are frequently found in biofilms colonizing pure-water systems, where they cause technical and hygienic problems. In this study, physiological properties of sphingomonads for biofilm formation on plastic surfaces were analysed. Sphingomonas sp. strain S2M10 was isolated from a used water-filtration membrane and submitted to transposon mutagenesis for isolating mutants with altered biofilm formation. Mutants showing strongly decreased biofilm formation carried transposon insertions in genes for the biosynthesis of the polysaccharide sphingan and for flagellar motility. Flagella-mediated attachment was apparently important for biofilm formation on plastic materials of intermediate hydrophobicity, while a mutant with defect in spnB, encoding the first enzyme in sphingan biosynthesis, showed no biofilm formation on all tested materials. Sphingan-dependent biofilm formation was induced in the presence of specific carbon sources while it was not induced in complex medium with yeast extract and tryptone. The regulation of sphingan-based biofilm formation was investigated by interfering with the CckA/ChpT/CtrA phosphorelay, a central signal-transduction pathway in most Alphaproteobacteria. Construction and ectopic expression of a kinase-deficient histidine kinase CckA caused cell elongation and massive sphingan-dependent cell aggregation. In addition, it caused increased activity of the promotor of spnB. In conclusion, these results indicate that sphingan-based biofilm formation by sphingomonads might be triggered by specific carbon sources under prototrophic conditions resembling a milieu that often prevails in pure-water systems.