14 research outputs found
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Structure-Property Relationships of Polymer Films and Hydrogels to Control Bacterial Adhesion
The emergence and spread of antibiotic resistance across microbial species necessitates the need for alternative approaches to mitigate the risk of infection without relying on commercial antibiotics. Biofilm-related infections are a class of notoriously difficult to treat healthcare-associated infections that frequently develop on the surface of implanted medical devices. As biofilm formation is a surface-associated phenomenon, understanding how the intrinsic properties of materials affect bacterial adhesion enables the development of structure-property relationships that can guide the future design of infection-resistant materials. Despite lacking visual, auditory, and olfactory perception, bacteria still manage to sense and attach to surfaces. Previously, it has been reported that bacteria can detect and differentiate the surface chemistry and topography of surfaces; however, the influence of the stiffness and thickness on bacterial-surface interactions remains unknown.
In this thesis, the effect that the fundamental material properties of polymer films and hydrogels (stiffness, thickness, and chemistry) have on the adhesion and surface-associated transport of bacteria was investigated. By decoupling the effect of the hydrogelâs stiffness and thickness from their chemistry, we suggest a key takeaway design rule: to optimize fouling-resistance, hydrogel coatings should be thick and soft. Two chemically distinct hydrogels, poly(ethylene glycol) and agar, were synthesized over a 1-1000 kPa range of Youngâs modulus. Static adhesion experiments, conducted on 150 ”m thick hydrogels, determined that Escherichia coli and Staphylococcus aureus colony surface coverage correlated positively with an increase in Youngâs modulus. Notably, a substantial increase in adhesion occurred for both bacteria when the thickness of the hydrogels was reduced to 10 ”m. The stiffness of poly(ethylene glycol) brushes and hydrogels was also found to influence the length and frequency of Staphylococcus aureus surface-associated transport via dynamic shear flow experiments. Furthermore, a universal hydrogel functionalization platform was developed for instances where mechanical properties of hydrogels are not adjustable. The incorporation of the fouling-resistant polymer zwitterion, poly(2-methacryloyloxyethyl phosphorylcholine), enhanced resistance to bacterial adhesion without altering the mechanical properties of covalently or physically crosslinked hydrogels. This thesis demonstrates that by combining structure-property relationships with fouling-resistant zwitterionic chemistry, the adhesion of proteins and microorganisms to polymer hydrogels is reduced
Green Materials Science and Engineering Reduces Biofouling: Approaches for Medical and Membrane-Based Technology
Numerous engineered and natural environments suffer deleterious effects from biofouling and/or biofilm formation. For instance, bacterial contamination on biomedical devices pose serious health concerns. In membrane-based technologies, such as desalination and wastewater reuse, biofouling decreases membrane lifetime, and increases the energy required to produce clean water. Traditionally, approaches have combatted bacteria using bactericidal agents. However, due to globalization, a decline in antibiotic discovery, and the widespread resistance of microbes to many commercial antibiotics and metallic nanoparticles, new materials, and approaches to reduce biofilm formation are needed. In this mini-review, we cover the recent strategies that have been explored to combat microbial contamination without exerting evolutionary pressure on microorganisms. Renewable feedstocks, relying on structure-property relationships, bioinspired/nature-derived compounds, and green processing methods are discussed. Greener strategies that mitigate biofouling hold great potential to positively impact human health and safety
Graphene-Based Microfluidics for Serial Crystallography
Microfluidic strategies to enable the growth and subsequent serial crystallographic analysis of micro-crystals have the potential to facilitate both structural characterization and dynamic structural studies of protein targets that have been resistant to single-crystal strategies. However, adapting microfluidic crystallization platforms for micro-crystallography requires a dramatic decrease in the overall device thickness. We report a robust strategy for the straightforward incorporation of single-layer graphene into ultra-thin microfluidic devices. This architecture allows for a total material thickness of only âŒ1 ÎŒm, facilitating on-chip X-ray diffraction analysis while creating a sample environment that is stable against significant water loss over several weeks. We demonstrate excellent signal-to-noise in our X-ray diffraction measurements using a 1.5 ÎŒs polychromatic X-ray exposure, and validate our approach via on-chip structure determination using hen egg white lysozyme (HEWL) as a model system. Although this work is focused on the use of graphene for protein crystallography, we anticipate that this technology should find utility in a wide range of both X-ray and other lab on a chip applications
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Gecko-Inspired Biocidal Organic Nanocrystals Initiated from a Pencil-Drawn Graphite Template
The biocidal properties of gecko skin and cicada wings have inspired the synthesis of synthetic surfaces decorated with high aspect ratio nanostructures that inactivate microorganisms. Here, we investigate the bactericidal activity of oriented zinc phthalocyanine (ZnPc) nanopillars grown using a simple pencil-drawn graphite templating technique. By varying the evaporation time, nanopillars initiated from graphite that was scribbled using a pencil onto silicon substrates were optimized to yield a high inactivation of the Gram-negative bacteria, Escherichia coli. We next adapted the procedure so that analogous nanopillars could be grown from pencil-drawn graphite scribbled onto stainless steel, flexible polyimide foil, and glass substrates. Time-dependent bacterial cytotoxicity studies indicate that the oriented nanopillars grown on all four substrates inactivated up to 97% of the E. coli quickly, in 15âmin or less. These results suggest that organic nanostructures, which can be easily grown on a broad range of substrates hold potential as a new class of biocidal surfaces that kill microbes quickly and potentially, without spreading antibiotic-resistance genes
Conjugation in Escherichia coli Biofilms on Poly(dimethylsiloxane) Surfaces with Microtopographic Patterns
Bacterial
biofilms are highly tolerant to antimicrobials and play
an important role in the development and spread of antibiotic resistance
based on horizontal gene transfer due to close cell-to-cell contact.
As an important surface property, topography has been shown to affect
bacterial adhesion and biofilm formation. Here, we demonstrate that
micrometer-scale surface topographies also affect horizontal gene
transfer through conjugation in bacterial biofilms. Specifically,
biofilm formation and associated conjugation on polyÂ(dimethylsiloxane)
(PDMS) surfaces with 10 ÎŒm tall protruding patterns were studied
using fluorescently labeled donor and recipient strains of Escherichia coli. The results demonstrate that square-shaped
topographic patterns with side length of 20, 50, and 100 ÎŒm
and interpattern distance equal to or larger than 10 ÎŒm promote
biofilm formation and conjugation compared to the smooth control.
The vertical sides of these topographic features were found to be
the âhot spotsâ for bacterial conjugation compared to
the top of patterns and grooves between topographic features. The
increase in conjugation frequency on the sides of topographic patterns
was attributed to the high cell density of recipient cells at these
locations. A motility (<i>motB</i>) mutant of the recipient
strain exhibited defects in biofilm formation at the âhot spotsâ
and conjugation, which were recovered by complementing the <i>motB</i> gene on a plasmid. These results also provided guidance
for designing surface topographies that can reduce conjugation. Specifically,
10 ÎŒm tall hexagon-shaped topographic patterns with side length
of 15 ÎŒm and interpattern distance of 2 ÎŒm were prepared
to reduce biofilm formation on the side of protruding patterns and
interrupt cellâcell interaction in the grooves. This topography
exhibited 85% and 46% reduction of biofilm formation and associated
conjugation, respectively, compared to the smooth control
Fewer Bacteria Adhere to Softer Hydrogels
Clinically, biofilm-associated infections
commonly form on intravascular
catheters and other hydrogel surfaces. The overuse of antibiotics
to treat these infections has led to the spread of antibiotic resistance
and underscores the importance of developing alternative strategies
that delay the onset of biofilm formation. Previously, it has been
reported that during surface contact, bacteria can detect surfaces
through subtle changes in the function of their motors. However, how
the stiffness of a polymer hydrogel influences the initial attachment
of bacteria is unknown. Systematically, we investigated polyÂ(ethylene
glycol) dimethacrylate (PEGDMA) and agar hydrogels that were 20 times
thicker than the cumulative size of bacterial cell appendages, as
a function of Youngâs moduli. Soft (44.05â308.5 kPa),
intermediate (1495â2877 kPa), and stiff (5152â6489 kPa)
hydrogels were synthesized. Escherichia coli and Staphylococcus aureus attachment
onto the hydrogels was analyzed using confocal microscopy after 2
and 24 h incubation periods. Independent of hydrogel chemistry and
incubation time, E. coli and S. aureus attachment correlated positively to increasing
hydrogel stiffness. For example, after a 24 h incubation period, there
were 52 and 82% fewer E. coli adhered
to soft PEGDMA hydrogels than to the intermediate and stiff PEGDMA
hydrogels, respectively. A 62 and 79% reduction in the area coverage
by the Gram-positive microbe S. aureus occurred after 24 h incubation on the soft versus intermediate and
stiff PEGDMA hydrogels. We suggest that hydrogel stiffness is an easily
tunable variable that could potentially be used synergistically with
traditional antimicrobial strategies to reduce early bacterial adhesion
and therefore the occurrence of biofilm-associated infections
Scaling Up Nature: Large Area Flexible Biomimetic Surfaces
The fabrication and advanced function
of large area biomimetic
superhydrophobic surfaces (SHS) and slippery lubricant-infused porous
surfaces (SLIPS) are reported. The use of roll-to-roll nanoimprinting
techniques enabled the continuous fabrication of SHS and SLIPS based
on hierarchically wrinkled surfaces. Perfluoropolyether hybrid molds
were used as flexible molds for roll-to-roll imprinting into a newly
designed thiolâene based photopolymer resin coated on flexible
polyethylene terephthalate films. The patterned surfaces exhibit feasible
superhydrophobicity with a water contact angle around 160° without
any further surface modification. The SHS can be easily converted
into SLIPS by roll-to-roll coating of a fluorinated lubricant, and
these surfaces have outstanding repellence to a variety of liquids.
Furthermore, both SHS and SLIPS display antibiofouling properties
when challenged with Escherichia coli K12 MG1655. The current article describes the transformation of
artificial biomimetic structures from small, lab-scale coupons to
low-cost, large area platforms
Bacterial Adhesion Is Affected by the Thickness and Stiffness of Poly(ethylene glycol) Hydrogels
Despite lacking visual,
auditory, and olfactory perception, bacteria sense and attach to surfaces.
Many factors, including the chemistry, topography, and mechanical
properties of a surface, are known to alter bacterial attachment,
and in this study, using a library of nine protein-resistant polyÂ(ethylene
glycol) (PEG) hydrogels immobilized on glass slides, we demonstrate
that the thickness or amount of polymer concentration also matters.
Hydrated atomic force microscopy and rheological measurements corroborated
that thin (15 ÎŒm), medium (40 ÎŒm), and thick (150 ÎŒm)
PEG hydrogels possessed Youngâs moduli in three distinct regimes,
soft (20 kPa), intermediate (300 kPa), and stiff (1000 kPa). The attachment
of two diverse bacteria, flagellated Gram-negative Escherichia coli and nonmotile Gram-positive Staphylococcus aureus was assessed after a 24 h incubation
on the nine PEG hydrogels. On the thickest PEG hydrogels (150 ÎŒm), E. coli and S. aureus attachment increased with increasing hydrogel stiffness. However,
when the hydrogelâs thickness was reduced to 15 ÎŒm, a
substantially greater adhesion of E. coli and S. aureus was observed. Twelve
times fewer S. aureus and eight times
fewer E. coli adhered to thin-soft
hydrogels than to thick-soft hydrogels. Although a full mechanism
to explain this behavior is beyond the scope of this article, we suggest
that because the Youngâs moduli of thin-soft and thick-soft
hydrogels were statistically equivalent, potentially, the very stiff
underlying glass slide was causing the thin-soft hydrogels to feel
stiffer to the bacteria. These findings suggest a key takeaway design
rule; to optimize fouling-resistance, hydrogel coatings should be
thick and soft