INFLUENCE OF POLYMER SURFACES ON BACTERIAL BIOFILM FORMATION

High throughput materials discovery screens have revealed polymers that reduce bacterial surface colonization which have progressed to ongoing clinical trials [Hook et al. Nature Biotech 2012]. These novel poly(meth)acrylate coatings reduced biofilm formation by Pseudomonas aeruginosa, Staphylococcus aureus and Escherichia coli in laboratory cultures in vitro and in vivo in a mouse foreign body infection model. These coatings are known to function by preventing biofilm formation; however, why the bacterial cells respond in this way to these polymers has yet to be elucidated. This knowledge gap leaves us unable to undertake rational design of novel materials to prevent bacteria attachment. In this thesis, we focus on understanding the influence of the polymer surface on attachment of bacteria and subsequent biofilm formation. Using ToF-SIMS and XPS, we carry out careful surface chemical analysis of adsorbates on two polymers known to exhibit drastically different biofilm formation in a standard biofilm promoting culture media: protein-free, amino acid containing bacterial RPMI. Amino acid adsorption is identified to correlate with polymer resisting biofilm formation. The amino acid adsorption process for these two polymers was modelled and two key descriptive parameters: adsorbent capacity and on/off rate of nutrients on polymer surfaces were obtained. To move the study from a small set of samples to a greater number from which to derive a structure-function relationship, we developed a high throughput surface characterisation approach. A cheap ninhydrin staining technique, which allows to quantify by fluorescence amount of adsorbed amino acids from standard RPMI onto surfaces of individual polymers in a microarray in high throughput manner was adapted. The amount of adsorbed amino acid on individual polymers together with ion fragments obtained from ToF-SIMS were used to develop a linear regression model and identify key fragments that promoted nutrient adsorption using a total of 141 polymers chosen on the basis of possessing carbon, hydrogen and oxygen atoms. To guide synthesis of novel anti-biofilm materials beyond the original monomer library, a simple predictive composite parameter termed alpha [Sanni et al. Adv Healthc Mater, 2015] that takes into consideration contributions from the partition coefficient (logP) and the number of rotatable bonds (nRotB) for hydrocarbon acrylate pendant groups was validated experimentally. We report the predictions of new monomers from the alpha QSAR model were successfully validated by the synthesis of new monomers, which were polymerized to create coatings found to be resistant to biofilm formation by six different bacteria pathogens: Pseudomonas aeruginosa, Proteus mirabilis, Enterococcus faecalis, Klebsiella pneumoniae, Escherichia coli and Staphylococcus aureus. Potential biological degradation of novel anti-biofilm material has been postulated as a possible mode of action for these materials through release of bactericidal compounds. Here we used a quick-acting esterase enzyme (PLE) to verify that the mechanistic mode of action for novel anti-biofilm material was not due to enzymatic release of bacteriostatic/bactericidal compounds

The association between ibuprofen administration in children and the risk of developing or exacerbating asthma: a systematic review and meta-analysis

Background: Ibuprofen is one of the most commonly used analgesic and antipyretic drugs in children. However, its potential causal role in childhood asthma pathogenesis remains uncertain. In this systematic review, we assessed the association between ibuprofen administration in children and the risk of developing or exacerbating asthma. Methods: We searched MEDLINE, Embase, Cochrane Library, CINAHL, Web of Science, and Scopus from inception to May 2022, with no language limits; searched relevant reviews; and performed citation searching. We included studies of any design that were primary empirical peer-reviewed publications, where ibuprofen use in children 0–18 years was reported. Screening was performed in duplicate by blinded review. In total, 24 studies met our criteria. Data were extracted according to PRISMA guidelines, and the risk of bias was assessed using RoB2 and NOS tools. Quantitative data were pooled using fixed effect models, and qualitative data were pooled using narrative synthesis. Primary outcomes were asthma or asthma-like symptoms. The results were grouped according to population (general, asthmatic, and ibuprofen-hypersensitive), comparator type (active and non-active) and follow-up duration (short- and long-term). Results: Comparing ibuprofen with active comparators, there was no evidence of a higher risk associated with ibuprofen over both the short and long term in either the general or asthmatic population. Comparing ibuprofen use with no active alternative over a short-term follow-up, ibuprofen may provide protection against asthma-like symptoms in the general population when used to ease symptoms of fever or bronchiolitis. In contrast, it may cause asthma exacerbation for those with pre-existing asthma. However, in both populations, there were no clear long-term follow-up effects. Conclusions: Ibuprofen use in children had no elevated risk relative to active comparators. However, use in children with asthma may lead to asthma exacerbation. The results are driven by a very small number of influential studies, and research in several key clinical contexts is limited to single studies. Both clinical trials and observational studies are needed to understand the potential role of ibuprofen in childhood asthma pathogenesis

Bacterial attachment to polymeric materials correlates with molecular flexibility and hydrophilicity

A new class of material resistant to bacterial attachment has been discovered that is formed from polyacrylates with hydrocarbon pendant groups. In this study, the relationship between the nature of the hydrocarbon moiety and resistance to bacteria is explored, comparing cyclic, aromatic, and linear chemical groups. A correlation is shown between bacterial attachment and a parameter derived from the partition coefficient and the number of rotatable bonds of the materials' pendant groups. This correlation is applicable to 86% of the hydrocarbon pendant moieties surveyed, quantitatively supporting the previous qualitative observation that bacteria are repelled from poly (meth)acrylates containing a hydrophilic ester group when the pendant group is both rigid and hydrophobic. This insight will help inform and predict the further development of polymers resistant to bacterial attachment

Achieving Microparticles with Cell-Instructive Surface Chemistry by Using Tunable Co-Polymer Surfactants

© 2020 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim A flow-focusing microfluidic device is used to produce functionalized monodisperse polymer particles with surface chemistries designed to control bacterial biofilm formation. This is achieved by using molecularly designed bespoke surfactants synthesized via catalytic chain transfer polymerization. This novel approach of using polymeric surfactants, often called surfmers, containing a biofunctional moiety contrasts with the more commonly employed emulsion methods. Typically, the surface chemistry of microparticles are dominated by unwanted surfactants that dilute/mask the desired surface response. Time of flight secondary ion mass spectrometry (ToF-SIMS) analysis of particles demonstrates that the comb-graft surfactant is located on the particle surface. Biofilm experiments show how specifically engineered surface chemistries, generated by the surfactants, successfully modulate bacterial attachment to both polymer films, and microparticles. Thus, this paper outlines how the use of designed polymeric surfactants and droplet microfluidics can exert control over both the surface chemistry and size distribution of microparticle materials, demonstrating their critical importance for controlling surface-cell response

Validating a Predictive Structure-Property Relationship by Discovery of Novel Polymers which Reduce Bacterial Biofilm Formation

ynthetic materials are an everyday component of modern healthcare yet often fail routinely as a consequence of medical‐device‐centered infections. The incidence rate for catheter‐associated urinary tract infections is between 3% and 7% for each day of use, which means that infection is inevitable when resident for sufficient time. The O'Neill Review on antimicrobial resistance estimates that, left unchecked, ten million people will die annually from drug‐resistant infections by 2050. Development of biomaterials resistant to bacterial colonization can play an important role in reducing device‐associated infections. However, rational design of new biomaterials is hindered by the lack of quantitative structure–activity relationships (QSARs). Here, the development of a predictive QSAR is reported for bacterial biofilm formation on a range of polymers, using calculated molecular descriptors of monomer units to discover and exemplify novel, biofilm‐resistant (meth‐)acrylate‐based polymers. These predictions are validated successfully by the synthesis of new monomers which are polymerized to create coatings found to be resistant to biofilm formation by six different bacterial pathogens: Pseudomonas aeruginosa, Proteus mirabilis, Enterococcus faecalis, Klebsiella pneumoniae, Escherichia coli, and Staphylococcus aureus

Prediction of broad-spectrum pathogen attachment to coating materials for biomedical devices

Bacterial infections in healthcare settings are a frequent accompaniment to both routine procedures such as catheterization and surgical site interventions. Their impact is becoming even more marked as the numbers of medical devices that are used to manage chronic health conditions and improve quality of life increases. The resistance of pathogens to multiple antibiotics is also increasing, adding an additional layer of complexity to the problems of employing safe and effective medical procedures. One approach to reducing the rate of infections associated with implanted and indwelling medical devices is the use of polymers that resist the formation of bacterial biofilms. To significantly accelerate the discovery of such materials, we show how state of the art machine learning methods can generate quantitative predictions for the attachment of multiple pathogens to a large library of polymers in a single model for the first time. Such models facilitate design of polymers with very low pathogen attachment across different bacterial species that will be candidate materials for implantable or indwelling medical devices such as urinary catheters, cochlear implants and pacemakers

Single-Cell Tracking on Polymer Microarrays Reveals the Impact of Surface Chemistry on Pseudomonas aeruginosa Twitching Speed and Biofilm Development

© 2020 American Chemical Society. Bacterial biofilms exhibit up to 1000 times greater resistance to antibiotic or host immune clearance than planktonic cells. Pseudomonas aeruginosa produces retractable type IV pili (T4P) that facilitate twitching motility on surfaces. The deployment of pili is one of the first responses of bacteria to surface interactions and because of their ability to contribute to cell surface adhesion and biofilm formation, this has relevance to medical device-associated infections. While polymer chemistry is known to influence biofilm development, its impact on twitching motility is not understood. Here, we combine a polymer microarray format with time-lapse automated microscopy to simultaneously assess P. aeruginosa twitching motility on 30 different methacrylate/acrylate polymers over 60 min post inoculation using a high-throughput system. During this critical initial period where the decision to form a biofilm is thought to occur, similar numbers of bacterial cells accumulate on each polymer. Twitching motility is observed on all polymers irrespective of their chemistry and physical surface properties, in contrast to the differential biofilm formation noted after 24 h of incubation. However, on the microarray polymers, P. aeruginosa cells twitch at significantly different speeds, ranging from 5 to ∼13 nm/s, associated with crawling or walking and are distinguishable from the different cell surface tilt angles observed. Chemometric analysis using partial least-squares (PLS) regression identifies correlations between surface chemistry, as measured by time-of-flight secondary ion mass spectrometry (ToF-SIMS), and both biofilm formation and single-cell twitching speed. The relationships between surface chemistry and these two responses are different for each process. There is no correlation between polymer surface stiffness and roughness as determined by atomic force measurement (AFM), or water contact angle (WCA), and twitching speed or biofilm formation. This reinforces the dominant and distinct contributions of material surface chemistry to twitching speed and biofilm formation

INFLUENCE OF POLYMER SURFACES ON BACTERIAL BIOFILM FORMATION

High throughput materials discovery screens have revealed polymers that reduce bacterial surface colonization which have progressed to ongoing clinical trials [Hook et al. Nature Biotech 2012]. These novel poly(meth)acrylate coatings reduced biofilm formation by Pseudomonas aeruginosa, Staphylococcus aureus and Escherichia coli in laboratory cultures in vitro and in vivo in a mouse foreign body infection model. These coatings are known to function by preventing biofilm formation; however, why the bacterial cells respond in this way to these polymers has yet to be elucidated. This knowledge gap leaves us unable to undertake rational design of novel materials to prevent bacteria attachment. In this thesis, we focus on understanding the influence of the polymer surface on attachment of bacteria and subsequent biofilm formation. Using ToF-SIMS and XPS, we carry out careful surface chemical analysis of adsorbates on two polymers known to exhibit drastically different biofilm formation in a standard biofilm promoting culture media: protein-free, amino acid containing bacterial RPMI. Amino acid adsorption is identified to correlate with polymer resisting biofilm formation. The amino acid adsorption process for these two polymers was modelled and two key descriptive parameters: adsorbent capacity and on/off rate of nutrients on polymer surfaces were obtained. To move the study from a small set of samples to a greater number from which to derive a structure-function relationship, we developed a high throughput surface characterisation approach. A cheap ninhydrin staining technique, which allows to quantify by fluorescence amount of adsorbed amino acids from standard RPMI onto surfaces of individual polymers in a microarray in high throughput manner was adapted. The amount of adsorbed amino acid on individual polymers together with ion fragments obtained from ToF-SIMS were used to develop a linear regression model and identify key fragments that promoted nutrient adsorption using a total of 141 polymers chosen on the basis of possessing carbon, hydrogen and oxygen atoms. To guide synthesis of novel anti-biofilm materials beyond the original monomer library, a simple predictive composite parameter termed alpha [Sanni et al. Adv Healthc Mater, 2015] that takes into consideration contributions from the partition coefficient (logP) and the number of rotatable bonds (nRotB) for hydrocarbon acrylate pendant groups was validated experimentally. We report the predictions of new monomers from the alpha QSAR model were successfully validated by the synthesis of new monomers, which were polymerized to create coatings found to be resistant to biofilm formation by six different bacteria pathogens: Pseudomonas aeruginosa, Proteus mirabilis, Enterococcus faecalis, Klebsiella pneumoniae, Escherichia coli and Staphylococcus aureus. Potential biological degradation of novel anti-biofilm material has been postulated as a possible mode of action for these materials through release of bactericidal compounds. Here we used a quick-acting esterase enzyme (PLE) to verify that the mechanistic mode of action for novel anti-biofilm material was not due to enzymatic release of bacteriostatic/bactericidal compounds

Protocol

The Files window in this project component contains the review protocol