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Conventional bioreactors are typically developed for the production of planktonic bacteria or submerged biofilms. In contrast, reactors for the continuous production of biofilms at the solid-air interface are scarce, and they require specific conditions since the bacteria need to attach firmly to the surface and require a permanent supply of moisture and nutrients from below. Recently, research from the field of civil engineering has pinpointed an increased need for the production of terrestrial biofilms: several variants of Bacillus subtilis biofilms have been shown to be useful additives to mortar that increase the water repellency, and, thus, the lifetime of the cementitious material. The bioreactor introduced here allows for the continuous production of such bacterial biofilms at the solid-air interface, and they have virtually identical properties as biofilms cultivated via classical microbiological techniques. This is made possible by equipping a rotating cylinder with a porous membrane that acts as a solid growth substrate the bacterial biomass can form on. In this configuration, nutrient supply is enabled via diffusive transport of a suitable growth medium from the core volume of the cylindrical reactor to the membrane surface. In addition to cultivating bacterial biofilms, the versatile and adaptable set up introduced here also enables the growth of other microbial organisms including the yeast Saccharomyces cerevisiae and the fungus Penicillium chrysogenum.

The viscosities of poly(3-hydroxybutyrate) (PHB) with mixed tacticities were determined as functions of temperature and shearing rate via plate–plate viscosimetry, and fitted by a combined Herschel–Bulkley–Cross–Doolittle model while applying Carvalho et al.’s single-point correction. They were compared to values of slit viscosimetry, obtained during processing at a temperature of 428 K. In both cases, measured values and fitted model parameters as a function of tacticity exhibited a discontinuous behaviour at a fraction of meso diads of 0.7. To further investigate, we calculated values of vibrational and excess free volume. We found that these correlate with structural and external properties, some of which were reported in earlier works, namely the paracrystalline contents and specific volumes of the materials at room temperature, as well as their energies of fracture during tensile testing. These, in turn, correlate with the statistical averages of relative lengths of chain segments of similar a- or iso-tacticity. Hence, we found that expressing changing tacticities simply by a continuous progression of the fraction of meso diads is insufficient to trace associated discontinuities of the flow behaviour in mixed-tacticity PHB. We conclude that free volume is generated by polymer chain conformational disorder, which should be treated on the oligomeric chain segment level.

Chemically fueled supramolecular materials offer unique properties that include spatial and temporal control and even the ability to self-heal. Indeed, a few studies have demonstrated the ability to self-heal, however, the underlying mechanisms remain unclear. Here, we designed a peptide that forms a fibrillar network upon chemical fueling. We were surprised that the hydrogel could self-heal despite the lack of dynamics in the fiber assembly and disassembly. We explain this behavior by a mechanism that involves the chemically fueled peptide molecules that cannot self-assemble due to the lack of nucleation sites. When the fibers are perturbed, new nucleation sites form that help the assembly resulting in the healing of the damaged network. Furthermore, we generalized the behavior for other peptides. We refer to this non-assembling, chemically-fueled peptide as a molecular glue. In future work, we aim to explore whether this self-healing mechanism applies to more complex structures, narrowing the gap between biological and synthetic self-assemblies.

Mucins are multifunctional glycosylated proteins that are increasingly investigated as building blocks of novel biomaterials. An attractive feature is their ability to modulate the immune response, in part by engaging with sialic acid binding receptors on immune cells. Once assembled into hydrogels, bovine submaxillary mucins (Muc gels) were shown to modulate the recruitment and activation of immune cells and avoid fibrous encapsulation in vivo. However, nothing is known about the early immune response to Muc gels. This study characterizes the response of macrophages, important orchestrators of the material-mediated immune response, over the first 7 days in contact with Muc gels. The role of mucin-bound sialic acid sugar residues was investigated by first enzymatically cleaving the sugar and then assembling the mucin variants into covalently cross-linked hydrogels with rheological and surface nanomechanical properties similar to nonmodified Muc gels. Results with THP-1 and human primary peripheral blood monocytes derived macrophages showed that Muc gels transiently activate the expression of both pro-inflammatory and anti-inflammatory cytokines and cell surface markers, for most makers with a maximum on the first day and loss of the effect after 7 days. The activation was sialic acid-dependent for a majority of the markers followed. The pattern of gene expression, protein expression, and functional measurements did not strictly correspond to M1 or M2 macrophage phenotypes. This study highlights the complex early events in macrophage activation in contact with mucin materials and the importance of sialic acid residues in such a response. The enzymatic glyco-modulation of Muc gels appears as a useful tool to help understand the biological functions of specific glycans on mucins which can further inform on their use in various biomedical applications.

With big datasets and highly efficient algorithms becoming increasingly available for many problem sets, rapid advancements and recent breakthroughs achieved in the field of machine learning encourage more and more scientific fields to make use of such a computational data analysis. Still, for many research problems, the amount of data available for training a machine learning (ML) model is very limited. An important strategy to combat the problems arising from data sparsity is feature elimination—a method that aims at reducing the dimensionality of an input feature space. Most such strategies exclusively focus on analyzing pairwise correlations, or they eliminate features based on their relation to a selected output label or by optimizing performance measures of a certain ML model. However, those strategies do not necessarily remove redundant information from datasets and cannot be applied to certain situations, e.g., to unsupervised learning models. Neither of these limitations applies to the network-based, correlation-driven redundancy elimination (NETCORE) algorithm introduced here, where the size of a feature vector is reduced by considering both redundancy and elimination efficiency. The NETCORE algorithm is model-independent, does not require an output label, and is applicable to all kinds of correlation topographies within a dataset. Thus, this algorithm has the potential to be a highly beneficial preprocessing tool for various machine learning pipelines.

Production and secretion of biomolecules can provide new emergent functionalities to the synthesizing organism. In particular, the secretion of extracellular polymeric substances (EPS) by biofilm forming bacteria creates a biofilm matrix that protects the individual bacteria within the biofilm from external stressors such as antibiotics, chemicals and shear flow. Although the main matrix components of biofilms formed by Bacillus subtilis are known, it remains unclear how these matrix components contribute to the erosion stability of B. subtilis biofilms. Here, we combine different biophysical techniques to assess this relation. In particular, we quantify the importance of specific biofilm matrix components on the erosion behavior of biofilms formed by the well-studied Bacillus subtilis NCIB 3610. We find that the absence of biofilm matrix components decreases the erosion stability of NCIB 3610 biofilms in water, largely by abolishing the hydrophobic surface properties of the biofilm and by reducing the biofilm stiffness. However, the erosion resistance of NCIB 3610 biofilms is strongly increased in the presence of metal ions or the antibiotic ciprofloxacin. In the first case, unspecific ionic cross-linking of biofilm components or individual bacteria seems to be responsible for the observed effect, and in the second case there seems to be an unspecific interaction between the antibiotic and the biofilm matrix. Taken together, our results emphasize the importance of the biofilm matrix to reduce biofilm erosion and give insights into how the specific biomolecules interact with certain chemicals to fulfill this task.

Immune-modulating biomaterials used to encapsulate cells and microtissue transplants can be engineered to dampen the immune reaction and increase treatment efficacy. Mucin-derived materials have gained attention for their ability to modulate macrophage and dendritic cell activity, and to trigger mild foreign body response when implanted in vivo. In this study, the potential of mucin hydrogels (Muc-gels) as cell-encapsulating materials is investigated. When placed in contact with blood, Muc-gels trigger significantly lower complement activation, compared to clinical grade alginate hydrogels. Muc-gel is a size-selective barrier strongly hindering the diffusion of molecules with a hydrodynamic radius larger than 6 nm such as immunoglobulins. Muc-gels support the growth of MIN6m9 insulin-secreting cells into islet-like organoids and the survival of primary human pancreatic islets, which maintained glucose responsiveness. Muc-gels can be shaped into microdroplets in which MIN6m9 cells or cell aggregates can be encapsulated without loss of viability. Microdroplet encapsulation will allow transplants to be easily injected and improve their survival by favoring mass transport through the capsule. The combination of strong immune modulatory properties, appropriate selective barrier profile, biocompatibility for embedded cells Muc-gels of particular value for microencapsulating cells or microtissues for transplantation.

Even though medical devices have improved a lot over the past decades, there are still issues regarding their anti-biofouling properties and tribological performance, and both aspects contribute to the short- and long-term failure of these devices. Coating these devices with a biocompatible layer that reduces friction, wear, and biofouling at the same time would be a promising strategy to address these issues. Inspired by the adhesion mechanism employed by mussels, here, dopamine is made use of to immobilize lubricious mucin macromolecules onto both manufactured commercial materials and real medical devices. It is shown that purified mucins successfully adsorb onto a dopamine pre-coated substrate, and that this double-layer is stable toward mechanical challenges and storage in aqueous solutions. Moreover, the results indicate that the dopamine/mucin double-layer decreases friction (especially in the boundary lubrication regime), reduces wear damage, and provides anti-biofouling properties. The results obtained in this study show that such dopamine/mucin double-layer coatings can be powerful candidates for improving the surface properties of medical devices such as catheters, stents, and blood vessel substitutes.

The aim of the present work was to evaluate the changes in instrumental measurements and dynamic sensory properties of chocolate as affected by the partial and total substitution of sucrose by dodecenyl-succinylated inulin upon storage. The results of textural, surface topology, and tribological properties of non-stored chocolates were found to be a function of modified inulin replacement, where an increase in modified inulin ratio allowed an increase in hardness, roughness, and friction coefficient. Compared to non-stored samples, the deterioration of textural properties after storage was inhibited in chocolate containing higher levels of modified inulin. Higher modified inulin ratios did not also induce an important change in NMR proton mobility, roughness, and friction coefficient upon storage. Confocal Raman microscopy revealed modified inulin located around sucrose and cocoa particles dispersed in fat phase, especially at the higher ratios. Temporal Dominance of Sensations (TDS) curves of non-stored samples elucidated that firmness was a dominant perception at the beginning of mastication, followed by melting rate, while cocoa flavor was experienced at the end of evaluation. However, these attributes were not perceived in stored chocolate with the lowest modified inulin. A PCA was performed to compare TDS scores and instrumental readings, showing a high correlation between instrumental measurement of hardness, friction coefficient, and NMR relaxation times and TDS score of firmness, bitterness, astringency, and melting rate. This work shows a new perspective to use biopolymeric surfactant for producing low-calorie chocolate, considering that hydrophobically modified inulin can diminish production costs and facilitate low-calorie product development.

Hydrogels made of crosslinked macromolecules used in regenerative medi-cine technologies can be designed to affect the fate of surrounding cells and tissues in defined ways. Their function typically depends on the type and number of bioactive moieties such as receptor ligands present in the hydrogel. However, the detail in how such moieties are presented to cells can also be instrumental. In this work, how the crosslinking architecture of a hydrogel can affect its bioactivity is explored. It is shown that bovine submaxillary mucins, a highly glycosylated and immune-modulating protein, exhibit strikingly different bioactivities whether they are crosslinked through their glycans or their protein domains. Both the susceptibility to enzymatic degradation and macrophage response are affected, while rheological proper-ties and barrier to diffusion are mostly unaffected. The results suggest that crosslinking architecture affects the accessibility of the substrate to pro-teases and the pattern of sialic acid residues exposed to the macrophages. Thus, modulating the accessibility of binding sites through the choice of the crosslinking strategy appears as a useful parameter to tune the bioactivity of hydrogel-based systems

Over millennia, bacteria have developed clever strategies to build biopolymer-based communities in which they can survive even extremely challenging conditions. Such bacterial biofilms come with a broad range of fascinating material properties that-in settings such as medicine, food production, or other areas of industry-make it difficult to remove or inactivate them: they can stick to many surfaces, repel water and oils, and can even transport electrons. Inspired by the outstanding versatility and sturdiness of such bacterial biofilms, material scientists have set out to harness those properties and to create bacterial materials for different applications. However, as the range of technological applications employing biofilms keeps expanding, improved material properties or broader functionalities are desired. Here, such attempts where materials with improved properties were created by making use of either natural or modified bacterial biofilms are reviewed. The areas in which those bacterial materials may be used range from agriculture and (environmental) biotechnology over biomedical and electrical engineering to construction engineering.

Even though polyurethanes (PU) constitute a class of highly versatile and customizable polymeric materials, being able to modify their surface properties, for example, their wettability, without altering the composition of the bulk material would often be desirable. However, PU-based materials can be both rather diverse and resilient to chemical modification. Thus, in this study, three PU variants are subjected to three different treatments that aim at altering the wetting properties of the materials: We assess the feasibility of plasma treatment, dopamine incubation, and chemical etching, and evaluate the stability of the obtained surface modifications with regard to wet and dry storage, UV exposure, and application-specific properties such as lubricity and colonization with eukaryotic cells. The results obtained here can be used to achieve an additional customization of PU surfaces to tailor their behavior for selected applications where dedicated surface properties are required. © 2021 The Authors. Plasma Processes and Polymers published by Wiley-VCH GmbH.

Mucin glycoproteins are the matrix-forming key components of mucus, the innate protective barrier protecting us from pathogenic attack. However, this barrier is constantly challenged by mucin-degrading enzymes, which tend to target anionic glycan chains such as sulfate groups and sialic acid residues. Here, we demonstrate that the efficiency of both unspecific and specific binding of small molecules to mucins is reduced when sulfate groups are enzymatically removed from mucins; this is unexpected because neither of the specific mucin-binding partners tested here targets these sulfate motifs on the mucin glycoprotein. Based on simulation results obtained from a numerical model of the mucin macromolecule, we propose that anionic motifs along the mucin chain establish intramolecular repulsion forces which maintain an elongated mucin conformation. In the absence of these repulsive forces, the mucin seems to adopt a more compacted structure, in which the accessibility of several binding sites is restricted. Our results contribute to a better understanding on how different glycans contribute to the broad spectrum of functions mucin glycoproteins have. © 2020 American Chemical Society.

Most biofilm research has so far focused on investigating biofilms generated by single bacterial strains. However, such single-species biofilms are rare in nature where bacteria typically coexist with other microorganisms. Although, from a biological view, the possible interactions occurring between different bacteria are well studied, little is known about what determines the material properties of a multi-species biofilm. Here, we ask how the co-cultivation of two B. subtilis strains affects certain important biofilm properties such as surface topography and wetting behavior. We find that, even though each daughter colony typically resembles one of the parent colonies in terms of morphology and wetting, it nevertheless exhibits a significantly different surface topography. Yet, this difference is only detectable via a quantitative metrological analysis of the biofilm surface. Furthermore, we show that this difference is due to the presence of bacteria belonging to the ‘other’ parent strain, which does not dominate the biofilm features. The findings presented here may pinpoint new strategies for how biofilms with hybrid properties could be generated from two different bacterial strains. In such engineered biofilms, it might be possible to combine desired properties from two strains by co-cultivation.

Mucin glycoproteins, the macromolecular components of mucus, combine a broad range of biomedically important properties. Among those is the ability of mucin solutions to act as excellent lubricants. However, to be able to use purified, endogenous mucin glycoproteins as components of a biomedical product, the mucins need to be sterile; this, in turn, makes it necessary to subject the mucins to quite harsh physical treatments, such as heat exposure, autoclaving, UV-, or γ-irradiation, which might compromise the functionality of the glycoproteins. Here, it is shown that mucins are indeed able to withstand most of those treatments without suffering significant lubrication impairment or structural degradation. Among those treatments, which left the mucins unharmed, γ-irradiation is identified to be the most powerful one in terms of inactivating microbial contaminations. The obtained results demonstrate a remarkable sturdiness of mucins, which opens up broad possibilities for them to be further processed into materials, e.g., as parts of biomedical products.

Surface superhydrophobicity makes bacterial biofilms very difficult to fight, and it is a combination of their matrix composition and complex surface roughness which synergistically protects these biomaterials from wetting. Although trying to eradicate biofilms with aqueous (antibiotic) solutions is common practice, this can be a futile approach if the biofilms have superhydrophobic properties. To date, there are not many options available to reduce the liquid repellency of biofilms or to prevent this material property from developing. Here, we present a solution to this challenge. We demonstrate how the addition of metal ions such as copper and zinc during or after biofilm formation can render the surface of otherwise superhydrophobic B. subtilis NCIB 3610 biofilms completely wettable. As a result of this procedure, these smoother, hydrophilic biofilms are more susceptible to aqueous antibiotics solutions. Our strategy proposes a scalable and widely applicable step in a multi-faceted approach to eradicate biofilms.

A decade ago, environmental issues, such as air pollution and the contamination of the oceans with microplastic, were prominently communicated in the media. However, these days, political topics, as well as the ongoing COVID-19 pandemic, have clearly taken over. In spite of this shift in focus regarding media representation, researchers have made progress in evaluating the possible health risks associated with particulate contaminations present in water and air. In this review article, we summarize recent efforts that establish a clear link between the increasing occurrence of certain pathological conditions and the exposure of humans (or animals) to airborne or waterborne particulate matter. First, we give an overview of the physiological functions mucus has to fulfill in humans and animals, and we discuss different sources of particulate matter. We then highlight parameters that govern particle toxicity and summarize our current knowledge of how an exposure to particulate matter can be related to dysfunctions of mucosal systems. Last, we outline how biophysical tools and methods can help researchers to obtain a better understanding of how particulate matter may affect human health. As we discuss here, recent research has made it quite clear that the structure and functions of those mucosal systems are sensitive toward particulate contaminations. Yet, our mechanistic understanding of how (and which) nano- and microparticles can compromise human health via interacting with mucosal barriers is far from complete.

The production of biomolecules can provide new functionalities to the synthesizing organism. One important example is the secretion of extracellular polymeric substances (EPS) by biofilm forming bacteria. This biofilm matrix protects the individual bacteria within the biofilm from external stressors such as antibiotics, chemicals and shear flow. Previous studies have determined several main matrix components of biofilms formed by Bacillus subtilis. However, how these matrix components influence the growth behavior and final dimensions of B. subtilis biofilms has not yet been determined. Here, we combine different experimental techniques with theoretical modeling to assess this relation. In particular, we quantify the area covered by the biofilm and the biofilm height by performing time-lapse microscopy and light profilometry, respectively. We study the development of biofilms formed by two wild-type strains (B-1 and NCIB 3610) differing in their matrix composition and NCIB 3610 mutant strains lacking the ability to produce specific EPS. Based on the experimentally obtained growth dynamics, we develop a mathematical model that allows us to quantify the influence of three key biofilm matrix components on the final NCIB 3610 biofilm colony dimensions. In detail, we show that two matrix components, the exopolysaccharide produced by the epsA-O operon and the surface layer protein BslA control the area covered by the biofilm colony. The height of these mature biofilm colonies is mostly affected by BslA. Together, our results emphasize the importance of the biofilm matrix composition for biofilm growth and the final dimensions of mature B. subtilis NCIB 3610 biofilm colonies.

Mucins are multifunctional glycosylated proteins that are increasingly investigated as building blocks of novel biomaterials. Once assembled into hydrogels (Muc gels), mucins were shown to modulate the recruitment and activation of immune cells and avoid fibrous encapsulationin vivo. However, nothing is known about the early immune response to Muc gels. This study characterizes the response of macrophages, important orchestrators of the material-mediated immune response, over the first 7 days in contact with Muc gels. The role of mucin-bound sialic acid sugar residues was investigated by first enzymatically cleaving the sugar, then assembling the mucin variants into covalently crosslinked hydrogels with rheological and surface nanomechanical properties similar to non-modified Muc gels. Results with THP1 and human primary peripheral blood monocytes-derived macrophages were strikingly consistent and showed that Muc gels transiently activate the expression of both pro-inflammatory and anti-inflammatory cytokines and cell surface markers, with a maximum on the first day and loss of the effect after 7 days. The activation was sialic acid-dependent for a majority of the markers followed. The pattern of gene expression, protein expression, and functional measurements did not strictly correspond to M1 or M2 macrophage phenotypes. This study highlights the complex early events in macrophage activation in contact with mucin materials and the importance of sialic acid residues in such a response. The enzymatic glyco-modulation of Muc gels appears as a useful tool to help understand the biological functions of specific glycans on mucins which can further inform on their use in various biomedical applications.

Recent research indicates that the progression of Parkinson's disease can start from neurons of the enteric nervous system, which are in close contact with the gastrointestinal epithelium: α-synuclein molecules can be transferred from these epithelial cells in a prion-like fashion to enteric neurons. Thin mucus layers constitute a defense line against the exposure of noninfected cells to potentially harmful α-synuclein species. We show that - despite its mucoadhesive properties - α-synuclein can translocate across mucin hydrogels, and this process is accompanied by structural rearrangements of the mucin molecules within the gel. Penetration experiments with different α-synuclein variants and synthetic peptides suggest that two binding sites on α-synuclein are required to accomplish this rearrangement of the mucin matrix. Our results support the notion that the translocation of α-synuclein across mucus barriers observed here might be a critical step in the infection of the gastrointestinal epithelium and the development of Parkinson's disease.

The respiratory tract surface is protected from inhaled pathogens by a secreted layer of mucus that is rich in mucin glycoproteins. Disrupted mucus production is a cardinal feature of chronic respiratory diseases but how this alteration affect interactions between mucins and pathogens is complex and poorly understood. Here, we identify a central and unexpected role for the major airway mucin MUC5AC in pathogenesis of virus-induced exacerbations of chronic obstructive pulmonary disease (COPD). Virus induction of MUC5AC is augmented in COPD compared to healthy subjects, is enhanced in frequent exacerbators and correlates with inflammation, symptom severity and secondary bacterial infection during exacerbation. MUC5AC is functionally related to inflammation as MUC5AC-deficient (Muc5ac-/-) mice had attenuated rhinovirus-induced airway inflammation whilst exogenous MUC5AC glycoprotein administration augmented virus-induced inflammatory responses and bacterial load. Mechanistically, MUC5AC-augmentation of rhinovirus-induced inflammation occurred through release of extracellular adenosine triphosphate (ATP). Therapeutic suppression of virus-induced MUC5AC release using an epidermal growth factor receptor (EGFR) inhibitor ameliorated exaggerated pro-inflammatory responses in a mouse COPD exacerbation model. Collectively, these studies demonstrate previously unrecognised pro-inflammatory effects of MUC5AC during infection and thus highlight a key unforeseen role in driving COPD exacerbation severity.

The immune-mediated foreign body response to biomaterial implants can trigger the formation of insulating fibrotic capsules that can compromise implant function. To address this challenge, we leverage the intrinsic bioactivity of the mucin biopolymer, a heavily glycosylated protein that forms the protective mucus gel covering mucosal epithelia. By using a bioorthogonal inverse electron demand Diels-Alder reaction, we crosslink mucins into implantable hydrogels. We show that mucin hydrogels (Muc-gels) modulate the immune response driving biomaterial-induced fibrosis. Muc-gels did not elicit fibrosis 21 days after implantation in the peritoneal cavity of C57Bl/6 mice, whereas medical-grade alginate hydrogels (Alg-gels) were covered by fibrous tissues. Further, Muc-gels dampened the recruitment of innate and adaptive immune cells to the gel and triggered a pattern of very mild activation marked by a noticeably low expression of the fibrosis-stimulating TGF-β1 cytokine. With this advance in mucin materials, we provide an essential tool to better understand mucin bioactivities and to initiate the development of new mucin-based and mucin-inspired ‘immune-informed’ materials for implantable devices subject to fibrotic encapsulation.

Solutions of manually purified gastric mucins have been shown to be promising lubricants for biomedical purposes, where they can efficiently reduce friction and wear. However, so far, such mucin solutions have been mostly tested in specific tribological settings, i.e., in combination with different material pairings; variations in the composition of the lubricating fluid have not been systematically explored yet. We here fill this gap and determine the viscosity, adsorption behavior, and lubricity of porcine gastric mucin solutions on hydrophobic surfaces at different pH levels, mucin and salt concentrations, and in the presence of other proteins. We demonstrate that mucin solutions provide excellent lubricity even at very low concentrations of 0.01% (w/v), over a broad range of pH levels and even at an elevated ionic strength. Furthermore, we provide mechanistic insights into mucin lubricity, which help explain how certain variations in physiologically relevant parameters can limit the lubricating potential of mucin solutions. Our results show that solutions of manually purified mucin solutions can be powerful biomedical lubricants, e.g., serving as artificial joint fluids for viscosupplementation, as eye drops or mouth spray, or as a personal lubricant for intercourse.

This article presents a novel computational model to study the selective filtering of biological hydrogels due to the surface charge and size of diffusing particles. It is the first model that includes the random three-dimensional fibre orientation and connectivity of the biopolymer network and that accounts for elastic deformations of the fibres by means of beam theory. As a key component of the model, novel formulations are proposed both for the electrostatic and repulsive steric interactions between a spherical particle and a beam. In addition to providing a thorough validation of the model, the presented computational studies yield new insights into the underlying mechanisms of hindered particle mobility, especially regarding the influence of the aforementioned aspects that are unique to this model. It is found that the precise distribution of fibre and thus charge agglomerations in the network have a crucial influence on the mobility of oppositely charged particles and gives rise to distinct motion patterns. Considering the high practical significance for instance with respect to targeted drug release or infection defence, the provided proof of concept motivates further advances of the model towards a truly predictive computational tool that allows a case- and patient-specific assessment for real (biological) systems.

Although many surfaces in industry and medicine are colonized by bacterial biofilms, little is known about the physical principles that govern the adhesion properties of such bacterial communities. In part, this is due to the technical challenge associated with the characterization of a biofilm directly on the substrate it is grown on. Moreover, distinguishing between the cohesive and adhesive properties of a (bio)material requires information on the amount of material transferred between the interacting surfaces, which is not easily possible in existing measurement techniques applied in biofilm research. Here, a new method is introduced which allows for characterizing the detachment process of biofilms in situ and makes it possible to identify the dominant mode of fracture. As a countersurface in those detachment tests with biofilm layers, either a synthetic/inorganic material surface or another biofilm layer can be used. By comparing results obtained with different biofilms generated at distinct cultivation conditions, how two selected material properties, i.e., the biofilm wettability and the biofilm stiffness, contribute to the detachment process can be shown. The novel measurement approach demonstrated here can easily be adapted further to enable adhesion/detachment measurements with a broad range of other biofilms including those grown at submerged conditions.

Bacterial biofilms are able to resist a broad range of chemical challenges as well as mechanical stress. The mechanical properties of natively grown biofilms, however, remain largely unknown. This is mostly due to a lack of suitable experimental setups which are capable of quantifying the mechanical properties of those biofilms in their naturally grown state, i.e., without harvesting and transferring the biofilm material into a measuring device. Here, we present a customized device which allows measuring material parameters of bacterial biofilms in situ. Parameters that can be obtained from our stretching experiments include the tensile strength and rupture energy of native and chemically treated biofilms. Although the example measurements shown here have all been conducted with biofilms formed by the apathogenic soil bacterium B. subtilis B-1, the setup should be applicable to a broad range of bacterial biofilms or other viscoelastic materials.

Closely related microorganisms often cooperate, but the prevalence and stability of cooperation between different genotypes remain debatable. Here, we track the evolution of pellicle biofilms formed through genetic division of labour and ask whether partially deficient partners can evolve autonomy. Pellicles of Bacillus subtilis rely on an extracellular matrix composed of exopolysaccharide (EPS) and the fibre protein TasA. In monocultures, ∆eps and ∆tasA mutants fail to form pellicles, but, facilitated by cooperation, they succeed in co-culture. Interestingly, cooperation collapses on an evolutionary timescale and ∆tasA gradually outcompetes its partner ∆eps. Pellicle formation can evolve independently from division of labour in ∆eps and ∆tasA monocultures, by selection acting on the residual matrix component, TasA or EPS, respectively. Using a set of interdisciplinary tools, we unravel that the TasA producer (∆eps) evolves via an unconventional but reproducible substitution in TasA that modulates the biochemical properties of the protein. Conversely, the EPS producer (ΔtasA) undergoes genetically variable adaptations, all leading to enhanced EPS secretion and biofilms with different biomechanical properties. Finally, we revisit the collapse of division of labour between Δeps and ΔtasA in light of a strong frequency versus exploitability trade-off that manifested in the solitarily evolving partners. We propose that such trade-off differences may represent an additional barrier to evolution of division of labour between genetically distinct microorganisms.

For an efficient distribution of drugs and drug carriers through biological barriers such as the vascular system, the size and surface properties of nanoparticles and molecules play a key role. To screen for important parameters which determine the ability of drugs or drug carriers to translocate through complex biological barriers, an in vitro assay which correctly predicts the behavior of those objects in vivo would be highly desirable. Here, we present a microfluidic setup to probe the diffusive spreading of molecules with different net charges and molecular weights through a basal lamina interface - a biopolymer system which contributes to the barrier function of the vascular system and the skin. From our data, we find a charge dependent accumulation of molecules at the gel interface which is consistent with transient binding of those molecules to the gel constituents. We also observe a similar charge-dependent accumulation of molecules in living mice where the test molecules colocalize with collagen IV, a key component of the basal lamina. Our assay may serve as a platform to perform penetration experiments with even more complex interfaces combining cellular barriers with biopolymer coatings.

Microbial biofilms are tightly packed, heterogeneous structures that serve as arenas for social interactions. Studies on Gram negative models reveal that during evolution in structured environments like biofilms, isogenic populations commonly diversify into phenotypically and genetically distinct variants. These variants can settle in alternative biofilm niches and develop new types of interactions that greatly influence population productivity. Here, we explore the evolutionary diversification of pellicle biofilms of the Gram positive, spore-forming bacterium Bacillus subtilis. We discover that - similarly to other species - B. subtilis diversifies into distinct colony variants. These variants dramatically differ in biofilm formation abilities and expression of biofilm-related genes. In addition, using a quantitative approach, we reveal striking differences in surface complexity and hydrophobicity of the evolved colony types. Interestingly, one of the morphotypes completely lost the ability of independent biofilm formation and evolved to hitchhike with other morphotypes with improved biofilm forming abilities. Genome comparison suggests that major phenotypic transformations between the morphotypes can be triggered by subtle genetic differences. Our work demonstrates how positive complementarity effects and exploitative interactions intertwine during evolutionary diversification in biofilms.

The colonization of surfaces by bacterial biofilms constitutes a huge problem in healthcare and industry. When attempting biofilm inactivation or removal, it is crucial to sufficiently wet the biofilm surface with antibacterial agents; however, certain biofilms efficiently resist wetting, and the origin of this behavior remains to date unclear. Here, we demonstrate that, depending on the growth medium used, the model bacterium Bacillus subtilis can form biofilm colonies with distinct surface properties: we find either hydrophilic or two variants of hydrophobic behavior. We show that those differences in biofilm wetting correlate with distinct surface topologies which, in turn, give rise to different physical wetting regimes known from lotus leaves or rose petals. Forming biofilms with different wetting properties may help bacteria to survive in both arid and humid conditions. Furthermore, converting the surface polarity of a biofilm could facilitate their removal from surfaces by increasing their wettability.

Many biological materials exist in non-equilibrium states driven by the irreversible consumption of high-energy molecules like ATP or GTP. These energy-dissipating structures are governed by kinetics and are thus endowed with unique properties including spatiotemporal control over their presence. Here we show man-made equivalents of materials driven by the consumption of high-energy molecules and explore their unique properties. A chemical reaction network converts dicarboxylates into metastable anhydrides driven by the irreversible consumption of carbodiimide fuels. The anhydrides hydrolyse rapidly to the original dicarboxylates and are designed to assemble into hydrophobic colloids, hydrogels or inks. The spatiotemporal control over the formation and degradation of materials allows for the development of colloids that release hydrophobic contents in a predictable fashion, temporary self-erasing inks and transient hydrogels. Moreover, we show that each material can be re-used for several cycles., Biological systems vital functions are based on non-equilibrium states driven by consumption of chemical fuels. Here the authors show a spatiotemporal control over the formation of hydrophobic colloids, hydrogels or inks through a chemical reaction network of dicarboxylate compounds fuelled by carbodiimide.