Bacterial nanocellulose enables auxetic supporting implants.

Owing to its purity and exceptional mechanical performance, bacterial nanocellulose (BNC) is well suited for tissue engineering applications. BNC assembles as a network that features similarities with the extracellular matrix (ECM) while exhibiting excellent integrity in the wet state, suitable for suturing and sterilization. The development of complex 3D forms is shown by taking advantage of the aerobic process involved in the biogenesis of BNC at the air/culture medium interphase. Hence, solid supports are used to guide the formation of BNC biofilms that easily form auxetic structures. Such biomaterials are demonstrated as implantable meshes with prescribed opening size and infill density. The measured mechanical strength is easily adjustable (48-456 MPa tensile strength) while ensuring shape stability (>87% shape retention after 100 burst loading/unloading cycles). We further study the cytotoxicity, monocyte/macrophage pro-inflammatory activation, and phenotype to demonstrate the prospective use of BNC as supportive implants with long-term comfort and minimal biomaterial fatigue.

Impact of incubation conditions and post-treatment on the properties of bacterial cellulose membranes for pressure-driven filtration.

Bacterial cellulose (BC) has shown potential as a separation material. Herein, the performance of BC in pressure-driven separation is investigated as a function of incubation conditions and post-culture treatment. The pure water flux of never-dried BC (NDBC), was found to be 9 to 16 times higher than that for dried BC (DBC), in a pressure range of 0.25 to 2.5 bar. The difference in pressure response of NDBC and DBC was observed both in cross-flow filtration and capillary flow porometry experiments. DBC and NDBC were permeable to polymers with a hydrodynamic radius of ∼60 nm while protein retention was possible by introducing anionic surface charges on BC. The results of this work are expected to expand the development of BC-based filtration membranes, for instance towards the processing of biological fluids.

Guiding Bacterial Activity for Biofabrication of Complex Materials via Controlled Wetting of Superhydrophobic Surfaces.

Superhydrophobic surfaces are promising for preventing fouling and the formation of biofilms, with important implications in the food chain, maritime transport, and health sciences, among others. In this work, we exploit the interplay between wetting principles of superhydrophobic surfaces and microbial fouling for advanced three-dimensional (3D) biofabrication of biofilms. We utilize hydrostatic and capillary pressures to finely control the air-water interface and the aerotaxis-driven biofabrication on superhydrophobic surfaces. Superhydrophobic 3D molds are produced by a simple surface modification that partially embeds hydrophobic particles in silicone rubber. Thereafter, the molds allow the templating of the air-water interface of the culture medium, where the aerobic nanocellulose-producing bacteria (Komagataeibacter medellinensis) are incubated. The biofabricated replicas are hollow and seamless nanofibrous objects with a controlled morphology. Gradients of thickness, topographical feature size, and fiber orientation on the biofilm are obtained by controlling wetting, incubation time, and nutrient availability. Furthermore, we demonstrate that capillary length limitations are overcome by using pressurized closed molds, whereby a persistent air plastron allows the formation of 3D microstructures, regardless of their morphological complexity. We also demonstrate that interfacial biofabrication is maintained for at least 12 days without observable fouling of the mold surface. In summary, we achieve controlled biofouling of the air-water interface as imposed by the experimental framework under controlled wetting. The latter is central to both microorganism-based biofabrication and fouling, which are major factors connecting nanoscience, synthetic biology, and microbiology.

Effects of Chloride Concentration on the Water Disinfection Performance of Silver Containing Nanocellulose-based Composites.

The availability of microbially-safe drinking water is a challenge in many developing regions. Due to the well-known antibacterial effect of silver ions, materials used for their controlled release have been widely studied for point-of-use water disinfection. However, even if it is in principle known that chloride anions can suppress the antibacterial efficiency of silver, the majority of previous studies, surprisingly, have not focused on chloride concentrations relevant for freshwaters and thus for practical applications. Here, we prepared low-cost nanocellulose-aluminium oxyhydroxide nanocomposites functionalized with silver nanoparticles. Field samples obtained from Chennai, India were used as a guideline for choosing relevant chloride concentrations for the antibacterial studies, i.e., 10, 90, and 290 ppm. The antibacterial performance of the material against Escherichia coli and Bacillus subtilis was demonstrated and the influence of chloride concentration on the antibacterial effect was studied with E. coli. A 1 h contact time led to bacterial reductions of 5.6 log10, 2.9 log10, and 2.2 log10, respectively. This indicates that an increase of chloride concentration leads to a substantial reduction of antibacterial efficiency, even within chloride concentrations found in freshwaters. This work enables further insights for designing freshwater purification systems that utilize silver-releasing materials.

Adsorption and Assembly of Cellulosic and Lignin Colloids at Oil/Water Interfaces.

The surface chemistry and adsorption behavior of submicrometer cellulosic and lignin particles have drawn wide-ranging interest in the scientific community. Here, we introduce their assembly at fluid/fluid interfaces in Pickering systems and discuss their role in reducing the oil/water interfacial tension, limiting flocculation and coalescence, and endowing given functional properties. We discuss the stabilization of multiphase systems by cellulosic and lignin colloids and the opportunities for their adoption. They can be used alone, as dual components, or in combination with amphiphilic molecules for the design of multiphase systems relevant to household products, paints, coatings, pharmaceutical, foodstuff, and cosmetic formulations. This invited feature article summarizes some of our work and that of colleagues to introduce the readers to this fascinating and topical area.

Advanced Biomass-Derived Electrocatalysts for the Oxygen Reduction Reaction.

Recent progress in advanced nanostructures synthesized from biomass resources for the oxygen reduction reaction (ORR) is reviewed. The ORR plays a significant role in the performance of numerous energy-conversion devices, including low-temperature hydrogen and alcohol fuel cells, microbial fuel cells, as well as metal-air batteries. The viability of such fuel cells is strongly related to the cost of the electrodes, especially the cathodic ORR electrocatalyst. Hence, inexpensive and abundant plant and animal biomass have become attractive options to obtain electrocatalysts upon conversion into active carbon. Bioresource selection and processing criteria are discussed in light of their influence on the physicochemical properties of the ORR nanostructures. The resulting electrocatalytic activity and durability are introduced and compared to those from conventional Pt/C-based electrocatalysts. These ORR catalysts are also active for oxygen or hydrogen evolution reactions.

Regulation of prostate cell collagen receptors by malignant transformation.

Cell adhesion receptors, including the integrin-type collagen receptors (alpha1beta1, alpha2beta1, alpha10beta1 and alpha11beta1) participate in cancer progression and invasion. Quantitative RT-PCR indicated that all 4 receptors are abundantly expressed in sarcoma-derived cell lines, whereas most carcinoma-derived cells express alpha1beta1 and alpha2beta1 only. This was surprising because alpha11beta1 has been connected previously to the progression of lung adenocarcinomas. To test the hypothesis that alpha11 expression may not persist in cultured cancer cells we analyzed fresh tissue samples of 104 total prostatectomies, keeping in mind that prostate cancer cell lines showed negligible alpha11 mRNA levels. In prostate alpha2 expression was significantly lower in poorly differentiated carcinomas when compared to benign lesions (p = 0.0331). In immunohistochemistry the protein levels of alpha2 integrin decreased significantly (p = 0.0001) and the protein levels of alpha11 subunit increased significantly (p = 0.029) with the increasing grade of carcinoma. Thus alpha11beta1 may replace alpha2beta1 during tumor progression. Our observations support the idea that alpha11beta1 may be expressed in tumors but the corresponding cell lines may lose the expression of this integrin. Previous studies have shown that in cell culture androgen receptor (AR) controls alpha2beta1 expression. We measured AR mRNA levels and the number of AR positive nuclei in the prostate samples and the results showed a significant correlation between alpha2beta1 and AR. Androgen receptors may control the mechanisms regulating integrin expression in prostate.