Honeycomb-like architecture produced by living bacteria, Gluconacetobacter xylinus

Biofabrication with microbial cellulose: from bioadaptive designs to living materials

Nanocellulose is not only a renewable material but also brings functions that are opening new technological opportunities. Here we discuss a special subset of this material, in its fibrillated form, which is produced by aerobic microorganisms, namely, bacterial nanocellulose (BNC). BNC offers distinct advantages over plant-derived counterparts, including high purity and high degree of polymerization as well as crystallinity, strength, and water-holding capacity, among others. More remarkably, beyond classical fermentative protocols, it is possible to grow BNC on non-planar interfaces, opening new possibilities in the assembly of advanced bottom-up structures. In this review, we discuss the recent advances in the area of BNC-based biofabrication of three-dimensional (3D) designs by following solid- and soft-material templating. These methods are shown as suitable platforms to achieve bioadaptive constructs comprising highly interlocked biofilms that can be tailored with precise control over nanoscale morphological features. BNC-based biofabrication opens applications that are not possible by using traditional manufacturing routes, including direct ink writing of hydrogels. This review emphasizes the critical contributions of microbiology, colloid and surface science, as well as additive manufacturing in achieving bioadaptive designs from living matter. The future impact of BNC biofabrication is expected to take advantage of material and energy integration, residue utilization, circularity and social latitudes. Leveraging existing infrastructure, the scaleup of biofabrication routes will contribute to a new generation of advanced materials rooted in exciting synergies that combine biology, chemistry, engineering and material sciences.

Honeycomb-like porous chitosan films prepared via phase transition of poly(N-isopropylacrylamide) during water evaporation under ambient conditions

Honeycomb-like porous chitosan (CS) films are attractive tools for developing functional materials for filters, catalyses, adsorbents, biomaterials, etc. A simple method for fabricating honeycomb-like porous CS films without special reagents, facilities, and techniques would make them accessible. Here we introduce an easily available method for fabricating honeycomb-like CS films without a strong acid/base, toxic reagents, or special facilities/techniques. An aqueous solution containing CS and poly(N-isopropylacrylamide) (PNIPAm) was allowed to stand at 25 °C to evaporate water. After 3 days, CS–PNIPAm composite films with homogenously phase-separated PNIPAm particles were obtained. The PNIPAm particles were removed by immersion in methanol, and the resulting films dried under reduced pressure to become honeycomb-like porous CS films. The pore size could be varied in the range of 0.5–3.0 μm by altering the CS concentration and the molecular weight of CS where the pore size was reduced under conditions with stronger interaction between CS molecules. We reveal that the key to success with this system is the decrease of lower critical solution temperature (LCST) of PNIPAm with water evaporation. In addition, we confirmed the removed PNIPAm was recyclable in this system. Furthermore, we found this method was also applicable to alginate. The proposed facile method for fabricating honeycomb-like porous polymeric films could provide various functional porous materials.

A simple method for fabricating honeycomb-like porous chitosan films without special reagents, facilities, and techniques was achieved by using poly(N-isopropylacrylamide).

Bioengineering tunable porosity in bacterial nanocellulose matrices

A facile and effective method is described to engineer original bacterial cellulose fibrous networks with tunable porosity. We showed that the pore shape, volume, and size distribution of bacterial nanocellulose membranes can be tailored under appropriate culture conditions specifically carbon sources. Pore characterization techniques such as capillary flow porometry, the bubble point method, and gas adsorption-desorption technique as well as visualization techniques such as scanning electron and atomic force microscopy were utilized to investigate the morphology and shape of the pores within the membranes. Engineering various shape, size and volume characteristics of the pores available in pristine bacterial nanocellulose membranes leads to fabrication and development of eco-friendly materials with required characteristics for a broad range of applications.

The logic of biologically active small molecules: amazing ability of microorganisms*

In this review article, I will outline my way of thinking about biologically active small molecules. The structure of liposidomycin B from Streptomyces species resulted in my initial sense that a structure tells its function. A biologically active small molecule may save directly or indirectly a number of people. Even if the molecule has not been used as a therapeutic agent, it can be used as a useful chemical probe for dissecting a living cell into different biochemical pieces. Such biologically active small molecules derived from microorganisms have been primarily found in cultivable microorganisms that make up only 1% of total microbes in nature. Discovery of novel growth factors, zincmethylphyrin, zinc coproporphyrin, and coproporphyrin enabled laboratory cultivation of previously uncultured Leucobacter sp. These findings might expand the possibility for further discovery of novel therapeutic agents or chemical probes.

A Perspective on Bio-Mediated Material Structuring

Bioinspiration, biomorphy, biomimicry, biomimetics, bionics, and biotemplating are terms used to describe the fabrication of materials or, more generally, systems to solve technological problems by abstracting, emulating, using, or transferring structures from biological paradigms. Herein, a brief overview of how the different terminologies are being typically applied is provided. It is proposed that there is a rich field of research that can be expanded by utilizing various novel approaches for the guidance of living organisms for "bio-mediated" material structuring purposes. As examples of contact-based or contact-free guidance, such as substrate patterning, the application of light, magnetic fields, or chemical gradients, potentially interesting methods of creating hierarchically structured monolithic engineering materials, using live patterned biomass, biofilms, or extracellular substances as scaffolds, are presented. The potential advantages of such materials are discussed, and examples of live self-patterning of materials are given.

Designing 3D Biological Surfaces via the Breath-Figure Method

The fabrication of biointerfaces that mimic cellular physiological environments is critical to understanding cell behaviors in vitro and for the design of tissue engineering. Breath figure is a self-assemble method that uses water droplets condensed from moisture as template and ends up with a highly ordered hexagonal pore array; this approach is used to fabricate various biological substrates. This progress report provides an overview of strategies to achieve topographical modifications and chemical-patterned arrays, such as modulation of the pore size, shape and selective decoration of the honeycomb holes. Using recent results in the biological fields, potential future applications and developments of honeycomb structures are commented upon.

Control of bacterial adhesion and growth on honeycomb-like patterned surfaces

It is a great challenge to construct a persistent bacteria-resistant surface even though it has been demonstrated that several surface features might be used to control bacterial behavior, including surface topography. In this study, we develop micro-scale honeycomb-like patterns of different sizes (0.5-10 μm) as well as a flat area as the control on a single platform to evaluate the bacterial adhesion and growth. Bacteria strains, Escherichia coli and Staphylococcus aureus with two distinct shapes (rod and sphere) are cultured on the platforms, with the patterned surface-up and surface-down in the culture medium. The results demonstrate that the 1 μm patterns remarkably reduce bacterial adhesion and growth while suppressing bacterial colonization when compared to the flat surface. The selective adhesion of the bacterial cells on the patterns reveals that the bacterial adhesion is cooperatively mediated by maximizing the cell-substrate contact area and minimizing the cell deformation, from a thermodynamic point of view. Moreover, study of bacterial behaviors on the surface-up vs. surface-down samples shows that gravity does not apparently affect the spatial distribution of the adherent cells although it indeed facilitates bacterial adhesion. Furthermore, the experimental results suggest that two major factors, i.e. the availability of energetically favorable adhesion sites and the physical confinements, contribute to the anti-bacterial nature of the honeycomb-like patterns.

Dehydrogenative polymerization of coniferyl alcohol in artificial polysaccharides matrices: effects of xylan on the polymerization

To elucidate the influence of wood polysaccharide components on lignin formation in vitro, models for polysaccharide matrix in wood secondary cell wall were fabricated from two types of bacterial cellulosic films, flat film (FBC) and honeycomb-patterned film (HPBC), as basic frameworks by depositing xylan onto the films. An endwise type of dehydrogenative polymerization, "Zutropfverfahren", of coniferyl alcohol was attempted in the films with/without xylan. The resultant dehydrogenation polymer (DHP) was generated inside and outside xylan-deposited films, whereas DHP was deposited only outside the films without xylan. The amount of the generated DHP in the xylan-deposited films was larger than that in the films without xylan. The frequency of 8-O-4' interunitary linkage in DHP was also increased by the xylan deposition. These results suggest that xylan acts as a scaffold for DHP deposition in polysaccharides matrix and as a structure regulator for the formation of the 8-O-4' linkage. In addition, mechanical properties, i.e., tensile strength and modulus of elasticity (MOE), of both cellulosic films were found to be augmented by the deposition of xylan and DHP. Especially, DHP deposition remarkably enhanced MOE. Such effects of xylan on DHP formation and augmentation of mechanical strength were clearly observed for HPBC, revealing that HPBC is a promising framework model to investigate wood cell wall formation in vitro.

Agarose particle-templated porous bacterial cellulose and its application in cartilage growth in vitro

Bacterial cellulose (BC) is a biocompatible hydrogel with a three-dimensional (3-D) structure formed by a dense network of cellulose nanofibers. A limitation of using BC for applications in tissue engineering is that the pore size of the material (∼0.02-10μm) is smaller than the dimensions of mammalian cells and prevents cells from penetrating into the material and growing into 3-D structures that mimic tissues. This paper describes a new route to porous bacterial cellulose (pBC) scaffolds by cultivating Acetobacter xylinum in the presence of agarose microparticles deposited on the surface of a growing BC pellicle. Monodisperse agarose microparticles with a diameter of 300-500μm were created using a microfluidic technique, layered on growing BC pellicles and incorporated into the polymer as A. xylinum cells moved upward through the growing pellicle. Removing the agarose microparticles by autoclaving produced BC gels containing a continuous, interconnected network of pores with diameters ranging from 300 to 500μm. Human P1 chondrocytes seeded on the scaffolds, replicated, invaded the 3-D porous network and distributed evenly throughout the substrate. Chondrocytes grown on pBC substrates displayed a higher viability compared to growth on the surface of unmodified BC substrates. The approach described in this paper introduces a new method for creating pBC substrates with user-defined control over the physical dimensions of the pore network, and demonstrates the application of these materials for tissue engineering.

Advances in Fabrication Materials of Honeycomb Structure Films by the Breath-Figure Method

Creatures in nature possess almost perfect structures and properties, and exhibit harmonization and unification between structure and function. Biomimetics, mimicking nature for engineering solutions, provides a model for the development of functional surfaces with special properties. Recently, honeycomb structure materials have attracted wide attention for both fundamental research and practical applications and have become an increasingly hot research topic. Though progress in the field of breath-figure formation has been reviewed, the advance in the fabrication materials of bio-inspired honeycomb structure films has not been discussed. Here we review the recent progress of honeycomb structure fabrication materials which were prepared by the breath-figure method. The application of breath figures for the generation of all kinds of honeycomb is discussed.

Bacterial cellulose-based materials and medical devices: current state and perspectives

Bacterial cellulose (BC) is a unique and promising material for use as implants and scaffolds in tissue engineering. It is composed of a pure cellulose nanofiber mesh spun by bacteria. It is remarkable for its strength and its ability to be engineered structurally and chemically at nano-, micro-, and macroscales. Its high water content and purity make the material biocompatible for multiple medical applications. Its biocompatibility, mechanical strength, chemical and morphologic controllability make it a natural choice for use in the body in biomedical devices with broader application than has yet been utilized. This paper reviews the current state of understanding of bacterial cellulose, known methods for controlling its physical and chemical structure (e.g., porosity, fiber alignment, etc.), biomedical applications for which it is currently being used, or investigated for use, challenges yet to be overcome, and future possibilities for BC.