Macromolecular crowding for materials-directed controlled self-assembly

Bottom-Up Synthesized Glucan Materials: Opportunities from Applied Biocatalysis

Linear d-glucans are natural polysaccharides of simple chemical structure. They are comprised of d-glucosyl units linked by a single type of glycosidic bond. Noncovalent interactions within, and between, the d-glucan chains give rise to a broad variety of macromolecular nanostructures that can assemble into crystalline-organized materials of tunable morphology. Structure design and functionalization of d-glucans for diverse material applications largely relies on top-down processing and chemical derivatization of naturally derived starting materials. The top-down approach encounters critical limitations in efficiency, selectivity, and flexibility. Bottom-up approaches of d-glucan synthesis offer different, and often more precise, ways of polymer structure control and provide means of functional diversification widely inaccessible to top-down routes of polysaccharide material processing. Here the natural and engineered enzymes (glycosyltransferases, glycoside hydrolases and phosphorylases, glycosynthases) for d-glucan polymerization are described and the use of applied biocatalysis for the bottom-up assembly of specific d-glucan structures is shown. Advanced material applications of the resulting polymeric products are further shown and their important role in the development of sustainable macromolecular materials in a bio-based circular economy is discussed.

Extracellular Matrix Cues Regulate Mechanosensing and Mechanotransduction of Cancer Cells

Extracellular biophysical properties have particular implications for a wide spectrum of cellular behaviors and functions, including growth, motility, differentiation, apoptosis, gene expression, cell-matrix and cell-cell adhesion, and signal transduction including mechanotransduction. Cells not only react to unambiguously mechanical cues from the extracellular matrix (ECM), but can occasionally manipulate the mechanical features of the matrix in parallel with biological characteristics, thus interfering with downstream matrix-based cues in both physiological and pathological processes. Bidirectional interactions between cells and (bio)materials in vitro can alter cell phenotype and mechanotransduction, as well as ECM structure, intentionally or unintentionally. Interactions between cell and matrix mechanics in vivo are of particular importance in a variety of diseases, including primarily cancer. Stiffness values between normal and cancerous tissue can range between 500 Pa (soft) and 48 kPa (stiff), respectively. Even the shear flow can increase from 0.1-1 dyn/cm2 (normal tissue) to 1-10 dyn/cm2 (cancerous tissue). There are currently many new areas of activity in tumor research on various biological length scales, which are highlighted in this review. Moreover, the complexity of interactions between ECM and cancer cells is reduced to common features of different tumors and the characteristics are highlighted to identify the main pathways of interaction. This all contributes to the standardization of mechanotransduction models and approaches, which, ultimately, increases the understanding of the complex interaction. Finally, both the in vitro and in vivo effects of this mechanics-biology pairing have key insights and implications for clinical practice in tumor treatment and, consequently, clinical translation.

Trend of Developing Aqueous Liquid and Gel Electrolytes for Sustainable, Safe, and High-Performance Li-Ion Batteries

Current lithium-ion batteries (LIBs) rely on organic liquid electrolytes that pose significant risks due to their flammability and toxicity. The potential for environmental pollution and explosions resulting from battery damage or fracture is a critical concern. Water-based (aqueous) electrolytes have been receiving attention as an alternative to organic electrolytes. However, a narrow electrochemical-stability window, water decomposition, and the consequent low battery operating voltage and energy density hinder the practical use of aqueous electrolytes. Therefore, developing novel aqueous electrolytes for sustainable, safe, high-performance LIBs remains challenging. This Review first commences by summarizing the roles and requirements of electrolytes-separators and then delineates the progression of aqueous electrolytes for LIBs, encompassing aqueous liquid and gel electrolyte development trends along with detailed principles of the electrolytes. These aqueous electrolytes are progressed based on strategies using superconcentrated salts, concentrated diluents, polymer additives, polymer networks, and artificial passivation layers, which are used for suppressing water decomposition and widening the electrochemical stability window of water of the electrolytes. In addition, this Review discusses potential strategies for the implementation of aqueous Li-metal batteries with improved electrolyte-electrode interfaces. A comprehensive understanding of each strategy in the aqueous system will assist in the design of an aqueous electrolyte and the development of sustainable and safe high-performance batteries.

Carrageenan as a macromolecular crowding agent in human umbilical cord derived mesenchymal stromal cell culture

Cell sheet tissue engineering requires prolonged in vitro culture for the development of implantable devices. Unfortunately, lengthy in vitro culture is associated with cell phenotype loss and substantially higher cost of goods, which collectively hinder clinical translation and commercialisation of tissue engineered medicines. Although macromolecular crowding has been shown to enhance and accelerate extracellular matrix deposition, whilst maintaining cellular phenotype, the optimal macromolecular crowding agent still remains elusive. Herein, we evaluated the biophysical properties of seven different carrageenan molecules at five different concentrations and their effect on human umbilical cord-derived mesenchymal stromal cell morphology, viability, metabolic activity, proliferation, extracellular matrix deposition and surface marker expression. All types of carrageenan (CR) assessed demonstrated a hydrodynamic radius increase as a function of increasing concentration; high polydispersity; and negative charge. Two iota CRs were excluded from further analysis due to poor solubility in cell culture. Among the remaining five carrageenans, the lambda medium viscosity type at concentrations of 10 and 50 μg/ml did not affect cell morphology, viability, metabolic activity, proliferation and expression of surface markers and significantly increased the deposition of collagen types I, III and IV, fibronectin and laminin. Our data highlight the potential of lambda medium viscosity carrageenan as a macromolecular crowding agent for the accelerated development of functional tissue engineered medicines.

Interplay of Depletion Forces and Biomolecular Recognition in the Hierarchical Assembly of Supramolecular Tubes

Crowding effects have a profound impact on the hierarchical organization of cellular architectures. In the fields of systems chemistry and soft matter, this effect has not received much attention so far. Here, it is explored how poly(ethylene glycol) (PEG) as a crowding agent invokes depletion forces that act on synthetic supramolecular tubes. Hence, supramolecular tubes are pushed from their random orientation into hierarchically assembled bundles due to the PEG-induced crowded environment. The resulting morphology of formed bundled architectures can be tuned by the concentrations of both the supramolecular tubes and the PEG. The introduction of biotin groups at the surface of the tubes allows the engineering of biotin-streptavidin crosslinks between them. The order of introducing PEG and streptavidin in the system further affects the formed hierarchical assemblies, as well as their resistance toward dilution. The strategy described here provides a new route to establish hierarchically organized supramolecular architectures, combining crowding and specific biomolecular interactions, which shows the potential for controlling the structure of supramolecular materials and other soft matter systems.

Biophysical cues of in vitro biomaterials-based artificial extracellular matrix guide cancer cell plasticity

Clinical evidence supports a role for the extracellular matrix (ECM) in cancer plasticity across multiple tumor types. The lack of in vitro models that represent the native ECMs is a significant challenge for cancer research and drug discovery. Therefore, a major motivation for developing new tumor models is to create the artificial ECM in vitro. Engineered biomaterials can closely mimic the architectural and mechanical properties of ECM to investigate their specific effects on cancer progression, offering an alternative to animal models for the testing of cancer cell behaviors. In this review, we focused on the biomaterials from different sources applied in the fabrication of the artificial ECM and their biophysical cues to recapitulate key features of tumor niche. Furthermore, we summarized how the distinct biophysical cues guided cell behaviors of cancer plasticity, including morphology, epithelial-to-mesenchymal transition (EMT), enrichment of cancer stem cells (CSCs), proliferation, migration/invasion and drug resistance. We also discuss the future opportunities in using the artificial ECM for applications of tumorigenesis research and precision medicine, as well as provide useful messages of principles for designing suitable biomaterial scaffolds.

Bioinspired crowding directs supramolecular polymerisation

Crowding effects are crucial to maintaining functionality in biological systems, but little is known about their role in analogous artificial counterparts. Within the growing field of supramolecular polymer science, crowding effects have hitherto remained underappreciated. Herein, we show that crowding effects exhibit strong and distinct control over the kinetics, accessible pathways and final outcomes of supramolecular polymerisation processes. In the presence of a pre-formed supramolecular polymer as crowding agent, a model supramolecular polymer dramatically changes its self-assembly behaviour and undergoes a morphological transformation from bundled fibres into flower-like hierarchical assemblies, despite no co-assembly taking place. Notably, this new pathway can only be accessed in crowded environments and when the crowding agent exhibits a one-dimensional morphology. These results allow accessing diverse morphologies and properties in supramolecular polymers and pave the way towards a better understanding of high-precision self-assembly in nature.

Progress on Crowding Effect in Cell-like Structures

Several biological macromolecules, such as proteins, nucleic acids, and polysaccharides, occupy about 30% of the space in cells, resulting in a crowded macromolecule environment. The crowding effect within cells exerts an impact on the functions of biological components, the assembly behavior of biomacromolecules, and the thermodynamics and kinetics of metabolic reactions. Cell-like structures provide confined and independent compartments for studying the working mechanisms of cells, which can be used to study the physiological functions arising from the crowding effect of macromolecules in cells. This article mainly summarizes the progress of research on the macromolecular crowding effects in cell-like structures. It includes the effects of this crowding on actin assembly behavior, tubulin aggregation behavior, and gene expression. The challenges and future trends in this field are presented at the end of the paper.

Engineering cascade biocatalysis in whole cells for bottom-up synthesis of cello-oligosaccharides: flux control over three enzymatic steps enables soluble production

BACKGROUND

Soluble cello-oligosaccharides (COS, β-1,4-D-gluco-oligosaccharides with degree of polymerization DP 2-6) have been receiving increased attention in different industrial sectors, from food and feed to cosmetics. Development of large-scale COS applications requires cost-effective technologies for their production. Cascade biocatalysis by the three enzymes sucrose-, cellobiose- and cellodextrin phosphorylase is promising because it enables bottom-up synthesis of COS from expedient substrates such as sucrose and glucose. A whole-cell-derived catalyst that incorporates the required enzyme activities from suitable co-expression would represent an important step towards making the cascade reaction fit for production. Multi-enzyme co-expression to reach distinct activity ratios is challenging in general, but it requires special emphasis for the synthesis of COS. Only a finely tuned balance between formation and elongation of the oligosaccharide precursor cellobiose results in the desired COS.

RESULTS

Here, we show the integration of cellodextrin phosphorylase into a cellobiose-producing whole-cell catalyst. We arranged the co-expression cassettes such that their expression levels were upregulated. The most effective strategy involved a custom vector design that placed the coding sequences for cellobiose phosphorylase (CbP), cellodextrin phosphorylase (CdP) and sucrose phosphorylase (ScP) in a tricistron in the given order. The expression of the tricistron was controlled by the strong T7_lacO promoter and strong ribosome binding sites (RBS) for each open reading frame. The resulting whole-cell catalyst achieved a recombinant protein yield of 46% of total intracellular protein in an optimal ScP:CbP:CdP activity ratio of 10:2.9:0.6, yielding an overall activity of 315 U/g dry cell mass. We demonstrated that bioconversion catalyzed by a semi-permeabilized whole-cell catalyst achieved an industrial relevant COS product titer of 125 g/L and a space-time yield of 20 g/L/h. With CbP as the cellobiose providing enzyme, flux into higher oligosaccharides (DP ≥ 6) was prevented and no insoluble products were formed after 6 h of conversion.

CONCLUSIONS

A whole-cell catalyst for COS biosynthesis was developed. The coordinated co-expression of the three biosynthesis enzymes balanced the activities of the individual enzymes such that COS production was maximized. With the flux control set to minimize the share of insolubles in the product, the whole-cell synthesis shows a performance with respect to yield, productivity, product concentration and quality that is promising for industrial production.

Porous carbon nanoarchitectonics for the environment: detection and adsorption

As a post-nanotechnology concept, nanoarchitectonics has emerged from the 20th century to the 21st century. This review summarizes the recent progress in the field of metal-free porous carbon nanoarchitectonics.

Macromolecular cryoprotectants for the preservation of mammalian cell culture: lessons from crowding, overview and perspectives

Cryopreservation is a process used for the storage of mammalian cells at a very low temperature, in a state of 'suspended animation.' Highly effective and safe macromolecular cryoprotectants (CPAs) have gained significant attention as they obviate the toxicity of conventional CPAs like dimethyl sulfoxide (DMSO) and reduce the risks involved in the storage of cultures at liquid nitrogen temperatures. These agents provide cryoprotection through multiple mechanisms, involving extracellular and intracellular macromolecular crowding, thereby impacting the biophysical and biochemical dynamics of the freezing medium and the cryopreserved cells. These CPAs vary in their structures and physicochemical properties, which influence their cryoprotective activities. Moreover, the introduction of polymeric crowders in the cryopreservation media enables serum-free storage at low-DMSO concentrations and high-temperature vitrification of frozen cultures (-80 °C). This review highlights the need for macromolecular CPAs and describes their mechanisms of cryopreservation, by elucidating the role of crowding effects. It also classifies the macromolecules based on their chemistry and their structure-activity relationships. Furthermore, this article provides perspectives on the factors that may influence the outcomes of the cell freezing process or may help in designing and evaluating prospective macromolecules. This manuscript also includes case studies about cellular investigations that have been conducted to demonstrate the cryoprotective potential of macromolecular CPAs. Ultimately, this review provides essential directives that will further improve the cell cryopreservation process and may encourage the use of macromolecular CPAs to fortify basic, applied, and translational research.

Beyond Color: The New Carbon Ink

For thousands of years, carbon ink has been used as a black color pigment for writing and painting purposes. However, recent discoveries of nanocarbon materials, including fullerenes, carbon nanotubes, graphene, and their various derivative forms, together with the advances in large-scale synthesis, are enabling a whole new generation of carbon inks that can serve as an intrinsically programmable materials platform for developing advanced functionalities far beyond color. The marriage between these multifunctional nanocarbon inks with modern printing technologies is facilitating and even transforming many applications, including flexible electronics, wearable and implantable sensors, actuators, and autonomous robotics. This review examines recent progress in the reborn field of carbon inks, highlighting their programmability and multifunctionality for applications in flexible electronics and stimuli-responsive devices. Current challenges and opportunities will also be discussed from a materials science perspective towards the advancement of carbon ink for new applications beyond color.

Recent advances in enzymatic synthesis of β-glucan and cellulose

Bottom-up synthesis of β-glucans such as callose, fungal β-(1,3)(1,6)-glucan and cellulose, can create the defined compounds that are needed to perform fundamental studies on glucan properties and develop applications. With the importance of β-glucans and cellulose in high-profile fields such as nutrition, renewables-based biotechnology and materials science, the enzymatic synthesis of such relevant carbohydrates and their derivatives has attracted much attention. Here we review recent developments in enzymatic synthesis of β-glucans and cellulose, with a focus on progress made over the last five years. We cover the different types of biocatalysts employed, their incorporation in cascades, the exploitation of enzyme promiscuity and their engineering, and reaction conditions affecting the production as well as in situ self-assembly of (non)functionalised glucans. The recent achievements in the application of glycosyl transferases and β-1,4- and β-1,3-glucan phosphorylases demonstrate the high potential and versatility of these biocatalysts in glucan synthesis in both industrial and academic contexts.

Self-assembly of cellulose for creating green materials with tailor-made nanostructures

Inspired by living systems, biomolecules have been employed in vitro as building blocks for creating advanced nanostructured materials. In regard to nucleic acids, peptides, and lipids, their self-assembly pathways and resulting assembled structures are mostly encoded in their molecular structures. On the other hand, outside of its chain length, cellulose, a polysaccharide, lacks structural diversity; therefore, it is challenging to direct this homopolymer to controllably assemble into ordered nanostructures. Nevertheless, the properties of cellulose assemblies are outstanding in terms of their robustness and inertness, and these assemblies are attractive for constructing versatile materials. In this review article, we summarize recent research progress on the self-assembly of cellulose and the applications of assembled cellulose materials, especially for biomedical use. Given that cellulose is the most abundant biopolymer on Earth, gaining control over cellulose assembly represents a promising route for producing green materials with tailor-made nanostructures.

Tuneable Hybrid Hydrogels via Complementary Self-Assembly of a Bioactive Peptide with a Robust Polysaccharide

Synthetic materials designed for improved biomimicry of the extracellular matrix must contain fibrous, bioactive, and mechanical cues. Self-assembly of low molecular weight gelator (LMWG) peptides Fmoc-DIKVAV (Fmoc-aspartic acid-isoleucine-lysine-valine-alanine-valine) and Fmoc-FRGDF (Fmoc-phenylalanine-arginine-glycine-aspartic acid-phenylalanine) creates fibrous and bioactive hydrogels. Polysaccharides such as agarose are biocompatible, degradable, and non-toxic. Agarose and these Fmoc-peptides have both demonstrated efficacy in vitro and in vivo. These materials have complementary properties; agarose has known mechanics in the physiological range but is inert and would benefit from bioactive and topographical cues found in the fibrous, protein-rich extracellular matrix. Fmoc-DIKVAV and Fmoc-FRGDF are synthetic self-assembling peptides that present bioactive cues "IKVAV" and "RGD" designed from the ECM proteins laminin and fibronectin. The work presented here demonstrates that the addition of agarose to Fmoc-DIKVAV and Fmoc-FRGDF results in physical characteristics that are dependent on agarose concentration. The networks are peptide-dominated at low agarose concentrations, and agarose-dominated at high agarose concentrations, resulting in distinct changes in structural morphology. Interestingly, at mid-range agarose concentration, a hybrid network is formed with structural similarities to both peptide and agarose systems, demonstrating reinforced mechanical properties. Bioactive-LMWG polysaccharide hydrogels demonstrate controllable microenvironmental properties, providing the ability for tissue-specific biomaterial design for tissue engineering and 3D cell culture.

Kinetic modeling of phosphorylase-catalyzed iterative β-1,4-glycosylation for degree of polymerization-controlled synthesis of soluble cello-oligosaccharides

BACKGROUND

Cellodextrin phosphorylase (CdP; EC 2.4.1.49) catalyzes the iterative β-1,4-glycosylation of cellobiose using α-D-glucose 1-phosphate as the donor substrate. Cello-oligosaccharides (COS) with a degree of polymerization (DP) of up to 6 are soluble while those of larger DP self-assemble into solid cellulose material. The soluble COS have attracted considerable attention for their use as dietary fibers that offer a selective prebiotic function. An efficient synthesis of soluble COS requires good control over the DP of the products formed. A mathematical model of the iterative enzymatic glycosylation would be important to facilitate target-oriented process development.

RESULTS

A detailed time-course analysis of the formation of COS products from cellobiose (25 mM, 50 mM) and α-D-glucose 1-phosphate (10-100 mM) was performed using the CdP from Clostridium cellulosi. A mechanism-based, Michaelis-Menten type mathematical model was developed to describe the kinetics of the iterative enzymatic glycosylation of cellobiose. The mechanistic model was combined with an empirical description of the DP-dependent self-assembly of the COS into insoluble cellulose. The hybrid model thus obtained was used for kinetic parameter determination from time-course fits performed with constraints derived from initial rate data. The fitted hybrid model provided excellent description of the experimental dynamics of the COS in the DP range 3-6 and also accounted for the insoluble product formation. The hybrid model was suitable to disentangle the complex relationship between the process conditions used (i.e., substrate concentration, donor/acceptor ratio, reaction time) and the reaction output obtained (i.e., yield and composition of soluble COS). Model application to a window-of-operation analysis for the synthesis of soluble COS was demonstrated on the example of a COS mixture enriched in DP 4.

CONCLUSIONS

The hybrid model of CdP-catalyzed iterative glycosylation is an important engineering tool to study and optimize the biocatalytic synthesis of soluble COS. The kinetic modeling approach used here can be of a general interest to be applied to other iteratively catalyzed enzymatic reactions of synthetic importance.

The Lack of a Representative Tendinopathy Model Hampers Fundamental Mesenchymal Stem Cell Research

Overuse tendon injuries are a major cause of musculoskeletal morbidity in both human and equine athletes, due to the cumulative degenerative damage. These injuries present significant challenges as the healing process often results in the formation of inferior scar tissue. The poor success with conventional therapy supports the need to search for novel treatments to restore functionality and regenerate tissue as close to native tendon as possible. Mesenchymal stem cell (MSC)-based strategies represent promising therapeutic tools for tendon repair in both human and veterinary medicine. The translation of tissue engineering strategies from basic research findings, however, into clinical use has been hampered by the limited understanding of the multifaceted MSC mechanisms of action. In vitro models serve as important biological tools to study cell behavior, bypassing the confounding factors associated with in vivo experiments. Controllable and reproducible in vitro conditions should be provided to study the MSC healing mechanisms in tendon injuries. Unfortunately, no physiologically representative tendinopathy models exist to date. A major shortcoming of most currently available in vitro tendon models is the lack of extracellular tendon matrix and vascular supply. These models often make use of synthetic biomaterials, which do not reflect the natural tendon composition. Alternatively, decellularized tendon has been applied, but it is challenging to obtain reproducible results due to its variable composition, less efficient cell seeding approaches and lack of cell encapsulation and vascularization. The current review will overview pros and cons associated with the use of different biomaterials and technologies enabling scaffold production. In addition, the characteristics of the ideal, state-of-the-art tendinopathy model will be discussed. Briefly, a representative in vitro tendinopathy model should be vascularized and mimic the hierarchical structure of the tendon matrix with elongated cells being organized in a parallel fashion and subjected to uniaxial stretching. Incorporation of mechanical stimulation, preferably uniaxial stretching may be a key element in order to obtain appropriate matrix alignment and create a pathophysiological model. Together, a thorough discussion on the current status and future directions for tendon models will enhance fundamental MSC research, accelerating translation of MSC therapies for tendon injuries from bench to bedside.

Biomolecular interactions of ultrasmall metallic nanoparticles and nanoclusters

The use of nanoparticles (NPs) in biomedicine has made a gradual transition from proof-of-concept to clinical applications, with several NP types meeting regulatory approval or undergoing clinical trials. A new type of metallic nanostructures called ultrasmall nanoparticles (usNPs) and nanoclusters (NCs), while retaining essential properties of the larger (classical) NPs, have features common to bioactive proteins. This combination expands the potential use of usNPs and NCs to areas of diagnosis and therapy traditionally reserved for small-molecule medicine. Their distinctive physicochemical properties can lead to unique in vivo behaviors, including improved renal clearance and tumor distribution. Both the beneficial and potentially deleterious outcomes (cytotoxicity, inflammation) can, in principle, be controlled through a judicious choice of the nanocore shape and size, as well as the chemical ligands attached to the surface. At present, the ability to control the behavior of usNPs is limited, partly because advances are still needed in nanoengineering and chemical synthesis to manufacture and characterize ultrasmall nanostructures and partly because our understanding of their interactions in biological environments is incomplete. This review addresses the second limitation. We review experimental and computational methods currently available to understand molecular mechanisms, with particular attention to usNP-protein complexation, and highlight areas where further progress is needed. We discuss approaches that we find most promising to provide relevant molecular-level insight for designing usNPs with specific behaviors and pave the way to translational applications.

Does polysaccharide glycogen behave as a promoter of amyloid fibril formation at physiologically relevant concentrations?

We investigated the influence of glycogen (GG), phytoglycogen (PG), mannan (MAN) and cinnamoyl-modified GG (GG-CIN) on amyloid fibril formation. We used hen egg-white lysozyme (HEWL) as a model system and amyloid beta peptide (1-42) (Aβ1-42) as an Alzheimer's disease-relevant system. For brief detection of fibrils was used thioflavin T (ThT) fluorescence assay and the results were confirmed by transmission electron microscopy (TEM). We also deal with the interaction of polysaccharides and HEWL with isothermal titration calorimetry (ITC) and dynamic light scattering (DLS). We found that all polysaccharides accelerated the formation of amyloid fibrils from both HEWL and Aβ1-42. At high but physiologically relevant concentrations of GG, amyloid fibril formation was extremely accelerated for HEWL. Therefore, on the basis of the herein presented in vitro data, we hypothesize, that dietary d-glucose intake may influence amyloid fibril formation not only by influencing regulatory pathways, but also by direct glycogen-amyloid precursor protein molecular interaction, as glycogen levels in tissues are highly dependent on d-glucose intake.

Aqueous Suspensions of Cellulose Oligomer Nanoribbons for Growth and Natural Filtration-Based Separation of Cancer Spheroids

In vitro growth of cancer spheroids (CSs) and the subsequent separation of CSs from a 2D or 3D cell culture system are important for fundamental cancer studies and cancer drug screening. Although biopolymer-based or synthetic hydrogels are suitable candidates to be used as 3D cell culture scaffolds, alternatives with better processing capabilities are still required to set up cell culture microenvironment. In this study, we show that aqueous suspensions of crystalline nanoribbons composed of cellulose oligomers have a potential for CS growth and separation. The nanoribbon suspensions in serum-containing cell culture media fixed single cancer cells and CSs with large sizes in a 3D space, leading to suspension cultures for CS growth corresponding to culture time. Well-grown CSs were easily separated from the suspensions by natural filtration using a mesh filter with a suitable pore size. Cell viability tests revealed negligible cytotoxicity of the nanoribbons. In addition, physical damages to CSs by the separation procedures were negligible. Stable suspensions of biocompatible nanomaterials will thus provide novel microenvironments for growth and separation of diverse cell aggregates.

Mineralized DNA-collagen complex-based biomaterials for bone tissue engineering

DNA is a highly polyanionic biomolecule that complexes with both collagen and hydroxyapatite. By combining these complexes, we synthesized nucleic-acid collagen complexes (NACC) mineralized with hydroxyapatite. The composite complexes were made using a short, monodisperse single-stranded DNA, type I collagen, and mineralizing medium. They rapidly self-assembled into both mineralized NACC microfibers and 3D NACC gels. At the nanoscale, these complexes are hierarchical, interwoven, curly nanofibrils resembling native extracellular matrix, which mineralized an interpenetrating nanocrystalline hydroxyapatite phase. Mineralization was able to be done either before or after NACC formation enabling temporal control of the process. In response to the NACC material, primary human osteoblasts took on an osteocyte-like morphology. Moreover, the cells agglomerated and remodeled the NACC gels into densified, tissue-like structures within 3 days. NACC fibers and gels have promise not only as osteoconductive coatings and scaffolds, but as coatings and scaffolds for any tissue using this new form of naturally-derived biomaterials.

Phosphorylase-catalyzed bottom-up synthesis of short-chain soluble cello-oligosaccharides and property-tunable cellulosic materials

Cellulose-based materials are produced industrially in countless varieties via top-down processing of natural lignocellulose substrates. By contrast, cellulosic materials are only rarely prepared via bottom up synthesis and oligomerization-induced self-assembly of cellulose chains. Building up a cellulose chain via precision polymerization is promising, however, for it offers tunability and control of the final chemical structure. Synthetic cellulose derivatives with programmable material properties might thus be obtained. Cellodextrin phosphorylase (CdP; EC 2.4.1.49) catalyzes iterative β-1,4-glycosylation from α-d-glucose 1-phosphate, with the ability to elongate a diversity of acceptor substrates, including cellobiose, d-glucose and a range of synthetic glycosides having non-sugar aglycons. Depending on the reaction conditions leading to different degrees of polymerization (DP), short-chain soluble cello-oligosaccharides (COS) or insoluble cellulosic materials are formed. Here, we review the characteristics of CdP as bio-catalyst for synthetic applications and show advances in the enzymatic production of COS and reducing end-modified, tailored cellulose materials. Recent studies reveal COS as interesting dietary fibers that could provide a selective prebiotic effect. The bottom-up synthesized celluloses involve chains of DP ≥ 9, as precipitated in solution, and they form ~5 nm thick sheet-like crystalline structures of cellulose allomorph II. Solvent conditions and aglycon structures can direct the cellulose chain self-assembly towards a range of material architectures, including hierarchically organized networks of nanoribbons, or nanorods as well as distorted nanosheets. Composite materials are also formed. The resulting materials can be useful as property-tunable hydrogels and feature site-specific introduction of functional and chemically reactive groups. Therefore, COS and cellulose obtained via bottom-up synthesis can expand cellulose applications towards product classes that are difficult to access via top-down processing of natural materials.

Confined Microenvironments from Thermoresponsive Dendronized Polymers

Confined microenvironments in biomacromolecules arising from molecular crowding account for their well-defined biofunctions and bioactivities. To mimick this, synthetic polymers to form confined structures or microenvironments are of key scientific value, which have received significant attention recently. To create synthetic confined microenvironments, molecular crowding effects and topological cooperative effects have been applied successfully, and the key is balance between self-association of structural units and self-repulsion from crowding-induced steric hindrance. In this article, formation of confined microenvironments from stimuli-responsive dendronized polymers carrying densely dendritic oligoethylene glycols (OEGs) moieties in their pendants is presented. These wormlike thick macromolecules exhibit characteristic thermoresponsive properties, which can provide constrained microenvironments to encapsulate effectively guest molecules including dyes, proteins, or nucleic acids to prevent their protonation or biodegradation. This efficient shielding effect can also mediate chemical reactions in aqueous phase, and even enhance chirality transferring efficiency. All of these can be switched off simply through the thermally-induced dehydration and collapse of OEG dendrons due to the amphiphilicity of OEG chains. Furthermore, the switchable encapsulation and release of guests can be greatly enhanced when these dendronized polymers are used as major constituents for fabricating bulk hydrogels or nanogels, which provide a higher-level confinement.

Depletion-driven morphological transitions in hexagonal crystallites of virus rods

The assembly of nanometer-sized building blocks into complex morphologies is not only of fundamental interest but also plays a key role in material science and nanotechnology. We show that the shape of self-assembled superstructures formed by rod-like viruses can be controlled by tuning the attraction via the depletion interaction between the rods. Using non-adsorbing polymers as a depleting agent, we demonstrate that a hierarchical unidimensional self-organization into crystalline clusters emerges progressively upon increasing depletion attraction and enhanced growth kinetics. We observe a polymorphic change proceeding from two-dimensional (2D) crystalline monolayers at weak depletion to one-dimensional (1D) columnar fibers at strong depletion, via the formation of smectic fibrils at intermediate depletion strength. A simple theory for reversible polymerization enables us to determine the typical bond energy between monomeric units making up the smectic fibrils. We also demonstrate that gentle flow-assistance can be used to template filament-like structures into highly aligned supported films. Our results showcase a generic bottom-up approach for tuning the morphology of crystalline superstructures through modification of the interaction between non-spherical building blocks. This provides a convenient pathway for controlling self-organization, dimensionality and structure-formation of anisotropic nanoparticles for use in nanotechnology and functional materials.

Biocatalytic oligomerization-induced self-assembly of crystalline cellulose oligomers into nanoribbon networks assisted by organic solvents

Crystalline poly- and oligosaccharides such as cellulose can form extremely robust assemblies, whereas the construction of self-assembled materials from such molecules is generally difficult due to their complicated chemical synthesis and low solubility in solvents. Enzyme-catalyzed oligomerization-induced self-assembly has been shown to be promising for creating nanoarchitectured crystalline oligosaccharide materials. However, the controlled self-assembly into organized hierarchical structures based on a simple method is still challenging. Herein, we demonstrate that the use of organic solvents as small-molecule additives allows for control of the oligomerization-induced self-assembly of cellulose oligomers into hierarchical nanoribbon network structures. In this study, we dealt with the cellodextrin phosphorylase-catalyzed oligomerization of phosphorylated glucose monomers from ᴅ-glucose primers, which produce precipitates of nanosheet-shaped crystals in aqueous solution. The addition of appropriate organic solvents to the oligomerization system was found to result in well-grown nanoribbon networks. The organic solvents appeared to prevent irregular aggregation and subsequent precipitation of the nanosheets via solvation for further growth into the well-grown higher-order structures. This finding indicates that small-molecule additives provide control over the self-assembly of crystalline oligosaccharides for the creation of hierarchically structured materials with high robustness in a simple manner.

Assembly of reduced graphene oxides into a three-dimensional porous structure via confinement within robust cellulose oligomer networks

The assembly of nanomaterials into a networked superstructure is a strategy used to construct macroscopic porous materials having the functional properties of nanomaterials. However, because nanomaterials generally prefer densely packed assembled states owing to their high surface energies, the construction of a fine porous structure is still a challenge. In this study, we demonstrate the assembly of reduced graphene oxides (rGOs) into a fine porous structure via confinement within robust cellulose oligomer networks. The confinement of rGOs within cellulose oligomer networks was achieved in one step via the enzymatic synthesis of cellulose oligomers. When the resultant cellulose oligomer gels confining rGOs were reduced by hydrogen iodide, the robust cellulose oligomer networks served as a confinement space for rGOs, preventing excessive aggregation of the rGOs and thus encouraging their assembly into a fine porous structure. Electrochemical measurements revealed that the porous rGO materials could act as electrode materials for supercapacitors. Our strategy based on simple physical confinement will allow for the creation of functional porous materials with excellent nanomorphologies from various nanomaterials.

Reduced graphene oxides were assembled into a fine porous structure via confinement within robust cellulose oligomer networks.