Nanofibrillar cellulose hydrogel promotes three-dimensional liver cell culture

Poro-elasto-capillary wicking of cellulose sponges

We mundanely observe cellulose (kitchen) sponges swell while absorbing water. Fluid flows in deformable porous media, such as soils and hydrogels, are classically described on the basis of the theories of Darcy and poroelasticity, where the expansion of media arises due to increased pore pressure. However, the situation is qualitatively different in cellulosic porous materials like sponges because the pore expansion is driven by wetting of the surrounding cellulose walls rather than by increase of the internal pore pressure. We address a seemingly so simple but hitherto unanswered question of how fast water wicks into the swelling sponge. Our experiments uncover a power law of the wicking height versus time distinct from that for nonswelling materials. The observation using environmental scanning electron microscopy reveals the coalescence of microscale wall pores with wetting, which allows us to build a mathematical model for pore size evolution and the consequent wicking dynamics. Our study sheds light on the physics of water absorption in hygroscopically responsive multiscale porous materials, which have far more implications than everyday activities (for example, cleaning, writing, and painting) carried out with cellulosic materials (paper and sponge), including absorbent hygiene products, biomedical cell cultures, building safety, and cooking.

Engineering 3D Hydrogels for Personalized In Vitro Human Tissue Models

There is a growing interest in engineering hydrogels for 3D tissue and disease models. The major motivation is to better mimic the physiological microenvironment of the disease and human condition. 3D tissue models derived from patients' own cells can potentially revolutionize the way treatment and diagnostic alternatives are developed. This requires development of tissue mimetic hydrogels with user defined and tunable properties. In this review article, a recent summary of 3D hydrogel platforms for in vitro tissue and disease modeling is given. Hydrogel design considerations and available hydrogel systems are summarized, followed by the types of currently available hydrogel models, such as bulk hydrogels, porous scaffolds, fibrous scaffolds, hydrogel microspheres, hydrogel sandwich systems, microwells, and 3D bioprinted constructs. Although hydrogels are utilized for a wide range of tissue models, this article focuses on liver and cancer models. This article also provides a detailed section on current challenges and future perspectives of hydrogel-based tissue models.

Engineering Biocompatible Hydrogels from Bicomponent Natural Nanofibers for Anticancer Drug Delivery

Natural hydrogels have attracted extensive research interest and shown great potential for many biomedical applications. In this study, a series of biocompatible hydrogels was reported based on the self-assembly of positively charged partially deacetylated α-chitin nanofibers (α-DECHN) and negatively charged 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-oxidized cellulose nanofibers (TOCNF) for anticancer drug delivery. The formation mechanisms of the α-DECHN/TOCNF hydrogels with different mixing proportions were studied, and their morphological, mechanical, and swelling properties were comprehensively investigated. Additionally, the drug delivery performance of the hydrogels was compared via sustained release test of an anticancer drug (5-fluorouracil). The results showed that the hydrogel with higher physical cross-linking degree exhibited a higher drug loading efficiency and drug release percentage.

Self-Assembly of Cellulose Oligomers into Nanoribbon Network Structures Based on Kinetic Control of Enzymatic Oligomerization

The ability to chemically synthesize desired molecules followed by their in situ self-assembly in reaction solution has attracted much attention as a simple and environmentally friendly method to produce self-assembled nanostructures. In this study, α-d-glucose 1-phosphate monomers and cellobiose primers were subjected to cellodextrin phosphorylase-catalyzed reverse phosphorolysis reactions in aqueous solution in order to synthesize cellulose oligomers, which were then in situ self-assembled into crystalline nanoribbon network structures. The average degree-of-polymerization (DP) values of the cellulose oligomers were estimated to be approximately 7-8 with a certain degree of DP distribution. The cellulose oligomers crystallized with the cellulose II allomorph appeared to align perpendicularly to the base plane of the nanoribbons in an antiparallel manner. Detailed analyses of reaction time dependence suggested that the production of nanoribbon network structures was kinetically controlled by the amount of water-insoluble cellulose oligomers produced.

Engineered Paper-Based Cell Culture Platforms

Paper is used in various applications in biomedical research including diagnostics, separations, and cell cultures. Paper can be conveniently engineered due to its tunable and flexible nature, and is amenable to high-throughput sample preparation and analysis. Paper-based platforms are used to culture primary cells, tumor cells, patient biopsies, stem cells, fibroblasts, osteoblasts, immune cells, bacteria, fungi, and plant cells. These platforms are compatible with standard analytical assays that are typically used to monitor cell behavior. Due to its thickness and porous nature, there are no mass transport limitations to/from the cells in paper scaffolds. It is possible to pattern paper in different scales (micrometer to centimeter), generate modular configurations in 3D, fabricate multicellular and compartmentalized tissue mimetics for clinical applications, and recover cells from the scaffolds for further analysis. 3D paper constructs can provide physiologically relevant tissue models for personalized medicine. Layer-by layer strategies to assemble tissue-like structures from low-cost and biocompatible paper-based materials offer unique opportunities that include understanding fundamental biology, developing disease models, and assembling different tissues for organ-on-paper applications. Paper-based platforms can also be used for origami-inspired tissue engineering. This work provides an overview of recent progress in engineered paper-based biomaterials and platforms to culture and analyze cells.

Nanocellulose as a sustainable biomass material: structure, properties, present status and future prospects in biomedical applications

Nanocellulose, extracted from the most abundant biomass material cellulose, has proved to be an environmentally friendly material with excellent mechanical performance owing to its unique nano-scaled structure, and has been used in a variety of applications as engineering and functional materials. The great biocompatibility and biodegradability, in particular, render nanocellulose promising in biomedical applications. In this review, the structure, treatment technology and properties of three different nanocellulose categories, i.e., nanofibrillated cellulose (NFC), nanocrystalline cellulose (NCC) and bacterial nanocellulose (BNC), are introduced and compared. The cytotoxicity, biocompatibility and frontier applications in biomedicine of the three nanocellulose categories were the focus and are detailed in each section. Future prospects concerning the cytotoxicity, applications and industrial production of nanocellulose are also discussed in the last section.

Mechanically Tunable Bioink for 3D Bioprinting of Human Cells

This study introduces a thermogelling bioink based on carboxylated agarose (CA) for bioprinting of mechanically defined microenvironments mimicking natural tissues. In CA system, by adjusting the degree of carboxylation, the elastic modulus of printed gels can be tuned over several orders of magnitudes (5-230 Pa) while ensuring almost no change to the shear viscosity (10-17 mPa) of the bioink solution; thus enabling the fabrication of 3D structures made of different mechanical domains under identical printing parameters and low nozzle shear stress. Human mesenchymal stem cells printed using CA as a bioink show significantly higher survival (95%) in comparison to when printed using native agarose (62%), a commonly used thermogelling hydrogel for 3D-bioprinting applications. This work paves the way toward the printing of complex tissue-like structures composed of a range of mechanically discrete microdomains that could potentially reproduce natural mechanical aspects of functional tissues.

Nanofibrillar cellulose-alginate hydrogel coated surgical sutures as cell-carrier systems

Hydrogel nanomaterials, especially those that are of non-human and non-animal origins, have great potential in biomedical and pharmaceutical sciences due to their versatility and inherent soft-tissue like properties. With the ability to simulate native tissue function, hydrogels are potentially well suited for cellular therapy applications. In this study, we have fabricated nanofibrillar cellulose-alginate (NFCA) suture coatings as biomedical devices to help overcome some of the limitations related to cellular therapy, such as low cell survivability and distribution out of target tissue. The addition of sodium alginate 8% (w/v) increased the NFCA hydrogel viscosity, storage and loss moduli by slightly under one order of magnitude, thus contributing significantly to coating strength. Confocal microscopy showed nearly 100% cell viability throughout the 2-week incubation period within and on the surface of the coating. Additionally, typical morphologies in the dual cell culture of spheroid forming HepG2 and monolayer type SK-HEP-1 were observed. Twelve out of 14 NFCA coated surgical sutures remained intact during the suturing operation with various mice and rat tissue; however, partial peeling off was observed in 2 of the coated sutures. We conclude that NFCA suture coatings could perform as cell-carrier systems for cellular based therapy and post-surgical treatment.

Smart Carriers and Nanohealers: A Nanomedical Insight on Natural Polymers

Biodegradable polymers are popularly being used in an increasing number of fields in the past few decades. The popularity and favorability of these materials are due to their remarkable properties, enabling a wide range of applications and market requirements to be met. Polymer biodegradable systems are a promising arena of research for targeted and site-specific controlled drug delivery, for developing artificial limbs, 3D porous scaffolds for cellular regeneration or tissue engineering and biosensing applications. Several natural polymers have been identified, blended, functionalized and applied for designing nanoscaffolds and drug carriers as a prerequisite for enumerable bionano technological applications. Apart from these, natural polymers have been well studied and are widely used in material science and industrial fields. The present review explains the prominent features of commonly used natural polymers (polysaccharides and proteins) in various nanomedical applications and reveals the current status of the polymer research in bionanotechnology and science sectors.

Multicellular dosimetric chain for molecular radiotherapy exemplified with dose simulations on 3D cell spheroids

PURPOSE

Absorbed radiation dose-response relationships are not clear in molecular radiotherapy (MRT). Here, we propose a voxel-based dose calculation system for multicellular dosimetry in MRT. We applied confocal microscope images of a spherical cell aggregate i.e. a spheroid, to examine the computation of dose distribution within a tissue from the distribution of radiopharmaceuticals.

METHODS

A confocal microscope Z-stack of a human hepatocellular carcinoma HepG2 spheroid was segmented using a support-vector machine algorithm and a watershed function. Heterogeneity in activity uptake was simulated by selecting a varying amount of the cell nuclei to contain ¹¹¹In, ¹²⁵I, or ¹⁷⁷Lu. Absorbed dose simulations were carried out using vxlPen, a software application based on the Monte Carlo code PENELOPE.

RESULTS

We developed a schema for radiopharmaceutical dosimetry. The schema utilizes a partially supervised segmentation method for cell-level image data together with a novel main program for voxel-based radiation dose simulations. We observed that for ¹⁷⁷Lu, radiation cross-fire enabled full dose coverage even if the radiopharmaceutical had accumulated to only 60% of the spheroid cells. This effect was not found with ¹¹¹In and ¹²⁵I. Using these Auger/internal conversion electron emitters seemed to guarantee that only the cells with a high enough activity uptake will accumulate a lethal amount of dose, while neighboring cells are spared.

CONCLUSIONS

We computed absorbed radiation dose distributions in a 3D-cultured cell spheroid with a novel multicellular dosimetric chain. Combined with pharmacological studies in different tissue models, our cell-level dosimetric calculation method can clarify dose-response relationships for radiopharmaceuticals used in MRT.

Hydrogels for Biomedical Applications: Cellulose, Chitosan, and Protein/Peptide Derivatives

Hydrogels based on polysaccharide and protein natural polymers are of great interest in biomedical applications and more specifically for tissue regeneration and drug delivery. Cellulose, chitosan (a chitin derivative), and collagen are probably the most important components since they are the most abundant natural polymers on earth (cellulose and chitin) and in the human body (collagen). Peptides also merit attention because their self-assembling properties mimic the proteins that are present in the extracellular matrix. The present review is mainly focused on explaining the recent advances on hydrogels derived from the indicated polymers or their combinations. Attention has also been paid to the development of hydrogels for innovative biomedical uses. Therefore, smart materials displaying stimuli responsiveness and having shape memory properties are considered. The use of micro- and nanogels for drug delivery applications is also discussed, as well as the high potential of protein-based hydrogels in the production of bioactive matrices with recognition ability (molecular imprinting). Finally, mention is also given to the development of 3D bioprinting technologies.

Polysaccharide matrices used in 3D in vitro cell culture systems

Polysaccharides comprise a diverse class of polymeric materials with a history of proven biocompatibility and continual use as biomaterials. Recent focus on new matrices appropriate for three-dimensional (3D) cell culture offers new opportunities to apply polysaccharides as extracellular matrix mimics. However, chemical and structural bases for specific cell-polysaccharide interactions essential for their utility as 3-D cell matrices are not well defined. This review describes how these naturally sourced biomaterials satisfy several key properties for current 3D cell culture needs and can also be synthetically modified or blended with additional components to tailor their cell engagement properties. Beyond their benign interactions with many cell types in cultures, their economical and high quality sourcing, optical clarity for ex situ analytical interrogation and in situ gelation represent important properties of these polymers for 3D cell culture applications. Continued diversification of their versatile glycan chemistry, new bio-synthetic sourcing strategies and elucidation of new cell-specific properties are attractive to expand the polysaccharide polymer utility for cell culture needs. Many 3D cell culture priorities are addressed with the portfolio of polysaccharide materials available and under development. This review provides a critical analysis of their properties, capabilities and challenges in 3D cell culture applications.

Ultrastrong and Bioactive Nanostructured Bio-Based Composites

Nature's design of functional materials relies on smart combinations of simple components to achieve desired properties. Silk and cellulose are two clever examples from nature-spider silk being tough due to high extensibility, whereas cellulose possesses unparalleled strength and stiffness among natural materials. Unfortunately, silk proteins cannot be obtained in large quantities from spiders, and recombinant production processes are so far rather expensive. We have therefore combined small amounts of functionalized recombinant spider silk proteins with the most abundant structural component on Earth (cellulose nanofibrils (CNFs)) to fabricate isotropic as well as anisotropic hierarchical structures. Our approach for the fabrication of bio-based anisotropic fibers results in previously unreached but highly desirable mechanical performance with a stiffness of ∼55 GPa, strength at break of ∼1015 MPa, and toughness of ∼55 MJ m^-3. We also show that addition of small amounts of silk fusion proteins to CNF results in materials with advanced biofunctionalities, which cannot be anticipated for the wood-based CNF alone. These findings suggest that bio-based materials provide abundant opportunities to design composites with high strength and functionalities and bring down our dependence on fossil-based resources.

Cellulose Nanofibers from Softwood, Hardwood, and Tunicate: Preparation-Structure-Film Performance Interrelation

This work reveals the structural variations of cellulose nanofibers (CNF) prepared from different cellulose sources, including softwood (Picea abies), hardwood (Eucalyptus grandis × E. urophylla), and tunicate (Ciona intestinalis), using different preparation processes and their correlations to the formation and performance of the films prepared from the CNF. Here, the CNF are prepared from wood chemical pulps and tunicate isolated cellulose by an identical homogenization treatment subsequent to either an enzymatic hydrolysis or a 2,2,6,6-tetramethylpiperidinyl-1-oxyl (TEMPO)-mediated oxidation. They show a large structural diversity in terms of chemical, morphological, and crystalline structure. Among others, the tunicate CNF consist of purer cellulose and have a degree of polymerization higher than that of wood CNF. Introduction of surface charges via the TEMPO-mediated oxidation is found to have significant impacts on the structure, morphology, optical, mechanical, thermal, and hydrophobic properties of the prepared films. For example, the film density is closely related to the charge density of the used CNF, and the tensile stress of the films is correlated to the crystallinity index of the CNF. In turn, the CNF structure is determined by the cellulose sources and the preparation processes. This study provides useful information and knowledge for understanding the importance of the raw material for the quality of CNF for various types of applications.

Selective Expansion of Skeletal Muscle Stem Cells from Bulk Muscle Cells in Soft Three-Dimensional Fibrin Gel

Muscle stem cells (MuSCs) exhibit robust myogenic potential in vivo, thus providing a promising curative treatment for muscle disorders. Ex vivo expansion of adult MuSCs is highly desired to achieve a therapeutic cell dose because of their scarcity in limited muscle biopsies. Sorting of pure MuSCs is generally required for all the current culture systems. Here we developed a soft three‐dimensional (3D) salmon fibrin gel culture system that can selectively expand mouse MuSCs from bulk skeletal muscle preparations without cell sorting and faithfully maintain their regenerative capacity in culture. Our study established a novel platform for convenient ex vivo expansion of MuSCs, thus greatly advancing stem cell‐based therapies for various muscle disorders. Stem Cells Translational Medicine2017;6:1412–1423

Hydrogels for Biomedical Applications: Their Characteristics and the Mechanisms behind Them

Hydrogels are hydrophilic, three-dimensional networks that are able to absorb large quantities of water or biological fluids, and thus have the potential to be used as prime candidates for biosensors, drug delivery vectors, and carriers or matrices for cells in tissue engineering. In this critical review article, advantages of the hydrogels that overcome the limitations from other types of biomaterials will be discussed. Hydrogels, depending on their chemical composition, are responsive to various stimuli including heating, pH, light, and chemicals. Two swelling mechanisms will be discussed to give a detailed understanding of how the structure parameters affect swelling properties, followed by the gelation mechanism and mesh size calculation. Hydrogels prepared from natural materials such as polysaccharides and polypeptides, along with different types of synthetic hydrogels from the recent reported literature, will be discussed in detail. Finally, attention will be given to biomedical applications of different kinds of hydrogels including cell culture, self-healing, and drug delivery.

In vitro biological responses to nanofibrillated cellulose by human dermal, lung and immune cells: surface chemistry aspect

BACKGROUND

Nanocellulose, and particularly nanofibrillated cellulose (NFC), has been proposed for a diversity of applications in industry and in the biomedical field. Its unique physicochemical and structural features distinguish nanocellulose from traditional materials and enable its use as an advance nanomaterial. However, its nanoscale features may induce unknown biological responses. Limited studies with NFC are available and the biological impacts of its use have not been thoroughly explored. This study assesses the in vitro biological responses elicited by wood-derived NFC gels, when human dermal fibroblasts, lung MRC-5 cells and THP-1 macrophage cells are exposed to the nanomaterial. Furthermore, whether the presence of surface charged groups (i.e. carboxymethyl and hydroxypropyltrimethylammonium groups) on NFC can induce distinct biological responses is investigated.

RESULTS

The introduction of surface charged groups resulted in individual nanofibrils, while fibril aggregates predominated in the unmodified NFC gel suspensions as observed by transmission electron microscopy. In the presence of proteins, the surface modified NFCs formed compact agglomerates while the agglomeration pattern of the unmodified NFC was similar in the presence of proteins and in physiological buffer. Unmodified and modified NFC gels did not induce cytotoxicity in human dermal fibroblasts, lung and macrophage cells. No significant ROS production by THP-1 macrophages was found and no cellular uptake was observed. However, an inflammatory response was detected when THP-1 macrophages were treated with unmodified NFC as assessed by an increase in TNF-α and IL1-β levels, an effect that was absent when surface charged groups were introduced into NFC.

CONCLUSIONS

Taken together, the data presented here show the absence of cytotoxic effects associated with the exposure to unmodified, carboxymethylated and hydroxypropyltrimethylammonium-modified NFCs. Unmodified NFC presented a pro-inflammatory effect which can be further moderated by introducing surface modifications such as carboxymethyl and hydroxypropyltrimethylammonium groups into the nanofibrils. The present findings suggest that the inflammatory response to NFC might be driven by the material surface chemistry, and thus open up for the possibility of designing safe nanocellulose materials.

Mineralization potential of cellulose-nanofibrils reinforced gelatine scaffolds for promoted calcium deposition by mesenchymal stem cells

Cellulose-nanofibrils (CNFs) enriched gelatine (GEL) scaffolds were fabricated in-situ by the combined freeze-thawing process and carbodiimide crosslinking chemistry. The original- and variously surface anionised CNFs (carboxylated/CNF-COOH/, and phosphonated with 3-AminoPropylphosphoric Acid/CNF-COOH-ApA/) were used in order to tune the scaffolds' biomimetic structure towards a more intensive mineralization process. The pore size reduction (from 208±35μm to 91±35μm) after 50% v/v of CNFs addition to GEL was identified, while separated pore-walls' alignment vs. shorter, dense and elongated pores are observed when using 80% v/v of original-CNFs vs. anionised-CNFs, all of them possessed osteoid-like compressive strength (0.025-0.40MPa) and elasticity (0.04-0.15MPa). While randomly distributed Ca²⁺-deficient hydroxyapatite/HAp/(Ca/P≈1.4) aggregates were identified in the case of original-CNF prevalent scaffolds after four weeks of incubation in SBF, the more uniform and intensified deposition with HAp-like (Ca/P≈1.69) structures were established using CNF-COOH-Apa. The growth of Mesenchymal Stem Cells (MSCs) was observed on all CNF-containing scaffolds, resulting in more extensive Ca²⁺ deposition compared to the positive control or pure GEL scaffold. Among them, the scaffold prepared with the 50% v/v CNF-COOH-ApA showed significantly increased mineralization kinetic as well as the capacity for bone-like patterning in bone tissue regeneration.

Native cellulose nanofibrills induce immune tolerance in vitro by acting on dendritic cells

Cellulose nanofibrills (CNFs) are attractive biocompatible, natural nanomaterials for wide biomedical applications. However, the immunological mechanisms of CNFs have been poorly investigated. Considering that dendritic cells (DCs) are the key immune regulatory cells in response to nanomaterials, our aim was to investigate the immunological mechanisms of CNFs in a model of DC-mediated immune response. We found that non-toxic concentrations of CNFs impaired the differentiation, and subsequent maturation of human monocyte-derived (mo)-DCs. In a co-culture with CD4⁺T cells, CNF-treated mo-DCs possessed a weaker allostimulatory and T helper (Th)1 and Th17 polarizing capacity, but a stronger capacity to induce Th2 cells and CD4⁺CD25^hiFoxP3^hi regulatory T cells. This correlated with an increased immunoglobulin-like transcript-4 and indolamine dioxygenase-1 expression by CNF-treated mo-DCs, following the partial internalization of CNFs and the accumulation of CD209 and actin bundles at the place of contacts with CNFs. Cumulatively, we showed that CNFs are able to induce an active immune tolerance by inducing tolerogenic DCs, which could be beneficial for the application of CNFs in wound healing and chronic inflammation therapies.

Regulation of Human Pluripotent Stem Cell-Derived Hepatic Cell Phenotype by Three-Dimensional Hydrogel Models

Human-induced pluripotent stem cell (hiPSC)-derived hepatocytes are anticipated as important surrogates for primary human hepatocytes in applications ranging from basic research to drug discovery and regenerative medicine. Although methods for differentiating hepatocyte-like cells (HLCs) from hiPSCs have developed remarkably, the limited yield of fully functional HLCs is still a major obstacle to their utility. A three-dimensional (3D) culture environment could improve the in vitro hepatic maturation of HLCs. Here we compare 3D hydrogel models of hiPSC-derived HLCs in agarose microwells (3D Petri Dish; 3DPD), nanofibrillar cellulose hydrogels (Growdex; 3DNFC), or animal extracellular matrix-based hydrogels (3D Matrigel; 3DMG). In all the tested 3D biomaterial systems, HLCs formed aggregates. In comparison with two-dimensional monolayer culture, 3DPD and 3DMG models showed both phenotypic and functional enhancement in HLCs over 2.5 weeks of 3D culture. Specifically, we found higher hepatocyte-specific gene expression levels and enhanced cytochrome P450 functions. Our work suggests that transferring HLCs into 3D hydrogel systems can expedite the hepatic maturation of HLCs irrespective of the biochemical nature of the 3D hydrogel. Both plant-based nonembedding and animal-based embedding 3D hydrogel models enhanced the maturation.

Biocompatibility of Subcutaneously Implanted Plant-Derived Cellulose Biomaterials

There is intense interest in developing novel biomaterials which support the invasion and proliferation of living cells for potential applications in tissue engineering and regenerative medicine. Decellularization of existing tissues have formed the basis of one major approach to producing 3D scaffolds for such purposes. In this study, we utilize the native hypanthium tissue of apples and a simple preparation methodology to create implantable cellulose scaffolds. To examine biocompatibility, scaffolds were subcutaneously implanted in wild-type, immunocompetent mice (males and females; 6-9 weeks old). Following the implantation, the scaffolds were resected at 1, 4 and 8 weeks and processed for histological analysis (H&E, Masson's Trichrome, anti-CD31 and anti-CD45 antibodies). Histological analysis revealed a characteristic foreign body response to the scaffold 1 week post-implantation. However, the immune response was observed to gradually disappear by 8 weeks post-implantation. By 8 weeks, there was no immune response in the surrounding dermis tissue and active fibroblast migration within the cellulose scaffold was observed. This was concomitant with the deposition of a new collagen extracellular matrix. Furthermore, active blood vessel formation within the scaffold was observed throughout the period of study indicating the pro-angiogenic properties of the native scaffolds. Finally, while the scaffolds retain much of their original shape they do undergo a slow deformation over the 8-week length of the study. Taken together, our results demonstrate that native cellulose scaffolds are biocompatible and exhibit promising potential as a surgical biomaterial.

Supramolecular Engineering of Hierarchically Self-Assembled, Bioinspired, Cholesteric Nanocomposites Formed by Cellulose Nanocrystals and Polymers

Natural composites are hierarchically structured by combination of ordered colloidal and molecular length scales. They inspire future, biomimetic, and lightweight nanocomposites, in which extraordinary mechanical properties are in reach by understanding and mastering hierarchical structure formation as tools to engineer multiscale deformation mechanisms. Here we describe a hierarchically self-assembled, cholesteric nanocomposite with well-defined colloid-based helical structure and supramolecular hydrogen bonds engineered on the molecular level in the polymer matrix. We use reversible addition-fragmentation transfer polymerization to synthesize well-defined hydrophilic, nonionic polymers with a varying functionalization density of 4-fold hydrogen-bonding ureidopyrimidinone (UPy) motifs. We show that these copolymers can be coassembled with cellulose nanocrystals (CNC), a sustainable, stiff, rod-like reinforcement, to give ordered cholesteric phases with characteristic photonic stop bands. The dimensions of the helical pitch are controlled by the ratio of polymer/CNC, confirming a smooth integration into the colloidal structure. With respect to the effect of the supramolecular motifs, we demonstrate that those regulate the swelling when exposing the biomimetic hybrids to water, and they allow engineering the photonic response. Moreover, the amount of hydrogen bonds and the polymer fraction are decisive in defining the mechanical properties. An Ashby plot comparing previous ordered CNC-based nanocomposites with our new hierarchical ones reveals that molecular engineering allows us to span an unprecedented mechanical property range from highest inelastic deformation (strain up to ∼13%) to highest stiffness (E ∼ 15 GPa) and combinations of both. We envisage that further rational design of the molecular interactions will provide efficient tools for enhancing the multifunctional property profiles of such bioinspired nanocomposites.

Development of nanocellulose scaffolds with tunable structures to support 3D cell culture

Swollen three-dimensional nanocellulose films and their resultant aerogels were prepared as scaffolds towards tissue engineering application. The nanocellulose hydrogels with various swelling degree (up to 500 times) and the resultant aerogels with desired porosity (porosity up to 99.7% and specific surface area up to 308m(2)/g) were prepared by tuning the nanocellulose charge density, the swelling media conditions, and the material processing approach. Representative cell-based assays were applied to assess the material biocompatibility and efficacy of the human extracellular matrix (ECM)-mimicking nanocellulose scaffolds. The effects of charge density and porosity of the scaffolds on the biological tests were investigated for the first time. The results reveal that the nanocellulose scaffolds could promote the survival and proliferation of tumor cells, and enhance the transfection of exogenous DNA into the cells. These results suggest the usefulness of the nanocellulose-based matrices in supporting crucial cellular processes during cell growth and proliferation.

Bioinspired Mechanical Gradients in Cellulose Nanofibril/Polymer Nanopapers

Mechanical gradients are important as tough joints, for strain field engineering in printable electronics, for actuators, and for biological studies, yet they are difficult to prepare and quantitatively characterize. We demonstrate the additive fabrication of gradient bioinspired nanocomposites based on stiff, renewable cellulose nanofibrils that are bottom-up toughened via a tailor-made copolymer. Direct filament writing of different nanocomposite hydrogels in patterns, and subsequent healing of the filaments into continuous films while drying leads to a variety of linear, parabolic and striped bulk gradients. In situ digital image correlation under tensile deformation reveals important differences in the strain fields regarding asymmetry and step heights of the patterns. We envisage that merging top-down and bottom-up structuring of nanocellulose hybrids opens avenues for aperiodic and multiscale, bioinspired nanocomposites with optimized combinations of stiffness and toughness.