Cellulose and collagen: from fibres to tissues

Three-Dimensional Meltblowing as a High-Speed Fabrication Process for Tendon Tissue Engineered Scaffolds

Rotator cuff tears continue to be a critical challenge for successful repair due to the formation of fibrotic scar tissue during healing. Tendon tissue engineering seeks to improve these outcomes using nonwoven fabrication methods to produce biomimetic scaffolds. Meltblowing has several advantages over other nonwoven approaches including non-toxic fabrication processes and being high-throughput and economical, while accurately producing fiber diameters comparable to native tendon microstructure. Recently 3D meltblowing (3DMB) introduced high degrees of tunability to the core process, allowing for production of highly aligned fiber mats at anatomically relevant dimensions. Here, we evaluated 3DMB scaffolds fabricated using poly-L-lactic acid (PLA) and poly-ε-caprolactone (PCL) by characterizing scaffold properties before and after culture with human adipose stem cells (hASCs). Mechanical and fiber characterization of 3DMB scaffolds closely resembled tendon microarchitecture by exhibiting high fiber alignment and mechanical anisotropy. hASC-seeded 3DMB scaffolds after 28 days of culture proliferated and deposited aligned tendon-like extracellular matrix. Furthermore, cell culture enhanced the Young's modulus of PLA 3DMB scaffolds and improved yield stress, yield stretch, and stiffness of both 3DMB scaffolds. The proteome of cultured 3DMB scaffolds increased expression of tendon-related proteins after 28 days of culture, but polymer-dependent differences in glycoprotein composition was observed. Together, 3DMB is a promising method for tendon tissue engineering, by showing improved fiber and mechanical properties compared to meltblown scaffolds. However, while an improvement on prior iterations, continued development of this 3DMB technology is needed to better mimic the mechanical properties and biologic composition of native tendon.

Tough Cortical Bone-Inspired Tubular Architected Cement-Based Material with Disorder

Cortical bone is a tough biological material composed of tube-like osteons embedded in the organic matrix surrounded by weak interfaces known as cement lines. The cement lines provide a microstructurally preferable crack path, hence triggering in-plane crack deflection around osteons due to cement line-crack interaction. Inspired by this toughening mechanism and facilitated by a hybrid (3D-printing/casting) process, the study engineers architected tubular cement-based materials with the stepwise cracking toughening mechanism, that enables a non-brittle fracture. Using experimental and theoretical approaches, the study demonstrates the competition between tube size and shape on stress intensity factor from which engineering stepwise cracking can emerge. Two competing mechanisms, both positively and negatively affected by the growing tube size, arise to significantly enhance the overall fracture toughness by up to 5.6-fold compared to the monolithic brittle counterpart without sacrificing the specific strength. This is enabled by crack-tube interaction and engineering the tube size, shape, and orientation, which promotes rising resistance-curves (R-curve). "Disorder" curves and statistical mechanics parameters are proposed for the first time to quantitatively characterize the degree of disorder for describing the representation of the architected arrangement of materials in lieu of otherwise inadequate "periodicity" classification and misperceived disorder parameters (perturbation and Voronoi tessellation methods).

From farm to function: Exploring new possibilities with jute nanocellulose applications

Recent scientific interest has surged in the application of bioresources within nanotechnology, primarily because of their eco-friendly nature, wide availability, and cost-effectiveness. Jute is globally recognized as the second most prevalent source of natural cellulose fibers, and it produces a significant quantity of jute sticks as a byproduct. Nanocellulose (NC), which includes cellulose nanofibrils (CNF) and cellulose nanocrystals (CNC), exhibits exceptional properties such as high strength, toughness, crystallinity, thermal stability, and stiffness. These attributes enable its versatile use across various sectors. The extensive surface areas and abundant hydroxyl groups of nanocellulose allow for diverse surface modifications, facilitating the design of advanced functional materials. This comprehensive review provides an overview of recent advancements in the synthesis, characterization, and potential applications of nanocellulose derived from jute. As a versatile natural fiber, jute holds immense potential across various research domains, including nanocellulose synthesis, scaffold fabrication, nanocarbon material preparation, life sciences, electronics and energy storage devices, drug delivery systems, nanomaterial synthesis, food packaging and paper industries. Additionally, its use extends to polymeric nanocomposites, sensors, and coatings. This study summarizes the extensive utilization of jute, emphasizing its versatility and potential across diverse research fields.

Gradients of properties increase the morphing and stiffening performance of bioinspired synthetic fin rays

State-of-the-art morphing materials are either very compliant to achieve large shape changes (flexible metamaterials, compliant mechanisms, hydrogels), or very stiff but with infinitesimal changes in shape that require large actuation forces (metallic or composite panels with piezoelectric actuation). Morphing efficiency and structural stiffness are therefore mutually exclusive properties in current engineering morphing materials, which limits the range of their applicability. Interestingly, natural fish fins do not contain muscles, yet they can morph to large amplitudes with minimal muscular actuation forces from the base while producing large hydrodynamic forces without collapsing. This sophisticated mechanical response has already inspired several synthetic fin rays with various applications. However, most 'synthetic' fin rays have only considered uniform properties and structures along the rays while in natural fin rays, gradients of properties are prominent. In this study, we designed, modeled, fabricated and tested synthetic fin rays with bioinspired gradients of properties. The rays were composed of two hemitrichs made of a stiff polymer, joined by a much softer core region made of elastomeric ligaments. Using combinations of experiments and nonlinear mechanical models, we found that gradients in both the core region and hemitrichs can increase the morphing and stiffening response of individual rays. Introducing a positive gradient of ligament density in the core region (the density of ligament increases towards the tip of the ray) decreased the actuation force required for morphing and increased overall flexural stiffness. Introducing a gradient of property in the hemitrichs, by tapering them, produced morphing deformations that were distributed over long distances along the length of the ray. These new insights on the interplay between material architecture and properties in nonlinear regimes of deformation can improve the designs of morphing structures that combine high morphing efficiency and high stiffness from external forces, with potential applications in aerospace or robotics.

Harnessing precursor-directed biosynthesis with glucose derivatives to access cotton fibers with enhanced physical properties

Cotton ovule in vitro cultures are a promising platform for exploring biofabrication of fibers with tailored properties. When the ovules' growth medium is supplemented with chemically synthesized cellulose precursors, it results in their integration into the developing fibers, thereby tailoring their end properties. Here, we report the feeding of synthetic glucosyl phosphate derivative, 6-deoxy-6-fluoro-glucose-1-phosphate (6F-Glc-1P) to cotton ovules growing in vitro, demonstrating the metabolic incorporation of 6F-Glc into the fibers with enhanced mechanical properties and moisture-retention capacity while emphasizing the role of molecular hierarchical architecture in defining functional characteristics and mechanical properties. This incorporation strategy bypasses the early steps of conventional metabolic pathways while broadening the range of functionalities that can be employed to customize fiber end properties. Our approach combines materials science, chemistry, and plant sciences to illustrate the innovation required to find alternative solutions for sustainable production of functional cotton fibers with enhanced and emergent properties.

Limits of economy and fidelity for programmable assembly of size-controlled triply periodic polyhedra

We propose and investigate an extension of the Caspar-Klug symmetry principles for viral capsid assembly to the programmable assembly of size-controlled triply periodic polyhedra, discrete variants of the Primitive, Diamond, and Gyroid cubic minimal surfaces. Inspired by a recent class of programmable DNA origami colloids, we demonstrate that the economy of design in these crystalline assemblies-in terms of the growth of the number of distinct particle species required with the increased size-scale (e.g., periodicity)-is comparable to viral shells. We further test the role of geometric specificity in these assemblies via dynamical assembly simulations, which show that conditions for simultaneously efficient and high-fidelity assembly require an intermediate degree of flexibility of local angles and lengths in programmed assembly. Off-target misassembly occurs via incorporation of a variant of disclination defects, generalized to the case of hyperbolic crystals. The possibility of these topological defects is a direct consequence of the very same symmetry principles that underlie the economical design, exposing a basic tradeoff between design economy and fidelity of programmable, size controlled assembly.

Application of pulsed electric field technology to skin engineering

Tissue engineering encompasses a range of techniques that direct the growth of cells into a living tissue construct for regenerative medicine applications, disease models, drug discovery, and safety testing. These techniques have been implemented to alleviate the clinical burdens of impaired healing of skin, bone, and other tissues. Construct development requires the integration of tissue-specific cells and/or an extracellular matrix-mimicking biomaterial for structural support. Production of such constructs is generally expensive and environmentally costly, thus eco-sustainable approaches should be explored. Pulsed electric field (PEF) technology is a nonthermal physical processing method commonly used in food production and biomedical applications. In this review, the key principles of PEF and the application of PEF technology for skin engineering will be discussed, with an emphasis on how PEF can be applied to skin cells to modify their behaviour, and to biomaterials to assist in their isolation or sterilisation, or to modify their physical properties. The findings indicate that the success of PEF in tissue engineering will be reliant on systematic evaluation of key parameters, such as electric field strength, and their impact on different skin cell and biomaterial types. Linking tangible input parameters to biological responses critical to healing will assist with the development of PEF as a sustainable tool for skin repair and other tissue engineering applications.

Review paper: The importance of consideration of collagen cross-links in computational models of collagen-based tissues

Collagen as the main protein in Extra Cellular Matrix (ECM) is the main load-bearing component of fibrous tissues. Nanostructure and architecture of collagen fibrils play an important role in mechanical behavior of these tissues. Extensive experimental and theoretical studies have so far been performed to capture these properties, but none of the current models realistically represent the complexity of network mechanics because still less is known about the collagen's inner structure and its effect on the mechanical properties of tissues. The goal of this review article is to emphasize the significance of cross-links in computational modeling of different collagen-based tissues, and to reveal the need for continuum models to consider cross-links properties to better reflect the mechanical behavior observed in experiments. In addition, this study outlines the limitations of current investigations and provides potential suggestions for the future work.

Cell Guiding Multicomponent Nanoyarn Tendon Scaffolds with Tunable Morphology and Flexibility

Nanofibrous scaffolds are widely investigated for tendon tissue engineering due to their porous structure, high flexibility, and the ability to guide cells in a preferred direction. Previous research has shown that providing a microenvironment similar to in vivo settings improves tissue regeneration. Therefore, in this work, ingenious multicomponent nanoyarn scaffolds that mimic the fibrillar and tubular structures of tendons are developed for the first time through electrospinning and bundling nanoyarns followed by electrospinning of a nanofibrous shell around the bundle. Multicomponent nanoyarn scaffolds out of poly(ε-caprolactone) with varying porosity, density, and diameter were successfully produced by coelectrospinning with water-soluble poly(2-ethyl-2-oxazoline) as a sacrificial component. The diameter and fiber orientation of the nanoyarns were successfully tuned based on parameter-morphology models obtained by the design of experiments. Cyclic bending tests were performed, indicating that the flexibility of the multicomponent nanoyarn scaffolds depends on the morphology and can be tuned through controlling the number of nanoyarns in the bundle and the porosity. Indirect and direct cell culture tests using mouse and equine tendon cells revealed excellent cytocompatibility of the nanofibrous products and demonstrated the potential of the nanoyarns to guide the growing cells along the nanofiber direction, which is crucial for tendon tissue engineering.

Peptide-triggered self-assembly of collagen mimetic peptides into nanospheres by electrostatic interaction and π-π stacking

Collagen is the most abundant protein in various connective tissues, providing mechanical integrity as well as regulating cellular activities. Self-assembled peptides have been extensively explored to develop collagen mimetic materials, due to their attractive features such as easy synthesis, selective sequences and low immunogenicity. Metal ion-triggered self-assembly of collagen mimetic peptides has recently received increasing interests, since the addition of external stimuli offers programmable control of the self-assembly process. We have for the first time reported a peptide-stimulated self-assembly of collagen mimetic peptides into nanospheres by electrostatic interaction and π-π stacking. We have accidentally discovered that FAM-modified positively-charged triple helical peptide FAM-PRG was highly soluble, while the addition of a single-stranded negatively-charged peptide EOG-10 efficiently drove its self-assembly into well-ordered spherical nanomaterials. Peptide EOG-10 has been shown to mediate similar self-assembly of TPE-modified triple-helical peptide TPE-PRG into luminescent exquisite nanospheres, consistently demonstrating the robustness of this peptide-triggered strategy. Fluorescence monitoring of the interaction of EOG-10 and TPE-PRG at different ratios indicated that EOG-10 specifically binds to TPE-PRG to form a 3 : 1 complex. High salt concentration was shown to inhibit the self-assembly of TPE-PRG with EOG-10, suggesting that their self-assembly was controlled by electrostatic interaction. The self-assembly of TPE-PRG with EOG-10 has been further revealed to require the exact lengths of both peptides as well as complementary sequences without mutations, indicating a pairwise "side-by-side" binding mode. Notably, the identity of the N-terminal residues of X-PRG has been found to play a determinant role in the self-assembly, while non-aromatic residues lost the self-assembling capability, suggesting that π-π stacking and electrostatic interactions collectively modulate the self-assembly of X-PRG and EOG-10. To conclude, we have developed a highly biocompatible and programmably controlled peptide-triggered self-assembly approach to create novel collagen mimetic nanomaterials, which may have great potential in advanced functional materials.

Surface modification of hydroxyapatite nanoparticles for bone regeneration by controlling their surface hydration and protein adsorption states

Autogenous bone and metallic implant grafting has been used to repair and regenerate bone defects. However, there are still many unresolved problems. It is suggested that bioceramic nanoparticles should be developed and designed to promote effective bone regeneration. In addition, it is necessary to synthesize bioceramic nanoparticles that can support proteins related to bone repair and regeneration such as collagen and albumin. As the protein-interactive bioceramic, hydroxyapatite (HA) deserves to be mentioned and has several attractive properties that are useful in biomedical fields (e.g., biocompatibility, protein adsorption capacity and stability in the physiological environment). In order to prepare novel HA nanoparticles with high biocompatibility, it can be considered that human bones are mainly composed of HA and contain a small amount of silicate, and therefore, the design of coexistence of HA with silicate can be focused. Moreover, it is proposed that the state of the hydration layer on the nanoparticle surfaces can be controlled by introducing heteroelements and polymer chains, which have a great influence on the subsequent protein adsorption and cell adhesion. In this perspective, in order to develop novel bioceramic nanoparticles for the treatment of bone defect, the design of highly biocompatible HA nanoparticles and the control of the hydration layer and protein adsorption states on the surfaces were systematically discussed based on their surface modification techniques, which are very important for the proper understanding of the interface between cells and bioceramics, leading to the further application in biomedical fields.

Tropocollagen springs allow collagen fibrils to stretch elastically

The mechanical properties of connective tissues are tailored to their specific function, and changes can lead to dysfunction and pathology. In most mammalian tissues the mechanical environment is governed by the micro- and nano-scale structure of collagen and its interaction with other tissue components, however these hierarchical properties remain poorly understood. In this study we use the human cornea as a model system to characterise and quantify the dominant deformation mechanisms of connective tissue in response to cyclic loads of physiological magnitude. Synchronised biomechanical testing, x-ray scattering and 3D digital image correlation revealed the presence of two dominant mechanisms: collagen fibril elongation due to a largely elastic, spring-like straightening of tropocollagen supramolecular twist, and a more viscous straightening of fibril crimp that gradually increased over successive loading cycles. The distinct mechanical properties of the two mechanisms suggest they have separate roles in vivo. The elastic, spring-like mechanism is fast-acting and likely responds to stresses associated with the cardiac cycle, while the more viscous crimp mechanism will respond to slower processes, such as postural stresses. It is anticipated that these findings will have broad applicability to understanding the normal and pathological functioning of other connective tissues such as skin and blood vessels that exhibit both helical structures and crimp.

Statement of significance

The tropocollagen spring mechanism allows collagen fibrils from some tissues to elongate significantly under small loads, and its recent discovery has the potential to change our fundamental understanding of how tissue deforms. This time-resolved study quantifies the contribution of the spring mechanism to the local strain in stretched tissue and compares it to the contribution associated with the straightening of fibril waviness, the widely accepted primary low-load strain mechanism. The spring mechanism contributed more to the local tissue strain than fibril straightening, and was found to be elastic while fibril straightening was more viscous. The results suggest that the viscoelastic behaviour of a biomaterial is controlled, at least in part, by the relative amount of fibril-scale crimp and tropocollagen supramolecular twist.

Topoarchitected polymer networks expand the space of material properties

Many living tissues achieve functions through architected constituents with strong adhesion. An Achilles tendon, for example, transmits force, elastically and repeatedly, from a muscle to a bone through staggered alignment of stiff collagen fibrils in a soft proteoglycan matrix. The collagen fibrils align orderly and adhere to the proteoglycan strongly. However, synthesizing architected materials with strong adhesion has been challenging. Here we fabricate architected polymer networks by sequential polymerization and photolithography, and attain adherent interface by topological entanglement. We fabricate tendon-inspired hydrogels by embedding hard blocks in topological entanglement with a soft matrix. The staggered architecture and strong adhesion enable high elastic limit strain and high toughness simultaneously. This combination of attributes is commonly desired in applications, but rarely achieved in synthetic materials. We further demonstrate architected polymer networks of various geometric patterns and material combinations to show the potential for expanding the space of material properties.

Prokaryotic Collagen-Like Proteins as Novel Biomaterials

Collagens are the major structural component in animal extracellular matrices and are critical signaling molecules in various cell-matrix interactions. Its unique triple helical structure is enabled by tripeptide Gly-X-Y repeats. Understanding of sequence requirements for animal-derived collagen led to the discovery of prokaryotic collagen-like protein in the early 2000s. These prokaryotic collagen-like proteins are structurally similar to mammalian collagens in many ways. However, unlike the challenges associated with recombinant expression of mammalian collagens, these prokaryotic collagen-like proteins can be readily expressed in E. coli and are amenable to genetic modification. In this review article, we will first discuss the properties of mammalian collagen and provide a comparative analysis of mammalian collagen and prokaryotic collagen-like proteins. We will then review the use of prokaryotic collagen-like proteins to both study the biology of conventional collagen and develop a new biomaterial platform. Finally, we will describe the application of Scl2 protein, a streptococcal collagen-like protein, in thromboresistant coating for cardiovascular devices, scaffolds for bone regeneration, chronic wound dressing and matrices for cartilage regeneration.

Enthalpy of collagen interfibrillar bonds in fetal membranes

During pregnancy, the fetal membrane (FM) is subjected to mechanical stretching that may result in preterm labor. The structural integrity of the FM is maintained by its collagenous layer. The disconnection and reconnection of molecular bonds between collagen fibrils are the fundamental processes that govern the irreversible mechanical and supermolecular changes in the FM. Here, we study the activation enthalpy of interfibrillar bonds in ex-vivo human FM. We analyze the strain-rate and temperature dependence of the irreversible deformations in FM subjected to inflation tests, which apply mechanical conditions similar to those experienced by the FM prior to and during the initiation of labor contractions. The obtained activation enthalpy of interfibrillar bonds matches the typical enthalpy values of polyvalent ionic bonds, implying on another important role that ions like Ca and Mg may play in the gestation and labor.

Mechanical Strain Alters the Surface Charge of Collagen Fibrils

Collagen fibrils act like nanoscale cables in the extracellular matrix of vertebrate tissues and provide a scaffold for cells to attach to. However, beyond this mechanical function, the surface charge of collagen fibrils is also likely to play an important role. Here, we show that native, type I collagen fibrils from a mammal tendon exhibit a particular dependence of surface charge on longitudinal strain. Fibrils first become more positive with strain of up to 10% and then become more negative again with strain between 10 and 17%. The effect correlates with the stiffness of fibrils and can be explained by structural rearrangements, which expose hidden, ionizable residues. Fibrils treated with glutaraldehyde did not show any change in surface charge when strained. The electrical surface potential, which is directly related to the number ratio of exposed amine and carboxy groups on the surface, was determined by Kelvin-probe force microscopy of fibrils attached on an extensible, thin polymer film. By stretching the film, a large number of individual fibrils could be strained simultaneously without resorting to sophisticated nanomechanical devices. It is conceivable that cells react to such changes of the fibril charge and that this effect is an additional contributor, besides mechanics, to a number of physiological processes. It may also need to be considered in the design of tissue-engineering scaffolds.

Fractional-order viscoelastic model of musculoskeletal tissues: correlation with fractals

Self-similar fractals are widely obtained from biomaterials within the human musculoskeletal system, and their viscoelastic behaviours can be described by fractional-order derivatives. However, existing viscoelastic models neglect the internal correlation between the fractal structure of biomaterials and their fractional-order temporal responses. We further expanded the fractal hyper-cell (FHC) viscoelasticity theory to investigate this spatio-temporal correlation. The FHC element was first compared with other material elements and spring–dashpot viscoelastic models, thereby highlighting its discrete and fractal nature. To demonstrate the utility of an FHC, tree-like, ladder-like and triangle-like FHCs were abstracted from human cartilage, tendons and muscle cross-sections, respectively. The duality and symmetry of the FHC element were further discussed, where operating the duality transformation generated new types of FHC elements, and the symmetry breaking of an FHC altered its fractional-order viscoelastic responses. Thus, the correlations between the staggering patterns of FHCs and their rheological power-law orders were established, and the viscoelastic behaviour of the multi-level FHC elements fitted well in stress relaxation experiments at both the macro- and nano-levels of the tendon hierarchy. The FHC element provides a theoretical basis for understanding the connections between structural degeneration of bio-tissues during ageing or disease and their functional changes.

Equilibrium mechanisms of self-limiting assembly

Self-assembly is a ubiquitous process in synthetic and biological systems, broadly defined as the spontaneous organization of multiple subunits (e.g. macromolecules, particles) into ordered multi-unit structures. The vast majority of equilibrium assembly processes give rise to two states: one consisting of dispersed disassociated subunits, and the other, a bulk-condensed state of unlimited size. This review focuses on the more specialized class of self-limiting assembly, which describes equilibrium assembly processes resulting in finite-size structures. These systems pose a generic and basic question, how do thermodynamic processes involving non-covalent interactions between identical subunits "measure" and select the size of assembled structures? In this review, we begin with an introduction to the basic statistical mechanical framework for assembly thermodynamics, and use this to highlight the key physical ingredients that ensure equilibrium assembly will terminate at finite dimensions. Then, we introduce examples of self-limiting assembly systems, and classify them within this framework based on two broad categories: self-closing assemblies and open-boundary assemblies. These include well-known cases in biology and synthetic soft matter - micellization of amphiphiles and shell/tubule formation of tapered subunits - as well as less widely known classes of assemblies, such as short-range attractive/long-range repulsive systems and geometrically-frustrated assemblies. For each of these self-limiting mechanisms, we describe the physical mechanisms that select equilibrium assembly size, as well as potential limitations of finite-size selection. Finally, we discuss alternative mechanisms for finite-size assemblies, and draw contrasts with the size-control that these can achieve relative to self-limitation in equilibrium, single-species assemblies.

Lignocellulose aerogel and amorphous silica nanoparticles from rice husks

Abstract

Rice Husks (RHs) are one of the most abundant sources of biomass in the world due to rice consumption. Lignocellulose and silica are two of the main components of RHs, which allow RHs to be applied in different areas. Lignocellulose can be partially dissolved in 1-butyl-3-methylimidazolium chloride (BMIMCl), which is a simple way of competing with the traditional extraction methods that suffer from high chemical consumption. A lignocellulose freeze gel is obtained via a cyclic liquid nitrogen freeze-thaw (NFT) process. Multi-functional self-assembled lignocellulose aerogel is obtained after CO2 supercritical drying. Based on the aerogel’s special properties, two routes are developed for practical applications. On one hand, the aerogel is coated to exhibit a superhydrophobic property that can be applied as an absorbent for oil spills. On the other hand, a carbon aerogel is synthesized via a pyrolysis process, resulting in a porous amorphous carbon. The residue after partially dissolving lignocellulose in BMIMCl is further calcined to obtain amorphous silica nanoparticles, achieving a comprehensive application of RHs.

Graphical abstract

Engineered Collagen Matrices

Collagen is the most abundant protein in mammals, accounting for approximately one-third of the total protein in the human body. Thus, it is a logical choice for the creation of biomimetic environments, and there is a long history of using collagen matrices for various tissue engineering applications. However, from a biomaterial perspective, the use of collagen-only scaffolds is associated with many challenges. Namely, the mechanical properties of collagen matrices can be difficult to tune across a wide range of values, and collagen itself is not highly amenable to direct chemical modification without affecting its architecture or bioactivity. Thus, many approaches have been pursued to design scaffold environments that display critical features of collagen but enable improved tunability of physical and biological characteristics. This paper provides a brief overview of approaches that have been employed to create such engineered collagen matrices. Specifically, these approaches include blending of collagen with other natural or synthetic polymers, chemical modifications of denatured collagen, de novo creation of collagen-mimetic chains, and reductionist methods to incorporate collagen moieties into other materials. These advancements in the creation of tunable, engineered collagen matrices will continue to enable the interrogation of novel and increasingly complex biological questions.

A Design and Fabrication Method for Wood-Inspired Composites by Micro X-Ray Computed Tomography and 3D Printing

Developments in 3D printing and CT scanning technologies have facilitated the imitation of natural wood structures. However, creating composites from the elementary features of anisotropic wood structures remains a new frontier. This paper aims to investigate the potential of constructing and 3D printing mechanically customizable composites by combining anisotropic elementary models reconstructed from the micro X-ray computed tomography (μ-CT) scanning of wood. In this study, an arbitrary region of interest selected from the μ-CT scanning of a sample of Manchurian walnut (Juglans mandshurica) was reconstructed into isosurfaces that constituted the 3D model of an elementary model. Elementary models were combined to form the wood-inspired composites in various arrangements. The surface and interior structures of the elementary model were found to be customizable through adjusting the image Threshold and Surface Quality Factors during 3D volume reconstruction. Compressional simulations and experiments performed on the elementary model (digital and 3D printed) revealed that its compressive behavior was wood-like and anisotropic. Numerical analysis established a preliminary link between the arrangements of elementary models and the compressive stiffness of respective composites, showing that it is possible to control the compressive behaviors of the composites through the design of specific elementary model arrangements.

Stretching Single Collagen Fibrils Reveals Nonlinear Mechanical Behavior

The mechanical properties of collagen fibrils play an important role in cell-matrix interactions and are a manifestation of their molecular structure. Using a, to our knowledge, novel combination of uniaxial, longitudinal straining and radial nanoindentation, we found that type I collagen fibrils show a pronounced nonlinear behavior in the form of strain stiffening at strains from 0 to 15%, followed by strain softening at strains from 15 to 25%. At the molecular scale, this surprising phenomenon can be explained by the combination of unfolding of disordered domains and breaking of native cross-links at different stages of strain. Fibrils cross-linked artificially by glutaraldehyde do not show such a behavior, and nanoindentation allowed us to measure the mechanics of the overlap and gap regions in the D-banding individually. The results could have consequences for our understanding of matrix mechanics and the influence of excessive glycation, which has been linked with age-related diseases such as diabetes. Furthermore, the simplicity of the straining method could be attractive in other areas of biophysics at the nanometer scale because it does not require any bespoke instrumentation and is easy to use.

Chiral and achiral mechanisms of self-limiting assembly of twisted bundles

A generalized theory of the self-limiting assembly of twisted bundles of filaments and columns is presented. Bundles and fibers form in a broad variety of supramolecular systems, from biological to synthetic materials. A widely-invoked mechanism to explain their finite diameter relies on chirality transfer from the molecular constituents to collective twist of the assembly, the effect of which frustrates the lateral assembly and can select equilibrium, finite diameters of bundles. In this article, the thermodynamics of twisted-bundle assembly is analyzed to understand if chirality transfer is necessary for self-limitation, or instead, if spontaneously-twisting, achiral bundles also exhibit self-limited assembly. A generalized description is invoked for the elastic costs imposed by twist for bundles of various states of intra-bundle order from nematic to crystalline, as well as a generic mechanism for generating twist, classified both by chirality but also the twist susceptibility of inter-filament alignment. The theory provides a comprehensive set of predictions for the equilibrium twist and size of bundles as a function of surface energy as well as chirality, twist susceptibility, and elasticity of bundles. Moreover, it shows that while spontaneous twist can lead to self-limitation, assembly of twisted achiral bundles can be distinguished qualitatively in terms of their range of equilibrium sizes and thermodynamic stability relative to bulk (untwisted) states.

Multiscale Toughening Mechanisms in Biological Materials and Bioinspired Designs

Biological materials found in Nature such as nacre and bone are well recognized as light-weight, strong, and tough structural materials. The remarkable toughness and damage tolerance of such biological materials are conferred through hierarchical assembly of their multiscale (i.e., atomic- to macroscale) architectures and components. Herein, the toughening mechanisms of different organisms at multilength scales are identified and summarized: macromolecular deformation, chemical bond breakage, and biomineral crystal imperfections at the atomic scale; biopolymer fibril reconfiguration/deformation and biomineral nanoparticle/nanoplatelet/nanorod translation, and crack reorientation at the nanoscale; crack deflection and twisting by characteristic features such as tubules and lamellae at the microscale; and structure and morphology optimization at the macroscale. In addition, the actual loading conditions of the natural organisms are different, leading to energy dissipation occurring at different time scales. These toughening mechanisms are further illustrated by comparing the experimental results with computational modeling. Modeling methods at different length and time scales are reviewed. Examples of biomimetic designs that realize the multiscale toughening mechanisms in engineering materials are introduced. Indeed, there is still plenty of room mimicking the strong and tough biological designs at the multilength and time scale in Nature.

Jute Based Bio and Hybrid Composites and Their Applications

The popularity of jute-based bio and hybrid composites is mainly due to an increase in environmental concerns and pollution. Jute fibers have low cost, high abundance, and reasonable mechanical properties. Research in all-natural fibers and composites have increased exponentially due to the environment concerns of the hazards of synthetic fibers-based composites. Jute based bio and hybrid composites have been extensively used in number of applications. Hybrid jute-based composites have enhanced mechanical and physical properties, reasonably better than jute fiber composites. A detailed analysis of jute-based bio and hybrid composites was carried out in this review. The primary aim of this review paper is to provide a critical analysis and to discuss all recent developments in jute-based composites. The content covers different aspects of jute-based composites, including their mechanical and physical properties, structure, morphology, chemical composition, fiber modification techniques, surface treatments, jute based hybrid composites, limitations, and applications. Jute-based composites are currently being used in a vast number of applications such as in textiles, construction, cosmetics, medical, packaging, automobile, and furniture industries.

Synthetic scaffolds for musculoskeletal tissue engineering: cellular responses to fiber parameters

Tissue engineering often uses synthetic scaffolds to direct cell responses during engineered tissue development. Since cells reside within specific niches of the extracellular matrix, it is important to understand how the matrix guides cell response and then incorporate this knowledge into scaffold design. The goal of this review is to review elements of cell-matrix interactions that are critical to informing and evaluating cellular response on synthetic scaffolds. Therefore, this review examines fibrous proteins of the extracellular matrix and their effects on cell behavior, followed by a discussion of the cellular responses elicited by fiber diameter, alignment, and scaffold porosity of two dimensional (2D) and three dimensional (3D) synthetic scaffolds. Variations in fiber diameter, alignment, and scaffold porosity guide stem cells toward different lineages. Cells generally exhibit rounded morphology on nanofibers, randomly oriented fibers, and low-porosity scaffolds. Conversely, cells exhibit elongated, spindle-shaped morphology on microfibers, aligned fibers, and high-porosity scaffolds. Cells migrate with higher velocities on nanofibers, aligned fibers, and high-porosity scaffolds but migrate greater distances on microfibers, aligned fibers, and highly porous scaffolds. Incorporating relevant biomimetic factors into synthetic scaffolds destined for specific tissue application could take advantage of and further enhance these responses.

* Meltblown Polymer Fabrics as Candidate Scaffolds for Rotator Cuff Tendon Tissue Engineering

Various biomaterial technologies are promising for tissue engineering, including electrospinning, but commercial scale-up of throughput is difficult. The goal of the study was to evaluate meltblown fabrics as candidate scaffolds for rotator cuff tendon tissue engineering. Meltblown poly(lactic acid) fabrics were produced with several polymer crystallinities and airflow velocities [500(low), 900(medium) or 1400(high) m³air/h/m fabric]. Fiber diameter, alignment, and baseline bidirectional tensile mechanical properties were evaluated. Attachment and spreading of human adipose-derived stem cells (hASCs) were evaluated over 3 days immediately following seeding. After initial screening, the fabric with the greatest Young's modulus and yield stress was selected for 28-day in vitro culture and for evaluation of tendon-like extracellular matrix production and development of mechanical properties. As expected, airflow velocity of the polymer during meltblowing demonstrated an inverse relationship with fiber diameter. All fabrics exhibited fiber alignment parallel to the direction of collector rotation. All fabrics demonstrated mechanical anisotropy at baseline. Cells attached, proliferated, and spread on all fabrics over the initial three-day culture period. Consistent with the observed loss of integrity of the unseeded biomaterial, hASC-seeded scaffolds demonstrated a significant decrease in Young's modulus over 28 days of culture. However, dsDNA, sulfated glycosaminoglycan, and collagen content increased significantly over 28 days. Histology and polarized light microscopy demonstrated collagen deposition and alignment throughout the thickness of the scaffolds. While fiber diameters approximated an order of magnitude greater than those previously reported for electrospun scaffolds intended for tendon tissue engineering, they were still within the range of collagen fiber diameters found in healthy tendon. The extent of matrix production and alignment was similar to that previously observed for multilayered electrospun scaffolds. While the Young's modulus of scaffolds after 28 days of culture was lower than native rotator cuff tendon, it approximated that reported previously following culture of electrospun scaffolds and was on the same order of magnitude as of current Food and Drug Administration-approved patches for rotator cuff augmentation. Together, these data suggest that with minor polymer and parameter modifications, meltblown scaffolds could provide an economical, high-throughput production alternative method to electrospinning for use in rotator cuff tendon tissue engineering.

Bioinspired Wood Nanotechnology for Functional Materials

It is a challenging task to realize the vision of hierarchically structured nanomaterials for large-scale applications. Herein, the biomaterial wood as a large-scale biotemplate for functionalization at multiple scales is discussed, to provide an increased property range to this renewable and CO₂ -storing bioresource, which is available at low cost and in large quantities. The Progress Report reviews the emerging field of functional wood materials in view of the specific features of the structural template and novel nanotechnological approaches for the development of wood-polymer composites and wood-mineral hybrids for advanced property profiles and new functions.

Scanning X-ray diffraction on cardiac tissue: automatized data analysis and processing

A scanning X-ray diffraction study of cardiac tissue has been performed, covering the entire cross section of a mouse heart slice. To this end, moderate focusing by compound refractive lenses to micrometer spot size, continuous scanning, data acquisition by a fast single-photon-counting pixel detector, and fully automated analysis scripts have been combined. It was shown that a surprising amount of structural data can be harvested from such a scan, evaluating the local scattering intensity, interfilament spacing of the muscle tissue, the filament orientation, and the degree of anisotropy. The workflow of data analysis is described and a data analysis toolbox with example data for general use is provided. Since many cardiomyopathies rely on the structural integrity of the sarcomere, the contractile unit of cardiac muscle cells, the present study can be easily extended to characterize tissue from a diseased heart.

A new mode of contrast in biological second harmonic generation microscopy

Enhanced image contrast in biological second harmonic imaging microscopy (SHIM) has previously been reported via quantitative assessments of forward- to epi-generated signal intensity ratio and by polarization analysis. Here we demonstrate a new form of contrast: the material-specific, wavelength-dependence of epi-generated second harmonic generation (SHG) excitation efficiency, and discriminate collagen and myosin by ratiometric epi-generated SHG images at 920 nm and 860 nm. Collagen shows increased SHG intensity at 920 nm, while little difference is detected between the two for myosin; allowing SHIM to characterize different SHG-generating components within a complex biological sample. We propose that momentum-space mapping of the second-order non-linear structure factor is the source of this contrast and develop a model for the forward and epi-generated SHG wavelength-dependence. Our model demonstrates that even very small changes in the assumed material fibrillar structure can produce large changes in the wavelength-dependency of epi-generated SHG. However, in the case of forward SHG, although the same changes impact upon absolute intensity at a given wavelength, they have very little effect on wavelength-dependency beyond the expected monotonic fall. We also propose that this difference between forward and epi-generated SHG provides an explanation for many of the wavelength-dependency discrepancies in the published literature.

Aligning cellulose nanofibril dispersions for tougher fibers

Nanocomposite materials made from cellulose show a great potential as future high-performance and sustainable materials. We show how high aspect ratio cellulose nanofibrils can be efficiently aligned in extrusion to fibers, leading to increased modulus of toughness (area under the stress-strain curve), Young’s modulus, and yield strength by increasing the extrusion capillary length, decreasing its diameter, and increasing the flow rate. The materials showed significant property combinations, manifesting as high modulus of toughness (~28–31 MJ/m³) vs. high stiffness (~19–20 GPa), and vs. high yield strength (~130–150 MPa). Wide angle X-ray scattering confirmed that the enhanced mechanical properties directly correlated with increased alignment. The achieved moduli of toughness are approximately double or more when compared to values reported in the literature for corresponding strength and stiffness. Our results highlight a possibly general pathway that can be integrated to gel-spinning process, suggesting the hypothesis that that high stiffness, strength and toughness can be achieved simultaneously, if the alignment is induced while the CNF are in the free-flowing state during the extrusion step by shear at relatively low concentration and in pure water, after which they can be coagulated.

How geometric frustration shapes twisted fibres, inside and out: competing morphologies of chiral filament assembly

Chirality frustrates and shapes the assembly of flexible filaments in rope-like, twisted bundles and fibres by introducing gradients of both filament shape (i.e. curvature) and packing throughout the structure. Previous models of chiral filament bundle formation have shown that this frustration gives rise to several distinct morphological responses, including self-limiting bundle widths, anisotropic domain (tape-like) formation and topological defects in the lateral inter-filament order. In this paper, we employ a combination of continuum elasticity theory and discrete filament bundle simulations to explore how these distinct morphological responses compete in the broader phase diagram of chiral filament assembly. We show that the most generic model of bundle formation exhibits at least four classes of equilibrium structure-finite-width, twisted bundles with isotropic and anisotropic shapes, with and without topological defects, as well as bulk phases of untwisted, columnar assembly (i.e. 'frustration escape'). These competing equilibrium morphologies are selected by only a relatively small number of parameters describing filament assembly: bundle surface energy, preferred chiral twist and stiffness of chiral filament interactions, and mechanical stiffness of filaments and their lateral interactions. Discrete filament bundle simulations test and verify continuum theory predictions for dependence of bundle structure (shape, size and packing defects of two-dimensional cross section) on these key parameters.

Midsubstance Tendinopathy, Surgical Management

Noninsertional Achilles tendinopathy often responds to nonoperative treatment. When nonoperative treatment fails, the clinician must distinguish between paratendinopathy and noninsertional tendinopathy. In paratendinopathy, myofibroblasts synthesize collagen, causing adhesions, and the paratenon may be released or excised. If a core area of tendinopathy is identified on MRI, the area is excised longitudinally and repaired with a side-to-side suture. If greater than 50% of the tendon diameter is excised, the authors recommend a short flexor hallucis longus tendon transfer with an interference screw. A turndown flap of the gastrocnemius aponeurosis is also described with good results.

New insights and perspectives into biological materials for flexible electronics

Materials based on biological materials are becoming increasingly competitive and are likely to be critical components in flexible electronic devices.

Liquid chromatography-electrospray ionization mass spectrometry for the simultaneous quantitation of collagen and elastin crosslinks

We have developed a novel chromatographic analytical method for the simultaneous quantitation of collagen crosslinks. Seven non-derivatised crosslinks could be separated on a Cogent Diamond Hydride HPLC column using either isocratic or gradient conditions then detected by mass spectrometry. The total run time was less than 10min which is significantly shorter than that previously reported. This is the first method in which histidinohydroxylysinonorleucine (HHL) and histidinohydroxymero-desmosine (HHMD) were separated and identified by mass spectrometry without the need for pre- or post-column derivatization. The CVs of the retention times of all seven crosslinks were less than 1% and the limit of detection (LOD) and the limits of quantitation (LOQ) were 0.07-0.13pmol/μL and 0.20-0.38pmol/μL, respectively. This novel method was used for the routine analysis and quantitation of crosslinks in different animal skins in which potential new collagen crosslinks were identified that are as yet undocumented.

Theory and Simulation of Cholesteric Film Formation Flows of Dilute Collagen Solutions

Dilute isotropic collagen solutions are usually flow processed into monodomain chiral nematic thin films for obtaining highly ordered materials by a multistep process that starts with complex inhomogeneous flow kinematics. Here we present rigorous theory and simulation of the initial precursors during flow steps in cholesteric collagen film formation. We first extract the molecular shape parameter and rotational diffusivity from previously reported simple shear data of dilute collagen solutions, where the former leads the reactive parameter (tumbling function) which determines the net effect of vorticity and strain rate on the average orientation and where the latter establishes the intensity of strain required for flow-birefringence, both crucial quantities for controlled film formation flow. We find that the tumbling function is similar to those of rod-like lyotropic liquid crystalline polymers and hence it is predicted that they would tumble in the ordered high concentration state leading to flow-induced texturing. The previously reported experimental data is well fitted with rotational diffusivities whose order of magnitude is consistent to those of other biomacromolecules. We then investigate the response of the tensor order parameter to complex flow kinematics, ranging from pure vorticity, through simple shear, to extensional flow, as may arise in typical flow casting and film flows. The chosen control variable to produce precursor cholesteric films is the director or average orientation, since the nematic order is set close to typical values found in concentrated cholesteric type I collagen solutions. Using the efficient four-roll mill kinematics, we summarize the para-nematic structure-flow process diagram in terms of the director orientation and flow type. Using analysis and computation, we provide a parametric envelope that is necessary to eventually produce well-aligned cholesteric films. We conclude that extensional flow is an essential ingredient of well-ordered film precursors with required Deborah numbers on the order of unity.

Geometric reconstruction of biological orthogonal plywoods

In this paper we focus on the structural determination of biological orthogonal plywoods, fiber-like composite analogues of liquid crystalline phases, where the fibrils of the building blocks show sharp 90° orientation jumps between fibers in adjacent domains. We present an original geometric and computational modelling that allows us to determine the fibrillary orientation in biological plywoods from periodic herringbone patterns commonly observed in cross-sections. Although herringbone patterns were long reported, the specific and quantitative relationships between herringbones and the orthogonal plywoods were absent or at best incomplete. Here we provide an efficient and new procedure to perform an inverse problem that connects two specific features of the herringbone patterns (aperture angle and wavelength) with the 3D morphology of the structure, whose accuracy and validity were ascertained through in silico simulations and also with real specimens ("Eremosphaera viridis"). This contribution extends significantly the better known characterization methods of 2D cross sections, such as the arced patterns observed in biological helicoidal plywoods, and with the present proposed methodology it adds another characterization tool for a variety of biological fibrous composites that form cornea-like tissues.

Nanoscale and mechanical properties of the physiological cell-ECM microenvironment

Studying biological processes in vitro requires faithful and successful reconstitution of the in vivo extracellular matrix (ECM) microenvironment. However, the physiological basis behind in vitro studies is often forgotten or ignored. A number of diverse cell-ECM interactions have been characterized throughout the body and in disease, reflecting the heterogeneous nature of cell niches. Recently, a greater emphasis has been placed on characterizing both the chemical and physical characteristics of the ECM and subsequently mimicking these properties in the lab. Herein, we describe physiological measurement techniques and reported values for the three main physical aspects of the ECM: tissue stiffness, topography, and ligand presentation.