Porous Cellulose Scaffold Research Articles

Cellulose supported and strengthened shear stiffening gel with enhanced impact-resistant performance

Shear stiffening gel (SSG) is a promising cushioning material for impact-resistant applications as its moduli significantly increase under shear. However, SSG cannot retain its shape due to cold flow effect, which severely restricts its broad applications. In this study, both “top-down” and “bottom-up” strategies were respectively employed to construct cellulose supported and strengthened polyborosiloxane SSG (PSSG), resulting in stable shapes with significantly enhanced mechanical properties and impact-resistant performance attributed to reinforced concrete-like “steel-and-cement” structure. In “top-down” strategy, porous cellulose scaffolds (CS) were fabricated by removing lignin and hemicellulose from wood and then used as templates to encapsulate PSSG (PSSG@CS). In “bottom-up” strategy, cellulose nanofibers (CNFs) were well dispersed in PSSG and employed as nanofillers to strengthen PSSG (PSSG@CNF). Both PSSG@CS and PSSG@CNF effectively inhibited the cold flow deformation of PSSG and exhibited significantly enhanced shear stiffening properties. Rigid and hydrophobic PSSG@CS with fixed shape inherits the excellent mechanical properties of wood, with maximum storage modulus of 908 MPa, much higher than PSSG@CNF (15.3 MPa) and pristine PSSG (4.7 MPa). PSSG@CNF is flexible, self-healable, and adhesive, and could be processed to varied shapes. Both PSSG@CS and PSSG@CNF displayed outstanding impact-resistant performance when employed as protective cushion for glass.

Insulin production from hiPSC-derived pancreatic cells in a novel wicking matrix bioreactor.

Clinical use of pancreatic β islets for regenerative medicine applications requires mass production of functional cells. Current technologies are insufficient for large-scale production in a cost-efficient manner. Here, we evaluate advantages of a porous cellulose scaffold and demonstrate scale-up to a wicking matrix bioreactor as a platform for culture of human endocrine cells. Scaffold modifications were evaluated in a multiwell platform to find the optimum surface condition for pancreatic cell expansion followed by bioreactor culture to confirm suitability. Preceding scale-up, cell morphology, viability, and proliferation of primary pancreatic cells were evaluated. Two optimal surface modifications were chosen and evaluated further for insulin secretion, cell morphology, and viable cell density for human-induced pluripotent stem cell-derived pancreatic cells at different stages of differentiation. Scale-up was accomplished with uncoated, amine-modified cellulose in a miniature bioreactor, and insulin secretion and cell metabolic profiles were determined for 13 days. We achieved 10-fold cell expansion in the bioreactor along with a significant increase in insulin secretion compared with cultures on tissue culture plastic. Our findings define a new method for expansion of pancreatic cells a on wicking matrix cellulose platform to advance cell therapy biomanufacturing for diabetes.

Hierarchical Porous Wood Cellulose Scaffold with Atomically Dispersed Pt Catalysts for Low-Temperature Ethylene Decomposition.

Despite the excellent catalytic properties of individual nanoparticles and atomic clusters, the current capabilities to assemble them into a complex system are insufficient for many practical applications. An objective of this work is to develop a fabrication technology that allows for the simultaneous control of the nanoparticle surface chemistry, elemental distribution, microscale geometry, and large-scale assembly. Using a cellulose structure derived from wood, we fabricate hierarchical porous cellulose scaffolds combining with cerium-doped TiO2. This hybrid material serves as the support for atomically dispersed Pt catalysts and is used to successfully decompose ethylene at 0 °C. The fabrication concept developed in this work would allow mitigating the conflict between the required large active surfaces and the difficulties in handling nanopowders in environmental catalysis, including food preservation and indoor air purification. We thus discover a promising route to manufacture multifunctional materials with complex structures by combining a controllable chemical synthesis with the nature-designed wood scaffold.

A Novel Approach for the Sustainable Synthesis of Carbon Fibers Using Light Induced Dielectrophoresis of Bacteria

Presented here are preliminary results on the use of the cellulose-extruding bacteria Gluconoacetobacter xylinus as a sustainable tool for manufacturing carbon fibers. G. xylinus has the natural ability to extrude highly crystalline cellulose nanofibers with higher purity and superior mechanical properties compared to cellulose extracted from plants [1]. Traditionally, the movement of the bacteria within a cellulose culture is random and leads to a porous cellulose scaffold with no apparent order. Light induced dielectrophoresis (LiDEP), or the movement of electrically polarized cells in response to a non-uniform electric field created by incident light, will permit controllable cell movement. LiDEP will be utilized to selectively position G. xylinus at specified locations. A microfluidic chamber will be used to perfuse the trapped G. xylinus in a continuous flow of nutrient-rich media, allowing for the continuous extrusion of straight cellulose fibers (figure 1). These fibers are carbonized using an optimized pyrolysis protocol at 900 oC in a nitrogen atmosphere. This technology is important because it utilizes G. xylinus as the enabling tool for fiber extrusion and thus eliminates the need for expensive machinery and its’ associated processes [2-3]. Air, water, and soil pollution created by oil refineries and diminishing supplies of petroleum has sparked a push towards the development of sustainable approaches for manufacturing carbon fibers. Our end goal is to develop such an approach. To the authors best knowledge, no technique to pattern a single bacterial cellulose fiber exists. However, wet spinning and drawing processes have been used to align and assemble bacterial cellulose bundles into high performance macro fibers [3]. Cellulose has also been cultivated on an agarose film with honeycomb microgrooves to form a cellulose bundle with honeycombed architecture [4]. In this work, we present the initial characterization of the response of G. xylinus to electrical stimuli of varying frequencies as well as the heat treatment protocol developed for carbonizing bacterial cellulose. The dielectrophoretic response was characterized using AC signals from 1-20MHz frequencies at a constant voltage of 20 . The results indicate a positive DEP response across the spectrum of 7.5-20 MHz with the largest DEP force at a frequency of 20 MHz (figure 2). Frequencies above 20 MHz were not investigated because the voltage generator used in this experiment is limited to generating frequencies below 20 MHz. Additional work focused on the carbonization of bacterial cellulose nanofibers. Amorphous carbon was successfully obtained through heat treatment of bacterial cellulose in a nitrogen atmosphere to 900⁰C with 5 ⁰C/min heating ramp. A dwell time of 30 minutes at 300 ⁰C was included to enable the release of oxygen from the sample and prevent burning at higher temperatures. Such a step is also pertinent because the removal of the hydroxyl groups stabilizes the carbon polymer by producing conjugated double bonds, thus forming an aromatic structure [5]. An optimal heating rate was determined to be 5 ⁰C/min to achieve high carbon yield without making the process prohibitively long. Although we observed cellulose to carbonize at around 400 ⁰C, 900 ⁰C was used to ensure a high degree of carbonization [6]. Ongoing work is on developing the infrastructure to reliably position individual G. xylinus bacteria, as well as characterizing the fiber properties and dimensions depending on the suspending media and its flow rate over the cells. The goal is to understand how the conditions in the microfluidic chamber lead to the tailoring of the fiber properties and a maximized throughput. References “Recent advances in bacterial cellulose,” Y. Huang, C. Zhu, J. Yang, Y. Nie, C. Chen, D. Sun, Cellulose, 21, 1 (2014).“Manufacture and application of lignin-based carbon fibers (LCFs) and lignin-based carbon nanofibers (LCNFs),” W. Fang, S. Yang, X. L. Wang, T. Q. Yuan, R. C. Sun, Green Chemistry, 19, 1794 (2017).“Macrofibers with High Mechanical Performance Based on Aligned Bacterial Cellulose Nanofibers,” J. Yao, Chen, Y. Chen, B. Wang, Q. Pei, & H. Wang, ACS Applied Materials & Interfaces, (2017).“Honeycomb-like architecture produced by living bacteria, Gluconacetobacter xylinus,” Y. Uraki, J. Nemoto, H. Tamai, J. Sugiyama, T. Kishimoto, ... & M. Shimomura, Carbohydrate polymers, 69, 1 (2007).“Low temperature mechanism for the formation of polycyclic aromatic hydrocarbons from the pyrolysis of cellulose,” T. E. McGrath, W. G. Chan, & M. R. Hajaligol, Journal of Analytical and Applied Pyrolysis, 66, 1 (2003).“Changes in the thermophysical properties of microcrystalline cellulose as function of carbonization temperature, Y. R. Rhim, D. Zhang, M. Rooney, D. C. Nagle, D. H. Fairbrother, C. Herman, & D. G. Drewry, Carbon, 48, 1 (2010). Figure 1

Natural cellulose ionogels for soft artificial muscles

Rapid development of soft micromanipulation techniques for human friendly electronics has raised the demand for the devices to be able to carry out mechanical work on a micro- and macroscale. The natural cellulose-based ionogels (CEL-iGEL) hold a great potential for soft artificial muscle application, due to its flexibility, low driving voltage and biocompatibility. The CEL-iGEL composites undergo reversible bending already at ±500mV step-voltage values. A fast response to the voltage applied and high ionic conductivity of membranous actuator is achieved by a complete dissolution of cellulose in 1-ethyl-3-methylimidazolium acetate [EMIm][OAc]. The CEL-iGEL supported cellulose actuator films were cast out of cellulose-[EMIm][OAc] solution via phase inversion in H2O. The facile preparation method ensured uniform morphology along the layers and stand for the high ionic-liquid loading in a porous cellulose scaffold. During the electromechanical characterization, the CEL-iGEL actuators showed exponential dependence to the voltage applied with the max strain difference values reaching up to 0.6% at 2 V. Electrochemical analysis confirmed the good stability of CEL-iGEL actuators and determined the safe working voltage value to be below 2.5V. To predict and estimate the deformation for various step input voltages, a mathematical model was proposed.