Anisotropic, Mesoporous Microfluidic Frameworks with Scalable, Aligned Cellulose Nanofibers

Abstract

Cellulose paper has been extensively used in microfluidic analytical devices because of its hydrophilic nature. However, cellulose is randomly packed in paper without any particular orientation or channels within the bulk of the material, necessitating a complicated design of hydrophilic microchannels to guide the liquid flow. Herein, we develop an anisotropic mesoporous microfluidic framework (named as white wood) with aligned cellulose nanofibers and inherent microchannels via a facile one-step delignification process from natural wood. The hydrophilic nature of the innate microchannels in white wood makes it ideal for application as a pump-free microfluidic chip, exhibiting a fast and anisotropic liquid and large solid particle (as demonstrated with carbon nanotubes) mass transport, with a high transport speed along the channel direction approximately five times faster than that perpendicular to the channel direction. The anisotropic mass transport is further exemplified in the fabrication of chitosan films with aligned microstructures and birefringence, formed by virtue of unidirectional capillary forces exerted by the microchannels. We envision that our anisotropic mesoporous framework can have great applications to pump-free microfluidics, and the simple preparation process will pave a new way for the development of microfluidic devices based on chemically modified wood.

Lightweight, Anisotropic, Compressible, and Thermally-Insulating Wood Aerogels with Aligned Cellulose Fibers

“…By further loading tin oxide nanoparticles, the composites showed excellent near-infrared and ultraviolet absorbency. Jia et al fabricated an anisotropic microfluidic framework via a delignification process from natural wood [25]. The natural microchannels have an ability to transport liquid and solid particles.…”

Breathable Nanowood Biofilms as Guiding Layer for Green On‐Skin Electronics

“…As seen in Figure a and Table 1 , wood slice has higher cross‐plane breathability than plastic films, with a WVTR of 185.7 g m −2 day −1 (but still less than that of normal skin (≈204 g m −2 day −1 )) and an oxygen transmission rate (OTR) of 82.4 cm 3 m −2 day −1 (comparable to the reported value), owing to its lumen structures. Interestingly, benefiting from the newborn inter‐CN pores successfully preserved by our AD method and the more opened and broadened pits on lumens (Figure b) caused by lignin removal, forming more gas channels for water vapor and O 2 to pass through adjacent lumens, our porous biofilms gain up to 325.2 g m −2 day −1 in WVTR, substantially larger even than that of first degree burn skin (279 g m −2 day −1 ), as well as 151.7 cm 3 m −2 day −1 in OTR.…”

“…Pore structures normally suffer from volume shrinkage during drying because of the solvent evaporation capillary stress ( P c ) and the relatively weak framework stiffness (χ). So far, all the porous nanowoods have been made by freeze‐drying the delignified wood slices . Freeze‐drying preserves the pore structures by “avoiding” the capillary action.…”

“…As seen in Figure a, sweat droplets are all‐direction equally spread on the reference PET film with no further transport (no channels thus no transport) but can be transported in the wood slice. This is because wood slice has lumen channels, along which sweat transport // is promoted readily by virtue of capillary force and on the surface of which pits (Figure a) allow the transport ⊥ …”

“…Trees transport the water, salts, and other nutrients for photosynthesis through their anisotropic tubular structures, where most of the CNs are “naturally well‐aligned” along the wood growth direction in the cell wall matrix of hemicellulose and lignin . Recently, a large‐scale, hierarchal alignment of CNs directly fabricated from wood is referred to as “nanowood,” top‐down methods have been designed to take advantage of the naturally well‐aligned CNs to make advanced nanowood biofilms capable of highly in‐plane anisotropic water transport, optical transparency, and mechanical properties (but permit low cross‐plane breathability due to extremely densified structure) and bulk nanowoods for anisotropic heat‐insulating and microfluidic applications. But the method for tailoring the structure of nanowood biofilm to achieve strong heat‐ and sweat‐guiding performance and simultaneously guarantee adequate cross‐plane breathability has yet to be explored.…”