Abstract Micro/nano-fabrication technology via two-photon polymerization (TPP) nanolithography is a powerful and useful manufacturing tool that is capable of generating two dimensional (2D) to three dimensional (3D) arbitrary micro/nano-structures of various materials with a high spatial resolution. This technology has received tremendous interest in cell and tissue engineering and medical microdevices because of its remarkable fabrication capability for sophisticated structures from macro- to nano-scale, which are difficult to be achieved by traditional methods with limited microarchitecture controllability. To fabricate precisely designed 3D micro/nano-structures for biomedical applications via TPP nanolithography, the use of photoinitiators (PIs) and photoresists needs to be considered comprehensively and systematically. In this review, widely used commercially available PIs are first discussed, followed by elucidating synthesis strategies of water-soluble initiators for biomedical applications. In addition to the conventional photoresists, the distinctive properties of customized stimulus-responsive photoresists are discussed. Finally, current limitations and challenges in the material and fabrication aspects and an outlook for future prospects of TPP for biomedical applications based on different biocompatible photosensitive composites are discussed comprehensively. In all, this review provides a basic understanding of TPP technology and important roles of PIs and photoresists for fabricating high-precision stimulus-responsive micro/nano-structures for a wide range of biomedical applications.

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Two-photon polymerization nanolithography technology for fabrication of stimulus-responsive micro/nano-structures for biomedical applications

Abstract Hyaluronic acid (HA) is widely distributed in the human body, and it is heavily involved in many physiological functions such as tissue hydration, wound repair, and cell migration. In recent years, HA and its derivatives have been widely used as advanced bioactive polymers for bone regeneration. Many medical products containing HA have been developed because this natural polymer has been proven to be nontoxic, noninflammatory, biodegradable, and biocompatible. Moreover, HA-based composite scaffolds have shown good potential for promoting osteogenesis and mineralization. Recently, many HA-based biomaterials have been fabricated for bone regeneration by combining with electrospinning and 3D printing technology. In this review, the polymer structures, processing, properties, and applications in bone tissue engineering are summarized. The challenges and prospects of HA polymers are also discussed.

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Hyaluronic acid as a bioactive component for bone tissue regeneration: Fabrication, modification, properties, and biological functions

Abstract Cellulose is the most abundant natural polymer on earth, which has obtained increasing interest in the field of functional materials development for its renewable, high mechanical performance and environmental benign. In this study, the traditional processing method (wet spinning and film production) of cellulose-based materials was applied by using cellulose solution for 3D printing, which can directly build complex 3D patterns. Herein, a natural cellulose is dissolved in an effective mixed aqueous solution of dimethyl sulfoxide (DMSO) and tetrabutylammonium hydroxide (TBAH). The cellulose solution extrusion was controlled by a modified fused deposition modeling (FDM) 3D printer. During the controlled extrusion 3D printing process, the viscous cellulose solution will gelifies and further solidifies into a predetermined 3D pattern at room temperature in air. Subsequently, a cellulose hydrogel skeleton was obtained, when the 3D pattern was solvent-exchanged with deionized water. Finally, the mechanical and swelling performance of the cellulose hydrogel scaffold was improved by a cross-linking agent treatment method. With treatment of the 3D printed scaffolds in 0.8 wt% cross-linking agent solution, the obtained cellulose hydrogel could absorb 28 g/g water, and the compression strength was 96 kPa. This work provided an efficient way to prepare natural cellulose hydrogel by 3D printing under room temperature.

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Cellulose hydrogel skeleton by extrusion 3D printing of solution

The rapid economic growth and environmental concerns have led to high demands on paper
 and paper-based products in terms of variety, quantity, quality, and specialty. Enhancement
 and functionalization with additives are constantly required. Moving away from traditional
 petroleum-based additives, researchers have attempted to use “green” nanoadditives
 by introducing renewable environmentally friendly nanocellulose. This article studies
 the functions of nanocellulose as bio-additives (enhancer, retention and filtration
 reagent, and coating aid) in paper and paper products, and overviews the research
 development of nanocellulose-based additives and their applications in the paper industry
 for both efficient production and paper functionalization. The review shows that (1)
 a variety of nanocellulose-based bioadditives have been reported for various applications
 in paper and paper-based products, while commercially viable developments are to be
 advanced; (2) nanocellulose was mostly formulated with other polymer and particles
 as additives to achieve their synergistic effects; (3) major interests have concentrated
 on the nanocellulose in the specialty papers as representing more value added products
 and in the efficient utilization of recycled fibers, which remains most attractive
 and promising for future development. This report shall provide most useful database
 information for researchers and industries for paper recycling and enhancement, and
 paper-based products innovation and application.

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Overview of nanocellulose as additives in paper processing and paper products

Review on design strategies and applications of metal-organic framework-cellulose composites.

3D printing of polyurethane/nanocellulose shape memory composites with tunable glass transition temperature

The determination of molecular weight of natural cellulose remains a challenge nowadays, due to the difficulty in dissolving cellulose. In this work, tetra-n-butylammonium hydroxide (TBAH) and dimethyl sulfoxide (DMSO) aqueous solution (THDS) were used to dissolve cellulose in a few minutes under room temperature into true molecular solutions. That is to say, the cellulose was dissolved in the solution in molecular level, and the viscosity of the solution is linearly dependent on the concentration of cellulose. The relationship between the molecular weight of cellulose and the intrinsic viscosity tested in such dilute solutions has been established in the form of the Mark-Houwink equation, η=0.24×DP1.21. The value of 1.21 indicates that the cellulose molecules dissolve in THDS quite well. The cellulose dispersion in the THDS was proved to be in molecular level by atomic force microscope (AFM) and dynamic light scattering (DLS). The reliability of the established Mark-Houwink equation was cross-checked by the gel permeation chromatography (GPC) and traditional copper (II) ethylenediamine (CED) method. No considerate degradation was observed by comparing the intrinsic viscosity and the degree of polymerization (DP) values of the original with and the regenerated cellulose samples. The natural cellulose can be molecularly dispersed in the multiple-component solvent (THDS), and kept stable for a certain period. A time efficient and reliable method has been supplied for determination of the degree of polymerization and the molecular weight of cellulose.

Elucidation of the Relationship between Intrinsic Viscosity and Molecular Weight of Cellulose Dissolved in Tetra-N-Butyl Ammonium Hydroxide/Dimethyl Sulfoxide.

Preparation of single O-methoxyphenol from lignin and related liquor products as reinforcement for epoxy resin

Deep eutectic-like solvents (DESs) are recognized as environmentally benign media with highly tunable structures and properties. The usage of DES is promising in the field of biomass treatment and transformation, including pretreatment, selective dissolution, and separation of the main components. It serves as a green medium for modification of the biomass components, as well as preparation of biomass-derived nanomaterials. In this paper, the development on DES, including composition, properties, and characteristics was studied. The application of DES in biomass-derived nanomaterials is especially discussed. This review intends to provide references for adopting DES to improve biomass-based environmentally friendly nanomaterials.

Xiangzhou Hu

Papers

Cellulose hydrogel skeleton by extrusion 3D printing of solution

3D printing of polyurethane/nanocellulose shape memory composites with tunable glass transition temperature

Elucidation of the Relationship between Intrinsic Viscosity and Molecular Weight of Cellulose Dissolved in Tetra-N-Butyl Ammonium Hydroxide/Dimethyl Sulfoxide.

Preparation of single O-methoxyphenol from lignin and related liquor products as reinforcement for epoxy resin

Deep eutectic-like solvents: Promising green media for biomass treatment and preparation of nanomaterials