3D printing alias additive manufacturing can transform 3D virtual models created by computer-aided design (CAD) into physical 3D objects in a layer-by-layer manner dispensing with conventional molding or machining. Since the incipiency, significant advancements have been achieved in understanding the process of 3D printing and the relationship of component, structure, property and application of the created objects. Because hydrogels are one of the most feasible classes of ink materials for 3D printing and this field has been rapidly advancing, this Review focuses on hydrogel designs and development of advanced hydrogel-based biomaterial inks and bioinks for 3D printing. It covers 3D printing techniques including laser printing (stereolithography, two-photon polymerization), extrusion printing (3D plotting, direct ink writing), inkjet printing, 3D bioprinting, 4D printing and 4D bioprinting. It provides a comprehensive overview and discussion of the tailorability of material, mechanical, physical, chemical and biological properties of hydrogels to enable advanced hydrogel designs for 3D printing. The range of hydrogel-forming polymers covered encompasses biopolymers, synthetic polymers, polymer blends, nanocomposites, functional polymers, and cell-laden systems. The representative biomedical applications selected demonstrate how hydrogel-based 3D printing is being exploited in tissue engineering, regenerative medicine, cancer research, in vitro disease modeling, high-throughput drug screening, surgical preparation, soft robotics and flexible wearable electronics. Incomparable by thermoplastics, thermosets, ceramics and metals, hydrogel-based 3D printing is playing a pivotal role in the design and creation of advanced functional (bio)systems in a customizable way. An outlook on future directions of hydrogel-based 3D printing is presented.

3D printing of hydrogels: Rational design strategies and emerging biomedical applications

Biopolymer-based particles as stabilizing agents for emulsions and foams

Manufacturing of hydrogel biomaterials with controlled mechanical properties for tissue engineering applications.

https://shimadzu.com.cn/an/upload/spm/spmroom/2011/chuandapigexuanyong-6/3.pdf

Modification of collagen with a natural cross-linker, procyanidin.

Biopolymer nanofibrils: structure, modeling, preparation, and applications

In this paper, we report for the first time the use of a well-dispersed gelatin particle as a representative of natural and biocompatible materials to be an effective particle stabilizer for high internal phase emulsion (HIPE) formulation. Fairly monodispersed gelatin particles (∼200 nm) were synthesized through a two-step desolvation method and characterized by dynamic light scattering, ζ-potential measurements, scanning electron microscopy, and atomic force microscopy. Those protein latexes were then used as sole emulsifiers to fabricate stable oil-in-water Pickering HIPEs at different concentrations, pH conditions, and homogenization times. Most of the gelatin particles were irreversibly adsorbed at the oil-water interface to hinder droplet coalescence, such that Pickering HIPEs can be formed by a small amount of gelatin particles (as low as 0.5 wt % in the water phase) at pH far away from the isoelectric point of the gelatin particles. In addition, increasing homogenization time led to narrow size distribution of droplets, and high particle concentration resulted in more solidlike Pickering HIPEs. In vitro controlled-release experiments revealed that the release of the encapsulated β-carotene can be tuned by manipulating the concentration of gelatin particles in the formulation, suggesting that the stable and narrow-size-distributed gelatin-stabilized HIPEs had potential in functional food and pharmaceutical applications.

Gelatin Particle-Stabilized High Internal Phase Emulsions as Nutraceutical Containers

Concomitant degradation in periodate oxidation of carboxymethyl cellulose

The denaturation of collagen solution in acetic acid has been investigated by using ultra-sensitive differential scanning calorimetry (US-DSC), circular dichroism (CD), and laser light scattering (LLS). US-DSC measurements reveal that the collagen exhibits a bimodal transition, i.e., there exists a shoulder transition before the major transition. Such a shoulder transition can recover from a cooling when the collagen is heated to a temperature below 35 degrees C. However, when the heating temperature is above 37 degrees C, both the shoulder and major transitions are irreversible. CD measurements demonstrate the content of triple helix slowly decreases with temperature at a temperature below 35 degrees C, but it drastically decreases at a higher temperature. Our experiments suggest that the shoulder transition and major transition arise from the defibrillation and denaturation of collagen, respectively. LLS measurements show the average hydrodynamic radius R(h), radius of gyration R(g)of the collagen gradually decrease before a sharp decrease at a higher temperature. Meanwhile, the ratio R(g)/R(h) gradually increases at a temperature below approximately 34 degrees C and drastically increases in the range 34-40 degrees C, further indicating the defibrillation of collagen before the denaturation.

Temperature induced denaturation of collagen in acidic solution.

A 3D spongy collagen cryogel was prepared using DAS as the cross-linker. FTIR and CD studies demonstrate that crosslinking is achieved through the reaction of the DAS aldehyde groups with the free amino groups in collagen without affecting the triple helix of collagen. SEM demonstrates that the cryogel has a heteroporous structure with interconnecting pores. DSC measurements reveal that the cryogels have improved thermal stability in comparison with pure collagen. Moreover, the ESR shows that the water uptake of the cryogel decreases with DAS content. Evaporation tests indicate that the cryogel can hold moisture for a long time. Since both collagen and DAS are nontoxic and the resultant cryogel is blood-compatible, the cryogel is expected to be useful, e.g., as wound dressing.

Wei Lin

Papers

Modification of collagen with a natural cross-linker, procyanidin.

Gelatin Particle-Stabilized High Internal Phase Emulsions as Nutraceutical Containers

Concomitant degradation in periodate oxidation of carboxymethyl cellulose

Temperature induced denaturation of collagen in acidic solution.

Collagen Cryogel Cross‐Linked by Dialdehyde Starch