Hydrogels have become popular in biomedical applications, but their applications in muscle and tendon-like bioactuators have been hindered by low toughness and elastic modulus. Recently, a significant toughness enhancement of a single hydrogel network has been successfully achieved by the Hofmeister effect. However, little has been conducted for the Hofmeister effect on the hybrid hydrogels, although they have a special network structure consisting of two types of polymer components. Herein we fabricated hybrid poly(2-hydroxyethyl methacrylate) (PHEMA)–gelatin hydrogels with high mechanical performance and stimuli response. An ideal bicontinuous phase separation structure of the PHEMA (rigid) and gelatin (ductile) was observed with embedded microdisc-like gelatin in the three-dimensional polymeric network of PHEMA. A significant enhancement of mechanical performance by the Hofmeister effect was attributed to the salting-out-induced stronger and closer interphase interaction between PHEMA and gelatin. A superior comprehensive mechanical performance with fracture elongation over 650%, tensile strength of 5.2 MPa, toughness of 13.5 MJ/m3, and modulus of 45.6 MPa was achieved with the salting-out effect. More specifically, the synergy of phase separation and Hofmeister effect enable the hydrogel to contract with an enhanced modulus in high-concentration salt solutions, while the same hydrogel swells and relaxes in dilute solutions, exhibiting an ionic stimulus response and excellent shape-memory properties like those of most artificial muscle. This is manifested in highly stretched, twisted, and knotted hydrogel strips that can rapidly recover their original shape in a dilute salt solution. The high strength and modulus, ionic stimuli response, and shape memory property make the hybrid hydrogel a promising material for bioactuators in various biomedical applications.
Microporous structure plays a significant role in bone tissue engineering, to influence inductive bone formation and elevate bone ingrowth inside microporous scaffolds. We hereby fabricated microporous scaffolds by 3D printing with mixture of porogens and photopolymerizing resin. Our method can tune the microporosity of scaffolds from 0% to 36% by varying the porogen concentration in the inks from zero to 60 vol%. The microporosity and microspore size of scaffolds can affect in vitro expansion of preosteoblast cells. We evaluated the attachment, spreading and proliferation of MC3T3-E1 mouse preosteoblast cells on the printed porous scaffolds. Our studies revealed that preosteoblast cells' in vitro adhesion and proliferation were significantly mediated by the printed scaffolds. Cells proliferation on scaffolds with 20%-30% microporosity showed much higher rate than on other scaffolds. In this microporosity range, scaffolds also showed much better cell spreading and morphologies. At a low level of microporosity (< 7%), the cell proliferation rate was even lower than the solid scaffolds, which indicates that the microporous structure is "toxic" for cells at low microporosity range. A higher microporosity (> 35%) led to very poor cell attachment and is unfavorable for the proliferation of MC3T3-E1 cells. Furthermore, the printed dual macro-/micro-porous scaffolds showed higher proliferation rate of MC3T3-E1 cells as compared to mono-pore sized scaffolds, either the macro-porous or microporous structure. K E Y W O R D S3D printing, additive manufacturing, bone tissue engineering, microporosity, vat photopolymerization INTRODUCTIONAnnually, millions of bone transplants are performed worldwide. [1] Traditional autografts and allografts have been used for decades, but they have many limitations, including the limited size and supply, the risk of diseaseThis is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
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