Ultrastretchable and Self-Healing Double-Network Hydrogel for 3D Printing and Strain Sensor

On the basis of the thermoreversible sol–gel transition behavior of κ-carrageenan in water, a double-network (DN) hydrogel has been fabricated by combining an ionically cross-linked κ-carrageenan network with a covalently cross-linked polyacrylamide (PAAm) network. The κ-carrageenan/PAAm DN hydrogel demonstrated an excellent recoverability and significant self-healing capability (even when notched). More importantly, the warm pregel solution of κ-carrageenan/AAm can be used as an ink of a three-dimensional (3D) printer to print complex 3D structures with remarkable mechanical strength after UV exposure. Furthermore, the κ-carrageenan/PAAm DN hydrogel exhibited a great strain sensitivity with a gauge factor of 0.63 at the strain of 1000%, and thus, the hydrogel can be used as sensitive strain sensors for applications in robotics and human motion detection

Rheological Properties and Scaling Laws of κ‑Carrageenan in Aqueous Solution

Rheological properties, gel network structures, and scaling laws for κ-carrageenan in aqueous solution were studied by rheology and field emission scanning electron microscopy (FESEM). The FESEM micrographs verified that the κ-carrageenan gels were formed by the formation of fibrils. The critical gel concentration, <i>c</i>_g, obtained using the Winter–Chambon criterion, was found to be proportional to temperature as expressed by <i>c</i>_g ∼ <i>T</i>^0.85 where <i>T</i> is the temperature in °C. At the gel point, the critical relaxation exponent <i>n</i> obtained was a constant (<i>n</i> = 0.62) and independent of temperature. The critical gel strength <i>S</i>_g increased with increasing <i>c</i>_g. A constant gel strength <i>S</i>_g/<i>c</i>_g was obtained by normalizing <i>S</i>_g with <i>c</i>_g to eliminate the effect of temperature, showing a unique character of κ-carrageenan in aqueous solution during gelation. The molecular structure of the junctions at the gel point was analyzed using the modified Eldridge–Ferry model, which supported the similarity of the fractal structure in the κ-carrageenan gels. Before the gel point, the zero shear viscosity η₀ of κ-carrageenan solutions diverged as the gelling system approached to the gel point, and a scaling law, η₀ ∼ ε^–γ, was established, where ε is the relative distance of κ-carrageenan concentration <i>c</i> from <i>c</i>_g and γ is the scaling exponent that was found to be 1.6. Beyond the gel point, the plateau modulus <i>G</i>_e of κ-carrageenan gels depended on the polymer concentration according to a power law, <i>G</i>_e ∼ ε^<i>z</i>, where <i>z</i> was found to be 2.7. The critical gel exponent <i>n</i> evaluated from γ and <i>z</i> agreed well with the value of <i>n</i> determined from the Winter–Chambon criterion, further indicating that the characteristic relaxation time of the pregel and the postgel follows the same power law (symmetry at <i>c</i> = <i>c</i>_g) for κ-carrageenan in aqueous solution

A 3D Printable and Mechanically Robust Hydrogel Based on Alginate and Graphene Oxide

Sodium alginate (SA) was used for the first time to noncovalently functionalize amino-graphene oxide (aGO) to produce the SA-functionalized GO, A-aGO. A-aGO was then filled into a double-network (DN) hydrogel consisting of an alginate network (SA) and a polyacrylamide (PAAm) network. Before UV curing, A-aGO was able to provide the SA/PAAm DN hydrogel with a remarkable thixotropic property, which is desirable for 3D printing. Thus, the A-aGO-filled DN hydrogel could be nicely used as an “ink” of a 3D printer to print complicated 3D structures with a high stackability and high shape fidelity. After UV curing, the 3D-printed A-aGO filled DN hydrogel showed robust mechanical strength and great toughness. For the function of A-aGO it was considered that A-aGO acted as a secondary but physical cross-linker, not only to give the hydrogel a satisfactory thixotropic property but also to increase the energy dissipation by combining the physical SA network and the chemical PAAm network. As an exciting result we successfully developed a 3D printable and mechanically robust hydrogel

Three-Dimensional Bioprinting of Oppositely Charged Hydrogels with Super Strong Interface Bonding

A novel strategy to improve the adhesion between printed layers of three-dimensional (3D) printed constructs is developed by exploiting the interaction between two oppositely charged hydrogels. Three anionic hydrogels [alginate, xanthan, and κ-carrageenan (Kca)] and three cationic hydrogels [chitosan, gelatin, and gelatin methacrylate (GelMA)] are chosen to find the optimal combination of two oppositely charged hydrogels for the best 3D printability with strong interface bonding. Rheological properties and printability of the hydrogels, as well as structural integrity of printed constructs in cell culture medium, are studied as functions of polymer concentration and the combination of hydrogels. Kca2 (2 wt % Kca hydrogel) and GelMA10 (10 wt % GelMA hydrogel) are found to be the best combination of oppositely charged hydrogels for 3D printing. The interfacial bonding between a Kca layer and a GelMA layer is proven to be significantly higher than that of the bilayered Kca or bilayered GelMA because of the formation of polyelectrolyte complexes between the oppositely charged hydrogels. A good cell viability of >96% is obtained for the 3D-bioprinted Kca–GelMA construct. This novel strategy has a great potential for 3D bioprinting of layered constructs with a strong interface bonding

Three-Dimensional Bioprinting of Oppositely Charged Hydrogels with Super Strong Interface Bonding

A novel strategy to improve the adhesion between printed layers of three-dimensional (3D) printed constructs is developed by exploiting the interaction between two oppositely charged hydrogels. Three anionic hydrogels [alginate, xanthan, and κ-carrageenan (Kca)] and three cationic hydrogels [chitosan, gelatin, and gelatin methacrylate (GelMA)] are chosen to find the optimal combination of two oppositely charged hydrogels for the best 3D printability with strong interface bonding. Rheological properties and printability of the hydrogels, as well as structural integrity of printed constructs in cell culture medium, are studied as functions of polymer concentration and the combination of hydrogels. Kca2 (2 wt % Kca hydrogel) and GelMA10 (10 wt % GelMA hydrogel) are found to be the best combination of oppositely charged hydrogels for 3D printing. The interfacial bonding between a Kca layer and a GelMA layer is proven to be significantly higher than that of the bilayered Kca or bilayered GelMA because of the formation of polyelectrolyte complexes between the oppositely charged hydrogels. A good cell viability of >96% is obtained for the 3D-bioprinted Kca–GelMA construct. This novel strategy has a great potential for 3D bioprinting of layered constructs with a strong interface bonding

Ten most abundant transcripts in the gut and whole aphid (WA) transcriptomes based on depth of reads assembled into contigs.

<p> Ten most abundant transcripts in the gut and whole aphid (WA) transcriptomes based on depth of reads assembled into contigs.</p

PCR detection of <i>Wolbachia</i> 23S rDNA from the soybean aphid.

<p>Markers, 1 kb DNA ladder (Fisher). NC, negative control (no template). Arrow indicates PCR product of the expected size (2.1 kbp).</p

Phylogenetic relatedness of soybean aphid aminopeptidese N (APN) derived from the gut transciptome with lepidopteran APN.

<p>The phylogenetic tree drawn to scale was generated by using the maximum-likelihood method using <u>MEGA</u> 5.0 with a bootstrap value of 500. Soybean aphid (SA), and pea aphid (PA) sequences are boxed. GenBank accession numbers: <i>Bombyx mori</i>: BmAPN1, AAC33301, BmAPN2, BAA32140, BmAPN3, AAL83943, BmAPN4, BAA33715; <i>Epiphyas postvittana</i>, EpAPN, AAF99701; <i>Helicoverpa armigera</i>, HaAPN1, AAW72993, HaAPN2, AAN04900, HaAPN3, AAM44056, HaAPN4, AAK85539; <i>Helicoverpa punctigera</i>: HpAPN1, AAF37558, HpAPN2, AAF37560; <i>Heliothis virescens</i>: HvAPN1, AAF08254, HvAPN2, AAK58066; <i>Lymantria dispar</i>: LdAPN1, AAD31183, LdAPN2, AAD31184, LdAPN3, AAL26894; LdAPN4, AAL26895; <i>Plutella xylostella</i>: PxAPN1, AAB70755, PxAPN2, CAA66467, PxAPN3, AAF01259, PxAPN4, CAA10950; <i>Manduca sexta</i>: MsAPN1, CAA61452, MsAPN2, CAA66466, MsAPN3, AAM13691, MsAPN4, AAM18718; <i>Spodoptera exigua</i>: SeAPN1, AAP44964, SeAPN2, AAP44965, SeAPN3, AAP44966, SeAPN4, AAP44967; <i>Spodoptera litura</i>: SlAPN, AAK69605; <i>Trichoplusia ni</i>, TnAPN1, AAX39863, TnAPN2, AAX39864, TnAPN3, AAX39865, TnAPN4, AAX39866; <i>Tribolium castaneum</i>: TcAPN1, EEZ99298; TcAPN2, XP_001812439; TcAPN3, XP_972987; TcAPN4, XP_972951; TcAPN5, XP_973022; the pea aphid, <i>A. pisum</i>: PAAPN1, NP_001119606, PAAPN2, XP_001946370, PAAPN3, XP_001946754, PAAPN4, XP_001948442 PAAPN5, XP_001948350, SAAPN1 JN135242; SAAPN2, JN135243; SAAPN3, JN135244, SAAPN4, JN135245.</p

Distribution of <i>Buchnera</i> sequences by gene ontology.

<p>(GO: level 2; filtered by sequence number cutoff  = 5) for biological processes, cellular components, and molecular functions.</p

Summary of BLAST analysis and annotation of soybean aphid sequences.

*<p>% of total number of contigs</p