3D-printing of dynamic self-healing cryogels with tuneable properties

Abstract

We report a novel synthetic and processing methodology for the preparation of doubly dynamic, selfhealing, 3D-printable macroporous gels. 3D-printable oxime hydrogels were prepared by cross-linking poly(n-hydroxyethyl acrylamide-co-methyl vinyl ketone) (PHEAA-co-PMVK) with a bifunctional hydroxylamine. 3D-printed oxime hydrogels were subjected to post-printing treatment by thermally induced phase separation (TIPS), which facilitated the formation of hydrogen bonding and oxime cross-links, and dramatically increased the mechanical strength of soft oxime objects in a well-controlled manner by up to ∼1900%. The mechanical properties of the cryogels were tuned by freezing conditions, which affected the microstructure of the cryogels. These doubly dynamic 3D-printed cryogels are macroporous, exhibit outstanding swelling performances, and can fully, rapidly and autonomously self-heal. † Electronic supplementary information (ESI) available. See

Extrusion 3D Printing of Polymeric Materials with Advanced Properties

“…The adjustment and optimization of ink formulations should be carefully executed through precise control of the polymer concentration and degrees of crosslinking. [ 86,114,115 ] There is a clear operational window for DIW printing: the gels should not be too soft and spreadable (low concentration and crosslinking density) nor too stiff to be extruded (high concentration and crosslinking density). In contrast to physically crosslinked hydrogels, the use of dynamic covalent crosslinked hydrogels as the ink enabled the formation of well‐structured and mechanical stable filamentous strands.…”

“…In contrast to physically crosslinked hydrogels, the use of dynamic covalent crosslinked hydrogels as the ink enabled the formation of well‐structured and mechanical stable filamentous strands. [ 114,115 ] Subsequent printing of multiple ink layers on top of each other does not cause spreading or collapsing of the network.…”

“…The use of dynamic bonds which undergo reversible breaking, exchange and reformation could be utilized to modify the printability of polymers as well as imparting various advanced functions. [ 41–58,62–67,59,68,60,69,70,72,61,73,71,82,86–88,74–81,83–85,89–133,244,258 , …”

Advanced Polymer Designs for Direct‐Ink‐Write 3D Printing

“…By varying the polymer concentrations and the degree of cross‐linking, a series of inks with different viscosities and storage moduli was obtained and the optimized gel with balanced rheological properties was 3D printed successfully. They later reported a 3D printable oxime hydrogel formed through cross‐linking poly( n ‐hydroxyethyl acrylamide‐co‐methyl vinyl ketone) with a bifunctional hydroxylamine (Figure b) . Burdick et al.…”

“…For example, Connal et al synthesized [94] benzaldehyde-functionalized poly(2-hydroxyethyl methacrylate) (PHEMA) polymers and mixed them with ethylenediamine (EDA) as ac ross-linker.B yv arying the polymer concentrations and the degree of cross-linking, a series of inks with different viscosities and storagem oduli was obtained and the optimized gel with balanced rheological properties was 3D printed successfully.T hey later reported a 3D printable oxime hydrogel formed through cross-linking poly(n-hydroxyethyl acrylamide-co-methyl vinyl ketone) with a bifunctional hydroxylamine (Figure 6b). [95] Burdicke tal. reported [96] ah ydrazone-based 3D printable hydrogel by cross-linking hydrazide-modified hyaluronic acid and aldehyde-modified hyaluronic acid.…”