Nathaniel Skillin1,2,Kristi Anseth1,Timothy White1
University of Colorado Boulder1,University of Colorado Anschutz Medical Campus2
Nathaniel Skillin1,2,Kristi Anseth1,Timothy White1
University of Colorado Boulder1,University of Colorado Anschutz Medical Campus2
Liquid crystal polymer networks (LCNs) and elastomers (LCEs) are gaining attention as bio-inspired materials for tissue engineering because of their parallels to biological architecture at multiple length scales. At the tissue level, dynamic epithelial monolayers can be modeled as active nematic liquid crystals and muscle tissues possess anisotropic material properties analogous to monodomain LCNs or LCEs. On the molecular scale, (pro)collagen fibers display liquid crystalline phases and cytoskeletal proteins within the cell can self-organize into nematic phases. Prior research has focused on 2-dimensional LCN substrates and rigid, porous scaffolds. These LCNs are stiff (E~MPa–GPa) compared to native tissues (E~Pa–kPa) and do not present the 3-dimensional (3D) cell-matrix interactions that cells normally experience <i>in vivo</i>. Meanwhile, poly(ethylene glycol) (PEG) based hydrogels have been used extensively as synthetic matrices for 3D cell culture.<br/>We hypothesized that introducing PEG into LCE compositions would be a route to better match native tissue properties while retaining the anisotropy of liquid crystals. To this end, we detail an approach in which we oligomerize commercially available reactive liquid crystal mesogens and linear hydrophilic PEG spacers. Using base-catalyzed thiol-Michael addition followed by acrylate or thiol-ene photopolymerization, we retain and can dynamically adjust liquid crystalline character in the final hydrogel. X-ray studies, differential scanning calorimetry, and mechanical testing of bulk hydrogels (shear rheology, dynamic mechanical analysis) confirm the retention of the liquid crystalline phases in swollen gels. While PEG hydrogels require the use of adhesive peptide sequences to facilitate cell adhesion and proliferation, cells grew on LC-PEG hydrogels without these modifications. Furthermore, LC-PEG block copolymers were amenable to 3D extrusion printing. Hydrated oligomers were molecularly aligned after printing and retained alignment after secondary photo-crosslinking even when subject to repeated swelling and drying cycles. While cells can easily be cultured on the top of these printed scaffolds, cells can also be mixed with LC-PEG oligomers before printing, enabling 3D bioprinting into complex geometries.