Improving Printability of a Thermoresponsive Hydrogel Biomaterial Ink by Nanoclay Addition

Abstract

As a promising biofabrication technology, extrusion-based bioprinting has gained significant attention in the last decade and major advances have been made in the development of bioinks. However suitable synthetic and stimuli-responsive bioinks are underrepresented in this context. <a>In this work, we described a hybrid system of nanoclay Laponite XLG and thermoresponsive block copolymer poly(2-methyl-2-oxazoline)-<i>b</i>-poly(2-<i>n</i>-propyl-2-oxazine) (PMeOx-<i>b</i>-PnPrOzi) as a novel biomaterial ink, and discussed its critical properties relevant for extrusion-based bioprinting, including viscoelastic properties and printability.</a> <a>The hybrid hydrogel retains the thermogelling properties but is strengthened by the added clay (over 5 kPa of storage modulus, and 240 Pa of yield stress). Importantly, the shear-thinning character is further enhanced, which, in combination with very rapid viscosity recovery (~1 s) and structure recovery (~10 s) is highly beneficial for extrusion-based 3D printing. Accordingly, various 3D patterns could be printed with markedly enhanced resolution and shape fidelity compared to the biomaterial ink without added clay.</a>

A Thermogelling Organic-Inorganic Hybrid Hydrogel with Excellent Printability, Shape Fidelity and Cytocompatibility for 3D Bioprinting

“…The diblock copolymer PMeOx-b-PnPrOzi was synthesized by LCROP of the monomers MeOx and nPrOzi as previously reported and characterized accordingly (Figure S1, Supporting Information). 36,39 Specifically, 20 wt% POx-b-POzi were combined with 1, 2 and 3 wt% sodium alginate.…”

“…The clay addition leads to an extension of the LVE, which is in line with observations for the plain POx-b-POzi thermogelling system. 39 A subsequent dynamic frequency sweep under a strain of 0.1% within the LVE range showed a dominating G' value over G'' in the entire investigated frequency range (0.1-100 rad s -1 ), indicating their stable gel-like character (Figure 3c). While the G' were rather stable, the values for G'' went through a minimum at around 10 rad s -1 .…”

“…It defines the hydrogel´s resistance against deformation from gravity or surface tension, and therefore, is a potential predictor of how well an ink keeps its shape fidelity after extrusion. [49][50] From the dynamic oscillatory stress sweep, a well improved yield stress of around addition of clay increased the yield stress to 240 Pa. 39 Therefore, it appears that the addition of 1 wt% alginate generally decreases the yield stress of the POx-b-POzi thermogel while addition of clay increases it and overcompensates the loss from alginate addition. Furthermore, another parameter important for 3D printing is the shear-thinning of the material.…”

“…The POx-b-POzi diblock copolymer was synthesized using MeOTf to initiate a cationic ring-opening polymerization of monomers MeOx followed by nPrOzi, as previously described. 36,39 Specifically, under dry and inert conditions, 0.48 g (2.92 mmol, 1 eq.) MeOTf and 24.81 g (291.5 mmol, 100 eq.)…”

“…36 This could be significantly improved by addition of clay as rheological modifiers. 39 Very recently, Haider et al introduced an alternative in with the PMeOx block was exchanged with an poly(2-ethyl-2-oxazoline). 40 However, the lacking long-term stability of the printed constructs remains a major drawback -upon addition of excess cell culture media necessary for longer-term cell culture, these constructs will simply dissolve.…”