Polyoxazoline hydrogels fabricated by stereolithography.

The development of hydrogel materials in additive manufacturing displaying stiff and strong mechanical properties while maintaining high water uptake remains a great challenge. Taking advantage of the versatility of poly(oxazoline) (POx) chemistry and properties, we investigated in this article a new generation of POx hydrogels fabricated by stereolithography (SLA). A large range of photosensitive poly(2-methyl-2-oxazoline) resins were synthesized as hydrogel precursors for SLA photofabrication. Functionalization has been performed by direct di-methacrylation of POx terminal groups (MA2POxn) or by multi-methacrylation of poly(ethyleneimine) (PEI) units resulting from partial POx hydrolysis (MAmPOxn-PEIp). The length and the functionality of these UV-active macro-crosslinkers influence both the mechanical properties and the hydration behavior of the resulting hydrogels. The benefit of the layer-by-layer crosslinking of the POx resin during the vat photopolymerization allowed the fabrication of complex and well-defined 3D objects. The high-definition and high mechanical strength of these copolymers allow the fabrication of stiff and strong 3D hydrogels. The cytocompatibility test of the POx derivatives was conducted in solution and once the cells are encapsulated within 3D hydrogels. Finally, porous 3D scaffolds with gyroid architectures were built which provide opportunities for POx materials in tissue engineering applications.

Photoprintable Gelatin-graft-Poly(trimethylene carbonate) by Stereolithography for Tissue Engineering Applications.

The stereolithography process is a powerful additive manufacturing technology to fabricate scaffolds for regenerative medicine. Nevertheless, the quest for versatile inks allowing one to produce scaffolds with controlled properties is still unsatisfied. In this original article, we tackle this bottleneck by synthesizing a panel of photoprocessable hybrid copolymers composed of gelatin-graft-poly(trimethylene carbonate)s (Gel-g-PTMCn). We demonstrated that by changing the length of PTMC blocks grafted from gelatin, it is possible to tailor the final properties of the photofabricated objects. We reported here on the synthesis of Gel-g-PTMCn with various lengths of PTMC blocks grafted from gelatin using hydroxy and amino side groups of the constitutive amino acids. Then, the characterization of the resulting hybrid copolymers was fully investigated by quantitative NMR spectroscopy before rendering them photosensitive by methacrylation of the PTMC terminal groups. Homogeneous composition of the photocrosslinked hybrid polymers was demonstrated by EDX spectroscopy and electronic microscopy. To unravel the individual contribution of the PTMC moiety on the hybrid copolymer behavior, water absorption, contact angle measurements, and degradation studies were undertaken. Interestingly, the photocrosslinked materials immersed in water were examined using tensile experiments and displayed a large panel of behavior from hydrogel to elastomer-like depending on the PTMC/gel ratio. Moreover, the absence of cytotoxicity was conducted following the ISO 10993 assay. As a proof of concept, 3D porous objects were successfully fabricated using stereolithography. Those results validate the great potential of this panel of inks for tissue engineering and regenerative medicine.

Synthesis of Poly(Trimethylene Carbonate) from Amine Group Initiation: Role of Urethane Bonds in the Crystallinity.

Semi-crystalline poly(trimethylene carbonate) (PTMC) can be efficiently prepared by ring-opening polymerization (ROP) initiated by amine using various catalysts. More promising results were reached with the one-step process of stannous octanoate unlike the two-step one-pot reaction using TBD and MSA catalysts. The ROP-amine of TMC consists in a simple isocyanate free process to produce polycarbonate-urethanes, compatible with the large availability of amines ranging from mono- to multifunctional until natural amino acids. ROP-amine of TMC leads to urethane bonds monitored by FTIR spectroscopy. The relationship between the nature of amines and the crystallinity of PTMC was discussed through X-ray diffraction and thermal studies by DSC and TGA. The impact of the crystallinity was also demonstrated on the mechanical properties of semi-crystalline PTMC in comparison to amorphous PTMC, synthesized by ROP initiated by alcohol. The semi-crystalline PTMC synthesized by ROP-amine opens many perspectives.