A dual-gelling poly(N-isopropylacrylamide)-based ink and thermoreversible poloxamer support bath for high-resolution bioprinting

Extrusion bioprinting is a popular method for fabricating tissue engineering scaffolds because of its potential to rapidly produce complex,bioactive or cell-laden scaffolds.However,due to the relatively high viscosity required to maintain shape fidelity during printing,many extrusion-based inks lack the ability to achieve precise structures at scales lower than hundreds of micrometers.In this work,we present a novel poly(N-isopropylacrylamide)(PNIPAAm)-based ink and poloxamer support bath system that produces precise,multi-layered structures on the tens of micrometers scale.The support bath maintains the structure of the ink in a hydrated,heated environment ideal for cell culture,while the ink undergoes rapid thermogelation followed by a spontaneous covalent crosslinking reaction.Through the combination of the PNIPAAm-based ink and poloxamer bath,this system was able to produce hydrogel scaffolds with uniform fibers possessing diameters tunable from 80 to 200μm.A framework of relationships between several important printing factors involved in maintaining support and thermogelation was also elucidated.As a whole,this work demonstrates the ability to produce precise,acellular and cell-laden PNIPAAm-based scaffolds at high-resolution and contributes to the growing body of research surrounding the printability of extrusion-based bioinks with support baths.

Development of photoreactive demineralized bone matrix 3D printing colloidal inks for bone tissue engineering

Demineralized bone matrix(DBM)has been widely used clinically for dental,craniofacial and skeletal bone repair,as an osteoinductive and osteoconductive material.3D printing(3DP)enables the creation of bone tissue engineering scaffolds with complex geometries and porosity.Photoreactive methacryloylated gelatin nanoparticles(GNP-MAs)3DP inks have been developed,which display gel-like behavior for high print fidelity and are capable of post-printing photocrosslinking for control of scaffold swelling and degradation.Here,novel DBM nanoparticles(DBM-NPs,∼400 nm)were fabricated and characterized prior to incorporation in 3DP inks.The objectives of this study were to determine how these DBM-NPs would influence the printability of composite colloidal 3DP inks,assess the impact of ultraviolet(UV)crosslinking on 3DP scaffold swelling and degradation and evaluate the osteogenic potential of DBM-NP-containing composite colloidal scaffolds.The addition of methacryloylated DBM-NPs(DBM-NP-MAs)to composite colloidal inks(100:0,95:5 and 75:25 GNP-MA:DBM-NP-MA)did not significantly impact the rheological properties associated with printability,such as viscosity and shear recovery or photocrosslinking.UV crosslinking with a UV dosage of 3 J/cm2 directly impacted the rate of 3DP scaffold swelling for all GNP-MA:DBM-NP-MA ratios with an∼40%greater increase in scaffold area and pore area in uncrosslinked versus photocrosslinked scaffolds over 21 days in phosphate-buffered saline(PBS).Likewise,degradation(hydrolytic and enzymatic)over 21 days for all DBM-NP-MA content groups was significantly decreased,∼45%less in PBS and collagenase-containing PBS,in UV-crosslinked versus uncrosslinked groups.The incorporation of DBM-NP-MAs into scaffolds decreased mass loss compared to GNP-MA-only scaffolds during collagenase degradation.An in vitro osteogenic study with bone marrow-derived mesenchymal stem cells demonstrated osteoconductive properties of 3DP scaffolds for the DBM-NP-MA contents examined.The creation of photoreactive DBM-NP-MAs and their application in 3DP provide a platform for the development of ECM-derived colloidal materials and tailored control of biochemical cue presentation with broad tissue engineering applications.