COMMUNICATION (1 of 7)© 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Mechanically Tunable Bioink for 3D Bioprinting of Human CellsAurelien Forget, Andreas Blaeser, Florian Miessmer, Marius Köpf, Daniela F. Duarte Campos, Nicolas H. Voelcker, Anton Blencowe, Horst Fischer,* and V. Prasad Shastri* DOI: 10.1002/adhm.201700255 medium-the bioink. [5] The former approach offers the advantage that the 3D scaffold does not have to be fabricated under cytocompatible conditions. Therefore, a broader range of materials can be employed, for example, thermoplasts, such as poly(caprolactone), [6] and additionally, other alternative scaffold fabrication techniques, such as electrospinning, or pressurized gyration can be combined with subsequent functionalization of the scaffold with proteins. [7] In contrast, the latter approach, that is, direct fabrication of cellloaded constructs by hydrogel molding or 3D printing, places high demands on the cytocompatibility of the material and the fabrication process and the resolution is limited by the size of the extrusion nozzle utilized in the fabrication process. [8] However, the advantage of direct fabrication techniques, especially of 3D bioprinting, is its ability to generate constructs with spatially defined cell and material composition. Moreover, biomaterials that are conventionally used in cell culture such as alginate, [9] Pluronic, [10] gelatin, [11] nanocellulose, [12] self-assembling peptides, [13] and agarose [14] are highly advantageous for direct cell printing as they are soluble in water and hence can be formulated as a cell carrier. There has been extensive effort to build on and improve the properties of watersoluble polymers as bioinks. [15,16] For example, to overcome the limitation of the solubilization of Pluronic and its limited diversity of mechanical properties, blending of Pluronic with alginate [17] and crosslinking using acrylate-modified Pluronic have been explored. [10] Notwithstanding these advances that utilize chemical crosslinking to control the mechanical properties of the bioinks, controlling the shear behavior and mechanical This study introduces a thermogelling bioink based on carboxylated agarose (CA) for bioprinting of mechanically defined microenvironments mimicking natural tissues. In CA system, by adjusting the degree of carboxylation, the elastic modulus of printed gels can be tuned over several orders of magnitudes (5-230 Pa) while ensuring almost no change to the shear viscosity (10-17 mPa) of the bioink solution; thus enabling the fabrication of 3D structures made of different mechanical domains under identical printing parameters and low nozzle shear stress. Human mesenchymal stem cells printed using CA as a bioink show significantly higher survival (95%) in comparison to when printed using native agarose (62%), a commonly used thermogelling hydrogel for 3D-bioprinting applications. This work paves the way toward the printing of complex tissue-like structures composed of a range of mechanically discrete microdomains that could potent...

Hydrogel forming polysaccharides, such as the seaweed derived agarose, are well suited for wound dressing applications as they have excellent cell and soft tissue compatibility. For wound dressings, fibrous structure is desirable as the high surface area can favor adsorption of wound exudate and promote drug delivery. Although electrospinning offers a straightforward means to produce nonwoven fibrous polymeric structures, processing agarose and its derivatives into fibers through electrospinning is challenging as it has limited solubility in solvents other than water. In this study we describe the processing of carboxylated agarose (CA) fibers with antibacterial properties by electrospinning from a solution of the ionic liquid (IL) 1-butyl-3-methylimidazolium chloride ([Bmim]Cl) possessing antimicrobial properties. The extent of carboxylation was found to impact fiber diameter, mesh elastic modulus, fiber swelling, and the loading and release of IL. IL-bearing CA fibers inhibited the growth of Staphylococcus aureus and Pseudomonas aeruginosa, bacteria commonly found in wound exudate. In sum, nonwoven CA fibers processed from IL are promising as biomaterials for wound dressing applications.

The mechanical properties of agarose-derived hydrogels depend on the scaffolding of the polysaccharide network. To identify and quantify such higher order structure, we applied Raman optical activity (ROA)-a spectroscopic technique that is highly sensitive toward carbohydrates-on native agarose and chemically modified agarose in the gel phase for the first time. By spectral global fitting, we isolated features that change as a function of backbone carboxylation (28, 40, 50, 60, 80, and 93 %) from other features that remain unchanged. We assigned these spectral features by comparison to ROA spectra calculated for different oligomer models. We found a 60:40 ratio of double- and single-stranded α-helix in the highly rigid hydrogel of native agarose, while the considerably softer hydrogels made from carboxylated agarose use a scaffold of unpaired β-strands.

The mechanical properties of agarose-derived hydrogels depend on the scaffolding of the polysaccharide network. To identify and quantify such higher order structure, we applied Raman optical activity (ROA)-a spectroscopic technique that is highly sensitive towardc arbohydrates-on native agarose and chemically modified agarose in the gel phase for the first time.B ys pectral global fitting,w ei solated features that change as af unction of backbone carboxylation (28, 40, 50, 60, 80, and 93 %) from other features that remain unchanged. We assigned these spectral features by comparison to ROAs pectra calculated for different oligomer models.W e found a6 0:40 ratio of double-and single-stranded a-helix in the highly rigid hydrogel of native agarose,w hile the considerably softer hydrogels made from carboxylated agarose use ascaffold of unpaired b-strands.Water swollen cross-linked polymer networks, [1] otherwise known as hydrogels,h ave found extensive applications in consumer products, [2] pharmaceuticals, [1,3] regenerative medicine, [2,4] and microfluidics devices. [5] Then etwork formation in hydrogels involves covalent, ionic, or physical crosslinks between polymer chains. [1] Then ature of the crosslinks can impact many important properties of the gel, such as stiffness, porosity,a nd rheology.H ydrogels formed from agarose, Supportinginformation and the ORCID identification number(s) for the author(s) of this article can be found under: http://dx.