Biofabrication of tissue engineering constructs with tailored architecture and organized cell placement using rapid prototyping technologies is a major research focus in the field of regenerative therapies. This study describes a novel alginate-based material suitable for both cell embedding and fabrication of three-dimensional (3D) structures with predefined geometry by 3D plotting. The favourable printing properties of the material were achieved by using a simple strategy: addition of methylcellulose (MC) to a 3% alginate solution resulted in a strongly enhanced viscosity, which enabled accurate and easy deposition without high technical efforts. After scaffold plotting, the alginate chains were crosslinked with Ca ; MC did not contribute to the gelation and was released from the scaffolds during the following cultivation. The resulting constructs are characterized by high elasticity and stability, as well as an enhanced microporosity caused by the transient presence of MC. The suitability of the alginate/MC blend for cell embedding was evaluated by direct incorporation of mesenchymal stem cells during scaffold fabrication. The embedded cells showed high viability after 3 weeks of cultivation, which was similar to those of cells within pure alginate scaffolds which served as control. Maintenance of the differentiation potential of embedded cells, as an important requirement for the generation of functional tissue engineering constructs, was proven for adipogenic differentiation as a model for soft tissue formation. In conclusion, the temporary integration of MC into a low-concentrated alginate solution allowed the generation of scaffolds with dimensions in the range of centimetres without loss of the positive properties of low-concentrated alginate hydrogels with regard to cell embedding. Copyright © 2015 John Wiley & Sons, Ltd.

Embedding of mammalian cells into hydrogel scaffolds of predesigned architecture by rapid prototyping technologies has been intensively investigated with focus on tissue engineering and organ printing. The study demonstrates that such methods can be extended to cells originating from the plant kingdom. By using 3D plotting, microalgae of the species Chlamydomonas reinhardtii were embedded in 3D alginate‐based scaffolds. The algae survived the plotting process and were able to grow within the hydrogel matrix. Under illumination, the cell number increased as indicated by microscopic analyses and determination of the chlorophyll content which increased 16‐fold within 12 days of cultivation. Photosynthetic activity was evidenced by measurement of oxygen release: within the first 24 h, an oxygen production rate of 0.05 mg L−1 h−1 was detected which rapidly increased during further cultivation (0.25 mg L−1 h−1 between 24 and 48 h). Furthermore, multichannel plotting was applied to combine human cells and microalgae within one scaffold in a spatially organized manner and hence, to establish a patterned coculture system in which the algae are cultivated in close vicinity to human cells. This might encourage the development of new therapeutic concepts based on the delivery of oxygen or secondary metabolites as therapeutic agents by microalgae.

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Biotechnological processes using photosynthetic microorganisms are of growing industrial interest for the production of renewable energies, platform chemicals or pharmaceutical drugs. Microalgae can be cultivated in suspension, or immobilized by active or passive approaches. We analyzed microalgae growth and population dynamics at different temperatures and illumination conditions in suspension and immobilized in 3D-plotted hydrogels. For microbial processes, the viability of the organisms is essential as productivity depends directly on the number of active catalytic units. Therefore it is important to understand how cultivation conditions influence the population viability. We found that even under non-optimal temperatures, the number of viable microalgae was directly influenced by length of exposure to light for both suspension and immobilized cultures. The cultivation of microalgae in 3D-plotted hydrogels, a highly organized immobilization technique, affords new fields of applications, e.g. the co-cultivation of different microorganisms in close vicinity but without direct contact.www.els-journal.com Page 3 Engineering in Life SciencesThis article is protected by copyright. All rights reserved. AbstractIn this study, microalgae were cultivated in the form of suspension cultures using a new structurally organized immobilization technique called "Green Bioprinting". This technique allows the co-cultivation of different microorganisms in close vicinity to, but without direct contact with microalgae. The goal is to improve the oxygen supply of different cell types by photosynthetic oxygen evolution. However, more information on the optimum culture conditions for different microalgae is necessary. Therefore, Chlamydomonas reinhardtii 11.32b and Chlorella sorokiniana UTEX1230 were suspended in culture medium or embedded in hydrogels by the 3D-bioprinting process followed by cultivation under different temperatures (26 °C, 30 °C or 37 °C) and modes of illumination (continuous illumination or a 14/10 hours light/dark cycle). Concluding, the 3D-bioprinting immobilization represents a technique to cultivate microalgae at a high viability and growth rate even under non-optimal temperature conditions.

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Additive manufacturing (AM) allows the free form fabrication of three-dimensional (3D) structures with distinct external geometry, fitting into a patient-specific defect, and defined internal pore architecture. However, fabrication of predesigned collagen scaffolds using AM-based technologies is challenging due to the low viscosity of collagen solutions, gels or dispersions commonly used for scaffold preparation. In the present study, we have developed a straightforward method which is based on 3D plotting of a highly viscous, high density collagen dispersion. The swollen state of the collagen fibrils at pH 4 enabled the homogenous extrusion of the material, the deposition of uniform strands and finally the construction of 3D scaffolds. Stabilization of the plotted structures was achieved by freeze-drying and chemical crosslinking with the carbodiimide EDC. The scaffolds exhibited high shape and dimensional fidelity and a hierarchical porosity consisting of macropores generated by strand deposition as well as an interconnected microporosity within the strands as result of the freeze-drying process. Cultivation of human mesenchymal stromal cells on the scaffolds, with and without adipogenic or osteogenic stimulation, revealed their cytocompatibility and potential applicability for adipose and bone tissue engineering.