Despite the tremendous potential of bioprinting techniques toward the fabrication of highly complex biological structures and the flourishing progress in 3D bioprinting, the most critical challenge of the current approaches is the printing of hollow tubular structures. In this work, an advanced 4D biofabrication approach, based on printing of shape-morphing biopolymer hydrogels, is developed for the fabrication of hollow self-folding tubes with unprecedented control over their diameters and architectures at high resolution. The versatility of the approach is demonstrated by employing two different biopolymers (alginate and hyaluronic acid) and mouse bone marrow stromal cells. Harnessing the printing and postprinting parameters allows attaining average internal tube diameters as low as 20 µm, which is not yet achievable by other existing bioprinting/biofabrication approaches and is comparable to the diameters of the smallest blood vessels. The proposed 4D biofabrication process does not pose any negative effect on the viability of the printed cells, and the self-folded hydrogel-based tubes support cell survival for at least 7 d without any decrease in cell viability. Consequently, the presented 4D biofabrication strategy allows the production of dynamically reconfigurable architectures with tunable functionality and responsiveness, governed by the selection of suitable materials and cells.

4D Biofabrication Using Shape-Morphing Hydrogels

Ions-induced gelation of alginate: Mechanisms and applications.

Islets encapsulated in immunoprotective microcapsules are being proposed as an alternative for insulin therapy for treatment of type 1 diabetes. Many materials for producing microcapsules have been proposed but only alginate does currently qualify as ready for clinical application. However, many different alginate-based capsule systems do exist. A pitfall in the field is that these systems are applied without a targeted strategy with varying degrees of success as a consequence. In the current review the different properties of alginate-based systems are reviewed in view of future application in humans. The use of allogeneic and xenogeneic islet sources are discussed with acknowledging the different degrees of immune protection the encapsulation system should supply. Also issues such as oxygen supply and the role of danger associated molecular patterns (DAMPS) in immune activation are being reviewed. A common property of the encapsulation systems is that alginates for medical application should have an extreme high degree of purity and lack pathogen-associated molecular patterns (PAMPs) to avoid activation of the recipient’s immune system. Up to now, non-inflammatory alginates are only produced on a lab-scale and are not yet commercially available. This is a major pitfall on the route to human application. Also the lack of predictive pre-clinical models is a burden. The principle differences between relevant innate and adaptive immune responses in humans and other species are reviewed. Especially the extreme differences between the immune system of non-human primates and humans are cumbersome as non-human primates may not be predictive of the immune responses in humans, as opposed to the popular belief of regulatory agencies. Current insight is that although the technology is versatile major research efforts are required for identifying the mechanical, immunological and physico-chemical requirements for successful human application.

/pdf/immunological-and-technical-considerations-in-application-of-q2guy3jkpj.pdf

Immunological and technical considerations in application of alginate-based microencapsulation systems

Recent advances in composites based on cellulose derivatives for biomedical applications.

https://repositorium.sdum.uminho.pt/bitstream/1822/51432/1/document_47308_1.pdf

Effect of alginate molecular weight and M/G ratio in beads properties foreseeing the protection of probiotics

Biocompatibility and physicochemical characteristics of alginate-polycation microcapsules.

Direct effect of alginate purification on the survival of islets immobilized in alginate-based microcapsules

Bioencapsulation of Living Cells for Diverse Medical Applications

Understanding the biocompatibility of microcapsules designed for islet cell transplantation

There is a need for better understanding of the biocompatibility of alginate–polycation microcapsules based on their physicochemical characteristics Microcapsules composed of alginate with 44% (IntG) or 71% (HiG) guluronate, gelled with calcium (Ca) or barium (Ba) and coated with poly-L-lysine (PLL) or poly-L-ornithine (PLO), followed by IntG alginate were compared For microcapsules with an IntG(Ca) gel core, using PLO instead of PLL resulted in less immune cell adhesion after 2 days in C57BL/6J mice The PLO microcapsules were also characterized by greater hydrophilicity and superior resistance to swelling and damage under osmotic stress For microcapsules with a PLL membrane, replacing the IntG(Ca) gel core with IntG(Ba) or HiG(Ca) gel resulted in stronger immune responses (p < 005) This was explained by poor penetration of PLL into the gel, as demonstrated by Fourier transform infrared spectroscopy analyses and membrane rupturing during osmotic swelling X-ray photoelectron spectroscopy analyses show that all microcapsules had the same amount of polycation at their surface Moreover, alginate coatings had non-significant effects on the biocompatibility and physicochemical properties of the microcapsules Thus, alginate–polycation interactions for membrane formation are more important for biocompatibility than either the quantity of polycation at the surface or the alginate coating

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