Search

Cartilage tissue presents low self-repair capability and lesions often undergo irreversible progression. Structures obtained by tissue engineering, such as those based in extrusion bioprinting of constructs loaded with stem cell spheroids may offer valuable alternatives for research and therapeutic purposes. Human mesenchymal stromal cell (hMSC) spheroids can be chondrogenically differentiated faster and more efficiently than single cells. This approach allows obtaining larger tissues in a rapid, controlled and reproducible way. However, it is challenging to control tissue architecture, construct stability, and cell viability during maturation. Herein, this work reports a reproducible bioprinting process followed by a successful post-bioprinting chondrogenic differentiation procedure using large quantities of hMSC spheroids encapsulated in a xanthan gum-alginate hydrogel. Multi-layered constructs are bioprinted, ionically crosslinked, and post chondrogenically differentiated for 28 days. The expression of glycosaminoglycan, collagen II and IV are observed. After 56 days in culture, the bioprinted constructs are still stable and show satisfactory cell metabolic activity with profuse extracellular matrix production. These results show a promising procedure to obtain 3D models for cartilage research and ultimately, an in vitro proof-of-concept of their potential use as stable chondral tissue implants.

Digital light processing (DLP) is an accurate and fast additive manufacturing technique to produce a variety of products, from patient-customized biomedical implants to consumer goods. However, DLP's use in tissue engineering has been hampered due to a lack of biodegradable resin development. Herein, a library of biodegradable poly(esters) capped with urethane acrylate (with variations in molecular weight) is investigated as the basis for DLP printable resins for tissue engineering. The synthesized oligomers show good printability and are capable of creating complex structures with mechanical moduli close to those of medium-soft tissues (1-3 MPa). While fabricated films from different molecular weight resins show few differences in surface topology, wettability, and protein adsorption, the adhesion and metabolic activity of NCTC clone 929 (L929) cells and human dermal fibroblasts (HDFs) are significantly different. Resins from higher molecular weight oligomers provide greater cell adhesion and metabolic activity. Furthermore, these materials show compatibility in a subcutaneous in vivo pig model. These customizable, biodegradable, and biocompatible resins show the importance of molecular tuning and open up new possibilities for the creation of biocompatible constructs for tissue engineering.

There is increasing evidence that cells cultured in three-dimensional (3D) settings have superior performance compared to their traditional counterparts in monolayers. This has been attributed to cell-cell and cell-extracellular matrix interactions that more closely resemble the in vivo tissue architecture. The rapid adoption of 3D cell culture systems as experimental tools for diverse applications has not always been matched by an improved understanding of cell behavior in different 3D environments. Here, we studied human mesenchymal stem/stromal cells (hMSCs) as scaffold-free self-assembled aggregates of low and high cell number and compared them to cell-laden alginate hydrogels with and without arginine-glycine-aspartic acid peptides. We observed a significant decrease in the size of cell-only aggregates over 14 days in culture compared to the cells encapsulated in alginate hydrogels. Alginate hydrogels had persistently more living cells for a longer period (14 days) in culture as measured by total DNA content. Proliferation studies revealed that a weeklong culture of hMSCs in 3D culture, whether as aggregates or cell-laden alginate hydrogels, reduced their proliferation over time. Cell cycle analysis found no significant differences between days 1 and 7 for the different culture systems. The findings of this study improve our understanding of how aggregate cultures differ with or without a hydrogel carrier, and whether aggregation itself is important when it comes to the 3D culture of hMSCs.

Shape morphing materials, especially those fabricated by 4D printing, are gaining much attention due to their versatility of actuation and capability of being programmed in advance. These materials become particularly interesting for biomedical applications where implant materials could be remotely actuated, exerting a force on the surrounding tissues and cells. However, applications in this field have been restricted due to the biocompatibility of the materials and the character of the required stimuli, generally not compatible with physiological environments. Magnetic nanoparticles (MNPs) represent a great opportunity to this end; however, the actuation results in a uniform movement toward the magnet that requires anchoring of the object. Here, for the first time, the application of anisotropic Fe3O4 MNPs is described, and synthesized by a novel and easy route, that can be aligned on pre-defined patterns within objects printed by digital light processing, resulting in materials that can be actuated remotely (4D printing). These nanoparticles (178 nm x 55 nm), show good biocompatibility when directly seeded on top of human mesenchymal stem cells, despite being uptaken. Most importantly, the alignment of the MNPs can tune the movement of fabricated nanocomposite materials, resulting in complex movements of attraction or repulsion depending on the direction of the applied magnetic field. T.K., and S.C.-E. contributed equally to this work. This work was supported financially by the Province of Limburg and the Brightlands Materials Center. The authors were also grateful to the research program Innovation Fund Chemistry, which was partly financed by the Netherlands Organization for Scientific Research (NWO) under TA grant agreement 731.016.202 ("DynAM"). The authors acknowledge the Texas A&M Health Science Center College of Medicine Institute for Regenerative Medicine at Scott & White who isolated and provided the cells through a grant from NCRR of the NIH (Grant #P40RR017447).

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI TOF MS) was used to analyze a series of synthetic organic ions bearing fixed multiple charges. Despite the multiple intrinsic charges, only singly charged ions were recorded in each case. In addition to the pseudo-molecular ions formed by counterion adduction, deprotonation and electron capture, a number of fragment ions were also observed. Charge splitting by fragmentation was found to be a viable route for charge reduction leading to the formation of the observed singly charged fragment ions. Unlike multivalent metal ions, organic ions can rearrange and/or fragment during charge reduction. This fragmentation process will evidently complicate the interpretation of the MALDI MS spectrum. Because MALDI MS is usually considered as a soft ionization technique, the fragment ion peaks can easily be erroneously interpreted as impurities. Therefore, the awareness and understanding of the underlying MALDI-induced fragmentation pathways is essential for a proper interpretation of the corresponding mass spectra. Due to the fragment ions generated during charge reduction, special care should be taken in the MALDI MS analysis of multiply charged ions. In this work, the possible mechanisms by which the organic ions bearing fixed multiple charges fragment are investigated. With an improved understanding of the fragmentation mechanisms, MALDI TOF MS should still be a useful technique for the characterization of organic ions with fixed multiple charges.

Functionalized benzotrifurans can be accessed in one efficient acylation step from previously unreported benzotrifuranone. DFT calculations have confirmed the aromaticity of the heteroaromatic system and determined its electronic structure that is relevant to applications in materials and supramolecular chemistry.