Modelos tridimensionais de cultura de células: aproximando o in vitro do in vivo

Introduction: Biotechnological advances in association with the pressure to substitute animal experimentation impelled the development of in vitro models that are more physiological and predictive of in vivo response. Objective: To discuss advantages and limitations of threedimensional (3D) cell culture models. Method: Review of the scientific literature at PubMed using the keywords “3D culture”, spheroid, organoid, “organotypic culture”, “alternative model”, microfluidic, organ-on-a-chip and biotechnology, individually and in different combinations. The search period was from 1971 to 2017. Results: Traditional monolayer cell culture assays, although extensively used, do not reproduce the cell-cell and cellextracellular matrix interactions that create physical and chemical gradients and that control cell functions, such as survival, proliferation, differentiation, migration, and protein and gene expression. 3D cell culture models are able to mimic more physiological microenvironment. The number of manuscripts published in this period reflects the scientific interest in the field. Conclusions: Although 3D models have unequivocally contributed to the bioengineering, morphogenesis, oncology, and toxicology fields, many challenges remain. The high cost of some of these models, to reproduce the mechanical spatiotemporal features of the tissues, as wells as the lack of standard protocols should be taken into account. Here we discuss the advantages and limitations of some 3D cell culture models.Introdução: Os avanços biotecnológicos em associação com a pressão para substituir a experimentação animal impulsionam o desenvolvimento de modelos in vitro mais fisiológicos e preditivos da resposta in vivo. Objetivo: Discutir vantagens e limitações de modelos tridimensionais (3D) de cultura de células. Método: Revisão da literatura na base PubMed utilizando os termos “3D culture”, spheroid, organoid, “organotypic culture”, “alternative model”, microfluidic, organ-on-a-chip e biotechnology, individualmente e em diferentes combinações. A pesquisa abrangeu o período de 1971 a 2017. Resultados: Ensaios tradicionais de cultura em monocamada, embora sejam amplamente utilizados, não reproduzem as interações célula-célula e célula-matriz extracelular, que criam gradientes físicos e químicos e controlam funções celulares, como sobrevivência, proliferação, diferenciação, migração e expressão de genes e proteínas. Modelos 3D de cultura de células são capazes de mimetizar um microambiente mais fisiológico. O número de publicações no período estudado reflete o crescente interesse científico no tema. Conclusões: Embora os modelos 3D tenham inequivocamente contribuído para as áreas de bioengenharia, morfogênese, oncologia e toxicologia, muitos desafios permanecem. O custo elevado de alguns destes modelos, reproduzir as características mecânicas, espaciais e temporais dos tecidos, assim como a necessidade de desenvolver protocolos padronizados devem ser considerados

Search for dark matter produced in association with bottom or top quarks in √s = 13 TeV pp collisions with the ATLAS detector

A search for weakly interacting massive particle dark matter produced in association with bottom or top quarks is presented. Final states containing third-generation quarks and miss- ing transverse momentum are considered. The analysis uses 36.1 fb−1 of proton–proton collision data recorded by the ATLAS experiment at √s = 13 TeV in 2015 and 2016. No significant excess of events above the estimated backgrounds is observed. The results are in- terpreted in the framework of simplified models of spin-0 dark-matter mediators. For colour- neutral spin-0 mediators produced in association with top quarks and decaying into a pair of dark-matter particles, mediator masses below 50 GeV are excluded assuming a dark-matter candidate mass of 1 GeV and unitary couplings. For scalar and pseudoscalar mediators produced in association with bottom quarks, the search sets limits on the production cross- section of 300 times the predicted rate for mediators with masses between 10 and 50 GeV and assuming a dark-matter mass of 1 GeV and unitary coupling. Constraints on colour- charged scalar simplified models are also presented. Assuming a dark-matter particle mass of 35 GeV, mediator particles with mass below 1.1 TeV are excluded for couplings yielding a dark-matter relic density consistent with measurements