Cell-extracellular communication in granular systems might be explored for tissue engineering and to understand and mimic physiological responses. Particulate systems can be designed as attractive platforms with free movement controlled mainly by intracellular forces and cell migration. We here explore the possibility that the size of the particles composing these systems might have a role in cell response in a sense that a successful long-term cell-particle adhesion might require a minimum traction force for the bond reinforcement. In this work, commercial polystyrene microspheres (type I-collagen coated) are freely assembled and loosely packed as a quasi-3D granular system in a liquid environment. Three size ranges of microspheres (14-20 μm, 38-45 μm, 85-105 μm) were chosen to evaluate the response of human mesenchymal stem cells derived from the adipose tissue (hASC) in these spherical substrates. Cellular characterization was evaluated from 4 hours to a week via metabolic activity, cell adhesion and morphology. Experimental data indicates that objects with increasing diameters (from ~40 μm to ~100 μm) are able to sustain cell adhesion and promote proliferation within seven days of culture. On the other hand, the less explored size comprising 14-20 μm microparticles is more susceptible to cell-mediated mobility, arresting a cell-ECM reinforcement causing early cell detachment. Mechanistic experimental controls through particle sintering allowed to overcome particle mobility and promote cell adhesion in small particles (14-20 μm) as well as increased viability. Weakening cell contractility in larger microspheres (85-105 μm) difficulted the adhesion reinforcement contributing to cell detachment in an otherwise favourable substrate for long-term cell maintenance. Furthermore, an in-silico model addressing pertinent mechanisms of cell attachment to particle beds was developed, corroborating particle free and fixed scenarios. Combining such models with biological assessments could ease the understanding and design of innovative platforms for healthcare-associated problematics.
The authors acknowledge the financial support given by the Portuguese Foundation for Science and Technology (FCT) with the project “CellFi” (PTDC/BTM-ORG/3215/2020), and the European Research Council for the project “ATLAS” (ERC-2014-AdG-669858). This work was developed within the scope of the project CICECO-Aveiro Institute of Materials, UIDB/50011/2020, UIDP/50011/2020 & LA/P/0006/2020, financed by national funds through the FCT/MEC (PIDDAC) and when appropriate co-financed by FEDER under the PT2020 Partnership Agreement. We also acknowledge financial support from the Portuguese Foundation for Science and Technology (FCT) under Contracts no. PTDC/FIS-MAC/28146/2017 (LISBOA-01-0145-FEDER-028146), PTDC/FIS-MAC/5689/2020, UIDB/00618/2020, UIDP/00618/2020, CEECIND/00586/2017, CEECIND/03605/2017, 2021.04817.BD and SFRH/BD/143955/2019.