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Efforts to selectively convert polypropylene (≈30 % of all plastic waste) have not been particularly successful. Typical distributions span from gas to solid products, highlighting a challenging cleavage control. Here, carbon‐supported platinum nanoparticles were designed for complete hydrocracking into liquid hydrocarbons (C5–C45). The metal and carrier phases operated synergistically. The cleavage activity depended on platinum and its rate rose with decreasing particle size. The carbon carrier controlled selectivity via hydrocarbon binding strength, which depended on the chain length and on the surface oxygen concentration. An optimal binding provided by carbons with high oxygen content promoted both adsorption of long chains and desorption of short products. This strategy achieved an unprecedented 80 % selectivity toward motor oil (C21–C45). Carbons exhibiting too strong binding (low oxygen content) hindered product desorption, while non‐binding materials (e. g., silica or alumina) did not promote plastic–Pt contact, leading in both cases to low performance. This work pioneers design guidelines in a key process towards a sustainable plastic economy.

Biophysical properties of the cellular microenvironment, including stiffness and geometry, have been shown to influence cell function. Recent findings have implicated 3D confinement as an important regulator of cell behavior. The understanding of how mechanical signals direct cell function is based primarily on 2D studies. To investigate how the extent of 3D confinement affects cell function, a single cell culture platform is fabricated with geometrically defined and fully enclosed microwells and it is applied to investigate how niche volume and stiffness affect human mesenchymal stem cells (hMSC) life and death. The viability and proliferation of hMSCs in confined 3D microniches are compared with unconfined cells in 2D. Confinement biases hMSC viability and proliferation, and this influence depends on the niche volume and stiffness. The rate of cell death increases and proliferation markedly decreases upon 3D confinement. The observed differences in hMSC behavior are correlated to changes in nuclear morphology and YES-associated protein (YAP) localization. In smaller 3D microniches, hMSCs display smaller and more rounded nuclei and primarily cytoplasmic YAP localization, indicating reduced mechanical activation upon confinement. Interestingly, these effects scale with the extent of 3D confinement. These results demonstrate that the extent of confinement in 3D can be an important regulator of cell function.

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Biophysical properties of the cellular microenvironment, including stiffness and geometry, influence cell fate. Recent findings have implicated geometric confinement as an important regulator of cell fate determination. Our understanding of how mechanical signals direct cell fate is based primarily on two-dimensional (2D) studies. To investigate the role of confinement on stem cell fate in three-dimensional (3D) culture, we fabricated a single cell microwell culture platform and used it to investigate how niche volume and stiffness affect human mesenchymal stem cell (hMSC) fate. The viability and proliferation of hMSCs in confined 3D microniches were compared with the fate of unconfined cells in 2D culture. Physical confinement biased hMSC fate, and this influence was modulated by the niche volume and stiffness. The rate of cell death increased, and proliferation markedly decreased upon 3D confinement. We correlated the observed differences in hMSC fate to YES-associated protein (YAP) localization. In 3D microniches, hMSCs displayed primarily cytoplasmic YAP localization, indicating reduced mechanical activation upon confinement. These results demonstrate that 3D geometric confinement can be an important regulator of cell fate, and that confinement sensing is linked to canonical mechanotransduction pathways.

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