Unlocking the potential of polyester-polymer: Assisting cold sintering of insoluble ceramics

The cold sintering process (CSP) is a green and innovative method of material densification at low temperatures (<350 ​°C). The traditional CSP entails the addition of liquid phases as a solvent to achieve material densification through the dissolution-precipitation mechanism. However, it is difficult to realize for materials with low solubility. To address this challenge, a universal cold sintering method without the addition of liquid phases has been proposed in this work. The addition of a special polyester-polymer assisted the densification of insoluble ceramics, and hydroxyapatite (HA) and Al₂O₃ were successfully sintered below 100 ​°C, achieving 95–100 ​% densities in a short time (5–20 ​min). This achievement can be attributed to the low glass transition temperature and the abundance of active sites (C=O) of the polyester-polymer. The denser ceramics exhibited enhanced mechanical properties, with the compression strength of polymer-assisted CSP HA increasing by 147.3 ​% compared to the nanoparticles. Additionally, serving as an advanced bone substitute material, HA underwent quantitative analysis using the CCK-8 method and assessed the impact of polymer presence on cell proliferation and cytotoxicity. Meanwhile, a tight bonding between the polymer and ceramic materials was achieved during CSP, providing a generalized method for designing multifunctional ceramic-polymer.