(315e) Microstructure-Property Correlation in Hybrid Colloidal Gels Based on Gelatin Nanoparticles and Silicate Nanoplatelets

Nowadays, bioprinting opens up a new direction in biomedical engineering as an efficient, low-cost, and precise method. The critical point to guarantee high quality and accuracy of the printing process is to formulate an ink with appropriate rheological characteristics. Here, we show that the controlled assembly between 300-nm spherical gelatin nanoparticles (GelNP) and 25-nm silicate nanoplatelets (SNP) results in a hybrid colloidal gel with tunable rheological properties. Specifically, we show that at a given solid content, pH and ionic strength, the formation mechanism, microscopic structure, and the macroscopic properties of the GelNP-SNP hybrid colloidal gels dramatically vary by the composition (SNP/GelNP ratio) and the nature of charges on the 2D building blocks. The characterization of microstructure and viscoelastic properties by dynamic light scattering, electron microscopy, and rheological measurements suggests that the electrostatic interactions between GelNP and SNP govern the gel properties at SNP/GelNP ratio <1. On the other hand, the interactions between 2D building blocks become more dominant at higher SNP/GelNP ratios. To confirm this, we used two SNP types with identical structures and negatively charged faces but different charge types on their edges. At low SNP/GelNP ratios, both SNP types equally improved the elasticity of a 10 wt.% system due to charge-driven self-assembly between the positively charged GelNP and negatively charged faces on SNP, as confirmed by dynamic light scattering measurements. However, at SNP/GelNP ratios > 1, the viscoelastic behavior shows two opposite trends for the systems with different SNP types. In the system based on SNPs with positively charged edges, the storage modulus kept increasing with increasing the SNP/GelNP ratio and an elasticity of 10⁴ Pa at SNP/GelNP = 5 was obtained. In contrast, at the same ratio, the storage modulus declined to 300 Pa when SNPs with negatively charged faces and edges were used. The capability to adjust the properties of hybrid colloidal gels over a wide range of elasticity by combining building blocks of different shapes and length scales suggests these systems as ideal candidates for engineering bioinks and other injectable formulations.