# Encapsulation Strategy Matters: Pre- and Post-Loading of Macromolecules into Surface-Supported Microgels Formed via Vaterite Templates

## TL;DR

This study compares two methods for loading macromolecules into microgels made using vaterite templates, finding pre-loading to be more effective for encapsulation.

## Contribution

The paper introduces a comparison of pre- and post-loading strategies for macromolecule encapsulation in vaterite-based microgels.

## Key findings

- Pre-loading achieved up to 9% w/w encapsulation efficiency, while post-loading resulted in less than 1% w/w.
- Dextran adsorption followed the Langmuir model, while its derivatives followed the Freundlich model.
- Trypsin-induced PLL degradation enabled sustained dextran release from microgels.

## Abstract

Calcium carbonate vaterite crystals have attracted increasing
attention
as sacrificial templates for forming polymer microgels. Vaterite’s
porous structure, biocompatibility, and eco-friendly synthesis make
it ideal for biomedical applications. In this study, vaterite is grown
on the surface, and surface-supported (ss)-microgels are formed by
coating it with alternating layers of polyelectrolytes, sodium alginate
(ALG), and poly-l-lysine (PLL), followed by core dissolution.
Pre-loading (during vaterite synthesis) and post-loading (after microgel
formation) of macromolecules are compared using dextran and its charged
derivatives. Pre-loading proved to be more efficient, achieving up
to 9% w/w encapsulation. Dextran adsorption follows the Langmuir model
(ΔG = – 31.0 kJ/mol), while its derivatives
follow the Freundlich model (1/n = 0.7–0.8),
indicating intermolecular repulsion. Post-loading resulted in encapsulation
levels below 1% w/w and exhibited pH-independent behavior. The microgels
remained stable in acidic environments, but PLL degradation via trypsin
enabled the sustained release of dextran. These findings clarify the
mechanisms of macromolecular adsorption on ss-vaterite, highlight
the importance of considering the loading strategy when designing
microgels for specific applications, and support the use of ss-microgels
for therapeutic delivery.