# Rheological Behavior, Filament Stability, and Microstructure of an Extrusion-Processable Kefiran–PG Formulation

## TL;DR

This study explores a kefiran–PG formulation for 3D printing, showing how its physical structure improves over time without chemical cross-linking.

## Contribution

The study demonstrates that extrusion fidelity in a kefiran–PG formulation is achieved through time-dependent supramolecular consolidation rather than chemical cross-linking.

## Key findings

- Filaments showed improved self-supporting capability after 15 minutes, with normalized deflection below 0.03.
- Storage modulus increased from ~100 to ~1200 Pa over 1800 seconds, indicating progressive viscoelastic stiffening.
- Freeze-dried constructs had a porosity of 60.9 ± 1.2% with pore sizes between 6 and 20 µm.

## Abstract

Microbial polysaccharides are attracting increasing interest as water-processable polymers for extrusion-based additive manufacturing due to their ability to form physically stabilized networks without covalent cross-linking. In this study, a kefiran–propylene glycol (PG) formulation was developed to investigate whether time-dependent supramolecular reorganization can be exploited to control print fidelity. Extrusion performance was assessed through quantitative filament collapse analysis, while rheological behavior was characterized by oscillatory strain, frequency, and time sweep measurements. Filaments printed 5 min after PG addition showed pronounced sagging (δ/(L/2) ≈ 0.35 at the largest spans), whereas after 15 min the normalized deflection decreased below 0.03, indicating a marked improvement in self-supporting capability. Time sweep experiments revealed a continuous increase in storage modulus from ~100 to ~1200 Pa over 1800 s, consistent with progressive viscoelastic stiffening. Freeze-dried constructs exhibited an interconnected porous architecture with a predominant pore population between 6 and 20 µm and an apparent porosity of 60.9 ± 1.2%. Upon rehydration at 37 °C, samples swelled to ~350% within 5 h and showed gradual mass loss over 56 days while remaining intact. ATR–FTIR confirmed the preservation of the polysaccharide backbone without evidence of new covalent functionalities. Extrusion fidelity is therefore governed by progressive supramolecular consolidation within a physically assembled network, rather than by any form of chemical cross-linking.