Smart Chitosan-Based Hydrogel for Sustained Peptide Delivery

Preclinical Development of a Depot System for the Neurotherapeutic Peptide NX210c

Therapeutic peptides occupy a unique position in modern drug development. They combine high biological specificity with comparatively low toxicity and favorable tissue penetration. However, their clinical application is often limited by rapid in vivo degradation and short systemic half-life.

The neuroprotective peptide NX210c illustrates this challenge. Although it shows promising therapeutic potential in neurodegenerative diseases, its half-life is approximately 15 minutes, requiring repeated intravenous administration in clinical settings. To address this limitation, a biodegradable, injectable chitosan-based hydrogel was developed to enable sustained subcutaneous delivery of NX210c.

Material Design: Medical-Grade Chitosan and DOTAGA Functionalization

The hydrogel system is based on medical-grade chitosan with a number-average molecular weight (Mn) of approximately 124 kDa and a high degree of deacetylation (DA ≈ 95%), determined by ¹H NMR. A high DA ensures a large density of free amino groups, which are essential for electrostatic interactions and gel network formation.
To enable physiological in situ gelation, part of the chitosan was functionalized with the macrocyclic polycarboxylate ligand DOTAGA. The substitution degree was approximately 17%. This modification introduces ampholytic behavior and imparts a zwitterionic character to the polymer derivative.
The combination of native chitosan and Chitosan@DOTAGA allows the formulation to remain injectable under mildly acidic conditions while forming a stable hydrogel upon exposure to physiological pH and ionic strength.

Mechanism of In Situ Gelation

After subcutaneous injection, gelation occurs sequentially under physiological conditions (pH 7.4, ~300 mOsm/L).

First, salt diffusion promotes polyelectrolyte complexation between oppositely charged polymer segments. Subsequently, partial deprotonation of chitosan’s amine groups reduces electrostatic repulsion and facilitates hydrogen bonding, hydrophobic interactions, and partial backbone crystallization. These physical crosslinking points stabilize the three-dimensional hydrogel network.
Importantly, this system is solvent-free, biodegradable, and does not rely on chemical crosslinkers.

Influence of Formulation Parameters on Structure and Release

Polymer concentrations between 25 and 50 g/L and varying peptide concentrations were investigated. Both parameters significantly influenced network density, mechanical properties, and release kinetics. Higher polymer concentrations resulted in a denser fibrillar structure with smaller pore sizes. NX210c itself contributed to electrostatic interactions within the network and partly acted as an ionic crosslinker. Peptide–polymer interactions were found to be predominantly electrostatic in nature.
In vitro release studies demonstrated a biphasic profile. An initial diffusion-controlled phase occurred during the first 24 hours, followed by a prolonged, slower release phase. Application of the Ritger–Peppas model yielded a release exponent n < 0.5, indicating diffusion-dominated kinetics.

Biodegradability and Biocompatibility

In vivo studies in rodents demonstrated complete hydrogel degradation within approximately 15 to 21 days. Degradation products were eliminated primarily via the renal pathway, with no significant organ accumulation observed.
Histological analysis showed a mild and transient inflammatory response typical for biodegradable biomaterials. Notably, local tissue reaction was more pronounced after administration of free NX210c compared to the hydrogel formulation, suggesting that the matrix may protect surrounding tissue from acute exposure effects.

Significant Prolongation of Systemic Exposure

Pharmacokinetic evaluation revealed the most striking findings. After intravenous administration, NX210c was rapidly eliminated, with an estimated half-life of approximately 8 to 15 minutes. Subcutaneous administration of the free peptide slightly prolonged detectability but remained limited to a few hours.

In contrast, when delivered via the chitosan hydrogel, NX210c plasma levels were sustained for 10 to 15 days. The area under the curve (AUC) increased by several orders of magnitude compared to free administration.
This transformation of a short-lived peptide into a long-acting depot system significantly reduces dosing frequency and may improve patient compliance in chronic neurological indications.

Which Type of Chitosan Is Suitable for Depot Systems?

The study highlights key material characteristics required for reproducible depot formation:
Medical-grade chitosan with a high degree of deacetylation (> 90%) ensures sufficient positive charge density for electrostatic network formation. A molecular weight in the range of 100 - 150 kDa provides a suitable balance between injectability and structural stability.
For zwitterionic in situ systems, partial functionalization - such as DOTAGA substitution in the range of 15 to 20% - appears optimal. Lower substitution levels may weaken interaction sites, while excessive modification could impair gel network integrity.

Implications for Future Peptide Therapeutics

This work demonstrates how rational polymer modification can convert a natural, biodegradable polysaccharide into a sophisticated controlled-release platform.
Particularly for neurodegenerative diseases requiring long-term therapy, such depot systems offer significant advantages over repeated intravenous infusion. Subcutaneous administration combined with sustained release has the potential to enhance patient comfort while maintaining therapeutic exposure.
The Chitosan@DOTAGA platform thus represents a promising strategy for clinically translatable, long-acting peptide delivery.

Reference
Rosson E., Thomas E., Sidi-Boumedine J., et al. Smart zwitterionic biodegradable hydrogel for sustained peptide delivery: Application to the neurotherapeutic peptide NX210c. Biomaterials Advances, 178 (2026) 214437. https://doi.org/10.1016/j.bioadv.2025.214437

First published on 26th of February 2026

Revised on 26th of February 2026