# Structural Instability of Human Serum Albumin during Microparticles Synthesis

## TL;DR

Human serum albumin microparticles are structurally stable but lose some protein function, which could be useful for controlled drug delivery.

## Contribution

The study reveals structural changes in human serum albumin during microparticle synthesis that affect its binding properties.

## Key findings

- Microparticles made from human serum albumin are mechanically robust but undergo structural changes during agglomeration.
- The protein's secondary structure shifts from α-helices to β-sheets, reducing its binding capability for molecules like hemin.
- Reduced binding on the microparticle surface prevents unwanted ligand interactions, which could be beneficial for targeted drug delivery.

## Abstract

Human serum albumin,
the most abundant plasma protein, plays vital
roles in maintaining oncotic pressure, modulates drugs pharmacokinetics
and pharmacodynamics, and features antioxidant and enzyme-like properties.
This protein also exhibits high-affinity binding to a wide range of
endogenous and exogenous molecules. Combined with its excellent solubility,
biocompatibility, biodegradability, low toxicity, and nonimmunogenicity,
these properties make human serum albumin an attractive platform for
biomedical applications, particularly in drug delivery. This study
reports a detailed physicochemical characterization of human serum
albumin microparticles obtained via the coprecipitation-cross-linking-dissolution
method. The resulting submicron particles are peanut-shaped, exhibit
uniform morphology, and show robust mechanical properties, including
high stiffness and colloidal stability. However, we observed that
the microparticle agglomeration process induces significant structural
changes in the protein. Notably, Raman and FTIR spectroscopies highlighted
a partial switch from α-helices to β-sheets secondary
structure, which leads to diminished HSA binding capability as here
demonstrated in the case of hemin. This trade-off between mechanical
integrity and biological activity poses challenges for applications
requiring native protein interactions, such as the HSA-dependent efficient
drug binding and controlled release. Conversely, the reduced binding
capability of HSA molecules localized on the surface of MPs implies
that these HSA-MPs cannot bind to plasma ligands (e.g., drugs, heme,
bacteria toxins). This prevents unwanted ligands from being transported
to cellular targets, ensuring that only those located within the HSA-MP
are transported. Our findings open new avenues for engineering microsystems
that could couple the structural resilience of these microparticles
with restored functional surfaces.