New results on stabilising the boundary between collapsed and swollen phases in microgels

2022-02-01

In a new article published in Gels, Yassir Al-Tikriti, PhD student at SweDeliver, presents results supporting the hypothesis that the boundary between collapsed and swollen phases in the same microgel is stabilised by thermodynamic factors.

Yassir Al-Tikriti, PhD student at SweDeliver
Yassir Al-Tikriti, PhD student at SweDeliver

Polyelectrolyte microgels may undergo volume phase transition upon loading and the release of amphiphilic molecules, a process important in drug delivery. The new phase is “born” in the outermost gel layers, whereby it grows inward as a shell with a sharp boundary to the “mother” phase (core). The swelling and collapse transitions have previously been studied with microgels in large solution volumes, where they go to completion.

"We have a hypothesis that the boundary between core and shell is stabilised by thermodynamic factors, and thus that collapsed and swollen phases should be able to also coexist at equilibrium. In this study we investigated the interaction between sodium polyacrylate microgel networks and the amphiphilic drug amitriptyline hydrochloride (AMT) in the presence of NaCl/phosphate buffer of ionic strength, says Yassir Al-Tikriti, PhD Student at SweDeliver."

The team used a specially constructed microscopy cell and micromanipulators to study the size and internal morphology of single microgels equilibrated in small liquid volumes of AMT solution. To probe the distribution of AMT micelles the team used the fluorescent probe rhodamine B. The amount of AMT in the microgel was determined by a spectrophotometric technique. In separate experiments the binding of AMT and the distribution between different microgels in a suspension were studied.

"We found that collapsed, AMT-rich, and swollen AMT-lean phases coexisted in equilibrium or as long-lived metastable states at intermediate drug loading levels. In single microgels at I = 10 mM, the collapsed phase formed after loading deviated from the core-shell configuration by forming either discrete domains near the gel boundary or a calotte shaped domain. At I = 155 mM, single microgels, initially fully collapsed, displayed a swollen shell and a collapsed core after partial release of the AMT load. Suspensions displayed a bimodal distribution of swollen and collapsed microgels. These results support our hypothesis that the boundary between collapsed and swollen phases in the same microgel is stabilised by thermodynamic factors."

The results are published in the article Drug-Induced Phase Separation in Polyelectrolyte Microgels in the scientific journal Gels.

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CONTACT

Yassir Al-Tikriti, PhD student
Department of Medicinal Chemistry
yassir.al-tikriti@ilk.uu.se

Currently at SweDeliver

Last modified: 2022-03-31