Smarter release of medications thanks to control over the encapsulation



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Researchers at the University of Technology in Eindhoven and the University of Utrecht have discovered the parameters governing drug encapsulation. This gives more control over the slow and steady release of drugs into patients. In addition, designing encapsulations for new drugs will now require far fewer experiments, which contribute to faster and cheaper drug development. The researchers believe that this work will have a significant impact in the biomedical field and in the design of future drugs.

Many drugs are hydrophobic – they do not dissolve well in water – making it difficult to administer medications to patients. One possible solution is to encapsulate the drugs in small packages that are hydrophobic (water repellent) in the interior and hydrophilic (water soluble) on the outside. The drugs will accumulate inside these packages and the transport of the drug through the patient's body becomes much easier. Packages usually consist of associated surfactants, which are approved by the pharmaceutical industry. When dissolved in water, a physiological solution, or blood, these molecules direct their hydrophobic part towards the inner nucleus (with affinity for the insoluble drugs) and its hydrophilic side to the outside, forming a spherical "package", called micelle.

The whereabouts in a micelle

The transport of drugs throughout the body in this way has been possible for decades, but only now researchers understand what factors dictate exactly where drugs within the micelle accumulate. This spatial distribution can drastically affect the rate of drug release within a patient. Some drugs concentrate at the center of the hydrophobic core of the micelle and release slowly, which is desirable for drug absorption from a patient. Other drugs come together at the core-shell interface of the micelle and are released normally fast. Therefore, the control of drug localization in the micellar encapsulation controls the rate of drug release.

Using a dye to track drugs

To investigate where insoluble drugs come together, the researchers used the Nile Red, a dye molecule that resembles the size and solubility of typical drugs. The dye has a very clever property: it not only absorbs a specific color of light, but also that color depends on its environment. If the dye is dissolved in pure water, it absorbs light of a different color than if there is also some alcohol dissolved in the water. Changing the water / alcohol ratio is a smart way to simulate a good solvent or a weak solvent for the dye. This is analogous to working with a water-soluble drug or an insoluble drug. By measuring light absorption, the researchers were able to determine how much dye accumulated in the micelle core and how much at the core-shell interface.

Experiments combined with computer simulations

To confirm their findings, the researchers did computer simulations to determine the location of the dissolved drugs and the form of the block copolymer micelle. The calculations reveal the arrangement of the components inside and outside the micelle, allowing evaluation of the preferred regions of the drug.

From the experiments and computations, it was concluded that the preferred region of the drug within the block copolymer micelles is mainly determined by the concentration and solubility of the drug molecules in the surrounding medium (water / physiological medium / blood). If the drug concentration is below the water solubility of the solvent, the drug molecules meet at the core-shell interface of the micelle, while if the concentration is above solubility, they accumulate in the core.

Less trail experimentation and error

Current research on drug encapsulation is dominated by trail experimentation and error. The results reported in this study allow easier and cheaper development of smart drugs. This will help reduce the side effects associated with the therapy and will facilitate the creation of customized therapeutic treatments in which the release of the drug is tailored to the patient's individual needs.

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Article reference

"Controlling the spatial distribution of solubilized compounds within copolymer micelles", Alessandro Ianiro, Álvaro González Garcia, Stefan Wijker, Joseph P. Patterson, A. Catarina C. Esteves and Remco Tuinier Langmuir I only accept Manuscript DOI: 10.1021 / acs.langmuir.9b00180

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