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# Human Serum Albumin-Alginate Esters Microparticles Prepared by Transacylation: Effect of Ester Group

Imane Hadef, Mehdi Omri, Christophe Bliard, Barbara Rogé, Florence

Edwards-Lévy

► To cite this version:

Imane Hadef, Mehdi Omri, Christophe Bliard, Barbara Rogé, Florence Edwards-Lévy. Human Serum Albumin-Alginate Esters Microparticles Prepared by Transacylation: Effect of Ester Group. 1st European Conference on Pharmaceutics, Apr 2015, Reims, France. hal-02894581

HAL Id: hal-02894581

https://hal.science/hal-02894581

Submitted on 9 Jul 2020

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Distributed under a Creative Commons Attribution 4.0 International License
# Human Serum Albumin-Alginate Esters Microparticles
Prepared by Transacylation: Effect of Ester Group

Imane HADEF (a, b); Mehdi OMRI(a, b); Christophe BLIARD (b); Barbara ROGE (b); Florence EDWARDS-LEVY (a)

## 1. Introduction

Microencapsulation using the transacylation reaction in a W/O emulsion is based on the creation of amide bonds between free amine functions of a protein and polysaccharide ester groups in the aqueous phase after alkalization. Several proteins have been implicated in this process, whereas commercial propylene glycol alginate (PGA) has been the only modified polysaccharide used up to now (1,2). The intrinsic properties of PGA such as viscosity, molecular mass, ester type and substitution degree limit its use in microparticle preparation hence the need to study other potential polysaccharide esters.

<figure><img src="image_3.png" /><figcaption>Propylene Glycol Alginate (PGA)</figcaption></figure>

<figure><img src="image_4.png" /><figcaption>Transacylation reaction between protein and PGA</figcaption></figure>

## 2. Purpose

Study the effect of the alginate polysaccharide ester structure and properties on the transacylation reaction and on microparticle characteristics.

## 3.1. Alginate ester synthesis (3)

<figure><img src="image_5.png" /></figure>

$$R = CH_3CH_2-, OHCH_2CH_2-, CH_3CH_2CH_2-, CH_3CHOHCH_2- \text{ or } OHCH_2CH_2CH_2-$$

## 3.2. Alginate ester characterization

* The degree of esterification (DE) by ¹H-NMR and titrimetry;

* Viscosity measurement of 2% ester aqueous solution (w/w);

* Critical aggregation concentration (CAC) via Coomassie blue test(4).

## 3. Methods

## 3.3. Microparticle preparation

<figure><img src="image_6.png" /></figure>

Microparticles are stable, biocompatible and biodegradable

## 3.4. Microparticle characterization

* Size distribution by laser diffraction granulometry;

* Morphology by optical microscopy;

* Inner structure after microparticle cross-section.

## 4. Results
### 4.1. Alginate derivative DE

<figure><img src="image_7.png" /><figcaption>Propyl Alginate (DE= 80%) ¹H-NMR spectrum
(D₂O, 318K, 600MHz)</figcaption></figure>

<figure><img src="image_8.png" /><figcaption>Esterification degree by ¹H-NMR vs titration</figcaption></figure>

* Good agreement between ¹H-NMR and titrimetric results.

* The DE could be controlled by adjusting the quantity of bromide reagent.

## 4.2. Alginate ester microparticles

<figure><img src="image_9.png" /><figcaption>10% HSA-2% alginate ester (w/w) microparticles prepared by transacylation</figcaption></figure>

<figure><img src="image_10.png" /><figcaption>Alginate microparticle size in relation with aqueous solution viscosities</figcaption></figure>

## 4.3. Critical aggregation concentrations(CAC)

The spectral change of Coomassie blue was studied in the presence of alginate derivatives in water at increasing concentrations.

<figure><img src="image_11.png" /></figure>

<figure><img src="image_12.png" /></figure>

<figure><img src="image_13.png" /><figcaption>Absorbance change of Coomassie blue as a function of alginate ester concentration: effect of ester type and substitution degree</figcaption></figure>

* Alkyl alginate (propyl and ethyl) → no microparticle.

* Hydroxyalkyl alginate with ↗DE→ microparticles with lacework inner structure.

* **1-Bromo-2-propanol** was less reactive during esterification → 2-Hydroxypropyl alginate with ↗DE→ No microparticle.

* ↗ alginate molecular weight → ↗ aqueous solution viscosity

→ ↗microparticle size.

* For alkyl esters, **hydrophobic microdomains** were formed due to the association of alkyl chains at lower polymer concentrations compared to hydroxyalkyl esters.

* Increasing the **esterification degree** or the **length of the ester** chain led to the formation of hydrophobic microdomains at lower polymer concentrations, **except** for propylene glycol alginates (2OH-propyl alginate) for which increasing the esterification degree reduced significantly their hydrophobicity.

* The formation of hydrophobic microdomains seemed unfavorable to the reaction with HSA.

## 5. Conclusion

* The replacement of commercial PGA by a variety of other synthetic alginate esters in the process of microparticle formation using the transacylation procedure was studied.

* The best candidates for the reaction with HSA were alginate esters with the highest critical aggregation concentrations observed with the hydroxyalkylated esters.

* Alkyl alginates or low DE alginate esters didn't lead to microparticle formation under the given conditions of transacylation.

* The use of low molecular weight alginates, displaying low aqueous solution viscosity, led to the formation of smaller microparticles.

## 6. References

1. Levy, M.-C. & Edwards-Levy, F. Coating alginate beads with cross-linked biopolymers: A novel method based on a transacylation reaction. J. Microencapsul. 13, 169–183 (1996).

2. McDowell, R. New reactions of propylene glycol alginate. J. Soc. Cosmet. Chem. 21, 441–457 (1970).

3. Della Valle, F., & Romeo, A. Polysaccharide esters and their salts. US Patent, No.4, 965, 353 (1990).

4. Rastello De Boisseson, M. et al. Physical alginate hydrogels based on hydrophobic or dual hydrophobic/ionic interactions: Bead formation, structure, and stability. J. Colloid Interface Sci. 273, 131–139 (2004).