Abstract
Herein, we describe the production of poly(hydroxybutyrate-co-hydroxyvalerate) [P(HB-HV)]-based microspheres containing coumarin-6 (C6) or pyrene (Py) fluorophores as additives and models for hydrophobic and hydrophilic drug encapsulation. Their photophysical and morphological properties, as well as encapsulation efficiencies, are studied as this work aims to describe the influence of additive hydrophobicity/hydrophilicity on microparticle formation. These properties were studied by scanning electron microscopy, fluorescence confocal laser scanning microscopy (FCLSM), and steady-state fluorescence spectroscopy. The results show that the surfactant concentration, polymer molar mass, emulsification stirring rate, and the presence of the fluorophore and its nature are determinants of the P(HB-HV) microsphere properties. Also, encapsulation efficiency is shown to be governed by synergic effects of these parameters on the formation of microspheres. Moreover, size distribution is proved to be strongly influenced by the surfactant poly(vinyl alcohol) content. FCLSM showed that the fluorophores were efficiently encapsulated in P(HB-HV) microspheres at distinct distributions within the copolymer matrix. Surprisingly, nanospheres were observed in the microsphere surface, suggesting that microspheres are formed from nanosphere coalescence.
Highlights
P(HB-HV) microspheres containing fluorophores and microspheres without fluorophores were produced by mixing P(HBHV) of two distinct molar masses (130 and 450 kg mol−1) to a Poly(vinyl alcohol) (PVA) emulsifier in a 1.0% w/v content, and the role of the P(HB-HV) copolymer molar mass on the size and size distribution of the produced microspheres was evaluated
We showed that, the use of fluorophores in the P(PH-HV) microsphere production does not significantly influence their morphological characteristics, fluorophore characteristics presented a role in particle properties assignment, including size, size distribution, surface charge, and entrapment efficiency
By comparing the microspheres produced under distinct conditions, such as polymer molar mass, stirring rates, and surfactant and fluorophore contents, it was clear that the P(HB-HV) molar mass exerted a high influence on the size and surface morphology
Summary
Biodegradable polymer microspheres have been extensively investigated as potential carriers for drugs,[1−4] cosmetic products,[5−7] delivery systems, and for diagnostic purposes because of their biocompatibility, biodegradability, stability, and sustained-release properties.[8,9] Among the most studied materials for encapsulation are derivatives of poly(D,L-lactide), poly(D,L-lactide-co-glycolide) (PLGA), and poly-ε-caprolactones,[10] and the most widespread mechanism for encapsulation with them is the total enfold of the molecule of interest by the polymeric thin film to generate a spherical microparticle.Among the polymers that can produce microspheres, poly(hydroxybutyrate) (PHB) and its copolymer with hydroxyvalerate (P(HB-HV)) have attracted the scientific interest, especially in biomedical field, because of its unique tunable mechanical properties, biocompatibility, and biodegradability.[11,12] These polymers, obtained from natural raw materials,[13,14] are considered green polymers, as they belong to the family of bacterial storage polyesters, which is another reason for their growing application.[15−17]Drug delivery efficiency of these polymers can be controlled by tuning the polymer properties upon structure modification, for instance. Delivery systems consisting of biodegradable polymer spheres[22−31] are interesting because they present several special characteristics, such as high surface-to-volume ratio, low density, and low coefficient of thermal expansion, which enable an efficient encapsulation and time-controlled drug release.[32] With this respect, it is important to ensure the internal and external morphology control of the microspheres, as they can influence the interaction with both the encapsulated drug and the microenvironment after the drug delivery For this purpose, particles can be prepared by several methods, including oil/water emulsion and drying by solvent evaporation.[14,33−35] not new, emulsion techniques are very convenient to prepare microspheres, when a single emulsion is employed, or microcapsules, when double emulsions are employed. Both can encapsulate hydrophobic compounds, most drugs and chemical compounds.[36−40] Poly(vinyl alcohol) (PVA) is the most common emulsion stabilizer to achieve polymeric nano- and microparticles of PLGA, PHB, and P(HB-HV), allowing the Received: March 25, 2019 Accepted: April 25, 2019 Published: May 3, 2019
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