Characterization of protein-loaded poly(epsilon-caprolactone) microparticles based on a factorial design

Developing micro-/nanoparticulate drug delivery systems using "design of experiments"

Of late, micro and nanoparticluate drug delivery systems have been gaining immense importance primarily attributed to their improved drug release controlling and targeting efficiencies. Also, the small particle size and desirable surface charge associated with these delivery systems render them suitable for specific applications like lymphatic uptake, pulmonary uptake, tumor targeting, brain targeting, etc. For decades, micro and nanoparticulate systems have been prepared by the conventional "trial and error" approach of changing One Variable at a Time (OVAT). Using this methodology, the solution of a specific problematic formulation characteristic can certainly be achieved, but attainment of the true optimal composition is never guaranteed. Thus, the present manuscript provides an updated account of the systematic approach "Design of Experiments (DoE)" as applicable to formulation development of microparticles and nanostructured systems. Besides providing a bird's eye view of the various experimental designs and optimization techniques employed for DoE optimization of such systems, the present manuscript also presents a copilation of the major micro/nano-structuctred systems optimized through DoE till date. In a nutshell, the article will act both as a ready reckoner of DoE optimization of micro/nano drug delivery systems and a catalyst in providing an impetus to young pharmaceutical "nano & micro" researchers to venture into the rewarding field of systematic DoE optimization.

Microspheres Made of Poly(ɛ-caprolactone)-Based Amphiphilic Copolymers: Potential in Sustained Delivery of Proteins

Microspheres of amphiphilic multi-block poly(ester-ether)s (PEE)s and poly(ester-ether-amide)s (PEEA)s based on poly(epsilon-caprolactone) (PCL) were investigated as delivery systems for proteins. The interest was mainly focused on the effect of their molecular structure and composition on the overall properties of the microspheres, encapsulating bovine serum albumin (BSA) as a model protein. PEEs and PEEAs were prepared using a alpha,omega-dihydroxy-terminated PCL macromer (Mn= 2.0 kDa) as a hydrophobic component. Hydrophilic oxyethylene sequences were generated using poly(ethylene oxide)s (PEO)s of different molecular mass (Mn= 300-600 Da) in the case of PEEs, or 4,7,10-trioxa-1,13-tridecanediamine (Trioxy) and PEO150 (Mn= 150 Da) in the case of PEEAs. The copolymers showed a decrease of Tm and crystallinity values as compared with PCL. Within each class of copolymers, the bulk hydrophilicity increased with increasing the number of oxyethylene groups in the chain repeat unit. PEEAs were more hydrophilic than PEEs with a similar number of oxyethylene groups. Discrete spherical particles were prepared by both PEEs and PEEAs and their BSA encapsulation efficiency related to copolymer properties. Interestingly, the insertion of short hydrophilic segments is enough to significantly affect protein distribution inside microspheres and its release profiles, as compared to PCL microspheres. Different degradation rates and mechanisms were observed for copolymer microspheres, mainly depending on the distribution of oxyethylene units along the chain. The results highlight that a fine control over the structural parameters of amphiphilic PCL-based multi-block copolymers is a key factor for their application in the field of protein delivery.

Strategic approaches for overcoming peptide and protein instability within biodegradable nano- and microparticles

This paper reviews the major factors that are closely involved in peptide and protein degradation during the preparation of biodegradable nano- and microparticles. The various means usually employed for overcoming these obstacles are described, in order to bring to the fore the strategies for protein stabilization. Both processing and formulation parameters can be modified and are distinctly considered from a strategic point of view. We describe how partial or full protein stability retention within the carriers and during drug release might be achieved by individual or combined optimized strategies. Additionally, problems commonly encountered during protein quantification, stability determination and release are briefly reviewed. Artefacts that might occur during sampling and analytical procedures and which might hinder critical interpretation of results are discussed.

Poly-epsilon-caprolactone microspheres and nanospheres: an overview

Poly-epsilon-caprolactone (PCL) is a biodegradable, biocompatible and semicrystalline polymer having a very low glass transition temperature. Due to its slow degradation, PCL is ideally suitable for long-term delivery extending over a period of more than one year. This has led to its application in the preparation of different delivery systems in the form of microspheres, nanospheres and implants. Various categories of drugs have been encapsulated in PCL for targeted drug delivery and for controlled drug release. Microspheres of PCL either alone or of PCL copolymers have been prepared to obtain the drug release characteristics. This article reviews the advancements made in PCL-based microspheres and nanospheres with special reference to the method of preparation of these and their suitability in developing effective delivery systems.

Poly‐Epsilon‐Caprolactone Nanocapsules Containing Octyl Methoxycinnamate: Preparation and Characterization

This study investigates the different nanocapsules (NCs) made of poly-epsilon-caprolactone (PCL) containing the lipophilic sunscreen Escalol 557 [octyl methoxycinnamate (OMC)] and analyzes the influence of nanoparticle-based systems on light-induced decomposition of the sunscreen agent. The NCs were designed and prepared by the solvent displacement method. Formulation parameters, such as the nature and volume of the organic and aqueous phase and the nature and concentration of the surfactants and polymer, have relevant implications on NC elaboration. We investigated the influence of several technological (stirring speed: 300-800 rpm) and formulation factors [polymer amount, 195-244.5 mg; surfactant, Tween 85 (Polysorbate 85), Montanox 80 (Polysorbate 80), and Synperonic PE/F68 (Poloxamer 188) as stabilizing agents; and volume of the organic phase, 20-30 mL of acetone] on the particle size and the OMC loading capacity of the formulations--encapsulation efficiency and yield. The sizes of NC obtained were in the range of 309 to 1042 nm, the encapsulation efficiencies ranged from 93.82% to 99.97%, and yields of NC encapsulation ranged from 48.12% to 86.28%. Of all the preset experimental conditions, Montanox 80, 30 mL of acetone, 244.5 mg of polymer, and a stirring speed of 350 rpm have been selected as the best in this experimental design study. The experimental conditions selected to obtain OMC-loaded NC of 374 nm resulted in a high entrapment percentage (97.52%) and yield (82.95%). The PCL nanoparticles loaded with OMC were effective in reducing light-induced degradation of the sunscreen agent.

Recent trends in stabilizing protein structure upon encapsulation and release from bioerodible polymers

Sustained release of pharmaceutical proteins from biocompatible polymers offers new opportunities in the treatment and prevention of disease. The manufacturing of such sustained-release dosage forms, and also the release from them, can impose substantial stresses on the chemical integrity and native, three-dimensional structure of proteins. Recently, novel strategies have been developed towards elucidation and amelioration of these stresses. Non-invasive technologies have been implemented to investigate the complex destabilization pathways that can occur. Such insights allow for rational approaches to protect proteins upon encapsulation and release from bioerodible systems. Stabilization of proteins when utilizing the most commonly employed procedure, the water-in-oil-in-water (w/o/w) double emulsion technique, requires approaches that are based mainly on either increasing the thermodynamic stability of the protein or preventing contact of the protein with the destabilizing agent (e.g. the water/oil interface) by use of various additives. However, protein stability is still often problematic when using the w/o/w technique, and thus alternative methods have become increasingly popular. These methods, such as the solid-in-oil-in-oil (s/o/o) and solid-in-oil-in-water (s/o/w) techniques, are based on the suspension of dry protein powders in an anhydrous organic solvent. It has become apparent that protein structure in the organic phase is stabilized because the protein is "rigidified" and therefore unfolding and large protein structural perturbations are kinetically prohibited. This review focuses on strategies leading to the stabilization of protein structure when employing these different encapsulation procedures.

Fabrication of porous poly(epsilon-caprolactone) microparticles for protein release

The particle morphology and in vitro release of protein from porous and non-porous PCL-F127 blended microparticles were evaluated. The BSA loaded PCL microparticles were prepared by the w/o/o/o emulsion-solvent evaporation method. Two types of homogenizer, a Polytron homogenizer and a probe ultrasonicator, were used to prepare the emulsion systems. The effects of solvent evaporation rate on the crystallinity and the performance of the microparticles were investigated. Both microparticles showed quite different shapes as well as surface morphology and release characteristics. The microparticles prepared with a Polytron homogenizer were quite porous in structure, which created channels for protein to continuously diffuse out, and resulted in sustained- and controlled-release characteristics. In addition, the initial burst release of protein from the microparticles was also reduced. Alteration of the evaporation rate of solvent did not change the crystallinity of the final microparticles. An influence of evaporation rate on the size of resulting microparticles was observed. The porous PCL microparticles were developed by choosing a proper homogenizer and fabrication conditions. Carefully controlling these variables resulted in microparticles with desirable release performance.