Polylactide Microparticles Research Articles

Alkylated derivatives of chitosan for stabilization of polylactide microparticles used as building blocks for 3D structures

AbstractModification of the chitosan chemical structure by grafting hydrophobic fragments makes it possible to synthesize derivatives with amphiphilic properties. These derivatives were used as emulsifiers in the aqueous phase during the production of polylactide microparticles via the oil/water solvent evaporation technique. The application of the derivatives allows to achieve a high yield of the microparticles and to provide a hydrophilic coating on the surface of polylactide microparticle. The chitosan‐coated polylactide microparticles were analyzed in terms of mean size, size distribution, surface, and internal morphology. The ability of the obtained microparticles to be used as a starting component for the fabrication of 3D materials through the surface‐selective laser sintering was evaluated, and the optimal parameters for the process have been determined.

Porous Polylactide Microparticles as Effective Fillers for Hydrogels.

High-strength composite hydrogels based on collagen or chitosan-genipin were obtained via mixing using highly porous polylactide (PLA) microparticles with diameters of 50-75 µm and porosity values of over 98%. The elastic modulus of hydrogels depended on the filler concentration. The modulus increased from 80 kPa to 400-600 kPa at a concentration of porous particles of 12-15 wt.% and up to 1.8 MPa at a filling of 20-25 wt.% for collagen hydrogels. The elastic modulus of the chitosan-genipin hydrogel increases from 75 kPa to 900 kPa at a fraction of particles of 20 wt.%. These elastic modulus values cover a range of strength properties from connective tissue to cartilage tissue. It is important to note that the increase in strength in this case is accompanied by a decrease in the density of the material, that is, an increase in porosity. PLA particles were loaded with C-phycocyanin and showed an advanced release profile up to 48 h. Thus, composite hydrogels mimic the structure, biomechanics and release of biomolecules in the tissues of a living organism.

Polylactide microparticles stabilized by chitosan graft-copolymer as building blocks for scaffold fabrication via surface-selective laser sintering

Polylactide microparticles stabilized by chitosan graft-copolymer as building blocks for scaffold fabrication via surface-selective laser sintering

Polysaccharides as Stabilizers for Polymeric Microcarriers Fabrication.

Biodegradable polymeric microparticles are widely used in drug delivery systems with prolonged-release profiles and/or cell microcarriers. Their fabrication via the oil/water emulsion solvent evaporation technique has normally required emulsifiers in the aqueous phase. The present work aims to evaluate the effectiveness of various polysaccharides, such as chitosan, hyaluronic acid, cellulose, arabinogalactan, guar and their derivatives, as an alternative to synthetic surfactants for polylactide microparticle stabilization during their fabrication. Targeted modification of the biopolymer’s chemical structure was also tested as a tool to enhance polysaccharides’ emulsifying ability. The transformation of biomacromolecules into a form of nanoparticle via bottom-up or top-down methods and their subsequent application for microparticle fabrication via the Pickering emulsion solvent evaporation technique was useful as a one-step approach towards the preparation of core/shell microparticles. The effect of polysaccharides’ chemical structure and the form of their application on the polylactide microparticles’ total yield, size distribution and morphology was evaluated. The application of polysaccharides has great potential in terms of the development of green chemistry and the biocompatibility of the formed microparticles, which is especially important in biomedicine application.

Design of Sodium Alginate/Gelatin-Based Emulsion Film Fused with Polylactide Microparticles Charged with Plant Extract.

This study aimed at designing emulsion films based on sodium alginate, gelatin, and glycerol, and their modification by the addition of lipids (cottonseed oil and beeswax). Film composition with the most promising properties was further modified by the incorporation of polylactide (PLA) microparticles with Calendula officinalis flower extract. PLA microspheres were obtained by the emulsion/solvent evaporation method. The size distribution of oily particles in emulsions was investigated. Mechanical properties, moisture content, UV-Vis spectra, and the color of films were analyzed, while biophysical skin parameters were assessed after their application to the skin. Moreover, the contact angles were measured, and the surface free energy of polymeric films was determined. An investigation of the amount of Calendula officinalis flower extract which can be incorporated into PLA microparticles was performed. The modification of the composition of films significantly influenced their physicochemical properties. The selected active ingredient in the form of plant extract was successfully incorporated into polymeric microparticles that were further added into the developed emulsion film. The condition of the skin after the application of obtained emulsion films improved. The prepared materials, especially containing microparticles with plant extract, can be considered for designing new cosmetic forms, such as cosmetic masks, as well as new topical formulations for pharmaceutical delivery.

Drug-loading capacity of polylactide-based micro- and nanoparticles - Experimental and molecular modeling study.

Micro- and nanostructures prepared from biodegradable homopolymers and amphiphilic block copolymers (AmBCs) have found application as drug-delivery systems (DDSs). The ability to accumulate a drug is a very important parameter characterizing a given DDS. This work focuses on the impact of DDS size, the packing of polymer chains in the DDS, and drug - polymer matrix compatibility on the hydrophobic drug - loading capacity (DLC) of nano/microcarriers prepared from a biodegradable polymer or its copolymer. Using experimental measurements in combination with atomistic molecular dynamics simulations, an analysis of curcumin encapsulation in microspheres (MSs) from polylactide (PLA) homopolymer and nanoparticles (NPs) from PLA-block-poly(2-methacryloyloxyethylphosphorylcholine) AmBC was performed. The results show that curcumin has good affinity for the PLA matrix due to its hydrophobic nature. However, the DLC value is limited by the fact that curcumin only accumulates in the peripheral part of these structures. Such uneven drug distribution in the PLA matrix results from the non-homogeneous density of MSs (non-uniform packing of the polymer chains in the coil). The results also indicate that the MSs can retain a greater amount of hydrophobic drug compared to the NPs, which is associated with the formation of drug aggregates inside the PLA microparticles.

Fabrication of PLA/CNC/CNT conductive composites for high electromagnetic interference shielding based on Pickering emulsions method

In this study, we proposed a new strategy to fabricate polylactide (PLA) based conductive polymer composites with excellent electrical conductivity, superior electromagnetic interference shielding efficiency (EMI SE) and good mechanical properties using a Pickering emulsions method. Cellulose nanocrystals (CNCs) were used as a stabilizer for oil-in-water Pickering emulsions and a dispersant for carbon nanotubes (CNTs) at the same time. CNC/CNT suspensions and dichloromethane (DCM) solution of PLA were used as aqueous phase and oil phase respectively. With the evaporation of DCM, PLA microparticles coated by entangled CNCs and CNTs could be formed. After compression molding, the PLA/CNC/CNT composites showed an outstanding EMI SE of 41.8 dB with only 4.3 wt% CNT loading. Simultaneously, the mechanical performance of the sample maintained a high level (tensile strength: 45.52 MPa, Young’s Modulus: 3152 MPa). Our findings provide a simple, cost-effective and environmentally friendly manufacturing route for functionalpolymer nanocomposites with excellent comprehensive properties.

Osteoinducing scaffolds with multi-layered biointerface

This study was aimed to design and characterise hybrid tissue-engineered constructs composed of osteoinducing polylactide-based scaffolds with multi-layered cellular biointerface for bone tissue reconstruction. Three-dimensional scaffolds with improved hydrophilic and osteoinducing properties were produced using the surface-selective laser sintering (SSLS) method. The designed scaffold pattern had dimensions of 8 × 8 × 2.5 mm and ladder-like pores (∼700 μm in width). Hyaluronic acid-coated polylactide microparticles (∼100 μm in diameter) were used as building blocks and water was used as the photosensitizer for SSLS followed by photocross-linking with Irgacure 2959 photoinitiator. Resulting scaffolds provided successful adhesion and expansion of human bone marrow mesenchymal stromal cells from a single-cell suspension. Induced calcium deposition by the cells associated with osteogenic differentiation was detected in 7–21 days of culturing in basal medium. The values were up to 60% higher on scaffolds produced at a higher prototyping speed under the experimental conditions. Innovative approach to graft the scaffolds with multi-layered cell sheets was proposed aiming to facilitate host tissue-implant integration. The sheets of murine MS-5 stromal cell line exhibited contiguous morphology and high viability in a modelled construct. Thus, the SSLS method proved to be effective in designing osteoinducing scaffolds suitable for the delivery of cell sheets.

Application of micro- and nanocrystalline cellulose

Micro- and nanocrystalline forms of cellulose were extracted from flax stalks and evaluated in terms of their applicability for various materials science tasks. It was revealed that both form of cellulose had anisometric morphology with length of 27.1 μm and 159 nm; diameter of 8.7 μm and 85 nm, respectively. They were used as reinforcing fillers for fabrication of composite films based on hydroxyethylcellulose. Film-forming and mechanical properties of the composite materials were significantly varied in dependence on filler content (0–10 wt.%) and size. As a second option of micro- and nanocrystalline cellulose application, a study of their effectiveness as stabilizing agents for oil/water Pickering emulsions was carried out. In contrast to micron-sized cellulose the nanocrystalline form appeared to be successful in the process of CH2Cl2/water interface stabilization and fabrication of polylactide microparticles via oil/water Pickering emulsion solvent evaporation technique.

Preparation of Poly(L,L‐Lactide) Microparticles via Pickering Emulsions Using Chitin Nanocrystals

The aim of the present study was to investigate an ability of chitin nanocrystals to be used as stabilizing components for fabrication of poly(L,L‐lactide) microparticles via the Pickering oil/water emulsion solvent evaporation technique. The anisometric chitin nanocrystals were extracted from two different samples of crab shell chitin via acetic hydrolysis and analyzed using atomic force microscopy, dynamic light scattering, and FTIR spectroscopy. The extracted nanocrystals showed no difference in the chemical structure but possessed different morphology and aspect ratios as a function of raw chitin used. The effect of chitin nanocrystals characteristics and concentration in the aqueous phase on the total yield, size distribution, and shape and surface morphology of the prepared polylactide microparticles was evaluated.

Fabrication of the Components for a Sustained-Release Injectable Dosage Form of Acetylsalicylic Acid Using Supercritical Carbon Dioxide

Fabrication of fine-grained (10–100 μm) bioresorbable powders of aliphatic polyesters containing therapeutically significant (up to 10 wt %) concentrations of acetylsalicylic acid using supercritical CO2 is studied. The process for fabricating the components of sustained-release injectable dosage forms of acetylsalicylic acid is elaborated. The kinetics of release of acetylsalicylic acid from polylactide microparticles into the normal saline solution in vitro is studied by high-performance liquid chromatography.

Amphiphilic Linear-Branched Copolylactides and Disperse Systems on Their Basis

The linear-branched copolylactides containing linear side poly(ethylene oxide) blocks are synthesized and characterized. The critical micelle concentrations and the aggregative stability and the dispersity of oil/water emulsions stabilized by these copolymers are estimated. The polylactide microparticles are obtained by emulsification followed by evaporation of an organic solvent using acetylsalicylic acid as a model drug. The structure of copolylactides strongly affects the properties of the microparticles. On one hand, the presence of large poly(ethylene oxide) blocks in the linear-branched macromolecules leads to the formation of colloidal systems with a higher aggregative stability of emulsions and a lower size of particles, and on the other hand, the microparticles formed from these copolymers possess a lower incorporation efficiency relative to water-soluble low-molecular-mass compounds and the profile of the release of these compounds is nonlinear and contains the region of accelerated release.

Development and characterization of bioresorbable polyglycerol esters and drug-loaded microparticles

Linear-hyperbranched co(polylactides) containing hyperbranched polyglycerol (PG) block were synthesized and characterized. An estimate of critical micelle concentration as well as aggregative stability and droplet sizes in the emulsion stabilized by the obtained polymers was made. It was shown that an architecture of linear-branched co(polylactides) defines its surface-active properties and characteristics of dispersion systems obtained from it. With an increase in PG block content in copolymers, critical micelle concentration and aggregative stability of emulsions increase. Polylactide microparticles were obtained by organic solvent evaporation technique using acetylsalicylic acid as a drug model. Some properties of microparticles, such as size, incorporation efficiency and in vitro release of immobilized substance, were examined. It was noticed that branching architecture of co(polylactides) has a significant influence on the properties of microparticles. On the one hand, the presence of large PG blocks in linear-branched macromolecules results in the formation of colloidal systems with higher aggregative stability of emulsions and smaller particle size; on the other hand, microparticles formed from such copolymers have lower incorporation efficiency towards water-soluble low-molecular-weight compounds and nonlinear release profile for these substances with a segment of accelerated primary release.

Preparation and properties of textile materials modified with triclosan-loaded polylactide microparticles

A convenient and simple method for preparation of commercial nonwovens with antimicrobial properties was elaborated. The process consists in preparation of poly(l-lactide) microspheres (from poly(l-lactide) with Mn = 10,560 and Mw/Mn = 1.39) containing triclosan (5-chloro-2-(2,4-dichlorophenoxy) phenol) and loading them onto the nonwovens. The microspheres were prepared by spray drying (Dn = 3.91 μm, Dw/Dn = 2.43) and oil-in-water emulsification-solvent evaporation method (Dn = 5.84 μm, Dw/Dn = 1.25). Content of triclosan in microspheres ranged from 4.65 to 4.95 wt%. The antibacterial nonwovens were prepared by padding of the fibers with the microspheres using the microsphere suspension. The resulting antibacterial nonwovens were examined using inhibition zone measurement method. Inhibition zones from 4 to 9 mm indicated that the modified nonwovens had antibacterial properties against Gram (+)—Staphylococcus aureus and Gram (−)—Klebsiella pneumoniae. Nonwovens were conditioned up to 12 months at relative humidity <5%, 50%, and 100% in desiccators and up to 6 months air-conditioning system at relative humidity = 65%. Antimicrobial activity of the modified nonwovens was examined as a function of time and air humidity. Time of conditioning has strong influence on antibacterial activity, whereas the impact of the air humidity was negligible. All nonwovens had antibacterial properties even after 12 months of conditioning. Copyright © 2017 John Wiley & Sons, Ltd.

Influences of process and formulation parameters on powder flow properties and immunogenicity of spray dried polymer particles entrapping recombinant pneumococcal surface protein A

Particle size, antigen load and its release characteristic are the three the main attributes of polymer particles based vaccine delivery systems. The present studies focus on the formulation of spray dried polylactide microparticles entrapping pneumococcal surface protein A (PspA). Influence of process variables during polymer particle formation were optimized by using half-factorial design. Feed rate and atomization pressure during spray drying were found to be the most important parameters for achieving uniform size particles. Spray drying of preformed particles from different stages of solvent evaporation method resulted in formation of particle having different porosity and protein release profile. Presence of polyvinyl alcohol in the external aqueous phase not only contributed towards regulating the size of particles but also influenced the burst release of protein from particles. Polymer particles entrapping PspA elicited robust IgG responses both in mice and in rats. Antigen load in microparticles correlated with the antibody titer indicating the maintenance of protein integrity during particle formation using spray drying. Both, process engineering and formulation parameters during spray drying influenced the particles in terms of size, load and antigen release characteristics.

Cytotoxic and Immunochemical Properties of Viscumin Encapsulated in Polylactide Microparticles

Biodegradable polylactide microparticles with encapsulated cytotoxic protein viscumin were obtained via the ultrasound-assisted supercritical fluid technique. The size of the microparticles was 10-50 µM, as shown by electron microscopy. The time course of viscumin release from microparticles was studied using an immunoenzyme test system with anti-viscumin monoclonal antibodies. It was found that 99.91% of the cytotoxic protein was incorporated into polymer microparticles. Only 0.08% of the initially encapsulated viscumin was released from the microparticles following incubation for 120 h in a phosphate-buffered saline at neutral pH. Importantly, the method of ultrasonic dry supercritical fluid encapsulation failed to alter both the cytotoxic potency and the immunochemical properties of the encapsulated viscumin. Thus, this procedure can be used to generate biodegradable polylactide microparticles with encapsulated bioactive substances.

Role of alum in improving the immunogenicity of biodegradable polymer particle entrapped antigens

This study was aimed at understanding the role of alum in improving the immunogenicity of biodegradable polymer particle entrapped antigens. Presence of alum formed a fine network around PLA particles holding them together and promoted attachment of higher number of particles on macrophage surface for a considerable period of time. Use of alum lowered the burst release of the entrapped antigen from particles and thereafter also reduced the cumulative release of antigen from particles. Apart from this, PLA microparticles alone induced macrophages to release TNF-α similar to that induced by alum. However admixture of PLA particles and alum enhanced the secretion of TNF-α from 876 pg/ml at 6 h to 3500 pg/ml at 24 h which was higher than that induced by alum adsorbed TT. Immunization with admixture of antigen loaded polylactide (PLA) microparticles (2–8 μm) and alum improved the antibody titers almost twice than that achieved from particle alone in experimental animals. Single point immunization with particle entrapped antigens and alum also elicited antibody titers comparable to two doses of alum adsorbed tetanus toxoid (TT) or diphtheria toxoid (DT). Our results suggest that presence of alum acts in multiple ways to improve the antibody titers of polymer particles entrapped antigens. Such co-operative adjuvant action of alum and polymer particles can be exploited to improve the immunogenicity of other antigens.

Interactions of antigen-loaded polylactide particles with macrophages and their correlation with the immune response

Size of the polymeric particulate antigen delivery system and its interactions with antigen-presenting cells (APCs) influence the immune response both qualitatively and quantitatively. In this paper, we report that antigen-loaded polymeric microparticles elicit antibody titers without being phagocytosed by macrophages; and size of the antigen-loaded particles modulates immune response from single-point immunization. Antibody titers varied significantly from single-point immunization with different sized polylactide (PLA) particles entrapping hepatitis B surface antigen. Nanoparticles (200–600 nm) were efficiently taken up by macrophages and elicited lower antibody titers in comparison to microparticles (2–8 μm). PLA microparticles that elicited highest and long-lasting antibody titers from single-point immunization were not taken up by the macrophages and found attached to the surface of the macrophages. Immunization with nanoparticles (200–600 nm) was associated with higher levels of IFN- γ production, upregulation of MHC class I molecules along with antibody isotypes favoring Th1-type immune response. Immunization with microparticles (2–8 μm size) promoted IL-4 secretion, upregulated MHC class II molecules and favored Th2-type immune response. Western blot analysis showed that release of HBsAg from surface-attached microparticles into macrophages increased with time, but was more or less constant in case of nanoparticles. Our results suggest that continuous release of high concentration of antigen from cell surface-attached PLA microparticles into APCs results in improved antibody response from single-point immunization. It also offers an exciting possibility of designing size-based polymer particle delivery system to modulate immune response.

Preparation and characterization of collagen-modified polylactide microparticles

To improve cytocompatibility of polylactide (PLA) and to obtain an injectable scaffold for tissue engineering, collagen-modified PLA (CPLA) microparticles were prepared. Poly-(α-methacrylic acid)-grafted PLA (PMAA-PLA) was obtained by photooxidization and UV induced polymerization. Suspension of PMAA-PLA microspheres with an average size of 172.8 ± 3.6 nm was prepared with solvent evaporation technique. CPLA microparticles were prepared by adding collagen acetic acid solution into PMAA-PLA microsphere suspension prepared above. FTIR spectrum of PMAA-PLA confirmed that PMAA had been grafted on PLA surface. Analytical results of FTIR, XPS, SEM, hematoxylin and eosin (HE) stained and zeta potential measurement showed that the CPLA microparticles obtained by modifying PMAA-PLA microspheres with collagen molecules uniformly have a microporous structure and a particle size of less than 100 μm. The CPLA microparticles were expected to be used as an injectable scaffold for tissue regeneration.

Immunological responses after immunisation of mice with microparticles containing antigen and single stranded RNA (polyuridylic acid)

Certain toll-like receptor (TLR) agonists, e.g. CpG DNA, can be used as potent vaccine ‘adjuvants’. It is known that some sequences of single stranded (ss) RNA stimulate proinflammatory and antiviral responses following interaction with TLR 7 and 8. We have encapsulated ovalbumin (OVA) in the presence and absence of polyuridylic acid (poly-U) inside polylactide microparticles. In comparison to microparticles containing only OVA, bulk cultures of bone marrow-derived plasmacytoid and myeloid dendritic cells produced more ( P < 0.05) IL-12 and interferon (IFN)-alpha when stimulated with microparticles containing OVA and poly-U. Subcutaneous injection of comicroencapsulated OVA and poly-U resulted in statistically elevated levels of serum anti-OVA IgG1 ( P < 0.05 versus naïve mice). Conversely, anti-OVA IgG1 levels in C57 BL6 mice immunised with OVA loaded microparticles (without RNA) were statistically indifferent to naïve animals. Furthermore, injection of coencapsulated OVA and poly-U resulted in ( P < 0.05) greater numbers of OVA specific IFN-gamma secreting T-cells as compared with mice injected with OVA loaded microparticles. A similar trend was seen in mice immunised with OVA loaded microparticles decorated with CpG or solutions of admixed OVA and CpG ( P < 0.05). These data demonstrate, for the first time, that appropriately formulated ssRNA can act as a potent adjuvant and modulator of adaptive immunological responses.