Polylactide Microspheres Research Articles

Mechanical properties and degradation of laser sintered structures of PLA microspheres obtained by dual beam laser sintering method

This paper discusses the influence of process parameters on the degradation and the mechanical properties of laser-sintered polylactide (PLA) microspheres obtained using the novel dual beam laser sintering method (DBLS). DBLS is a technique developed by our team that is a modification of standard polymer laser sintering (pLS), with the potential to reduce polymer degradation during the process. The PLA microspheres were produced using the standard emulsion-solvent evaporation method. The laser sintering process was carried out in a wide range of process parameters to obtain samples with various degrees of sintering. Next a number of tests were conducted to assess the physicochemical properties of these samples, including visualization techniques (SEM, digital microscopy and photography), gel permeation chromatogrphy (GPC), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), dynamic mechanical thermal analysis (DMTA) and static compression tests. The work shows that for different sets of process parameters, it is possible to obtain a product with similar mechanical properties, but at the same time with a completely different degree of polymer degradation. Hence, the hypothesis that when assessing the sinter quality one should take into account not only the mechanical properties of the detail, but also the degree of polymer degradation, which is of great importance, for example, in biomedical applications. It has also been shown that the DBLS method has a potential to reduce the degree of degradation of the sintered polymers and the post-process material outside the sintering zone.

Influence of Thermal Annealing on the Sinterability of Different Grades of Polylactide Microspheres Dedicated for Laser Sintering.

We present a comparison of the influence of the conditioning temperature of microspheres made of medical grade poly(L-lactide) (PLLA) and polylactide with 4 wt % of D-lactide content (PLA) on the thermal and structural properties. The microspheres were fabricated using the solid-in-oil-in-water method for applications in additive manufacturing. The microspheres were annealed below the glass transition temperature (Tg), above Tg but below the onset of cold crystallization, and at two temperatures selected from the range of cold crystallization corresponding to the crystallization of the α’ and α form of poly(L-lactide), i.e., at 40, 70, 90, and 120 °C, in order to verify the influence of the conditioning temperature on the sinterability of the microspheres set as the sintering window (SW). Based on differential scanning calorimetry measurements, the SWs of the microspheres were evaluated with consideration of the existence of cold crystallization and reorganization of crystal polymorphs. The results indicated that the conditioning temperature influenced the availability and range of the SWs depending on the D-lactide presence. We postulate the need for an individual approach for polylactide powders in determining the SW as a temperature range free of any thermal events. We also characterized other core powder characteristics, such as the residual solvent content, morphology, particle size distribution, powder flowability, and thermal conductivity, as key properties for successful laser sintering. The microspheres were close to spheres, and the size of the microspheres was below 100 µm. The residual solvent content decreased with the increase of the annealing temperature. The thermal conductivities were 0.073 and 0.064 W/mK for PLA and PLLA microspheres, respectively, and this depended on the spherical shape of the microspheres. The wide angle X-ray diffraction (WAXD) studies proved that an increase in the conditioning temperature caused a slight increase in the crystallinity degree for PLLA microspheres and a clear increase in crystallization for the PLA microspheres.

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.

Preparation and surface morphology of herbal based polylactide microspheres

Polymeric microspheres from polylactide and infusion of Woodfordia fruticosa flower were prepared using emulsion-solvent evaporation method. The obtained microspheres were spherical to oval in shape with the size ranging from 1 to 29.8 µM with WFPM-2 yielding the major population within a range of 1–6 µm.

Morphology and internal structure control over PLA microspheres by compounding PLLA and PDLA and effects on drug release behavior.

The applications of Polylactide (PLA) microspheres in biomedical areas are greatly determined by the size, morphology and internal structure. Taking advantage of the formation of stereocomplex (SC) crystallites between poly(L-lactide) (PLLA) and poly(D-lactide) (PDLA), we propose a facile strategy to prepare PLA microspheres with tunable morphology and crystalline structure by compounding PLLA and PDLA. With increasing PDLA content, the crystallinity of SC-PLA rose gradually until the ratio of PLLA and PDLA reached 1:1 and then fell. Correspondingly, the morphology of the microspheres were varied (smooth, porous, golf-ball like, guava like) and higher crystallinity of SC-PLA would lead to a more coarse and porous structure. Finally, three typical kinds of Rifampicin-loaded microspheres with different ratio of PLLA and PDLA (7:3, 3:7, 10:0, sorted by porosity from high to low) were prepared and the release behavior was compared. At 30 h, the cumulative release of 7:3, 3:7 and 10:0 microspheres were 32.6%, 17.8% and 6.0% respectively, indicating that the release profiles were generally determined by the porosity of the microspheres. Our findings not only provide a new strategy to prepare PLA microspheres with controllable morphology but offer additional possibilities for the applications of SC-PLA products in biomedical area.

Preparation of Porous Polylactide Microspheres and Their Application in Tissue Engineering

In this study, porous polylactide (PLA) microspheres with different structures were prepared through the multiple emulsion solvent evaporation method. By changing organic solvents (ethyl acetate and chloroform) and adding effervescent salt NH4HCO3 in the inner water phase, microspheres with porous capsular, matrix, microcapsular and multivesicular structures were prepared. The protein encapsulation and release, and the cell growth behavior of porous microspheres were further explored. Under the same inner water phase, microspheres prepared with chloroform had higher protein encapsulation efficiency and less protein release rate as compared with those prepared with ethyl acetate. Cell experiments showed that the relatively rough surface of microspheres prepared with chloroform was more favorable for the cell growth in comparison with the smooth surface of microspheres prepared with ethyl acetate. This study shows a simple and effective method to control the protein release and cell growth behaviors of polymer microspheres by tuning their porous structure.

Preparation of 5-Flurouracil Loaded Microspheres

Polylactide (PLA) is a kind of biodegradable and biocompatible material. In recent years, polylactide (PLA) and its copolymers have received significant attention from researchers. 5-Fluorouracil (5-Fu) is an antimetabolite of the pyrimidine analog type and is widely used for cancer treatment. As many other kinds of hydrophilic medicines, 5-Fu is difficult to be encapsulated by a water-in-oil-in-water emulsion solvent evaporation technique and the drug content is affected by the volume of the internal phase the increase in which resultes in a decrease in the yield of microspheres. In this study, 5-Fu loaded PLA microspheres which has quite high yield were prepared by a particular oil-in-water evaporation method. During the process of microspheres preparation, nano-silica was used in order to achieve high drug content. The size and morphology of the microspheres were observed by the scanning electron microscope (SEM). According to the results, these microspheres have smooth, spherical surface structure, with no apparent evidence of collapsing which can ensure the even release of the drug. Their size depends on the concentration of dispersed phase and gelatin and the size of nano-silica particles. The nano-silica content was determined by thermogravimetry analyzer (TGA) and by a spectrophotometer, the 5-Fu content in the microspheres could be calculated. It was shown that the PLA microspheres containing lower amount of nano-silica have higher ability to incorporate 5-Fu.

Metallo-Polymer Chain Extension Controls the Morphology and Release Kinetics of Microparticles Composed of Terpyridine-Capped Polylactides and their Stereocomplexes.

Control over morphology and porosity of supramolecular complexed polylactide (PLA) microparticles can be achieved by manipulation of the supramolecular interactions between their constituent polymeric building blocks. It is expected that such modular systems are ideal candidates to serve as degradable delivery carriers. In view of this goal, this study reports about a modular fabrication of biodegradable microparticles from terpyridine (TPy) and bisterpyridine (bisTPy) end-functionalized PLAs that can be transiently extended by chain association through differently strong complexation to three metal cations: Ni2+ , Co2+ , or Fe2+ . Further influence on the morphology of the particles can be exerted by hydrogen-bonding association of enantiomeric l- and d-PLA chains in the form of stereocomplexes. Both effects cause different stabilization of phase-separating TPy and bisTPy PLA micrograins in a process of droplet-based microfluidic particle templating, resulting in different forms of microparticle porosity. If the resulting particles are tailored such to be highly porous, they exhibit a faster release of a model drug, (S)-(+)-4-(3-amino-pyrrolidino)-7-nitrobenzo-furazan, than if they have smooth surfaces. As a result, control over the synthetic parameters, and hence, the particle porosity, can be used to tune the release profiles of drugs from the PLA microspheres.

Sustained release of isoniazid from polylactide microspheres prepared using solid/oil drug loading method for tuberculosis treatment

Polylactide (PLA) microspheres were prepared using the solid-in-oil (S/O) spray-drying method to achieve the sustained release of a hydrophilic drug for the treatment of tuberculosis, via intratracheal instillation. Isoniazid (IN), a low-molecular-weight hydrophilic drug, was used as a model drug. The effects of various sizes of micronized IN powder, different drug/polymer ratios, spray-drying process parameters, and drug-release characteristics were studied to optimize the manufacturing parameters. A high entrapment efficiency (87.3%) was obtained using this method; furthermore, the microspheres were spherical and smooth. They were individually and homogenously distributed, with a mean diameter of 5.6 μm; furthermore, they showed a satisfactory extended sustained-release phase. After administration of the microspheres to rats, pulmonary drug concentrations were maintained at a relatively stable level for up to 4 weeks.

A tubular gelatin scaffold capable of the time-dependent controlled release of epidermal growth factor and mitomycin C

A tubular gelatin scaffold for the time-dependent controlled release of epidermal growth factor (EGF) and mitomycin C (MMC) was fabricated. EGF was incorporated using silk fibroin carriers, and MMC was planted using polylactide (PLA) microspheres. The relationship between scaffold properties and crosslinking degrees was evaluated. As the crosslinking degree was increased from 23.7% to 65.3%, the mechanical properties of the scaffold obviously improved, and the compressive modulus increased to approximately 65kPa. The mass degradation of the scaffold was also controlled from 9 days to approximately 1 month. In vitro release tests indicated that the scaffold mainly released EGF in the early period and MMC in the later period. Urethral epithelial cells (UECs) and urethral scar derived fibroblast cells (UFCs) were coseeded in the scaffold at a ratio of 1:1. After 9 days of coculture, immunostaining results displayed that the proportion of UECs continuously increased to approximately 71%. These changes in cell proportion were confirmed by the results of Western blot analysis. Therefore, the scaffold promoted the growth but inhibited the regeneration of UFCs. This scaffold for time-dependent controlled release of multiple biofactors may be potentially useful in urethral reconstruction and other tissue engineering studies.

Biodegradable polylactide microspheres enhance specific immune response induced by Hepatitis B surface antigen

Hepatitis B (HB) infection caused by Hepatitis B virus (HBV) is the most common liver disease in the world. HB vaccine, when administered in conjunction with alum adjuvants, induces Th2 immunity that confers protection against HBV. However, currently available vaccine formulations and adjuvants do not elicit adequate Th1 and CTL responses that are important for prevention of maternal transmission of the virus. Microspheres synthesized from poly (D, L-lactide-co-glycolide) (PLGA) or poly (D, L-lactide) (PLA) polymers have been considered as promising tools for in vivo delivery of antigens and drugs. Here we describe PLA microspheres synthesized by premix membrane emulsification method and their application in formulating a new microsphere based HB vaccine. To evaluate the immunogenicity of this microsphere vaccine, BALB/c mice were immunized with microsphere vaccine and a series of immunological assays were conducted. Results of Enzyme-linked ImmunoSpot (ELISPOT) assays revealed that the number of interferon-gamma (IFN-γ)-producing splenocytes and CD8+ T cells increased significantly in the microsphere vaccine group. Microsphere vaccine group showed enhanced specific cell lysis when compared with HB surface antigen (HBsAg) only group in 51Cr cytotoxicity assays. Moreover, microsphere vaccine elicited a comparable level of antibody production as that of HB vaccine administered with alum adjuvant. We show that phagocytosis of HBsAg by dendritic cells is more pronounced in microsphere vaccine group when compared with other control groups. These results clearly demonstrate the potential of using PLA microspheres as effective HB vaccine adjuvants for an enhanced Th1 immune response.

Preparation and Physicochemical Characteristics of Polylactide Microspheres of Emamectin Benzoate by Modified Solvent Evaporation/Extraction Method

Emamectin benzoate is highly effective against insect pests and widely used in the world. However, its biological activity is limited because of high resistance of target insects and rapid degradation speed in fields. Preparation and physicochemical characterization of degradable microcapsules of emamectin benzoate were studied by modified solvent evaporation/extraction method using polylactide (PLA) as wall material. The influence of different compositions of the solvent in internal organic phase and external aqueous phase on diameter, span, pesticide loading, and entrapment rate of the microspheres was investigated. The results indicated that the process of solvent extraction and the formation of the microcapsules would be accelerated by adding water-miscible organic solvents such as ethyl ether, acetone, ethyl acetate, or n-butanol into internal organic phase and external aqueous phase. Accelerated formation of the microcapsules would result in entrapment rates of emamectin benzoate increased to as high as 97%. In addition, by adding ethanol into the external aqueous phase, diameters would reduce to 6.28 μm, whereas the loading efficiency of emamectin benzoate did not increase. The PLA microspheres prepared under optimum conditions were smoother and more spherical. The degradation rate in PLA microspheres of emamectin benzoate on the 10th day was 4.29 ± 0.74%, whereas the degradation rates of emamectin benzoate in methanol solution and solid technical material were 46.3 ± 2.11 and 22.7 ± 1.51%, respectively. The PLA skeleton had combined with emamectin benzoate in an amorphous or molecular state by using differential scanning calorimetry (DSC) determination. The results indicated that PLA microspheres of emamectin benzoate with high entrapment rate, loading efficiency, and physicochemical characteristics could be obtained by adding water-miscible organic solvents into the internal organic phase and external aqueous phase.

Humoral and cell-mediated immune responses elicited by poly (dl-lactide) adjuvanted filarial antigen molecules

Context: In our recent studies, Brugia malayi molecules have shown interesting immune-stimulating and immune-suppressive properties. Among these, F6 a pro-inflammatory (54–68 kDa) SDS-PAGE resolved fraction of the parasite when administered with Freund’s complete/incomplete adjuvant in animals, elicited both Th1 and Th2 type immune responses and protects the host from filarial parasite.Objective: The present study was aimed at developing biodegradable microspheres for filarial antigenic protein molecules and to investigate the immunoadjuvanticity of microspheres (Ms)-loaded F6 molecules.Materials and methods: Poly-lactide microspheres (DL-PLA-Ms) were prepared using double emulsification and solvent evaporation method; and studied their size, shape, antigen adsorption efficiency, in-process stability, and antigen release profiles. F6 and B. malayi adult worm (BmA: ∼17 to 180 kDa) protein molecules adsorbed on the Ms were administered in a single shot into Swiss mice, subcutaneously, and investigated their immunoadjuvant effect and compared with one/two doses-schedule of plain F6/BmA.Results: Immunization with F6/BmA-loaded DL-PLA-Ms resulted in upregulation of cellular proliferation, IFN- γ, TNF-α and NO release from host’s cells stimulated with F6/BmA or LPS/Con A, IgG, IgG1 and IgG2a levels. These responses were well comparable with the responses produced by two doses of plain BmA/F6.Discussion and conclusion: In conclusion, a single dose of DL-PLA-Ms-F6 induced predominantly Th1 immune responses and well comparable with two doses of plain F6. This is the first ever report on potential of DL-PLA-Ms as adjuvant for filarial immunogen.

Novel PLA microspheres with hydrophilic and bioadhesive surfaces for the controlled delivery of fenretinide

Novel polylactide (PLA) microspheres endowed with hydrophilic and bioadhesive surfaces as injectable formulations for the controlled release of fenretinide were prepared, using a novel technique based on the co-precipitation of PLA with gelatin, at the interface of a liquid dispersion formed by the addition of N-methylpyrrolidone containing PLA and dextrin (DX), towards an aqueous solution of gelatin (G). The resulting PLA–G–DX microspheres were compared with others prepared by the same technique using polylactide-co-glycolide (PLGA), with or without DX, and with or without phosphatidylcholine. Of the different systems, the PLA–G–DX microspheres had the best morphological, dimensional and functional characteristics. They had the highest drug loading, and their drug release was the most efficient over time without any burst effect. Their in vitro anti-tumoural activity was strongly enhanced with respect to the pure fenretinide. This paralleled the increased drug concentration inside the cells due to their marked bioadhesion to the tumour cell membranes as indicated by scanning electron microscope images.

Effects of surface modification on the properties of magnetic nanoparticles/PLA composite drug carriers and in vitro controlled release study

Biodegradable polylactide (PLA) microspheres containing magnetic nanoparticles (MNPs) and anti-inflammatory drug Ibuprofen (IBF) were synthesized by using emulsion solvent evaporation technology. With surface modification, the magnetic nanoparticles/PLA composite drug carriers showed excellent magnetite content and magnetic susceptibility. SEM and TEM showed that the magnetic microspheres were spherical in shape with a smooth surface, and of a mean diameter in the micrometer range. The incorporation of MNPs and IBF into the PLA matrix was confirmed by FTIR. XRD and VSM further confirmed the existence of MNPs in the microspheres which maintained superparamagnetic behavior with a saturation magnetization of 31.4emu/g. The magnetite content of 28.4wt% was assessed by TGA. In addition, the drug release profiles showed that the IBF-loaded PLA magnetic microspheres are pH-induced release of IBF and are promising for controlled release drug delivery.

Antitumor activity of fenretinide encapsulated in novel based PLA microspheres

Several studies reported fenretinide (4-HPR) can be used as antitumoral drug in many types of cancer cell lines such as neuroblastoma, mammary carcinoma and melanoma. In vitro 4-HPR inhibits growth of neuroblastoma in a dose dependent manner with an high antitumor activity at 5–10 μM (Ponzoni et al., 1995).The main disadvantage of 4HPR in clinical application is its lipophilic behavior which hinders the possibility to maintain therapeutic concentration for long period of time. To bypass this drawback, new drug delivery systems consisting in polylactide (PLA) or polylactide-co-glycolid (PLGA) microspheres were developd. A novel solvent extraction method based on the co-precipitation of PLA or PLGA with gelatin has been utilized. Phosphatidylcholine (PC) or dextrin (DX) were added to improve the hydrophilic character of the microsphere surface. After a preliminary study of physical characteristics in terms of encapsulation efficiency, mean size and release profile of drug, PLA/gelatin/dextrin MS were chosen to test the antitumor activity in SH-SY5Y neuroblastoma cell line. After 3 and 24 hours of treatment a cell viability of 50 % and 0% was observed respectively. Empty MS did not affect the cell viability at the same time points. High resolution SEM showed an high bioadhesion of PLA/gelatin/dextrin microspheres to cell membrane. Cell uptake experiments demonstrated an high intracellular concentrations of fenretinide in the presence of the PLA/gelatin/dextrin microspheres rather than in the presence of pure fenretinide. In conclusion, 4-HPR loaded in PLA/gelatin/dextrin microspheres represent a powerful tool for drug delivery systems for hydrophobic antitumor drugs whose therapeutic potential is hindered by their low availability.

FORMATION MECHANISM OF SOLVENT-INDUCED POROUS PLA MICROSPHERES

Porous polylactide(PLA) microspheres were prepared by means of the modified double emulsion solvent evaporation.The organic solvents with different boiling points and aqueous solubility were used to prepare PLA microspheres with different porous structures.Microspheres prepared with methylene chloride,chloroform and toluene as solvents had the similar homogeneous porous structure,while those microspheres with ethyl acetate as solvent showed a hollow structure with a porous thin shell.The effects of solvent types on porous structure of microspheres were discussed.It was concluded that the removal rate of solvent plays the decisive role in determining the porous structure of microspheres.Accordingly,a formation mechanism of porous microspheres fabricated with different solvents was proposed.

Co‐encapsulation of Proteins into Polylactide Microspheres

Biodegradable microspheres of polylactide have been prepared for the controlled release of model proteins. Studies have shown that release from these microspheres is dependent on properties of the polymer and the protein encapsulated. The combination of two proteins will have an effect on the characteristics of the particles produced and the release profiles obtained. Using a solvent evaporation technique, low molecular weight poly(L)lactide microspheres were produced, loaded with different ratios of a number of model proteins. The effects on loading efficiency, particle size, surface charges and release were examined. The results suggest that the outcome of the presence of carrier proteins, and co-encapsulated adjuvants on the properties of the microspheres produced must be studied for each combination employed.

Continuous fabrication of monodisperse polylactide microspheres by droplet-to-particle technology using microfluidic emulsification and emulsion–solvent diffusion

Monodisperse polylactide (PLA) microspheres were continuously fabricated by microfluidic emulsification and subsequent dilution in water. The diameter was precisely tuned from 6 to 50 μm by changing the flow rate of the fluids in microfluidics or the PLA concentration in the dispersed phase. The use of amphiphilic oil-soluble poly(ethylene glycol)-b-polylactide (o-PEG–PLA) as a matrix resulted in a highly porous microsphere morphology, and the porosity was controlled by blending PLA. Therefore, monodisperse PLA microspheres with the predetermined surface porosity were continuously produced by just enough reagents and energy.

Effects of Controlled Released BMP-7 on Markers of Inflammation and Degradation During the Cultivation of Human Osteoarthritic Chondrocytes

The aim of the present study is to investigate the effects of BMP-7 released from polylactide microspheres on the appearance of various catabolic and inflammatory cytokines secreted by osteoarthritic chondrocytes cultivated in a collagen gel. Articular chondrocytes of 15 patients suffering from osteoarthritis are transferred to a collagen type-I gel. Additionally, BMP-7 encapsulated into polylactide microspheres (50 ng BMP-7/mL gel) is added. After 14 days, gene expression and protein appearance of various genes involved in matrix turnover and inflammation are investigated by immunohistochemical staining and RT-PCR and compared to untreated controls. TNF-α, MMP-13, IL-6, IL-1β, and VEGF gene expressions are decreased in the treatment group. In contrast, BMP-7-induced matrix synthesis is not affected, leaving collagen type-II (Col-II) gene expression to be elevated, while collagen type-I (Col-I) is decreased. In summary, controlled release of low concentrated BMP-7 from polylactide microspheres leads to a decrease in gene expression of the investigated inflammation and matrix degradation markers whereas matrix synthesis is induced.