PLA-microparticles formulated by means a thermoreversible gel able to modify protein encapsulation and release without being co-encapsulated

Tailoring structural properties of spray-dried methotrexate-loaded poly (lactic acid)/poloxamer microparticle blends

Drug delivery systems can overcome cancer drug resistance, improving the efficacy of chemotherapy agents. Poly (lactic acid) (PLA) microparticles are an interesting alternative because their hydrophobic surface and small particle size could facilitate interactions with cells. In this study, two poloxamers (PLX 407 and 188) were applied to modulate the structural features, the drug release behavior and the cell viability from spray-dried microparticles. Five formulations with different PLA: PLX blend ratio (100:0, 75:25, 50:50, 25:50, and 0:100) were well-characterized by SEM, particle size analysis, FTIR spectroscopy, differential scanning calorimetry (DSC), and X-ray diffraction analysis (XRD). The spray-dried microparticles showed higher drug loading, spherical-shape, and smaller particle size. The type of poloxamer and blend ratio affected their structural and functional properties such as morphology, crystallinity, blend miscibility, drug release rate, and cell viability. The methotrexate (MTX), a model drug, was loaded in amorphous spray-dried microparticles. Moreover, the drug release studies demonstrated that PLX induced a leaching-effect of MTX from PLA: PLX blends, suggesting the formation of MTX/PLX micelles in aqueous medium. This finding was better established by cell viability assays. Therefore, biocompatible PLA: PLX blends showed promising in vitro results, and further in vivo studies will be performed to evaluate the performance of this chemotherapeutic agent.

Polymeric protective agents for nanoparticles in drug delivery and targeting

Surface modification/functionalization of nanoparticles (NPs) using polymeric protective agents is an issue of great importance and actuality for drug delivery and targeting. Improving the blood circulation half-life of surface-protected nanocarriers is closely related to the elimination of main biological barriers and limiting factors (protein absorption and opsonization), due to the phagocytic activity of reticuloendothelial system. For passive or active targeted delivery, in biomedical area, surface-functionalized NPs with tissue-recognition ligands were designed and optimized as a result of modern research techniques. Also, multi-functionalized nanostructures are characterized by enhanced bioavailability, efficacy, targeted localization, active cellular uptake, and low side effects. Surface-protected NPs are obtained from biocompatible, biodegradable and less toxic natural polymers (dextran, β-cyclodextrin, chitosan, hyaluronic acid, heparin, gelatin) or synthetic polymers, such as poly(lactic acid), poly(lactic-co-glycolic) acid, poly(ε-caprolactone) and poly(alkyl cyanoacrylates). PEGylation is one of the most important functionalization methods providing steric stabilization, long circulating and 'stealth' properties for both polymeric and inorganic-based nanosystems. In addition, for their antimicrobial, antiviral and antitumor effects, cutting-edge researches in the field of pharmaceutical nanobiotechnology highlighted the importance of noble metal (platinum, gold, silver) NPs decorated with biopolymers.

Smart Polymeric Nanoparticles as Emerging Tools for Imaging--The Parallel Evolution of Materials

The field of imaging has developed considerably over the past decade and recent advances in the area of nanotechnology, in particular nanomaterials, have opened new opportunities. Polymeric nanoparticles are particularly interesting and a number of novel materials, characterized by stimuli-responsive characteristics and fluorescent tagging, have allowed visualization, intracellular labeling and real-time tracking. In some of the latest applications the nanoparticles have been used for imagining of tumor cells, both in vivo and ex vivo.

Dual pH- and temperature-responsive microparticles for protein delivery to ischemic tissues

Injectable "smart" microspheres that are sensitive to both temperature and pH have been fabricated and tested for controlled delivery of therapeutic proteins to ischemic skeletal muscle. A library of copolymers composed of N-isopropyl acrylamide (NIPAAm), propyl acrylic acid (PAA), and butyl acrylate (BA) was used to fabricate microspheres using a double emulsion method, and an optimal formulation made from copolymers composed of 57 mol.% NIPAAm, 18 mol.% PAA and 25 mol.% BA copolymers was identified. At 37°C and pH representative of ischemic muscle (i.e. pH 5.2-7.2), these microspheres produced sustained, diffusion-controlled release, and at normal, physiological pH (i.e. pH 7.4), they underwent dissolution and rapid clearance. Delivery of fibroblast growth factor 2 was used to confirm that protein bioactivity was retained following microsphere encapsulation/release based on a dose-dependent increase in NIH3T3 fibroblast proliferation in vitro. Microsphere-loaded or free Cy5.5-labeled albumin was injected into ischemic and control gastrocnemii of mice following unilateral induction of hind limb ischemia to model peripheral arterial disease. In the ischemic limb at days 3.5 and 7, there was higher local retention of the protein delivered via microspheres relative to injected free protein (p<0.05). However, clearance of protein delivered via microspheres was equivalent to free protein at later time points that correspond to ischemic recovery in this model. Finally, histological analysis of the gastrocnemius revealed that the polymeric microspheres did not produce any microscopic signs of toxicity near the injection site. These combined results suggest that the pH- and temperature-responsive microspheres presented herein are a promising technological platform for controlled protein delivery to ischemic tissue.

In vitro evaluation of the effects of various additives and polymers on nerve growth factor microspheres

OBJECTIVE

To evaluate the effects of various additives or polymers on the in vitro characteristics of nerve growth factor (NGF) microspheres.

MATERIALS AND METHODS

NGF microspheres were fabricated using polyethylene glycol (PEG), ovalbumin (OVA), bovine serum albumin (BSA) or glucose as protein protectors, and poly(lactide-co-glycolide) (PLGA) or poly(lactic acid) (PLA)/PLGA blends as encapsulation materials.

RESULTS

Encapsulation efficiencies of the NGF microspheres with various additives or polymers were not more than 30%. A comparative study revealed that OVA was somewhat superior over others, and was thus chosen as the protective additive in subsequent experiments. Polymer analysis showed that NGF release from 1:1 PLA (η = 0.8):PLGA (75/25, η = 0.45) microspheres lasted for 90 d with a burst release rate of 12.7%. About 40% of the original bioactivity was retained on the 28th day, while 10% was left on the 90th day.

DISCUSSION AND CONCLUSION

The combination of OVA as an additive and the PLA/PLGA blend as the coating matrix is suitable for encapsulation of NGF in microspheres for extended release.

Use of lectin-functionalized particles for oral immunotherapy

Immunotherapy, in recent times, has found its application in a variety of immunologically mediated diseases. Oral immunotherapy may not only increase patient compliance but may, in particular, also induce both systemic as well as mucosal immune responses, due to mucosal application of active agents. To improve the bioavailability and to trigger strong immunological responses, recent research projects focused on the encapsulation of drugs and antigens into polymer particles. These particles protect the loaded antigen from the harsh conditions in the GI tract. Furthermore, modification of the surface of particles by the use of lectins, such as Aleuria aurantia lectin, wheatgerm agglutinin or Ulex europaeus-I, enhances the binding to epithelial cells, in particular to membranous cells, of the mucosa-associated lymphoid tissue. Membranous cell-specific targeting leads to an improved transepithelial transport of the particle carriers. Thus, enhanced uptake and presentation of the encapsulated antigen by antigen-presenting cells favor strong systemic, but also local, mucosal immune responses.

Engineering biodegradable polyester particles with specific drug targeting and drug release properties

Poly(lactic acid) (PLA) and poly(lactic-co-glycolic acid) (PLGA) microspheres and nanoparticles remain the focus of intensive research effort directed to the controlled release and in vivo localization of drugs. In recent years engineering approaches have been devised to create novel micro- and nano-particles which provide greater control over the drug release profile and present opportunities for drug targeting at the tissue and cellular levels. This has been possible with better understanding and manipulation of the fabrication and degradation processes, particularly emulsion-solvent extraction, and conjugation of polyesters with ligands or other polymers before or after particle formation. As a result, particle surface and internal porosity have been designed to meet criteria-facilitating passive targeting (e.g., for pulmonary delivery), modification of the drug release profile (e.g., attenuation of the burst release) and active targeting via ligand binding to specific cell receptors. It is now possible to envisage adventurous applications for polyester microparticles beyond their inherent role as biodegradable, controlled drug delivery vehicles. These may include drug delivery vehicles for the treatment of cerebral disease and tumor targeting, and co-delivery of drugs in a pulsatile and/or time-delayed fashion.