Effect of mean diameter and polydispersity of PLG microspheres on drug release: Experiment and theory

Polymer Delivery Systems for Long-Acting Antiretroviral Drugs

The success of long-acting (LA) drug delivery systems (DDSs) is linked to their biocompatible polymers. These are used for extended therapeutic release. For treatment or prevention of human immune deficiency virus type one (HIV-1) infection, LA DDSs hold promise for improved regimen adherence and reduced toxicities. Current examples include Cabenuva, Apretude, and Sunlenca. Each is safe and effective. Alternative promising DDSs include implants, prodrugs, vaginal rings, and microarray patches. Each can further meet patients' needs. We posit that the physicochemical properties of the formulation chemical design can optimize drug release profiles. We posit that the strategic design of LA DDS polymers will further improve controlled drug release to simplify dosing schedules and improve regimen adherence.

Investigations into the effects of scaffold microstructure on slow-release system with bioactive factors for bone repair

In recent years, bone tissue engineering (BTE) has played an essential role in the repair of bone tissue defects. Although bioactive factors as one component of BTE have great potential to effectively promote cell differentiation and bone regeneration, they are usually not used alone due to their short effective half-lives, high concentrations, etc. The release rate of bioactive factors could be controlled by loading them into scaffolds, and the scaffold microstructure has been shown to significantly influence release rates of bioactive factors. Therefore, this review attempted to investigate how the scaffold microstructure affected the release rate of bioactive factors, in which the variables included pore size, pore shape and porosity. The loading nature and the releasing mechanism of bioactive factors were also summarized. The main conclusions were achieved as follows: i) The pore shapes in the scaffold may have had no apparent effect on the release of bioactive factors but significantly affected mechanical properties of the scaffolds; ii) The pore size of about 400 μm in the scaffold may be more conducive to controlling the release of bioactive factors to promote bone formation; iii) The porosity of scaffolds may be positively correlated with the release rate, and the porosity of 70%-80% may be better to control the release rate. This review indicates that a slow-release system with proper scaffold microstructure control could be a tremendous inspiration for developing new treatment strategies for bone disease. It is anticipated to eventually be developed into clinical applications to tackle treatment-related issues effectively.

Injectable multifunctional hydrogel based on carboxymethylcellulose/polyacrylamide/polydopamine containing vitamin C and curcumin promoted full-thickness burn regeneration

Burn injuries are a major global problem, with a high risk of infection and mortality. This study aimed to develop an injectable hydrogel for wound dressings, composed of sodium carboxymethylcellulose/polyacrylamide/polydopamine containing vitamin C (CMC/PAAm/PDA ^VitC) for its antioxidant and antibacterial properties. Simultaneously, silk fibroin/alginate nanoparticles (SF/SANPs) loaded with curcumin (SF/SANPs ^CUR) were incorporated into the hydrogel to enhance wound regeneration and reduce bacterial infection. The hydrogels were fully characterized and tested in vitro and in preclinical rat models for biocompatibility, drug release, and wound healing efficacy. Results showed stable rheological properties, appropriate swelling and degradation ratios, gelation time, porosity, and free radical scavenging capacity. Biocompatibility was confirmed through MTT, lactate dehydrogenase, and apoptosis evaluations. Hydrogels containing curcumin demonstrated antibacterial activity against methicillin-resistant Staphylococcus aureus (MRSA). In the preclinical study, hydrogels containing both drugs showed superior support for full-thickness burn regeneration, with improved wound closure, re-epithelialization, and collagen expression. The hydrogels also showed neovascularization and anti-inflammatory effects, as confirmed by CD31 and TNF-α markers. In conclusion, these dual drug-delivery hydrogels showed significant potential as wound dressings for full-thickness wounds.

Model-based Optimization of Drug Release Rate from a Size Distributed Population of Biodegradable Polymer Carriers

In the present study, a comprehensive polymer degradation-drug diffusion model is developed to describe the polymer degradation kinetics and quantify the release rate of an active pharmaceutical ingredient (API) from a size-distributed population of drug-loaded poly(lactic-co-glycolic) acid (PLGA) carriers in terms of material and morphological properties of the drug carriers. To take into account the spatial-temporal variation of the drug and water diffusion coefficients, three new correlations are developed in terms of spatial-temporal variation of the molecular weight of the degrading polymer chains. The first one relates the diffusion coefficients with the time-spatial variation of the molecular weight of PLGA and initial drug loading and, the second one with the initial particle size, and the third one with evolution of the particle porosity due to polymer degradation. The derived model, comprising a system of partial differential and algebraic equations, is numerically solved using the method of lines and validated against published experimental data on the drug release rate from a size distributed population of piroxicam-PLGA microspheres. Finally, a multi-parametric optimization problem is formulated to calculate the optimal particle size and drug loading distributions of drug-loaded PLGA carriers to realize a desired zero-order drug release rate of a therapeutic drug over a specified administration period of several weeks. It is envisaged that the proposed model-based optimization approach will aid the optimal design of new controlled drug delivery systems and, consequently, the therapeutic outcome of an administered drug.

Machine learning models to accelerate the design of polymeric long-acting injectables

Long-acting injectables are considered one of the most promising therapeutic strategies for the treatment of chronic diseases as they can afford improved therapeutic efficacy, safety, and patient compliance. The use of polymer materials in such a drug formulation strategy can offer unparalleled diversity owing to the ability to synthesize materials with a wide range of properties. However, the interplay between multiple parameters, including the physicochemical properties of the drug and polymer, make it very difficult to intuitively predict the performance of these systems. This necessitates the development and characterization of a wide array of formulation candidates through extensive and time-consuming in vitro experimentation. Machine learning is enabling leap-step advances in a number of fields including drug discovery and materials science. The current study takes a critical step towards data-driven drug formulation development with an emphasis on long-acting injectables. Here we show that machine learning algorithms can be used to predict experimental drug release from these advanced drug delivery systems. We also demonstrate that these trained models can be used to guide the design of new long acting injectables. The implementation of the described data-driven approach has the potential to reduce the time and cost associated with drug formulation development.

Advanced Multifunctional Wound Dressing Hydrogels as Drug Carriers

Skin injuries, especially chronic wounds, remain a significant healthcare system problem. The number of burns, diabetic patients, pressure ulcers, and other damages is also growing, particularly in elderly populations. Several investigations are pursued in designing more effective therapeutics for treating different wound injuries. These efforts have resulted in developing multifunctional wound dressings to improve wound repair. For this, preparing multifunctional dressings using various methods has provided a new attitude to support effective skin regeneration. This review focuses on the recent developments in designing multifunctional hydrogel dressings with hemostasis, adhesiveness, antibacterial, and antioxidant properties.

3D-printed hydrogel scaffold-loaded granulocyte colony-stimulating factor sustained-release microspheres and their effect on endometrial regeneration

After injury, the endometrium cannot self-repair or regenerate because damages of the basal layer of the uterine, which often lead to intrauterine adhesions (IUAs), which can cause serious problems such...

Phenomenology of the Initial Burst Release of Drugs from PLGA Microparticles

Poly(lactic-co-glycolic acid) (PLGA) is the most prevalent polymer drug delivery vehicle in use today. There are about 20 commercialized drug products in which PLGA is used as an excipient. In more than half of these formulations, PLGA is used in the form of microparticles (with sizes in the range between 60 nm and 100 μm). The primary role of PLGA is to control the kinetics of drug release toward achieving sustained release of the drug. Unfortunately, most drug-loaded PLGA microparticles exhibit a common drawback: an initial uncontrolled burst of the drug. After 30 years of utilization of PLGA in controlled drug delivery systems, this initial burst drug release still remains an unresolved challenge. In this Review, we present a summary of the proposed mechanisms responsible for this phenomenon and the known factors affecting the burst release process. Also, we discuss examples of recent efforts made to reduce the initial burst release of the drug from PLGA particles.

Quality by design thinking in the development of long-acting injectable PLGA/PLA-based microspheres for peptide and protein drug delivery

Adopting the Quality by Design (QbD) approach in the drug development process has transformed from "nice-to-do" into a crucial and required part of the development, ensuring the quality of pharmaceutical products throughout their whole life cycles. This review is discussing the implementation of the QbD thinking into the production of long-acting injectable (LAI) PLGA/PLA-based microspheres for the therapeutic peptide and protein drug delivery. Various key elements of the QbD approaches are initially elaborated using Bydureon®, a commercial product of LAI PLGA/PLA-based microspheres, as a classical example. Subsequently, the factors influencing the release patterns and the stability of the peptide and protein drugs are discussed. This is followed by a summary of the state-of-the-art of manufacturing LAI PLGA/PLA-based microspheres and the related critical process parameters (CPPs). Finally, a landscape of generic product development of LAI PLGA/PLA-based microspheres is reviewed including some major challenges in the field.

Investigation of the Size Distribution for Diffusion-Controlled Drug Release From Drug Delivery Systems of Various Geometries

Various drug delivery systems (DDSs) are often used in modern medicine to achieve controlled and targeted drug release. Diffusional release of drugs from DDSs is often the main mechanism, especially at early times. Generally, average dimensions of DDS are used to model the drug release, but our recent work on drug release from fibers demonstrated that taking into account diameter distribution is essential. This work systematically investigated the effect of size distribution on diffusional drug release from DDSs of various geometric forms such as membranes, fibers, and spherical particles. The investigation clearly demonstrated that the size distribution has the largest effect on the drug release profiles from spherical particles compared to other geometric forms. Published experimental data for drug release from polymer microparticles and nanoparticles were fitted, and the diffusion coefficients were determined assuming reported radius distributions. Assuming the average radius when fitting the data leads to up to 5 times underestimation of the diffusion coefficient of drug in the polymer.

Design, Characterization, and Biopharmaceutical Behavior of Nanoparticles Loaded with an HIV-1 Fusion Inhibitor Peptide

New therapeutic alternatives to fight against the spread of HIV-1 are based on peptides designed to inhibit the early steps of HIV-1 fusion in target cells. However, drawbacks, such as bioavailability, short half-life, rapid clearance, and poor ability to cross the physiological barriers, make such peptides unattractive for the pharmaceutical industry. Here we developed, optimized, and characterized polymeric nanoparticles (NPs) coated with glycol chitosan to incorporate and release an HIV-1 fusion inhibitor peptide (E1) inside the vaginal mucosa. The NPs were prepared by a modified double emulsion method, and optimization was carried out by a factorial design. In vitro, ex vivo, and in vivo studies were carried out to evaluate the optimized formulation. The results indicate that the physicochemical features of these NPs enable them to incorporate and release HIV fusion inhibitor peptides to the vaginal mucosa before the fusion step takes place.

Drug delivery systems and materials for wound healing applications

Chronic, non-healing wounds place a significant burden on patients and healthcare systems, resulting in impaired mobility, limb amputation, or even death. Chronic wounds result from a disruption in the highly orchestrated cascade of events involved in wound closure. Significant advances in our understanding of the pathophysiology of chronic wounds have resulted in the development of drugs designed to target different aspects of the impaired processes. However, the hostility of the wound environment rich in degradative enzymes and its elevated pH, combined with differences in the time scales of different physiological processes involved in tissue regeneration require the use of effective drug delivery systems. In this review, we will first discuss the pathophysiology of chronic wounds and then the materials used for engineering drug delivery systems. Different passive and active drug delivery systems used in wound care will be reviewed. In addition, the architecture of the delivery platform and its ability to modulate drug delivery are discussed. Emerging technologies and the opportunities for engineering more effective wound care devices are also highlighted.

Strengths, weaknesses, opportunities and challenges for long acting injectable therapies: Insights for applications in HIV therapy

Advances in solid drug nanoparticle technologies have resulted in a number of long-acting (LA) formulations with the potential for once monthly or longer administration. Such formulations offer great utility for chronic diseases, particularly when a lack of medication compliance may be detrimental to treatment response. Two such formulations are in clinical development for HIV but the concept of LA delivery has its origins in indications such as schizophrenia and contraception. Many terms have been utilised to describe the LA approach and standardisation would be beneficial. Ultimately, definitions will depend upon specific indications and routes of delivery, but for HIV we propose benchmarks that reflect perceived clinical benefits and available data on patient attitudes. Specifically, we propose dosing intervals of ≥1week, ≥1month or ≥6months, for oral, injectable or implantable strategies, respectively. This review focuses upon the critical importance of potency in achieving the LA outcome for injectable formulations and explores established and emerging technologies that have been employed across indications. Key technological challenges such as the need for consistency and ease of administration for drug combinations, are also discussed. Finally, the review explores the gaps in knowledge regarding the pharmacology of drug release from particulate-based LA injectable suspensions. A number of hypotheses are discussed based upon available data relating to local drug metabolism, active transport systems, the lymphatics, macrophages and patient-specific factors. Greater knowledge of the mechanisms that underpin drug release and protracted exposure will help facilitate further development of this strategy to achieve the promising clinical benefits.

Computational and experimental approaches for investigating nanoparticle-based drug delivery systems

Most therapeutic agents suffer from poor solubility, rapid clearance from the blood stream, a lack of targeting, and often poor translocation ability across cell membranes. Drug/gene delivery systems (DDSs) are capable of overcoming some of these barriers to enhance delivery of drugs to their right place of action, e.g. inside cancer cells. In this review, we focus on nanoparticles as DDSs. Complementary experimental and computational studies have enhanced our understanding of the mechanism of action of nanocarriers and their underlying interactions with drugs, biomembranes and other biological molecules. We review key biophysical aspects of DDSs and discuss how computer modeling can assist in rational design of DDSs with improved and optimized properties. We summarize commonly used experimental techniques for the study of DDSs. Then we review computational studies for several major categories of nanocarriers, including dendrimers and dendrons, polymer-, peptide-, nucleic acid-, lipid-, and carbon-based DDSs, and gold nanoparticles. This article is part of a Special Issue entitled: Membrane Proteins edited by J.C. Gumbart and Sergei Noskov.

Hot melt extruded and injection moulded disulfiram-loaded PLGA millirods for the treatment of glioblastoma multiforme via stereotactic injection

Glioblastoma multiforme (GBM) has a poor prognosis and is one of the most common primary malignant brain tumours in adults. Stereotactic injections have been used to deliver chemotherapeutic drugs directly into brain tumours. This paper describes the development of disulfiram (DSF)-loaded biodegradable millirods manufactured using hot melt extrusion (HME) and injection moulding (IM). The paper demonstrates that the stability of the DSF within the millirods is dependent on the manufacturing technique used as well as the drug loading. The physical state of the DSF within the millirods was dependent on the fabrication process, with the DSF in the HME millirods being either completely amorphous within the PLGA, while the DSF within the IM millirods retained between 54 and 66% of its crystallinity. Release of DSF from the millirods was dependent on the degradation rate of the PLGA, the manufacturing technique used as well as the DSF loading. DSF in the 10% (w/w) DSF loaded HME millirods and the 20% (w/w) DSF-loaded HME and IM millirods had a similar cytotoxicity against a GBM cell line compared to the unprocessed DSF control. However, the 10% (w/w) DSF-loaded IM millirods had a significantly lower cytotoxicity when compared to the unprocessed control.

Optimization of nanoparticles for cardiovascular tissue engineering

Nano-particulate delivery systems have increasingly been playing important roles in cardiovascular tissue engineering. Properties of nanoparticles (e.g. size, polydispersity, loading capacity, zeta potential, morphology) are essential to system functions. Notably, these characteristics are regulated by fabrication variables, but in a complicated manner. This raises a great need to optimize fabrication process variables to ensure the desired nanoparticle characteristics. This paper presents a comprehensive experimental study on this matter, along with a novel method, the so-called Geno-Neural approach, to analyze, predict and optimize fabrication variables for desired nanoparticle characteristics. Specifically, ovalbumin was used as a protein model of growth factors used in cardiovascular tissue regeneration, and six fabrication variables were examined with regard to their influence on the characteristics of nanoparticles made from high molecular weight poly(lactide-co-glycolide). The six-factor five-level central composite rotatable design was applied to the conduction of experiments, and based on the experimental results, a geno-neural model was developed to determine the optimum fabrication conditions. For desired particle sizes of 150, 200, 250 and 300 nm, respectively, the optimum conditions to achieve the low polydispersity index, higher negative zeta potential and higher loading capacity were identified based on the developed geno-neural model and then evaluated experimentally. The experimental results revealed that the polymer and the external aqueous phase concentrations and their interactions with other fabrication variables were the most significant variables to affect the size, polydispersity index, zeta potential, loading capacity and initial burst release of the nanoparticles, while the electron microscopy images of the nanoparticles showed their spherical geometries with no sign of large pores or cracks on their surfaces. The release study revealed that the onset of the third phase of release can be affected by the polymer concentration. Circular dichroism spectroscopy indicated that ovalbumin structural integrity is preserved during the encapsulation process. Findings from this study would greatly contribute to the design of high molecular weight poly(lactide-co-glycolide) nanoparticles for prolonged release patterns in cardiovascular engineering.

Rate-programming of nano-particulate delivery systems for smart bioactive scaffolds in tissue engineering

Development of smart bioactive scaffolds is of importance in tissue engineering, where cell proliferation, differentiation and migration within scaffolds can be regulated by the interactions between cells and scaffold through the use of growth factors (GFs) and extra cellular matrix peptides. One challenge in this area is to spatiotemporally control the dose, sequence and profile of release of GFs so as to regulate cellular fates during tissue regeneration. This challenge would be addressed by rate-programming of nano-particulate delivery systems, where the release of GFs via polymeric nanoparticles is controlled by means of the methods of, such as externally-controlled and physicochemically/architecturally-modulated so as to mimic the profile of physiological GFs. Identifying and understanding such factors as the desired release profiles, mechanisms of release, physicochemical characteristics of polymeric nanoparticles, and externally-triggering stimuli are essential for designing and optimizing such delivery systems. This review surveys the recent studies on the desired release profiles of GFs in various tissue engineering applications, elucidates the major release mechanisms and critical factors affecting release profiles, and overviews the role played by the mathematical models for optimizing nano-particulate delivery systems. Potentials of stimuli responsive nanoparticles for spatiotemporal control of GF release are also presented, along with the recent advances in strategies for spatiotemporal control of GF delivery within tissue engineered scaffolds. The recommendation for the future studies to overcome challenges for developing sophisticated particulate delivery systems in tissue engineering is discussed prior to the presentation of conclusions drawn from this paper.

Biodegradable Polymeric Microsphere-Based Drug Delivery for Inductive Browning of Fat

Brown and beige adipocytes are potent therapeutic agents to increase energy expenditure and reduce risks of obesity and its affiliated metabolic symptoms. One strategy to increase beige adipocyte content is through inhibition of the evolutionarily conserved Notch signaling pathway. However, systemic delivery of Notch inhibitors is associated with off-target effects and multiple dosages of application further faces technical and translational challenges. Here, we report the development of a biodegradable polymeric microsphere-based drug delivery system for sustained, local release of a Notch inhibitor, DBZ. The microsphere-based delivery system was fabricated and optimized using an emulsion/solvent evaporation technique to encapsulate DBZ into poly(lactide-co-glycolide) (PLGA), a commonly used biodegradable polymer for controlled drug release. Release studies revealed the ability of PLGA microspheres to release DBZ in a sustained manner. Co-culture of white adipocytes with and without DBZ-loaded PLGA microspheres demonstrated that the released DBZ retained its bioactivity, and effectively inhibited Notch and promoted browning of white adipocytes. Injection of these DBZ-loaded PLGA microspheres into mouse inguinal white adipose tissue depots resulted in browning in vivo. Our results provide the encouraging proof-of-principle evidence for the application of biodegradable polymers as a controlled release platform for delivery of browning factors, and pave the way for development of new translational therapeutic strategies for treatment of obesity.

Long-term controlled release of PLGA microparticles containing antidepressant mirtazapine

The aim of the study was to prepare PLGA microparticles for prolonged release of mirtazapine by o/w solvent evaporation method and to evaluate effects of PVA concentration and organic solvent choice on microparticles characteristics (encapsulation efficiency, drug loading, burst effect, microparticle morphology). Also in vitro drug release tests were performed and the results were correlated with kinetic model equations to approximate drug release mechanism. It was found that dichloromethane provided microparticles with better qualities (encapsulation efficiency 64.2%, yield 79.7%). Interaction between organic solvent effect and effect of PVA concentration was revealed. The prepared samples released the drug for 5 days with kinetics very close to that of zero order (R(2 )= 0.9549 - 0.9816). According to the correlations, the drug was probably released by a combination of diffusion and surface erosion, enhanced by polymer swelling and chain relaxation.

Transplantation of Nogo-66 receptor gene-silenced cells in a poly(D,L-lactic-co-glycolic acid) scaffold for the treatment of spinal cord injury

Inhibition of neurite growth, which is in large part mediated by the Nogo-66 receptor, affects neural regeneration following bone marrow mesenchymal stem cell transplantation. The tissue engineering scaffold poly(D,L-lactide-co-glycolic acid) has good histocompatibility and can promote the growth of regenerating nerve fibers. The present study used small interfering RNA to silence Nogo-66 receptor gene expression in bone marrow mesenchymal stem cells and Schwann cells, which were subsequently transplanted with poly(D,L-lactide-co-glycolic acid) into the spinal cord lesion regions in rats. Simultaneously, rats treated with scaffold only were taken as the control group. Hematoxylin-eosin staining and immunohistochemistry revealed that at 4 weeks after transplantation, rats had good motor function of the hind limb after treatment with Nogo-66 receptor gene-silenced cells plus the poly(D,L-lactide-co-glycolic acid) scaffold compared with rats treated with scaffold only, and the number of bone marrow mesenchymal stem cells and neuron-like cells was also increased. At 8 weeks after transplantation, horseradish peroxidase tracing and transmission electron microscopy showed a large number of unmyelinated and myelinated nerve fibers, as well as intact regenerating axonal myelin sheath following spinal cord hemisection injury. These experimental findings indicate that transplantation of Nogo-66 receptor gene-silenced bone marrow mesenchymal stem cells and Schwann cells plus a poly(D,L-lactide-co-glycolic acid) scaffold can significantly enhance axonal regeneration of spinal cord neurons and improve motor function of the extremities in rats following spinal cord injury.

Enhancing human islet transplantation by localized release of trophic factors from PLG scaffolds

Islet transplantation represents a potential cure for type 1 diabetes, yet the clinical approach of intrahepatic delivery is limited by the microenvironment. Microporous scaffolds enable extrahepatic transplantation, and the microenvironment can be designed to enhance islet engraftment and function. We investigated localized trophic factor delivery in a xenogeneic human islet to mouse model of islet transplantation. Double emulsion microspheres containing exendin-4 (Ex4) or insulin-like growth factor-1 (IGF-1) were incorporated into a layered scaffold design consisting of porous outer layers for islet transplantation and a center layer for sustained factor release. Protein encapsulation and release were dependent on both the polymer concentration and the identity of the protein. Proteins retained bioactivity upon release from scaffolds in vitro. A minimal human islet mass transplanted on Ex4-releasing scaffolds demonstrated significant improvement and prolongation of graft function relative to blank scaffolds carrying no protein, and the release profile significantly impacted the duration over which the graft functioned. Ex4-releasing scaffolds enabled better glycemic control in animals subjected to an intraperitoneal glucose tolerance test. Scaffolds releasing IGF-1 lowered blood glucose levels, yet the reduction was insufficient to achieve euglycemia. Ex4-delivering scaffolds provide an extrahepatic transplantation site for modulating the islet microenvironment to enhance islet function posttransplant.

Biodegradable injectable in situ implants and microparticles for sustained release of montelukast: in vitro release, pharmacokinetics, and stability

The objective of this study was to investigate the sustained release of a hydrophilic drug, montelukast (MK), from two biodegradable polymeric drug delivery systems, in situ implant (ISI) and in situ microparticles (ISM). N-Methyl pyrrolidone (NMP), dimethyl sulfoxide (DMSO), triacetin, and ethyl acetate were selected as solvents. The release of 10% (w/v) MK from both systems containing poly-lactic-co-glycolic acid (PLGA) as the biodegradable polymer was compared. Upon contact with the aqueous medium, the PLGA in ISI and ISM systems solidified resulting in implants and microparticles, respectively. The in vitro drug release from the ISI system showed marked difference from miscible solvents (NMP and DMSO) than the partially miscible ones (triacetin and ethyl acetate), and the drug release decreased with increased PLGA concentration. In the ISM system, the initial in vitro drug release decreased with decreased ratio of polymer phase to external oil phase. In vivo studies in rats showed that ISM had slower drug release than the drug release from ISI. Also, the ISM system when compared to ISI system had significantly reduced initial burst effect. In vitro as well as the in vivo studies for both ISI and ISM systems showed sustained release of MK. The ISM system is suitable for sustained release of MK over 4-week period with a lower initial burst compared to the ISI system. Stability studies of the ISI and ISM formulations showed that MK is stable in the formulations stored at 4°C for more than 2 years.

Pharmacodynamics of diclofenac from novel Eudragit entrapped microspheres

Effective clinical utilization of non-steroidal anti-inflammatory drugs such as diclofenac sodium (DS) is significantly limited by their ulcerogenic potential and poor bioavailability after oral administration, thus necessitating the need for a better carrier to minimize these obvious limitations. The objective of this study was to evaluate Eudragit® RS100/RL100 microspheres formulated by the solvent-evaporation technique for improved delivery of diclofenac. Three batches of (DF1, DF2 and DF3) microspheres were prepared using different ratios of Eudragit RS-100 and RL-100 polymers based on the solvent-evaporation method. The microspheres were characterized based on morphological properties, particle size analysis and encapsulation efficiency (EE%). In vitro release of DS was investigated in both 0.1 N HCl (pH 1.2) and phosphate-buffered saline (pH 7.4), while anti-inflammatory studies were evaluated in the rat model. Maximum EE% of 86.61 ± 0.11, 88.14 ± 0.16 and 85.50 ± 0.21 was obtained for DF1, DF2 and DF3, respectively. Discrete, smooth and brownish microspheres of size range 437 ± 0.01-479 ± 0.21 µm were obtained. Release of DS from the formulation depends on the polymer ratio. All the batches exhibited good anti-inflammatory activities. Microsphere formulations based on Eudragit® polymers would likely offer a reliable and alternative means of delivering DS orally.

Respirable low-density microparticles formed in situ from aerosolized brittle matrices

PURPOSE

Inhalation of low-density porous particles enables deep lung delivery with less dependence on device design and patient inspiration. The purpose of this study was to implement Thin Film Freezing (TFF) to investigate a novel approach to dry powder inhalation.

METHODS

Powders produced by TFF were evaluated for aerodynamic and geometric particle size by cascade impaction and laser light scattering, respectively. Density measurements were conducted according to USP methods and calculated using data from particle size measurements. Excipient inclusion and its effect on moisture sorption was measured by Dynamic Vapor Sorption (DVS).

RESULTS

TFF-produced brittle matrix powders were sheared apart into respirable microparticles using a passive DPI device, producing fine particle fractions (FPF) up to 69% and mass median aerodynamic diameters (MMAD) as low as 2.6 μm. Particles had a mean geometric diameter ranging from 25 μm to 50 μm and mass densities of approximately 0.01 g/cm(3). Powders were susceptible to moisture-induced matrix collapse, capillary forces and electrostatic charging; although formulations containing mannitol or no sugar excipient proved to be more robust.

CONCLUSIONS

Aerosolized brittle matrices produced by TFF may prove to be a useful platform for highly efficient pulmonary delivery of thermally labile, highly potent, and poorly soluble drugs.

Mathematical modeling of drug delivery from autocatalytically degradable PLGA microspheres--a review

PLGA microspheres are widely studied for controlled release drug delivery applications, and many models have been proposed to describe PLGA degradation and erosion and drug release from the bulk polymer. Autocatalysis is known to have a complex role in the dynamics of PLGA erosion and drug transport and can lead to size-dependent heterogeneities in otherwise uniformly bulk-eroding polymer microspheres. The aim of this review is to highlight mechanistic, mathematical models for drug release from PLGA microspheres that specifically address interactions between phenomena generally attributed to autocatalytic hydrolysis and mass transfer limitation effects. Predictions of drug release profiles by mechanistic models are useful for understanding mechanisms and designing drug release particles.

Accelerated in-vitro release testing methods for extended-release parenteral dosage forms

OBJECTIVES

This review highlights current methods and strategies for accelerated in-vitro drug release testing of extended-release parenteral dosage forms such as polymeric microparticulate systems, lipid microparticulate systems, in-situ depot-forming systems and implants.

KEY FINDINGS

Extended-release parenteral dosage forms are typically designed to maintain the effective drug concentration over periods of weeks, months or even years. Consequently, 'real-time' in-vitro release tests for these dosage forms are often run over a long time period. Accelerated in-vitro release methods can provide rapid evaluation and therefore are desirable for quality control purposes. To this end, different accelerated in-vitro release methods using United States Pharmacopeia (USP) apparatus have been developed. Different mechanisms of accelerating drug release from extended-release parenteral dosage forms, along with the accelerated in-vitro release testing methods currently employed are discussed.

SUMMARY

Accelerated in-vitro release testing methods with good discriminatory ability are critical for quality control of extended-release parenteral products. Methods that can be used in the development of in-vitro-in-vivo correlation (IVIVC) are desirable; however, for complex parenteral products this may not always be achievable.

Poly Lactic-co-Glycolic Acid (PLGA) as Biodegradable Controlled Drug Delivery Carrier

In past two decades poly lactic-co-glycolic acid (PLGA) has been among the most attractive polymeric candidates used to fabricate devices for drug delivery and tissue engineering applications. PLGA is biocompatible and biodegradable, exhibits a wide range of erosion times, has tunable mechanical properties and most importantly, is a FDA approved polymer. In particular, PLGA has been extensively studied for the development of devices for controlled delivery of small molecule drugs, proteins and other macromolecules in commercial use and in research. This manuscript describes the various fabrication techniques for these devices and the factors affecting their degradation and drug release.

Development of chondroitin sulfate encapsulated PLGA microsphere delivery systems with controllable multiple burst releases for treating osteoarthritis

The purpose of the study was to design and develop unique drug delivery systems with controllable multiple burst releases of drugs for treating osteoarthritis. Chondroitin sulfate (CS) was encapsulated into four types of PLGA materials, that is, PLGA 50:50, PLGA 65:35, PLGA 75:25, and PLGA 85:15. The effects of microsphere size and various combinations of blend PLGA microspheres on CS release were investigated. The cytotoxicity of the CS-encapsulated microspheres was investigated according to the ISO 10993 guideline. Our study showed that the encapsulation efficiency of CS into PLGA 50:50 microspheres varied with the size of microspheres; however, the encapsulation efficiencies of CS into PLGA microspheres were independent of the types of PLGA materials. The size of PLGA microspheres was shown to affect the rate of CS release. With the increase of microsphere size from 75-150 μm to 300-355 μm, the initial CS release decreased. Further increase in microsphere size led to an increase in the initial CS release. In addition, combination of different types of PLGA microspheres was shown to be capable of achieving multiple burst CS releases. Moreover, the CS encapsulated PLGA microspheres were shown to be non-cytotoxic. This study proved the concept of multiple burst drug releases that were achieved by encapsulating CS into different types of PLGA microspheres and delivering CS from systems consisting of mixed types of PLGA microspheres, which may be applied to treat osteoarthritis by mimicking multiple intra-joint injection of therapeutic agents.

Designing bioactive delivery systems for tissue regeneration

The direct infusion of macromolecules into defect sites generally does not impart adequate physiological responses. Without the protection of delivery systems, inductive molecules may likely redistribute away from their desired locale and are vulnerable to degradation. In order to achieve efficacy, large doses supplied at interval time periods are necessary, often at great expense and ensuing detrimental side effects. The selection of a delivery system plays an important role in the rate of re-growth and functionality of regenerating tissue: not only do the release kinetics of inductive molecules and their consequent bioactivities need to be considered, but also how the delivery system interacts and integrates with its surrounding host environment. In the current review, we describe the means of release of macromolecules from hydrogels, polymeric microspheres, and porous scaffolds along with the selection and utilization of bioactive delivery systems in a variety of tissue-engineering strategies.

Polymeric Microspheres for Medical Applications

Synthetic polymeric microspheres find application in a wide range of medical applications. Among other applications, microspheres are being used as bulking agents, embolic- or drug-delivery particles. The exact composition of the spheres varies with the application and therefore a large array of materials has been used to produce microspheres. In this review, the relation between microsphere synthesis and application is discussed for a number of microspheres that are used for different treatment strategies.