Three-month, zero-order piroxicam release from monodispersed double-walled microspheres of controlled shell thickness

An overview of the production methods for core-shell microspheres for parenteral controlled drug delivery

Core-shell microspheres hold great promise as a drug delivery system because they offer several benefits over monolithic microspheres in terms of release kinetics, for instance a reduced initial burst release, the possibility of delayed (pulsatile) release, and the possibility of dual-drug release. Also, the encapsulation efficiency can significantly be improved. Various methods have proven to be successful in producing these core-shell microspheres, both the conventional bulk emulsion solvent evaporation method and methods in which the microspheres are produced drop by drop. The latter have become increasingly popular because they provide improved control over the particle characteristics. This review assesses various production methods for core-shell microspheres and summarizes the characteristics of formulations prepared by the different methods, with a focus on their release kinetics.

Drug delivery systems for programmed and on-demand release

With the advancement in medical science and understanding the importance of biodistribution and pharmacokinetics of therapeutic agents, modern drug delivery research strives to utilize novel materials and fabrication technologies for the preparation of robust drug delivery systems to combat acute and chronic diseases. Compared to traditional drug carriers, which could only control the release of the agents in a monotonic manner, the new drug carriers are able to provide a precise control over the release time and the quantity of drug introduced into the patient's body. To achieve this goal, scientists have introduced "programmed" and "on-demand" approaches. The former provides delivery systems with a sophisticated architecture to precisely tune the release rate for a definite time period, while the latter includes systems directly controlled by an operator/practitioner, perhaps with a remote device triggering/affecting the implanted or injected drug carrier. Ideally, such devices can determine flexible release pattern and intensify the efficacy of a therapy via controlling time, duration, dosage, and location of drug release in a predictable, repeatable, and reliable manner. This review sheds light on the past and current techniques available for fabricating and remotely controlling drug delivery systems and addresses the application of new technologies (e.g. 3D printing) in this field.

Single Step Double-walled Nanoencapsulation (SSDN)

A quick fabrication method for making double-walled (DW) polymeric nanospheres is presented. The process uses sequential precipitation of two polymers. By choosing an appropriate solvent and non-solvent polymer pair, and engineering two sequential phase inversions which induces first precipitation of the core polymer followed by precipitation of the shell polymer, DW nanospheres can be created instantaneously. A series of DW formulations were prepared with various core and shell polymers, then characterized using laser diffraction particle sizing, scanning electron microscopy, atomic force microscopy, Fourier transform infrared spectroscopy, and differential scanning calorimetry (DSC). Atomic force microscopy (AFM) imaging confirmed existence of a single core polymer coated with a second polymer. Insulin (3.3% loading) was used as a model drug to assess its release profile from core (PLGA) and shell (PBMAD) polymers and resulted with a tri-phase release profile in vitro for two months. Current approaches for producing DW nanoparticles (NPs) are limited by the complexity and time involved. Additional issues include aggregation and entrapment of multiple spheres and the undesired formation of heterogeneous coatings. Therefore, the technique presented here is advantageous because it can produce NPs with distinct, core-shell morphologies through a rapid, spontaneous, self-assembly process. This method not only produces DW NPs, but can also be used to encapsulate therapeutic drug. Furthermore, modification of this process to other core and shell polymers is feasible using the general guidelines provided in this paper.

Evaluation of a transtympanic delivery system in Mus musculus for extended release steroids

OBJECTIVE

The current investigation evaluated a novel extended release delivery system for treating inner ear diseases. The platform technology consists of a film forming agent (FFA) and microsphere component to localize and extend drug delivery within the ear.

STUDY DESIGN

Studies evaluated dissolution kinetics of microspheres with multiple encapsulates, testing of a variety of FFAs, and ability to localize to the round window membrane in mice in vivo.

SETTING

Studies were completed at Orbis Biosciences and The University of Kansas Medical Center.

SUBJECTS

In conjunction with in vitro characterization, an infrared dye-containing microsphere formulation was evaluated for round window membrane (RWM) localization and general tolerability in C57/BL6 Mus musculus for 35 days.

METHODS

In vitro characterization was performed using upright diffusion cells on cellulose acetate membranes, with drug content quantified by high performance liquid chromatography. Mus musculus dosing of infrared dye-containing microspheres was performed under anesthesia with a 27 GA needle and 2.0 μL injection volume RESULTS: In vitro dissolution demonstrates the ability of the FFA with microsphere platform to release steroids, proteins, peptides, and nucleic acids for at least one month, while necroscopy shows the ability of the FFA with dye-loaded microspheres to remain localized to Mus musculus RWM for the same period of time, with favorable tolerability.

CONCLUSIONS

Combining FFA and microsphere for localized drug delivery may enable cost-effective, extended release local delivery to the inner ear of new and existing small molecules, proteins, peptides, and nucleic acids.

Sustained-releasing hollow microparticles with dual-anticancer drugs elicit greater shrinkage of tumor spheroids

Polymeric particulate delivery systems are vastly explored for the delivery of chemotherapeutic agents. However, the preparation of polymeric particulate systems with the capability of providing sustained release of two or more drugs is still a challenge. Herein, poly (D, L-lactic-co-glycolic acid, 50:50) hollow microparticles co-loaded with doxorubicin and paclitaxel were developed through double-emulsion solvent evaporation technique. Hollow microparticles were formed through the addition of an osmolyte into the fabrication process. The benefits of hollow over solid microparticles were found to be higher encapsulation efficiency and a more rapid drug release rate. Further modification of the hollow microparticles was accomplished through the introduction of methyl-β-cyclodextrin. With this, a higher encapsulation efficiency of both drugs and an enhanced cumulative release were achieved. Spheroid study further demonstrated that the controlled release of the drugs from the methyl-β-cyclodextrin -loaded hollow microparticles exhibited enhanced tumor regressions of MCF-7 tumor spheroids. Such hollow dual-drug-loaded hollow microparticles with sustained releasing capabilities may have a potential for future applications in cancer therapy.

Droplet Microfluidics for the Production of Microparticles and Nanoparticles

Droplet microfluidics technology is recently a highly interesting platform in material fabrication. Droplets can precisely monitor and control entire material fabrication processes and are superior to conventional bulk techniques. Droplet production is controlled by regulating the channel geometry and flow rates of each fluid. The micro-scale size of droplets results in rapid heat and mass-transfer rates. When used as templates, droplets can be used to develop reproducible and scalable microparticles with tailored sizes, shapes and morphologies, which are difficult to obtain using traditional bulk methods. This technology can revolutionize material processing and application platforms. Generally, microparticle preparation methods involve three steps: (1) the formation of micro-droplets using a microfluidics generator; (2) shaping the droplets in micro-channels; and (3) solidifying the droplets to form microparticles. This review discusses the production of microparticles produced by droplet microfluidics according to their morphological categories, which generally determine their physicochemical properties and applications.

Delivery of doxorubicin and paclitaxel from double-layered microparticles: The effects of layer thickness and dual-drug vs. single-drug loading

Double-layered microparticles composed of poly(d,l-lactic-co-glycolic acid, 50:50) (PLGA) and poly(l-lactic acid) (PLLA) were loaded with doxorubicin HCl (DOX) and paclitaxel (PCTX) through a solvent evaporation technique. DOX was localized in the PLGA shell, while PCTX was localized in the PLLA core. The aim of this study was to investigate how altering layer thickness of dual-drug, double-layered microparticles can influence drug release kinetics and their antitumor capabilities, and against single-drug microparticles. PCTX-loaded double-layered microparticles with denser shells retarded the initial release of PCTX, as compared with dual-drug-loaded microparticles. The DOX release from both DOX-loaded and dual-drug-loaded microparticles were observed to be similar with an initial burst. Through specific tailoring of layer thicknesses, a suppressed initial burst of DOX and a sustained co-delivery of two drugs can be achieved over 2months. Viability studies using spheroids of MCF-7 cells showed that controlled co-delivery of PCTX and DOX from dual-drug-loaded double-layered microparticles were better in reducing spheroid growth rate. This study provides mechanistic insights into how by tuning the layer thickness of double-layered microparticles the release kinetics of two drugs can be controlled, and how co-delivery can potentially achieve better anticancer effects.

STATEMENT OF SIGNIFICANCE

While the release of multiple drugs has been reported to achieve successful apoptosis and minimize drug resistance, most conventional particulate systems can only deliver a single drug at a time. Recently, although a number of formulations (e.g. micellar nanoparticles, liposomes) have been successful in delivering two or more anticancer agents, sustained co-delivery of these agents remains inadequate due to the complex agent loading processes and rapid release of hydrophilic agents. Therefore, the present work reports the multilayered particulate system that simultaneously hosts different drugs, while being able to tune their individual release over months. We believe that our findings would be of interest to the readers of Acta Biomaterialia because the proposed system could open a new avenue on how two drugs can be released, through rate-controlling carriers, for combination chemotherapy.

Inhibition of 3-D tumor spheroids by timed-released hydrophilic and hydrophobic drugs from multilayered polymeric microparticles

First-line cancer chemotherapy necessitates high parenteral dosage and repeated dosing of a combination of drugs over a prolonged period. Current commercially available chemotherapeutic agents, such as Doxil and Taxol, are only capable of delivering single drug in a bolus dose. The aim of this study is to develop dual-drug-loaded, multilayered microparticles and to investigate their antitumor efficacy compared with single-drug-loaded particles. Results show hydrophilic doxorubicin HCl (DOX) and hydrophobic paclitaxel (PTX) localized in the poly(dl-lactic-co-glycolic acid, 50:50) (PLGA) shell and in the poly(l-lactic acid) (PLLA) core, respectively. The introduction of poly[(1,6-bis-carboxyphenoxy) hexane] (PCPH) into PLGA/PLLA microparticles causes PTX to be localized in the PLLA and PCPH mid-layers, whereas DOX is found in both the PLGA shell and core. PLGA/PLLA/PCPH microparticles with denser shells allow better control of DOX release. A delayed release of PTX is observed with the addition of PCPH. Three-dimensional MCF-7 spheroid studies demonstrate that controlled co-delivery of DOX and PTX from multilayered microparticles produces a greater reduction in spheroid growth rate compared with single-drug-loaded particles. This study provides mechanistic insights into how distinctive structure of multilayered microparticles can be designed to modulate the release profiles of anticancer drugs, and how co-delivery can potentially provide better antitumor response.

Pulsatile protein release from monodisperse liquid-core microcapsules of controllable shell thickness

PURPOSE

Pulsatile delivery of proteins, in which release occurs over a short time after a period of little or no release, is desirable for many applications. This paper investigates the effect of biodegradable polymer shell thickness on pulsatile protein release from biodegradable polymer microcapsules.

METHODS

Using precision particle fabrication (PPF) technology, monodisperse microcapsules were fabricated encapsulating bovine serum albumin (BSA) in a liquid core surrounded by a drug-free poly(lactide-co-glycolide) (PLG) shell of uniform, controlled thickness from 14 to 19 μm.

RESULTS

When using high molecular weight PLG (Mw 88 kDa), microparticles exhibited the desired core-shell structure with high BSA loading and encapsulation efficiency (55-65%). These particles exhibited very slow release of BSA for several weeks followed by rapid release of 80-90% of the encapsulated BSA within 7 days. Importantly, with increasing shell thickness the starting time of the pulsatile release could be controlled from 25 to 35 days.

CONCLUSIONS

Biodegradable polymer microcapsules with precisely controlled shell thickness provide pulsatile release with enhanced control of release profiles.

Optimal Control of One-dimensional Cellular Uptake in Tissue Engineering

A control problem motivated by tissue engineering is formulated and solved in which control of the uptake of growth factors (signaling molecules) is necessary to spatially and temporally regulate cellular processes for the desired growth or regeneration of a tissue. Four approaches are compared for determining 1D optimal boundary control trajectories for a distributed parameter model with reaction, diffusion, and convection: (i) basis function expansion, (ii) method of moments, (iii) internal model control (IMC), and (iv) model predictive control (MPC). The proposed method-of-moments approach is computationally efficient while enforcing a non-negativity constraint on the control input. While more computationally expensive than methods (i)-(iii), the MPC formulation significantly reduced the computational cost compared to simultaneous optimization of the entire control trajectory. A comparison of the pros and cons of each of the four approaches suggests that an algorithm that combines multiple approaches is most promising for solving the optimal control problem for multiple spatial dimensions.

Building functional materials for health care and pharmacy from microfluidic principles and Flow Focusing

In this review, we aim at establishing a relationship between the fundamentals of the microfluidics technologies used in the Pharmacy field, and the achievements accomplished by those technologies. We describe the main methods for manufacturing micrometer drops, bubbles, and capsules, as well as the corresponding underlying physical mechanisms. In this regard, the review is intended to show non-specialist readers the dynamical processes which determine the success of microfluidics techniques. Flow focusing (FF) is a droplet-based method widely used to produce different types of fluid entities on a continuous basis by applying an extensional co-flow. We take this technique as an example to illustrate how microfluidics technologies for drug delivery are progressing from a deep understanding of the physics of fluids involved. Specifically, we describe the limitations of FF, and review novel methods which enhance its stability and robustness. In the last part of this paper, we review some of the accomplishments of microfluidics when it comes to drug manufacturing and delivery. Special attention is paid to the production of the microencapsulated form because this fluidic structure gathers the main functionalities sought for in Pharmacy. We also show how FF has been adapted to satisfy an ample variety of pharmaceutical requirements to date.

Protein encapsulation in and release from monodisperse double-wall polymer microspheres

Biodegradable polymer double-wall microspheres (DWMS) are promising vehicles for macromolecular therapeutics such as proteins and peptides. Using precision particle fabrication (PPF) technology, uniform DWMS with outer diameter approximately 55 μm were fabricated comprising poly(lactide-co-glycolide) cores encapsulating bovine serum albumin (BSA) and approximately 10 μm thick, drug-free, poly(lactic acid) (PLA) shells of varying PLA molecular weight. Also, monolithic single-wall microspheres (SWMS) were fabricated to mimic the BSA-loaded core. The use of relatively fast-extracting ethyl acetate and slowly extracting dichloromethane as shell- and core-phase solvents, respectively, was found to produce DWMS with well-defined core-shell structure, high BSA encapsulation efficiency, and the desired localization of protein in the particle core. Initial protein distribution, particle erosion, and in vitro protein release from DWMS and SWMS were examined. The presence of a BSA-free shell in DWMS decreased the protein release rate and extended the duration of release from approximately 50 days to 70-80 days, demonstrating the capacity of such DWMS to provide enhanced control of protein delivery rates.

Mechanism of drug release from double-walled PDLLA(PLGA) microspheres

The drug release and degradation behavior of two double-walled microsphere formulations consisting of a doxorubicin-loaded poly(d,l-lactic-co-glycolic acid) (PLGA) core (∼46 kDa) surrounded by a poly(d,l-lactic acid) (PDLLA) shell layer (∼55 and 116 kDa) were examined. It was postulated that different molecular weights of the shell layer could modulate the erosion of the outer coating and limit the occurrence of water penetration into the inner drug-loaded core on various time scales, and therefore control the drug release from the microspheres. For both microsphere formulations, the drug release profiles were observed to be similar. The degradation of the microspheres was monitored for a period of about nine weeks and analyzed using scanning electron microscopy, laser scanning confocal microscopy, and gel permeation chromatography. Interestingly, both microsphere formulations exhibited occurrence of bulk erosion of PDLLA on a similar time scale despite different PDLLA molecular weights forming the shell layer. The shell layer of the double-walled microspheres served as an effective diffusion barrier during the initial lag phase period and controlled the release rate of the hydrophilic drug independent of the molecular weight of the shell layer.

Monodisperse double-walled microspheres loaded with chitosan-p53 nanoparticles and doxorubicin for combined gene therapy and chemotherapy

We have designed and evaluated a dual anticancer delivery system to provide combined gene therapy and chemotherapy. Double-walled microspheres consisting of a poly(d,l-lactic-co-glycolic acid) (PLGA) core surrounded by a poly(lactic acid) (PLA) shell were fabricated via the precision particle fabrication (PPF) technique. We make use of the advantages of double-walled microspheres to deliver chitosan-DNA nanoparticles containing the gene encoding the p53 tumor suppressor protein (chi-p53) and/or doxorubicin (Dox), loaded in the shell and core phases, respectively. Different molecular weights of PLA were used to form the shell layer for each formulation. The microspheres were monodisperse with a mean diameter of 65 to 75 μm and uniform shell thickness of 8 to 17 μm. Blank and Dox-loaded microspheres typically exhibited a smooth surface with relatively few small pores, while chi-microspheres containing p53 nanoparticles, with and without Dox, presented rough and porous surfaces. The encapsulation efficiency of Dox was significantly higher when it was encapsulated alone compared to co-encapsulation with chi-p53 nanoparticles. The encapsulation efficiency of chi-p53 nanoparticles, on the other hand, was not affected by the presence of Dox. As desired, chi-p53 nanoparticles were released first, followed by simultaneous release of chi-p53 nanoparticles and Dox at a near zero-order rate. Thus, we have demonstrated that the PPF method is capable of producing double-walled microspheres and encapsulating dual agents for combined modality treatment, such as gene therapy and chemotherapy.

Designing multilayered particulate systems for tunable drug release profiles

Triple-layered microparticles comprising poly(D,L-lactide-co-glycolide, 50:50) (PLGA), poly(L-lactide) (PLLA) and poly(ethylene-co-vinyl acetate, 40 wt.% vinyl acetate) (EVA) were fabricated using a one-step solvent evaporation technique, with ibuprofen drug localized in the EVA core. The aim of this study was to investigate the drug release profiles of these triple-layered microparticles in comparison to double-layered (PLLA/EVA and PLGA/EVA) (shell/core) and single-layered EVA microparticles. Double- and triple-layered microparticles were shown to eliminate burst release otherwise observed for single-layered microparticles. For triple-layered microparticles, the migration of acidic PGA oligomers from the PLGA shell accelerated the degradation of the PLLA mid-layer and subsequently enhanced drug release in comparison to double-layered PLLA/EVA microparticles. Further studies showed that drug release rates can be altered by changing the layer thicknesses of the triple-layered microparticles, and through specific tailoring of layer thicknesses, a zero-order release can be achieved. This study therefore provides important mechanistic insights into how the distinctive structural attributes of triple-layered microparticles can be tuned to control the drug release profiles.

Revolutionizing drug delivery through biodegradable multilayered particles

Modern drug discovery technologies are discovering more and more potent therapeutic agents with narrow therapeutic windows, thus necessitating the improvement of current particulate drug delivery systems. Conventional single-layered polymeric particles have limited control over drug release profiles, including burst release, the inability to provide zero-order, pulsatile, time-delayed release and controlled release of multiple drugs. In an attempt to better control drug release kinetics, the development of multilayered microparticles has been introduced. In this review, we give an overview of the fabrication and characterization techniques of multilayered polymeric microparticles. We also focus on the one-step solvent evaporation technique, and the key process parameters in this technique that affect the formation of microparticle configurations. In addition, the benefits and challenges of multilayered microparticulate system for drug delivery were discussed. This review intends to portray how distinctive structural attributes and degradation behaviors of multilayered microparticles can be exploited to fine-tune drug release profiles and kinetics.

Controlled-release and preserved bioactivity of proteins from (self-assembled) core-shell double-walled microspheres

In order to address preserved protein bioactivities and protein sustained-release problems, a method for preparing double-walled microspheres with a core (protein-loaded nanoparticles with a polymer-suspended granule system-formed core) and a second shell (a polymer-formed shell) for controlled drug release and preserved protein bioactivities has been developed using (solid-in-oil phase-in-hydrophilic oil-in-water (S/O/O_h/W)) phases. The method, based on our previous microsphere preparation method (solid-in-oil phase-in-hydrophilic oil-in-water (S/O/O_h/W), employs different concentric poly(D,L-lactide-co-glycolide), poly(D,L-lactide), and protein-loaded nanoparticles to produce a suspended liquid which then self-assembles to form shell-core microspheres in the hydrophilic oil phase, which are then solidified in the water phase. Variations in the preparation parameters allowed complete encapsulation by the shell phase, including the efficient formation of a poly(D,L-lactide) shell encapsulating a protein-loaded nanoparticle-based poly(D,L-lactide-co-glycolide) core. This method produces core-shell double-walled microspheres that show controlled protein release and preserved protein bioactivities for 60 days. Based upon these results, we concluded that the core-shell double-walled microspheres might be applied for tissue engineering and therapy for chronic diseases, etc.

Designing drug-loaded multi-layered polymeric microparticles

This work reports how novel multi-layered (from double-layered to quadruple-layered) microparticles comprising immiscible polymers can be fabricated through a simple, economical, reliable and versatile one-step solvent evaporation method. These multi-layered microparticles would be excellent candidates to overcome problems inherent in single-layered microparticles for drug delivery. Particle morphologies, layer configurations, and drug distribution were determined by scanning electron microscopy and Raman mapping. Key process parameters achieving the formation of the multi-layered structure were identified. Encapsulation of multiple drugs and layer localization of these drugs within these multi-layered microparticles have also shown to be possible, which were driven by drug-polymer affinity. This one-step fabrication technique can therefore be used for tailoring particle designs, thus facilitating the development of multiparticulate drug delivery devices.

In vitro cytotoxicity and drug release properties of pH- and temperature-sensitive core-shell hydrogel microspheres

A simple method has been developed to prepare smart P(N,N-diethylacrylamide-co-methacrylic acid) (P(DEA-co-MAA)) microspheres that consist of well-defined temperature-sensitive cores and pH sensitive shells. The microgels have been prepared by surfactant-free emulsion polymerization using water as the solvent. The core-shell hydrogel microspheres have been characterized by Fourier transform infrared (FTIR) spectroscopy, UV spectrometry, dynamic light scattering (DLS) and transmission electron micrograph (TEM). Preliminary characterization of the biocompatibility of hydrogel microspheres has been done by the cytotoxicity assays using the HeLa human breast cancer cell line as probes. The in vitro drug release indicates that drug release rate, encapsulation efficiency (EE) and release kinetics depend upon the pH value and copolymer composition. According to this study, the hydrogel microspheres based on P(DEA-co-MAA) could serve as suitable candidate for drug site-specific carrier in intestine.

PLGA particle production for water-soluble drug encapsulation: degradation and release behaviour

Particles for subcutaneous depot use encapsulating a model water-soluble drug have been produced from poly(lactic-glycolic acid) (PLGA) using a membrane emulsification-solvent evaporation technique. The release behaviour, mainly the change in size and inner morphology are reported. During release, the particles initially swelled in size, then reduced. A diffusion based model, taking in to account the change in particle size, is presented. Surface erosion is evident from the particle size and image evidence, and the diffusion model provides a fit to the data even during the surface erosion period, suggesting that the model drug diffuses before the particle degrades.

Microenvironment-Controlled Encapsulation (MiCE) Process: Effects of PLGA Concentration, Flow Rate, and Collection Method on Microcapsule Size and Morphology

PURPOSE

To evaluate the real-time effects of formulation and instrumental variables on microcapsule formation via natural jet segmentation, a new microencapsulation system termed the microenvironment-controlled encapsulation (MiCE) process was developed.

METHODS

A modified flow cytometer nozzle hydrodynamically focuses an inner drug and outer polymer solution emanating from a coaxial needle assembly into a two-layer compound jet. Poly(lactic-co-glycolic acid) (PLGA) dissolved in a water-miscible organic solvent resulted in formation of reservoir-type microcapsules by interfacial phase separation induced at the boundary between the PLGA solution and aqueous sheath.

RESULTS

The MiCE process produced microcapsules with mean diameters ranging from 15-25 microm. The resultant microcapsule size distribution and number of drug cores existing within each microcapsule was largely influenced by the PLGA concentration and microcapsule collection method. Higher PLGA concentrations yielded higher mean diameters of single-core microcapsules. Higher drug solution flow rates increased the core size, while higher PLGA solution flow rates increased the PLGA film thickness.

CONCLUSION

The MiCE microencapsulation process allows effective monitoring and control of the instrumental parameters affecting microcapsule production. However, the microcapsule collection method in this process needs to be further optimized to obtain microcapsules with desired morphologies, precise membrane thicknesses, high encapsulation efficiencies, and tight size distributions.

Use of thermodynamic parameters for design of double-walled microsphere fabrication methods

Double-walled microspheres (DWMS), with drug localized to the particle core, present a promising route for control of drug release rates, for example, by varying the degradation rate or erosion mechanism of the polymer used to form the shell or the thickness of the shell. DWMS are often difficult to fabricate, however. Thermodynamic descriptions for polymer-polymer immiscibility, drug distribution between phases and polymer-solution spreading coefficient provide predictions of appropriate solvents and polymer concentrations for efficiently producing well-formed DWMS. As an example, thermodynamic parameters for a polyphosphoester/poly(D,L-lactide-co-glycolide) (PLG) DWMS system, encapsulating piroxicam, have been calculated and the predictions tested experimentally. Appropriate choices of solvents and initial polymer concentrations resulted in DWMS with the desired polyphosphoester shells and piroxicam located selectively in PLG cores.

Small-molecule release from poly(D,L-lactide)/poly(D,L-lactide-co-glycolide) composite microparticles

Addition of biodegradable polymer shells surrounding polymeric, drug-loaded microparticles offers the opportunity to control drug release rates. A novel fabrication method was used to produce microparticles with precise control of particle diameter and the thickness of the polymer shell. The effect of shell thickness on release of a model drug, piroxicam, has been clearly shown for 2- to 15-microm thick shells of poly(D,L-lactide) (PDLL) surrounding a poly(D,L-lactide-co-glycolide) (PLG) core and compared to pure PLG microspheres loaded with piroxicam. Furthermore, the core-shell microparticles are compared to microspheres containing blended polymers in the same mass ratios to demonstrate the importance of the core-shell morphology. Combining PDLL(PLG) microcapsules of different shell thicknesses allows nearly constant release rates to be attained for a period of 6 weeks.

In vitro degradation of polyanhydride/polyester core-shell double-wall microspheres

Double-wall microspheres (DWMS), comprising distinct polymer core and shell phases, are useful and interesting for controlled-release drug delivery. In particular, the presence of a surface-eroding polymer core may be expected to limit water penetration and, therefore, delay degradation of the core phase and drug release. In this study, solid microspheres and DWMS were fabricated using a surface-eroding polymer (poly[1,6-bis(p-carboxyphenoxy)hexane]; PCPH) and a bulk-eroding polymer (poly(D,L-lactide-co-glycolide); PLG). Erosion of the particles was observed by optical and electron microscopy, while polymer degradation was followed by gel permeation chromatography, during incubation in buffer at 37 degrees C. Degradation and erosion were very different depending on which polymer formed the particle shell. Nevertheless, the relatively thin (approximately 5 microm) PCPH shells could not prevent water penetration, and the PLG cores completely eroded by 6 weeks of incubation.

Microspheres for Drug Delivery

With advances in biotechnology, genomics, and combinatorial chemistry, a wide variety of new, more potent and specific therapeutics are being created. Because of common problems such as low solubility, high potency, and/or poor stability of many of these new drugs, the means of drug delivery can impact efficacy and potential for commercialization as much as the nature of the drug itself. Thus, there is a corresponding need for safer and more effective methods and devices for drug delivery. Indeed, drug delivery systems—designed to provide a therapeutic agent in the needed amount, at the right time, to the proper location in the body, in a manner that optimizes efficacy, increases compliance and minimizes side effects—were responsible for $47 billion in sales in 2002, and the drug delivery market is expected to grow to $67 billion by 2006.