Preparation of porous microsphere-scaffolds by electrohydrodynamic forming and thermally induced phase separation

Effect of processing parameters on characteristics of biodegradable extended-release microspheres containing leuprolide acetate

OBJECTIVE

Poly(lactic-co-glycolic acid) microsphere containing leuprolide acetate - an extended-release drug delivery system whose characteristics (i.e. loading capacity, particle size and initial burst phase) depend on processing parameters.

METHODS

Microspheres were prepared by water/oil/water double-emulsion solvent evaporation method; drug content in microspheres was determined by high-performance liquid chromatography (HPLC); peptide concentration in the release medium was measured by fluorescence spectrometer; particle size and particle size distribution were measured by laser diffraction method; interaction between poly(lactic-co-glycolic acid) (PLGA) and leuprolide acetate (LA) was determined by differential scanning calorimetry (DSC) and Fourier-transform infrared spectroscopy (FTIR).

RESULTS

DSC curves and assay results proved LA adsorption ability of PLGA film. FTIR spectra proved ionic interactions between positive charged LA molecules and negative charged PLGA chains in phosphate buffer pH 7.4. Ten processing parameters including LA concentration (mg/mL), PLGA concentration (mg/mL), W1/O ratio (v/v), the first homogenization time (min), the first homogenization speed (rpm), O/W2 ratio (v/v), PVA concentration of W2 phase (mg/ml), the second homogenization time (s), the volume of diluted solution (ml) and nitrogen aeration time (min) have impacts on loading capacity, particle size and initial burst phase of microspheres. The release exponent (n) of Korsmeyer-Peppas model was 0.3571 (lower than 0.43), indicating that Fickian diffusion manipulated release kinetics of initial burst phase.

CONCLUSIONS

Processing parameter modification contributes to small microspheres with high loading capacity and controlled initial burst phase.

Macroporous 3D Scaffold with Self-Fitting Capability for Effectively Repairing Massive Rotator Cuff Tear

The postoperative retear rate of direct repair of massive rotator cuff tear has risen up to 40% because of the dissatisfied tendon-to-bone healing and poor regenerative potential of remnant rotator cuff tissue. A biological scaffold that connects the remnant rotator cuff tissue and bone might be a promising substitute. In the present study, we have developed a macroporous three-dimensional scaffold poly(ester-urethane)urea (PEUU), with self-fitting capability employing thermally induced phase separation (TIPS) technique. The scaffold provides oriented connected macropores for cells migration, and promoted tendon-to-bone healing on the basis of surgical repair. The scaffolds were characterized by scanning electron microscopy, stress-strain test and cell biocompatibility study. In vitro studies exhibited that PEUU scaffold with suitable elastic mechanical properties can better support proliferation and migration of rabbit bone mesenchymal stem cells (RBMSCs). After three months postreconstruction of massive rotator cuff tear in a rabbit model using PEUU scaffold, there was complete regeneration of rotator cuff with physical tendon-to-bone interface and continuous tendon tissue, as observed from histological analysis. Further, biomechanical testing demonstrated that rotator cuff induced by PEUU scaffold had no significant difference as compared to normal rotator cuff. This macroporous, mechanically matched scaffold is potentially suitable for the application in massive rotator cuff repair. In conclusion, this study demonstrates the high efficiency of the macroporous 3D scaffold with self-fitting capability in facilitating rotator cuff regeneration.

Functionalised thermally induced phase separation (TIPS) microparticles enabled for "click" chemistry

Due to their homogeneity, tuneable properties, low cost and ease of manufacture, thermally induced phase separation (TIPS) polymeric microparticles are emerging as an exciting class of injectable device for the treatment of damaged tissue or complex diseases, such as cancer. However, relatively little work has explored enhancing surface functionalisation of this system. Herein, we present the functionalisation of TIPS microparticles with both small molecules and an antibody fragment of Herceptin™, via a heterobifunctional pyridazinedione linker capable of participating in SPAAC "click" chemistry, and compare it to the traditional method of preparing active-targeted microparticle systems, that is, physisorption of antibodies to the microparticle surface. Antigen-binding assays demonstrated that functionalisation of microparticles with Herceptin Fab, via a pyridazinedione linker, provided an enhanced avidity to HER2+ when compared to traditional physisorption methods.

Modular Strategies to Build Cell-Free and Cell-Laden Scaffolds towards Bioengineered Tissues and Organs

Engineering three-dimensional (3D) scaffolds for functional tissue and organ regeneration is a major challenge of the tissue engineering (TE) community. Great progress has been made in developing scaffolds to support cells in 3D, and to date, several implantable scaffolds are available for treating damaged and dysfunctional tissues, such as bone, osteochondral, cardiac and nerve. However, recapitulating the complex extracellular matrix (ECM) functions of native tissues is far from being achieved in synthetic scaffolds. Modular TE is an intriguing approach that aims to design and fabricate ECM-mimicking scaffolds by the bottom-up assembly of building blocks with specific composition, morphology and structural properties. This review provides an overview of the main strategies to build synthetic TE scaffolds through bioactive modules assembly and classifies them into two distinct schemes based on microparticles (µPs) or patterned layers. The µPs-based processes section starts describing novel techniques for creating polymeric µPs with desired composition, morphology, size and shape. Later, the discussion focuses on µPs-based scaffolds design principles and processes. In particular, starting from random µPs assembly, we will move to advanced µPs structuring processes, focusing our attention on technological and engineering aspects related to cell-free and cell-laden strategies. The second part of this review article illustrates layer-by-layer modular scaffolds fabrication based on discontinuous, where layers' fabrication and assembly are split, and continuous processes.

Influence of Solvent Selection in the Electrospraying Process of Polycaprolactone

Electrosprayed polycaprolactone (PCL) microparticles are widely used in medical tissueengineering, drug control release delivery, and food packaging due to their prominent structuresand properties. In electrospraying, the selection of a suitable solvent system as the carrier of PCL isfundamental and a prerequisite for the stabilization of electrospraying, and the control ofmorphology and structure of electrosprayed particles. The latter is not only critical for diversifyingthe characteristics of electrosprayed particles and achieving improvement in their properties, butalso promotes the efficiency of the process and deepens the applications of electrosprayed particlesin various fields. In order to make it systematic and more accessible, this review mainly concludesthe effects of different solution properties on the operating parameters in electrospraying on theformation of Taylor cone and the final structure as well as the morphology. Meanwhile,correlations between operating parameters and electrospraying stages are summarized as well.Finally, this review provides detailed guidance on the selection of a suitable solvent systemregarding the desired morphology, structure, and applications of PCL particles.

Double-layered microsphere based dual growth factor delivery system for guided bone regeneration

Microsphere based drug delivery systems show great advantages for tissue engineering. However, it is still a big challenge to fabricate microspheres with capability in delivering and controlled releasing multiple growth factors. In the present study, double-layered microspheres consisting of an inner-layer of small core particles and an outer-layer of big shell particles were developed to sequentially release cell homing factors (SDF-1) and osteoinductive growth factors (BMP-2) for bone regeneration. In vitro release testing showed that bioactivity of both growth factors retained within the microspheres and differential release of SDF-1 and BMP-2 was achieved. Microspheres with both growth factors showed an obvious chemotaxis effect on preosteoblasts by inducing more cell migration. In osteoinductive ability tests, the microspheres with both growth factors showed higher ALP activity and more mineralized modules than control groups after culturing for 2 weeks. The expression of bone development transcription factors (Runx2, OCN, Osterix) as well as Smad signals (Smad 1, 5, 8) showed higher gene expression in the dual growth factor group. Our results suggest that a double-layered microsphere system enhances the recruitment of osteogenic cells and osteoinduction, which provides a promising platform for bone regeneration.

Sustained release ophthalmic dexamethasone: In vitro in vivo correlations derived from the PK-Eye

Corticosteroids have long been used to treat intraocular inflammation by intravitreal injection. We describe dexamethasone loaded poly-DL-lactide-co-glycolide (PLGA) microparticles that were fabricated by thermally induced phase separation (TIPS). The dexamethasone loaded microparticles were evaluated using a two-compartment, in vitro aqueous outflow model of the eye (PK-Eye) that estimates drug clearance time from the back of the eye via aqueous outflow by the anterior route. A dexamethasone dose of 0.20±0.02mg in a 50μL volume of TIPS microparticles resulted in a clearance t_1/2 of 9.6±0.3days using simulated vitreous in the PK-Eye. Since corticosteroids can also clear through the retina, it is necessary to account for clearance through the back of the eye. Retinal permeability data, published human ocular pharmacokinetics (PK) and the PK-Eye clearance times were then used to establish in vitro in vivo correlations (IVIVCs) for intraocular clearance times of corticosteroid formulations. A t_1/2 of 48h was estimated for the dexamethasone-TIPS microparticles, which is almost 9 times longer than that reported for dexamethasone suspension in humans. The prediction of human clearance times of permeable molecules from the vitreous compartment can be determined by accounting for drug retinal permeation and determining the experimental clearance via the anterior aqueous outflow pathway using the PK-Eye.

Micropatterned fabrication of chitosan-based thermoresponsive membranes for improving cell adhesion and gene expression

A simple, rapid, and economical method to fabricate micropatterned thermoresponsive chitosan membranes was developed. Porous polystyrene films were prepared by liquid-induced phase separation. The size of pores on polystyrene films could be regulated by adjusting the composition of coagulation bath and changing the solvent evaporation rate. Subsequently, chitosan-based thermoresponsive membranes with island protrusions were fabricated using porous polystyrene films as templates. The effects of the micropatterns on the behaviors of mouse fibroblast L929 were investigated. The presence of micropatterns altered the cell cycle distribution and enhanced the gene expression of cyclin D1 and integrin β1. The micro-convex surface could promote the adhesion and proliferation of L929 cells. These results provided valuable guidance to design appropriate topographic surfaces for tissue engineering applications.

Electrospray synthesis and properties of hierarchically structured PLGA TIPS microspheres for use as controlled release technologies

Microsphere-based controlled release technologies have been utilized for the long-term delivery of proteins, peptides and antibiotics, although their synthesis poses substantial challenges owing to formulation complexities, lack of scalability, and cost. To address these shortcomings, we used the electrospray process as a reproducible, synthesis technique to manufacture highly porous (>94%) microspheres while maintaining control over particle structure and size. Here we report a successful formulation recipe used to generate spherical poly(lactic-co-glycolic) acid (PLGA) microspheres using the electrospray (ES) coupled with a novel thermally induced phase separation (TIPS) process with a tailored Liquid Nitrogen (LN2) collection scheme. We show how size, shape and porosity of resulting microspheres can be controlled by judiciously varying electrospray processing parameters and we demonstrate examples in which the particle size (and porosity) affect release kinetics. The effect of electrospray treatment on the particles and their physicochemical properties are characterized by scanning electron microscopy, confocal Raman microscopy, thermogravimetric analysis and mercury intrusion porosimetry. The microspheres manufactured here have successfully demonstrated long-term delivery (i.e. 1week) of an active agent, enabling sustained release of a dye with minimal physical degradation and have verified the potential of scalable electrospray technologies for an innovative TIPS-based microsphere production protocol.

Synthesis and characterization of nanofibrous hollow microspheres with tunable size and morphology via thermally induced phase separation technique

Nanofibrous hollow microspheres with tunable size and morphology were fabricated by using the thermally induced phase separation technique.

Microfluidic preparation of polymer nanospheres

In this work, solid polymer nanospheres with their surface tailored for drug adhesion were prepared using a V-shaped microfluidic junction. The biocompatible polymer solutions were infused using two channels of the microfluidic junction which was also simultaneously fed with a volatile liquid, perfluorohexane using the other channel. The mechanism by which the nanospheres are generated is explained using high speed camera imaging. The polymer concentration (5-50 wt%) and flow rates of the feeds (50-300 µl min^-1) were important parameters in controlling the nanosphere diameter. The diameter of the polymer nanospheres was found to be in the range of 80-920 nm with a polydispersity index of 11-19 %. The interior structure and surfaces of the nanospheres prepared were studied using advanced microscopy and showed the presence of fine pores and cracks on surface which can be used as drug entrapment locations.

Didanosine-loaded poly(epsilon-caprolactone) microparticles by a coaxial electrohydrodynamic atomization (CEHDA) technique

The goal of this study was to investigate the electrohydrodynamic atomization (EHDA) technology to encapsulate the water-soluble antiretroviral didanosine (ddI) within poly(epsilon-caprolactone) (PCL) particles and stabilize it in the gastric medium where it undergoes fast degradation. A preliminary study employing a one-needle setup enabled the adjustment of the critical process parameters. Then, a configuration of two concentric needles named coaxial electrohydrodynamic atomization (CEHDA) led to the formation of ddI-loaded PCL microcapsules. Scanning electron microscopy analysis showed that the microparticles were spherical and with narrow size distribution. Attenuated total reflectance/Fourier transform infrared spectroscopy confirmed that most of the drug was efficiently encapsulated within the particles, whereas differential scanning calorimetry and X-ray powder diffraction revealed that the drug was preserved mainly in crystalline form. The loading capacity was relatively high (approximately 12% w/w), and the encapsulation efficiency was approximately 100%. In vitro release assays (PBS pH = 7.4) indicated that ddI was released almost completely within 2 h. Moreover, the delayed release was expected to isolate ddI from the biological fluids during the gastric transit. Finally, pharmacokinetics studies in rats showed that ddI-loaded particles lead to a statistically significant increase of the oral bioavailability of almost 4 times and a 2-fold prolongation of the half-life with respect to a ddI aqueous solution, supporting the use of CEHDA as a promising reproducible, scalable and cost-viable technology to encapsulate water-soluble drugs within polymeric particles.

Translating textiles to tissue engineering: Creation and evaluation of microporous, biocompatible, degradable scaffolds using industry relevant manufacturing approaches and human adipose derived stem cells

Polymeric scaffolds have emerged as a means of generating three-dimensional tissues, such as for the treatment of bone injuries and nonunions. In this study, a fibrous scaffold was designed using the biocompatible, degradable polymer poly-lactic acid in combination with a water dispersible sacrificial polymer, EastONE. Fibers were generated via industry relevant, facile scale-up melt-spinning techniques with an islands-in-the-sea geometry. Following removal of EastONE, a highly porous fiber remained possessing 12 longitudinal channels and pores throughout all internal and external fiber walls. Weight loss and surface area characterization confirmed the generation of highly porous fibers as observed via focused ion beam/scanning electron microscopy. Porous fibers were then knit into a three-dimensional scaffold and seeded with human adipose-derived stem cells (hASC). Confocal microscopy images confirmed hASC attachment to the fiber walls and proliferation throughout the knit structure. Quantification of cell-mediated calcium accretion following culture in osteogenic differentiation medium confirmed hASC differentiation throughout the porous constructs. These results suggest incorporation of a sacrificial polymer within islands-in-the-sea fibers generates a highly porous scaffold capable of supporting stem cell viability and differentiation with the potential to generate large three-dimensional constructs for bone regeneration and/or other tissue engineering applications.