Fariba Dehghani

Electrospun scaffolds for tissue engineering of vascular grafts

There is a growing demand for off-the-shelf tissue engineered vascular grafts (TEVGs) for the replacement or bypass of damaged arteries in various cardiovascular diseases. Scaffolds from the decellularized tissue skeletons to biopolymers and biodegradable synthetic polymers have been used for fabricating TEVGs. However, several issues have not yet been resolved, which include the inability to mimic the mechanical properties of native tissues, and the ability for long-term patency and growth required for in vivo function. Electrospinning is a popular technique for the production of scaffolds that has the potential to address these issues. However, its application to human TEVGs has not yet been achieved. This review provides an overview of tubular scaffolds that have been prepared by electrospinning with potential for TEVG applications.

Conventional and Dense Gas Techniques for the Production of Liposomes: A Review

The aim of this review paper is to compare the potential of various techniques developed for production of homogenous, stable liposomes. Traditional techniques, such as Bangham, detergent depletion, ether/ethanol injection, reverse-phase evaporation and emulsion methods, were compared with the recent advanced techniques developed for liposome formation. The major hurdles for scaling up the traditional methods are the consumption of large quantities of volatile organic solvent, the stability and homogeneity of the liposomal product, as well as the lengthy multiple steps involved. The new methods have been designed to alleviate the current issues for liposome formulation. Dense gas liposome techniques are still in their infancy, however they have remarkable advantages in reducing the use of organic solvents, providing fast, single-stage production and producing stable, uniform liposomes. Techniques such as the membrane contactor and heating methods are also promising as they eliminate the use of organic solvent, however high temperature is still required for processing.

Utilization of supercritical carbon dioxide for complex formation of ibuprofen and methyl-β-cyclodextrin

The dissolution rate of a drug into the biological environment can be enhanced by forming complexes with cyclodextrins and their derivatives. In this study, ibuprofen-methyl-beta-cyclodextrin complexes were prepared successfully by passing ibuprofen-laden CO(2) through a methyl-beta-cyclodextrin packed bed. The maximum drug loading obtained in this work was 10.8 wt.%, which was comparable to that of a 1:1 complex (13.6 wt.% of ibuprofen). The complex exhibited instantaneous dissolution profiles in water solution. The enhanced dissolution rate was attributed to the amorphous character and improved wettability of the product.

Fabrication of porous chitosan scaffolds for soft tissue engineering using dense gas CO2

The aim of this study was to investigate the feasibility of fabricating porous crosslinked chitosan hydrogels in an aqueous phase using dense gas CO(2) as a foaming agent. Highly porous chitosan hydrogels were formed by using glutaraldehyde and genipin as crosslinkers. The method developed here eliminates the formation of a skin layer, and does not require the use of surfactants or other toxic reagents to generate porosity. The chitosan hydrogel scaffolds had an average pore diameter of 30-40 μm. The operating pressure had a negligible effect on the pore characteristics of chitosan hydrogels. Temperature, reaction period, type of biopolymer and crosslinker had a significant impact on the pore size and characteristics of the hydrogel produced by dense gas CO(2). Scanning electron microscopy and histological analysis confirmed that the resulting porous structures allowed fibroblasts seeded on these scaffolds to proliferate into the three-dimensional (3-D) structure of these chitosan hydrogels. Live/dead staining and MTS analysis demonstrated that fibroblast cells proliferated over 7 days. The fabricated hydrogels exhibited comparable mechanical strength and swelling ratio and are potentially useful for soft tissue engineering applications such as skin and cartilage regeneration.

Synthesis of highly porous crosslinked elastin hydrogels and their interaction with fibroblasts in vitro

In this study the feasibility of using high pressure CO2 to produce porous alpha-elastin hydrogels was investigated. Alpha-elastin was chemically crosslinked with hexamethylene diisocyanate that can react with various functional groups in elastin such as lysine, cysteine, and histidine. High pressure CO2 substantially affected the characteristics of the fabricated hydrogels. The pore size of the hydrogels was enhanced 20-fold when the pressure was increased from 1 bar to 60 bar. The swelling ratio of the samples fabricated by high pressure CO2 was also higher than the gels produced under atmospheric pressure. The compression modulus of alpha-elastin hydrogels was increased as the applied strain magnitude was modified from 40% to 80%. The compression modulus of hydrogels produced under high pressure CO2 was 3-fold lower than the gels formed at atmospheric conditions due to the increased porosity of the gels produced by high pressure CO2. The fabrication of large pores within the 3D structures of these hydrogels substantially promoted cellular penetration and growth throughout the matrices. The highly porous alpha-elastin hydrogel structures fabricated in this study have potential for applications in tissue engineering.

Generation of micro-particles of proteins for aerosol delivery using high pressure modified carbon dioxide.

AbstractPurpose. To investigate the feasibility of using the Aerosol Solvent Extraction System (ASES) to generate microparticles of proteins suitable for aerosol delivery from aqueous-based solutions. Methods. The ASES technique using high- pressure carbon dioxide modified with ethanol was utilised for the generation of microparticles of proteins (lysozyme, albumin, insulin and recombinant human deoxyribonuclease (rhDNase)) from aqueous solutions. Particle size, morphology, size distributions and powder aerosol performance were examined. The biochemical integrity of the processed proteins was assessed by testing the level of molecular aggregation using size exclusion chromatography and by bioassay technique for lysozyme. Results. Proteins were precipitated as spherical particles ranging in size from 100 to 500 nm. The primary nano-sized particles agglomerated to form micron-sized particles during the precipitation process. The median size of the particles was a function of the operating conditions. In-vitro aerosol performance tests showed that the percent fine particle mass (< 5μm) was approximately 65%, 40% and 20% for lysozyme, albumin and insulin, respectively. Negligible loss in the monomer content or biological activity was observed for lysozyme. Insulin exhibited slight aggregation and 93% of the monomer was retained after processing. Albumin was affected by processing and only 50-75% of the monomer was retained compared with 86% in the original material. However, rhDNase was substantially denatured during processing as shown by the significantly reduced monomer content. Conclusions. Micron-sized particles of lysozyme, albumin and insulin with satisfactory inhalation performance were successfully generated from aqueous solutions using the modified ASES technique. The biochemical integrity of the processed proteins was a function of the operating conditions and the nature of the individual protein.

The fabrication of elastin-based hydrogels using high pressure CO2

The aim of this study was to investigate the effect of high pressure CO(2) on the crosslinking of elastin-based polymers and the characteristics of the fabricated hydrogels. A hydrogel was fabricated by chemically crosslinking alpha-elastin with glutaraldehyde at high pressure CO(2). The effects of pressure, reaction time, and crosslinker concentration on the characteristics of the fabricated hydrogels were determined. The reaction time had negligible effect on either the swelling ratio or the pore size of the fabricated hydrogels. Increasing the processing pressure from 30bar to 150bar resulted in a 60% increase in the hydrogel swelling ratio. The crosslinked hydrogels displayed stimuli-responsive characteristics towards temperature and salt concentration. The dense gas process facilitated coacervation, expedited the crosslinking reaction, and dramatically affected the micro- and macrostructures of pores within the sample. The results of micro-CT scan and SEM images demonstrated that pore interconnectivity was substantially enhanced for alpha-elastin hydrogels fabricated using high pressure CO(2). Dense gas CO(2) reduced the wall thickness and size of the pores and importantly induced channels within the structure of the alpha-elastin hydrogels. In vitro cell culture studies demonstrated that the channels facilitated fibroblast penetration and proliferation within alpha-elastin structures.

Micronisation and microencapsulation of pharmaceuticals using a carbon dioxide antisolvent

Abstract Micron-sized and microencapsulated drugs are desirable in the pharmaceutical industry for drug targeting and controlled release systems. The current methods available for micronisation and microencapsulation, however, are limited by various factors. In this study, the feasibility of using dense CO 2 with the technique known as the Aerosol Solvent Extraction System (ASES) to micronise and microencapsulate para -hydroxybenzoic acid ( p -HBA) and lysozyme, with a bioerodible polymer, poly( l -lactic acid) ( l -PLA), from various organic solutions, was examined. In the micronisation studies, the effects of various parameters, such as pressure, temperature, solution concentration, solvent system and spraying velocity, on the nature of the particles were determined. Effective size reduction of the particles was achieved at low to moderate temperatures in a fundamental one-step process. In general, it was found that the high-molecular-weight compounds, l -PLA and lysozyme, precipitated as microspheres and nanospheres, whereas the lighter-weight compound, p -HBA, precipitated as crystalline particles resembling platelets averaging 3 μm in length. The feasibility of microencapsulating p -HBA and lysozyme with l -PLA using the ASES process incorporating a multiple nozzle was then assessed. Various parameters, such as the flow configuration, drug-to-polymer ratio, pressure, temperature and nozzle geometry, were varied to examine their effects on the size and morphology of the particles formed, particle drug loading and encapsulation efficiencies. The drug loading and encapsulation efficiency of particles can be improved by changes to the operating conditions. The maximum encapsulation efficiencies for p -HBA/ l -PLA particles obtained in this work were 9.2%. Higher encapsulation efficiencies of 15.6% were achieved with lysozyme, possibly due to its smaller particle size upon precipitation from dimethylsulfoxide solvent. Whilst loadings are lower than those achieved in some conventional encapsulation techniques, the results suggest that improvements can be obtained by maximising the contact between the drug and polymer phases during the rapid precipitation process.

Current issues relating to anti-solvent micronisation techniques and their extension to industrial scales

Realisation of the potential of dense gas anti-solvent precipitation for commercially viable processing of fine chemicals is hindered by our inability to fully exploit the advantages afforded to dense gases. The feasibility of producing dry uniformly sized micronised material using dense gas technology has been well established on a bench scale. However, translating these advantages to an industrial scale remains a challenge for engineers. In this paper, issues specific to the process scale up of dense gas anti-solvent precipitation are discussed. Anti-solvent precipitation is essentially a mixing process and any predictable increase in production rate is impossible without a thorough understanding of the dominant controlling factors. In this paper the dominant process variables, issues such as safety, cleaning, residual solvent concerns, precipitate sizing and product handling are addressed.

Engineering porous scaffolds using gas-based techniques

Scaffolds are used in tissue engineering as a matrix for the seeding and attachment of human cells. The creation of porosity in three-dimensional (3D) structures of scaffolds plays a critical role in cell proliferation, migration, and differentiation into the specific tissue while secreting extracellular matrix components. These pores are used to transfer nutrients and oxygen and remove wastes produced from the cells. The lack of oxygen and nutrient supply impedes the cell migration more than 500μm from the surface. The physical properties of scaffolds such as porosity and pore interconnectivity can improve mass transfer and have a great impact on the cell adhesion and penetration into the scaffolds to form a new tissue. Various techniques such as electrospinning, freeze-drying, and solvent casting/salt leaching have been used to create porosity in scaffolds. The major issues in these methods include lack of 3D structure, control on pore size, and pore interconnectivity. In this review, we provide a brief overview of gas-based techniques that have been developed for creating porosity in scaffolds.