Selected advances in drug delivery and tissue engineering

Cross-linking porcine peritoneum by oxidized konjac glucomannan: a novel method to improve the properties of cardiovascular substitute material

The use of natural polysaccharide crosslinkers for decellularized matrices is an effective approach to prepare cardiovascular substitute materials. In this research, NaIO4 was applied to oxidize konjac glucomannan to prepare the polysaccharide crosslinker oxidized konjac glucomannan (OKGM). The as-prepared crosslinker was then used to stabilize collagen-rich decellularized porcine peritoneum (DPP) to construct a cardiovascular substitute material (OKGM-fixed DPP). The results demonstrated that compared with GA-fixed DPP and GNP-fixed DPP, 3.75% OKGM [1:1.5 (KGM: NaIO4)]-fixed DPP demonstrated suitable mechanical properties, as well as good hemocompatibility, excellent anti-calcification capability, and anti-enzymolysis in vitro. Furthermore, 3.75% OKGM [1:1.5 (KGM: NaIO4)]-fixed DPP was suitable for vascular endothelial cell adhesion and rapid proliferation, and a single layer of endothelial cells was formed on the fifth day of culture. The in vivo experimental results also showed excellent histocompatibility. The current results demonstrted that OKGM was a novel polysaccharide cross-linking reagent for crosslinking natural tissues featured with rich collagen content, and 3.75% OKGM [1:1.5 (KGM: NaIO4)]-fixed DPP was a potential cardiovascular substitute material.

Graphical Abstract

Hybrid Alginate-Brushite Beads Easily Catalyze the Knoevenagel Condensation On-Water

An innovative hybrid organic-inorganic material composed of alginate-brushite xerogel beads was successfully applied for the catalysis of the Knoevenagel condensation. The catalyst was derived from phosphated alginate xerogel microspheres formed from the ionotropic gelling effect of phosphated alginate. To this end, alginate was phosphated by the addition of diammonium hydrogen phosphate in a 1% w/w alginate gel. The phosphated alginate was subsequently precipitated by chelation of Ca²⁺ cations, generating a phosphated alginate hydrogel microsphere, which was washed and dried, forming hybrid organic-inorganic xerogel beads as a crystalline phosphate-rich mineral fraction covered by alginate. X-ray diffraction analysis revealed that the crystalline inorganic matrix of the material was composed predominantly of brushite. SEM analysis revealed plate-like, ribbon-like, or needle-like morphologies in the hybrid alginate-brushite beads. The hybrid material was tested as a catalyst for Knoevenagel condensation, which was performed ″on-water″ under mild conditions with aromatic aldehydes and activated methylene compounds, giving high yields (up to 97%). The reaction rate and product yield increased together with the reaction temperature for all reagents. The recyclable solid catalyst was effective for three runs, revealing the potential of the innovative hybrid catalyst as an eco-friendly heterogeneous catalyst.

Hair follicle stem cells differentiation into bone cells on collagen scaffold

The hair follicle is a dynamic structure which contains different niches for stem cells, therefore; it has been considered as valuable and rich sources of stem cells, due to easy access, multipotency and non-oncogenic properties. In the present study, the differentiation capacities of hair follicle stem cells into bone cells on the natural collagen scaffolds were investigated. The stem cells were extracted from the hair follicle bulge area of male Wistar rats' whisker and cultured until 3rd passage, then osteogenic differentiations were induced by culturing the cells in the specific osteogenic medium. After 3 weeks, the differentiation parameters, including morphological changes, levels of calcification and expression of the bone specific genes were detected. The hydrogel preparation and scaffold fabrication was carried out using the extracted collagen and was studied by scanning electron microscope. Comparison of the stem cells' growth and changes on the scaffold and non-scaffold conditions showed that, in the both situation, the cells revealed differentiation signs of osteocytes, including large and cubic morphology with a star-shaped nucleus. Staining by Alizarin-red and Von-Kossa methods showed the presence of red and black calcium mass on the scaffold. Expression of the osteopontin and alkaline phosphatase genes confirmed the differentiation. Considerable porosity in the surface of the scaffold was recorded by scanning electron microscopy, which made it convenient for cells' attachment and growth. The data showed that the bulge stem cells possess significant capacity for osteoblastic differentiation and collagen scaffolds were found to be an appropriate matrix for growth and differentiation of the cell.

Poly(propylene fumarate)-based materials: Synthesis, functionalization, properties, device fabrication and biomedical applications

Poly(propylene fumarate) (PPF) is a biodegradable polymer that has been investigated extensively over the last three decades. It has led many scientists to synthesize and fabricate a variety of PPF-based materials for biomedical applications due to its controllable mechanical properties, tunable degradation and biocompatibility. This review provides a comprehensive overview of the progress made in improving PPF synthesis, resin formulation, crosslinking, device fabrication and post polymerization modification. Further, we highlight the influence of these parameters on biodegradation, biocompatibility, and their use in a number of regenerative medicine applications, especially bone tissue engineering. In particular, the use of 3D printing techniques for the fabrication of PPF-based scaffolds is extensively reviewed. The recent invention of a ring-opening polymerization method affords precise control of PPF molecular mass, molecular mass distribution (Ɖ_M) and viscosity. Low Ɖ_M facilitates time-certain resorption of 3D printed structures. Novel post-polymerization and post-printing functionalization methods have accelerated the expansion of biomedical applications that utilize PPF-based materials. Finally, we shed light on evolving uses of PPF-based materials for orthopedics/bone tissue engineering and other biomedical applications, including its use as a hydrogel for bioprinting.

Evaluation of ceftiofur-PHBV microparticles in rats

Despite the high number of antibiotics used for the treatment of infectious disease in animals, the development of slow release formulations presents a significant challenge, particularly in using novel biomaterials with low cost. In this report, we studied the pharmacokinetics, toxicity, and therapeutic activity of ceftiofur–PHBV (ceftiofur–poly(3-hydroxybutyrate-co-3-hydroxyvalerate)) in rats. The pharmacokinetic study demonstrated a sustained release of ceftiofur into the bloodstream, with detectable levels over the minimum inhibitory concentration for at least 17 days after a single intramuscular injection of ceftiofur–PHBV (10 mg/kg weight). In addition, the toxicological evaluation of biochemical, hematological, and coagulation blood parameters at the therapeutic dose demonstrated the safety of ceftiofur–PHBV, with no adverse effects. In addition, ceftiofur–PHBV exhibited a therapeutic effect for a longer time period than the nonencapsulated ceftiofur in rats challenged with Salmonella Typhimurium. The slow release of ceftiofur from the ceftiofur–PHBV, its low toxicity in the blood parameters evaluated, and the efficacy in the rats infected with Salmonella Typhimurium make ceftiofur–PHBV a strong candidate for biotechnological applications in the veterinary industry.

Development of a bone reconstruction technique using a solid free-form fabrication (SFF)-based drug releasing scaffold and adipose-derived stem cells

For tissue regeneration, three essential components of scaffolds, signals (biomolecules), and cells are required. Moreover, because bony defects are three-dimensional in many clinical circumstances, an exact 3D scaffold is important. Therefore, we proposed an effective reconstruction tool for cranial defects using human adipose-derived stem cells (hADSCs) and a 3D functional scaffold fabricated by solid free-form fabrication (SFF) technology that secretes biomolecules. We fabricated poly(propylene fumarate)-based 3D scaffolds with embedded microsphere-deliverable bone morphogenetic protein-2 (BMP-2) by microstereolithography. BMP-2-loaded SFF scaffolds with/without hADSCs (SFF/BMP/hADSCs scaffolds and SFF/BMP scaffolds, respectively) and BMP-2-unloaded SFF scaffolds (SFF scaffolds) were then implanted in rat crania, and in vivo bone formation was observed. Analyses of bone formation areas using micro-computed tomography (micro-CT) showed the superiority of SFF/BMP/hADSCs scaffolds. Hematoxylin and eosin stain, Masson's trichrome stain, and collagen type-I stain supported the results of the micro-CT scan. And human leukocyte antigen-ABC showed that seeded, differentiated hADSCs were well grown and changed to the bone tissue at the inside of the scaffold. Results showed that our combination of a functional 3D scaffold and hADSCs may be a useful tool for improving the reconstruction quality of severe bony defects in which thick bone is required.

Review paper: Critical Issues in Tissue Engineering: Biomaterials, Cell Sources, Angiogenesis, and Drug Delivery Systems

Tissue engineering is a newly emerging biomedical technology, which aids and increases the repair and regeneration of deficient and injured tissues. It employs the principles from the fields of materials science, cell biology, transplantation, and engineering in an effort to treat or replace damaged tissues. Tissue engineering and development of complex tissues or organs, such as heart, muscle, kidney, liver, and lung, are still a distant milestone in twenty-first century. Generally, there are four main challenges in tissue engineering which need optimization. These include biomaterials, cell sources, vascularization of engineered tissues, and design of drug delivery systems. Biomaterials and cell sources should be specific for the engineering of each tissue or organ. On the other hand, angiogenesis is required not only for the treatment of a variety of ischemic conditions, but it is also a critical component of virtually all tissue-engineering strategies. Therefore, controlling the dose, location, and duration of releasing angiogenic factors via polymeric delivery systems, in order to ultimately better mimic the stem cell niche through scaffolds, will dictate the utility of a variety of biomaterials in tissue regeneration. This review focuses on the use of polymeric vehicles that are made of synthetic and/or natural biomaterials as scaffolds for three-dimensional cell cultures and for locally delivering the inductive growth factors in various formats to provide a method of controlled, localized delivery for the desired time frame and for vascularized tissue-engineering therapies.

Fabrication and characteristic analysis of a poly(propylene fumarate) scaffold using micro-stereolithography technology

Scaffold fabrication for regenerating functional human tissues has an important role in tissue engineering, and there has been much progress in research on scaffold fabrication. However, current methods are limited by the mechanical properties of existing biodegradable materials and the irregular structures that they produce. Recently, several promising biodegradable materials have been introduced, including poly(propylene fumarate) (PPF). The development of micro-stereolithography allows the fabrication of free-form 3D microstructures as designed. Since this technology requires a low-viscosity resin to fabricate fine structures, we reduced the viscosity of PPF by adding diethyl fumarate. Using our system, the curing characteristics and material properties of the resin were analyzed experimentally. Then, we fabricated waffle shape and 3D scaffolds containing several hundred regular micro pores. This method controlled the pore size, porosity, interconnectivity, and pore distribution. The results show that micro-stereolithography has big advantages over conventional fabrication methods. In addition, the ultimate strength and elastic modulus of the fabricated scaffolds were measured, and cell adhesion to the fabricated scaffold was observed by growing seeded cells on it. These results showed that the PPF/DEF scaffold is a potential bone scaffold for tissue engineering.

Release Properties and Acute Biosecurity Determination of Collagen-Polyvinylpyrrolidone Loaded in Ordered Mesoporous Silica

Mesoporous silica type SBA-15 has high specific surface area, well ordered pores and renders larges volumes, reasons for its potential use in controlled drug delivery system; in addition its non toxic nature and good biocompatibility. The aim of this work is to determine the feasibility of loading collagen-polyvinylpyrrolidone (collagen-PVP) molecules into Biocompatible Nanostructured Ordered Mesoporous Silica (BINOM-Silica). Collagen-PVP has several medical uses, such as fibrolytic activity and tissue regeneration. Therefore, this BINOM-Silica/collagen- PVP material could be used as drug delivery system for hypertrophic scarring. Different BINOMSilica materials were prepared using a triblock copolymer in an acid medium and stabilized at 557°C and later, collagen-PVP was loaded into the material. The small angle powder X-ray diffraction patterns of BINOM-Silica materials, in some cases, indicate the existence of a high degree of hexagonal mesoscopic organization. The nitrogen sorption isotherms are type IV typical of mesoporous materials with large surface area. In vitro release of collagen-PVP was carried out by mean of UV/VIS spectroscopy. The cumulative release profiles of Silica-collagen PVP in distilled water indicate a two step release, an initial fast release and a relatively slow subsequent release, indicating an appropriate delivery of collagen-PVP for therapeutic administration. BINOMSilica/ collagen-PVP intradermical administration stimulated inflammatory infiltrates only in an acute phase (day 3), demonstrating that silica materials and their combination with chemical and biological drugs could be safe for therapeutics. The absence of inflammatory infiltrates at day 7 suggested an appropriate integration of BINOM-Silica/collagen-PVP into the tissue. These results indicate that we obtained biocompatible nanostructured ordered mesoporous silica materials useful for delivery systems.

Mesoporous silica/apatite nanocomposite: special synthesis route to control local drug delivery

Synthetic hydroxyapatite is widely used in medicine and dentistry due its notable biocompatibility and bioactivity properties. The hydroxyapatite incorporation into silica has demonstrated excellent bioactivity or biodegradability, according to the content of calcium ions. Procedures to obtain ordered mesoporous silicates rely on the micelle-forming properties of a surfactant, whose chemical composition, size and concentration control the structural dimensions of the final material. This paper reports the synthesis of two types mesoporous materials: pure MCM-41 and a nanocomposite of apatite and mesoporous silica, MCM-41-HA. The samples were charged with atenolol as a model drug and in vitro release essays were carried out. The bioactivity behavior was investigated as a function of soaking time in simulated body fluid. The materials were characterized by X-ray diffraction, N2 adsorption, FTIR spectroscopy, scanning electron microscopy, dispersive energies spectroscopy, and transmission electron microscopy. The influence of the release rate of atenolol molecules from pure MCM-41 mesoporous and containing hydroxyapatite was demonstrated, since it results in a very slowly drug delivery from the nanocomposite system.

Osteochondral defects: present situation and tissue engineering approaches

Articular cartilage is often damaged due to trauma or degenerative diseases, resulting in severe pain and disability. Most clinical approaches have been shown to have limited capacity to treat cartilage lesions. Tissue engineering (TE) has been proposed as an alternative strategy to repair cartilage. Cartilage defects often penetrate to the subchondral bone, or full-thickness defects are also produced in some therapeutic procedures. Therefore, in TE strategies one should also consider the need for a simultaneous regeneration of both cartilage and subchondral bone in situations where osteochondral defects are present, or to provide an enhanced support for the cartilage hybrid construct. In this review, different concepts related to TE in osteochondral regeneration will be discussed. The focus is on the need to produce new biphasic scaffolds that will provide differentiated and adequate conditions for guiding the growth of the two tissues, satisfying their different biological and functional requirements.

Bone Tissue Engineering Constructs Based on Starch Scaffolds and Bone Marrow Cells Cultured in a Flow Perfusion Bioreactor

This study aims to investigate the effect of culturing conditions (static and flow perfusion) on the proliferation and osteogenic differentiation of rat bone marrow (RBM) stromal cells seeded on two starch based three-dimensional scaffolds exhibiting distinct porous structures. For this purpose, it was selected: i) a scaffold based on SEVA-C (a blend of starch with ethylene vinyl alcohol) obtained by extrusion with a blowing agent and ii) a scaffold based on SPCL (a blend of starch with polycaprolactone) obtained by a fiber bonding process. The obtained results suggest that flow perfusion culture enhances the osteogenic differentiation of RBM cells and improves their distribution in 3-D starch-based scaffolds, by improving nutrients delivery in the interior of the scaffolds and simultaneously by stimulating the seeded cells by exposing them to fluid shear forces. They also indicate that scaffold architecture and pore interconnectivity affect the homogeneity of the formed tissue.

Development of a single unit extended release formulation for ZK 811 752, a weakly basic drug

ZK 811 752, a potent candidate for the treatment of autoimmune diseases, demonstrated pH-dependent solubility. The resulting release from conventional matrix tablets decreased with increasing pH-values of the dissolution medium. The aim of this study was to overcome this problem and to achieve pH-independent drug release. Three different polymers were used as matrix formers, the partly water-soluble and poorly swellable mixture of polyvinylacetate/polyvinylpyrrolidone, the water-insoluble and almost unswellable ethylcellulose (EC) and the water-soluble and highly swellable hydroxypropyl methylcellulose (HPMC). To solve the problem of pH-dependent solubility different organic acids, such as fumaric, tartaric, adipic, glutaric and sorbic acid were added to the drug-polymer system. The addition of organic acids to all three matrix formers was found to maintain low pH-values within the tablets during release of ZK 811 752 in phosphate buffer pH 6.8. Thus, the micro-environmental conditions for the dissolution of the weakly basic drug were kept almost constant. An extended release matrix tablet for ZK 811 752 consisting of drug, polymer and organic acid providing the desired pH-independent drug release has been developed.

Dynamic reassembly of peptide RADA16 nanofiber scaffold

Nanofiber structures of some peptides and proteins as biological materials have been studied extensively, but their molecular mechanism of self-assembly and reassembly still remains unclear. We report here the reassembly of an ionic self-complementary peptide RADARADARADARADA (RADA16-I) that forms a well defined nanofiber scaffold. The 16-residue peptide forms stable beta-sheet structure and undergoes molecular self-assembly into nanofibers and eventually a scaffold hydrogel consisting of >99.5% water. In this study, the nanofiber scaffold was sonicated into smaller fragments. Circular dichroism, atomic force microscopy, and rheology were used to follow the kinetics of the reassembly. These sonicated fragments not only quickly reassemble into nanofibers that were indistinguishable from the original material, but their reassembly also correlated with the rheological analyses showing an increase of scaffold rigidity as a function of nanofiber length. The disassembly and reassembly processes were repeated four times and, each time, the reassembly reached the original length. We proposed a plausible sliding diffusion model to interpret the reassembly involving complementary nanofiber cohesive ends. This reassembly process is important for fabrication of new scaffolds for 3D cell culture, tissue repair, and regenerative medicine.

Effects of crosslinking degree of an acellular biological tissue on its tissue regeneration pattern

It was reported that acellular biological tissues can provide a natural microenvironment for host cell migration and may be used as a scaffold for tissue regeneration. To reduce antigenicity, biological tissues have to be fixed with a crosslinking agent before implantation. As a tissue-engineering scaffold, it is speculated that the crosslinking degree of an acellular tissue may affect its tissue regeneration pattern. In the study, a cell extraction process was employed to remove the cellular components from bovine pericardia. The acellular tissues then were fixed with genipin at various known concentrations to obtain varying degrees of crosslinking. It was shown in the in vitro degradation study that after fixing with genipin, the resistance against enzymatic degradation of the acellular tissue increased significantly with increasing its crosslinking degree. In the in vivo subcutaneous study, it was found that cells (inflammatory cells, fibroblasts, endothelial cells, and red blood cells) were able to infiltrate into acellular tissues. Generally, the depth of cell infiltration into the acellular tissue decreased with increasing its crosslinking degree. Infiltration of inflammatory cells was accompanied by degradation of the acellular tissue. Due to early degradation, no tissue regeneration was observed within fresh (without crosslinking) and the 30%-degree-crosslinking acellular tissues. This is because the scaffolds provided by these two samples were already completely degraded before the infiltrated cells began to secrete their own extracellular matrix. In contrast, tissue regeneration (fibroblasts, neo-collagen fibrils, and neo-capillaries) was observed for the 60%- and 95%-degree-crosslinking acellular tissues by the histological examination, immunohistological staining, transmission electron microscopy, and denaturation temperature measurement. The 95%-degree-crosslinking acellular tissue was more resistant against enzymatic degradation than its 60%-degree-crosslinking counterpart. Consequently, tissue regeneration was limited in the outer layer of the 95%-degree-crosslinking acellular tissue throughout the entire course of the study (1-year postoperatively), while tissue regeneration was observed within the entire sample for the 60%-degree-crosslinking acellular tissue. In conclusion, the crosslinking degree determines the degradation rate of the acellular tissue and its tissue regeneration pattern.

Aggregation properties of a HPMA-camptothecin copolymer in isotonic solutions

Copolymers of camptothecin (CPT) and [N-(2-hydroxypropyl) methacrylamide] (HPMA) are novel anticancer drugs that show improved pharmacological profile in animal models as compared to the free drug CPT. We investigate here the aggregation properties of a HPMA-glycyl-6-aminohexanoyl-glycyl-CPT copolymer ( approximately 20,000 Da). The molecular size of HPMA-copolymer CPT is followed over 5 orders of magnitudes of concentration in isotonic buffer by measuring either the time resolved fluorescence anisotropy (FA) of CPT or the autocorrelation function of the light scattered by the copolymer. A detailed analysis of these data suggests the presence of elongated structures with axial ratio approximately 3 in the range 0.1-0.5 microg/ml and aggregates with association number higher than 2 in more concentrated solutions (up to 10 mg/ml). The binding affinity of HPMA-copolymer CPT for serum albumin is inversely dependent on the degree of aggregation of the copolymer. We also show that the copolymer concentration in plasma from mice treated with an active, non-toxic, dose of HPMA-copolymer CPT, decreases from 3 to 0.01 mg/ml in 72 h. In the same range of concentrations in vitro, we do not detect hydrophobic aggregates of polymers with high (>3) association number. Our study indicates that the circulating HPMA-copolymer CPT in mice should not undergo extensive aggregation and should interact with serum albumin more weakly than free CPT.

Emerging technologies that overcome biological barriers for therapeutic protein delivery

In the past decade, genomic research and the nascent field of proteomics have exponentially increased the number of potential protein therapeutic molecules for treating medical needs that were previously unmet. To realise the full clinical potential of many of the novel protein drug entities arising from these intense research efforts, emerging protein delivery technologies may be required. Advanced delivery technologies may offer the ability to overcome biochemical and anatomical barriers to protein drug transport, without incurring adverse events, to deliver the agent(s) at a certain desired rate and duration, to protect therapeutic macromolecules from in situ or systemic degradation, as well as increase their therapeutic index by targeting the drug action to a specific site. This review will cover a myriad of novel and emerging technologies that are directed at bypassing biological barriers and that have shown promise in advancing the therapeutic potential of protein drugs.

Effect of flow perfusion on the osteogenic differentiation of bone marrow stromal cells cultured on starch-based three-dimensional scaffolds

This study aims to investigate the effect of culturing conditions (static and flow perfusion) on the proliferation and osteogenic differentiation of rat bone marrow stromal cells seeded on two novel scaffolds exhibiting distinct porous structures. Specifically, scaffolds based on SEVA-C (a blend of starch with ethylene vinyl alcohol) and SPCL (a blend of starch with polycaprolactone) were examined in static and flow perfusion culture. SEVA-C scaffolds were formed using an extrusion process, whereas SPCL scaffolds were obtained by a fiber bonding process. For this purpose, these scaffolds were seeded with marrow stromal cells harvested from femoras and tibias of Wistar rats and cultured in a flow perfusion bioreactor and in 6-well plates for 3, 7, and 15 days. The proliferation and alkaline phosphatase activity patterns were similar for both types of scaffolds and for both culture conditions. However, calcium content analysis revealed a significant enhancement of calcium deposition on both scaffold types cultured under flow perfusion. This observation was confirmed by Von Kossa-stained sections and tetracycline fluorescence. Histological analysis and confocal images of the cultured scaffolds showed a much better distribution of cells within the SPCL scaffolds than the SEVA-C scaffolds, which had limited pore interconnectivity, under flow perfusion conditions. In the scaffolds cultured under static conditions, only a surface layer of cells was observed. These results suggest that flow perfusion culture enhances the osteogenic differentiation of marrow stromal cells and improves their distribution in three-dimensional, starch-based scaffolds. They also indicate that scaffold architecture and especially pore interconnectivity affect the homogeneity of the formed tissue.

Mesoporous SBA-15 HPLC evaluation for controlled gentamicin drug delivery

Mesoporous silica SBA-15 was prepared to evaluate its application as gentamicin drug delivery system. Two procedures were used to evaluate the delivery: calcined powder and disk conformed. The samples were charged with gentamicin sulphate and the experiments were carried out in vitro. No significant difference between powder and disk was observed in the tests. The release profiles exhibited a pronounced initial burst release effect of 60%, followed by a very slow release pattern. A new HPLC method was employed for calculated gentamicin amount in the delivery test. This method requires a small amount of sample, very advisable in these kinds of assays.

Simulation of intratumoral release of Etanidazole: effects of the size of surgical opening

The efficacy of radiotherapy can be enhanced by the delivery of radiosensitizer (Etanidazole) to brain tumor from biodegradable polymer implants. This process is investigated by simulation carried out at a cut section of tumor with polymeric wafers of Etanidazole loading implanted in the resected cavity. The coupled mass and momentum equations are solved to obtain the transient solution of the drug distribution in the tumor. The polymeric delivery shows high therapeutic index, indicating the wafers' success in delivering more drugs to the tumor rather than to the tissue. The penetration distance of Etanidazole was found to decrease from 14 mm (at 5th/40th day after implantation) to 6.5 mm (at 30th/75th day), suggesting an initial high burst of drug release which cause nearby tissue toxicity and a low effective drug delivery towards the later stages. The short penetration depth is due to Etanidazole having low interstitial Peclet number and high elimination/diffusion modulus. Edema causes the interstitial pressure, velocity, and concentration to increase in all domains, and leads to enhanced convection and a lowering of therapeutic index. Simulations on the open tumor geometry show significantly lower efficacy of the drug delivery due to the uneven distribution of drug in the tumor zone.

Characterization of biodegradable drug delivery vehicles with the adhesive properties of leukocytes

The site-specific expression of selectins (E- and P-selectin) on endothelial cells of blood vessels during inflammation provides an opportunity for the targeted delivery of anti-inflammatory drugs to inflammatory sites. Previous work in our laboratory has shown that artificial capsules with the adhesive properties of leukocytes can be made by attaching leukocyte adhesive ligands to polystyrene microspheres. In this work, we have adapted this technology to create a targeted delivery system using biodegradable, poly lactic-co-glycolic-acid (PLGA) microspheres. Biotinylated-Sialyl Lewis(x) (sLe(x)), a carbohydrate that serves as a ligand to selectins, was attached to the surface of avidin-linked PLGA microspheres. These carbohydrate-coated microspheres mimic the adhesive behavior of leukocytes on selectins in flow chambers, displaying slow rolling under flow. The rolling velocities displayed by sLe(x)-coated microspheres were similar to those displayed by leukocytes rolling on P- or E-selectin coated surfaces, and these rolling velocities, which relate to the residence time of the capsules, can be tuned by changing the density of carbohydrate residues on microsphere surfaces. We have also demonstrated that these microspheres will release model drugs on a time scale of several days. Therefore, we have made a targeted drug delivery vehicle that mimics the adhesive properties of leukocytes and is biodegradable.