Macroporous biodegradable natural/synthetic hybrid scaffolds as small intestine submucosa impregnated poly(D,L-lactide-co-glycolide) for tissue-engineered bone

—Poly( D , L-lactide-co-glycolide) (PLGA), a biodegradable synthetic polymer, is widely used in a variety of tissue-engineered applications, including drug-delivery systems. However, the PLGA scaffolds, macroporous and three-dimensional structure, are difficult to cell attachment and in-growth due to surface hydrophobicity. In order to introduce in new bioactive functionality from porcine small intestine submucosa (SIS) as natural source for PLGA, we fabricated SIS-powder-impregnated PLGA (SIS/PLGA) hybrid scaffolds. Fabrication parameters, including ratios of SIS, PLGA and salt, were optimized to produce the desired macroporous foam. The scaffolds had a relatively homogeneous pore structure, good interconnected pores from the surface to core region and showed an average pore size in the range 69.23–105.82 μm and over 90% porosity. The SIS/PLGA scaffolds degraded with a rate depending on the contents of the SIS. After the fabrication of the SIS/PLGA hybrid scaffolds the wettability of the scaffold was greatly enhanced, resulting in uniform cell seeding and distribution. So, it was observed that BMSC attachment to the SIS/PLGA scaffolds increased gradually with increasing SIS contents. Scaffolds of PLGA alone and SIS/PLGA were implanted subcutaneously under dorsal skin of athymic nude mouse to observe the osteoconductivity. It was found from the result that the effects of the SIS/PLGA scaffolds on bone formation are stronger than control PLGA scaffolds. In summary, the SIS/PLGA scaffolds have osteoconductive effects to allow remodeling and replacement by osseous tissue.     

In vitro and in vivo analysis of macroporous biodegradable poly(D,L-lactide-co-glycolide) scaffolds containing bioactive glass

Recent studies have demonstrated the angiogenic potential of 45S5 Bioglass. However, it is not known whether the angiogenic properties of Bioglass remain when the bioactive glass particles are incorporated into polymer composites. The objectives of the current study were to investigate the angiogenic properties of 45S5 Bioglass particles incorporated into biodegradable polymer composites. In vitro studies demonstrated that fibroblasts cultured on discs consisting of specific quantities of Bioglass particles mixed into poly(D,L-lactide-co-glycolide) secreted significantly increased quantities of vascular endothelial growth factor. The optimal quantity of Bioglass particles determined from the in vitro experiments was incorporated into three-dimensional macroporous poly(D,L-lactide-co-glycolide) foam scaffolds. The foam scaffolds were fabricated using either compression molding or thermally induced phase separation processes. The foams were implanted subcutaneously into mice for periods of up to 6 weeks. Histological assessment was used to determine the area of granulation tissue around the foams, and the number of blood vessels within the granulation tissue was counted. The presence of Bioglass particles in the foams produced a sustained increase in the area of granulation tissue surrounding the foams. The number of blood vessels surrounding the neat foams was reduced after 2 weeks of implantation; however, compression-molded foams containing Bioglass after 4 and 6 weeks of implantation had significantly more blood vessels surrounding the foams compared with foams containing no Bioglass at the same time points. These results indicate that composite polymer foam scaffolds containing Bioglass particles retain granulation tissue and blood vessels surrounding the implanted foams. The use of this polymer composite for tissue engineering scaffolds might provide a novel approach for ensuring adequate vascular supply to the implanted device.     

In vitro degradation of three-dimensional porous poly(D,L-lactide-co-glycolide) scaffolds for tissue engineering

In vitro degradation behaviors of three-dimensional tissue engineering porous scaffolds made from amorphous poly(D,L-lactide-co-glycolide) with three different formulations have been systematically investigated up to 26 weeks in phosphate buffer saline solution at 37 degrees C. The following properties of the scaffolds were measured as a function of degradation time: dimensions, weight, compressive strength and modulus, polymer molecular weight and its distribution, and pore morphology. Of special interest was the determination of mechanical properties in wet environment. The pH of the PBS media was also detected. According to the characteristic changes of the various properties of porous scaffolds, the degradation process is suggested to be roughly divided into three stages tentatively named as quasi-stable stage, decrease-of-strength stage, loss-of-weight and disruption-of-scaffold stage.     

Nanoparticulate drug carriers based on hybrid poly(D,L-lactide-co-glycolide)-dendron structures

We describe a general method for incorporating target moieties in a well-defined arrangement into the surface of biocompatible polyester poly(D,L-lactic-co-glycolic acid) (PLGA) materials using dendrons. In this way it is possible to obtain nanoparticles (NPs) with a high degree of surface coverage. This new strategy was successfully applied to the preparation of peptide- and beta-D-glucose-covered NPs. The first application is based on the discovery of NPs made of conjugates between PLGA and short peptidic sequences able to cross the blood-brain barrier (BBB) after systemic administration. In this paper, we used a branched structure (dendron) in order to prepare a derivative of PLGA able to form, by simple nanoprecipitation, NPs with a higher degree of surface coverage than previously reported by us, characteristic that could influence the uptake by the liver and spleen. The NPs thus obtained retain the ability to cross the BBB and possess a core-shell structure, as evidenced from zeta-potential, X-ray photoelectron (ESCA) spectroscopy and elemental analyses. These results are comparable with the NPs obtained by the derivatization of preformed NPs. The same strategy, namely the use of a branched spacer (a dendron or a G1 dendrimer) inserted between one end of the PLGA chain and a derivatizing molecule, was also successfully applied to obtain beta-D-glucose-covered NPs; in this case, the surface analysis of the NPs was performed by using high resolution magic angle spinning (HRMAS) NMR spectroscopy and zeta-potential measurements.     

Regeneration of completely transected spinal cord using scaffold of poly(D,L-lactide-co-glycolide)/small intestinal submucosa seeded with rat bone marrow stem cells

Using a complete spinal cord transection model, the present study employed a combinatorial strategy comprising rat bone marrow stem cells (rBMSCs) and polymer scaffolds to regenerate neurological function after spinal cord injury (SCI) of different lengths. SCI models with completely transected lesions were prepared by surgical removal of 1?mm (SC1) or 3?mm (SC3) lengths of spinal cord in the eighth-to-ninth spinal vertebrae, a procedure that resulted in bilateral hindlimb paralysis. A cylindrical poly(D,L-lactide-co-glycolide)/small intestinal submucosa scaffold 1 or 3?mm in length with or without rBMSCs was fitted into the completely transected lesion. Rats in SC1 and SC3 groups implanted with rBMSC-containing scaffolds received Basso-Beattie-Bresnahan scores for hindlimb locomotion of 15 and 8, respectively, compared with ～3 for control rats in SC1-C and SC3-C groups implanted with scaffolds lacking rBMSCs. The amplitude of motor-evoked potentials recorded in the hindlimb area of the sensorimotor cortex after stimulation of the injured spinal cord averaged ～100?μV in SC1-C and 10-50?μV in SC3-C groups at 4 weeks, and then declined to nearly zero at 8 weeks. In contrast, the amplitude of motor-evoked potentials increased from ～300 to 350?μV between 4 and 8 weeks in SC1 rats and from ～200 to ～250?μV in SC3 rats. These results demonstrate functional recovery in rBMSC-transplanted rats, especially those with smaller defects. Immunohistochemically stained sections of the injury site showed clear evidence for axonal regeneration only in rBMSC-transplanted SC1 and SC3 models. In addition, rBMSCs were detected at the implanted site 4 and 8 weeks after transplantation, indicating cell survival in SCI. Collectively, our results indicate that therapeutic rBMSCs in a poly(D,L-lactide-co-glycolide)/small intestinal submucosa scaffold induced nerve regeneration in a complete spinal cord transection model and showed that functional recovery further depended on defect length.     

Solvent effects on the microstructure and properties of 75/25 poly(D,L-lactide-co-glycolide) tissue scaffolds

Poly(lactide-co-glycolide) (PLGA) is used in many biomedical applications because it is biodegradable, biocompatible, and FDA approved. PLGA can also be processed into porous tissue scaffolds, often through the use of organic solvents. A static light scattering experiment showed that 75/25 PLGA is well solvated in acetone and methylene chloride, but forms aggregates in chloroform. This led to an investigation of whether the mechanical properties of the scaffolds were affected by solvent choice. Porous 75/25 PLGA scaffolds were created with the use of the solvent casting/particulate leaching technique with three different solvents: acetone, chloroform, and methylene chloride. Compression testing resulted in stiffness values of 21.7 +/- 4.8 N/mm for acetone, 18.9 +/- 4.2 N/mm for chloroform, and 30.2 +/- 9.6 N/mm for methylene chloride. Permeability testing found values of 3.9 +/- 1.9 x 10(-12) m2 for acetone, 3.6 +/- 1.3 x 10(-12) m2 for chloroform, and 2.4 +/- 1.0 x 10(-12) m2 for methylene chloride. Additional work was conducted to uncouple polymer/solvent interactions from evaporation dynamics, both of which may affect the scaffold properties. The results suggest that solvent choice creates small but significant differences in scaffold properties, and that the rate of evaporation is more important in affecting scaffold microstructure than polymer/solvent interactions.     

Degradation behaviour in vitro for poly(D,L-lactide-co-glycolide) as drug carrier

Biodegradable polymers have been extensively investigated because of regulating drug release rate easily, obviating the need to remove the device, and good biocompatibility. Among the biodegradable polymers currently under investigation, poly(D,L-lactide-co-glycolide) (PLGA) copolymers are the most widely studied because of their long history of safe clinical use as drug carrier. 50 : 50 PLGA was used as a model degradable polymer in this study to investigate the degradation behaviour on drug release from bulk degradable polymers in vitro. 5-fluorouracil (5-FU) was used as a model drug. Molecular weight change, residual mass, water uptake, morphological change of PLGA wafers, and pH of release test medium were characterized to investigate the effect of polymer degradation on drug release. The release rate of 5-FU increased with the increase of 5-FU loading amount and the release profiles of 5-FU irrespective of 5-FU loading amount followed near first order release kinetics.     

A novel hemostatic delivery device for thrombin: biodegradable poly(D,L-lactide-co-glycolide) 50:50 microspheres

Topical thrombins are locally active hemostatic agents that can be used to minimize blood loss during any surgery. The aim of this study was to design and investigate a thrombin-containing biodegradable hemostyptic device with an optimized drug release profile to promote local blood clot formation. It is effective with ongoing systemic antithrombotic therapy and can be used in all types of bone-related surgery, for example, in dental surgery. Thrombin-loaded poly(D,L-lactide-co-glycolide) microspheres were synthesized by means of complex (w/o/w) emulsion evaporation method. The resulting enzyme activity of the serine-protease thrombin was verified by the specific chromogenic substrate S-2238. The thrombin release profile depended on four factors: (1) thrombin dosage, (2) polymer concentration in the o-phase, (3) phase quotient w1:0 in the primary emulsion, and (4) the addition of pore-introducing agents. A collagenous sponge containing thrombin-loaded microspheres by means of lyophilization was developed. The impact of several production factors of the (w1/o/w2) solvent evaporation method to optimize thrombin encapsulation, morphology of the spheres, and desired drug release profile have been investigated. The in vitro thrombin release was dependent on the polymer-to-oil phase ratio, the polymer concentration, and the type of solvent and polymer. The porosity of the spheres and release rate of the active agent were enhanced by increasing the inner aqueous w1 phase. With this study, a new biodegradable hemostyptic device could be verified and established for a potentially safe and locally controlled thrombin release to manage postsurgical hemorrhage in patients undergoing anticoagulant therapy.     

Preformed grafts of porcine small intestine submucosa (SIS) for bridging segmental bone defects

Previous studies suggest that fresh, morselized porcine small intestine submucosa (SIS) may have promise in the treatment of large bone defects. This study evaluated the bone regenerative potential of preformed tubular SIS grafts, designed to provide a scaffold for regeneration of diaphyseal bone. Critical length segmental defects in the femurs of male rats were either left unfilled (n = 11) or filled with morselized cancellous bone (n = 12), or spanned with intramedullary tubes (n = 12) or periosteal sleeves (n = 12) fabricated from SIS. All of the animals were euthanized 12 weeks postoperatively. Healing was assessed with biweekly radiographs, routine histology, and mechanical testing. Copious new bone formed in the defects of all of the animals treated with cancellous bone; 10 of the 12 animals in that group had healed their defects. In contrast, no new bone was formed in the defects left unfilled or treated with SIS; only fibrous tissue was found. In both of the SIS-treated groups, the SIS persisted at twelve weeks. The cellular response to the SIS involved a mild mononuclear infiltrate in the loose or delaminated superficial layers of the tubes and sleeves, with few cells in the deeper layers. The results of this study cast doubt on the ability of SIS to support or stimulate growth of bone across a critical length segmental bone defect. Additional work will be required to determine whether our results reflect the protocols used to prepare and fabricate the SIS grafts used in the study or the inherent inability of SIS to support new bone growth.     

Functional and morphological characteristics of bovine adrenal chromaffin cells on macroporous poly(D,L-lactide-co-glycolide) scaffolds

Adrenal chromaffin cells (ACCs) secrete several neuroactive substances that are effective in influencing pain sensitivity in the central nervous system as well as enhancing the recovery of the intrinsic nigrostriatal dopaminergic system in patients with Parkinson's disease. ACC transplantation may be upregulated by the use of three-dimensional (3-D) scaffolds. In this study, we determined whether biodegradable poly(D,L-lactic-coglycolic acid) (PLGA) (85:15) sponges could be used as support for chromaffin cells. ACCs were isolated from bovine adrenal glands by standard perfusion (95% purity) followed by additional purification (>99.5% purity). ACC (approximately 5 x 10(5) cells) suspension in collagen (type I) was seeded on prewetted sponges and cultured in DMEM-F12 (1:1) medium (5% fetal bovine serum). The catecholamine and enkephalin levels of the samples were measured by high-performance liquid chromatography and radioimmunoassay. Cell morphology was examined by transmission electron microscopy. Morphological evidence showed prolonged viability of chromaffin cells on scaffolds having pores of 250-400 microm. Cell counts and scanning electron microscopy demonstrated that the majority of seeded cells were located within the scaffold. Chromaffin cells exhibited higher levels of enkephalins and catecholamines on PLGA scaffold compared with their monolayer cultures. By the use of 3-D PLGA as support for ACCs, it is possible to upregulate metabolic function and localize a high number of morphologically healthy-looking cells. Highly purified ACCs cultured on PLGA scaffold may have promise in transplantation studies, because these cells are less immunogenic and may be applied to in vivo settings by using short-term immunosuppression.     

Polyetheretherketone/poly (glycolic acid) blend scaffolds with biodegradable properties

Polyetheretherketone (PEEK) is widely applied in tissue engineering due to its good biocompatibility and mechanical properties. However, the slow degradation rate limits its further application. In this study, PEEK blended with plyglycolicacid (PGA) was used to fabricate porous scaffolds via selective laser sintering. The results demonstrated that the blend scaffolds could gradually degrade, and the degradation rate was able to regulate by tailoring the PGA content. Moreover, the scaffolds maintained good biocompatibility and suitable mechanical properties. These were explained as follows: PGA on the surface layer of the scaffolds might degrade first owing to its exposure to the ambient medium. The degraded PGA left much space, which could promote cell attachment and proliferation. Meanwhile, the slow degradation of PEEK was beneficial to sustaining the scaffolds’ strength and stable structure.     

Preparation of biodegradable microspheres of testosterone with poly(D,L-lactide-co-glycolide) and test of drug release in vitro

Biodegradable microspheres formulation of testosterone (T) can be used as a new physiological approach for androgen replacement in hypogonadal men. In this study, poly(D,L-lactide-co-glycolide) (PLGA) microspheres containing T were prepared by a solvent-evaporation/solvent-diffusion process and the drug release tests of the microspheres were carried out in vitro. T/PLGA microspheres with good yield, desired size and satisfied drug loading were obtained. A significant testosterone sustained release was shown in the drug release tests in vitro. Since PLGA microspheres preparations are normally sterilized by colbat-60 irradiation, the effects of 25 kGy colbat-60 irradiation on physicochemical properties and in vitro drug release profile of T/PLGA microsphere were investigated. The results showed that the irradiation didn't have any effects on the physicochemical properties of T. Though about one-third decrease in molecular weight of PLGA was caused by the irradiation, no significant changes were observed on the drug release profile in vitro.     

Biocompatibility of poly(D,L-lactide-co-glycolide) nanoparticles conjugated with alendronate

Nanoparticles made of a conjugate of poly(D,L-lactide-co-glycolide) with alendronate (PLGA-ALE NPs), were prepared by emulsion/solvent evaporation technique. The conjugation yield, determined by MALDI TOF analysis, was 30-35%. PLGA-ALE NPs size, evaluated by photon correlation spectroscopy, was 198.7+/-0.2 nm. Haemocompatibility studies using different concentrations of PLGA-ALE NPs did not show any significant effect on haemolysis, leukocyte number, platelet activation, APTT and complement consumption, in comparison with blood incubated with phosphate buffered saline (PBS). A significant reduction of the prothrombin activity was demonstrated after incubation with 560 microg/ml of PLGA-ALE NPs; a significant increase was observed at the highest dilutions. The viability of human umbilical vein endothelial cells and bone marrow stromal cells (BMSC), evaluated through the neutral red test, was not affected by PLGA-ALE NPs. There were no significant differences in cell-associated alkaline phosphatase between BMSC incubated with PLGA-ALE NP- and PBS-added media. These results demonstrated that PLGA-ALE NPs had an acceptable degree of blood compatibility and were not cytotoxic; therefore, they may be considered suitable for intravenous administration.     

Evaluation of type II collagen scaffolds reinforced by poly(epsilon-caprolactone) as tissue-engineered trachea

A novel composite scaffold comprising a poly(epsilon-caprolactone) (PCL) stent and a type II collagen sponge for tissue-engineered trachea was developed. The PCL stent with surface grooves was fabricated by casting and freeze drying the PCL solution in a mold container. The grooves on the stent were filled by the type II collagen with crosslinking treatment (ring-shaped collagen sponge). The rabbit chondrocytes (3 x 10(6) cells for each ring) were seeded onto the collagen sponge of the scaffold. The cell-scaffold constructs were implanted subcutaneously in the dorsum of nude mice. After 4 and 8 weeks, constructs were harvested and dedicated for measurement of mechanical properties, histology, and biochemical assays. It was found that the constructs were strong enough to retain their tubular shape against extrinsic forces in the dorsum of nude mice. The gross appearance of the constructs revealed cartilage-like tissue at 8 weeks, with modulus higher than that of native trachea. Histological and biochemical analyses of the tissue-engineered tracheal cartilage revealed evenly spaced lacunae embedded in the matrix, with abundant proteoglycans and type II collagen. The stent-sponge composite facilitated the proliferation of chondrocytes and was expected to provide adequate mechanical strength, and therefore was a promising material for use in trachea tissue engineering.     

Crosslinked poly(epsilon-caprolactone/D,L-lactide)/bioactive glass composite scaffolds for bone tissue engineering

A series of elastic polymer and composite scaffolds for bone tissue engineering applications were designed. Two crosslinked copolymer matrices with 90/10 and 30/70 mol % of epsilon-caprolactone (CL) and D,L-lactide (DLLA) were prepared with porosities from 45 to 85 vol % and their mechanical and degradation properties were tested. Corresponding composite scaffolds with 20-50 wt % of particulate bioactive glass (BAG) were also characterized. Compressive modulus of polymer scaffolds ranged from 190+/-10 to 900+/-90 kPa. Lactide rich scaffolds absorbed up to 290 wt % of water in 4 weeks and mainly lost their mechanical properties. Caprolactone rich scaffolds absorbed no more than 110 wt % of water in 12 weeks and kept their mechanical integrity. Polymer and composite scaffolds prepared with P(CL/DLLA 90/10) matrix and 60 vol % porosity were further analyzed in simulated body fluid and in osteoblast culture. Cell growth was compromised inside the 2 mm thick three-dimensional scaffold specimens as a static culture model was used. However, composite scaffolds with BAG showed increased osteoblast adhesion and mineralization when compared to neat polymer scaffolds.     

Effects of porosity and pore size on in vitro degradation of three-dimensional porous poly(D,L-lactide-co-glycolide) scaffolds for tissue engineering

In vitro degradation of seven three-dimensional porous scaffolds composed of PLGA85/15, a very useful poly(D,L-lactide-co-glycolide), was performed in phosphate-buffered saline solution at 37 degrees C up to 26 weeks, and effects of porosity (80-95%) and pore size (50-450 mum) on the degradation of the scaffolds were investigated. A series of quantities were measured during the degradation processes: molecular weight and its distribution of PLGA; compressive strength and modulus; and weight, dimension, and porosity of scaffolds. In all of cases with different pore morphologies, the degradation processes obeyed a three-stage model. Scaffolds with a higher porosity or a smaller pore size degraded more slowly than and thus outlasted those with a lower porosity or a larger pore size. The effects are both attributed to a wall effect and a surface area effect because the scaffolds with lower porosities or larger pores possess thicker pore walls and smaller surface area, which depress the diffusion of acidic degradation products and thus results in a stronger acid-catalyzed hydrolysis. This work suggests that, in designing a tissue-engineering scaffold composed of PLGA and adjusting its degradation rate, the effects of pore morphologies should be taken into consideration in addition to those of chemical composition and condensed state of raw materials.     

In vivo evaluation of a novel electrically conductive polypyrrole/poly(D,L-lactide) composite and polypyrrole-coated poly(D,L-lactide-co-glycolide) membranes

This study evaluated the in vivo biocompatibility and biodegradation behavior of a novel polypyrrole (PPy)/poly(D,L-lactide) (PDLLA) composite and PPy-coated poly(D,L-lactide-co-glycolide) membranes. Test membranes were implanted subcutaneously in rats for 3-120 days. The biocompatibility was assessed by quantifying the alkaline and acid phosphatase secretion, the immunohistochemical staining of the ED-2-positive macrophages, and the histology at the tissue/material interface. The degradation was investigated using scanning electron microscopy. Pure PDLLA and poly(D,L-lactide-co-glycolide) membranes were used as references, whereas expanded polytetrafluoroethylene and a commercial styrene-butadiene rubber were used as controls. The enzyme activity of the PPy-containing specimens was shown to be similar to that of the references. The histological findings were consistent with the enzymatic results, showing a mild-to-moderate acute inflammation followed by a resolution of the inflammatory response with a decrease in inflammatory cells for each biodegradable membrane. The tissue reactions to the PPy, which was either in the form of nanoparticles or surface coating, were comparable to the response to the neighboring biodegradable materials. Elevated ED-2-positive macrophage populations appeared as early as day 3 in the loose connective tissue surrounding the implants. The density of these populations was related to the degree of inflammation. Scanning electron microscopy showed that the degradation of the PPy/PDLLA composite was not affected by the presence of PPy.     

Preparation and characterization of cationic chitosan-modified poly(D,L-lactide-co-glycolide) copolymer nanospheres as DNA carriers

Chitosan (CS)-modified poly(D,L-lactide-co-glycolide) (PLGA/CS) nanoparticles with cationic surface were prepared by means of emulsion-solvent evaporation technique using polyviny alcohol and chitosan as costabilizers. The preparation conditions of the cationic nanoparticles were optimized by orthogonal factorial design, and the influences of the experiment variables such as polymer concentration, the molecular weight of chitosan, etc., on the size and zeta potential of the nanoparticles were evaluated. It was shown that the diameter of the PLGA/CS nanoparticles can be controlled in the range of 150-200 nm as determined by dynamic light scattering with the optimized conditions. The zeta potential of PLGA/CS nanoparticles increased with increasing the concentration of CS (C(CS)) or decreasing the pH, it was up to 55 mV when C(CS) was 3 mg/mL at pH 4 and inversed around pH 8. The optimization conditions for fabricating the relatively small diameter and high zeta potential cationic nanoparticles were C(CS) 3 mg/mL, C(PLGA) 10 mg/mL, and the volume ratio of organic solution to aqueous medium 1/4. X-ray photo electron spectroscopy and fluorescence inverted microscope observations approved that CS molecules were adsorbed on the surface of PLGA nanoparticles, DNA-condensing ability of the PLGA/CS nanoparticles and cell transfection efficiency of the nanoparticle-DNA complexes were estimated by gel electrophoresis and transfection experiment to 293FT cell, respectively.     

Fabrication and characterization of controlled release poly(D,L-lactide-co-glycolide) millirods

A compression-heat molding procedure was developed to fabricate poly(D,L-lactide-co-glycolide) (PLGA) controlled release drug delivery devices for the local treatment of tumors. The drug delivery devices were designed in the shape of a cylindrical millirod (1.6-mm diameter, 10-mm length), which allows them to be implanted by a modified 14-gauge tissue biopsy needle into tumor tissues via image-guided interventional procedures. In this study, the prototype trypan blue-containing PLGA millirods were fabricated under a compression pressure of 4.6 x 10(6) Pa and different fabrication temperatures for 2 h. The scanning electron microscopy results showed complete polymer annealing for millirods fabricated at 80 and 90 degrees C, while the cross sections of the 60 and 70 degrees C millirods showed incompletely annealed PLGA microspheres and trypan blue powders. The density, flexural modulus, and release properties of the PLGA millirods were also characterized and compared. The average values of the density and flexural modulus of the millirods increased with an increase in fabrication temperature. The flexural modulus values of most PLGA millirods were above 1 x 10(8) Pa, which provides sufficient stiffness for implantation within the tumor tissue. In addition, a Delta c(p) method was developed to determine the loading density of trypan blue in the PLGA millirods by differential scanning calorimetry. Results from the Delta c(p) measurement showed that trypan blue was homogeneously distributed in the millirod. Release studies in phosphate-buffered saline showed that the release rate decreased for the millirods fabricated at higher temperatures. The times for the release of 50% trypan blue were 5, 25, 25, and 25 h for millirods fabricated at 60, 70, 80, and 90 degrees C, respectively. Millirods fabricated at 90 degrees C had the most reproducible release profiles. The results from this study established compression--heat molding as an effective method to fabricate controlled release PLGA millirods with sufficient mechanical strength and reproducible release profiles for local cancer therapy.     

Conjugated poly(D,L-lactide-co-glycolide) for the preparation of in vivo detectable nanoparticles

Cellular localization of nanoparticles (Np) represents an important target in the understanding of their distribution after endovenous injection. The need of suitable devices and methodologies capable to detect Np in tissues or in cellular districts can be satisfied by Np which have to be easily recognizable by simple methods. Conjugations of poly(D,L-lactide-co-glycolide) with fluorescein and biotin allow fluorescent and immuno-histochemically active Np to be obtained. The fluorescein Np are detectable using fluorescent microscopy whereas biotin Np can be detected by optical microscopy after streptavidin-biotin-peroxidase complexation. In vivo experiments confirm the ability of these particles to be easily detected in the brain parenchyma or in the liver cell population according to the infusion pathway.