Bioinspired gelatin/bioceramic composites loaded with bone morphogenetic protein-2 (BMP-2) promote osteoporotic bone repair.

There are currently several commercialized products approved by the Food and Drug Administration and the European Medicines Agency based on the use of recombinant human BMP-2 for the treatment of non-unions long fractures and spinal fusion. However, the adverse effects recorded with the use of BMPs suggest the need for drug delivery carriers that allow reducing the required doses and improve their cost-effectiveness. Herein, we have developed a new osteoconductive scaffold that reduces the required doses of BMP-2 for promoting bone regeneration in an osteoporotic defect model. The composite is, in brief, a gelatin-based 3D scaffold reinforced with either calcium sulfate or hydroxyapatite as an inorganic osteoconductive biomaterial. To this end, the organic/inorganic composite systems showed high hydration capacity and good in vitro degradability. The incorporation of 7.5% (m/v) ceramic compounds resulted in scaffolds with stiffer Young modulus (179 and 75 kPa for CaSO4_7 and HA_7, respectively) than bare gelatin hydrogels (48 kPa). Studies with human bone-marrow derived mesenchymal stem cells (hBM-MSCs) revealed that the 3D scaffolds promote cell adhesion and proliferation along with osteogenic differentiation capabilities. Specifically, downregulation of stemness (Nanog, Oct4) genes and upregulation of osteogenic markers (ALP, Col1a1, Fmod) by two fold were observed over 10 days under basal culture conditions. Promisingly, the sustained in vitro release of BMP-2 observed from the porous reinforced scaffolds allowed us to address the critical-sized osteoporotic mice calvarial defects with a relatively low growth factor doses (600 ng BMP-2/scaffold) compared to conventional doses at 2-15 micrograms. Overall, this study demonstrates the promising potential of osteoconductive gelatin/calcium bioceramics composites as osteogenic growth factors delivery carriers for bone-regeneration via ultra-low growth factor doses.

Bone critical defect repair with poloxamine-cyclodextrin supramolecular gels.

The aim of this study was to evaluate the osteoinductive capacity of a poloxamine (Tetronic(®) 908, T) and α-cyclodextrin (αCD) supramolecular gel (T-CD) as scaffold in a critical size defect in rat calvaria. The T-CD gel was evaluated solely and after being loaded with simvastatin (SV) and bone morphogenetic protein (BMP-2) separately and in combinations in order to reduce the doses of the active substances. Three doses of SV (7.5, 75, 750 µg) and two doses of BMP-2 (3 and 6 µg) were tested. The histology and histomorphometrical analysis showed improved bone repair with T-CD compared to T, probably due to better release control of both SV and BMP-2. In addition, as T-CD eroded more slowly than poloxamine alone, it remained longer in the defect site. Although synergism was not obtained with BMP-2 and SV, according to the observed regeneration of the defect, the dose of BMP-2 and SV can be reduced to 3 µg and 7.5 µg, respectively.

Bone regeneration induced by an in situ gel-forming poloxamine, bone morphogenetic protein-2 system.

The aim of this study was to confirm previously shown, in vitro osteogenic induction by the Tetronics T908 and T1307 in a critical-size, rat calvaria defect. In vivo, the osteogenic activity of the hydrogels was comparable to in vitro, but less pronounced. However, similar to in vitro, the system was strongly potentiated by incorporating 6.5 microg of bone morphogenetic protein-2 in solution or pre-encapsulated in poly(lactic-co-glycolic) acid microspheres. These two systems extended the in vivo release of bone morphogenetic protein-2, determined with 125I- bone morphogenetic protein-2, for one and two additional weeks, respectively, time enough to fill approximately 40% and 90% of the defect with well-organized bone. Furthermore, the structural characteristics of Tetronic hydrogels together with their biocompatibility, injectability, and adaptability to multiple defect sizes and shapes suggest their role as new, potential bone morphogenetic protein-2 delivery, low-cost scaffolds for minor as well as critical bone defects.

Repair of an osteochondral defect by sustained delivery of BMP-2 or TGFß1 from a bilayered alginate-PLGA scaffold.

Regeneration of cartilage defects can be accelerated by localized delivery of appropriate growth factors (GFs) from scaffolds. In the present study we analysed the in vitro and in vivo release rates and delivery efficacies of transforming growth factor-ß1 (TGFß1) and bone morphogenetic protein-2 (BMP-2) from a bilayered system, applied for osteochondral defect repair in a rabbit model. A bone-orientated, porous PLGA cylinder was overlaid with GF containing PLGA microspheres, dispersed in an alginate matrix. Four microsphere formulations were incorporated: (a) blank ones; (b) microspheres containing 50 ng TGFß1; (c) microspheres containing 2.5 µg BMP-2; and (d) microspheres containing 5 µg BMP-2. Release kinetics and tissue distributions were determined using iodinated ((125) I) GFs. Bioactivity of in vitro released BMP-2 and TGFß1 was confirmed in cell-based assays. In vivo release profiles indicated good GF release control. 20% of BMP-2 and 15% of TGFß1 were released during the first day. Virtually the total dose was delivered at the end of week 6. Significant histological differences were observed between untreated and GF-treated specimens, there being especially relevant short-term outcomes with 50 ng TGFß1 and 5 µg BMP-2. Although the evaluation scores for the newly formed cartilage did not differ significantly, 5 µg BMP-2 gave rise to higher quality cartilage with improved surface regularity, tissue integration and increased collagen-type II and aggrecan immunoreactivity 2 weeks post-implantation. Hence, the bilayered system controlled GF release rates and led to preserved cartilage integrity from 12 weeks up to at least 24 weeks.

Comparative, osteochondral defect repair: stem cells versus chondrocytes versus bone morphogenetic protein-2, solely or in combination.

Full-thickness articular cartilage damage does not resolve spontaneously. Studies with growth factors, implantation of autologous chondrocytes and mesenchymal stem cells have led to variable, to some extent inconsistent, results. This work compares osteochondral knee-defect repair in rabbits upon implantation of a previously described alginate/(poly(lactic-co-glycolic) acid (PLGA) osteochondral scaffold in distinct conditions. Systems were either in vitro pre-cultured with a small number of allogeneic chondrocytes under fibroblast growth factor (FGF)-2 stimulation or the same amount of allogeneic, marrow derived, mesenchymal stem cells (without any pre-differentiation), or loaded with microsphere-encapsulated bone morphogenetic protein (BMP)-2 within the alginate layer, or holding combinations of one or the other cell type with BMP-2. The experimental limit was 12 weeks, because a foregoing study with this release system had shown a maintained tissue response for at least 24 weeks post-operation. After only 6 weeks, histological analyses revealed newly formed cartilage-like tissue, which resembled the adjacent, normal cartilage in cell as well as BMP-2 treated defects, but cell therapy gave higher histological scores. This advantage evened out until 12 weeks. Combinations of cells and BMP-2 did not result in any additive or synergistic effect. Equally efficient osteochondral defect repair was achieved with chondrocyte, stem cell, and BMP-2 treatment. Expression of collagen X and collagen I, signs of ongoing ossification, were histologically undetectable, and the presence of aggrecan protein indicated cartilage-like tissue. In conclusion, further work should demonstrate whether spatiotemporally controlled, on-site BMP-2 release alone could become a feasible therapeutic approach to repair large osteochondral defects.

Osteogenic effect of local, long versus short term BMP-2 delivery from a novel SPU-PLGA-ßTCP concentric system in a critical size defect in rats.

A concentric delivery system, composed of the three biomaterials SPU, PLGA, and ßTCP (segmented polyurethane, poly[lactic-co-glycolic acid], and ß-tricalcium phosphate) was fabricated as an external, porous ring of ßTCP with a pasty core of a new SPU, mixed with PLGA microspheres. The regenerative effects of two distinct doses of either immediately available or continuously released rhBMP-2 were evaluated in an 8mm, critical calvaria defect in rats. Protein dose and release kinetics affected material resorption rates and the progression of the regeneration process. Groups treated with the empty system alone or in conjunction with free rhBMP-2 did not respond. By contrast, after 12 weeks, approximately 20% and 60% of the defects implanted with systems loaded with 1.6 µg and 6.5 µg rhBMP-2, respectively were healed, with all the growth factor being released in the course of 6 weeks. The NMR, FTIR, GPC, DSC, and histological analyses showed that PLGA microsphere degradation occurred independently of the regenerative process. However, the resorption rate of the SPU and ßTCP did depend on the regeneration process, which was governed by dose and release rate of rhBMP-2. Furthermore, the biocompatibility and high capacity of adaptation to the defect convert the herein proposed, new SPU polymer into a potential material for applications in tissue engineering and regenerative medicine.

Biodistribution of Nanostructured Lipid Carriers (NLCs) after intravenous administration to rats: influence of technological factors.

Nanoparticles for medical applications are frequently administered via parenteral administration. In this study, the tissue distribution of three lipid formulations based on Nanostructured Lipid Carriers (NLCs) after intravenous administration to rats was evaluated. NLCs were prepared by a high pressure homogenization method and varied in terms of particle size, surface charge, and surfactant content. The (99m)Tc radiolabeled NLCs were intravenously administered to rats, and radioactivity levels in blood and tissues were measured. Cmax, AUC0-24, and MRT0-24 were obtained from the radioactivity level versus time profiles. The radiolabeled nanocarriers exhibited a long circulation time since radioactivity was detected in blood even 24 h post-injection. No differences on the MRT values in blood among the NLCs were observed, in spite of the different particle size and surface charge. The highest radioactivity levels were measured in the kidney, followed by the bone marrow, the liver, and the spleen. In the kidney, there was a higher accumulation of the positive nanoparticles, and in the liver, uptake of negative nanoparticles was higher than positive ones. NLCs with the largest particle size showed a higher uptake in the lung and lower accumulation in liver and bone marrow, in comparison with the smaller ones.

Reticulated vitreous carbon: a useful material for cell adhesion and tissue invasion.

Diverse carbon materials have been used for tissue engineering and clinical implant applications with varying success. In this study, commercially available reticulated vitreous carbon (RVC) foams were tested in vitro and in vivo for compatibility with primary cell adhesion and tissue repair. Pores sizes were determined as 279 ± 98 µm. No hydroxyapatite deposition was detected after immersion of the foams in simulated body fluid. Nonetheless, RVC provided an excellent support for adhesion of mesenchymal stem cells (MSCs) as well as primary chondrocytes without any surface pre-treatment. Live cell quantification revealed neutral behaviour of the material with plastic adhered chondrocytes but moderate cytotoxicity with MSCs. Yet, rabbit implanted foams exhibited good integration in subcutaneous pockets and most importantly, total defect repair in bone. Probably due to the stiffness of the material, incompatibility with cartilage regeneration was found. Interestingly and in contrast to several other carbon materials, we observed a total lack of foreign body reactions. Our results and its outstanding porous interconnectivity and availability within a wide range of pore sizes convert RVC into an attractive candidate for tissue engineering applications in a variety of bone models and for ex vivo cell expansion for regenerative medical applications.

Efficacy of ciprofloxacin implants in treating experimental osteomyelitis.

Ciprofloxacin (CFX) implants containing poly(D,L-lactide) and calcium phosphates (tricalcium phosphate and hydroxyapatite) was evaluated in 50 rabbits in an experimental osteomyelitis model. Their femoral cavity was inoculated with Staphylococcus aureus. After 2 weeks, the infected focus was cleaned out and the delivery system implanted. The infection and subsequent response to treatment were evaluated by microbiological analysis, biochemical and hematological markers, body weight, temperature, clinical signs, X-rays, and histology. Infected bone cultures, treated with CFX implants, showed reduced bacterial growth against controls. All CFX was released within 6 weeks. All animals recovered within 4 weeks. Even 12 weeks after implantation, no recurrence of infection was observed. Serum C-reactive protein, platelet, and leukocyte levels increased in all animals before treatment, and 4 weeks after it were maintained or rose in control animals, while decreased to normal levels in treated ones. Body weight was characterized by pretreatment losses, then gains during recuperation, or further loss in untreated animals; with no significant intraindividual differences in body temperature. Body weight, leucocytes, platelets, and C-reactive protein turned out to be highly useful markers for monitoring this kind of infection and its treatment. CFX implants demonstrated to be an effective therapy for S. aureus bone infection. Their efficacy was also reflected in decreasing severity of clinical signs, nonprogress of radiological signs indicative of infection, and good integration into bone structure. Histological examination revealed repair, with new bone formation extending into implants.

Biodegradable implantable fluconazole delivery rods designed for the treatment of fungal osteomyelitis: influence of gamma sterilization.

Fluconazole poly(D,L-lactic) acid (PLA) and poly(L-lactic) acid (L-PLA) implantable delivery rods were studied, in vitro and in vivo, as an alternative treatment of fungal osteomyelitis. Implantable rods loaded with 5% fluconazole (FLU) were prepared by the injection-molding method and sterilized by gamma-irradiation at a dose of 25 kGy. Loading efficiency, physical chemistry (high performance liquid chromatography, X-ray diffraction, gel permeation chromatography), and in vitro and in vivo release assays were performed to evaluate the novel delivery systems and the sterilization effect on implant characteristics. In spite of polymer degradation after gamma-irradiation, the loading efficiency, chemical stability, and crystallographic structure of FLU were not affected. In vivo studies were carried out in femoral bone marrow of rabbits. Approximately 85 and 80% of the total dose were released within 12 and 4 weeks from PLA and L-PLA rods, respectively. This showed a faster release rate of FLU in vivo than in vitro, showing almost zero-order kinetics from PLA rods.

Two-month ciprofloxacin implants for multibacterial bone infections.

A ciprofloxacin implant formulation composed of 12% hydroxyapatite, 36% tricalcium phosphate, 12% poly(DL-lactide) (PLA) and 40% ciprofloxacin was characterized in vivo for use in treatment of multibacterial bone infection. After the implant was inserted in the femur of rabbits, approximately 90% of the total ciprofloxacin was released within 8 weeks, maintaining therapeutic levels in the femur and tibia. Throughout the femoral cortex and marrow these remained higher than the minimum inhibitory concentrations (MIC) against the most common pathogens causing osteomyelitis. Levels in tibia cortex were also above MIC for 6 weeks. The implant was characterized in terms of polymer degradation and morphological and crystallographic changes. X-ray analyses confirmed the osteoconductivity and biocompatibility of these materials. The sequential changes in the femur were those of a normal surgical trauma reaction followed by a repair process. All the results confirmed that ciprofloxacin release is limited by its low solubility, and that implant erosion and bone ingrowth into the implants enhance the antibiotic release.

PLA-PEG particles as nasal protein carriers: the influence of the particle size.

Previous studies have shown that PLA-PEG nanoparticles (NP) are able to enhance the transport of the encapsulated model protein, tetanus toxoid (TT), across the rat nasal mucosa. The aim of this work was to study if the size of PLA-PEG particles affects the nasal transport of the encapsulated protein and, also, the potential contribution of blank nanoparticles to the transport of the free protein. To achieve this purpose, 125I-TT was encapsulated into PLA-PEG particles of different sizes (200 nm, 1.5, 5 and 10 microm) prepared by the water-in-oil-in-water solvent evaporation technique. Firstly, in order to investigate the carrier role of the particles, two series of either conscious or anaesthetized rats were nasally treated with 125I-TT-loaded NP, free 125I-TT, and a physical mixture of blank NP and free 125I-TT. Secondly, the influence of the particle size on the nasal transport of TT encapsulated into PLA-PEG particles was evaluated in conscious rats. The amount of radioactivity recovered in the blood compartment, lymph nodes and other relevant tissues was monitored for up to 24h. Finally, the nasal bioavailability of 125I-TT-loaded PLA-PEG NP was calculated. The results indicated that the use of anaesthesia enhances the transport of 125I-TT and that the physical presence of PLA-PEG NP does not affect the transport of the toxoid. In contrast, when TT was encapsulated into the particles its transport across the nasal mucosa of conscious rats was significantly enhanced. Furthermore, the efficacy of this transport was related to the particle size, reaching the most important transport for the smallest particle size. The intensity of this transport was also illustrated by the high nasal bioavailability of TT encapsulated into nanoparticles (200 nm) (F = 70-80%). These results led us to conclude that PLA-PEG NP can be accepted as nasal protein carriers for nasal administration.

PEG-PLA nanoparticles as carriers for nasal vaccine delivery.

This report presents an overview of the potential of nanoparticles as nasal carriers for drug/vaccine administration. In addition, this report shows, for the first time, the efficacy of polylactic acid nanoparticles coated with a hydrophilic polyethyleneglycol coating (PEG-PLA nanoparticles) as carriers for the nasal transport of bioactive compounds. For this purpose, tetanus toxoid (TT), a high molecular weight protein (Mw 150,000 Da), was chosen as a model antigen and encapsulated in the PEG-PLA nano- and microparticles (200 nm and 1.5 microm respectively). These nanosystems were first characterized for their stability in the presence of lysozyme and also for their size, electrical charge, loading efficiency, in vitro release of antigenically active toxoid and afterwards, these formulations were administered intranasally to mice and the systemic and mucosal anti-tetanus responses were evaluated for up to 24 weeks. Additionally, PEG-PLA particles labeled with rhodamine 6G were administered intranasally to rats in order to visualize their interaction with the nasal mucosae by fluorescence microscopy. Their behavior was compared with that of the well known PLA nanoparticles (200 nm). The results showed that PLA nanoparticles suffered an immediate aggregation upon incubation with lysozyme, whereas the PEG-coated nanoparticles remained totally stable. The antibody levels elicited following i.n. administration of PEG-coated nanoparticles were significantly higher than those corresponding to PLA nanoparticles. Furthermore, PEG-PLA nanoparticles generated an increasing and a long lasting response. The qualitative fluorescence microscopy studies revealed that PEG-PLA particles are able to cross the rat nasal epithelium. These studies indicate that the PEG coating around the particles has a role in stabilizing PLA particles in mucosal fluids and that it facilitates the transport of the nanoencapsulated antigen, hence eliciting a high and long lasting immune response.

Methadone implants for methadone maintenance treatment. In vitro and in vivo animal studies.

Methadone implant formulations elaborated with polylactide-co-glycolide (PLGA) and polylactic acid (PLA) for 1 week and 1 month release duration, respectively, were evaluated in vitro and in vivo. One-week implants prepared with methadone clorhydrate, methadone clorhydrate/methadone base blend or methadone base were tested in vitro. Results showed that the methadone release rate decreased as the methadone base increased. The best release profile was achieve when the methadone base implants, made by compression of a 50:50 PLGA (12 kDa) and methadone base mix, were coated with PLA (30 kDa). For 1-month implants, the methadone base load was increased to 65% and PLA of 30 kDa was used as a matrix component. In this case the implants were coated with the same polymer. Deconvolution methods could not be used for in vivo release estimation because an increase in methadone clearance was observed with methadone clorhydrate solution multiple-dose treatment. Therefore the amount of drug remaining within the implants was evaluated and the deconvolution was only used to establish the release profile range. The upper limit was estimated applying the absorption-disposition function obtained after multiple-dose administrations while the lower curve was estimated using the single-dose function. Methadone serum levels were maintained around 200 ng/ml during 1 week and approximately 5 weeks with the optimised implants. In vivo-in vitro correlations were always very good with slopes near 1.

Ciprofloxacin implants for bone infection. In vitro-in vivo characterization.

To elucidate the antibiotic release mechanism from implants composed of calcium phosphates (hydroxyapatite [HAP] and tricalcium phosphate [TCP]), 30 kDa poly(DL-lactide) (PLA-30) and ciprofloxacin (CFX), nine formulations were prepared. In vitro results show that the release rate decreased as compression load and PLA/phosphates ratio increased. In contrast, a slower percent release rate was observed with higher drug loading. Swelling-erosion-disintegration of the implants was observed during the release assays, due to CFX swelling. Two CFX implant formulations were selected for implantation in the femur of rabbits, according to in vitro results. The implant drug loads tested were 10% and 40% of CFX. The in vivo results showed that the antibiotic concentrations achieved throughout the femur were higher for 4 weeks than the minimum inhibitory concentrations (MIC) against the most common of the pathogens that cause osteomyelitis. The CFX-10% implant was considered the best formulation as CFX was totally released within 6 weeks, and therapeutic bone levels were achieved, and the histological and radiographic analyses showed the osteoconductive properties of the materials. All these results showed that CFX release is limited by its solubility, and the erosion-disintegration and bone ingrowth into the implants enhanced the antibiotic release.

In vitro-in vivo characterization of gentamicin bone implants.

A gentamicin carrier system composed of calcium phosphates, poly(DL-lactide) (PLA) and gentamicin was developed and characterized in vitro and in vivo for use in the prevention and treatment of bone infection. Four formulations were prepared according to an experimental design based on the Hadamard matrix. The technological variables included in the design were: gentamicin loading with respect to the implant weight, weight average molecular weight (M(w)) of the PLA as a compound of the matrix and the presence or absence of a PLA coating of 200 kDa. The variable to be optimized in vitro was the gentamicin release level during the first week. According to this goal, the selected formulation was F-D which was composed of 80% phosphates (25% hydroxyapatite, HAP and 75% tricalcium phosphate, TCP), 20% PLA (M(w), 30 kDa) and 3.5% gentamicin sulfate (GS) and was coated with PLA (M(w), 200 kDa). To elucidate the in vitro release mechanism of this implant, another implant lot (F-X) uncoated, but with identical matrix composition, was prepared. Results showed that the PLA coating delay the gentamicin release, indicating that part of the antibiotic released from the matrix diffuses through the polymer coating film. The selected formulation was tested in the femur of rabbits and showed a faster release rate in vivo than in vitro. This is due to a greater degree of PLA degradation, changes in the phosphate blend, and bone tissue invading the implant. Gentamicin concentration in the areas of the bone closest to the implant was higher than the minimum inhibitory concentration (MIC) against Staphylococcus aureus.

In vivo-in vitro study of biodegradable and osteointegrable gentamicin bone implants.

Three implants composed of phosphate (25% hydroxyapatite, 75% tricalcium phosphate), 20% poly(DL-lactide) (DL-PLA; weight-average molecular weight (Mw), 30 kD) and 3% gentamicin sulphate (GS) were assayed in vitro and in vivo to study their release profiles as potential drug delivery systems to prevent or treat osteomyelitis. To prolong GS release, some implants were coated with poly(lactide-co-glycolide) (PLGA; Mw, 100 kD; I-PLGA) or DL-PLA (Mw, 200 kD; I-PLA). GS levels were measured in bone, kidney and blood after implantation into the femur of rats. The release profiles show a burst in the first few days, followed by a slower release rate. After I-PLA implantation, bone antibiotic concentrations higher than the minimum bactericidal concentration were maintained for 4 weeks. A linear correlation between in vitro and in vivo GS release was found to continue until complete drug release. Histological and radiological analysis showed that the implants were well tolerated and gradual new bone formation was observed.

Introducción a la farmacocinética. Modelo monocompartimental y administración mediante perfusion

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In vivo-in vitro study of biodegradable methadone delivery systems.

Three one-week controlled-release methadone formulations: polylactic acid microspheres (F-PLA) and poly(lactide-co-glycolide) microspheres (F-PLGA) with 24 and 30% methadone content, respectively, and an implant of 50:50 poly(lactide-co-glycolide): methadone, were evaluated in vitro and in vivo. The implant released the total amount of methadone in vitro while microsphere formulations released the methadone incompletely, 63% from F-PLA and 85% from F-PLGA in a week. Methadone release in vivo was estimated by deconvolution, F-PLGA giving a bioavailability >99% (methadone was totally released in 48h), while the estimated bioavailability of F-PLA was lower than expected. The bioavailability of the implant by deconvolution was around 60%, but absence of methadone in the implant indicated its complete release. These differences are due to an increase in methadone clearance after 72 h of the in vivo experimental period had passed, disturbing a good in vivo-in vitro correlation. A linear correlation between in vitro methadone release and in vivo release calculated from the amount of drug remaining within the implant, was found until the drug was completely released.

Radiolabelled biodegradable microspheres for lung imaging.

The effect on lung accumulation of modifying the surface compositions of (99m)Tc poly(lactide-co-glycolide) (PLGA) and (99m)Tc poly(ethylene glycol)-poly(lactide-co-glycolide) (PEG-PLGA) microspheres with different surfactants was assessed after intravenous injection into rats. Microspheres were prepared with PLGA or PEG-PLGA by the emulsion solvent evaporation method using polyvinyl alcohol (PVA), polyethylene glycol (PEG), albumin (BSA) or poloxamer 188 as surfactant, in the external aqueous phase. Commercial human albumin microspheres (Sferotec((R)), HAM) were used as reference. According to the European Pharmacopeia, >80% of (99m)Tc-HAM in the size range 10-50 microm, must be accumulated in the lung 15 min after intravenous administration. By modifying the surfactant, the resulting lung accumulation was 99% for (99m)Tc-HAM, and more than 50% for PLGA microspheres prepared with poloxamer 188 (1 and 4%), reaching 67% with 8% Poloxamer 188 and around 30-39% for PLGA and PEG-PLGA microspheres prepared with the other surfactants. PLGA microspheres made with 8% poloxamer 188 gave good quality lung images under a gamma camera for the first few minutes, subsequently liver radioactivity masked lung images.