I. Soriano

Formulation of calcium phosphates/poly (d, l-lactide) blends containing gentamicin for bone implantation

Implants to prevent or treat osteomyelitis are described, composed of phosphate/poly(d,l-lactide) blends containing the antibiotic gentamicin. Seven formulations of implants containing 3% gentamicin sulfate (GS) were prepared at 433 MPa and 693 MPa of compression pressure. The blends contained phosphates (25% hydroxyapatite (HAP), 75% tricalcium phosphate (TCP)) and 20% dl-PLA (weight average molecular weight, M(w): 30 kD). To prolong GS release, implants were coated with PLGA (M(w):100 kD) or dl-PLA (M(w): 200 kD). Various durations of GS release from these devices were demonstrated as feasible. Release times of more than 10 weeks were attained with implants coated with dl-PLA (M(w): 200 kD), greatly exceeding the performance of the commercial formulation.

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.

Material-related effects of BMP-2 delivery systems on bone regeneration

Material-related effects of a brushite and a PLGA controlled release system loaded with two distinct doses of bone morphogenetic protein-2 (BMP-2) (3.5 and 17.5 μg), pre-encapsulated in poly(lactic-co-glycolic acid) (PLGA), were investigated in an intramedullary femur defect model in rabbits. The systems were characterized in vitro and in vivo over 12 weeks in terms of morphology, release kinetics, porosity, molecular weight, and composition using scanning electron microscopy, mercury porosimetry, radioactivity counting, X-ray diffractometry, differential scanning calorimetry, and gel permeation chromatography. During the experimental period the investigated systems underwent significant changes in vitro as well as in vivo. It should be stressed that the two in vitro release patterns were similar, however in vivo parallel profiles were observed with a higher burst effect for BMP-2 in the PLGA system. The PLGA system degraded and disintegrated significantly faster than the brushite system, which suffered slowly progressing external erosion and, additionally, material resorption by osteoclasts in vivo. The consequences of this were reflected in the degree of bone regeneration. Although a sustained delivery of BMP-2 was achieved with both systems, the brushite construct, independent of the loaded growth factor dose, failed to consistently induce defect repair, a result attributed to its slow resorption rate. In contrast, the PLGA system resulted in complete regeneration with mature trabecular bone formation 8 weeks after implantation.

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.

Preparation and evaluation of insulin-loaded poly(dl-lactide) microspheres using an experimental design

Twenty formulations of bovine insulin in poly(dl-lactide) (dl-PLA) microspheres were elaborated to study the influence of polymer molecular weight, insulin content and polyvinylalcohol (PVA) concentration on microsphere characteristics and in vitro release profile. Ten of them released nearly all the incorporated insulin in 24 h. Of the rest, four were porous, presenting a burst effect over 40% and releasing 70% in 48 h. The other six formulations were non-porous; four released the insulin in 1 week and the other two only released 28% in 15 days. None of these 10 formulations were able to release the total amount of incorporated insulin, probably due to the adsorption of insulin by the polymer. From the results obtained with the experimental design, one more lot was prepared and tested in vitro and in vivo. The in vitro release profile was much slower than the in vivo one; 16% and 28% were released in vitro on the first day and in the following 10 days, respectively, while the corresponding figures for in vivo release were 60% and 90%.

Release control of albumin from polylactic acid microspheres

This paper reports how poly(DL-lactide) microspheres of different molecular weight and BSA content were manufactured in order to evaluate the influence of these two variables on the protein release profile, using a composite central rotational design. The microspheres were prepared by a double emulsion method using different w/o phase ratios. The BSA encapsulated was about 80% of the theoretical amount incorporated. The resulting microspheres proved porous except for three batches. The release of BSA from microspheres presented two phases, first a high burst effect ranging from 37.3 to 75% of the protein incorporated, and a second slower one. Analysis of the release results clearly shows a positive linear dependence of the slope of the slow release phase on the molecular weight of polymer, due most likely to the formation of hydrogen bridges between the terminal -OH groups of the polymer chains and the solitary pairs of donor atoms of the protein. Non-porous microspheres with a lesser burst effect were obtained by decreasing the w/o ratio of the first emulsion during the preparation process.

Use of Surfactants in Polylactic Acid Protein Microspheres

AbstractThis paper describes the effect on the in vitro release profile of poly(D,L-lactic) acid (DL-PLA), and poly(D,L-lactic-co-glycolic) acid (D,L-PLGA), microspheres containing BSA as a model protein prepared by the double emulsion technique, due to the addition of surfactant agents in the first emulsion (W/O) made using two type of homogenizer. In the first stage D,L-PLA microspheres were prepared with a mixture of Span-40® and Tween-80® to get HLB 6 and 7, W/O ratio in the first emulsion 1:3 and two types of homogenizers (High pressure homogenizer and Sonicator) against microspheres without surfactants. The microspheres made with high pressure homogenizer presented less BSA trapping efficiency and higher burst effect than those made with sonicator which showed a very slow release rate. In the second stage D,L-PLA and D,L-PLGA microspheres with and without surfactant agents and using sonicator were compared. The BSA release from D,L-PLGA microspheres was continuous, but batches with HLB 6 and without...

Effect of surfactant agents on the release of 125I-bovine calcitonin from PLGA microspheres : in vitro - in vivo study.

Abstract DL,PLGA-microspheres of 125 I-Bovine calcitonin prepared by the double emulsion technique (including Tween®-80 in the water phase and Span®-60 in the oil phase of the first emulsion) were studied in vitro and in vivo. The release of 125 I-bovine calcitonin was determined in vitro at 37°C in isotonic phosphate buffer (pH 7.4). 125 I-bovine calcitonin microspheres (5 mg) were administered under the skin on the back of Wistar rats and the radioactivity at the injection site was subsequently measured over a 6-week period. The in vivo and in vitro 125 I-bovine calcitonin profiles were affected by the surfactant agents, but in vivo release was much faster than in vitro. Following injection in rats, microspheres made with Tween®-80 and Span®-60 to give a hydrophile-lypophile balance (HLB) value of 6 and 8 in the first emulsion, released 20 and 14% of the radioactivity within the first 24 h, but only 1.3 and 1.2%/day at later times (up to 6 weeks) respectively. Under these conditions, they take 8 and 10 weeks, respectively, to release the total amount of calcitonin.

Effect of Surfactant Agents on the in Vitro Release of Insulin from DL-PLA Microspheres

This paper describes the effect of surfactants on the in vitro release profile of bovine insulin from DL-polyacetic acid (DL-PLA) microspheres prepared by the double-emulsion technique. The surfactants, Tween®-80 and Span®-60, were included in the water and oil phases, respectively, of the first emulsion. The presence of these agents affected the burst effect but not the subsequent release phase. The latter is more controllable by PLA molecular weight selection, with slower release being achieved as the molecular weight increases.