Injectable Microspheres Research Articles

Poly(ɛ-Caprolactone) and Poly (L-Lactic-Co-Glycolic Acid) Degradable Polymer Sponges Attenuate Astrocyte Response and Lesion Growth in Acute Traumatic Brain Injury

This study evaluated the response of rat brain to 2 degradable polymers (poly (L-lactic-co-glycolic acid) (PLGA), and poly(epsilon-caprolactone) (PCL)), two common materials in tissue engineering. PLGA has been extensively studied in the brain for controlled drug release as injectable microspheres and is generally accepted as biocompatible in that capacity. Biocompatibility in other forms and for different functions in the brain has not been widely studied. PCL was chosen as an alternative to PLGA for its slower degradation and less-acidic pH upon degradation. Porous scaffolds were made from both polymers and implanted into rat cerebral cortex for 1 and 4 weeks. Morphology, defect size, activation of microglia (OX-42) and astrocytes (glial fibrillary acidic protein (GFAP)), infiltration of activated macrophages (major histocompatibility complex (MHC)-II), and ingrowth of neurons (beta-tubulin type III (Tuj-1)) and progenitor cells (nestin) were analyzed using hematoxylin and eosin staining and immunofluorescence. PCL induced a lower inflammatory response than PLGA, as demonstrated by lower MHC-II and GFAP expression and greater ingrowth. Both polymers alleviated astrocytic activation and prevented enlargement of the defect. Tuj-1-, nestin-, and GFAP-positive cells were observed growing on both polymers at the peripheries of the sponge implants, demonstrating their permissiveness to neural ingrowth. These findings suggest that both polymers attenuate secondary death and scarring and that PCL might have advantages over PLGA.

In vitro Evaluation of Lysozyme-loaded Microspheres in Thermosensitive Methylcellulose-based Hydrogel

Abstract Long-term injectable microspheres have some inherent disadvantages such as migration of microspheres from the original site and the burst effect. In order to avoid these problems, microsphere-loaded thermosensitive hydrogel system was designed and expected to achieve a zero-order release of biomolecular drugs in relative high initial drug loadings. Lysozyme, an antibacterial protein usually used to reduce prosthetic valve endocarditis, was selected as the model drug. Poly (DL-lactide-co-glycolide) (PLGA) microspheres, prepared by solvent evaporation method, were employed to encapsulate lysozyme and dispersed into thermosensitive pre-gel solution containing methylcellulose (MC), polyethylene glycol (PEG), sodium citrate (SC), and sodium alginate (SA). The mixture could act as a drug reservoir by performing sol-gel transition rapidly if the temperature was raised from room temperature to 37°C. The in vitro release results showed that the burst effect was avoided due to strengthening of diffusion resistance in the gel. The formulation was able to deliver lysozyme for over 30 days in a nearly zero-order release profile with a rate of 32.8μg·d −1 which exhibits its remarkable potential for effective application in long-term drug delivery.

Partitioning locomotor energy use among and within muscles Muscle blood flow as a measure of muscle oxygen consumption

Linking the mechanics and energetics of locomotion in vertebrates has been hampered by a lack of information regarding the energy use of individual skeletal muscles in vivo. Here, we present a review of the available data concerning the relationship between the rates of skeletal muscle blood flow and oxygen consumption (V(O2)). In active muscle, during aerobically supported exercise, there is a linear relationship between these variables, irrespective of the muscle fiber type and intensity of exercise through most of the aerobic exercise range. We conclude that the rate of blood flow is the best available indicator of aerobic metabolic rate in multiple individual muscles or regions of muscles during locomotion. The practical considerations of using the injectable microsphere technique to measure muscle blood flow in this context are discussed.

3324: Study on optimal dosage of slow-released carboplatin microspheres for intratumoral injection on rabbit VX2 liver tumor

Objectives: To investigate the effect and the side effect of various doses treatment groups of slow-released carboplatin microspheres by intratumoral injection on the rabbit VX2 liver tumor. Methods: Rabbits with VX2 liver tumor were divided into five treatment groups and control group. Changes of the tumors’ volume and blood routine were observed during the 14 days therapy. Comparison was made between the five treatment groups and control group and within the five groups. Results: It was shown that slow-released carboplatin microspheres possessed obviously antitumoral effects, manifested as dose-dependence. The side effects between groups were insignificant (p > 0.05). Conclusions: Group E was evidenced to have the most effective tumor inhibition and no obvious side effect. It may be considered as the optimal dosage for the treatment of rabbit liver VX2 tumor.

Biodegradation and biocompatibility of contraceptive-steroid-loaded poly ( dl-lactide-co-glycolide) injectable microspheres: in vitro and in vivo study

Purpose A controlled-release drug delivery of contraceptive steroids levonorgestrel (LNG) and ethinyl estradiol (EE) has been developed by successful encapsulation of LNG and EE in poly (lactide-co-glycolide) (PLG) microspheres. Materials and Methods Smooth, spherical, steroid-loaded PLG microspheres with a mean size of 10–25 μm were prepared by using the water/oil/water double-emulsion solvent evaporation method. Results In vitro release profiles showed an increased burst release of LNG/EE on Week 1; thereafter, the release was sustained. At the end of Week 7, the release of LNG/EE from 1:5 and 1:10 PLG microspheres was 75.64% and 62.55%. respectively. In vitro degradation studies showed that the PLG microspheres maintained surface integrity up to Week 8 and then eroded completely by Week 20. In an in vivo study, the serum concentration of LNG/EE in rats showed a triphasic release response, with an initial burst release of 8 ng/mL LNG and 14 pg/mL EE on Day 1; thereafter, a controlled release of the drugs to the systemic circulation was maintained until Week 15, maintaining constant drug levels of 2 ng/mL LNG and 3–4 pg/mL EE in the blood. Histological examination of steroid-loaded PLG microspheres injected intramuscularly into the thigh muscle of Wistar rats showed minimal inflammatory reaction, demonstrating that contraceptive-steroid-loaded microspheres were biocompatible. Conclusion This controlled-release and biocompatible nature of the PLG microspheres may have potential application in contraceptive therapy.

Contrast-enhanced Duplex surveillance after endovascular abdominal aortic aneurysm repair: Improved efficacy using a continuous infusion technique

Currently, postoperative endoleak surveillance after endovascular aortic aneurysm repair (EVAR) is primarily done by computed tomography (CT). The purpose of this study was to determine the efficacy of contrast-enhanced ultrasonography scans to detect endoleaks by using a novel infusion method and compare these findings with those of CT angiography (CTA). Twenty male patients (mean age, 70.4 years) underwent surveillance utilizing both CTA and contrast-enhanced color Duplex imaging. One 3-mL vial of Optison (Perfluten Protein A microspheres for injection) and 57 mL normal saline, for a total of 60 mL, were administered to each patient as a continuous infusion at 4 mL/min via a peripheral vein. Each study was optimized with harmonic imaging, and a reduced mechanical index of 0.4 to 0.5, compression of 1 to 3, and a focal zone below the aorta to minimize microsphere rupture. One minute was allowed from the time of infusion to the appearance of contrast in the endograft. Flow was evaluated within the lumen of the graft and its components, as was the presence or absence of endoleaks. Findings were compared with standard color-flow Duplex imaging and CT utilizing CTA reconstruction protocols. All patients evaluated had modular endografts implanted for elective aneurysm repair. Contrast-enhanced duplex scans identified nine endoleaks: one type I and eight type II. No additional endoleaks were seen on CTA. However, CTA failed to recognize three type II endoleaks seen by contrast-enhanced ultrasound. The continuous infusion method allowed for longer and more detailed imaging. An average of 46.8 mL of the contrast infusion solution was used per patient. Contrast enhanced Duplex ultrasonography accurately demonstrates endoleaks after EVAR and may be considered as a primary surveillance modality. Continuous infusion permits longer imaging time.

Adjustably Bioresorbable Sol-Gel Derived SiO2 Matrices for Release of Large Biologically Active Molecules

Amorphous, sol-gel derived SiO2 are known to biocompatible and bioresorbable materials. Bioresorbable materials have potential applications as implants or injectable matrices in the controlled delivery of biologically active agents in the living tissue. Bioresorbable matrices provide desirable properties, e.g., extra removal operations that have to be done with biostable matrices are avoided and the release of large therapeutic molecules can be controlled by matrix degradation rather than by diffusion. New important groups of drugs, such as biotechnically-produced peptides and proteins, are potential to be encapsulated in bioresorbable SiO2, because they are typically larger in size and their direct oral administration without protecting matrix is difficult due to digestion. The methods to achieve a wide range of SiO2 bioresorption rates (from days to months) are introduced in this study. This is done by a “conventional” alkoxy-based sol-gel method at protein-friendly conditions by adjusting the precursor ratios, aging of the sol and by using different preparation methods (casting, spray-drying and freeze-drying). The prepared morphologies include implantable monolithic sticks and injectable microspheres. The importance of chemical structure is shown in comparison with the specific surface area and pore volume.

Effects of formulation factors on encapsulation efficiency and release behaviour in vitro of huperzine A-PLGA microspheres

To develop a long-acting injectable huperzine A-PLGA microsphere for the chronic therapy of Alzheimer's disease, the microsphere was prepared by using o/w emulsion solvent extraction evaporation method based on a series of formulation design of the emulsion. The dialysis method was used for release analysis. The encapsulation efficiency and release amount of the microspheres were determined by UV/VIS spectrophotometry. The morphology of the microspheres was observed by scanning electron microscopy. The distribution of the drug within microspheres was observed by a confocal laser scanning microscope. The results indicated that the PLGA 15 000 microspheres possessed a smooth and round appearance with average particle size of 50 µm or so. The encapsulation percentages of microspheres prepared from PLGA 15 000, 20 000 and 30 000 were 62.75, 27.52 and 16.63%, respectively. The drug release percentage during the first day decreased from 22.52% of PLGA 30 000 microspheres to 3.97% of PLGA 15 000 microspheres, the complete release could be prolonged to 3 weeks. The initial burst release of microspheres with higher molecular weight PLGA could be explained by the inhomogeneous distribution of drug within microspheres. The encapsulation efficiency of the microspheres improved as the polymer concentration increase in oil phase and PVA concentration decreased in aqueous phase. The burst release could be controlled by reducing the polymer concentration. Evaporation temperature had a large effect on the drug release profiles. It had better be controlled under 30°C. Within a certain range of particle size, encapsulation efficiency decreased and drug release rate increased with the reducing of the particle size.

Single and multiple dose pharmacokinetics of long-acting injectable naltrexone

Background Long-acting naltrexone (LA-NTX) is an injectable microsphere formulation being developed to achieve continuous naltrexone (NTX) exposure for 1 month in the treatment of alcohol dependence. Methods This was a single center, randomized, double-blind, placebo-controlled, parallel design study in healthy subjects (n=42) to evaluate the PK of LA-NTX following single (190mg; 380mg) and multiple (380mg; q28d) IM doses vs. oral naltrexone (50mg; qd). PK parameters for NTX and its primary metabolite, 6β-naltrexol (6β-NOH) were calculated by noncompartmental methods. Results Mean NTX concentrations were >1 ng/mL over 28 days following LA-NTX 380mg; 6β-NOH concentrations were greater than, but parallel to, NTX. Tmax was ~2–3 and t1/2 was ~5–7 days for NTX and 6β-NOH. NTX AUC0-∞ following LA-NTX 380mg (144±30 ng*days/mL) was 2-fold greater than following LA-NTX 190mg (72±9 ng*days/mL). Multiple dose PK was predicted by single dose; steady state was reached with the second LA-NTX 380mg dose. NTX and 6β-NOH accumulation was ≤13%. NTX AUC0–28d was 4-fold greater following LA-NTX 380mg (160 ng*days/mL) vs. oral 50mg daily (~41 ng*days/mL; dose=1400mg/28 days); 6β-NOH AUC0–28d (294 ng*days/mL) was 70% lower vs. oral (1002 ng*days/mL). Conclusions Single dose PK of LA-NTX was dose proportional and predicted steady state observations. LA-NTX provided greater exposure and less fluctuation in NTX concentrations over a 28 day period, with a lower overall dose, compared to daily oral administration. Clinical Pharmacology & Therapeutics (2005) 77, P42–P42; doi: 10.1016/j.clpt.2004.12.053

Effects of formulation factors on encapsulation efficiency and release behaviour in vitro of huperzine A-PLGA microspheres

To develop a long-acting injectable huperzine A-PLGA microsphere for the chronic therapy of Alzheimer's disease, the microsphere was prepared by using an o/w emulsion solvent extraction evaporation method based on a series of formulation design of the emulsion. The dialysis method was used for release analysis. The encapsulation efficiency and release amount of the microspheres were determined by a UV/VIS spectrophotometer. The morphology of the microspheres was observed by scanning electron microscopy. The distribution of the drug within microspheres was observed by a confocal laser scanning microscope. The results indicated that the PLGA 15 000 microspheres possessed a smooth and round appearance with average particle size of 50 µm or so. The encapsulation percentages of microspheres prepared from PLGA 15 000, 20 000 and 30 000 were 62.75%, 27.52% and 16.63%, respectively. The drug release percentage during the first day decreased from 22.52% of PLGA 30 000 microspheres to 3.97% of PLGA 15 000 microspheres, the complete release could be prolonged to 3 weeks. The initial burst release of microspheres with higher molecular weight PLGA could be explained by the inhomogeneous distribution of drug within microspheres. The encapsulation efficiency of the microspheres improved as the polymer concentration increased in the oil phase and PVA concentration decreased in the aqueous phase. The burst release could be controlled by reducing the polymer concentration. Evaporation temperature had a large effect on the drug release profiles. It had better be controlled under 30°C. Within a certain range of particle size, encapsulation efficiency decreased and drug release rate increased with the reducing of the particle size.

Influence of manufacturing parameters on development of contraceptive steroid loaded injectable microspheres.

The main objective of this work was to develop a system consisting of polymeric microspheres loaded with steroid drugs. The drugs were encapsulated using biodegradable poly(lactide-co-glycolide) (PLG) and poly(epsilon-caprolactone) (PCL) by double emulsion solvent evaporation method. The lipophilic drugs, levonorgestrel and ethinylestradiol were made soluble by adding ethanol/water mixture. The effects of parameters like polymer concentration and stabilizer concentration were studied on the size, size distribution, surface properties and loading efficiencies of microspheres. The formulated microspheres were smooth, spherical and uniform in shape and size. Fourier transformed infrared spectroscopy and differential scanning calorimetry studies seemed to confirm the absence of chemical interaction between the drugs and the polymers, while the drugs were dispersed in the polymer. The increase in polymer concentrations increased the size as well as the loading efficiency of microspheres. Data obtained in this study demonstrated that the PLG/PCL microspheres may be a suitable polymeric carrier for long acting injectable drug delivery.

Adhesion and Proliferation of Human Osteoblastic Cells Seeded on Injectable Hydroxyapatite Microspheres

In the present work, the interaction of human osteoblast-like MG63 cells with novel hydroxyapatite (HAp) microspheres was investigated. Cells were seeded on the microspheres and incubated for up to 7 days. The cell-material constructs were visual ised by scanning electron microscopy and confocal laser scanning microscopy, and the rate of cel l proliferation was estimated using the Neutral Red assay. The results showed that osteoblastic cells were able to adhere and proliferate on the HAp microspheres, which are intended to be used as i njectable support-materials for bone regeneration.

Preparation and characterization of injectable microspheres of contraceptive hormones

Present study describes the development of a new formulation of levonorgestrel and ethinylestradiol based on double emulsion-solvent evaporation technique using poly(ε-caprolactone) (PCL) as biodegradable polymer. The effect of polymer concentration on microspheres and entrapment of drug into microspheres were studied. PCL was selected because of its hydrophobicity and advantages over other biodegradable polymers. Characterization of biodegradable polymer used for controlled drug delivery is essential to ensure reproducibility of in vitro and in vivo performances. The selected characterisation techniques established for PCL microspheres include its loading and entrapment efficiencies, DSC to analyse thermal behaviour, SEM to observe surface morphology, drug content of microspheres and in vitro release of drugs from microspheres. The SEM reports showed that microspheres were with smooth surface and DSC thermograms revealed no interaction between drug and polymer. The entrapment was found to be 58 and 47% for 1:10 and 1:5 batches and in vitro release studies showed that about 69.7% of LNG and 66.7% of EE from 1:10 batch and about 80% of LNG and 75.5% of EE from 1:5 batch for 150 days.

Initial Experience With Long-Acting Risperidone Microspheres Injection

Objective: To report initial clinical experience with the injectable long-acting microspheres formulation of the atypical antipsychotic risperidone. Methods: Case reports. Results: The seven patients described have had good outcomes to date. A patient who has received the drug for 2 years has improved from a state of severe deterioration to full-time employment and participation in a relationship; he has reported mild erectile difficulties but is keen to continue. In all cases extrapyramidal side-effects have been uncommon and brief; weight gain or other physical adverse events have not been observed. Conclusion: Initial use of long-acting injectable risperidone suggests that the first ‘atypical depot’ is a welcome therapeutic development likely to provide significant clinical benefits, particularly for patients who have previously had unsatisfactory experiences with conventional antipsychotics.

Soft Tissue Substitutes in Perioral Augmentation

Each year the plastic surgery industry has a newer, better, soft tissue filler. Most plastic surgeons are very skeptical about the newest product. The goal is always an injectable, affordable, long-lasting filler. We have recently witnessed a dramatic increase in the available fillers for use in perioral rejuvenation. Thus, it is necessary to discuss state-of-the art fillers now available, the techniques used, potential pitfalls in use, and results. Solutions to problematic areas in perioral rejuvenation are presented. There does not appear yet to be an ideal filler; instead most plastic surgeons have an algorithm for modest, moderate, and dramatic improvement in facial soft tissue needs. Our practice has more recently focused on various combinations of Alloderm™, fat, and hydroxylapitate injectable microspheres (Radiance™) to fill most of these needs. We strongly suggest that plastic surgeons become facile with three or four fillers to address a wider range of soft tissue needs. We present an in-depth discussion of the most common available fillers and show the risks and benefits we have experienced with each.

Changes in cisplatin delivery due to surface-coated poly (lactic acid)-poly(epsilon-caprolactone) microspheres.

Smooth muscle cell proliferation plays a major role in the genesis of restenosis after angioplasty or vascular injury. Local delivery of agents capable of modulating vascular responses, have the potential to prevent restenosis. However, the development of injectable microspheres for sustained drug delivery to the arterial wall is a major challenge. We demonstrated the possibility of entrapping an antiproliferative agent, cisplatin, in a series of surface coated biodegradable microspheres composed of poly(lactic acid)poly(caprolactone) blends, with a mean diameter of 2-10 pm. The microspheres were surface coated with poly ethylene glycol (PEG), chitosan (Chit), or alginate (Alg). A solution of cisplatin and a 50:50 blend of polylactic acid (PLA)-polycaprolactone (PCL) dissolved in acetone-dichloromethane mixture was poured into an aqueous solution of PEG (or polyvinyl alcohol or Chit or Alg) with stirring using a high speed homogenizer, for the formation of microspheres. Cisplatin recovery in microspheres ranged from 25-45% depending on the emulsification system used for the preparations. Scanning electron microscopy revealed that the PLA-PCL microspheres were spherical in shape and had a smooth surface texture. The amount of drug release was much higher initially (20-30%), this was followed by a constant slow-release profile for a 30-day period of study. It has been found that drug release depends on the amount of entrapped drug, on the presence of extra cisplatin in the dispensing phase, and on the polymer coatings. This PEG or Alg-coated PLA/PCL microsphere formulation may have potential for the targeted delivery of antiproliferative agents to treat restenosis.

Determination of local tissue concentrations of bupivacaine released from biodegradable microspheres and the effect of vasoactive compounds on bupivacaine tissue clearance studied by microdialysis sampling.

Incorporation of bupivacaine, a short acting local analgesic, into injectable microspheres provides a long acting formulation. Co-incorporation of dexamethasone into the microspheres results in extended activity. The purpose of this study is to compare tissue concentrations of bupivacaine resulting from the two types of microspheres and to determine if the observed sustained tissue concentration of bupivacaine is due to changes in its tissue clearance. Microdialysis probes were implanted into rat muscle. Following microsphere injection, bupivacaine tissue concentration was monitored (HPLC-UV), and the tissues histologically examined. The effect of vasoactive compounds on the tissue concentration of bupivacaine, not formulated in microspheres, was monitored. Hind muscle histology showed significant granulomatous reactions around the probe and both types of microspheres. A higher, prolonged bupivacaine concentration was observed from microspheres. A higher, prolonged bupivacaine concentration was observed from microspheres with co-incorporated dexamethasone relative to those without dexamethasone. Addition of vasoconstrictors to the perfusate containing bupivacaine resulted in decreased bupivacaine delivery compared to bupivacaine alone, whereas the addition of a vasodilator increased bupivacaine delivery. The longer lasting effect of microspheres with co-incorporated dexamethasone results from higher, prolonged tissue concentrations of bupivacaine. Dexamethasone, a vasoconstrictor, decreases the clearance rate of bupivacaine from the tissue resulting in a higher, prolonged tissue concentration of bupivacaine.

Comparative Assessment of In Vitro Release Kinetics of Calcitonin Polypeptide from Biodegradable Microspheres

The objective of our study was to compare the in vitro release kinetics of a sustained-release injectable microsphere formulation of the polypeptide drug, calcitonin (CT), to optimize the characteristics of drug release from poly-(lactide-co-glycolide) (PLGA) copolymer biodegradable microspheres. A modified solvent evaporation and double emulsion technique was used to prepare the microspheres. Release kinetic studies were carried out in silanized tubes and dialysis bags, whereby microspheres were suspended and incubated in phosphate buffered saline, sampled at fixed intervals, and analyzed for drug content using a modified Lowry protein assay procedure. An initial burst was observed whereby about 50% of the total dose of the drug was released from the microspheres within 24 hr and 75% within 3 days. This was followed by a period of slow release over a period of 3 weeks in which another 10-15% of drug was released. Drug release from the dialysis bags was more gradual, and 50% CT was released only after 4 days and 75% after 12 days of release. Scanning electron micrographs revealed spherical particles with channel-like structures and a porous surface after being suspended in an aqueous solution for 5 days. Differential scanning calorimetric studies revealed that CT was present as a mix of amorphous and crystalline forms within the microspheres. Overall, these studies demonstrated that sustained release of CT from PLGA microspheres over a 3-week period is feasible and that release of drug from dialysis bags was more predictable than from tubes.

Therapeutic efficacy of IL-2-loaded hydrogels in a mouse tumor model.

Interleukin-2 (IL-2) is a highly effective anticancer drug if it is applied locally for 5 consecutive days. In most cases this requires 5 invasive treatments, which is not usually acceptable for either the patient or the clinician. For this reason we have developed dextran-based hydrogels from which the required amount of encapsulated IL-2 (1-4 x 10(6) IU of IL-2) is gradually released during 5-10 days. Initially IL-2-containing macroscopic cylinder-shaped gels (implants), and later IL-2-containing injectable microspheres, were developed. These preparations were characterized in vitro, and the therapeutic activity was tested in DBA/2 mice with SL2 lymphosarcoma. The therapy was given to mice with a large and extensively metastasized tumor load (at least 5% of the body weight). If 1-4 x 10(6) IU of IL-2 was slowly released from the hydrogels over a period of 5-10 days, the therapeutic effects were very good and comparable to the effects of free IL-2 injections for 5 consecutive days. In conclusion, dextran-based hydrogels are promising systems for the controlled release of IL-2.

Controlled delivery of taxol from poly(ethylene glycol)‐coated poly(lactic acid) microspheres

The development of injectable microspheres for sustained drug delivery to the arterial wall is a major challenge. We demonstrated the possibility of entrapping an antiproliferative agent, taxol, in poly(ethylene glycol) (PEG)-coated biodegradable poly(lactic acid) (PLA) microspheres with a mean diameter of 2–6 μm. A solution of taxol and PLA dissolved in an acetone/dichloromethane mixture was poured into an aqueous solution of PEG [or poly(vinyl alcohol) (PVA] with stirring with a high-speed homogenizer for the formation of microspheres. Taxol recovery in PLA–PEG microspheres was higher (61.2 ± 2.3%) than with PVA-based (41.6 ± 1.8%) preparations. An analysis by diffuse reflectance infrared Fourier transform spectroscopy revealed that PEG was incorporated well on the PLA microsphere surface. Scanning electron microscopy revealed that the PEG-coated PLA microspheres were spherical in shape and had a smooth surface texture like those of PVA-based preparations. The amount of drug release was much higher initially (25–30%); this was followed by a constant slow-release profile for a 30-day period of study. This PEG-coated PLA microsphere formulation may have potential for the targeted delivery of antiproliferative agents to treat restenosis. © 2001 John Wiley & Sons, Inc. J Biomed Mater Res 55: 96–103, 2001