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PubMed2005

Hydrophilic core-shell microspheres: a suitable support for controlled attachment of proteins and biomedical diagnostics.

Functional hydrophilic microspheres (latex particles) have found various applications in life sciences and in medicine - particularly in latex diagnostic tests. This paper presents a comprehensive review of studies on latex particles with a hydrophilic interfacial layer composed of various hydrophilic polymers with reactive groups at the ends of macromolecules or at each monomeric unit along the chain. Typical examples of these hydrophilic polymers are poly(2-hydroxyethyl methyl methacrylate), poly(acrylic acid), poly(N,N-dimethylacrylamide), polysaccharides, poly(ethylene oxide) and polyglycidol. Hydrophilic microspheres with different morphologies (uniform or core-shell, see Figure) have been synthesized by emulsion and dispersion polymerizations. The chemical structure of polymers which constitute the interfacial layer of microspheres has been investigated using a variety of instrumental techniques (such as XPS, SSIMS and NMR) and analytical methods based on specific chemical reactions suitable for the determination of particular functional groups. Microspheres are exposed to contact with proteins in the majority of medical applications. This paper presents examples of studies on the attachment of these biomacromolecules to microspheres. The relation between the structure of the interfacial layer of microspheres and the ability of these particles for the covalent binding of proteins is discussed. Several examples of diagnostic tests, in which hydrophilic microspheres with adsorbed or covalently immobilized proteins were used as reagents, are presented. The paper also contains a short review of the application of magnetic hydrophilic particles for protein separation. Examples of hydrophilic latex particles used for hemoperfusion or heavy metal ion separation are presented. Hydrophilic microspheres with uniform or core-shell morphologies.

Animals↗
PubMed2000

Intracerebral implantation of NGF-releasing biodegradable microspheres protects striatum against excitotoxic damage.

Intrastriatal implantation of genetically modified cells synthesizing nerve growth factor (NGF) constitutes one way to obtain a long-term supply of this neurotrophic factor and a neuronal protection against an excitotoxic lesion. We have investigated if NGF-loaded poly(d,l-lactide-co-glycolide) microspheres could represent an alternative to cell transplantations. These microspheres can be implanted stereotaxically and locally release the protein in a controlled and sustained way. In order to test this paradigm, the NGF release kinetics were characterized in vitro using radiolabeled NGF, immunoenzymatic assay, and PC-12 cells bioassay and then in vivo after implantation in the intact rat striatum. These microspheres were thus implanted into the rat striatum 7 days prior to infusing quinolinic acid. Control animals were either not treated or implanted with blank microspheres. The extent of the lesion and the survival of ChAT-, NADPH-d-, and DARPP-32-containing neurons were analyzed. In vitro studies showed that microspheres allowed a sustained release of bioactive NGF for at least 1 month. Microspheres implanted in the intact striatum still contained NGF after 2.5 months and they were totally degraded after 3 months. After quinolinic acid infusion, the lesion size in the group treated with NGF-releasing microspheres was reduced by 40% when compared with the control groups. A marked neuronal sparing was noted, principally concerning the cholinergic interneurons, but also neuropeptide Y/somatostatin interneurons and GABAergic striatofuge neurons. These results indicate that implantation of biodegradable NGF-releasing microspheres can be used to protect neurons from a local excitotoxic lesion and that this strategy may ultimately prove to be relevant for the treatment of various neurological diseases.

Animals↗
PubMed1993

Fifteen micrometer microspheres reflux up the pulmonary veins during pulmonary artery occlusion.

The systemic arterial blood supply to the lung (bronchial blood flow, Qbr) is commonly measured using the reference flow technique by injecting radiolabeled microspheres into the left atrium (LA) and simultaneously collecting a reference blood sample from a large artery such as the aorta. These measurements are often done with the pulmonary artery occluded prior to the time of injection. We have reported previously that left atrial blood refluxes up the pulmonary veins following pulmonary artery (PA) occlusion. We designed this experiment to determine if 15 mu microspheres reflux from the LA into the left lung (i) when the left PA is occluded prior to microsphere injection and (ii) when the left PA is open during the injection. We calculated Qbr to the left lung after simultaneous left ventricular (LV) and LA injections of different radiolabeled microspheres in anesthetized, closed-chest, prone goats. When the PA was open (but occluded 5 sec after the microsphere injection), Qbr calculated from an LA injection differed little from that calculated from an LV injection of microspheres. However, when the PA was occluded prior to injection of the microspheres, Qbr calculated from an LA injection was significantly higher than that calculated from an LV injection suggesting that microspheres reflux from the LA to the lung.

Animals↗
PubMed2005

Preparation of mucoadhesive chitosan-poly(acrylic acid) microspheres by interpolymer complexation and solvent evaporation method II.

A mucoadhesive microsphere was prepared by an interpolymer complexation and solvent evaporation method, using chitosan and poly(acrylic acid) (PAA), to prolong the gastric residence time of the delivery system. The Fourier transform infrared results showed that microspheres were formed by an electrostatic interaction between the carboxyl groups of the PAA and the amine groups of the chitosan. X-ray diffraction and differential scanning calorimetry analysis showed that the enrofloxacin in the chitosan-PAA microsphere was molecularly dispersed in an amorphous state. Scanning electron microscopy of the surface and the quantity of mucin attached to the microspheres indicated that chitosan-PAA microspheres had a higher affinity for mucin than those of chitosan alone. The swelling and dissolution of the chitosan-PAA microspheres were found to be dependent on the pH of the medium. The rate of enrofloxacin released from the chitosan-PAA microspheres was slower at higher pH; therefore, based on their mucoadhesive properties and morphology, the chitosan-PAA microspheres can be used as a mucoadhesive oral drug delivery system.

Acrylic Resins↗
PubMed2004

Intra-articular treatment of arthritis with microsphere formulations of paclitaxel: biocompatibility and efficacy determinations in rabbits.

OBJECTIVES: To assess the biocompatibility of controlled release microspheres prepared from different polymeric biomaterials in various size ranges in rabbit synovial joints and based on these data, design and evaluate the efficacy of an intra-articular, paclitaxel-loaded microspheres formulation in rabbit models of arthritis. METHODS: Paclitaxel-loaded microspheres of poly(lactide-co-glycolide) (PLGA), poly(L-lactic acid) (PLA) and poly(caprolactone) (PCL) were prepared in different size ranges and inflammatory responses monitored following injection into healthy rabbit joints. The efficacy of 20% paclitaxel-loaded PLA microspheres (35-105 microm size range) injected intra-articularly into antigen and carrageenan induced rabbit models of arthritis was monitored. RESULTS: Polymeric microspheres in the 35-105 microm size range were biocompatible whereas smaller microspheres (1-20 microm) produced an inflammatory response. Efficacy studies showed that injection of 20% paclitaxel-loaded PLA microspheres significantly reduced all measures of inflammation in the antigen arthritis rabbit model. CONCLUSIONS: Paclitaxel-loaded PLA microspheres in the 35-105 microm size range, released paclitaxel in a controlled manner over several weeks, and may be a potential formulation for the intra-articular treatment of inflammation in arthritic conditions.

Animals↗
PubMed1997

Use of receptors immobilized on microspheres to identify ligand binding sites in tissue sections: detection of lymph node ligands for L-Selectin.

Particulate microspheres bearing immobilized probes can be used to identify ligands expressed by cells and require only brightfield microscopy for detection. There are distinct advantages to using microspheres to detect low affinity interactions; microspheres require no secondary amplification or detection procedures subsequent to the binding interaction, reducing opportunities for detachment of bound probe, and concentrating probes on microspheres may greatly increase binding avidity. Selectin leukocyte-endothelial adhesion molecules undergo low affinity binding to ligands, and these interactions may be difficult to detect with standard techniques. The aim of this study was to determine if immobilizing recombinant L-Selectin on microspheres would facilitate detection of specific tissue ligands. Microspheres were incubated with sections of rabbit peripheral lymph node in a modified Stamper-Woodruff assay, and binding was assessed by brightfield microscopy. L-Selectin-IgG microspheres bound to high endothelial venules, known to be sites of expression for L-Selectin ligands. Specificity was indicated by the lack of binding of microspheres coated with control protein, and inhibition of binding by antibody to L-Selectin and by competitive antagonists of L-Selectin ligand interactions.

Animals↗
PubMed2006

Effect of polymer blending on the release of ganciclovir from PLGA microspheres.

PURPOSE: The aim of the study is to investigate the effect of polymer blending on entrapment and release of ganciclovir (GCV) from poly(D,L-lactide-co-glycolide) (PLGA) microspheres using a set of empirical equations. METHODS: Two grades of PLGA, PLGA 7525 [D,L-lactide:glycolide(75:25), MW 90,000-126,000 Da] and Resomer RG 502H [D,L-lactide:glycolide(50:50), MW 8000 Da], were employed in the preparation of PLGA microspheres. Five sets of microsphere batches were prepared with two pure polymers and their 1:3, 1:1, and 3:1 blends. Drug entrapment, surface morphology, particle size analysis, drug release, and differential scanning calorimetric studies were performed. In vitro drug-release data were fitted to a set of empirical sigmoidal equations by nonlinear regression analysis that could effectively predict various parameters that characterize both diffusion and degradation cum diffusion-controlled release phases of GCV. RESULTS: Entrapment efficiencies of GCV ranged from 47 to 73%. Higher amounts of GCV were entrapped in polymer blend microspheres relative to individual polymers. Triphasic GCV release profiles were observed, which consisted of both diffusion and degradation cum diffusion-controlled phases. In vitro GCV release was shortest for Resomer RG 502H microsphere (10 days) and longest for PLGA 7525 microspheres (90 days). Upon blending, the duration of release gradually decreased as the content of Resomer RG 502H in the matrix was raised. Equations effectively estimated the drug-release rate constants during both the phases with high R2 values (>0.990). GCV release was slower from the blend microsphere during the initial diffusion phase. Majority of entrapped drug (70-95%) was released during the matrix degradation cum diffusion phase. CONCLUSIONS: Drug entrapment and release parameters estimated by the equations indicate more efficient matrix packing between PLGA 7525 and Resomer RG 502H in polymer-blended microspheres. The overall duration of drug release diminishes with rising content of Resomer RG 502H in the matrix. Differential scanning calorimetry studies indicate stronger binding between the polymers in the PLGA 7525/Resomer RG 502HColon, two colons 3:1 blend. Polymer blending can effectively alter drug-release rates of controlled delivery systems in the absence of any additives.

Algorithms↗
PubMed1990

Relationship between reductive drug metabolism in tumour tissue of anthracyclines in microspherical form and anti-tumour activity.

Increased activity against a rat solid tumour of doxorubicin incorporated into protein microspheres and administered intratumourally was associated with both increased duration of exposure of tumour tissue to native drug and anaerobic bioreduction of doxorubicin to 7-deoxyaglycones, indicating formation of reactive drug intermediates within tumour tissue. To investigate which of these aspects of drug disposition determined activity we have compared the in vivo fate (clearance from and metabolism by tumour tissue) of doxorubicin in microspherical form with the analogue 4'-deoxydoxorubicin and related this to the tumour growth delay recorded for these drugs. Within the dose range 42 to 55 micrograms, growth delay (14-18 days) of doxorubicin in microspherical form was markedly superior to drug in solution, whereas growth delay of 4'-deoxydoxorubicin in microspherical form (4.3-7.2 days) was not greater than drug in solution. Metabolism to 7-deoxyaglycones by tumour tissue was not a prominent feature of either drug when administered in solution. However, in microspherical form both drugs were extensively metabolized (peak concentrations: 3.6 micrograms/g doxorubicin 7-deoxyaglycone; 2.5 micrograms/g 4'-deoxydoxorubicin 7-deoxyaglycone). Native drug concentrations in tumour tissue were similar after administration in microspherical form at 48 hr (doxorubicin 3.8 micrograms/g; 4'-deoxydoxorubicin 3.7 micrograms/g) and 72 hr (doxorubicin 2.4 micrograms/g; 4'-deoxydoxorubicin 2.7 micrograms/g). At both time points, following administration in microspherical form, tumour tissue concentrations of doxorubicin were significantly greater than when drug was administered in solution, whereas no significant differences were observed for 4'-deoxydoxorubicin. The results are inconsistent with the process of anaerobic bioreduction of doxorubicin to 7-deoxyaglycones being an important component of its anti-tumour activity in microspherical form and point to the importance of increased duration of exposure to native drug.

Animals↗
PubMed1988

Visualization of migration of transplanted astrocytes using polystyrene microspheres.

Fluorescent polystyrene microspheres have been used to mark rat astrocytes for transplantation. Highly fluorescent cells were generated by incorporation of microspheres over periods of the order of 10 h. Microspheres ranging in average diameter from 50 to 200 nm and derivatized with either rhodamine or fluorescein have been used to label cells. There were no apparent cytotoxic effects of microsphere incorporation. Loaded astrocytes retained their complement of microspheres over periods of at least several weeks. The microspheres could be visualized in the transmission electron microscope. They were most likely phagocytosed by a coated-pit mechanism and accumulated in various types of lysosomal vesicles. Labelled astrocytes from neonatal PVG rats were implanted stereotaxically (as a plasma clot) into hippocampi of recipient syngeneic adult rats. Donor cells migrated from transplant to host over about 7 days. Transplant cells tended to be close to blood vessels over this period. Their location in paravascular spaces was determined from observation of microsphere-bearing cells in electron microscopy. Microsphere-loading of astrocytes is a simple method for marking cells for extended periods of time for transplantation which allows direct identification of marked cells with both fluorescence and electron microscopes.

Animals↗
PubMed1994

Piroxicam release from spray-dried biodegradable microspheres.

Poly(D,L-lactide) (DL-PLA) and poly(D,L-lactide-co-glycolide) (DL-PLGA) microspheres containing a non-steroidal anti-inflammatory model drug, piroxicam, were prepared by a spray drying process. The microspheres were characterized for surface morphology by scanning electron microscopy, particle size distribution by laser diffraction spectrometry, drug content and in vitro drug release. The diameters of the microspheres ranged from 1 to 15 microns. The DL-PLA particles appeared to be more spherical and smooth than the DL-PLGA particles, which showed a more undulated surface. Piroxicam content in the microspheres was 10%. A very high encapsulation efficiency of 99.0% was achieved with both polymers. In vitro release studies were carried out in a flow-through cell. The in vitro release rate of the drug from the DL-PLA microspheres was very slow. Less than 20% of the loaded drug was released within 10 d. The release mechanism was diffusion controlled and followed a square root of time relationship. Only a very small initial burst effect was observed. In contrast, the DL-PLGA microspheres provided a much faster drug release: about 50% was released within the first 5 h of the experiment. The mechanism for piroxicam release from the DL-PLA microspheres is not matrix erosion, but mainly drug diffusion through the intact polymer barrier. For the DL-PLGA microspheres, a pore diffusion release mechanism is proposed.

Biodegradation, Environmental↗
PubMed1988

Considerations in use of microspheres for myocardial blood-flow measurements in long-term experiments on rats.

The loss of 15-micron radioactive microspheres from rat myocardium was determined in long-term experiments. Heterotopic heart transplantation was used for the evaluation of microsphere losses. Microspheres were injected into the left ventricle of a donor rat, and the number of microspheres entrapped in the heart was measured after its isolation. The heart was transplanted into the abdominal cavity of a recipient rat and left there for 1-3 wk. The number of microspheres entrapped in the donor heart before the transplantation was compared with the number of microspheres remaining there after 1-3 wk. The losses of radioactivity from the myocardium over 1-3 wk did not exceed 10%. In a control series of experiments, the loss of radioactivity from the microspheres placed in microporous capillaries implanted subcutaneously into rats was determined. The measured leach criterion in vivo was 0.58% instead of 0.30% indicated by the manufacturer for in vitro conditions. The loss of 15-micron microspheres from the rat myocardium taking into account the leach criterion in vivo was 1.54 +/- 1.64%.

Animals↗
PubMed1994

Transmitter-loaded polymeric microspheres induce regrowth of dopaminergic nerve terminals in striata of rats with 6-OH-DA induced parkinsonism.

Biodegradable controlled-release microspheres made with the biocompatible biodegradable polyester excipient poly (DL-lactide-co-glycolide) represent a new technology for drug delivery to the central nervous system (CNS). A suspension of 3 microliters of dopamine (DA) or NE containing microspheres, or empty microspheres, was implanted in 2 sites of the DA denervated striatum of rats previously unilaterally lesioned with 6-OH-DA. Contralateral rotational behavior induced by apomorphine was used as an index of lesion success. Following implantation of the microspheres, rotational behavior was also used as an index of functional recovery. Both DA and NE microsphere implanted rats displayed a 30-50% reduction in the number of apomorphine induced rotations up to 12 weeks post implantation. Empty microspheres caused no changes in rotational behavior. Implantation of a mixture of DA/NE microspheres resulted in an 80% decrease in the number of apomorphine induced rotations, registered up to 4 weeks. Immunocytochemical examination revealed growth of DA and tyrosine hydroxylase immunoreactive fibers in the striatum of DA and NE microsphere implanted rats. Interestingly, functional behavior correlated with the degree of fiber ingrowth. This method to deliver substances to the CNS will be tested for therapeutic usefulness in patients with Parkinson's disease, in a recently approved clinical trial in Göteborg.

Animals↗
PubMed1983

Selective targeting of magnetic albumin microspheres containing low-dose doxorubicin: total remission in Yoshida sarcoma-bearing rats.

Magnetically responsive albumin microspheres containing doxorubicin hydrochloride were selectively localized in Yoshida sarcoma tumors. Tumors were implanted subcutaneously in the tail of Holtzman rats and allowed to grow to at least 200 mm2 size before initiation of experimental treatment. Drug-bearing microspheres at a dose level of either 0.5 or 2.5 mg/kg were infused proximal to the tumor via the ventral caudal artery. A bipolar permanent magnet was placed adjacent to the tumor during the infusion to effect localization. Control animals were treated with free doxorubicin infused intra-arterially at 5.0 mg/kg or 0.5 mg/kg. In other test groups animals received placebo microspheres localized in the tumor via influence of the external magnetic field, or drug-containing microspheres were infused without utilization of the magnet to effect localization. Of the 22 animals receiving magnetically localized doxorubicin microspheres 17 had total histological remission of the tumor. The remaining animals demonstrated marked tumor regression representing as much as 500-600 mm2 decrease in tumor size. While no deaths or metastases occurred in the groups receiving localized drug, animals treated with free doxorubicin, placebo microspheres or non-localized doxorubicin microspheres exhibited a significant increase in tumor size with metastases and subsequent death in 90-100% of the animals. No significant differences were noted in tumor regression/remission data between the 0.5 and 2.5 mg/kg dose levels of magnetically localized doxorubicin spheres. These results represent a significant advance in targeted chemotherapy in that 77% of the animals in the magnetically localized doxorubicin microsphere treatment groups exhibited total remission after only one regimen of drug therapy.

Animals↗
PubMed2005

PLGA-microsphere mediated clearance of bilirubin in temporarily hyperbilirubinemic rats: an alternate strategy for the treatment of experimental jaundice.

In the present study, we have demonstrated the suitability of microspheres in removal of plasma bilirubin from systemic circulation of hyperbilirubinemic rats. Poly (lactide co-glycolide) microspheres (PLGA microspheres) have been shown to bind with bilirubin in both a concentration and time dependent manner. The binding affinity of bilirubin to microspheres was enhanced when rat serum albumin (RSA) was loaded into the microspheres. On evaluating the potential of microspheres in elimination of bilirubin from the systemic circulation, RSA bearing microspheres were found to be competent in both removing bilirubin from the systemic circulation and controlling elevated plasma levels of liver function enzymes in temporarily hyperbilirubinemic rats. On the basis of results of the present study, we suggest that microsphere-based delivery system may help in development of safe, effective and alternate strategy for the treatment of hyperbilirubinemic conditions in model animals.

Animals↗
PubMed2005

Collagen-coated polylactide microspheres as chondrocyte microcarriers.

Polylactide (PLA) microspheres were coated with collagen for cell culture and injectable cell carriers. Utilizing a method of emulsion-solvent evaporation, PLA microspheres with diameter ranging from 180 to 280 microm were prepared, followed with aminolysis in hexanediamine/n-propanol solution to introduce free amino groups on their surfaces. After the amino groups were transferred into aldehyde groups by a treatment of glutaraldehyde, collagen type I was covalently coupled via Schiff base formation between the aldehyde groups and the amino groups on collagen molecules. Meanwhile, physically entangled collagen molecules were retained following a grafting-coating protocol to yield microspheres coated with larger amount of collagen. Aminolysis resulted in weight loss of the microspheres following a linear relationship with the aminolysis time. The NH2 and collagen contents existed on the microsphere surface were quantitatively determined by ninhydrin and hydroproline (Hyp) analyses, respectively. Larger amount of collagen was immobilized on the microspheres with higher content of NH2. In vitro chondrocyte culture revealed that the cells could attach, proliferate and spread on these PLA microspheres, in particular on the ones having higher content of collagen. These results show that the collagen-coated PLA microspheres are promising candidate as cell microcarriers.

Animals↗
PubMed2006

Glutaraldehyde and glyoxal cross-linked chitosan microspheres for controlled delivery of centchroman.

Glutaraldehyde and glyoxal cross-linked microspheres were prepared using chitosan with different molecular weights (MWs) and degrees of deacetylation (DDAs) for sustained release of centchroman under physiological conditions. The DDA in chitosan was determined by different methods, and the samples were categorized as chitosan with low (48%), medium (62%), and high (75%) DDA. The size and shape of the microspheres were determined by scanning electron microscopy (SEM), and hydrophobicity was determined by adsorption of Rose Bengal dye on microspheres cross-linked with glutaraldehyde or glyoxal. The effect of MW, DDA, and degree of cross-linking in microspheres was studied on the degree of swelling, as well as by the loading and release of centchroman. The glyoxal cross-linked microspheres were more compact and hydrophobic and showed better sustained release in companion to chitosan microspheres and glutaraldehyde cross-linked microspheres. The linear fractional release of centchroman with the square root of time indicated a Fickian behavior of centchroman, and the microspheres also showed zero-order release kinetics for centchroman.

Acetylation↗
PubMed2004

Preparation and properties of monodispersed rifampicin-loaded poly(lactide-co-glycolide) microspheres.

Monodispersed rifampicin (RFP)-loaded poly(lactide-co-glycolide) (PLGA) microspheres were prepared by a solvent evaporation method. In order to control the sizes of the microspheres, a membrane emulsification technique using Shirasu porous glass (SPG) membranes was applied. RFP/PLGA microspheres with the average diameters of 1.3, 2.2, 5.2, and 9.0 microm were obtained. They were relatively monodisperse and the values of the coefficient of variation (CV) for the size distributions of the microspheres were in the range between 7.0 and 16.0%. The loading efficiency of RFP was in the range between 50.3 and 67.4% independent of the microsphere size. The release ratio of RFP from RFP/PLGA microspheres was measured in pH 7.4 PBS at 37 degrees C. From RFP/PLGA microspheres with average diameters of 1.3 and 2.2 microm, almost 60% of RFP loaded in the microspheres was released in the initial day and the release was terminated almost within 10 days. On the other hand, from those with average diameters of 5.2, and 9.0 microm, the release of RFP was observed even 20 days after the release started.

Antitubercular Agents↗
PubMed2005

pH-sensitive polyelectrolyte complex gel microspheres composed of chitosan/sodium tripolyphosphate/dextran sulfate: swelling kinetics and drug delivery properties.

Porous chitosan (CS) polyelectrolyte complex (PEC) hydrogel microspheres were prepared via either wet phase-inversion or ionotropic crosslinking with sodium tripolyphosphate (Na+ - TPP) and dextran sulfate (DS). The resulting microspheres were characterized using scanning electron microscopy (SEM) and elemental analysis (EA). The controlled release behavior of ibuprofen (IBU) from these microspheres was investigated. The PEC microspheres were about 700-950 microm in diameter with large pores and open porous structure. The CS/TPP/DS microspheres resisted hydrolysis in strong acid and biodegradation in enzymatic surroundings. The swelling kinetics for CS microspheres was close to Fickian diffusion, whereas those for CS/TPP and CS/TPP/DS were non-Fickian. Furthermore, the equilibrium water content (EWC) and water diffusion coefficient (D) increased with the pH of the media. The release profiles of IBU from CS/TPP/DS microspheres were slow in simulated gastric fluid (SGF, pH 1.4) over 3 h, but nearly all of the initial drug content was released in simulated intestinal fluid (SIF, pH 6.8) within 6 h after changing media. Overall the results demonstrated that CS/TPP/DS microspheres could successfully deliver a hydrophobic drug to the intestine without losing the drug in the stomach, and hence could be potential candidates as an orally administered drug delivery system.

Administration, Oral↗