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PubMed1998

Preparation and properties of radioactive rhenium glass microspheres intended for in vivo radioembolization therapy.

Rhenium glass microspheres composed of metallic rhenium particles dispersed within a magnesium alumino borate glass matrix were produced by sintering ReO2 powder and glass frit at 1050 degrees C. The in vitro chemical durability of radioactive and nonradioactive microspheres was determined from chemical corrosion tests on microspheres immersed in phosphate-buffered saline (PBS) solution at 37 degrees C. The dosimetric properties of these microspheres also were calculated. The rhenium glass microspheres are chemically durable in body fluids and release < 1.2% of radioactive rhenium after being immersed in PBS solution for 32 days at 37 degrees C. Therapeutic radioactive rhenium activities can be obtained in < 10 h by neutron activation of these microspheres in a thermal neutron flux of 8 x 10(13) cm(-2)s(-1). A 50 mg injection of radioactive rhenium glass microspheres containing 3.7 GBq of 186Re and 8.5 GBq of 188Re could deliver a 100 Gy dose to a cancerous liver while limiting the total body dose from rhenium dissolution in vivo to approximately 1 mGy.

Biocompatible Materials↗
PubMed2000

Cytoplasmic delivery of a macromolecular fluorescent probe by poly(d, l-lactic-co-glycolic acid) microspheres.

A macromolecular fluorescent probe encapsulated in poly(d, l-lactic-co-glycolic acid) (PLGA) microspheres was used as a model for studying cytoplasmic delivery of antigens. We hypothesized that Texas red dextran loaded in PLGA microspheres would be delivered to the cytoplasm and that cytoplasmic delivery would be affected by polymer molecular weight. Cellular localization of the Texas red dextran was investigated at two different molecular weights of PLGA: 6000 and 60,000 g/mol. Intracellular degradation and processing of Texas red dextran-loaded PLGA microspheres by mouse peritoneal macrophages was monitored both in vitro and in vivo for a 7-day period using confocal laser scanning microscopy (CLSM). The results revealed cytoplasmic delivery of the fluorescent probe at both molecular weights of PLGA. Furthermore, the CLSM images showed that both in vitro and in vivo, the kinetics of microsphere degradation and cytoplasmic delivery were more rapid for the 6000 g/mol PLGA microspheres than the 60,000 g/mol PLGA microspheres. Hence, this study provides physical evidence that PLGA microspheres are capable of cytoplasmic delivery and that delivery to the cytosol can be controlled by modifying formulation parameters such as polymer molecular weight.

Animals↗
PubMed2000

Lysozyme microencapsulation within biodegradable PLGA microspheres: urea effect on protein release and stability.

Lysozyme was encapsulated within biodegradable poly(D, L-lactide-co-glycolide) microspheres by a double emulsion solvent evaporation method for studying its release mechanism associated with protein stability problems. When urea, a protein unfolding agent, was added into the incubation medium lysozyme release rate from the microspheres increased with the increase in urea concentration. The enhanced lysozyme release was attributed to the suppression of protein aggregation, to the facilitated diffusion of unfolded lysozyme by an efficient reptile motion of unfolded protein molecules through porous channels in microspheres, and to the largely decreased extent of nonspecific protein adsorption onto the enlarged surface area of degrading polymer microspheres in the presence of urea. Encapsulating lysozyme in an unfolded form within PLGA microspheres was attempted by using urea as an excipient. This new urea-based formulation exhibited a more sustained lysozyme release profile than the control formulation, and released lysozyme from the microspheres showed a much less amount of lysozyme dimer population while maintaining a correct conformation after refolding in the incubation medium. This study provides new insights for the formulation of protein encapsulated PLGA microspheres.

Animals↗
PubMed2000

Development and in vitro characterization of vascular endothelial growth factor (VEGF)-loaded poly(DL-lactic-co-glycolic acid)/poly(ethylene glycol) microspheres using a solid encapsulation/single emulsion/solvent extraction technique.

Poly(DL-lactide-co-glycolide) (PLGA)/polyethylene glycol (PEG) microspheres are one modality of controlled delivery of biologically active molecules that would further the development of engineered tissues. As a possible mechanism to stimulate angiogenesis within an engineered tissue, vascular endothelial growth factor (VEGF) and bovine serum albumin (BSA) were coencapsulated into microspheres fabricated from PEG and 50/50 PLGA using a solid-encapsulation/single-emulsion/solvent extraction technique. Two VEGF/BSA ratios were studied: 1:2000 and 1:10,000. Analysis consisted of the loading efficiency, particle size distribution, bright-field microscopy, scanning electron microscopy, release kinetics, and an in vitro human umbilical vein endothelial cell proliferation assay to assess biological activity of the released VEGF. Results show the microspheres could be manufactured, stored, and degraded over 28 days. The burst release rates for 1:2000 and 1:10,000 VEGF/BSA microspheres were 71.87 +/- 8.11 and 27.91 +/- 1.71 ng/mL (mean +/- standard error of the mean), respectively; steady-state release rates were 6.56 +/- 1.10 and 2.21 +/- 0.47 ng/mL, respectively. The microspheres released biologically active VEGF, and the VEGF increased the proliferation of HUVECs in culture (p <.05). The successful development of a novel, cost-effective, scalable technique for producing microspheres loaded with biologically active proteins is presented. Using the data obtained from these studies, a defined concentration of microspheres will deliver a quantifiable level of VEGF at a known release rate.

Animals↗
PubMed2001

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 microm. 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.

Biocompatible Materials↗
PubMed2002

Determination of individual microsphere properties by capillary electrophoresis with laser-induced fluorescence detection.

Capillary electrophoresis with postcolumn laser-induced fluorescence detection was used to individually detect 6.0, 1.0, 0.5, and 0.2 num diameter polystyrene microspheres and individually measure their electrophoretic mobility. The analysis of a nanoliter-size volume from a microsphere suspension results in an electropherogram characterized by several narrow spikes in a well-defined migration time window. Each spike is associated with one microsphere because, when one single microsphere is introduced into the capillary by micromanipulation, the electropherogram has only one spike in the same migration time window. The distributions of individual measurements resulting from an electropherogram were used to evaluate the reproducibility from run to run, observe the effect of sodium dodecyl sulfate (SDS) added to the running buffer, and to investigate the origin of electrophoretic dispersion. As expected from the interactions between microspheres and SDS, the addition of this surfactant to the running buffer narrowed the range and shifted the average electrophoretic mobility to more negative values. After evaluating common sources of broadening in capillary electrophoresis, electrophoretic dispersion was attributed to microsphere heterogeneity. Unlike electropherograms displaying Gaussian-like profiles, the two-dimensional representations of the individual measurements provide a new alternative to evaluate and study electrophoretic-related properties of microspheres.

Electrophoresis, Capillary↗
PubMed2002

Uptake of poly(D,L-lactic-co-glycolic acid) microspheres by antigen-presenting cells in vivo.

Dendritic cells are the most potent antigen-presenting cells (APC) and the most effective stimulators of primary T cell responses. Based on the strong influence of the APC on the immune response, we investigated cellular uptake of a biodegradable antigen delivery system, poly(D,L-lactic-co-glycolic acid) (PLGA) microspheres, at two sites of injection: intraperitoneal and intradermal. We hypothesized that a fluorescent probe, tetramethylrhodamine labeled dextran, loaded in PLGA microspheres would be taken up by APCs and thereby provide a means for studying cellular uptake of PLGA microspheres in vivo. Phagocytic load and cell phenotype were determined using flow cytometry and confocal laser scanning microscopy. The results revealed cellular uptake of tetramethylrhodamine dextran loaded PLGA microspheres at both injection sites. After intraperitoneal immunization, the predominant cell phagocytosing PLGA microspheres in the peritoneal cavity was the macrophage whereas the intradermal immunization resulted in uptake of PLGA microspheres by dendritic cells. Hence, these results suggest that the profile for cellular uptake varies with the site of injection. More importantly, this study provides direct and conclusive evidence of uptake of PLGA microspheres by the most potent APC, the dendritic cell.

Animals↗
PubMed2003

Surface modification of PLGA microspheres.

Microspheres made of poly(lactic-co-glycolic acid) (PLGA) are biocompatible and biodegradable, rendering them a promising tool in the context of drug delivery. However, nonspecific adsorption of plasma proteins on PLGA micro- and nanospheres is a main limitation of drug targeting. Poly(L-lysine)-g-poly(ethylene glycol) (PLL-g-PEG), physisorbed on flat metal oxide surfaces, has previously been shown to suppress protein adsorption drastically. The goal of our work was to characterize the efficiency of the protein repellent character of PLL-g-PEG on PLGA microspheres and to show the feasibility of introducing functional groups on the PLGA microspheres via functionalized PLL-g-PEG. To quantify the adsorbed amount of protein, a semiquantitative method that uses confocal laser scanning microscopy (CLSM) was applied. The first part of the experiment confirms the feasibility of introducing specific functional groups on PLL-g-PEG-coated PLGA microspheres. In the second part of the experiment, PLL-g-PEG-coated PLGA microspheres show a drastic decrease of adsorbed proteins by two orders of magnitude in comparison to uncoated PLGA microspheres. Low protein-binding, functionalizable microspheres provide a fundamental basis for the design of drug delivery and biosensor systems.

Biosensing Techniques↗
PubMed2003

Preparation of antibacterial silver-doped silica glass microspheres.

Various types of inorganic substances doped with silver ions have been developed as antibacterial materials, and some have already been commercialized. Colorless and chemically durable materials that slowly release silver ions are, however, still need to be developed. The present authors have previously shown that when a silica glass doped with silver and aluminium ions is prepared using the sol-gel method, the resultant product is colorless, chemically durable, and slowly releases silver ions into water over a long period. The doped silica glass takes a form of microspheres <1 microm in diameter, it is easily mixed with organic polymers, and the mixture can be formed into a thin film or fine fibers, etc. We report on the preparation of silver doped silica glass microspheres having a diameter =1 microm, using the sol-gel method. Initially, tetraethoxysilane was partially prehydrolyzed by water in ethanol, and then aluminium triisopropoxide was added to the solution to form Si-O-Al bonds. Finally, an ammonia solution containing silver nitrate was added to form silica microspheres doped with silver ion together with aluminium ions. The results show monodispersed microspheres 0.4-0.6 microm in diameter were obtained with nominal compositions of Si/Al/Ag = 1/0.01-0.03/0.003-0.03, with a molar ratio of Al/Ag = 1-3.3. The microspheres were colorless, showed a high chemical durability, and slowly released silver ions into water at 37 degrees C. Microspheres with the composition Si/Al/Ag = 1/0.01/0.01 showed excellent antibacterial activity against Escherichia coli. The minimum inhibitory concentration (MIC) of the microspheres was 400, which is less than the MIC value (800) of commercial antibacterial materials.

Anti-Bacterial Agents↗
PubMed2005

Phagocytosis-mediated retroviral transduction: co-internalization of deactivated retrovirus and calcium-alginate microspheres by macrophages.

BACKGROUND: Efficiency of retrovirus-mediated gene transfer has been hampered by short retroviral half-life due to shedding of retroviral envelope proteins which is of utmost importance to the interaction between retrovirus and cell. METHODS: Calcium-alginate microspheres with average size of 780 nm were prepared by reverse emulsification and characterized by scanning electron microscopy and microelectrophoresis. To obtain deactivated retroviruses produced from 293 packaging cells, retrovirus-containing media were pre-incubated at 37 degrees C for 6, 12, 18, and 24 h, respectively. Murine J774A.1 macrophages were co-treated with Ca-alginate microspheres and deactivated retroviruses encoding the enhanced green fluorescent protein (eGFP) gene. Through phagocytosis, deactivated retroviruses and Ca-alginate microspheres were co-internalized into macrophages. After retroviral transduction for 24 and 48 h, the percentages of macrophages with eGFP expression were determined by bright-field and fluorescence microscopy. RESULTS: After 48-h incubation with Ca-alginate microspheres and deactivated retroviruses, phagosomes turned into large vacuoles occupied almost half of the cytoplasmic space. This was probably attributed to the erosion of Ca-alginate microspheres by destructive agents within vacuolar compartments and concomitant osmotic swelling. It was reasoned that deactivated retroviruses escaped such enlarged vesicles easily and underwent reverse transcription in the cytosol. The expression of eGFP in macrophages infected by retroviruses pre-incubated for 24 h in the presence of Ca-alginate microspheres was thereby augmented up to tenfold in comparison with the cells treated with 24-h deactivated retroviruses only. CONCLUSIONS: Ca-alginate microspheres performed as auxiliary agents for the enhancement of retrovirus-mediated gene transfer efficiency even though retroviruses had been deactivated due to the loss of envelope proteins.

Alginates↗
PubMed2005

Enhanced intracellular uptake and inhibition of NF-kappaB activation by decoy oligonucleotide released from PLGA microspheres.

BACKGROUND: Nuclear factor-kappaB (NF-kappaB) transcription factor regulates the expression of genes involved in immune response and inflammation. NF-kappaB activity can be efficiently inhibited by double-stranded oligodeoxynucleotides (ODNs). In the present study, we investigated the potential of poly(DL-lactic-co-glycolic acid) (PLGA) microspheres as delivery system for an ODN against NF-kappaB in RAW 264.7 macrophages stimulated with lipopolysaccharide (LPS). METHODS: Microspheres encapsulating ODN were prepared by the multiple emulsion/solvent evaporation technique and characterised in terms of size, morphology, encapsulation efficiency and in vitro release profile. In vitro uptake after 4 h and activity of ODN released from microspheres were evaluated in RAW 264.7 macrophages stimulated with LPS for 24, 48 and 72 h. RESULTS: We prepared microspheres with a high encapsulation efficiency showing a very slow and almost constant in vitro release of ODN for up to 1 month. ODN slowly released from microspheres translocated better into LPS-stimulated cells as compared with naked ODN. Incubation of cells with ODN-encapsulating microspheres resulted in a decrease of tumor necrosis factor-alpha (TNF-alpha) and nitrite production, inducible nitric oxide synthase (iNOS) protein expression, as well as NF-kappaB/DNA-binding activity. Similar results were obtained with naked ODN only at about 80 times higher concentrations. CONCLUSIONS: Our results suggest that PLGA microspheres could be a useful tool to improve pharmacokinetics of a ODN decoy to NF-kappaB and may represent a promising strategy to effectively inhibit the transcriptional activity of NF-kappaB in inflammatory process.

Animals↗
PubMed2002

X-ray powder diffractometric method for quantitation of crystalline drug in microparticulate systems. I. Microspheres.

Ethylcellulose microspheres containing tolnaftate (I) were prepared by the emulsion-solvent evaporation technique. An X-ray powder diffractometric method was developed to quantify the content of crystalline I in these microspheres. X-ray lines of I with d-spacings of 5.5 and 4.2 A were chosen for the quantitative analyses. Physical mixtures containing various weight fractions of I and blank (empty) microspheres were prepared and lithium fluoride (20% w/w) was added as the internal standard. The 5.5 and 4.3 A lines of I and the 2.3 A line of lithium fluoride were used for the quantitative analysis. A plot of the intensity ratio (intensity of the 5.5 A line of I/intensity of 2.3 A line of lithium fluoride) as a function of the weight percent of I in the mixture, resulted in a straight line. The crystalline content of I in the tolnaftate-loaded microspheres was determined using this standard curve. A second independent determination of the content of I was possible from the intensities of the 4.3 A line. The enthalpy of fusion of I, determined by differential scanning calorimetry (DSC), was also used as a measure of the crystalline content of I in the microspheres. The X-ray and DSC methods measure the content of crystalline I in the microspheres at room temperature ( approximately 25 degrees C) and at the melting point of I (111 degrees C), respectively. The total content of I in the microspheres was determined by HPLC. The DSC and X-ray results indicated that a substantial fraction of the incorporated I was dissolved in the ethylcellulose matrix.

Cellulose↗
PubMed2003

An experimental divalent vaccine based on biodegradable microspheres induces protective immunity against tetanus and diphtheria.

In an endeavor towards development of multivalent vaccines based on biodegradable microspheres, we tested the immunologic performance of several divalent microsphere formulations against tetanus and diphtheria. Microspheres were made by separate microencapsulation of tetanus and diphtheria toxoid in poly(lactide-co-glycolide) by either spray-drying or coacervation. Guinea pigs were subcutaneously immunized by a single injection of the divalent vaccines or, for control, an equivalent dose of a licensed vaccine containing both antigens adsorbed on aluminium hydroxide. All microsphere formulations were strongly immunogenic, irrespective of particle size and hydrophobicity. End point titers of ELISA antibodies, mainly of the IgG1 subtype, were comparable to those obtained after immunization with the licensed vaccine. The microspheres provided increasing levels of antibodies, during the 16 weeks of testing, and the antibodies were weakly polarized towards tetanus. The induced antibodies were also toxin neutralizing, as determined for both diphtheria (1-4 IU/mL) and tetanus (5-9 IU/mL) 8 weeks after immunization. These neutralization levels were several orders of magnitude above the level considered minimum for protection (0.01 IU/mL). When the animals were challenged with tetanus or diphtheria toxins 6 weeks after immunization, microsphere vaccines produced protective immunity that was comparable to or better than that induced by the licensed divalent vaccine. In conclusion, this study showed that a single administration of biodegradable microsphere vaccines provided protective immunity against diphtheria and tetanus, and that this immunization approach might be feasible for multivalent vaccines.

Animals↗
PubMed2004

Methotrexate loaded poly(L-lactic acid) microspheres for intra-articular delivery of methotrexate to the joint.

A controlled release delivery system that localizes methotrexate (MTX) in the synovial joint is needed to treat inflammation in rheumatoid arthritis (RA). The purpose of this work was to develop and characterize MTX loaded poly(l-lactic acid) (PLLA) microspheres and evaluate in vivo tolerability and MTX plasma concentrations following intra-articular injection into healthy rabbits. MTX loaded PLLA (2 kg/mole) microspheres were prepared using the solvent evaporation method and characterized in terms of size, molecular weight, thermal properties, and release rates into phosphate buffered saline (PBS) (pH 7.4) at 37 degrees C. Biocompatibility was evaluated by observing the swelling of the joints of the rabbits and histological analysis following the injection of the microspheres. MTX concentrations in the plasma and urine samples of rabbits were evaluated by high-performance liquid chromatography (HPLC). MTX loaded microspheres showed a rapid burst phase followed by a slow release phase. MTX loaded and control microspheres were biocompatible and plasma concentrations of MTX were tenfold higher in rabbits injected intra-articularly with free MTX than MTX microspheres. MTX microspheres may retain the drug in the joint by reducing clearance from the joint into the blood.

Animals↗
PubMed1986

Formation and characterization of cisplatin loaded poly(d,l-lactide) microspheres for chemoembolization.

Cisplatin, a slightly water soluble anticancer drug, has been incorporated into biodegradable poly(d,l-lactide) microspheres using the solvent evaporation process. The optimal experimental conditions to produce spherical and separate drug-loaded particles (45% cisplatin) were as follows: the dispersing phase was a mixture of 0.05% methylcellulose and 4% polyvinyl alcohol (8 mPa-s grade); and the optimal poly(d,l-lactide) concentration in the organic phase was found to be greater than or equal to 7.16%. Microscopic studies showed that increasing the drug content in the microspheres produced the appearance of rod-like crystals at the microparticle surface. In addition, the cisplatin crystals were found homogeneously distributed in the polymer matrix, even at a high drug content. Increased viscosities of the organic phase enhanced the mean microsphere size, while increasing the emulsifier concentration in the aqueous phase decreased the average particle size. The drug incorporation efficiency was markedly improved after saturation of the dispersing phase with cisplatin. It was also noted that the amount of drug incorporated increased with increasing mean microsphere diameter. The methylene chloride content entrapped within the microspheres was found to depend upon the microsphere size distribution and the cisplatin content. An increase of the microsphere system porosity, by the addition of 10% cyclohexane in the organic phase, caused a reduction in the residual methylene chloride content. Finally, the in vitro release kinetics of cisplatin were influenced by the drug loading.

Chemistry, Pharmaceutical↗
PubMed1994

In vitro and in vivo evaluation of thyrotrophin releasing hormone release from copoly(dl-lactic/glycolic acid) microspheres.

In vitro and in vivo release of thyrotrophin releasing hormone (TRH) from copoly(dl-lactic/glycolic acid) (PLGA) microspheres were evaluated. Factors affecting the TRH release from the microspheres were examined to clarify the release mechanisms by changing the medium composition in the in vitro release test. The hydrolysis rate of PLGA, the matrix-forming substance in the microspheres, was faster in acidic medium than in neutral medium. The release rate of TRH from the PLGA microspheres increased with the increase in the degradation rate of PLGA. A decrease in an osmolarity of the medium also caused an increase in the TRH release rate even though no significant change in PLGA degradation was observed. The effect of osmolarity appears to be characteristic of water-soluble drug-containing microspheres composed of hydrophobic polymer. The release rate of TRH from PLGA microspheres was largely affected by the medium composition in the in vitro release test. A proper choice of medium was found to be important for the estimation of in vivo release. The in vivo release rate of TRH from the PLGA microspheres following administration to rats correlated with the in vitro release in pH 7, 1/30 M buffer.

Animals↗
PubMed2004

In vitro release of vascular endothelial growth factor from gadolinium-doped biodegradable microspheres.

A drug delivery vehicle was constructed that could be visualized noninvasively with MRI. The biodegradable polymer poly(DL-lactic-co-glycolic acid) (PLGA) was used to fabricate microspheres containing vascular endothelial growth factor (VEGF) and the MRI contrast agent gadolinium diethylenetriamine pentaacetic acid (Gd-DTPA). The microspheres were characterized in terms of size, drug and contrast agent encapsulation, and degradation rate. The PLGA microspheres had a mean diameter of 48 +/- 18 microm. The gadolinium loading was 17 +/- 3 microg/mg polymer and the VEGF loading was 163 +/- 22 ng/mg polymer. Electron microscopy revealed that the Gd was dispersed throughout the microspheres and it was confirmed that the Gd loading was sufficient to visualize the microspheres under MRI. VEGF and Gd-DTPA were released from the microspheres in vitro over a period of approximately 6 weeks in three phases: a burst, followed by a slow steady-state, then a rapid steady-state. Biodegradable Gd-doped microspheres can be effectively used to deliver drugs in a sustained manner, while being monitored noninvasively with MRI.

Biodegradation, Environmental↗
PubMed1994

Synthesis, characterization, and use of immobilized polyacrolein microspheres in diagnostics: a model determination of alpha 1-antitrypsin in human serum.

Polyacrolein microspheres covalently coupled onto solid surfaces, e.g., glass, silicon crystals, and polystyrene, have been prepared and characterized. These surfaces were synthesized by derivatization of the substrate surfaces with SiCl3(CH2)3CN or Si(OEt)3-(CH2)4NH2. The terminal nitrile groups were then reduced to primary amine groups. Polyacrolein microspheres of various diameters (0.08 and 0.4 microns) were then covalently bound in a monolayer structure to the modified surfaces. This binding of the microspheres to the derivatized surfaces is achieved via polyvalent Schiff-base bonds formed by the interaction between aldehyde groups of the microspheres and omega-primary amine groups of the modified surfaces. Residual amine groups were blocked with acetic acid N-hydroxysuccinimide ester. The residual aldehyde groups of the immobilized microspheres can then be used for covalent binding of amino ligands, e.g., proteins, in a single step and at physiological pH (or any other desired pH). The potential use of the immobilized polyacrolein microsphere surfaces for diagnostics has been demonstrated by determination of alpha 1-antitrypsin in human serum with trypsin bound to the immobilized microspheres. The comparison between this new method for the determination of alpha 1-antitrypsin and the routine methods is discussed.

Acrolein↗