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At least 865 records · Page 48Linked to original sources

PubMed1995

Effectiveness of controlled release of a cyclophosphamide derivative with polymers against rat gliomas.

Most malignant gliomas grow despite treatment by standard chemotherapeutic agents. The authors explored the use of an innovative drug, 4-hydroperoxycyclophosphamide (4HC), delivered via a controlled-release biodegradable polymer to determine whether local delivery would enhance efficacy. This drug is an alkylator-type chemotherapeutic agent derived from cyclophosphamide. Unlike the parent drug, which requires activation by hepatic microsomes, 4HC is active in vitro. Two rat glioma cell lines, 9L and F98, were treated in cell culture with medium containing 4HC. Both cell lines were more sensitive to 4HC than to a nitrosourea, BCNU, an agent of established value in the local therapy of gliomas. Ninety Fischer 344 rats implanted with 9L or F98 gliomas were treated with an intracranial polymer implant containing 0% to 50% loaded 4HC in the polymer, and it was found that 20% 4HC-loaded polymers caused minimum local brain toxicity and maximum survival. These polymers were then used to compare the in vivo efficacy of 4HC to BCNU in rats implanted with 9L glioma. Animals with brain tumors treated with 4HC had a median survival span of 77 days compared to the median survival of 21 days in BCNU-treated animals and median survival of 14 days in untreated animals. Long-term survival for more than 80 days was 40% in the 4HC-treated rats versus 30% in the BCNU-treated rats. The polymer carrier used in this study was a copolyanhydride of dimer erucic acid and sebacic acid 1:1, which was able to maintain the hydrolytically unstable 4HC in a stable state for local delivery. Thus, it is concluded that 4HC-impregnated polymers provide an effective and safe local treatment for rat glioma.

Animals↗

PubMed2000

Bioconjugates of intelligent polymers and recognition proteins for use in diagnostics and affinity separations.

Polymers that respond to small changes in environmental stimuli with large, sometimes discontinuous changes in their physical state or properties are often called "intelligent" or "smart" polymers. We have conjugated these polymers to different recognition proteins, including antibodies, protein A, streptavidin, and enzymes. These bioconjugates have been prepared by random polymer conjugation to lysine amino groups on the protein surface, and also by site-specific conjugation of the polymer to specific amino acid sites, such as cysteine sulfhydryl groups, that are genetically engineered into the known amino acid sequence of the protein. We have conjugated several different smart polymers to streptavidin, including temperature-, pH-, and light-sensitive polymers. The preparation of these conjugates and their many fascinating applications are reviewed here.

Acrylamides↗

PubMed2002

Biodegradable synthetic polymer scaffolds for reinforcement of albumin protein solders used for laser-assisted tissue repair.

Laser tissue soldering has been investigated for several years by researchers in our laboratory as an alternative to conventional tissue fasteners, including sutures, staples and clips. Laser tissue soldering is a bonding technique in which protein solder is applied to the tissue surfaces to be joined, and laser energy is used to bond the solder to the tissue surfaces. Over the past four years we have been investigating the use of synthetic polymer membranes as a means for reinforcing the strength of tissue repairs formed using traditional laser tissue soldering techniques. The purpose of this study was to assess the influence of various processing parameters on the strength of tissue repairs formed using the reinforced solder. Biodegradable polymer membranes of specific porosity were fabricated by means of a solvent-casting and particulate-leaching technique, using three different poly(alpha ester)s: polyglycolic acid (PGA), polylactic acid (PLA) and poly(L-lactic-co-glycolic acid) (PLGA). In addition, several membranes were also prepared with poly(ethylene glycol) (PEG). The membranes were then doped with the traditional protein solder mixture of serum albumin and indocyanine green dye. Varied processing parameters included the polymer type, the PLGA copolymer blend ratio, the polymer/PEG blend ratio, the porosity of the polymer membrane and the initial albumin weight fraction. Variation of the polymer type had negligible effect on the strength of the repairs. Although it is known that alteration of the copolymer blend ratio of PLGA influences the degradation rate of the polymer, this variation also had no significant effect on the strength of the repairs formed. Increased membrane flexibility was observed when PEG was added during the casting stage. An increase in the porosity of the polymer membranes led to a subsequent increase in the final concentration of protein contained within the membranes, hence aiding in strengthening the resultant repairs. Likewise, an increase in the initial albumin weight fraction increased the strength of the resultant repairs.

Absorbable Implants↗

PubMed2002

Biodegradable polymer grafts for surgical repair of the injured spinal cord.

PURPOSE: Biodegradable polymers have been used in the surgical repair of peripheral nerves, but their potential for use in the central nervous system has not been exploited adequately. This article discusses concepts related to the engineering of a biodegradable polymer graft for surgical repair of the injured spinal cord and explores the potential means by which such a device might promote axon regeneration and functional recovery after spinal cord injury. CONCEPT: A biodegradable polymer implant with controlled microarchitecture can be engineered, and its composition can be optimized for implantation in the spinal cord. RATIONALE: The use of a biodegradable polymer implant has the dual advantages of providing a structural scaffold for axon growth and a conduit for sustained-release delivery of therapeutic agents. As a scaffold, the microarchitecture of the implant can be engineered for optimal axon growth and transplantation of permissive cell types. As a conduit for the delivery of therapeutic agents that may promote axon regeneration, the biodegradable polymer offers an elegant solution to the problems of local delivery and controlled release over time. Thus, a biodegradable polymer graft would theoretically provide an optimal structural, cellular, and molecular framework for the regrowth of axons across a spinal cord lesion and, ultimately, neurological recovery. CONCLUSION: Biodegradable polymer grafts may have significant therapeutic potential in the surgical repair of the injured spinal cord. Further research should be focused on the bioengineering, characterization, and experimental application of these devices.

Absorbable Implants↗

PubMedDate not supplied

Recent advances in polymer nanofibers.

Polymer nanofibers, with diameters in the nanometer range, possess larger surface areas per unit mass and permit easier addition of surface functionalities compared with polymer microfibers. Hence, polymer nanofiber mats are being considered for use as filters, scaffolds for tissue engineering, protective clothing, reinforcement in composite materials and sensors. Although some of these applications are in the development stage, a few have been commercially exploited. Research on polymer nanofibers, nanofiber mats, and their applications has seen a remarkable growth over the last few years. However, a review of the various issues related to these nanofibers has not been published. This article presents a review of the recent trends in the processing methods and characterization techniques for polymer nanofibers. Research challenges and future trends in the processing and characterization of polymer nanofibers are discussed in the article. Five processing methods have been examined in this review, namely drawing, template synthesis, phase separation, self-assembly, and electrospinning. Among these methods, electrospinning has been used to convert a large variety of polymers into nanofibers and may be the only process that has the potential for mass production. The structure, morphology, and geometry of nanofibers and the porosity and tensile properties of nanofiber mats can be investigated through conventional techniques and instruments. But new techniques are needed for the mechanical testing of single nanofibers. Although measurement of mechanical properties such as tensile modulus, strength, and elongation is difficult because of the small diameters of the fibers, these properties are crucial for the proper use of nanofiber mats.

Biocompatible Materials↗

PubMed1989

Scanning electron microscopic study of cell attachment to biodegradable polymer implants.

The biodegradable polymers--polylactic acid (PLA) and polyglycolic acid (PGA)--are currently being studied as carriers for bioactive bone regeneration compounds. The inclusion of osteo-inductive substances in poly-(DL, lactide-co-glycolide) copolymer alloplastic implants has been shown to enhance the repair of osseous defects. The purpose of this study was to examine, by SEM, the attachment relationship of biodegradable polymer implants to cells and tissue matrix. Three groups of copolymer implants were studied: (1) plain 50:50 PLA-PGA copolymer, (2) PLA-PGA copolymer with hydroxyapatite (HA), and (3) PLA-PGA copolymer with autolyzed, antigen-extracted (AA) bone particles. Polymer discs were surgically implanted into the pectoralis muscles of rats. At seven, 14, and 21 days post-implantation, the baskets were removed and the contents prepared for SEM. Results showed that at one week, implants were coated primarily with red and white blood cells in a fibrinoid clot. Degradation of the polymers was evidenced by irregular enlarging of polymer surface pores. At two and three weeks, polymers became lobular and then fibrinoid as degradation progressed. Inflammatory cell and red blood cell adhesions were increasingly replaced by fibroblasts and collagen matrix deposition. As polymer degradation progressed, AA and HA particles were exposed; however, the lack of cell or tissue adhesion in these areas suggests that degradation may be more influenced by the fluid environment than by direct cell attachment. Furthermore, degradation may inhibit direct cell attachment.

Animals↗

PubMed1981

Some methodical aspects and applications of freeze-etching in polymer research.

The freeze-etching method is used for investigating the morphology of aqueous polymer systems, e.g. network-like segregation structures of cryofixed polymer solutions and real network structures in polymer gels. The cooling rate, which is decisive for cryofixation of specimens, is measured by a thermocouple and a pyroelectric element in different coolants. The effect of the cooling rate on the freeze-etching structure of polymer solutions, polymer gels and a 10% aqueous glycerol solution as a model substance is determined and compared. The increase of the cooling rate in polymer gels results in maintaining the original network structure, in smaller segregation compartments in polymer solutions and in smaller crystallites in the cryofixed ice matrix.

Crystallization↗

PubMed1981

Prostaglandin releasing polymers - stability and efficacy.

In summary, PGI2 is approximately 3 orders of magnitude more potent than PGE1 in the prevention of platelet aggregation. Similarly PGE1 is an order of magnitude more potent than PGD2 (ID50's = 5.3 x 10(-10) M, 1.3 x 10(-7) M and 1.4 x 10(-6) M for PGI2, PGE1 and PGD2 respectively). Results from biological and infrared stability studies demonstrate that both PGI2 and PGE1 are stable for extended periods of time when dispersed within hydrophobic polymer matrices, an important consideration in the design of nonthrombogenic, prostaglandin controlled release polymers. Finally, both PGE1 and PGI2 controlled release polymers inhibit platelet aggregation in contacting blood, of which PGE1 produced greater platelet aggregation inhibition (90% inhibition) than did PGI2 (75% inhibition). However, PGE1 controlled release polymers significantly reduced platelet adhesion (11.25 +/- 3.68 platelets/mm2) compared to control polymers (50.65 +/- 8.8 platelets/mm2) while PGI2 controlled release polymers demonstrated no improvement in platelet adhesion (25.00 +/- 18.61 platelets/mm2) relative to control polymers (30.43 +/- 7.62 platelets/mm2). One cannot conclude that the lack of reduced platelet adhesion on the PGI2 controlled release surfaces is due to the instability of PGI2. The fact that significant inhibition of platelet aggregation in both blood fractions which contacted the PGI2 controlled release surfaces occurred substantiates that the released PGI2 was active. It must be concluded that PGI2 does not affect platelet adhesion. It is interesting to note that less platelets adhered to the PGI2 control PVC surfaces than on the PGE1 control PVC surfaces. The PGI2 control PVC surfaces were equilibrated with a TRIZMA buffer in 5% dextrose (to provide isotonicity) while the PGE1 control PVC surfaces were equilibrated in isotonic phosphate buffer saline.

Alprostadil↗

PubMed1996

Incorporation of a fluorocarbon polymer implanted at the posterior surface of the rabbit cornea.

An implant of porous expanded polytetrafluoroethylene (PTFE) in the corneal stroma allows fast cell colonization and can become translucent. We studied the behavior of the same polymer implanted in the anterior chamber of the rabbit eye and sutured to the posterior surface of the cornea. The expanded tetrafluoroethylene was provided as 200-micron thick sheets in 3 pore diameters (20, 50 and 80 microns). Disks (5 mm) were implanted in the anterior chambers of 20 rabbits and sutured to the posterior surface of the cornea. Histological and ultrastructural studies were performed after 3 and 4 months. Quantimetry was done on TEM images to analyze the fibrillar structure of the intercellular matrix inside and around the implanted polymer. The material was well tolerated. In all cases there was mild central corneal edema, which disappeared after 1 month. Mild neovascularization occurred in five cases, decreasing after 1 month. The polymer became translucent after 8 days. Keratocytes from the corneal stroma colonized the implant via breaks in the Descemet's membrane along the sutures. Quantimetry showed three types of fibrils inside and beside the polymer. Corneal endothelial cells regenerated over the fibroblasts and the polymer. This fluorocarbon polymer implanted in the anterior chamber and sutured to the posterior surface of the cornea was well tolerated, and there was real incorporation, with keratocytes producing collagen fibrils inside the polymer and endothelial cells forming a posterior cell monolayer. This is promising for the development of a keratoprothesis with posterior fixation.

Animals↗

PubMed1997

Reduction of surface-induced platelet activation on phospholipid polymer.

omega-Methacryloyloxyalkyl phosphorylcholine (MA-PC) polymers which have been synthesized with attention to the surface structure of a biomembrane show excellent blood compatibility, i.e., resistance to protein adsorption and blood cell adhesion. To clarify the stability of platelets in contact with the MAPC polymer surfaces, cytoplasmic free calcium concentration ([Ca2+],) in the platelets was measured. A platelet suspension was passed through a column packed with various polymer beads after treatment with plasma, and the [Ca2+]i in the platelets eluted from the column was measured. The [Ca2+]i in contact with the MAPC polymers, i.e., poly[2-methacryloyloxyethyl phosphorylcholine-co-nbutyl methacrylate (BMA)] (PMEB) and poly(6-methacryloyloxyhexyl phosphorylcholine-co-BMA) (PMHB), was less than that in contact with poly(BMA). However, poly(10-methacryloyloxydecyl phosphorylcholine-co-BMA) (PMDB) was not effective in suppressing the increase in [Ca2+]i, and thus was at the same level as in the poly(BMA). This result indicated that platelets in contact with PMEB or PMHB were less activated compared with those in contact with PMDB and poly(BMA). Moreover, the state of the platelets adhered to these polymer surfaces, both morphologically and immunologically, was examined. Scanning electron microscopic observation of the polymer surface after contact with a platelet suspension revealed that many platelets adhered and changed their shape on the poly(BMA). The numbers of adhetent platelets were reduced on all MAPC polymer surface. The relative amount of alpha-granule membrane glycoprotein (GMP-140) which appears on the cell membrane by activation of platelets on the PMEB surfaces was less than that on poly(BMA) and poly(2-hydroxyethyl methacrylate). These results suggest that PMEB and PMHB suppressed not only platelet adhesion but also activation of the platelets in contact with these surface.

Animals↗

PubMed1999

Evaluation of polymers based on a silicone backbone as pseudostationary phases for electrokinetic chromatography.

The feasibility of polymeric phases based on a silicone polymer backbone as pseudostationary phases for electrokinetic chromatography has been investigated. Silicone phases were studied because of the range of chemistries that could be developed based on these backbones, and because successful development of silicone phases would make it possible to employ much of the stationary phase chemistry developed in the past thirty years. Three silicone polymer structures have been investigated, but only one had sufficient aqueous solubility to permit application in electrokinetic chromatography. This phase was characterized by a variety of methods and was shown to be a mixture of partially hydrolyzed poly(bis-(3-cyanopropyl) siloxanes. When employed as a pseudostationary phase, this material provided selective and efficient separations. The electrophoretic mobility of the silicone polymer is greater than that of sodium dodecyl sulfate (SDS) micelles and poly(sodium 10-undecenylsulfate), providing an extended migration time range. A striking characteristic of the polymer is that the electrophoretic mobility is greater than typical electroosmotic mobilities. The chemical selectivity of the phase is significantly different from that of SDS micelles or poly(sodium 10-undecenylsulfate). The silicone phase is a more cohesive, basic and polar phase than SDS micelles. In buffers modified with a high concentration of organic solvents, the chromatographic properties of the silicone polymer are inferior to those of the poly(sodium 10-undecenylsulfate). The greatest limitation of silicone polymers for this application appears to be limited aqueous solubility, which will make it difficult to realize a family of such polymers with different chemical selectivities.

Acetates↗

PubMed2004

Structural studies of wheat flour glutenin polymers by CD spectroscopy.

A dissolution procedure of unreduced glutenin polymers of three wheat flour varieties (WRU 6981, Alisei 1, and Alisei 2) by sonication in the presence of SDS (sodium dodecyl sulphate), after the elimination of albumins, globulins, and gliadins, was achieved, and the molecular weight distribution of glutenin polymers obtained by this method was measured by matrix assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectrometry. A structural study by CD spectroscopy at different temperatures of WRU 6981 glutenin polymer and of 1Ax1 high-M(r) (relative molecular mass) glutenin subunit, which is the only high-M(r) subunit contained in WRU 6981 flour, was undertaken to understand if the information obtained from the single subunit were applicable to the total polymer. CD spectroscopy also has been employed to study the glutenin polymers obtained by Alisei 1 and Alisei 2 wheat flours; Alisei 1 biotype contained 1Bx7 and 1Dx2+1Dy12 high-M(r) subunits, whereas the Alisei 2 biotype contained only 1Bx7 and 1Dy12 subunits. A conformational study was undertaken by CD spectroscopy at different temperatures and in the presence of some chemical denaturant agents, such as urea and sodium dodecyl sulphate, in order to obtain information about their intrinsic stability and to verify if the 1Dx2 subunit presence determined a different structural behavior between Alisei 1 and Alisei 2 polymers. MALDI-TOF mass spectrometric experiments showed that the glutenin polymers molecular weights were in the mass range of 500000-5000000. CD spectra indicated that a single conformational state did not predominate in the temperature range studied but equilibrium between two distinct conformational states existed; moreover, all the changes induced by urea and by SDS followed a multistep transition process.

Biopolymers↗

PubMed2001

Effects of charged water-soluble polymers on the stability and activity of yeast alcohol dehydrogenase and subtilisin Carlsberg.

Remarkable increases in enzyme catalytic stability resulting from addition of charged water-soluble polymers have recently been reported, suggesting that use of these polymers may be an attractive general strategy for enzyme stabilization. To test the proposed hypothesis that coulombic forces between water-soluble polymers and enzymes are primarily responsible for enzyme stabilization, we examined the catalytic stability and activity of two enzymes in the presence of polymers differing in net charge. All polymers tested increased enzyme lifetimes, regardless of their net charge, suggesting that stabilization of these enzymes by water-soluble polymers is not solely dependent on simple electrostatic interactions between the polymers and enzymes.

Acrylic Resins↗

PubMed2005

Synthesis and properties of electrophosphorescent chelating polymers with iridium complexes in the conjugated backbone.

The synthesis of electrophosphorescent chelating polymers by Suzuki polycondensation of A-A- and B-B-type monomers is described, in which the fluorene-alt-carbazole (PFCz) segment is used as polymer backbone. By using alkyl-substituted ligands of iridium complex monomers, chelating copolymers with higher contents of iridium complex can be synthesized. Chemical and photophysical characterization confirm that the Ir complex is incorporated into the polymer backbone as one of the monomer repeat units by means of two 5-bromotolylpyridine ligands. Chelating polymers with Ir complexes in the conjugated polymer backbone show highly efficient energy transfer of excitons from the PFCz host segment to the Ir complex by an intramolecular trapping mechanism. The external quantum and luminous efficiencies of a device made with PFCzMppyIrhm4 copolymer reach 4.1 % ph/el (photons/electron) and 5.4 cd A(-1), respectively, at a current density of 32.2 mA cm(-2), an emission peak of 577 nm, and a luminance of 1730 cd cm(-2). Most important, the devices made from the chelating copolymers show no notable efficiency decay with increasing current density due to reduced concentration quenching and triplet-triplet (T-T) annihilation. This indicates that incorporation of the phosphorescent complex into the rigid conjugated polymer main chain is a new way to simultaneously realize high efficiency, long-term stability, and simple processing of phosphorescent polymer light-emitting diodes.

Journal Article↗

PubMed2005

Protein polymer drag-tags for DNA separations by end-labeled free-solution electrophoresis.

We demonstrate the feasibility of end-labeled free-solution electrophoresis (ELFSE) separation of DNA using genetically engineered protein polymers as drag-tags. Protein polymers are promising candidates for ELFSE drag-tags because their sequences and lengths are controllable not only to generate monodisperse polymers with high frictional drag, but also to meet other drag-tag requirements for high-resolution separations by microchannel electrophoresis. A series of repetitive polypeptides was designed, expressed in Escherichia coli, and purified. By performing an end-on conjugation of the protein polymers to a fluorescently labeled DNA oligomer (22 bases) and analyzing the electrophoretic mobilities of the conjugate molecules by free-solution capillary electrophoresis (CE), effects of the size and charge of the protein polymer drag-tags were investigated. In addition, the electrophoretic behavior of bioconjugates comprising relatively long DNA fragments (108 and 208 bases) and attached to uncharged drag-tags was observed, by conjugating fluorescently labeled polymerase chain reaction (PCR) products to charge-neutral protein polymers, and analyzing via CE. We calculated the amount of friction generated by the various drag-tags, and estimated the potential read-lengths that could be obtained if these drag-tags were used for DNA sequencing in our current system. The results of these studies indicate that larger and uncharged drag-tags will have the best DNA-resolving capability for ELFSE separations, and that theoretically, up to 233 DNA bases could be sequenced using one of the protein polymer drag-tags we produced, which is electrostatically neutral with a chain length of 337 amino acids. We also show that denatured (unfolded) polypeptide chains impose much greater frictional drag per unit molecular weight than folded proteins, such as streptavidin, which has been used as a drag-tag before.

DNA↗

PubMed1995

Adhesion and cytokine production by monocytes on poly(2-methacryloyloxyethyl phosphorylcholine-co-alkyl methacrylate)-coated polymers.

Human monocytes isolated from peripheral venous blood were assayed for their ability to adhere to various polymers. The culture supernatants were also assayed for the cytokines, interleukin-1 beta (IL-beta), interleukin-6 (IL-6), and tumor necrosis factor-alpha (TNF-alpha). The polymers evaluated for adherence and cytokine production included Pellethane, polyethylene and poly[n-butyl methacrylate (BMA)] coated with poly[2-methacryloyloxyethyl phosphorylcholine (MPC)-co-alkyl methacrylate] copolymers. In some experiments the test polymers were adsorbed with fibrinogen or IgG prior to the addition of monocytes. MPC copolymer-coated materials inhibited monocyte and macrophage adhesion after 1 and 8 days of culture relative to corresponding uncoated polymers and tissue culture polystyrene (TCPS). The degree of inhibition by coated Pellethane compared to uncoated Pellethane was the greatest, while inhibition of adhesion by coated poly(BMA) was the least compared to uncoated poly(BMA). However, adhesion was significantly decreased on both coated and uncoated poly(BMA) by day 8. While IL-1 beta, IL-6, and TNF-alpha release was variably influenced by polymer coating, release was consistently inhibited relative to TCPS on day 1. However, cytokine production was not inhibited compared to corresponding uncoated polymers on day 1. With or without protein preadsorption, IL-1 beta release was not detectable in the supernatants of any polymer on day 8, IL-6 production was diminished on day 8, and TNF-alpha production was sustained on day 8. Overall, MPC copolymer-coated and uncoated poly(BMA) were the least stimulating, while TCPS was the most stimulating.(ABSTRACT TRUNCATED AT 250 WORDS)

Biocompatible Materials↗

PubMed2003

Reduced adhesion of blood cells to biodegradable polymers by introducing phosphorylcholine moieties.

Aliphatic polyesters are believed to be good biocompatible polymers for tissue engineering because of their biodegradability and nontoxicity of the degradated products. However, it is necessary to reduce the nonspecific protein adsorption for the application of biodegradable polymers to drug delivery systems or antiadhesive membranes. We hypothesized that novel biodegradable polymers could be synthesized by introducing phosphorylcholine moieties into aliphatic polyesters. The L-lactide was polymerized in the presence of L-alpha-glycelophosphorylcholine (LGPC) using stannous octate as the catalyst. The molecular weight and crystallinity of poly(L-lactide) (PLLA)-based phospholipid polymers (PLLA-PC) decreased with an increase in the composition of the LGPC unit in the PLLA-PC. The hydrolysis of the PLLA-PC was evaluated by soaking the polymer membranes in a phosphate buffer solution. The rate of weight loss was increased with increasing the LGPC units in PLLA-PC. The surface analysis of the membranes using an X-ray photoelectron microscope showed the composition of phosphorylcoline groups on the surface. The amount of adsorbed protein and adherent blood cell on the polymer surface was decreased with introducing LGPC unit. PLLA-PC is a promising biodegradable polymer having blood compatibility and antiadhesive property.

Adsorption↗

PubMed2006

Influence of different polymers on the crystallization tendency of molecularly dispersed amorphous felodipine.

The ability of various polymers to inhibit the crystallization of amorphous felodipine was studied in amorphous molecular dispersions. Spin-coated films of felodipine with poly(vinylpyrrolidone) (PVP), hydroxypropylmethylcellulose acetate succinate (HPMCAS), and hydroxypropylmethylcellulose (HPMC) were prepared and used for measurement of the nucleation rate and to probe drug-polymer intermolecular interactions. Bulk solid dispersions were prepared by a solvent evaporation method and characterized using thermal analysis. It was found that each polymer was able to significantly decrease the nucleation rate of amorphous felodipine even at low concentrations (3-25% w/w). Each polymer was found to affect the nucleation rate to a similar extent at an equivalent weight fraction. For HPMC and HPMCAS, thermal analysis indicated that the glass transition temperature (T(g)) of the solid dispersions were not significantly different from that of felodipine alone, whereas an increase in T(g) was observed for the PVP containing solid dispersions. Infrared spectroscopic studies indicated that hydrogen bonding interactions were formed between felodipine and each of the polymers. These interactions were stronger between felodipine and PVP than for the other polymers. It was speculated that, at the concentrations employed, the polymers reduce the nucleation rate through increasing the kinetic barrier to nucleation.

Calorimetry, Differential Scanning↗