Biodegradable amphiphilic copolymers based on poly(epsilon-caprolactone)-graft chondroitin sulfate as drug carriers

The goal of this study was to develop a new type of core-shell micelles based on biocompatible and biodegradable amphiphilic copolymers, named PCL-CS, using chondroitin sulfate (CS) as a hydrophilic segment and poly(epsilon-caprolactone) (PCL) as a hydrophobic segment. The copolymers, prepared from the various compositions between CS and PCL, were characterized by Fourier transform infrared spectrometer, proton nuclear magnetic resonance spectrometer, and differential scanning calorimeter. The PCL-CS copolymers could be assembled into micelles using a simple emulsion. With the fluorescent probe technique, the critical micelle concentrations were obtained in the range of 1.26 x 10(-3)-8.86 x 10(-3) mg/mL. The spherical images of micelles were visualized in the presence of polyvinyl alcohol (PVA) with the use of the transmission electron microscope. The particle sizes of micelles were all smaller than 300 nm, neither aggregate nor change in hydrodynamic sizes after 15 days staying in solutions containing salts or PVA by dynamic light scattering. The intracellular uptake of KB cells incubated with PCL-CS micelles was evidenced by confocal laser scanning microscope upon loading fluorescein isothiocyanate labeled bovine serum albumin as a probe.     

In-situ formation of biodegradable hydrogels by stereocomplexation of PEG-(PLLA)8 and PEG-(PDLA)8 star block copolymers

Eight-arm poly(ethylene glycol)-poly(L-lactide), PEG-(PLLA)(8), and poly(ethylene glycol)-poly(D-lactide), PEG-(PDLA)(8), star block copolymers were synthesized by ring-opening polymerization of either L-lactide or D-lactide at room temperature in the presence of a single-site ethylzinc complex and 8-arm PEG (M(n) = 21.8 x 10(3) or 43.5 x 10(3)) as a catalyst and initiator, respectively. High lactide conversions (>95%) and well-defined copolymers with PLLA or PDLA blocks of the desired molecular weights were obtained. Star block copolymers were water-soluble when the number of lactyl units per poly(lactide) (PLA) block did not exceed 14 and 17 for PEG21800-(PLA)(8) and PEG43500-(PLA)(8), respectively. PEG-(PLA)(8) stereocomplexed hydrogels were prepared by mixing aqueous solutions with equimolar amounts of PEG-(PLLA)(8) and PEG-(PDLA)(8) in a polymer concentration range of 5-25 w/v % for PEG21800-(PLA)(8) star block copolymers and of 6-8 w/v % for PEG43500-(PLA)(8) star block copolymers. The gelation is driven by stereocomplexation of the PLLA and PDLA blocks, as confirmed by wide-angle X-ray scattering experiments. The stereocomplexed hydrogels were stable in a range from 10 to 70 degrees C, depending on their aqueous concentration and the PLA block length. Stereocomplexed hydrogels at 10 w/v % polymer concentration showed larger hydrophilic and hydrophobic domains as compared to 10 w/v % single enantiomer solutions, as determined by cryo-TEM. Correspondingly, dynamic light scattering showed that 1 w/v % solutions containing both PEG-(PLLA)(8) and PEG-(PDLA)(8) have larger "micelles" as compared to 1 w/v % single enantiomer solutions. With increasing polymer concentration and PLLA and PDLA block length, the storage modulus of the stereocomplexed hydrogels increases and the gelation time decreases. Stereocomplexed hydrogels with high storage moduli (up to 14 kPa) could be obtained at 37 degrees C in PBS. These stereocomplexed hydrogels are promising for use in biomedical applications, including drug delivery and tissue engineering, because they are biodegradable and the in-situ formation allows for easy immobilization of drugs and cells.     

Epidermal growth factor-conjugated poly(ethylene glycol)-block- poly(delta-valerolactone) copolymer micelles for targeted delivery of chemotherapeutics

Epidermal growth factor (EGF)-conjugated copolymer micelles were prepared from a mixture of diblock copolymers of methoxy poly(ethylene glycol)-block-poly(delta-valerolactone) (MePEG-b-PVL) and EGF-PEG-b-PVL for targeted delivery to EGF receptor (EGFR)-overexpressing cancers. The block copolymers and functionalized block copolymers were synthesized using PEG as the macroinitiator and HCl-diethyl ether as the catalyst. The MePEG-b-PVL and the carboxyl-terminated PEG-b-PVL (HOOC-PEG-b-PVL) copolymers were found to have molecular weights of 5940 and 5900, respectively, as determined by gel permeation chromatography (GPC) analyses. The HOOC-PEG-b-PVL copolymers were then activated by N-hydroxysuccinimide and subsequently reacted with EGF to form the EGF-PEG-b-PVL copolymers. The efficiency for the conjugation of EGF to the copolymer was found to be 60.9%. A hydrophobic fluorescent probe, CM-DiI, was loaded into both the nontargeted MePEG-b-PVL micelles and the targeted EGF-conjugated PEG-b-PVL micelles. The effective mean diameters of the CMDiI-loaded nontargeted and the CMDiI-loaded targeted micelles were found to be 32 +/- 1 nm and 45 +/- 2 nm, respectively, as determined by dynamic light scattering (DLS). The zeta potentials for the nontargeted micelles (no CM-DiI-loaded), CM-DiI-loaded nontargeted micelles, and CM-DiI-loaded targeted micelles were found to be -6.5, -8.7, and - 13.5 mV, respectively. Evaluation of the in vitro release of CM-DiI from the MePEG-b-PVL micelles in phosphate buffer saline (0.01 M, pH = 7.4) containing 10% (v/v) fetal bovine serum at 37 degrees C revealed that approximately 20% of the probe was released within the first 2 h. Confocal laser scanning microscopy (CLSM) analysis revealed that the targeted micelles containing CM-DiI accumulated intracellularly in EGFR-overexpressing MDA-MB-468 breast cancer cells following a 2 h incubation period, while no detectable cell uptake was observed for the nontargeted micelles. Results obtained from the confocal images were confirmed in an independent study by measuring the intracellular CM-DiI fluorescence in cell lysate. In addition, the presence of free EGF was found to decrease the extent of uptake of the targeted micelles. Nuclear staining of the cells with Hoechst 33258 indicated that the targeted micelles mainly localized in the perinuclear region and some of the micelles were localized in the nucleus. These results demonstrate that the EGF-conjugated copolymer micelles developed in this study have potential as vehicles for targeting hydrophobic drugs to EGFR-overexpressing cancers.     

Solubilization and controlled release of a hydrophobic drug using novel micelle-forming ABC triblock copolymers

Amphiphilic ABC triblock copolymers composed of monomethoxy-capped poly(ethylene glycol) (MPEG), poly(2-(dimethylamino)ethyl methacrylate) (DMA), and poly(2-(diethylamino)ethyl methacrylate) (DEA) have been synthesized by atom transfer radical polymerization (ATRP). These copolymers dissolve molecularly in acidic aqueous media at room temperature due to protonation of the tertiary amine groups on the DMA and DEA residues. On adjusting the pH with base, micellization occurred at pH 8, with the water-insoluble, deprotonated DEA block forming the hydrophobic cores and the MPEG and DMA blocks forming the hydrophilic micellar coronas and inner shells, respectively. This pH-induced micellization has been exploited to develop a solvent-free protocol for drug loading. A model hydrophobic drug, dipyridamole (DIP), which dissolves in acid but is insoluble above pH 5.8, was incorporated into the micelles by increasing the pH of an aqueous drug/copolymer mixture to 9. Both the empty and the drug-loaded micelles were characterized by dynamic light scattering and fluorescence studies. The interaction of both pyrene and DIP with the MPEG-DMA-DEA micelles was studied by fluorescence; both compounds had relatively high partition coefficients into the micelles, 4.5 x 10(5) and 1.5 x 10(4), respectively. Intensity-average micelle diameters ranged from 20 to 90 nm, depending on the polymer composition and concentration. Shorter MPEG blocks (Mn = 2000) produced larger micelles than longer MPEG blocks (Mn = 5000) due to the shift in the hydrophilic-hydrophobic balance of the copolymer. Transmission electron microscopy studies of the drug-loaded micelles indicated spherical morphologies and reasonably uniform particle size distributions, which is in marked contrast to the needlelike morphology observed for pure DIP in the absence of the copolymer. Experiments on controlled release demonstrated that DIP-loaded MPEG-DMA-DEA micelles act as a drug carrier, giving slow release to the surrounding solution over a period of days. Rapid release can be triggered by reducing the pH to reverse the micellization.     

Increased stability of malate dehydrogenase from Halobacterium salinarum at low salt concentration in reverse micelles

The stability of malate dehydrogenase (hMDH) from Halobacterium salinarum in aqueous medium at low salt concentrations (1 and 0.5 M NaCl) was studied at 4 degrees and 25 degrees C. The results showed that hMDH was more stable at the higher salt concentration and the low temperature. hMDH was introduced into reverse micelles of hexadecyltrimethylammonium bromide in cyclohexane with 1-butanol as co-surfactant. The hMDH stability in this system was studied at two omega(0) ([H(2)O]/[surfactant]) values and the effects of salt concentration, presence of substrate and dilution before or after its introduction into reverse micelles were examined. The results showed that the half-life of hMDH dissolved in buffer with 1 M NaCl was 12-50 days in reverse micelles (depending on the various conditions), in contrast to only about 1 day in aqueous medium at 25 degrees C. These observations indicate that reverse micelles provide a microenvironment that allows a much greater stability of this enzyme compared with an aqueous medium.     

Conjugation of arginine-glycine-aspartic acid peptides to poly(ethylene oxide)-b-poly(epsilon-caprolactone) micelles for enhanced intracellular drug delivery to metastatic tumor cells

An arginine-glycine-aspartic acid (RGD) containing model peptide was conjugated to the surface of poly(ethylene oxide)-block-poly(epsilon-caprolactone) (PEO-b-PCL) micelles as a ligand that can recognize adhesion molecules overexpressed on the surface of metastatic cancer cells, that is, integrins, and that can enhance the micellar delivery of encapsulated hydrophobic drug into a tumor cell. Toward this goal, PEO-b-PCL copolymers bearing acetal groups on the PEO end were synthesized, characterized, and assembled to polymeric micelles. The acetal group on the surface of the PEO-b-PCL micelles was converted to reactive aldehyde under acidic condition at room temperature. An RGD-containing linear peptide, GRGDS, was conjugated on the surface of the aldehyde-decorated PEO-b-PCL micelles by incubation at room temperature. A hydrophobic fluorescent probe, that is, DiI, was physically loaded in prepared polymeric micelles to imitate hydrophobic drugs loaded in micellar carrier. The cellular uptake of DiI loaded GRGDS-modified micelles by melanoma B16-F10 cells was investigated at 4 and 37 degrees C by fluorescent spectroscopy and confocal microscopy techniques and was compared to the uptake of DiI loaded valine-PEO-b-PCL micelles (as the irrelevant ligand decorated micelles) and free DiI. GRGDS conjugation to polymeric micelles significantly facilitated the cellular uptake of encapsulated hydrophobic DiI most probably by intergrin-mediated cell attachment and endocytosis. The results indicate that acetal-terminated PEO-b-PCL micelles are amenable for introducing targeting moieties on the surface of polymeric micelles and that RGD-peptide conjugated PEO-b-PCL micelles are promising ligand-targeted carriers for enhanced drug delivery to metastatic tumor cells.     

Core-cross-linked polymeric micelles as paclitaxel carriers

Cross-linkable di- and triblock copolymers of poly(epsilon-caprolactone) (PCL) and monomethoxyl poly(ethylene glycol) (MPEG) were synthesized. These amphiphilic copolymers self-assembled into nanoscale micelles capable of encapsulating hydrophobic paclitaxel in their hydrophobic cores in aqueous solutions. To further enhance their thermodynamic stability, the micelles were cross-linked by radical polymerization of the double bonds introduced into the PCL blocks. Reaction conditions were found to significantly affect both the cross-linking efficiency and the micelle size. The encapsulation of paclitaxel into the micelles was confirmed by the proton nuclear magnetic resonance (1H NMR) spectroscopy. Encouragingly, paclitaxel-loading efficiency of micelles was enhanced significantly upon micelle core-cross-linking. Both the micelle size and the drug loading efficiency increased markedly with increasing the PCL block lengths, no matter if the micelles were core-cross-linked or not. However, paclitaxel-loading did not obviously affect the micelle size or size distribution. The cross-linked micelles exhibited a significantly enhanced thermodynamic stability against dilution with aqueous solvents. The efficient cellular uptake of paclitaxel loaded in the nanomicelles was demonstrated by confocal laser scanning microscopy (CLSM) imaging. This new biodegradable nanoscale carrier system merits further investigations for parenteral drug delivery.     

Solution properties of gellan gum: change in chain stiffness between single- and double-stranded chains

Nine samples of gellan gum in the sodium form, ranging in weight-average molar mass from 3.47 x 10(4) to 1.15 x 10(5) at 40 degrees C, were investigated by static and dynamic light scattering and viscometry in 25 mM aqueous NaCl both at 40 and at 25 degrees C. The ratios of the molar mass at 25 degrees C (in the ordered state) to that at 40 degrees C (in the disordered state) were in the range of 1.99 to 2.07, supporting the scheme of the conformational transition of gellan gum between a disassociated single chain and an associated chain composed of two molecules. Focusing on the effects of polydispersity, the intrinsic viscosities, radii of gyration, and hydrodynamic radii were analyzed on the basis of unperturbed wormlike chain models. The persistence lengths were evaluated as 9.4 nm at 40 degrees C and 98 nm at 25 degrees C.     

Thermally induced conformation change of succinoglycan in aqueous sodium chloride

Static and dynamic light scattering, viscosity, and optical rotation measurements have been made at eight different temperatures between 25 and 75 degrees C on two succinoglycan samples (sodium salt) with weight-average molecular weights M(w) of 7.14 x 10(5) and 3.54 x 10(5) (at 25 degrees C) in 0.01 M aqueous NaCl to investigate the thermally induced order-disorder conformation change of the polysaccharide. Additionally, viscometry and polarimetry have been performed for a sodium salt sample (M(w) = 4.55 x 10(5) at 25 degrees C) whose M(w), z-average radius of gyration (z)(1/2), and hydrodynamic radius R(H) in the aqueous salt had been determined previously. As the temperature increases, M(w), (z)(1/2), R(H), and the intrinsic viscosity for every sample sharply decrease around 55 degrees C where the specific rotation at 300 nm sigmoidally increases. In particular, M(w) at 25 degrees C (i.e., in the ordered helical state) is twice as large as that at 75 degrees C (i.e., in the disordered state). These findings substantiate that the ordered structure is composed of two chains and hence is a double helix. Data analysis shows that this helix at 25 degrees C is characterized by an unperturbed wormlike chain with a helix pitch of about 2 nm (per repeating unit) and a persistence length of about 50 nm and that upon heating, it dissociates directly (i.e., in all-or-none fashion) to disordered chains of a similar contour length but with a much smaller persistence length of about 10 nm. The temperature dependence of the light scattering second viral coefficient is discussed in relation to the association of disordered chains in the cooling process.     

Bioreducible micelles self-assembled from amphiphilic hyperbranched multiarm copolymer for glutathione-mediated intracellular drug delivery

A new type of biodegradable micelles for glutathione-mediated intracellular drug delivery was developed on the basis of an amphiphilic hyperbranched multiarm copolymer (H40-star-PLA-SS-PEP) with disulfide linkages between the hydrophobic polyester core and hydrophilic polyphosphate arms. The resulting copolymers were characterized by nuclear magnetic resonance (NMR), Fourier transformed infrared (FTIR), gel permeation chromatography (GPC), and differential scanning calorimeter (DSC) techniques. Benefiting from amphiphilic structure, H40-star-PLA-SS-PEP was able to self-assemble into micelles in aqueous solution with an average diameter of 70 nm. Moreover, the hydrophilic polyphosphate shell of these micelles could be detached under reduction-stimulus by in vitro evaluation, which resulted in a rapid drug release due to the destruction of micelle structure. The glutathione-mediated intracellular drug delivery was investigated against a Hela human cervical carcinoma cell line. Flow cytometry and confocal laser scanning microscopy (CLSM) measurements demonstrated that H40-star-PLA-SS-PEP micelles exhibited a faster drug release in glutathione monoester (GSH-OEt) pretreated Hela cells than that in the nonpretreated cells. Cytotoxicity assay of the doxorubicin-loaded (DOX-loaded) micelles indicated the higher cellular proliferation inhibition against 10 mM of GSH-OEt pretreated Hela cells than that of the nonpretreated ones. As expected, the DOX-loaded micelles showed lower inhibition against 0.1 mM of buthionine sulfoximine (BSO) pretreated Hela cells. These reduction-responsive and biodegradable micelles show a potential to improve the antitumor efficacy of hydrophobic chemotherapeutic drugs.     

Degradation behavior of poly(epsilon-caprolactone)-b-poly(ethylene glycol)-b-poly(epsilon-caprolactone) micelles in aqueous solution

Poly(epsilon-caprolactone)-b-poly(ethylene glycol)-b-poly(epsilon-caprolactone) triblock copolymers were synthesized by the ring-opening polymerization of epsilon-caprolactone in the presence of hydroxyl-terminated poly(ethylene glycol) with different molecular weights, using stannous octoate catalyst. Micelles prepared by the precipitation method with these triblock copolymers exhibit a core-shell structure. The degradation behaviors of these core-shell micelles in aqueous solution were investigated by FT-IR, 1H NMR, GPC, DLS, TEM, and AFM. It was found that the degradation behavior of micelles in aqueous solution was quite different from that of bulk materials. The size of the micelles increased in the initial degradation stages and decreased gradually when the degradation period was extended. The caprolactone/ethylene oxide (CL/EO) ratio in micelles measured by NMR also shows an increase at the initial degradation stage and a decrease at later stages. The morphology of these micelles became more and more irregular during the degradation period. We explain the observed behavior by a two-stage degradation mechanism with interfacial erosion between the cores and the shells followed by core erosion.     

Comparative survival rates of human-derived probiotic Lactobacillus paracasei and L. salivarius strains during heat treatment and spray drying

Spray drying of skim milk was evaluated as a means of preserving Lactobacillus paracasei NFBC 338 and Lactobacillus salivarius UCC 118, which are human-derived strains with probiotic potential. Our initial experiments revealed that NFBC 338 is considerably more heat resistant in 20% (wt/vol) skim milk than UCC 118 is; the comparable decimal reduction times were 11.1 and 1.1 min, respectively, at 59 degrees C. An air outlet temperature of 80 to 85 degrees C was optimal for spray drying; these conditions resulted in powders with moisture contents of 4.1 to 4.2% and viable counts of 3.2 x 10(9) CFU/g for NFBC 338 and 5.2 x 10(7) CFU/g for UCC 118. Thus, L. paracasei NFBC 338 survived better than L. salivarius UCC 118 during spray drying; similar results were obtained when we used confocal scanning laser microscopy and LIVE/DEAD BacLight viability staining. In addition, confocal scanning laser microscopy revealed that the probiotic lactobacilli were located primarily in the powder particles. Although both spray-dried cultures appeared to be stressed, as shown by increased sensitivity to NaCl, bacteriocin production by UCC 118 was not affected by the process, nor was the activity of the bacteriocin peptide. The level of survival of NFBC 338 remained constant at approximately 1 x 10(9) CFU/g during 2 months of powder storage at 4 degrees C, while a decline in the level of survival of approximately 1 log (from 7.2 x 10(7) to 9.5 x 10(6) CFU/g) was observed for UCC 118 stored under the same conditions. However, survival of both Lactobacillus strains during powder storage was inversely related to the storage temperature. Our data demonstrate that spray drying may be a cost-effective way to produce large quantities of some probiotic cultures.     

Flexible chitin films: structural studies

Chitin gels were transformed into thin, flexible chitin films with minimal dimensional shrinkage and maximum flexibility and thickness in the range of 25-80 microm by a cold-press process. Solvent residue was removed by heating the films at 50 degrees C for 12 h, followed by rinsing in 95% ethanol. The crystallinity and mechanical properties of the flexible chitin films were found to be a function of the amount of shrinkage from the gel to the final film that was obtained. For 28-microm thick films with 30% shrinkage, transparency of up to 90% was found. X-ray diffractometry (XRD) showed that the number of diffraction peaks appearing at 2theta;=23 degrees and 2theta;=27 degrees became increasingly sharper with shrinkage. Topographical information obtained from scanning electron microscopy (SEM) and atomic force microscopy (AFM) attributed the structural morphology of the films to the formation of sub-microscopic micelles. Scanning transmission electron microscopy (STEM) showed that shrinkage resulted in coarser microstructure, affecting tensile properties, where the ductility and toughness were proportional to the amount of shrinkage. These flexible chitin films have potential as wound dressing materials.     

Stability of glucose 6-phosphate dehydrogenase complexed with its substrate and/or cofactor in aqueous and micellar environment

Inactivation of glucose 6-phosphate dehydrogenase (G6PDH) complexed with its substrate, glucose 6-phosphate (GP), and/or cofactor, NADP+, has been studied within the range 20-40 degrees C in three media: (a) 0.04 M NaOH-glycine buffer (pH 9.1); (b) Aerosol OT (AOT) reversed micelles in octane; and (c) Triton X-100 micelles in octane supplemented with 10% hexanol. The enzyme inactivation was characterized quantitatively by first order rate constants, kin (s-1). In the case of G6PDH-NADP+ complexes, the values of kin were independent of the initial concentrations of G6PDH, either in aqueous medium or AOT micelles. The values of kin for the complex G6PDH-GP were inversely related to the initial concentration of the enzyme, in both aqueous and micellar media. When inactivation of both complexes were studied in AOT micelles, minimum values of kin corresponded to the degree of hydration W0 = 16.7; at W0 > 16.7 and W0 < 16.7, kin increased. Within the range 20-40 degrees C, the values of kin measured for both complexes in aqueous medium were significantly lower than those measured in AOT micelles. Temperature dependences of kin were characterized by inflections in Arrhenius plots, which corresponded, depending on the medium, to certain temperatures from 33.6 degrees C to 40 degrees C. In all media studied, NADP+ complexes of the enzyme exhibited higher stability than their GP counterparts. The parameters of G6PDH and G6PDH-NADP+ melting, measured by differential scanning microcalorimetry (maximum temperature and half-width of the transition, enthalpy of denaturation, and van't Hoff enthalpy), provided unequivocal evidence of the higher stability of the complex as compared to that of the enzyme. In addition, this approach demonstrated that G6PDH undergoes destabilization in AOT micelles.     

Thermodynamics of the conversion of aqueous L-aspartic acid to fumaric acid and ammonia

The thermodynamics of the conversion of aqueous L-aspartic acid to fumaric acid and ammonia have been investigated using both heat conduction microcalorimetry and high-pressure liquid chromatography. The reaction was carried out in aqueous phosphate buffer over the pH range 7.25-7.43, the temperature range 13-43 degrees C, and at ionic strengths varying from 0.066 to 0.366 mol kg(-1). The following values have been found for the conversion of aqueous L-aspartateH- to fumarate2- and NH4+ at 25 degrees C and at zero ionic strength: K = (1.48 +/- 0.10) x 10(-3), DeltaG degrees = 16.15 +/- 0.16 kJ mol(-1), DeltaH degrees = 24.5 +/- 1.0 kJ mol(-1), and DeltaC(p) degrees = -147 +/- 100 J mol(-1) K(-1). Calculations have also been performed which give values of the apparent equilibrium constant for the conversion of L-aspartic acid to fumaric acid and ammonia as a function of temperature, pH and ionic strength.     

Structure and properties of enzyme graft copolymers: Temperature effects on HRP immobilization mechanism

The possibility of obtaining immobilized horseradish peroxidase (HRP) materials with K'(m) values close to that of the native enzyme, but with good thermal stability, was investigated. The photochemical reaction was used as the immobilization methodology. Temperature and catalyst concentration were found to be the main parameters able to control the immobilization reaction mechanism more than type of functional monomer, polymer-matrix, and enzyme-polymer ratios. By carrying out the immobilization reaction at 35 degrees C and using either bisacryloylpiperazine (BAP) or hexhydro-1,3,5-triacryloyl-s-triazine (HTsT) as the functional monomer, materials with a good thermal stabilization (the retained activity after 240 min at 60 degrees C was between 65-25%) as well as kinetic constants (0.6-0.8 x 10(-4)M) similar to that of the free enzyme (0.57 x 10(-4)M) were obtained. Since low K'(m) values were obtained also using a high polymer content (pBAP copolymers, 25%; pHTsT copolymers, 30%) and neither limitation to substrate diffusion nor a reduction of the enzyme mobility was found, the enzyme should be linked to the matrix during the last steps of monomer polymerization, and it should have an external disposition with respect to the support.     

Formation of core-shell type biodegradable polymeric micelles from amphiphilic poly(aspartic acid)-block-polylactide diblock copolymer

Poly(aspartic acid)-block-polylactide diblock copolymers (PAsp-b-PLAs) having both hydrophilic and hydrophobic segments of various lengths were synthesized. These PAsp-b-PLA diblock copolymers formed polymeric micelles consisting of a hydrophobic PLA core and a hydrophilic, pH-sensitive PAsp shell in aqueous solution. The effects of the segment length of both the PLA and the PAsp portions and the pH of the solution on the shapes and sizes of the PAsp-b-PLA polymeric micelles were investigated. The results indicated a balance between the effects of electrostatic repulsion, hydrogen bonding in the PAsp shell layer, and hydrophobic interactions in the PLA core determine the sizes of the PAsp-b-PLA polymeric micelles. Moreover, the PAsp-b-PLA polymeric micelles did not possess any cytotoxic activity against L929 fibroblast cells. The obtained polymeric micelle should be useful for biodegradable biomedical materials such as drug delivery vehicle.     

Methoxy poly(ethylene glycol)-block-poly(delta-valerolactone) copolymer micelles for formulation of hydrophobic drugs

Six amphiphilic diblock copolymers based on methoxy poly(ethylene glycol) (MePEG) and poly(delta-valerolactone) (PVL) with varying hydrophilic and hydrophobic block lengths were synthesized via a metal-free cationic polymerization method. MePEG-b-PVL copolymers were synthesized using MePEG with Mn = 2000 or Mn = 5000 as the macroinitiator. 1H NMR and GPC analyses confirmed the synthesis of diblock copolymers with relatively narrow molecular weight distributions (Mn/Mw = 1.05-1.14). DSC analysis revealed that the melting temperatures (Tm) of the copolymers (47-58 degrees C) approach the Tm of MePEG as the PVL content is decreased. MePEG-b-PVL copolymer aggregates loaded with the hydrophobic anti-cancer drug paclitaxel were found to have effective mean diameters ranging from 31 to 970 nm depending on the composition of the copolymers. A MePEG-b-PVL copolymer of a specific composition was found to form drug-loaded micelles of 31 nm in diameter with a narrow size distribution and improve the apparent aqueous solubility of paclitaxel by more than 9000-fold. The biological activity of paclitaxel formulated in the MePEG-b-PVL micelles was confirmed in human MCF-7 breast and A2780 ovarian cancer cells. Furthermore, the biocompatibility of the copolymers was established in CHO-K1 fibroblast cells using a cell viability assay. The in vitro hydrolytic and enzymatic degradation of the micelles was also evaluated over a period of one month. The present study indicates that the MePEG-b-PVL copolymers are suitable biomaterials for hydrophobic drug formulation and delivery.     

Solution properties of an alpha-(1-->3)-D-glucan from Lentinus edodes and its sulfated derivatives

A water-insoluble alpha-(1-->3)-D-glucan (A) from Lentinus edodes was fractionated into 13 fractions in dimethyl sulfoxide containing 0.25 M lithium chloride (0.25 M LiCl-Me(2)SO). Five fractions were treated with sulfur trioxide-pyridine complex at 25 degrees C to synthesize water-soluble sulfated derivatives (S-A). The weight-average molecular weights, M(w), and intrinsic viscosities [eta], of the samples A and S-A were determined by multi-angler laser light scattering (MALLS), and viscosity. The M(w) dependence of [eta] and of the radius of gyration (z)(1/2), was found to be represented approximately by [eta]=4.9 x 10(-2) M(w)(0.67) (cm(3) g(-1)), and (z)(1/2)=4.8 x 10(-2) M(w)(0.54) (nm) for the alpha-glucan in 0.25 M LiCl-Me(2)SO in the M(w) range from 7.24 x 10(4) to 4.21 x 10(5), and by [eta]=6.8 x 10(-4) M(w) 1.06 (cm(3) g(-1)), and (z)(1/2)=9.4 x 10(-4) M(w)(0.92) (nm) for the sulfated alpha-glucan in aqueous 0.5 M NaCl in the M(w) range from 5.92 x 10(4) to 1.42 x 10(5) at 25 degrees C. The results indicate that the alpha-(1-->3)-D-glucan exists as a flexible chain in 0.25 M LiCl-Me(2)SO, and its sulfated derivative in 0.5 M NaCl aqueous has stiffer chains than the original. (13)C NMR indicated that intramolecular hydrogen bonding occurred in the sulfated alpha-glucan, causing the observed chain stiffness.     

Self-assembled micelles of biodegradable triblock copolymers based on poly(ethyl ethylene phosphate) and poly(-caprolactone) as drug carriers

A series of novel amphiphilic triblock copolymers of poly(ethyl ethylene phosphate) and poly(-caprolactone) (PEEP-PCL-PEEP) with various PEEP and PCL block lengths were synthesized and characterized. These triblock copolymers formed micelles composed of a hydrophobic core of poly(-caprolactone) (PCL) and a hydrophilic shell of poly(ethyl ethylene phosphate) (PEEP) in aqueous solution. The micelle morphology was spherical, determined by transmission electron microscopy. It was found that the size and critical micelle concentration values of the micelles depended on both hydrophobic PCL block length and PEEP hydrophilic block length. The in vitro degradation characteristics of the triblock copolymers were investigated in micellar form, showing that these copolymers were completely biodegradable under enzymatic catalysis of Pseudomonas lipase and phosphodiesterase I. These triblock copolymers were used for paclitaxel (PTX) encapsulation to demonstrate the potential in drug delivery. PTX was successfully loaded into the micelles, and the in vitro release profile was found to be correlative to the polymer composition. These biodegradable triblock copolymer micelles are potential as novel carriers for hydrophobic drug delivery.