Xianmo Deng

Biodegradable poly(ε-caprolactone)-poly(ethylene glycol) block copolymers: characterization and their use as drug carriers for a controlled delivery system

Poly(epsilon-caprolactone)-poly(ethylene glycol) (PECL) copolymers were synthesized from polyethylene glycol (PEG) and epsilon-caprolactone (epsilon-CL) using stannous octoate as catalyst at 160 degrees C by bulk polymerization. The effect of the molecular weight of PEG and the copolymer ratio on the properties of the copolymers was investigated by (1)H-NMR, IR, DSC and GPC. PCL and PECL microspheres containing human serum albumin were elaborated by solvent extraction method based on the formation of double w/o/w emulsion. Microspheres were characterized in terms of morphology, size, loading efficiency, and the efficiency of microspheres formation. The results show that the microspheres prepared from PECL-10 and PECL-15 copolymers achieved the highest loading efficiency (about 50%) among all copolymers. These results indicate that the properties of copolymers could be tailored by adjusting polymer composition. It is suggested that these matrix polymers may be optimized as carriers in the protein (antigen) delivery system for different purposes.

Miscibility, crystallization and morphology of poly(β-hydroxybutyrate)/poly(d,l-lactide) blends

The miscibility, crystallization and morphology of poly(β-hydroxybutyrate) (PHB)/poly(d,l-lactide) (PLA) blends were investigated by means of differential scanning calorimetry, polarizing optical microscopy and scanning electron microscopy studies. The results indicated that PHB/PLA blends prepared by casting a film from a common solvent at room temperature were immiscible over the range of compositions studied, while the melt-blended sample prepared at high temperature showed some evidence of greater miscibility. The crystallization of PHB in the blends was affected by the level of addition of PLA. The thermal history caused a depression of the melting point and a decrease in the crystallinity of PHB in the blends. Compared with plain PHB, the blends exhibited a certain improvement in mechanical properties.

Investigation on a novel core-coated microspheres protein delivery system

Among the different approaches to achieve protein delivery, the use of polymers, specifically biodegraded, holds great promise. In this work, a new microsphere delivery system composed of alginate microcores surrounded by a biodegradable poly-DL-lactide-poly(ethylene glycol (PELA) was designed to improve the loading efficiency and stability of proteins. Alginate was solidified by calcium (MS-1), polylysine (MS-2) and chitosan (MS-3), respectively, to form different microcores. Human Serum Albumin (HSA), used as a model protein, was efficiently entrapped within the alginate microcores using a high-speed stirrer and then microencapsulated into PELA copolymer using a w/o/w solvent extraction method. DSC analysis of the microspheres revealed the efficient encapsulation of the alginate microcores, while the microcores were dispersed in the PELA matrix. SDS-PAGE results showed that HSA kept its structural integrity during encapsulation and release procedure. Microspheres were characterized in terms of morphology, size, loading efficiency, in vitro degradation and protein release. The degradation profiles were characterized by measuring the loss of microsphere mass, the decrease of polymer intrinsic viscosity and the reduction of PEG content of PELA coat. The release profiles were investigated from the measurement of protein presented in the release medium at various intervals. The results were that the degradation rate of these core-coated microspheres was MS-2>MS-1>MS-3. The extent of burst release from the core-coated microspheres in the initial protein release was lower than the 27% burst release from the conventional microspheres. In conclusion, the work presents a new approach for macromolecular drugs (such as protein, peptide drugs) delivery. The core-coated microspheres system may have potential use as a carrier for drugs that are poorly absorbed after oral administration.

Influence of process parameters on the protein stability encapsulated in poly-DL-lactide-poly(ethylene glycol) microspheres

Glucose oxidase (GOD) has been encapsulated as a model protein within poly-DL-lactide-poly(ethylene glycol) (PELA) microspheres to evaluate the activity retention during microencapsulation process. This paper was aimed to investigate the effect of process parameters, such as the preparation method, the used matrix polymer with different compositions, the solvent system and the addition of stabilizer on the structural integrity and activity retention of encapsulated protein. The stability of the protein released during in vitro assay was also assessed. The obtained results showed that the solvent extraction/evaporation method based on the formation of double emulsion w(1)/o/w(2) benefited the activity retention compared with the phase separation method based on the formation of w/o(1)/o(2). And in the emulsion-evaporation system most of the protein activity was lost during the first emulsification procedure to form primary emulsion w(1)/o (ca. 28%) and the second emulsification procedure to form the double emulsion w(1)/o/w(2) (ca. 20%), in contrast to other processes occurring during microspheres preparation. The matrix polymer and the solvent system in the oil phase had an impressive impact on the activity retention, while the addition of gelatin in the internal aqueous phase resulted in no major reduction of activity loss. GOD release from PELA microspheres exhibited a triphasic profile, that is, the initial burst release during the first day, the gradual release over about 1 month, and then the second burst release. The encapsulation of GOD in PELA microspheres was effective in reducing its specific activity loss. Sixty-seven per cent of the initial specific activity retention was detected for the released GOD from microspheres formulation during 1 week of incubation, but nearly all the activity was lost for GOD in solution incubated under the same condition. SDS-PAGE results showed that, although the activity loss was detected, no rough changes of molecular weight of GOD was observed during encapsulation procedure and the initial days of incubation into the in vitro release medium.

Optimization of preparative conditions for poly-DL-lactide- polyethylene glycol microspheres with entrapped Vibrio cholera antigens.

Poly-dl-lactide-polyethylene glycol (PELA) with different contents of polyethylene glycol(PEG) were synthesized and the PEG content was estimated according to the integral height of hydrogen shown in 1H-NMR. PELA microspheres containing V. cholera antigen, outer membrane protein (OMP) were prepared by a water-in-oil-in-water (W/O/W) based on solvent evaporation procedure. Antigen microspheres with smooth surface, suitable size for oral administration (0.5-5 microm), high loading efficiency (about 60%) and low level of residual solvent (lower than 20ppm) were obtained. Microspheres prepared from PELA with PEG content of about 10% achieved the highest loading efficiency among PELA copolymers and poly-dl-lactide (PLA) homopolymer, which suggested that microspheres size, morphology and the precipitation rate of polymer showed considerable relations with OMP loading efficiency. The regulation of the solvent components of the oil phase contributes to a stable emulsion W/O, and it is concluded that the stable emulsion W/O plays a significant role in improving the protein loading efficiency of obtained microspheres. The addition of stabilizer, such as gelatin and polyvinyl alcohol, into the internal water phase before emulsification produced no significant difference in OMP entrapment and microspheres size. A higher OMP loading efficiency was achieved by adding NaCl or adjusting the pH at the iso-electric point of OMP in the external water phase. It was indicated in vitro that PELA microspheres with smaller size showed larger extent of initial release and higher release rate, whereas microspheres with the diameter of 2.17 microm showed no apparent burst effect.

Investigation on process parameters involved in preparation of poly-dl-lactide-poly(ethylene glycol) microspheres containing Leptospira Interrogans antigens

Block copolymer, poly-DL-lactide-poly(ethylene glycol) (PELA) with 11.5% of poly(ethylene glycol) (PEG) content was prepared by bulk ring-opening polymerization using stannous chloride as initiator. PELA microspheres with entrapped Leptospira Interrogans antigens, outer membrane protein (OMP) were elaborated by solvent extraction method based on the formation of multiple w/o/w emulsion, and the resulting microspheres were characterized with respect to particle size, OMP entrapment and morphology characteristics. The purpose of the present study is to perform the optimization of preparative parameters for OMP-loaded PELA micropsheres to control particle size and improve the OMP encapsulation efficiency. Of all the parameters investigated, the polymer concentration of organic phase and the external aqueous phase volume play major roles on particle size, while the organic phase volume, internal aqueous phase volume and the addition of surfactant into the internal aqueous phase display considerable effects on OMP loading efficiency. A small volume of internal aqueous phase and intermediate volumes of organic phase and external aqueous phase were favorable to achieve micropsheres with a size of 1-2 microns and high antigen encapsulation efficiency (70-80%). In vitro OMP release profiles from PELA microspheres consist of a small burst release followed by a gradual release phase. The OMP release rate shows some relations with the porous and water-swollen inner structure of the microspheres matrix. The presence of surfactant in microspheres accelerates OMP release, but the OMP entrapment within microspheres shows limited effects on the release profile.

Investigation of nanocomposites based on semi-interpenetrating network of [l-poly (ε-caprolactone)]/[net-poly (ε-caprolactone)] and hydroxyapatite nanocrystals ☆

In this paper the semi-interpenetrating network (semi-IPN) technique was used for the first time to prepare bone implant composites containing hydroxyapatite (HAP) nanocrystals. The prepared nanocomposites are expected to combine several property advantages including good mechanical strength, modified degradation rate and excellent osteoconductivity. The semi-IPN matrix based on the linear poly (epsilon-caprolactone) (L-PCL) and the network poly (epsilon-caprolactone) (net-PCL) structures are revealed to be phase separation structures. The morphology of net-PCL is featured by intracrosslinked microdomains (1-10 microm) that further interconnect with each other to form the network over the whole sample. The net-PCL component is totally amorphous at room temperature for the nanocomposites containing HAP up to 12.3 wt%. Further, the crystallinity of L-PCL is greatly decreased due to the presence of net-PCL as compared with that for pure L-PCL. The incorporation of L-PCL into the net-PCL network could significantly improve the mechanical properties of pure net-PCL. A great improvement in mechanical properties is observed for the nanocomposites if the HAP content is increased to 15.8 wt%. This transition is in agreement with that the net-PCL component changes from amorphous state to crystalline state at this composition.

In vitro degradation and release profiles for poly-dl-lactide-poly(ethylene glycol) microspheres containing human serum albumin

Poly-dl-lactide-poly(ethylene glycol) (PELA) block copolymers containing same the content (10%) of polyethylene glycol (PEG) were synthesized with five different molecular weight of PEG by ring-opening polymerization. PELA microspheres containing human serum albumin (HSA) were elaborated by solvent extraction method based on the formation of double w/o/w emulsion. In vitro matrix degradation and protein release of these microspheres were performed in phosphate-buffered saline (PBS) (154 mM, pH 7.43). The degradation profiles were characterized by measuring the loss of microspheres mass, the decrease of polymer intrinsic viscosity, the decrease of pH value of degradation medium, the reduction of polymer number-average molecular weight (M(n)) and the change of molecular weight polydispersity (M(w)/M(n)). The release profiles were investigated from the measurement of protein presented in the release medium at various intervals. It showed that the matrix degradation and protein release profiles were highly polymer-dependent. The extent of burst release in the initial protein release increased with the decrease of molecular weight of PELA copolymer. It is suggested that these matrix polymers may be optimized as carriers in protein (antigen) delivery system for different purposes.

In vitro degradation and release profiles of poly‐DL‐lactide‐poly(ethylene glycol) microspheres with entrapped proteins

Poly-DL-lactide (PLA) and poly-DL-lactide-poly(ethylene glycol) (PELA) were produced by bulk ring-opening polymerization using stannous chloride as initiator. PLA, PELA microspheres, and PELA microspheres containing the outer membrane protein (OMP) of Leptospira interrogans with the size of 1.5–2 μm were prepared by a solvent evaporation process. In vitro degradation and release tests of PLA, PELA, and OMP-loaded PELA microspheres were performed in pH 7.4 buffer solution at 37°C. Quantitatively, the degree of degradation was monitored by detecting the molecular weight reduction, by evaluating the mass loss and the apparent degradation rate constant, and by determining the intrinsic viscosity and poly(ethylene glycol) content of retrieved polymer, while the release profile was assessed by measuring the amount of protein presented in the release medium at various intervals. Qualitatively, the morphological changes of microspheres were observed with scanning electron micrography. The observed relative rates of mass loss versus molecular weight reduction are consistent with a bulk erosion process rather than surface erosion for PELA microspheres. The introduction of hydrophilic poly(ethylene glycol) domains in copolymer PELA and the presence of OMP within microspheres show critical influences on the degradation profile. The OMP-loaded PELA microspheres present triphasic release profile and a close correlation is observed between the polymer degradation and the OMP release profiles. It is suggested that the polymer degradation rate, protein diffusion coefficient, and the water-swollen structure of microspheres matrix commonly contribute to the OMP release from PELA microspheres.

Biodegradable polymer blends of poly(3-hydroxybutyrate) and hydroxyethyl cellulose acetate

The melting and crystallization behaviour and phase morphology of poly(3-hydroxybutyrate) (PHB) and hydroxyethyl cellulose acetate (HECA) blends prepared by casting films have been studied by differential scanning calorimetry (d.s.c.), Fourier transform infra-red (FTi.r.), scanning electron microscopy and polarizing optical microscopy. The melting temperatures of PHB in the blends were independent of the blend composition with PHB contents above 20%. The melting enthalpy of the blends decreased with increase in the HECA component and was close to the additive value of the enthalpy of the two components. The glass transition temperatures of PHB in the blend were constant at about 8°C. No specific interaction between the two components was found by FTi.r. The crystallization of PHB in the blend was affected by the HECA component, especially in the PHB/HECA (20/80) blend. During the d.s.c. cooling run at a lower cooling rate, two separate transitions were found for PHB/HECA (80/20), (60/40) and (40/60) blends, which corresponded to the crystallization of PHB and the phase transition of HECA from an isotropic phase to a mesophase in the blends, respectively. The phase transformation of HECA from an isotropic phase to a mesophase was almost independent of the PHB component.