Amin Cao

Layered metal phosphonate reinforced poly(L-lactide) composites with a highly enhanced crystallization rate.

Layered metal phosphonate, zinc phenylphosphonate (PPZn), reinforced poly(L-lactide) (PLLA) composites were fabricated by a melt-mixing technique. The nonisothermal and isothermal crystallization, melting behavior, spherulite morphology, crystalline structure, and static and dynamic mechanical properties of the PLLA/PPZn composites were investigated. PPZn shows excellent nucleating effects on PLLA crystallization. With incorporation of 0.02% PPZn, PLLA can finish crystallization under cooling at 10 degrees C/min. The crystallization rate of PLLA further increases with increasing PPZn concentration. Upon the addition of 15% PPZn, the crystallization half-times of a PLLA/PPZn composite decrease from 28.0 to 0.33 min at 130 degrees C, and from 60.2 to 1.4 min at 140 degrees C, compared to the neat PLLA. With the presence of PPZn, the nuclei number of PLLA increases and the spherulite size reduces significantly. Through analysis of the crystal structures of PLLA and PPZn, it was proposed that the nucleation mechanism of the PLLA/PPZn system is epitaxial nucleation. The incorporation of PPZn has no discernible effect on the crystalline structure of PLLA. Moreover, PPZn has good reinforcement effects on the PLLA matrix. The tensile strength of the composite is enhanced with the addition of a relatively small amount of PPZn (<5%). The tensile and storage moduli of composites increase with increasing PPZn loadings, and they respectively improve by 28% and 34% with the incorporation of a 15% PPZn filler, as compared to the neat PLLA.

Studies on syntheses and physical properties of biodegradable aliphatic poly(butylene succinate-co-ethylene succinate)s and poly(butylene succinate-co-diethylene glycol succinate)s

Abstract Biodegradable aliphatic poly(butylene succinate-co-ethylene succinate) PBES and poly(butylene succinate-co-diethylene succinate) (PBDEGS) were synthesized from succinic acid and 1,4-butanediol/diethylene glycol through a direct polycondensation with titanium tetraisoproxide (TTP) and diphenylphosphinic acid (DPPA) as the co-catalysts. GPC and NMR results indicated molecular weight M n higher than 5.0×10 4 and 6.5×10 4 for the PBES and PBDEGS copolymers respectively, with ES/DEGS populations spanning the whole comonomer composition, and the BS and ES sequence distributions were found to be in close agreement with the random model. DSC analyses revealed that thermal and crystallization behaviour strongly depended on the corresponding comonomer composition for the PBES and PBDEGS copolymers, and that PDEGS was an amorphous poly(ester-ether). For thermal stability, TGA results indicated that thermal stabilities of the prepared PBDEGS significantly decreased with increasing the DEGS unit composition, while there was no remarked decrease detected for those of the PBES copolyesters. In addition, measurements of mechanical properties showed that incorporation of a small amount of ether groups into the DEGS unit could more remarkably improve the elongation behaviour of the semi-crystalline copolymer than that of the ES unit, and much larger elongation rates were exhibited for the copolymer samples bearing 47, 78 mol% ES and 8, 28 mol% DEGS.

Studies on syntheses and physical characterization of biodegradable aliphatic poly(butylene succinate-co-ε-caprolactone)s

Abstract Biodegradable aliphatic poly(butylene succinate-co-e-caprolactone) (PBSCs) were synthesized through a polycondensation with titanium tetraisoproxide (TTP), diphenylphosphinic acid (DPPA) and stannous octoate (Sn(Oct)2) as the novel co-catalysts. By means of gel permeation chromatography (GPC) and nuclear magnetic resonance spectrometer (NMR), it was revealed that the PBSC copolyesters had number average molecular weights Mn higher than 5.0×104, and that the polycondensations were in well agreement with a random copolymerization model. With respect to thermal properties, melting point, heat of fusion and glass transition temperature were found to decrease with increasing the CL/BS unit molar ratio up to 0.92, while thermal stability monotonously decreased with increasing the CL unit population spanning the whole CL unit composition. X-ray diffraction patterns indicated that the BS-rich/CL-rich PBSC organized the corresponding PBS/PCL-type of crystal structure. Moreover, it is worth to note that the PBS copolymerized with an appropriate amount of the minor CL component could significantly increase the fracture elongation of the resultant PBSC, and that mechanical properties of PBSC strongly depended on its CL unit population. In addition, biodegradabilities of PBSCs as well as PBS and PCL were tentatively assessed in a kind of compost soil, and the results suggest that chain flexibility may play an important role in the biodegradation as another factor besides the specificity of unit chemical structure and morphology.

Honeycomb-structured films by multifunctional amphiphilic biodegradable copolymers: surface morphology control and biomedical application as scaffolds for cell growth.

Recently, fabrication of functional porous polymer films with patterned surface structures at the scale from nanometer to micrometer has been attracting increasing interests in material science and nanobiotechnology. In this work, we present new preparation of two series of multifunctional amphiphilic copolymers and preparation of their microporous thin films on solid substrates. First, diblock dendritic poly(l-lysine)-b-poly(l-lactide)s and triblock dendritic poly(l-lysine)-b-poly(l-lactide)-b-dendritic poly(l-lysine)s (C1-C6) were synthesized through 4-dimethylaminopyridine (DMAP)-catalyzed living ring-opening polymerization of (l-)-lactide with (l-)-lysine dendron initiators, and their structures were characterized by nuclear magnetic resonance spectrometer (NMR), gel permeation chromatography (GPC) and matrix-assisted laser desorption/ionization Fourier-transformed mass spectra (MALDI-FTMS). Employing the breath-figure (BF) fabrication strategy, thin films of the synthesized amphiphiles (C1-C6) were drop-cast, and their surface topologies were examined by scanning electron microscopy (SEM) and atomic force microscopy (AFM), and the effects of new amphiphile structure and drop-casting parameters of amphiphile concentration, humidity and temperature on self-assembly of ordered porous surface were studied. Furthermore, the influence of surface energy of drop-casting substrates was additionally investigated. With a human cervical epithelial carcinoma cell line (HeLa), cytotoxicity of the prepared honeycomb-structured films by new amphiphile C6 was evaluated by thiazoyl-blue-tetrazolium-bromide (MTT) assay, and HeLa cell growth behavior with microporous amphiphile films as the scaffolds was also examined. It was found that tunable micropore diameter sizes and well ordered surface topologies of BF films could be achieved for the new prepared amphiphiles, and utilization of the honeycomb-like microporous films as scaffolds indicated favorable enhancement in cell proliferation. Therefore, the honeycomb-structured films by these biocompatible multifunctional amphiphiles may provide new materials as 3D-scaffold materials for potential application in tissue engineering and regeneration.

Dendritic Poly(l-lysine)-b-Poly(l-lactide)-b-Dendritic Poly(l-lysine) Amphiphilic Gene Delivery Vectors: Roles of PLL Dendritic Generation and Enhanced Transgene Efficacies via Termini Modification

As an effort to prepare new efficient gene delivery vectors, we have recently developed and reported an amphiphilic dendritic poly(L-lysine)-b-poly(L-lactide)-b-dendritic poly(L-lysine) D(2)-PLLA-D(2) with two-generation PLL dendrons and a PLLA block. In this work, we continued to explore the roles of dendritic PLL generation in DNA binding and intracellular delivery of gene, and a new series of amphiphilic dendritic poly(L-lysine)-b-poly(L-lactide)-b-dendritic poly(L-lysine)s D(n)-PLLA-D(n) (n = 3-5) were synthesized and were structurally characterized. Furthermore, plasmid DNA binding affinity for these cationic amphiphiles was examined by agarose gel electrophoresis and fluorescence titration assay in pure water and PBS buffer solution containing 150 mM NaCl (pH = 7.4), respectively. By dynamic light scattering (DLS) and transmission electronic microscopy (TEM), the interaction and complexation in between were investigated, concerning the DNA/vector polyplex particle morphologies and zeta potentials. Utilizing a human hepatocellular carcinoma cell-line SMMC-7721, cell toxicity, and gene transfection in vitro were explored. To further improve transgene efficiency for these synthetic cationic amphiphiles as gene delivery vectors, new structural DE(n)-PLLA-DE(n) (n = 2-3) were prepared through an amino termini modification of the D(n)-PLLA-D(n) (n = 2-3) with less toxic 4,7,10,13-tetraazatridecanoic acids, and gene transfection with these DE(n)-PLLA-DE(n) (n = 2-3) was examined with an alternative human gastric carcinoma cell-line HGC-27. As a result, the high plasmid DNA binding affinity, low cytotoxicity, and much enhanced transgene efficacy suggest a new possible clue to design effective synthetic gene delivery vectors with amphiphilic skeleton and less toxic polyamine building blocks.

Studies on comonomer compositional distribution of the bacterial poly(3-hydroxybutyric acid-co-3-hydroxypropionic acid)s and crystal and thermal characteristics of their fractionated component copolyesters

Abstract Two different kinds of natural poly(3-hydroxybutyric acid-co-3-hydroxypropionic acid)s [P(3HB-co-3HP)] with individual 3HP comonomer contents of 36.5 and 68.1 mol. % were biosynthesized by the bacteria Alcaligenes latus, fed on the cosubstrates of (R)-3-hydroxybutyric acid (3HBA) and 3-hydroxypropionic acid (3HPA). Employing the mixed chloroform/n-heptane solvent, the bacterial products were found to be fractionated into a number of fractions, and the presence of broad comonomer compositional distributions was unambiguously demonstrated. A deep insight into fractionation provided by means of g.p.c. and n.m.r. spectrometry confirmed that the fractionations were predominantly governed by the factor of comonomer composition, while the effect of molecular weight was not so significant. 13C n.m.r. investigation of carbonyl diad sequence distributions for the fractionated copolyesters along with the original bacterial product clearly revealed that the copolymerization occurring in the bacterial cell bodies was virtually in accordance with the random copolymerization model, and this feature was, however, obscured due to the presence of comonomer compositional distribution. Further, the crystal structures and thermal behaviors were investigated via WAXD and d.s.c. for the fractionated copolyesters with 3HP comonomer content spanning the whole comonomer composition. These investigations showed that both 3HB- and 3HP-rich copolyesters formed different 21 helix crystal structures, respectively, corresponding to the P(3HB) and P(3HP) types of lattice structures with distinctive fiber repeats, while those bearing intermediate 3HP content (about 48–75 mol.%) appeared as the amorphous state. The existence of the minor comonomer drastically retarded the crystallizability of either 3HB- or 3HP-rich copolyester chains; however, the glass transition behaviors reflected that the chain mobility in the amorphous state was enhanced linearly with the increase in the 3HP unit content. Moreover, the growth rates and morphologies of spherulites for the fractionated copolyesters revealed that the growth rates were markedly suppressed by the incorporated minor comonomer, and the uncrystallizable chains were likely trapped in the interfibrillar regions.

A study on biodegradable aliphatic poly(tetramethylene succinate): the catalyst dependences of polyester syntheses and their thermal stabilities

Abstract In this study, titanium alkoxide catalyst dependences of condensation polymerization, thermal degradation and stability were examined for a biodegradable aliphatic poly(tetramethylene succinate) (PTMS). A series of aliphatic PTMSs were synthesized through polycondensation of 1,4-butanediol and succinic acid in bulk with various amounts of titanium tetraisopropoxide (TTiPO) as the catalyst, and were further characterized by gel permeation chromatography, differential scanning calorimetry and thermogravimetric analysis. To reveal the presence and effect of catalyst residues, the crude product PTMS samples were precipitated in methanol from their chloroform solution, and were further refluxed in an acid solution to selectively hydrolyse the weak metal alkoxide moieties formed. Results of GPC analysis indicated that the original precipitated polyesters exhibited remarkably increasing molecular weights with a decrease in the catalyst/succinic acid feed molar ratio, and strong catalyst dependence of molecular weight and distribution were detected for the product polyesters. As for the acid deactivated samples, it was found that the higher the catalyst concentration used for polyester synthesis, the more remarkable was the decrease in molecular weight observed as compared with the corresponding original precipitated polyesters. Hence, a weak chain linker structure, such as (RO) n Ti(OP) m with m > 1 was reasonably suggested to be included in the macromolecular architecture of polyester, where RO and P respectively express the alkoxyl moiety and polyester chain. Thermal analysis showed similar melting points and glass transition temperatures for all polyester samples. In contrast, a strong catalyst dependence of thermal degradation and stability was found for the TTiPO catalysed polyesters, and can be interpreted for the formed weak (RO) n Ti(OP) m structures.

Interactions of new synthesized fluorescent cationic amphiphiles bearing pyrene hydrophobe with plasmid DNA: binding affinities, aggregation and intracellular uptake.

In this work, we prepared a novel series of cationic amphiphiles denoted as the Py-cations (Py-Gly, Py-Ala, Py-Cap, Py-G(1)-Lys and Py-G(2)-Lys) bearing fluorescent pyrene and various hydrocarbon linkers between the pyrene hydrophobe and cationic block. Employing these new cationic amphiphiles with pyrene as the fluorescent probe, the interactions between these Py-cations and plasmid DNA (pDNA) in distilled water and 0.1 M PBS buffer solution have been explored by means of UV-vis and fluorescent spectrometers, and ethidium bromide dye displacement and agarose-gel retardant assays were also implemented to evaluate their pDNA binding affinities in aqueous solution. Furthermore, the average sizes and morphologies of self-assembled Py-cation/pDNA lipoplex aggregates were examined by dynamic laser light scattering (DLS) and atomic force microscopy (AFM). It was found that these fluorescent cationic amphiphiles showed blue fluorescence emission of pyrene probe at λ = 340 nm in distilled water while their interactions with pDNA led to new strong green emission at λ = 490 nm, and this may be due to the stacking of pyrene and new formation of excimers via the rigid pDNA templated self-assembly. It was also revealed that the binding between new Py-cations and pDNA in aqueous solution was strongly influenced by the Py-cation hydrophobicity, charges of the cation and the presence of electrolytes. With respect to the Py-cation/pDNA aggregate morphologies, very interesting 1-D hybrid nanofibers were predominantly observed by AFM for the Py-Cap/pDNA aggregates. In addition, utilizing a COS-7 cell-line, in-vitro cellular uptakes of new cationic amphiphiles with pyrene probe were studied and visualized by fluorescent microscopy. As a result, this may provide a new approach to investigate the interactions between synthetic cationic lipids and nucleic acids, and pave an alternative clue to design new organic gene delivery carriers.

Solid structure and biodegradation of the compositionally fractionated poly(3-hydroxybutyric acid-co-3-hydroxypropionic acid)s

Abstract The solid structure and biodegradation behavior of the compositionally fractionated bacterial poly(3-hydroxybutyric acid-co-3-hydroxypropionic acid)s [P(3HB-co-3HP)] were examined. Utilizing the extracellular poly(3-hydroxybutyric acid) [P(3HB)]depolymerase purified from the bacterium strain Alcaligenes faecalis T1, enzymatic degradation behavior was investigated for P(3HB), poly(3-hydroxypropionic acid) [P(3HP)]and the fractionated P(3HB-co-3HP)s. It was revealed that P(3HB) and P(3HP) showed the distinguishable depolymerase concentration dependence of enzymatic degradation feature. For the fractionated copolyesters, the results indicated that P(3HB-co-3HP)s with higher 3HB contents which form P(3HB)-type of crystallites exhibited much higher enzymatic degradation rates than those of copolyesters with higher 3HP contents which form P(3HP)-type of crystallites, and that the amorphous copolyester could hardly be degraded. The 1H NMR analyses of the enzymatic degradation products revealed that P(3HB) was first degraded into dimers and then into monomers. In contrast, the presence of oligomers higher than dimers was suggested in the degradation products of P(3HP), and the 3HP content dependence of degradation products was confirmed for the fractionated P(3HB-co-3HP)s. In addition, environmental degradabilities were assessed by BOD method in the river water. The results confirmed the environmental degradabilities of P(3HB) and copolyesters except for P(3HP), indicating the inducing effect of 3HB comonomers on the biodegradation of 3HP units in copolyesters.

Amphiphilic cationic [dendritic poly(L-lysine)]-block-poly(L-lactide)-block-[dendritic poly(L-lysine)]s in aqueous solution: self-aggregation and interaction with DNA as gene delivery carriers.

A new series of triblock [dendritic poly(L-lysine)]-block-PLLA-block-[dendritic poly(L-lysine)]s (DL(2) -PLLA-DL(2) ) with PLLA block lengths of 11.5-26.5 and double 2-generation PLL dendrons DL(2) as model cationic amphiphiles were synthesized and characterized. Their CAC, self-aggregation and plasmid DNA binding affinities in pure water and PBS were studied. The PLLA block length dependence of particle size, morphology and ξ potential for organized pDNA/amphiphile polyplex aggregates were examined. Finally, toxicities of these DL(2) -PLLA-DL(2) amphiphiles and their polyplexes were assayed by MTT with HeLa, SMMC-7721 and COS-7 cells, and COS-7 cell luciferase and eGFP gene transfection efficacies with these amphiphiles as the delivery carriers were investigated.