In vitro degradation behaviour of non-porous ultra-fine poly(glycolic acid)/poly(l-lactic acid) fibres and porous ultra-fine poly(glycolic acid) fibres

The in vitro degradation behaviour of non-porous ultra-fine poly(glycolic acid)/poly(l-lactic acid) (PGA/PLA) fibres and porous ultra-fine PGA fibres was investigated. The non-porous ultra-fine PGA/PLA fibres were prepared by electrospinning of a PGA/PLA solution in 1,1,1,3,3,3-hexafluoro-2-propanol and the porous ultra-fine PGA fibres were obtained from them via selective removal of PLA with chloroform. Since PLA has a lower degradation rate than PGA, the degradation rates of the ultra-fine PGA/PLA fibres decreased with increasing content of PLA. The porous ultra-fine PGA fibres were degraded in vitro in the order of non-porous PGA > P-PGA/PLA(90/10) > P-PGA/PLA(70/30) > P-PGA/PLA(50/50) > P-PGA/PLA(30/70) due to autocatalytic hydrolysis.     

In vitro degradation and release behavior of porous poly(lactic acid) scaffolds containing chitosan microspheres as a carrier for BMP-2-derived synthetic peptide

To develop a novel tissue engineering scaffold with the capability of controlled releasing BMP-2-derived synthetic peptide, porous poly(lactic acid)/chitosan microspheres (PLA/CMs) composites containing different quantities of chitosan microspheres were prepared by a thermally induced phase separation method. FTIR analysis revealed that there were strong hydrogen bond interactions between the PLA and chitosan component. Introduction of less than 30% CMs (on PLA weight basis) did not remarkably affect the morphology and porosity of the PLA/CMs scaffolds. The compressive strength of the composite scaffolds increased from 0.48 to 0.66 MPa, while the compressive modulus increased from 7.29 to 8.23 MPa as the microspheres' contents increased from 0% to 50%. In vitro degradability investigation indicated that the dissolution of chitosan component was preferential than PLA matrix and the inclusion of CMs could neutralize the acidity of PLA degradation products. Compared with the rapid release from CMs, the synthetic peptide was released from PLA/CMs scaffolds in a temporally controlled manner, mainly depending on the degradation of PLA matrix. The promising microspheres based scaffold release system can be used to deliver bioactive factors for a variety of non-loaded bone regeneration and tissue engineering application.     

Elaboration of poly(ethyleneimine) coated poly( , -lactic acid) particles. Effect of ionic strength on the surface properties and DNA binding capabilities

Poly( , -lactic acid) (PLA)-based particles, obtained by the emulsification–diffusion process, were surface-modified by electrostatic adsorption of poly(ethylenimine) (PEI). The amount of immobilized PEI and the conformation of the polycation at the interface were dependent on the ionic strength of the media. In the absence of salt, or at low ionic strength, the adsorbed amounts of PEI, the surface charge and the critical concentration for coagulation (CCC) of the modified particles were lower than when the adsorption was achieved at elevated ionic strength. Moreover, at low salt concentration, isotherms were of Langmuir type, suggesting the formation of monolayers. The differences in PEI surface conformation had consequences on the DNA binding capacity of the particles, on the plasmid DNA conformation at the interface and on the DNA release in various media. When PEI was adsorbed in a 50 mM phosphate buffer, the amount of bound plasmid and the strength of binding were higher than when PEI was adsorbed in water. From these differences in physico-chemical properties, one can expect differences in transfection or immunization performances of the vectors.     

The synthesis of biodegradable graft copolymer cellulose-graft-poly(L-lactide) and the study of its controlled drug release

According to the concept of green chemistry and sustainable development, a new biodegradable copolymer comprised of hydrophobic poly(l-lactide) (PLLA) segments and hydrophilic cellulose segment (cellulose-g-PLLA) was designed and synthesized. The structure of the copolymer was characterized by (1)H NMR, FT-IR, (13)C NMR, DSC and WAXD. The cytotoxicity study shows that cellulose-g-PLLA exhibits good biocompatibility. The copolymer can self-assemble into micelles in water with the hydrophobic PLLA segments at the cores of micelles and the hydrophilic cellulose segments as the outer shells. Transmission electron microscopy (TEM) shows that the micelles exhibit nanospheric morphology within a size range of 30-80nm. The drug loaded micelles formed by the copolymer in aqueous media show sustained drug release which indicates their potential applicability in drug carrier.     

The role of polymer/drug interactions on the sustained release from poly(dl-lactic acid) tablets

The release profiles of model drugs (propranolol HCl, diclofenac sodium, salicylic acid and sulfasalazine) from low molecular weight poly(d,l-lactic acid) [d,l-PLA] tablets immersed in buffer solutions were investigated in an attempt to explore the mechanism of the related phenomena. It was confirmed that drug release is controlled by diffusion through the polymer matrix and by the erosion of the polymer. The pH of the surrounding medium influences the drug solubility as well as swelling and degradation rate of the polymer and therefore the overall drug release process. Physicochemical interaction between d,l-PLA and drug is an additional factor which influences the degree of matrix swelling and therefore its porosity and diffusion release process. Propranolol HCl shows extended delivery time at both examined pH values (5.4 and 7.4) and especially at pH 7.4 where release was accomplished in 190 days, most probably due to its decreased solubility at higher pH values. The acidic drugs gave shorter delivery times especially at pH 7.4. A slower drug release rate and more extended delivery time at pH 7.4 in comparison with that at pH 5.4 was recorded for tablets loaded with diclofenac sodium and salicylic acid. The opposite effect was observed with samples loaded with propranolol HCl.     

聚羟基乙酸(PGA)分子量测定的方法研究

基于目前测定聚羟基乙酸(PGA)分子量的常见方法:DMSO重结晶和急速冷却法,分别制得了两种待测样品。通过DSC、XRD表征了处理前后样品熔点、晶型、结晶度和晶粒大小的变化,比较了两种处理方法对PGA特性粘度的影响,考察了非晶态PGA在六氟异丙醇中的稳定性。结果表明:急速冷却法得到非晶态PGA可以有效地避免PGA在DMSO中的热降解情况,有利于准确测量PGA分子量;非晶态PGA在六氟异丙醇中降解速度较快,测分子量时,应当现配现测。根据Mark-Houwink方程,拟合了重均相对分子量和特性粘度之间关系Ln(η)=-10.90*Ln(Mw)+0.96,线性相关系数r=0.995,可以利用该方程通过测量PGA的特性粘度值来估算其重均相对分子量。     

Thermal degradation kinetics of the biodegradable aliphatic polyester, poly(propylene succinate)

The preparation of the biodegradable aliphatic polyester poly(propylene succinate) (PPSu) using 1,3-propanediol and succinic acid is presented. Its synthesis was performed by two-stage melt polycondensation in a glass batch reactor. The polyester was characterized by gel permeation chromatography, ¹H NMR spectroscopy and differential scanning calorimetry (DSC). It has a number average molecular weight 6880 g/mol, peak temperature of melting at 44 °C for heating rate 20 °C/min and glass transition temperature at −36 °C. After melt quenching it can be made completely amorphous due to its low crystallization rate. According to thermogravimetric measurements, PPSu shows a very high thermal stability as its major decomposition rate is at 404 °C (heating rate 10 °C/min). This is very high compared with aliphatic polyesters and can be compared to the decomposition temperature of aromatic polyesters. TG and Differential TG (DTG) thermograms revealed that PPSu degradation takes place in two stages, the first being at low temperatures that corresponds to a very small mass loss of about 7%, the second at elevated temperatures being the main degradation stage. Both stages are attributed to different decomposition mechanisms as is verified from activation energy determined with isoconversional methods of Ozawa, Flyn, Wall and Friedman. The first mechanism that takes place at low temperatures is auto-catalysis with activation energy E = 157 kJ/mol while the second mechanism is a first-order reaction with E = 221 kJ/mol, as calculated by the fitting of experimental measurements.     

Influence of the solvent on the spreading of poly[(D,L-lactic acid)-co-(glycolic acid)] monolayers

 The properties of mono layers of poly[(D,L-lactic acid)-co-(glycolic acid)] (PLA/GA) are strongly conditioned by the nature of the solvent from which they are spread. In this work, we studied the properties of PLA/GA films deposited on water from acetonitrile (a poor spreading solvent) and chloroform (a good one), observing marked differences with regard to the influence of the pH, temperature and ionic strength of the subphase. These differences were attributed to the structure of PLA/GA at the air/water interface, being pre-determined by its structure in the bulk spreading solvent (closely coiled in acetonitrile, unfolded in chloroform). Viscosity measurements on acetonitrile and chloroform solutions of PLA/GA, and the calculation of the corresponding intermolecular expansion factor, α, confirmed that PLA/GA was better solvated by chloroform than by acetonitrile, in which intramolecular interactions between polymer segments, and thus coiling, will therefore have predominated over polymer–solvent interactions. Received: 14 October 1996 Accepted: 7 January 1997     

Silkworm silk/poly(lactic acid) biocomposites: Dynamic mechanical, thermal and biodegradable properties

Silkworm silk/Poly(lactic acid) (silk/PLA) biocomposites with potential for environmental engineering applications were prepared by using melting compound methods. By means of Dynamic mechanical analysis (DMA), Differential scanning calorimetry (DSC), Thermogravimetric analysis (TGA), Coefficient of thermal expansion test, Enzymatic degradation test and Scanning electron microscopy (SEM), the effect of silk fiber on the structural, thermal and dynamic mechanical properties and enzymatic degradation behavior of the PLA matrix was investigated. As silk fiber was incorporated into PLA matrix, the stiffness of the PLA matrix at higher temperature (70-160 °C) was remarkably enhanced and the dimension stability also was improved, but its thermal stability became poorer. Moreover, the presence of silk fibers also significantly enhanced the enzymatic degradation ability of the PLA matrix. The higher the silk fiber content, the more the weight loss.     

Controlled release of atenolol from freeze/thawed poly(vinyl alcohol) hydrogel

Physically crosslinked polymeric films containing atenolol drug were formulated and the release of the drug was evaluated with view to investigate the feasibility of these films as drug delivery systems. Freezing and thawing process for PVA was used to prepare a controlled release device for atenolol drug. The process included incorporation of the drug into PVA film during the freezing and thawing process. The PVA has used a molecular weight of 125 k and degree of saponification of 98. Various amounts of the atenolol drug were incorporated into the freeze/thawed PVA. The in vitro release behavior of atenolol from these films was investigated. The drug release profiles from the polymeric formulations indicated initial high rate of release followed by slow rate of the release. The release of atenolol increased with increasing drug concentration in the film. The results showed the feasibility of the use of freezing and thawing technique to control the release of atenolol drug from PVA.     

Preparation and characterization of biodegradable gelatin-PAAm-based IPN hydrogels for controlled release of maleic acid to improve the solubility of phosphate fertilizers

In this study, interpenetrating polymer network (IPN) hydrogel systems including maleic acid (MA) were constituted to improve the solubility of phosphate fertilizers. A series of full and semi-IPN hydrogels were prepared from various gelatin/polyacrylamide mixtures by using two different cross-linkers. The effects of polymer composition on the morphological structures and swelling behaviors of the hydrogels were investigated. The swelling values of all hydrogels were found to be in between 435% and 830%. MA release from load0ed hydrogels was followed and it was determined that MA-loaded hydrogels efficiently decreased pH and improved the solubility of Ca₃(PO₄)₂ in releasing medium.     

Effect of molecular weight on thermal degradation mechanism of the biodegradable polyester poly(ethylene succinate)

A series of aliphatic polyesters, in particular poly(ethylene succinate), having different molecular weights, were synthesized from succinic acid and ethylene glycol, following the melt polycondensation process. Intrinsic viscosities (IV), GPC, DSC, ¹H NMR and carboxylic end group measurements were used for their characterisation. From thermogravimetric analysis, it was concluded that the molecular weight of polyesters achieved during polycondensation are strongly related to thermal stabilities of initial oligomers. In order to synthesise high molecular weight polyesters, the number average molecular weight of oligomers must not be lower than 2300–3000 g/mol, since thermal decomposition begins at temperatures lower than 200 °C. However, even in that case, polycondensation temperatures must not exceed 230–240 °C. From TGA studies, it was found that sample having different molecular weights could be divided into two groups characterized by different thermal stability. In the first group, belong samples with intrinsic viscosity of IV = 0.08 dL/g and in the second one all the other samples (IV > 15 dL/g). From kinetic analysis of thermal degradation, it was found that degradation of all polyesters takes place in three stages, its one corresponding to a different mechanisms. Degradation of samples with low molecular weight is more complex that that of polyesters having high molecular weights. The values of the activation energy and the exponent n for the two groups of samples—with different molecular weight—are similar, regarding the first two mechanisms, while there is an alteration in the case of the third mechanism.     

Rapid controlled hydrolytic degradation of poly(l-lactic acid) by blending with poly(aspartic acid-co-l-lactide)

Although poly(lactic acid) is known as a biodegradable polymer, its hydrolytic degradation is extremely slow, taking years in water and in the human body. In this study the effects of blending oligomeric poly(aspartic acid-co-lactide) (PALs) on the hydrolytic degradation of poly(l-lactic acid) (PLLA) were studied in detail. It was found that the addition of PAL did not accelerate the hydrolysis of the PLLA in air (25 °C, 60% relative humidity), but significantly accelerated it in a phosphate buffer solution. The degradation rate becomes higher for the blends containing PAL with higher molar ratios of lactide to aspartic acid units, [LA]/[Asp], when PLLA/PAL blends prepared with different PALs are compared at the same PAL concentration. TEM results, in which the distribution of PALs with higher [LA]/[Asp] occurs at a smaller scale in blends, imply that higher miscibility of the PAL with PLLA results in higher contact area between the components, thereby accelerating the degradation efficiently.     

Carboxymethylcellulose-coated magnesium-layered hydroxide nanocomposite for controlled release of 3-(4-methoxyphenyl)propionic acid

Carboxymethylcellulose (CMC) acts as a coating material for a magnesium-layered hydroxide-3-(4-methoxyphenyl)propionate (MLH-MPP) nanocomposite via spontaneous self-assembly. The resulting product is called a magnesium-layered hydroxide-3-(4-methoxyphenyl)propionate/carboxymethylcellulose (MLH-MPP/CMC) nanocomposite. The XRD pattern of the MLH-MPP/CMC nanocomposite showed that MPP was maintained in the interlayers of the MLH, thus confirming that CMC is only deposited on the surface of the MLH-MPP nanocomposite. These findings were also supported by FTIR spectra, SEM and TEM. TGA data showed that the thermal stability of the intercalated MPP was significantly enhanced compared to pure MPP and uncoated nanocomposite. The release of MPP from the interlayers of MLH-MPP/CMC nanocomposite showed slower release than did uncoated nanocomposite and followed pseudo–second-order kinetics. Since the herbicide, MPP was released from the synthesised nanocomposite in a sustained manner, thus, it has excellent potential to be used as a controlled-release herbicide formulation.     

Compatibilization of polypropylene/poly(glycolic acid) blend with maleated poe/attapulgite hybrid compatibilizer: Evaluation of mechanical,thermal, rheological,and morphological characteristics

In this work, the compatibilization effects of hybrid maleated POE/attapulgite hybrid compatibilizer (M-POE/ATP) on the immiscible polypropylene/poly(glycolic acid) (PP/PGA) blends was investigated. The hybrid compatibilizer integrating strengthening, toughening and compatibilization functions was prepared via one-step reactive extrusion using peroxidated ATP as the initiator. Then, the effects of compatibilizer dosage on the mechanical, thermal, rheological and morphological characteristics of blends were evaluated in detail. It was found that the hybrid compatibilizer resulted in the significantly enhanced compatibility and mechanical performance. Increased amount of compatibilizer content fractionated and almost wholly suppressed the crystallization process of PGA. The compatibilized blends showed higher thermal stability than pure PGA, and lower storage modulus and complex viscosity at higher shearing frequency. PGA in the blends presented a much lower degradation rate, which lead to the higher strength retention of 81% for the blend with 4 wt% of compatibilizer in buffer solution after 35 days.     

Novel method to characterize the hydrolytic decomposition of biopolymer surfaces

Present pharmaceutical research is focused on the development, modification and characterisation of new drug delivery systems. Among the many different substances, biodegradable polymers and copolymers are of practical importance, especially if their degradation byproducts are non-toxic. The polymeric drug carriers are not easily wettable by water or aqueous solutions, i.e. they are hydrophobic. This surface hydrophobicity is unfavourable for keeping drug carriers circulating in the blood long enough to release the drug so that it reaches its target. Therefore, copolymers with components of different hydrophobicity were introduced, to make them less hydrophobic and hence more suitable for drug delivery in the human body. Exploratory experiments with one homopolymer, , -poly(lactic acid), , -PLA and two of its copolymers, , -poly(lactic/glycolic acid), and , -PLGA with 85/15 and 50/50 copolymer ratios were carried out. Films of these substances were prepared by dip coating onto hydrophobic and hydrophilic substrates. The changes in wettability of the polymer layers, caused by the direct contact with an aqueous environment (soaking the samples in distilled water), have been studied to model the hydrolytic decomposition of polymer surfaces and to follow the changes in their wettability by dynamic contact angle measurements in a non-destructive manner. It was found that each polymer film became less hydrophobic (dynamic contact angles decreased) and more heterogeneous as the decomposition progressed with time. Increasingly significant decreases in contact angles were observed for the copolymer films containing 15 and 50% glycolic acid, during the 50–80-day-long study. These findings were supported by gel chromatographic analysis of the soaking liquids. It was concluded that the homopolymer layer of , -PLA was the most resistant to hydrolysis and the stability of copolymer films decreased with increasing glycolic acid ratio in the copolymers. This is accordance with the fact that the less crystalline poly(glycolic acid) is more hydrophilic and hence less resistant to hydrolytic decomposition, than the poly(lactic acid). The effect of pH on the rate of hydrolysis of polymer films was also established; the influence of pH on the decomposition was best demonstrated, again, for the copolymer with 50/50 component ratio. The outcome of these experiments showed that the contact angle measuring method enables us to detect, follow and interpret the hydrolytic decomposition of biopolymer substances in a non-invasive manner.     

Fracture evaluation of plasticized polylactic acid / poly (3-HYDROXYBUTYRATE) blends for commodities replacement in packaging applications

Nowadays, scientific and technological efforts are being carried out to diminish serious ecological problems caused by indiscriminate use of non-biocompostable polymers in the packaging industry. In this sense, novel biodegradable blends of different composition based on poly(lactic acid) (PLA), poly(3-hydroxybutyrate) (PHB) and tributyrin (TB) are developed and here proposed as an eco-friendly alternative. Materials are characterized by fracture experiments under quasi-static and biaxial impact loading. Fracture behavior is analyzed together with thermal, tensile and water permeation properties to evaluate their potential in-service performance. TB_PLA/PHB blends with 15 wt% TB exhibit better permeation and fracture toughness than currently used bio-based polymers, being in the range of polyethylene properties. Results highlight the potential of these new blends broadening the current application field of PLA.     

Thermal degradation and their kinetics of biodegradable poly(butylene succinate-co-butylene terephthate)s under nitrogen and air atmospheres

In this study, thermal degradation and their related kinetics have been investigated mainly by means of thermal gravimetrical analyzer (TGA) under the dynamic nitrogen and air atmospheres for the chemically prepared biodegradable aliphatic-aromatic copolyesters of poly(butylene succinate-co-butylene terephthalate) (PBST). To further shed new lights on the comonomer molar composition and experimental condition dependences of thermal degradation kinetics, the as-known Friedman model was at first applied to quantitatively evaluate the kinetic parameters in terms of activation energy (E), degradation reaction order (n) and the frequency factor (Z). The results clearly demonstrated that thermal stabilities of these PBST copolyesters were substantially enhanced with the incorporation of more rigid butylene terephthalate comonomer, and tended to be much better in nitrogen than in air. Furthermore, the Friedman, Freeman-Carroll and Chang models were concurrently employed to quantitatively evaluate the thermal degradation kinetic parameters of the PBST copolyesters in nitrogen at different heating rates of 1, 2 and 5 K/min. It was found that the thermal degradation kinetic parameters for the PBST copolyesters were strongly dependent on the heating rate and calculating models. In addition, life-time parameters of the biodegradable PBST copolyesters were first calculated to predict the maximum usable temperatures, and this would be useful for practical application of these new bio-based green plastics.     

Poly(l-lactic acid) nonwoven fabric prepared by carbon dioxide laser-thinning method

Poly(l-lactic acid) (PLLA) nonwoven fabric was obtained by using a carbon dioxide laser-thinning method. The obtained PLLA nonwoven fabric was made of endless microfibers with a uniform diameter without droplets. The fiber diameter can be varied by controlling an airflow rate supplied to the air jet, a supplying speed of an original fiber into a laser-irradiating point, and laser intensity. When the microfiber prepared by irradiating the laser operated at a laser intensity of 66 W cm⁻² to the original fiber supplied at S_s = 0.1 m min⁻¹ was dragged at an airflow rate of 30 L min⁻¹, the thinnest microfiber with an average diameter of 3.4 μm was obtained. The obtained microfiber had a degree of crystallinity of 45%, and the degree of crystal orientation of 84%. The existence of highly oriented crystallites suggests that a flow-induced crystallization occurred during the laser-thinning.     

Effect of phthalimide as an efficient nucleating agent on the crystallization kinetics of poly(lactic acid)

The effect of phthalimide compound on the nonisothermal and isothermal crystallization behavior of poly(lactic acid) (PLA) was investigated by differential scanning calorimetry (DSC) and polarized optical microscopy. It was found that the incorporation of a small amount of phthalimide promoted the crystallization of PLA significantly. The Avrami model was applied to analyze the isothermal crystallization kinetics. It was found that the Avrami exponent was higher for PLA/phthalimide blends than for neat PLA, indicating a heterogeneous nucleation mechanism. These results indicate that phthalimide may act as an efficient nucleating agent to improve the crystallization of PLA and expand its applications.