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Graphical abstract Highlights • A new CP-TIPS process was used to control the crystallization behavior of PLLA. • PLLA scaffolds were fabricated with macropores over 300 μm and nanofiber structure. • The swelling scaffold showed good flexibility enabling intake of chitosan solution. • The PLLA/chitosan scaffolds are promising for bone tissue engineering applications. Abstract A new method called cloud point thermally induced phase separation (CP-TIPS) was developed to prepare poly (l -lactic acid) (PLLA) scaffolds with macropores over 300 μm in PLLA/dioxane/H 2 O ternary system. The concentration of PLLA was 4% (w/v), and the solvent was dioxane with 14% of deionized water. By maintaining the clear solution of the ternary system near and above the cloud point for 2 h, followed by a large enough quenching depth (−80 °C), the crystallization of the α′-form crystal became privileged, and the microstructure of the pore wall was dominated with nanofibers. In contrast, conventional TIPS process resulted in scaffolds with similar pore size but platelet-like microstructure on the pore walls. The unique macroporous nanofibrous PLLA scaffold showed well elasticity and flexibility after swelling in 70% acetone. This property further enabled a facile "mechanical squeeze and intake" of high concentration viscous chitosan solution into the porous structure to modify the composite scaffolds. The compressive modulus of macroporous nanofibrous PLLA/CS scaffolds reached about 1 MPa. The hydrophilicity of the scaffold was greatly enhanced and the pH value remained stable in the first 3 weeks after degradation in vitro. The effect of chitosan concentration in the composite scaffolds on cell affinity and the osteogenic differentiation was evaluated. Finally, a critical-size rat calvarial bone defect model was used to evaluate the osteogenesis of the scaffolds in vivo and the composite scaffold with 3% chitosan significantly enhanced bone regeneration. [ABSTRACT FROM AUTHOR]

In cases of severe injuries or burns, skin grafts (scaffold) are often necessary skin substitutes. To not harm the patient or the donor, research is necessary to search for heterografts, that are formed by biomaterials and are also biodegradable and bioabsorbable to the human body, as is the case with poly (L-lactic acid) - PLA. However, the natural polymers placed on the skin suffer great degradation in media with large amounts of carbon and water, have little durability due to their low ductility. For the proposal, the graphene oxide (GO) nanocharge and pseudoboehmite (PB) were obtained. It is believed that the nanofillers dispersed in the polymer matrix can improve mechanical properties regarding ductility and tenacity, without losing thermal properties. Subsequently, the hybrid nanocharge dispersion methods were employed to obtain in the poly (L-Lactic Acid) (PLA) matrix, forming the material for the desired scaffold. For this research, injectable specimens of pure PLA, PLA structured with GO nanoparticles, and PLA structured with PB nanoparticles, were manufactured. The microstructural and mechanical characterizations were performed on the specimens, to compare the effect generated by the nanocharges on the bulk material. The results showed that the increase in the concentrations of PB and GO nanofillers showed an increase in tenacity and ductility compared to pure PLA, a property that is desired in the scaffold structure.

In this study, the effect of graphene nanoplatelets (GNPs) on the shape memory properties of poly(L-lactic acid) (PLLA) was studied. In addition to thermal activation, the possibility of infrared actuating of thermo-responsive shape memory PLLA/GNPs nanocomposite was investigated. The incorporated GNPs were expected to absorb infrared wave’s energy and activate shape memory PLLA/GNPs. Different techniques such as differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), field emission gun scanning electron microscope (FEG-SEM) and dynamic mechanical thermal analysis (DMTA) were used to characterize samples. DSC and WAXD results indicated that GNPs augmented crystallinity due to nucleating effect of graphene particles. GNPs improved both thermal and infrared activating shape memory properties along with faster response. Pure shape memory PLLA was slightly responsive to infrared light and its infrared actuated shape recovery ratio was 86% which increased to more than 95% with loading of GNPs. Drastic improvement in the crystallinity was obtained in nanocomposites with lower GNPs contents (0.5 and 1 wt%) due to finer dispersion of graphene which resulted in more prominent mechanical and shape memory properties enhancement. Infrared activated shape memory PLLA/GNPs nanocomposites can be developed for wireless remote shape control of smart medical and bio-systems.

In the present study the development of novel polymer-supported nanocomposite graphene oxide (GO)–TiO2 films, based on poly(L-lactic acid), one of the most exploited bioplastics worldwide, was explored for photocatalytic applications. The nanocomposites were synthesized and evaluated as photocatalysts for the removal of a mixture of nine antibiotics, consisting of two sulphonamides (sulfamethoxazole, sulfadiazine), three fluoroquinolones (levofloxacin, norfloxacin, moxifloxacin), one anti-TB agent (isoniazid), one nitroimidazole (metronidazole), one lincosamide (lincomycin) and one diaminopyrimidine (trimethoprim), which are commonly found in wastewaters. The films were synthesized using 1 wt% GO and different TiO2 content (10, 25, and 50 wt%) and characterized using Fourier transform infrared spectroscopy (FTIR), wide-angle X-ray diffraction (WAXD), thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). Findings confirmed the successful immobilization of GO/TiO2 in all cases. The PLLA–GO–TiO2 50 wt% composite film demonstrated higher photocatalytic efficiency and, thus, was further investigated demonstrating excellent photostability and reusability even after four cycles. Overall, PLLA–GO–TiO2 50 wt% nanocomposite demonstrated high efficiency in the photocatalytic degradation of the antibiotics in various matrices including pure water and wastewater.

Thermally induced phase separation method was used to make porous three-dimensional poly (L-lactic acid) scaffolds. The effect of imposed thermal profile during freezing of the poly (L-lactic acid) in dioxane solution on the scaffold was characterized by their micro-structure, porosity (%), pore sizes’ distribution, and mechanical strength. The porosity (%) decreased considerably with increasing concentrations of poly (L-lactic acid) in the solution, while a decreasing trend was observed with increasing cooling rates. The mechanical strength increases with increase in poly (L-lactic acid) concentration and also with increase in the cooling rate for both types of solvents. Therefore, mechanical strength was increased by higher cooling rates while the porosity (%) remained relatively consistent. Scaffolds made using higher concentrations of poly (L-lactic acid; 7% and 10% w/v) in solvent showed better mechanical strength which improved relatively with increasing cooling rates (1°C–40°C/min). This phenomenon of enhanced structural integrity with increasing cooling rates was more prominent in scaffolds made from higher initial poly (L-lactic acid) concentrations. Human adipose–derived stem cells were cultured on these scaffold (7% and 10% w/v) prepared by thermally induced phase separation at all cooling rates to measure the cell proliferation efficiency as a function of their micro-structural properties. Mean pore sizes played a crucial role in cell proliferation than percent porosity since all scaffolds were >88% porous. The viability percent of human adipose tissue–derived adult stem cells increased consistently with longer periods of culture. Thus, poly (L-lactic acid) scaffolds prepared by thermally controlled thermally induced phase separation method could be a prime candidate for making ex vivo tissue-engineered grafts for surgical implantation. [ABSTRACT FROM AUTHOR]

Radioembolization with radioactive microspheres has been an effective method for the treatment of liver lesions. The aim of this study was to prepare carrier‐free 188Re loaded poly (L‐lactic acid) (PLLA) microspheres through 188Re sulfide colloidal nanoparticles (188Re‐SC nanoparticles). The formation of 188Re‐SC nanoparticles was confirmed by ultraviolet‐visible spectrophotometry. The labeling yield of 188Re‐SC nanoparticles was verified using the RTLC method. Effects of synthesis parameters on morphology and size of prepared 188Re‐sulfide colloidal‐PLLA microspheres (188Re‐SC‐PLLA microspheres) were studied by scanning electron microscopy. In vitro stability of 188Re‐SC‐PLLA microspheres was investigated in normal saline at room temperature and in human serum at 37°C. In vivo distribution studies and gamma camera imaging were performed in healthy BALB/c mice. The microspheres could be prepared with sizes between 13 and 48 μm (modal value 29 μm) and radiolabeling efficiency >99%. After incubation, the microspheres were found stable in vitro up to 72 hours. The biodistribution after intravenous injection in healthy BALB/c mice showed high accumulation in lung as a first capture pathway organ for microsphere followed by great retention over 48 hours for these microspheres. These data show that 188Re‐SC‐PLLA microspheres are suitable candidate for clinical studies. [ABSTRACT FROM AUTHOR]

Diaphragmatic myoblasts (DM) are stem cells of the diaphragm, a muscle displaying high resistance to stress and exhaustion. We hypothesized that DM modified to overexpress connexin-43 (cx43), seeded on aligned poly (l-lactic acid) (PLLA) sheets would decrease infarct size and improve ventricular function in sheep with acute myocardial infarction (AMI). Sheep with AMI received PLLA sheets without DM (PLLA group), sheets with DM (PLLA-DM group), sheets with DM overexpressing cx43 (PLLA-DMcx43) or no treatment (control group, n = 6 per group). Infarct size (cardiac magnetic resonance) decreased ∼25% in PLLA-DMcx43 [from 8.2 ± 0.6 ml (day 2) to 6.5 ± 0.7 ml (day 45), p < .01, ANOVA-Bonferroni] but not in the other groups. Ejection fraction (EF%) (echocardiography) at 3 days post-AMI fell significantly in all groups. At 45 days, PLLA-DM y PLLA-DMcx43 recovered their EF% to pre-AMI values (PLLA-DM: 61.1 ± 0.5% vs. 58.9 ± 3.3%, p = NS; PLLA-DMcx43: 64.6 ± 2.9% vs. 56.9 ± 2.4%, p = NS), but not in control (56.8 ± 2.0% vs. 43.8 ± 1.1%, p < .01) and PLLA (65.7 ± 2.1% vs. 56.6 ± 4.8%, p < .01). Capillary density was higher (p < .05) in PLLA-DMcx43 group than in the remaining groups. In conclusion, PLLA-DMcx43 reduces infarct size in sheep with AMI. PLLA-DMcx43 and PLLA-DM improve ventricular function similarly. Given its safety and feasibility, this novel approach may prove beneficial in the clinic. [ABSTRACT FROM AUTHOR]

The crystallization activation energy (DE) of a polymer comprises the nucleation activation energy DF and the transport activation energy DE*. In this paper, the DE of poly (L-lactic acid) (PLLA) nucleated with nucleating agent p-tert-butylcalix[8]arene (tBC8) was calculated. The results showed that the DE of nucleated PLLA was 165.97 kJ/mol, which is higher than that of pure PLLA. The reason why DE of PLLA increased when incorporating nucleating agent was studied. The increment of glass transition temperature (Tg) for nucleated PLLA revealed that the polymer chain mobility was restricted by tBC8, which was considered as the reason for the increase of DE*. Further, polyethylene glycol (PEG) was added to improve the chain mobility, thus eliminated the variation of the transport activation energy DE* caused by tBC8. Then the effect of the increment of crystallization temperature range on the increase of DF was also taken into consideration. It was concluded that both decreasing the mobility of chain segments and increasing the crystallization temperature range caused an increase of DE for PLLA/tBC8. [ABSTRACT FROM AUTHOR]

The combination of polymer blends and nanofillers is an effective strategy for creating high-performance polymer alloys with a hierarchical structure. Herein, a one-pot synthesized polyvinyl acetate-modified cellulose nanocrystal (CNCs-PVAc) powder was used, without removing the ungrafted homopolymer, to enhance the properties of a poly (L-lactic acid) (PLLA)/poly (butylene adipate-co-terephthalate) (PBAT) blend for 3D filament via a simple melt-extrusion process. Compared with neat PVAc-grafted CNCs (CNCs-g-PVAc), it was found that the presence of ungrafted PVAc homopolymer is helpful for promoting the dispersion of CNCs in the PLLA/PBAT blend, leading to an improvement in both strength and toughness, as well as a decrease in the domain size of the PBAT disperse phase. Notably, the synergism of CNCs-PVAc and strong shear action in fused deposition modeling (FDM) resulted in the formation of highly oriented PBAT nanofibers in PLLA/PBAT/CNCs-PVAc nanocomposites, thereby contributing to the strength-toughness balance of 3D print objects. The tensile breaking energy and notch impact strength (90° infilled) of the prepared 3D print objects were enhanced by 896% and 969%, respectively, compared with pure PLLA. Additionally, the designed nanocomposites exhibit outstanding biodegradability, biocompatibility, and shape-memory properties, making them suitable for medical vascular clips and strong-toughness load-bearing frames. [Display omitted] • The melt processing of PLLA/PBAT/CNCs-PVAc nanocomposites has been realized. • The synergism of CNCs-PVAc and FDM makes PBAT oriented to form a fibrous structure. • PLLA/PBAT/CNCs-PVAc have biodegradability, biocompatibility and balanced mechanical properties. • The medical vascular clamp and load-bearing parts were prepared through FDM. [ABSTRACT FROM AUTHOR]

Magnesium (Mg) and its alloys have attracted extensive attention of researchers in the field of cardiovascular implants due to their good mechanical properties and biosafety. Constructing a multifunctional hybrid coating seems to be an effective strategy to address the insufficient endothelialization and poor corrosion resistance of Mg alloy vascular stents. In this study, a dense layer of magnesium fluoride (MgF 2) was prepared on the surface of Mg alloy aiming at better corrosion resistance; Thereafter, sulfonated hyaluronic acid (S-HA) was made into small sized nanoparticles (NP) which were deposited on the MgF 2 surface by self-assembly method, followed with poly-L-lactic acid (PLLA) coating preparation by one-step pulling method. The blood and cell tests showed that the composite coating had good blood compatibility, pro-endothelial, anti-hyperplasia and anti-inflammatory functions. Compared to current clinical PLLA@ Rapamycin coating, our PLLA/NP@S-HA coating showed better functions of promoting endothelial cells growth. These results strongly furnished a promising and feasible strategy for the surface modification of Mg-based degradable cardiovascular stents. [ABSTRACT FROM AUTHOR]

Controlled release of pesticides is eco-friendly and cost-effective. Thiram is a pesticide for fighting fungi and protection of cultivated products. This research aimed at controlled release of thiram pesticide from Poly (L-lactic acid) (PLLA) nanofibrous matrix. Solutions of PLLA (9% w/v) in chloroform-methanol (80-20 v/v) containing 5, 10, 15, 20, and 25% (w/w) thiram relative to the PLLA were electrospun. FESEM, FTIR, and XRD were employed to characterize the electrospun nanofibers. UV spectrophotometry was employed to study the release of thiram from PLLA nanofibers in deionized water. The results showed that the controlled release of thiram from PLLA nanofibers without annealing followed Fick mechanism, but after annealing, non-Fick mechanism prevailed. It was also observed that annealing led to lower level and lower initial rate of controlled release. It is concluded that electrospun PLLA-thiram nanofibers can be used for the controlled release of thiram in long-term periods in agriculture. [ABSTRACT FROM AUTHOR]

The fully biodegradable polymer stent is considered as the fourth-generation vascular implant with good biocompatibility and long-term therapeutic potential. It has attracted much attention because it overcomes the disadvantage of the permanently implanted metal stent. However, compared with the metal stent, its mechanical properties are slightly inferior, which is an urgent problem. Based on previous studies, fully biodegradable polymer stents are prone to experience cracks and damage in large deformation region during the crimping and expansion process. The large deformation region is mainly located at the ring bend of the stent. We supposed that these damages are the leading causes of weakening the mechanical performance of polymer stents and are mainly affected by the crucial deformation region. For this purpose, this work studies the relationship between different crucial deformation regions and the mechanical performance of the polymer stent. Firstly, the volume of the crucial deformation region is improved by increasing the ring width. Although the radial strength of the stent is enhanced with the increase in ring width, the radial stiffness also increases, and correspondingly, the flexibility of the stent decreases. To obtain acceptable comprehensive mechanical performance, two types of slotting design in critical deformation region were proposed. The proposed slotted stent with a bulge has sufficient radial strength and low radial stiffness, having a good radial support capacity and flexibility. In other words, the proposed stent has improved the radial support without sacrificing flexibility. Overall, different crucial deformation regions cause different degrees of damage to the stent during crimping and expansion, which affects the mechanical properties of the stent. Reasonable structural design of the crucial deformation region is the key to adjust the comprehensive performance of the stent. [Display omitted] • The crucial deformation region affects the mechanical properties of polymer stent. • Reasonable structural design of the crucial deformation region is the key to adjust the comprehensive performance of the stent. [ABSTRACT FROM AUTHOR]

• Synchrotron source was used to study PLA crystallization under different shear rates. • Experimental crystallinity evolutions showed that shear rate enhances kinetics. • A model and its parameters from previous studies was applied to describe kinetics. • The effect of nucleation rate under flow was shown to be determinant. In this work, the effect of shear rate on the isothermal crystallization of a poly(lactic acid), PLA, was analyzed. The crystallinity evolution of PLA during continuous shear was assessed by collecting X-ray diffraction data at short time intervals by adopting a synchrotron source. Shear rates in the range from 0.1 s−1 to 1.5 s−1 were analyzed. It was found that increasing the shear rate induced a dramatic decrease of the half crystallization times, more than one order of magnitude in the analyzed range of shear rates. A model for the description of crystallinity evolution was applied to describe the experimental results. It was found that the nucleation rate needed to describe the data are much larger than what measured in a previous work in the same range of shear rates but adopting a short step shear protocol. [ABSTRACT FROM AUTHOR]

Increased life expectancy has resulted in an increase in osteoporosis incidence worldwide. The coupling of angiogenesis and osteogenesis is indispensable for bone repair. Although traditional Chinese medicine (TCM) exerts therapeutic effects on osteoporosis, TCM-related scaffolds, which focus on the coupling of angiogenesis and osteogenesis, have not yet been used for the treatment of osteoporotic bone defects. Panax notoginseng saponin (PNS), the active ingredient of Panax notoginseng , was added to a poly ( L -lactic acid) (PLLA) matrix. Osteopractic total flavone (OTF), the active ingredient of Rhizoma Drynariae , was encapsulated in nano-hydroxyapatite/collagen (nHAC) and added to the PLLA matrix. Magnesium (Mg) particles were added to the PLLA matrix to overcome the bioinert character of PLLA and neutralize the acidic byproducts generated by PLLA. In this OTF-PNS/nHAC/Mg/PLLA scaffold, PNS was released faster than OTF. The control group had an empty bone tunnel; scaffolds containing OTF:PNS = 100:0, 50:50, and 0:100 were used as the treatment groups. Scaffold groups promoted new vessel and bone formation, increased the osteoid tissue, and suppressed the osteoclast activity around osteoporotic bone defects. Scaffold groups upregulated the expression levels of angiogenic and osteogenic proteins. Among these scaffolds, the OTF-PNS (50:50) scaffold exhibited a better capacity for osteogenesis than the OTF-PNS (100:0 and 0:100) scaffolds. Activation of the bone morphogenic protein ( BMP )- 2 /BMP receptor ( BMPR )- 1A /runt-related transcription factor ( RUNX )- 2 signaling pathway may be a possible mechanism for the promotion of osteogenesis. Our study demonstrated that the OTF-PNS/nHAC/Mg/PLLA scaffold could promote osteogenesis via the coupling of angiogenesis and osteogenesis in osteoporotic rats with bone defects, and activating the BMP-2/BMPR1A/RUNX2 signaling pathway may be an osteogenesis-related mechanism. However, further experiments are necessary to facilitate its practical application in the treatment of osteoporotic bone defects., (© 2023 IOP Publishing Ltd.)

In some traumatic nerve injuries, autologous nerve grafting is the first choice for bridging the gap between the severed nerve ends. However, this therapeutic strategy has some disadvantages, including permanent loss of donor function and requirement of multiple surgeries. An attractive alternative to this therapeutic technique is the use of artificial nerve conduit. Poly (L-lactic acid) (PLLA) is widely used as a substrate for artificial nerve conduit because it is readily biodegradable, but it is not inherently biologically active. In this study, we developed a PLLA nanofibrous nerve conduit, modified with a conjugate of oligo (D-lactic acid) (ODLA) and the neurite outgrowth, thereby promoting peptide AG73 (RKRLQVQLSIRT) to improve nerve regeneration. PLA/ODLA-AG73 nanofibrous conduit was fabricated by electrospinning and then transplanted at the 10 mm gap of rat sciatic nerve. After six months, electrophysiological evaluation revealed that it achieved better functional reinnervation than silicone tube (used as a reference) or unmodified PLLA nanofibrous conduit.

Poly (L-lactic acid) (PLLA) polymers are the most frequently used substrates for cell culture, tissue regeneration and orthopedic prostheses, mainly because of their atoxic characteristics and good biocompatibility. The objective of this study was to evaluate whether a higher density or different pore diameters (less than 45, 180-250, and 250-350 µm) would change the growth pattern of cultured cells. The cells were found to adhere to and spread over all PLLA scaffolds studied. The cells also showed similar proliferation on dense and porous PLLA scaffolds, except for PLLA scaffolds with a smaller pore diameter. The cytochemical data showed high metabolic cellular activity on the various substrates. Overall, the results indicated satisfactory cell growth and proliferation on the different PLLA scaffolds studied, especially for those with pore diameters of 180-250 µm and 250-350 µm.

Young's modulus of α′- and α-crystals of poly (l -lactic acid) (PLLA), more precisely, of aggregates of isotropically arranged lamellae, has been estimated based on dynamic-mechanical analysis of sets of isotropic film samples containing largely different though well-defined amounts of crystals. Evaluation of the modulus of elasticity of these film samples yielded the dependence of Young's modulus as a function of the enthalpy-based crystallinity, increasing with the crystal fraction in the assessed range, from zero to about 75% crystallinity. Extrapolation towards 100% crystallinity suggests values of Young's modulus of around 3.7 and 4.6 GPa for isotropic aggregates of α′- and α-crystals, respectively, being only slightly higher than the modulus of the unaged glassy amorphous phase of 3.0 GPa. Noting the inherent anisotropy of the crystal modulus, suggested in the literature, the average modulus determined in this work seems to be controlled by weaker interchain secondary bonding but not the modulus in chain direction. Great effort has been undertaken to minimize errors by keeping the lamellar thickness in samples of different crystallinity constant, and by providing evidence for independence of the moduli on the spherulitic superstructure. [ABSTRACT FROM AUTHOR]

• Analysis of the glass transition temperature of PLLA and PDLLA copolymers spanning seven orders of magnitude. • The infinity-molar-mass glass transition temperatures of PLA are independent of the chain stereoregularity. • Chain stereoregularity of PLA does not influence the cooperative molecular motions. To evaluate the glass transition of poly(d , l -lactic acid)s (PDLLA), three PDLLA grades of different molar mass were analyzed by fast scanning calorimetry (FSC), on cooling at rates between 0.01 and 100,000 K/s. Poly(l- lactic acid) (PLLA) is used as a reference and measured at similar conditions as PDLLA, however, assuring the absence of crystallization. By using the Vogel–Fulcher–Tammann–Hesse (VFTH) equation to fit the glass-transition dynamics of PDLLA and PLLA, it is found that the Vogel temperatures of PDLLA and PLLA are essentially the same. In addition, the dependencies of the glass transition temperature on the molar mass of PDLLA and PLLA are evaluated. The glass transition temperatures of PDLLA and PLLA of infinite molar mass are the same, suggesting that the stereoisomerism does not influence the glass transition dynamics. [Display omitted] [ABSTRACT FROM AUTHOR]

Thin film of carbon fiber (CF) and poly (L-lactic acid) (PLLA) composite was prepared by a solution casting technique. Influence of crystallization temperature (Tc) on morphology of transcrystalline (TC) on the interface between CF and PLLA was investigated under a temperature-controlled gradient (T-gradient) stage with temperature ranging from 90 °C to 140 °C. Morphology of TC was observed by polarized optical microscope (POM). Typical TC structure isothermally crystallized on the T-gradient stage was obtained at the surface of CF when Tc = 111 ∼ 132 °C. As Tc decreased from 132 to 111 °C, nuclei density on the surface of single fiber increased while the thickness of TC layer decreased. Crystallization kinetics of TC was investigated through isothermal crystalization under POM equipped with a temperature-controlled stage. As Tc decreased, the nucleation rate of TC increased and the growth rate of TC decreased. Furthermore, it revealed that the thickness of TC layer was conducted by the competition between heterogeneous nucleation on the surface of fiber and homogeneous nucleation in the bulk matrix around the fiber. The nucleation rate of TC structure was much higher than homogeneous nucleation rate of spherulites in the bulk matrix when Tc was above 118 °C. In this case, TC had enough space to develop perpendicular to fiber axis. Consequently, thickness of TC layer was larger at higher crystallization temperature. On the contrary, transcrystallization was suppressed by homogeneous crystallization when Tc was below 118 °C due to enhanced nucleation ability of spherulites. [ABSTRACT FROM AUTHOR]

Poly ( L -latic acid) (PLLA) is a bioresorbable polymer widely used as a biomaterial, but its fragility can limit its use. An alternative is to produce polymer nanocomposites, which can enhance the mechanical properties of polymeric matrix, resulting in a material with differentiated properties. In this work, PLLA based nanocomposites containing 0.25, 0.5 and 1.0 wt% of purified multiwalled carbon nanotubes (p-MWCNTs) were prepared by the solvent casting method. The morphology and mechanical properties results show an improvement in strain at break for 0.25 and 0.5 wt% p-MWCNTs and an increase in stiffness and elastic modulus for all compositions. Nanocomposites presented a p-MWCNTs agglomeration; however, there was a good stress transfer between PLLA and p-MWCNTs, which was confirmed by the increase in the hardness and elastic modulus. Atomic force microscopy analysis indicated an increase in roughness after nanotube addition. The in vitro biological study showed that PLLA/p-MWCNTs nanocomposites are cytocompatible with osteoblasts cells. The capacity of PLLA nanocomposites to stimulate osteogenesis was investigated by alkaline phosphatase (ALP) activity assay. Higher ALP activity was found on osteoblasts cultured on nanocomposites with 0.25 and 0.5 wt% p-MWCNT compared to neat PLLA, confirming that PLLA cytocompatibility was improved on these compositions. Finally, our results showed that by a simple and inexpensive solvent casting method, it is possible to manufacture biofunctional nanocomposites devices with potential for orthopedic applications. [ABSTRACT FROM AUTHOR]

Poly (L -lactic acid) microparticles (PLLAms) loaded with growth factors were prepared through the modified (ethanol as the modifier) solution enhanced dispersion by supercritical CO 2 (SEDS) for controlling release rate while maintaining bioactivity. Trypsin was used to explore operational parameters and their influence on release. Results showed that the optimized flow rate of polymer solution was 1.0 mL/min. Release rate of trypsin-PLLAms was regulated by molecular weight of PLLA and Polyethylene glycol (PEG) ratio. Bone morphogenetic protein (BMP-2), fibroblast growth factor-2 (FGF-2), and vascular endothelial growth factor (VEGF) was loaded into PLLAms. Encapsulation efficiency was 65.9%, 63.9%, and 64.3%, cumulative release rate was 63.2%, 74.8% and 84.1% for 7 days, respectively. BMP-2, VEGF and FGF-2 released from PLLAms significantly promoted cell proliferation and differentiation. Therefore, the modified SEDS effectively maintained drug bioactivity, which could be used to fabricate carriers for controlled bioactive drugs release. [Display omitted] • Solution enhanced dispersion by supercritical CO 2 (SEDS) was modified. • Polymeric microparticles loaded bioactive drugs were prepared by modified SEDS. • Bioactive drugs release was controlled by molecular weight and ratio of polymers. • Modified SEDS effectively maintained bioactivity of growth factors. [ABSTRACT FROM AUTHOR]

[Display omitted] Female malaria vector Anopheles arabiensis : laboratory-reared, insecticide susceptible KGB strain originating from Kanyemba, Zimbabwe. As photographed at the University of Pretoria, Institute for Sustainable Malaria Control insectary (2014) • The polymer/repellent system PLLA/IR3535 can be 3D-printed to obtain a drug-delivery device. • The maximum repellent loading achieved was 25 m%. • Evaporation of IR3535 at body temperature lasts at least 5–10 days. The polymer/solvent system poly (l -lactic acid)/ethyl butylacetylaminopropionate (PLLA/IR3535) is regarded as an insect-repellent-delivery system, serving, e.g., for fighting mosquito-borne tropical diseases. In such systems the solid polymer hosts the liquid repellent, with the latter slowly released to the environment, expelling mosquitoes. As a new approach, exceeding prior work about application of different technologies to obtain such devices, in this work, samples of the polymer/repellent system PLLA/IR3535 were prepared by 3D-printing. The experiments showed that it is possible to print 3D-parts containing up to 25 m% repellent, with an only minor loss of repellent during the printing process. For samples containing low amount of repellent, crystallization of PLLA was suppressed due to the rather fast cooling step and the low bed temperature of around 25 °C, being lower than the glass transition temperature of the homogeneous polymer/repellent strands. At higher repellent concentration, due to the lowering of the glass transition temperature to near or even below ambient temperature, the crystallinity slowly increased during storage after printing. For all samples, regardless of the initial repellent concentration, the repellent-release rate increases with temperature, and at ambient temperature the release-time constant is in the order of 10 days. The study successfully proved the applicability of the technology of extrusion-based 3D-printing for the preparation of polymer parts with a specific shape/design containing mosquito-repellent at a concentration which raises the expectation to be used as a repellent delivery-device. [ABSTRACT FROM AUTHOR]

The aim of this work was to prepare the scaffolds of pure poly (L-lactic acid) 3% (w/v), pure chitosan 3% (w/v), and PLLA/chitosan blend (1:5) 3% (w/v) using TIPS method and investigate their properties and application in tissue engineering. An in vitro degradation study of scaffolds showed the addition of chitosan to PLLA not only increased its degradation rate, but also slowed down its pH value reduction. Addition of chitosan to PLLA increased hydrophilicity, porosity, compressive properties, and cell viability of the scaffolds. The results indicate that among all scaffolds, the most appropriate candidate for tissue engineering is PLLA/chitosan blend. [ABSTRACT FROM PUBLISHER]

Honeycomb monolith structured porous poly (L-lactic acid, PLA) was simply fabricated by employing a unidirectional freeze-casting technique. Dimethyl sulfoxide (DMSO) was used as a solvent for PLA, and the solution was unidirectionally frozen. The DMSO was nucleated in the solution and was grown in the freezing direction. The PLA was solidified and structured with the DMSO crystal as a template. Then DMSO was leached by water, ethanol, or the mixture of them, and subsequently the porous PLA was dried by oven. It was found that the freeze-casting protocol can significantly influence the morphological features such as the tube diameter and wall thickness of tube can be tuned by varying of PLA concentration, freezing temperature, and the nature of leaching solvent. Because DMSO has a special solubility of a number of polymers, this method may be a general way for designing and preparing aligned porous materials. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The insect repellent ethyl butylacetylaminopropionate (IR3535) was used as a functional additive for poly (l-lactic acid) (PLLA) to modify its structure and mechanical properties and achieve insect repellency. PLLA/IR3535 mixtures at various compositions were prepared via melt extrusion. In the analyzed composition range of 0 to 23 m% IR3535, PLLA and IR3535 were miscible at the length scale represented by the glass transition temperature. Addition of IR3535 resulted in a significant decrease in the glass transition temperature of PLLA, as well as in the elastic modulus, indicating its efficiency as a plasticizer. All mixtures were amorphous after extrusion, though PLLA/IR3535 extrudates with an IR3535 content between 18 and 23 m% crystallized during long-term storage at ambient temperature, due to their low glass transition temperature. Quantification of the release of IR3535 into the environment by thermogravimetric analysis at different temperatures between 50 and 100 °C allowed the estimation of the evaporation rate at lower temperatures, suggesting an extremely low release rate with a time constant of the order of magnitude of 1-2 years at body temperature.

Injection-molding of rather slow crystallizing poly (l -lactic acid) (PLLA) was analyzed regarding the formation of crystal nuclei at different distances from the skin in a standard test bar. The relative number of nuclei in the various regions of fully amorphous test bars was estimated by evaluation of the kinetics of cold-crystallization, being faster in the skin than in the core region of the component. Simulation of the cooling-rate- and shear-rate-profiles along the cross-section of the molded bar suggests that the different nuclei numbers in skin and core mainly are caused by the higher shear rate in surface-near regions, though being supercritical for shear-induced nuclei formation also in the core. The latter conclusion is derived by comparing both the cold-crystallization kinetics and semicrystalline morphology with those of non-injection molded PLLA. The simulated shear-rate data, after conversion into specific-work-of-flow data, were found significantly exceeding the critical specific work of flow for shear-induced nuclei formation, being around 25 kPa, in all regions of the component. The results of the present study successfully demonstrate that knowledge about the crystallization kinetics of the sheared and quiescent melt of PLLA can be used to predict structure formation in industrial processing. [Display omitted] • Injection-molding simulation allows prediction of crystal-nuclei formation. • Prerequisite for prediction is knowledge of critical cooling and shearing conditions. • Nuclei formation in injection-molding can be quantified by cold-crystallization. [ABSTRACT FROM AUTHOR]

Architecture of the poly(L-lactic acid) (PLLA) scaffolds is known to affect protein affinity and binding strength. Here, we demonstrate that nanofibrous electrospun PLLA scaffolds reversibly absorb the pro-migratory serum factors that stimulate migration of vascular smooth muscle via an NFkB-dependent mechanism. Further, we demonstrate that mesenchymal stem cells seeded on the PLLA scaffolds do not enhance muscle migration but may maintain the ability of induced cells to migrate in an NFkB-independent manner. These findings further support the promising application of PLLA scaffolds for therapeutic angiogenesis and vascular graft engineering. [ABSTRACT FROM AUTHOR]

For its unique flexibility, self-expandable braided stent has been wildly used in the treatment of peripheral vascular diseases, such as the superficial femoral artery stenosis. With the application of bioabsorbable polymer materials, stent braided by polymer filaments is explored, and expected to minimize the complications caused by long-term retention of commercial metallic stents in the human body. Poly (L-lactic acid) (PLLA) is the representative of degradable polymer materials, and has been broadly applied in stent for its good mechanical properties and biocompatibility. This study aimed to propose a new preparation method for PLLA self-expandable braided stent by mixed-braided technology, and evaluate its mechanical properties especially in radial supporting performance and flexibility. For this purpose, a series of stent samples were prepared by mixed braiding PLLA monofilament with different diameters. In addition, the pitch angle and monofilament diameter are also considered as two critical design parameters affecting stent mechanical performance. Then, the radial strength and flexibility of different samples were evaluated respectively. The results show that the mixed-braided stent keep the excellent flexibility of thin monofilament braided stent, meanwhile it possesses the good radial supporting performance of the thick monofilament braided stent. This paper provides an idea to improve the comprehensive mechanical properties of PLLA self-expandable braided stent. [ABSTRACT FROM AUTHOR]

Owing to the renewable/biodegradable characters, cellulose nanomaterials have been proposed to modify poly (L-lactic acid) (PLLA) for producing fully green, high performance fused deposition modeling (FDM) consumables. However, to realize the industrial application, the efficient dispersion of hydrophilic cellulose nanofillers in hydrophobic PLLA matrix by industrial melt compounding route rather than solution compounding remains a challenge. Herein, by using polyvinyl acetate (PVAc) modified cellulose nanocrystals (CNCs) powder (CNCs-PVAc) containing mixture of CNCs grafted by PVAc and PVAc homopolymer latex, the homogeneous dispersion of CNCs in PLLA has been achieved by simple melt blend. The results show that the addition of CNCs-PVAc with 5 wt% loading enhances both the melt processibility and inter-fuse adhesion of PLLA remarkably, which in turn results in the improvement of tensile breaking energy by 257%, inter-layer adhesion strength and notched impact toughness by 103% and 57.0%, respectively, as well as good dimensional stability. This work provides an industrial route to prepare PLLA/CNCs-PVAc nanocomposites with high performance for meeting the requirements of strength and dimensional accuracy of FDM parts for end applications. Melt processing of PVAc modified CNCs powder (CNCs-PVAc) with PLLA to fabricate the PLLA/CNCs nanocomposite for high-performance 3D printing parts.▪ [ABSTRACT FROM AUTHOR]

Abstract: The structure, porosity and crystallization behavior of poly (L-lactic acid) and poly (L-lactic acid)/polyurethane porous membranes, prepared from ethanol/dioxane and ethanol/water coagulation baths through immersion precipitation, have been systematically investigated. The diffusion rate between solvent and nonsolvent as well as the equilibrium phase diagram of PLLA/solvent/nonsolvent system were also well studied. It has been proved that the ultimate structure and performance of the membranes could be mediated under control by suitable adjustment on phase separation behavior of the ternary system through varying coagulation bath compositions. The results show that the presence of lower ratio of dioxane in ethanol baths endows the resulting membranes with uniform sponge-like structure, higher porosity and crystallinity due to the moderate solidification and crystallization of PLLA, while increasing the water concentration tends to have a modestly opposite effect and obtains membranes with irregular finger-like structure, lower porosity and crystallinity. Under the same coagulation baths, PLLA/PU membranes possess slightly larger pores size and porosity than pure PLLA membranes, but the presence of PU appears to have no effect on the crystallinity of PLLA. [Copyright &y& Elsevier]

Abstract: Poly(l-lactic acid) (PLLA) microencapsulated vitamin E was prepared in oil in water (O/W) emulsion system using solvent evaporation technique. The influence of PLLA:vitamin E weight ratio on the encapsulation was studied. In the case of low molecular weight PLLA, the optimum ratio is 25:1. It was found that using smaller amount of PLLA, microcapsule could not formed. In contrast, vitamin E was well enveloped with lower amount of high molecular weight PLLA, PLLA:vitamin E at 3:1. The obtained capsule was observed with an optical and scanning electron microscopes. The amount of the encapsulated vitamin E was measured with gel permeation chromatograph. [Copyright &y& Elsevier]

The purpose of this research was to investigate the potential of surface modified Poly ( l-lactic acid) (PLA) microspheres as a carrier for site-specific delivery of anti-inflammatory drug, ketoprofen, for the treatment of rheumatoid arthritis. Microspheres were prepared by solvent evaporation method using 20% w/w PLA in methylene chloride and 100 mL of a 2.5% poly vinyl alcohol (PVA) solution. Formulations were optimized for several processing parameters like drug to polymer ratio, stirring rate and volume of preparation medium etc. The surface of PLA microspheres was modified with gelatin to impart fibronectin recognition. The microspheres were characterized by surface morphology, size distribution, encapsulation efficiency, and by in vitro drug release studies. The prepared microspheres were light yellow, discrete, and spherical. Formulation with optimum drug to polymer ratio exhibited smallest vesicle size (43.02), high drug encapsulation efficiency (81.11) and better process yield (83.45). The release of drug was extended up to 24 h with Higuchi pattern of drug release. The in vivo results showed that the gelatin modified formulation reduced paw edema at greater extent than pure drug and PLA microspheres and it could be a promising carrier system for controlled and site-specific delivery of ketoprofen with possible clinical applications. [ABSTRACT FROM AUTHOR]

Abstract: In this study, 10-hydroxycamptothecin (HCPT) and poly (l-lactic acid) (PLLA) are co-precipitated by the supercritical anti-solvent (SAS) process using a mixture of dichloromethane (DCM)/ethanol (EtOH) as co-solvent, and supercritical carbon dioxide as the anti-solvent. The effect of five operating conditions on particle morphology, mass median diameter (Dp50) and HCPT loading is investigated using the single-factor method. The results indicate that HCPT loading can be greatly increased by using DCM/EtOH co-solvent, and the suitable operating conditions for the experimental system are determined. Under suitable conditions, the HCPT loading is 13.3% and Dp50 is 794.5nm. The drug loaded microparticles are characterized in detail. The SEM images showed that most of the particles were spherical, and PLLA concentration has a major impact on the particle shape. Results of TEM, DSC and XRD indicate that the micronized HCPT is dispersed into the PLLA matrix. For low HCPT loading, most of HCPT existed in the drug loaded microparticles in an amorphous state, but for high HCPT loading, part of the encapsulated drug existed in crystalline form. FT-IR results show that SAS process does not change the chemical structure of HCPT. The result of in vitro drug release test indicated that the crystallinity of HCPT in microparticles affects the control release performance, and the good encapsulated microparticles with higher HCPT loading and higher crystallinity are better. [Copyright &y& Elsevier]

Abstract: Hydrolytic degradation of electrospun mats of poly(l-lactic acid), PLLA, as a function of crystallinity and fiber diameter has been studied. The degradation in a saline phosphate buffer solution (PBS) up to 20 weeks produced a slight decrease in the sample mass but a clear decrease of the polymer average molecular weight in the amorphous fibers. This effect decreases as crystallinity increases. It is important for applications that morphological characteristics of the membranes such as average fiber diameter and membrane porosity are also affected by the degradation process. Fiber diameter increases while membrane porosity decreases, resulting in closer packed fibers due to the release of internal tensions related to the electrospinning and/or thermal treatment processes. [Copyright &y& Elsevier]

A new process to prepare L-lactic acid based polymer with high molecular-weight was established. In this process, the carboxyl terminated poly (L-lactic acid) (PLLA) prepolymer was first synthesized via polycondensation of L-lactic acid and a little adipic acid, and then the molecular weight of PLLA was increased by a chain-extending reaction using bisphenol-A epoxy resin as a chain extender. In situ FTIR was used to characterize the activity of reaction between epoxy groups at the end of bisphenol-A epoxy resin and carboxyl groups at the end of PLLA prepolymer, and the results showed that the reaction was of high activity. The weight-average molecular weight of prepared L-lactic acid based copolymer (PLLA-co-BisA ER) was up to 210,000 at an optimum synthetic condition. The thermal property and crystallization behavior of prepared copolymer were also studied. [ABSTRACT FROM AUTHOR]

Abstract: Two kinds of low molecular weight aliphatic amides, N, N′-ethylenebis (12-hydroxystearamide) (EBH) and N, N′-ethylenebisstearamide (EBSA), have been selected in present study to mediate the crystallization behavior of poly (L-lactic acid) (PLLA). The results showed that the crystallization rate of PLLA was significantly improved with the addition of EBH and EBSA, and EBH presented a stronger nucleating efficiency. The correlation between the variation of chain conformation during the early stages of isothermal crystallization and the enhancement of crystallization rate for pure PLLA and its mixtures was investigated by time-resolved FTIR. The formation of interchain conformational-ordered structure and intrachain 103 helix structure for amide-doped PLLA preceded that for pure PLLA, suggesting a stimulatory nucleating effect of EBH and EBSA. In the case of PLLA/EBH, the interchain interactions of –(COC + CH3) and –CH3 groups were faster than the –(CH3+CC) intrachain interactions, while the interchain interactions and the intrachain 103 helix formation were nearly synchronous for PLLA/EBSA. The hydrogen bond interaction between hydroxyl groups in EBH and the carbonyl groups in PLLA was proposed to be an important factor influencing the conformation variation during isothermal crystallization of PLLA. [Copyright &y& Elsevier]

Abstract: Solution enhanced dispersion by supercritical CO2 (SEDS) was modified to prepare poly (l-lactic acid) (PLLA) microparticles used for controlled release of water soluble drugs. The preparation conditions of the water involved micronization process were explored. Results showed that the modifier (ethanol) promoted the mutual miscibility between water and supercritical CO2. The flow rates ratio (R) of the aqueous solution, ethanol and methylene chloride solution significantly affected the morphology of the microparticles and the optimized R was 1/7.5/2.5. Morphine loaded PLLA (MF-PLLA) spheroid microparticles with a mean diameter of 2.45μm were also prepared under the optimum conditions, and their drug loading was 4.73±0.34%. The in vitro release profile showed a burst increase in the first 4h followed by a slow sustained release over a period of about 168h, suggesting that the modified SEDS method could be used to prepare the water soluble drug-loaded microparticles with sustained release profile. [Copyright &y& Elsevier]

Coelectrospun polylactide(PLA)/gelatin (GE) composite fibrous matrixes have been identified to exhibit much improved performances compared to the respective components; however, the reasons for their water contact angles decreasing to zero at proper PLA/GE ratios remain unclear. To get a deep understanding of the phenomenon, PLA and GE were coelectrospun with different PLA/GE ratios in this study. Although the resulting composite fibers were homogeneous in appearance, they were detected different microscopic structures by transmission electron mircroscope (TEM) and via morphological observations after selective removal of either PLA or GE component. Together with the results of degradation study in phosphate buffered solution, a kind of cocontinuous phase separation microstructure could be identified for the PLA(50 wt%)/GE(50 wt%) composite fibers, which also showed the water contact angle of 0°. This value was far lower than those of electrospun PLA (∼123°) and GE (∼42°) fibrous matrixes. The X-ray photoelectron spectrometry (XPS) data revealed that the polar side groups of protein macromolecules have moved toward composite fiber surface with solvent evaporation during electrospinning, due to the hydrophobic interaction between PLA and GE. Then the excellent hydrophilicity of PLA(50 wt%)/GE(50 wt%) composite fibers could be suggested as the consequence of: (1) the cocontinuous phase separation structure could provide more interface and void for water molecules penetrating; and (2) the accumulation of polar groups on composite fiber surface significantly increased the surface wettability. Copyright © 2010 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: Tissue engineering scaffolds require cell affinity, biodegradability, and desirable mechanical properties. Poly-L-lactic acid (PLLA) has been investigated for tissue engineering scaffolds owing to its biodegradability and mechanical strength. Electrospun fibers have large surface area and the fibrous structure provides necessary properties for cell attachment, proliferation, differentiation, and sufficient stiffness. PLLA fibers were irradiated with Kr+ at an energy of 50keV with fluences of 1×1013, 1×1014, and 1×1015 ions/cm2 to improve cell affinity. Morphological change was observed by scanning electron microscopy (SEM). Surface properties were measured by FT-IR–ATR and Raman spectroscopy. L929 cell attachment to Kr+-irradiated fibers was evaluated. After the irradiation, the average fiber diameter decreased with high fluence. From the results of the surface analyses, the original chemical bonds were broken and new carbon structures were induced. L929 cell attachment was dramatically improved compared with non-irradiated fibers. Thus, ion-beam irradiated fibers are suitable for tissue engineering scaffolds. This technique is expected to be useful in repairing defects, such as those in nerve, vascular, and liver, in regenerative medicine. [Copyright &y& Elsevier]

Abstract: To promote the biomineralization, supersaturated simulated body fluids (SBFs), e.g. five times SBF (5×SBF), were usually applied. In these SBFs, however, homogeneous nucleation of Ca–P mineralites and deposition unavoidably took place owing to the HCO3 − decomposition and the pH value increment, which made the prediction of bone bioactivity of substrates controversial. In this study, the classically prepared 5×SBF was continuously bubbled with CO2 to keep the pH value stable at 6.4 and the solution transparent, and a kind of electrospun poly(l-lactic acid)/gelatin composite fibers was used for the biomineralization study. In such a modified 5×SBF, heterogenenous nucleation occurred dominantly and thermodynamical unstable brushites (dicalcium phosphate dihydrate, DCPD) were detected shortly on both electrospun PLLA fibers and PLLA/gelatin (1:1 in weight) composite fibers. In comparison with electrospun PLLA fibers, the sheet-like DCPD mineralites transformed into flaky carbonated calcium-deficient hydroxyapatite (CDHA) within 24h on the PLLA/gelatin composite fibers due to the accelerating effect of gelatin component. The formed apatite coating contained much less Mg2+ ions than that deposited in the classical 5×SBF. The results of this study showed that supersaturated SBFs buffered with gassy CO2 were expected good choices for the accelerated biomineralization, and for the prediction of the bone bonding bioactivity of substrates. [Copyright &y& Elsevier]

Anew category of nucleating agent for poly(L-lactic acid) (PLLA) was developed. An organic nucleating agent; N,N'-bis(benzoyl) suberic acid dihydrazide (NA) was synthesized from benzoyl hydrazine and suberoyl chloride which was deprived from suberic acid via acylation. The nucleation, melting behaviour and mechanical properties of the PLLA containing NA were investigated. NA showed excellent nucleating effects on PLLA crystallization. Compared to the neat PLLA, with the addition of 0.8 % NA, the crystallization temperature (To) increase from 105.88°C to 125.57°C and the crystallization enthalpy(ΔHc) increase from 1.379 J g-1to 31.63 J g-1 at a cooling rate of 1°C min-1 from melt. In the presence of NA, the melting behaviour of PLLA was affected significantly, and a double-melting peak resulted during melting-recrystallization. The tensile strengths and tensile modulus increase with the increase of NA content and possesses a maximum value for the critical NA loading of 0.8 %. However, the elongations at break of the samples decreased significantly. [ABSTRACT FROM AUTHOR]

Poly (L-lactic acid) (PLLA) microspheres were prepared by a solvent evaporation method based on an oil/water emulsion. The effect of the mass ratio of PLLA and poly(vinyl alcohol) (PVA) on the formation of the microspheres was discussed, and the influence of extraction speed of dichloromethane on the microsphere morphology was also studied. Moreover, the influences of the PLLA concentration and the volume ratio of water phase to dichloromethane phase were investigated. The results showed that stable microspheres can be obtained under the conditions that the mass ratio of PLLA to PVA is 20:1. Porous microspheres were obtained under faster evaporating speed of dichloromethane. The microsphere size increased with increasing PLLA concentration. The microsphere size also increased with the increase of the volume ratio of water phase to dichloromethane phase. [ABSTRACT FROM AUTHOR]