In Vivo Degradation Behavior of Porous Composite Scaffolds of Poly（lactide-co-glycolide） and Nano-hydroxyapatite Surface Grafted with Poly（L-lactide）

The biodegradable porous composite scaffold, composed of poly(lactide-co-glycolide)(PLGA) and hydroxyapatite nanoparticles(n-HAP) surface-grafted with poly(L-lactide)(PLLA)(g-HAP)(g-HAP/PLGA), was fabricated using the solvent casting/particulate leaching method, and its in vivo degradation behavior was investigated by the intramuscular implantation in rabbits. The composite of un-grafted n-HAP/PLGA and neat PLGA were used as controls. The scaffolds had interconnected pore structures with average pore sizes between 137 μm and 148 μm and porosities between 83% and 86%. There was no significant difference in the pore size and porosity among the three scaffolds. Compared with n-HAP/PLGA, the thermo-degradation temperature(Tc) of g-HAP/PLGA decreased while its glass transition temperature(Tg) increased. The weight change, grey value analysis of radiographs and SEM observation showed that the composite scaffolds of g-HAP/PLGA and n-HAP/PLGA showed slower degradation and higher mineralization than the pure PLGA scaffold after the intramuscular implantation. The rapid degradation of PLGA, g-HAP/PLGA and n-HAP/PLGA occurred at 8–12 weeks, 12–16 weeks and 16–20 weeks, respectively. Compared with n-HAP/PLGA, g-HAP/PLGA showed an improved absorption and biomineralization property mostly because of its improved distribution of HAP nanoparticles. The levels of both calcium and phosphorous in serum and urine could be affected to some extent at 3–4 weeks after the implantation of g-HAP/PLGA, but the biochemical detection of serum AST, ALT, ALP, and GGT as well as BUN and CRE showed no obvious influence on the functions of liver and kidney.     

Preparation and in vitro degradation of porous three-dimensional silk fibroin/chitosan scaffold

Degradation behaviors of porous scaffolds play an important role in the engineering process of a new tissue. In this study, three-dimensional porous silk fibroin/chitosan (SFCS) scaffolds were successfully prepared by freeze-drying method. In vitro degradation behaviors of SFCS scaffolds have been systematically investigated up to 8 weeks in phosphate buffer saline (PBS) solution at 37 °C. The following properties of the scaffolds were measured as a function of degradation time: pore morphology, structure, weight loss, and wet/dry weight value. The pH value of the PBS solution during degradation was also detected. SFCS scaffolds maintained its porous structure till 6 weeks of degradation. During the first 2 weeks, the pH value fluctuated in a narrow range from 6.53 to 6.93. SFCS scaffolds degraded much more quickly during the first 2 weeks, and the weight loss reached 19.28 wt% after 8 weeks of degradation. The degradation process affects little SFCS scaffolds' swelling properties.     

Biodegradation of poly(l-lactide-co-glycolide) tube stents in bile

The objective of this study was to evaluate degradation behavior and the feasibility of biodegradable polymeric stents in common bile duct (CBD) repair and reconstruction. Various molar ratios of lactide (LA) and glycolide (GA) in poly(l-lactide-co-glycolide) (PLGA) were synthesized and processed into a circular tubing of ∼10.0 mm outer diameter and a wall thickness of about 2.0 mm. This tubing was cut into 40.0 mm length to form CBD stents. The stents were placed into human bile to determine the degradation behavior in vitro. The morphology, configuration, mass loss, water uptake, molecular weight and composition changes were examined. The PLGA with LA/GA = 71/29 exhibited an acceptable degradation life and was chosen as an in vivo stent material. These PLGA stents were used in common bile duct exploration (CBDE) and primary suturing for rats. Degradation status of the stents was examined and comparison was made between those before and after surgical procedure. The results showed that the polymer stents exhibited the same biomedical functions as T tubes and spontaneously disappeared from CBD in 4-5 weeks. Therefore, the PLGA stents fits the requirements in repair and reconstruction of CBD, to support the duct, guide bile drainage and reduce T-tube-related complications.     

Preparation of poly(lactide-co-glycolide-co-caprolactone) nanoparticles and their degradation behaviour in aqueous solution

The tri-component copolymer poly(lactide-co-glycolide-co-caprolactone) (PLGC) was synthesized to prepare nanoparticles by the modified spontaneous emulsification solvent diffusion method (modified-SESD method); and the method was also modified by using the Tween60 instead of poly(vinyl alcohol) (PVA) as dispersing agent. The obtained nanoparticles have spherical shape and good particle distribution with mean size in the range from 100 to 200 nm. The in vitro degradation behaviour of PLGC nanoparticles was investigated. It was found that PLGC nanoparticles could remain stable during the degradation with no agglomeration. Compared with PLA and PLGA nanoparticles, the degradation rate of PLGC nanoparticles is faster. After 9 weeks of hydrolysis, the M_n of PLGC is less by 10% of the original M_n. The mean radius of the nanoparticles increases from 68 nm to 80 nm continuously during the first stage, and after 4 weeks of degradation, the particles' size decreases gradually from 80 nm to about 40 nm. These results suggest that the PLGC nanoparticles may show degradation-controlled drug release behaviour and seem to be a promising drug delivery system.     

In vitro and in vivo degradation behaviors of synthetic absorbable bicomponent monofilament suture prepared with poly(p-dioxanone) and its copolymer

A synthetic absorbable bicomponent monofilament suture (MonoFlex), composed of poly(p-dioxanone) and its copolymer, was prepared by a conjugate spinning method, and its degradation behavior was investigated in vitro and in vivo. MonoFlex degraded by hydrolysis, and retained approximately 55% of its original strength after four weeks of incubation in PBS at 37 °C. About 70% of the original strength was maintained after four weeks of implantation in rats, and the suture material was completely absorbed after 180-210 days post-implantation in rats. No remarkable tissue reactions were observed during degradation, and foreign body reactions were similar to those of commercially available suture materials composed of poly(p-dioxanone). This study to monitor the degradation behavior of monofilament sutures in vitro as well as in vivo may be useful in the development of novel suture materials for extended wound support.     

Mechanical properties and degradation studies of poly(D,L‐lactide‐co‐glycolide) 50:50/graphene oxide nanocomposite films

Poly(D,L‐lactide‐co‐glycolide) 50:50 (PLGA)/graphene oxide (GO) nanocomposite films were prepared with various GO weight fractions. A significant enhancement of mechanical properties of the PLGA/GO nanocomposite films was obtained with GO weight fractions. The incorporation of only 5 wt% of GO resulted in an ~2.5‐fold and ~4.7‐fold increase in the tensile strength and Young's modulus of PLGA, respectively. The thermomechanical behaviors of composite films were investigated by dynamic mechanical analysis. Results indicated that the values of T_g and storage moduli of the PLGA/GO composites were higher than those of the pristine PLGA. The improvement in oxygen barrier properties of composites was presumably attributed to the filler effect of the randomly dispersed GO throughout the PLGA matrix. In this work, we also studied in vitro biodegradation behavior. PLGA/GO composite films were hydrolyzed at 37°C for periods up to 49 days. Because of the presence of GO nanosheets, degradation of composite films took place more slowly with increasing GO amounts. Copyright © 2013 John Wiley & Sons, Ltd.     

In vitro degradation of porous poly(l-lactide-co-glycolide)/β-tricalcium phosphate (PLGA/β-TCP) scaffolds under dynamic and static conditions

In vitro degradation of porous poly(l-lactide-co-glycolide)/β-tricalcium phosphate (PLGA/β-TCP) scaffolds was studied by incubating the samples in phosphate buffered saline (PBS) at 37 °C and pH 7.4 under dynamic loading with respect to static conditions for 12 weeks. Under dynamic conditions, acidity of PBS was alleviated by the better solution circulation, and water absorption of the scaffolds increased more than that under static conditions in the first 8 weeks. Changes in mass, height, diameter, relative molecular mass and its distribution also happened more remarkably under dynamic conditions. Moreover, obvious cracks and a larger amount of β-TCP particles were observed on the wall of the scaffolds after degradation for 12 weeks under dynamic loading. Compressive modulus and strength showed an increase from the beginning to the 10th week but were lower after then. Results showed that degradation of PLGA/β-TCP scaffolds under dynamic conditions exhibited a significantly faster rate than that under static conditions.     

Synthesis and photocatalytic activity of co-doped mesoporous TiO2 on Brij98/CTAB composite surfactant template

Using composite surfactant templates, polyoxyethylene (20) oleyl ether (Brij98) and cetyl trimethyl ammonium bromide (CTAB), as structure-directing agents, N and La co-doped mesoporous TiO₂ complex photocatalysts were synthesized successfully. The micromorphology of co-doped mesoporous TiO₂ samples was characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transformed infrared spectroscopy (FT-IR), energy-dispersive X-ray spectrometer (EDS) and N₂ adsorption-desorption measurements. The results indicated that the complex photocatalyst prepared with a molar ratio of Brij98:CTAB=1:1 showed a uniform pore size of ca. 7 nm and a high specific surface area (S_BET) of 279.0 m² g⁻¹, and exhibited the highest photocatalytic activity for degradation of papermaking wastewater under ultra-violet light irradiation. The chemical oxygen demand (CODc_r) percent degradation was about 73% in 12 h and chroma percent degradation was 100% in 8 h.     

Preparation and mechanical behavior of PLGA/nano-BCP composite scaffolds during in-vitro degradation for bone tissue engineering

In this paper, the yield strength and elastic modulus of Poly (lactide-co-glycolide) (PLGA) and PLGA/nano-biphasic calcium phosphate (nBCP) composite scaffolds, before and during in-vitro degradation, have been evaluated. Composite scaffolds were made by using PLGA matrix and 10-50 wt.% nBCP powder as the reinforcement material. All scaffolds, with more than 89% porosity, were fabricated by thermally-induced phase separation (TIPS). During in-vitro degradation (0-8 weeks), the PLGA/nBCP scaffolds showed both more weight loss and better mechanical properties as compared to neat PLGA scaffolds. The PLGA/nBCP scaffolds with 30 wt.% nBCP illustrated the highest value of yield strength among the composite scaffolds, before and after degradation, until 6 weeks. After 8 weeks, the yield strength values were very poor and close to each other. The values of elastic modulus for all samples were less than the half of their initial values after 6 weeks. However, after 8 weeks, the elastic moduli of all samples reduced to negligible values.     

Phase behavior of biodegradable amphiphilic poly(l,l-lactide)-b-poly(ethylene glycol)-b-poly(l,l-lactide)

This study describes the miscibility phase behavior in two series of biodegradable triblock copolymers, poly(l-lactide)-block-poly(ethylene glycol)-block-poly(l-lactide) (PLLA-PEG-PLLA), prepared from two di-hydroxy-terminated PEG prepolymers (M_n = 4000 or 600 g mol⁻¹) with different lengths of poly(l-lactide) segments (polymerization degree, DP = 1.2-145.6). The prepared block copolymers presented wide range of molecular weights (800-25,000 g mol⁻¹) and compositions (16-80 wt.% of PEG). The copolymer multiphases coexistance and interaction were evaluated by DSC and TGA. The copolymers presented a dual stage thermal degradation and decreased thermal stability compared to PEG homopolymers. In addition, DSC analyses allowed the observation of multiphase separation; the melting temperature, T_m, of PLLA and PEG phases depended on the relative segment lengths and the only observed glass transition temperature (T_g) in copolymers indicated miscibility in the amorphous phase.     

Fabrication of poly(lactide‐co‐glycolide) scaffold embedded spatially with hydroxyapatite particles on pore walls for bone tissue engineering

Poly(lactide‐co‐glycolide) (PLGA) scaffolds embedded spatially with hydroxyapatite (HA) particles on the pore walls (PLGA/HA‐S) were fabricated by using HA‐coated paraffin spheres as porogens, which were prepared by Pickering emulsion. For comparisons, PLGA scaffolds loaded with same amount of HA particles (2%) in the matrix (PLGA/HA‐M) and pure PLGA scaffolds were prepared by using pure paraffin spheres as porogens. Although the three types of scaffolds had same pore size (450–600 µm) and similar porosity (90%–93%), the PLGA/HA‐S showed the highest compression modulus. The embedment of the HA particles on the pore walls endow the PLGA/HA‐S scaffold with a stronger ability of protein adsorption and mineralization as well as a larger mechanical strength against compression. In vitro culture of rat bone marrow stem cells revealed that cell morphology and proliferation ability were similar on all the scaffolds. However, the alkaline phosphatase activity was significantly improved for the cells cultured on the PLGA/HA‐S scaffolds. Therefore, the method for fabricating scaffolds with spatially embedded nanoparticles provides a new way to obtain the bioactive scaffolds for tissue engineering. Copyright © 2011 John Wiley & Sons, Ltd.     

hGH release from directly compressed hGH-PLGA biodegradable implantable tablets: Influence of physicomechanical factors

The incidence of compression conditions, porosity and polymer degradation on human growth hormone (hGH) release from PLGA implantable tablets was evaluated with the aim of gaining insight in the mechanism involved in drug delivery from biodegradable matrices. Tablets elaborated by direct compression of hGH with PLGA, applying various compression forces for different times, kept the integrity and the stability of the hormone. Tablet dimensions, viscoelastic properties, glass to rubber transition temperature (T_g), PLGA degradation rate and water uptake were analyzed in the freshly prepared implantable tablets as well as at several times during release test in phosphate buffer pH 7.4. Placebo tablets were also prepared to evaluate the incidence of hGH on the physicomechanical properties of the device and PLGA degradation rate. Porosity remarkably determined the amount of hGH released, through an effect on the easiness of water penetration in the tablet and on the beginning of PLGA degradation. The decrease in PLGA molecular weight during the first days in the release medium, despite of being minor, significantly conditioned hGH release rate. The more dramatic changes in PLGA molecular weight observed after 20 days in the release medium notably reduced the T_g and the viscous and elastic moduli of the tablets. The overall analysis of the events underwent by the tablets in contact with the aqueous medium was used to explain the drug release profile and may help to optimize the design of the PLGA-based implantable tablets as peptidic drug delivery systems.     

Novel low humidity sensor made of TiO(2) nanowires/poly(2-acrylamido-2-methylpropane sulfonate) composite material film combined with quartz crystal microbalance

A novel ceramic nanowires of TiO₂ and poly(2-acrylamido-2-methylpropane sulfonate) (TiO₂ NWs/PAMPS) composite material films coated on quartz crystal microbalance (QCM) was prepared as a low humidity sensor. The 50 wt.% of TiO₂ NWs/PAMPS composite material films showed excellent sensitivity (2.63 −ΔHz/Δppm_v) at 31.5 ppm_v), linearity (R² = 0.9959) and acceptable response time (64 s at 34.6 ppm_v). The low humidity sensing mechanism was discussed in terms of surface texture and nanostructured morphology of the composite materials. Moreover, the adsorption dynamic analysis, molecular mechanics calculation (association constant), was used to elucidate the effect of adding 50 wt.% TiO₂ NWs into PAMPS in the increased sensitivity of low humidity sensing.     

Electron-beam irradiation on poly(propylene carbonate) in the presence of polyfunctional monomers

Poly(propylene carbonate) (PPC) showed predominantly degradation under electron-beam irradiation, accompanied by deterioration of its mechanical performance due to sharp decrease of the molecular weight. Crosslinked PPC was prepared by addition of polyfunctional monomer (PFM) to enhance the mechanical performance of PPC. When 8 wt% of PFM like triallyl isocyanurate (TAIC) was added, crosslinked PPC with a gel fraction of 60.7% was prepared at 50 kGy irradiation dose, which showed a tensile strength at 20 °C of 45.5 MPa, whereas it was only 38.5 MPa for pure PPC. The onset degradation temperature (T_i) and glass transition temperature (T_g) of this crosslinked PPC was 246 °C and 45 °C, respectively, a significant increase related to pure PPC of 211 °C and 36 °C. Therefore, thermal and mechanical performances of PPC could be improved via electron-beam irradiation in the presence of suitable PFM.     

Compressive mechanical properties and biodegradability of porous poly(caprolactone)/chitosan scaffolds

Porous polycaprolactone(PCL)/chitosan(CH) scaffolds with large pore sizes and high porosities were fabricated via a particle-leaching technique using hexafluoro-2-propanol as a shared solvent and salt (sodium chloride) particles as porogen. By optimizing processing conditions, numerous PCL/CH scaffolds with CH proportion lower than 50 wt% and similar pore parameters were built. These scaffolds were further evaluated for their compressive mechanical properties and biodegradation behaviors. It was found that their compressive modulus and stress at 10% strain were basically maintained in their dry state in contrast to their individual components, and these scaffolds still showed well-defined compressive characteristics and dimension stability even in their hydrated state compared with pure chitosan scaffolds. After being exposed to PBS or enzymatic degradation systems in vitro for various periods up to 10 weeks, it was observed that degradation of the PCL component could be accelerated at various rates depending on the compositions of the scaffolds and the media, and the chiosan component could effectively buffer the acidic degradation products of the PCL component.     

Properties of PWA/ZrO2-doped phosphosilicate glass composite membranes for low-temperature H2/O2 fuel cell applications

Phosphosilicate doped with a mixture of phosphotungstic acid and zirconium oxide (PWA/ZrO₂–P₂O₂–SiO₂) was investigated as potential glass composite membranes for use as H₂/O₂ fuel cell electrolytes. The glass membranes were studied with respect to their structural and thermal properties, proton conductivity, pore characteristics, hydrogen permeability, and performance in fuel cell tests. Thermal analysis including TG and DTA confirmed that the glass was thermally stable up to 400 °C. The dependence of the conductivity on the humidity was discussed based on the PWA content in the glass composite membranes. The proton transfer in the nanopores of the PWA/ZrO₂–P₂O₅–SiO₂ glasses was investigated and it was found that a glass with a pore size of ∼3 nm diameters was more appropriate for fast proton conduction. The hydrogen permeability rate was calculated at various temperatures, and was found to be comparatively higher than for membranes based on Nafion^®. The performance of a membrane electrolyte assembly (MEA) was influenced by its PWA content; a power density of 43 mW/cm² was obtained at 27 °C and 30% relative humidity for a PWA/ZrO₂–P₂O₅–SiO₂ glass membrane with a composition of 6–2–5–87 mol% and 0.2 mg/cm² of Pt/C loaded on the electrode.     

The impact of chemical composition on the degradation kinetics of poly(lactic-co-glycolic) acid copolymers cast films in phosphate buffer solution

We have investigated the in vitro degradation of poly(lactic-co-glycolic) acid copolymer with different lactic to glycolic ratio: 50:50, 65:35, 75:25, 95:05 and 100:00 (mol. %). The degradation studies were performed on solvent cast films of controlled thickness and shape. The samples were incubated at 37 °C in phosphate buffered saline solution. The degradation was followed using potentiometry, light microscopy, gravimetry, size exclusion chromatography and differential scanning calorimetry. The same degradation process, as discussed in detail in our previous article for PLGA 50:50 (E. Vey et al., J. of Polym. Deg. and Stab. 2008, 93, 1896-1876), was observed for all the samples investigated, however the time scale over which the different events/degradation steps were observed increased with increasing lactic content of the polymer. The glass transition temperatures of the films increase with lactic content and are thought to have a significant impact on the rate of diffusion of water into the films - the higher the glass transition the slower the diffusion of water - and therefore on the degradation dynamics of the films. Kinetic parameters were extracted from the acid release, molecular weight and mass loss data. In each case linear correlations between the rate constants extracted and the lactic content of the polymer were found. The overall degradation rate of the films was found to decrease with increasing lactic content.     

Study of the in vitro degradation of poly(ethyl glyoxylate)

In vitro degradation of poly(ethyl glyoxylate) (PEtG), a functionalised polyacetal, was investigated. First, the thermodynamic polymerization parameters and the ceiling temperature (T_c) were determined (ΔH_p = 28 ± 3 kJ mol⁻¹, ΔS_p = 98 ± 7 J mol⁻¹ K⁻¹, T_c = 310 ± 4 K). Secondly, PEtG hydrolysis was investigated using potentiometry, weight loss measurements, SEC and ¹H NMR. The results show that PEtG is stable for at least 7 days in aqueous media. Then degradation occurs and releases ethanol and glyoxylic acid hydrate as final products. A scheme for the degradation mechanism involving chain scission and ester hydrolysis is proposed.     

Preparation and characterization of SiO2/TiO2 composite microspheres with microporous SiO2 core/mesoporous TiO2 shell

SiO₂/TiO₂ composite microspheres with microporous SiO₂ core/mesoporous TiO₂ shell structures were prepared by hydrolysis of titanium tetrabutylorthotitanate (TTBT) in the presence of microporous silica microspheres using hydroxypropyl cellulose (HPC) as a surface esterification agent and porous template, and then dried and calcined at different temperatures. The as-prepared products were characterized with differential thermal analysis and thermogravimetric (DTA/TG), scanning electron microscopy (SEM), X-ray diffraction (XRD), nitrogen adsorption. The results showed that composite particles were about 1.8 μm in diameter, and had a spherical morphology and a narrow size distribution. Uniform mesoporous titania coatings on the surfaces of microporous silica microspheres could be obtained by adjusting the HPC concentration to an optimal concentration of about 3.2 mmol L⁻¹. The anatase and rutile phase in the SiO₂/TiO₂ composite microspheres began to form at 700 and 900 °C, respectively. At 700 °C, the specific surface area and pore volume of the SiO₂/TiO₂ composite microspheres were 552 and 0.652 mL g⁻¹, respectively. However, at 900 °C, the specific surface area and pore volume significantly decreased due to the phase transformation from anatase to rutile.     

Preparation and characterization novel polymer-coated magnetic nanoparticles as carriers for doxorubicin

The poly(lactide-co-glycolide)-coated magnetic nanoparticles (PLGA MNPs) were prepared as carriers of doxorubicin (PLGA-DOX MNPs) through water-in-oil-in-water (W/O/W) emulsification method. The characteristics of PLGA-DOX MNPs were measured by using transmission electron microscopy (TEM) and vibrating-sampling magnetometry (VSM). It was found that the synthesized nanoparticles were spherical in shape with an average size of 100 ± 20 nm, low aggregation and good magnetic responsivity. Meanwhile, the drug content and encapsulation efficiency of nanoparticles can be achieved by varying the feed weight ratios of PLGA and DOX particles. These PLGA-DOX MNPs also demonstrated sustained release of DOX at 37 °C in buffer solution. Besides, influence of drug-loaded nanoparticles on in vitro cytotoxicity was determined by MTT assay, while cellular apoptosis was detected by Annexin V-FITC apoptosis detection kit. The results showed that PLGA-DOX MNPs retained significant antitumor activities. Therefore, PLGA-DOX MNPs might be considered a promising drug delivery system for cancer chemotherapy.