Characterization of 3D Printed Poly(3-Hydroxybutyric-Co-3-Hydroxyvalerate) by Fused Granular Fabrication through Thermal and Mechanical Analyses

Poly[R-3-hydroxybutyrate-co-(R-3-hydroxyvalerate)] (PHBVs) copolymers are promising biopolymers, which could substitute petroleum-based plastics for various applications. PHB and PHBV pellets were processed on a customized 3D printer via Fused Granular Manufacturing (FGM) approach modified with a Mahor screw extruder. To anticipate the behaviour of PHBVs when transformed using conventional thermo-mechanical shaping processes, thermal and mechanical analyses were carried out in order to better understand the effect of annealing temperature on their crystallization behaviour and mechanical properties of PHB polymer and PHBV copolymer. The objectives of the present work were to propose an experimental strategy to study the melting and crystallization events, crystalline structure changes, and mechanical performances of both PHB homopolymer and PHBV copolymer according to identical thermal annealing treatments. A monitoring of 3D printed PHB and PHBV structures was achieved by coupling Differential Scanning Calorimetry (DSC) and tensile tests. .

BIOSYNTHESIS AND THERMAL PROPERTIES OF POLY(3-HYDROXYBUTYRATE-co-3-HYDROXYVALERATE)WITH LARGE VARIETY OF HYDROXYVALERATE CONTENTS BY BACILLUS CEREUS

Biosynthesis and thermal properties of poly（3-hydroxybutyrate-co-3-hydroxyvalerate） （PHBV） with different HV （hydrovalerate） content produced by a Bacillus cereus strain were investigated. A large variety of HV contents （up to about 90 mol%） of PHBV could be produced by this strain. Combined nitrogen sources containing both yeast extract and ammonium sulphate were better for cell growth and polyhydroxyalkanoates （PHA） production than either yeast extract or ammonium sulphate alone. Propionic acid is more favorable for the production of HV content than that of valeric acid. Finally, thermal properties of PHBV produced by this strain are found close to the results of other groups.

STUDY ON BIODEGRADABILITY OF POLY (3-HYDROXYBUTYRATE-co-3-HYDROXYVALERATE)/ORGANOPHILIC MONTMORILLONITE NANOCOMPOSITES

Poly (3-hydroxybutyrate-co-3-hydroxyvalerate)/Organophilic montmorillonite (PHBV/OMMT) nanocomposites were prepared and the biodegradability of the PHBV/OMMT nanocomposites was studied by a cultivation degrading method in soil suspension. The relationship between structure and biodegradability of PHBV/OMMT nanocomposites was investigated. The results showed that the biodegradability of PHBV/OMMT nanocomposites decreased with increasing amount of OMMT and it was related to the number of PHBV degrading microorganisms in degradation environment, the anti-microbial property of OMMT and the degree of crystallinity of the nanocomposites.

Evaluation of Biodegradation in Aqueous Medium of Poly(Hydroxybutyrate-Co-Hydroxyvalerate)/Carbon Nanotubes Films in Respirometric System

Biodegradable polymers have been increasingly used for scientific and commercial applications because they are similar to some conventional thermoplastics and exhibit the ability of self-degradation.Poly(3-hydroxybutyrate-co-3-hydroxyvalerate)(PHBV)nanocomposites films with 1 and 2 wt% of carbon nanotubes(CNT)were prepared by solution mixing,followed by solvent evaporation.In this work,PHBV/CNT nanocomposites were submitted to biodegradation in an aqueous medium for 34 days through a respirometric system.Then,the PHBV films were analyzed by the CO2 production and mineralization as a response of a microbial attack,which was monitored by back titration during all the experiment.The films were also characterized by measuring the weight loss;crystallinity was evaluated by differential scanning calorimetry(DSC)and the surface morphology by scanning electron microscopy(SEM).By analyzing the weight loss of the films,it was observed that adding CNT increases the resistance to biodegradation process.The obtained values of CO2 production and mineralization of the samples,as well as the values of weight loss,showed that the biodegradation of PHBV/CNT nanocomposites was minor in comparison to neat PHBV.The addition of CNT in PHBV matrix influences the surface morphology,causing the presence of cavities and an increase of roughness.

Preparation and characterization of icariin/PHBV drug delivery coatings on anodic oxidized titanium

A composite material was fabricated by applying a biodegradable drug delivery coating,consisting of poly（3-hydroxyburyrate-co-3-hydroxyvalerate）（PHBV） and icariin,to an anodic oxidized titanium plate.The coating was prepared by evaporating chloroform solution containing PHBV and icariin on the titanium plate under vacuum condition.Icariin/PHBV coated titanium plates significantly enhance the proliferation of MG-63 cells compared with the PHBV coated and anodic oxidized ones.Increased icariin contained in the coating displays an elevated influence on cell proliferation.The results show that icariin gradually releases from the coating to cells mainly through the phospholipid-based cellular membrane instead of the culture medium.The overall results suggest that the novel icariin/PHBV coating can be used to enhance the bioactivity of titanium based orthopedic implants.

The Effects of Accelerated Photooxidation on Molecular Weight and Thermal and Mechanical Properties of PHBV/Cloisite 30B Bionanocomposites

The effects of accelerated photooxidation on the molecular weight and thermal and mechanical properties of Cast PHBV and PHBV/Cloisite 30B(3 wt%)bionanocomposites are investigated herein.Through size exclusion chromatography(SEC)analysis,a significant decrease in both weight and number average molecular weights was observed for all irradiated samples over time,resulting from the chain scission mechanism.Differential scanning calorimetry(DSC)data indicated a decrease in degree of crystallinity and melting temperature after UV exposure,with the appearance of double melting peaks related to the changes in the crystal structure of PHBV.Thermal stability,tensile and thermo-mechanical properties were also reduced consecutively in photooxidation,being more pronounced for Cast PHBV.This study shows that the incorporation of Cloisite 30B in PHBV provides a better resistance to photooxidation in comparison with the neat polymer.

The Effects of Gamma Irradiation on Molecular Weight, Morphology and Physical Properties of PHBV/Cloisite 30B Bionanocomposites

In this paper,the effects of gamma irradiation on Cast poly(3-hydroxybutyrate-co-3-hydroxyvalerate)(PHBV)and PHBV/Cloisite 30B(C30B)(3 wt%)bionanocomposite prepared by melt compounding,were evaluated at various doses,i.e.,5,15,20,50 and 100 kGy at room temperature in air.Changes in molecular weight,morphology and physical properties were investigated.The study showed that the main degradation mechanism occurring in gamma irradiation in both Cast PHBV and C-PHBV/3C30B bionanocomposite is chain scission,responsible for the decrease of molecular weight.Differential scanning calorimetry(DSC)data indicated a regular decrease in crystallization temperature,melting temperature and crystallinity index for all irradiated samples with increasing the dose.Further,DSC thermograms of both Cast PHBV and PHBV bionanocomposite exhibited double melting peaks due probably to changes in the PHBV crystal structure.Tensile and DMA data showed a reduction in Young’s modulus,strength,elongation at break and storage modulus with the radiation dose;the decrease was however more pronounced for Cast PHBV.The morphological damages were much less pronounced for the PHBV bionanocomposite sample compared to Cast PHBV,for which some irregularities and defects were observed at 100 kGy.This study highlighted the ability of C30B to counterbalance the detrimental effect of radiolytic degradation on the functional properties of PHBV up to 100 kGy,thus acting as a potential anti-rad.

Comparison of nitrate-removal efficiency and bacterial properties using PCL and PHBV polymers as a carbon source to treat aquaculture water

Nitrate(NO_(3)^(−))accumulation in recirculating aquaculture systems(RASs)with high stocking densities presents a problem for reared animals and the environment.The use of a biodegradable polymer as organic carbon for heterotrophic denitrification exhibits good performance for NO_(3)^(−)removal from wastewater.A comparison of NO_(3)^(−)–N removal efficiency and bacterial properties using polycaprolactone(PCL)and poly(3-hydroxybutyrateco-3-hydroxyvalerate)(PHBV)as carbon sources to treat aquaculture water was conducted for a 102-day period.The results indicated that the NO_(3)^(−)–N removal rates of 0.27±0.07 and 0.19±0.05 g/L per day,respectively,could be achieved with influent concentrations ranging from 81.1 to 132.75 mg/L and a flow rate of 1 L/h.The removal of NO_(3)^(−)–N versus consumed PCL(1:1 w/w)was significantly higher than that versus consumed PHBV(0.3:1 w/w)(P<0.05).The concentrations of effluent nitrite-nitrogen and total ammonium nitrogen were maintained at an acceptable level.The bacterial community structures between the two types of reactors varied significantly.Acidovorax and Denitratisoma were the top two genera of the bacterial community in the biofilm in the PCL beads with a dominance of 26.83%and 6.67%,respectively.In the PHBV beads,Acidovorax at 17.95%and Bdellovibrio at 6.37%were the top two genera.The PCL-denitrification reactor developed in this study showed better potential than the PHBV-denitrification reactor in removing NO_(3)^(−)from aquaculture water.

Efficacy of nanofibrous conduits in repair of longsegment sciatic nerve defects

Our previous studies have histomorphologically confirmed that nanofibrous poly（3-hydroxybutyrate- co-3-hydroxyvalerate） conduit can be used to repair 30-mm-long sciatic nerve defects. However, the repair effects on rat behaviors remain poorly understood. In this study, we used nanofibrous poly（3-hydroxybutyrate-co-3-hydroxyvalerate） conduit and autologous sciatic nerve to bridge 30-ram-long rat sciatic nerve gaps. Within 4 months after surgery, rat sciatic nerve functional re- covery was evaluated per month by behavioral analyses, including toe out angle, toe spread anal- ysis, walking track analysis, extensor postural thrust, swimming test, open-field analysis and no- ciceptive function. Results showed that rat sciatic nerve functional recovery was similar after nanofibrous poly（3-hydroxybutyrate-co-3-hydroxyvalerate） conduit and autologous nerve grafting. These findings suggest that nanofibrous poly（3-hydroxybutyrate-co-3-hydroxyvalerate） conduit is suitable in use for repair of long-segment sciatic nerve defects.

Comparative evaluation of physico-chemical characteristics of biopolyesters P（3HB） and P（3HB-co-3HV） produced by endophytic Bacillus cereus RCL 02

BACKGROUND： Bacteria endogenously residing within the plant tissues have attracted significant attention for production of biopolyester, polyhydroxyalkanoates （PHAs）. Bacillus cereus RCL 02 （MCC 3436）, a leaf endophyte of oleaginous plant Ricinus communis L. accumulates 81% poly（3-hydroxybutyrate） [P（3HB）] of its cell dry biomass when grown in mineral salts （MS） medium. METHODS： The copolymer production efficiency of B. cereus RCL 02 was evaluated in valeric acid supplemented MS medium under biphasic cultivation condition. The copolymer so produced has been compared with the P（3HB） isolated from RCL 02 in terms of thermal, mechanical and chemical properties. RESULTS： Valeric acid supplementation as co-substrate in the medium has led to the production of copolymer of 3- hydroxybutyrate （3HB） and 3-hydroxyvalerate （3HV） [P（3HB-co-3HV）] with 14.6 mol% 3HV. The identity of the polymers has been confirmed by X-ray diffraction （XRD） analysis, Fourier transform infrared （FTIR） and nuclear magnetic resonance （NMR） spectroscopic studies. Thermogravimetric analysis （TGA） revealed that P（3HB） and P（3HB-co-3HV） films degraded at 278.66℃ and 273.49℃, respectively. The P（3HB-co-3HV） showed lower melting temperature （165.03℃） compared to P （3HB） （170.74℃） according to differential scanning calorimetry （DSC）. Incorporation of 3HV monomers decreased the tensile strength （21.52 MPa）, tensile modulus （0.93 GPa）, storage modulus （E＇） （0.99 GPa） and increased % elongation at break （12.2%） of the copolyester. However, P（3HB） showed better barrier properties with lower water vapor transmission rate （WVTR） of 0.55 g-mil/100 in2/24 h. CONCLUSION： These findings emphasized exploration of endophytic bacterial strain （RCL 02） to produce biodegradable polyesters which might have significant potential for industrial application.

Doping Gd^(3+)Ion in PDA-PHBV Coating on Ti6Al4V Alloy for Enhancing Corrosion Resistance and Proliferation of Human Gingival Fibroblasts and Human Umbilical Vein Endothelial Cells

In this study,we fabricated poly(3-hydroxybutyrate-3-hydroxyvalerate)(PHBV)coatings doped with Gd^(3+)(1,5,and 10×10^(−4) mol/L)on Ti6Al4V alloy for the first time to promote soft tissue sealing around dental implants.The corrosion resistance of Gd^(3+)-modified PHBV-coated Ti6Al4V was studied by electrochemical and immersion tests,respectively,whereas CCK-8 and RT-PCR evaluated the biocompatibility to human gingival fibroblasts(HGFs)and human umbilical vein endothelial cells(HUVECs).It was found that the Gd^(3+)-modified PHBV coating could enhance the corrosion resistance of Ti6Al4V.In vitro cell tests showed that PHBV coatings with and without Gd^(3+) addition could promote adhesion and proliferation of HGFs and HUVECs,showing a Gd^(3+) content-dependent manner.Moreover,it was found that the PDA-PHBV@1Gd showed the best proliferation to HGFs by up-regulating gene expressions of VINCULIN,ITGB1,and ITGA3,whereas the best response to HUVECs with the highest gene expression of eNOS and HIF-1αgenes was found in the PDA-PHBV@5Gd-coated group.