Repeated-Batch and Continuous Production of L-Lactic Acid by Rhizopus oryzae Immobilized in Calcium Alginat Beads:ReactorPerformance and Kinetic Model

Repeated-batch and continuous production of L-lactic acid by immobilized Rhizopusoryzae with calcium alginate entrapment method in a three-phase fluidized-bed bioreactor was stud-ied.The operation conditions were optimized.The productivity based on total reactor volume wasabout 3 times higher than that with free cells in a traditional stirred tank bioreactor.A mathemat-ical model was proposed and the model predictions were in good agreement with the experimentaldat.

Synthesis of the Biomimetic Polymer: Aliphatic Diamine and RGDS Modified Poly(d,l-lactic acid)

A novel poly（d, /-lactic acid） （PDLLA） based biomimetic polymer was synthesized by grafting maleic anhydride, butanediamine and arg-gly-asp-ser （RGDS） peptides onto the backbone of PDLLA, aiming to overcome the acidity and auto-accelerating degradation of PDLLA during degradation and to improve its biospecificity and biocompatibility. The synthetic copolymer was characterized by FTIR, ^13C NMR and amino acid analyzer （AAA）.

Effect of a Novel Nucleating Agent on Isothermal Crystallization of Poly（L-lactic acid）

The effect of a novel active nucleating agent(TBC8-eb) on the isothermal crystallization of poly(L-lactic acid) (PLLA) was studied by differential scanning calorimetry(DSC) and Fourier transform infrared spectroscopy(FTIR) . The analysis on kinetics demonstrates that TBC8-eb can not only accelerate the crystallization rate but also transform most of the original spherulite crystals of PLLA into sheaf-like crystals. Furthermore,the free energy of folding(σe) of PLLA and PLLA with TBC8-eb is 0.15 and 0.06 J·m-2,respectively,which suggests that the addition of TBC8-eb favors the regular folding of molecule chains in the crystallization of PLLA,improv-ing its crystallization rate. The FTIR results show that TBC8-eb can accelerate the conformational ordering of PLLA in the isothermal crystallization. The conformational ordering of PLLA nucleated with TBC8-eb begins with the interchain interaction of CH3,and then a short helix emerges where a couple of CH3 groups interact.

L-LACTIC ACID FERMENTATION IN A ROTATING-DISC CONTACTOR WITH SIMULTANEOUS PRODUCT SEPARATION BY ION-EXCHANGE

A rotating disk contactor（RDC）was designed to perform L-lactic acid fermentation with afilamentous fungi,Rhizopus oryzae,which was immobilized on the surfaces of the rotating discs.Thebioreactor was operated using repeated-batch method as well as continuous feeding method.Ananionic resin,D354,slightly basic in nature and of high selectivity and capacity was chosen for lacticacid separation.A coupled process of L-lactic acid fermentation and ion-exchange separation wasevaluated experimentally.The results indicated that the pH value of the fermentation broth could bemaintained at about 3-3.5 without any addition of alkali.The conversion ratio of glucose to L-lacticacid was about 0.7 g·g-1 and the fermentation rate reached as high as 62.5 g·h-1·m-2.

Synthesis and Characterization of Chitosan-g-poly- (D, L-lactic acid) Copolymer

Biodegradable chitosan-g-poly (D, L-lactic acid) copolymers were prepared via two methods. (1) The lactide was grafted onto hydroxyl groups of chitosan by using macromolecular initiator sodium of trimethylsilyl-chitosan, (2) poly (D,L-lactic acid)(PLA) with low molecular weight can be linked to the amino group by coupling activated PLA to trimethylsilyl-chitosan. Two graft copolymers had hydrophilic-hydrophobic character and can be applied as carriers for drug delivery.

Preparation and Properties of Bio-Based Flame Retardant L-APP/Poly(L-lactic acid)Composites

Poly(L-lactic acid)(PLLA)is a thermoplastic material with complete degradability,high biocompatibility and excellent mechanical properties.It can replace petroleum-based polymers are currently being used in the fields of packaging,agriculture,textiles,medical and so on.However,PLLA’s extremely flammability greatly limits its wider application.An bio-based flame retardant L-APP/PLLA composites was prepared by melt blending of the L-APP and PLLA.The morphology,impact properties,thermal properties and flame retardant properties of composites were investigated by field emission scanning electron microscope(SEM),impact tester,differential scanning calorimeter(DSC),thermogravimetric analyzer(TGA),limiting oxygen indexer(LOI)and horizontalvertical burning tester.The results showed that the degree of crystallization(X_(c))and LOI of L-APP/PLLA composites increased as increasing of L-APP content.What’s more,the impact strength first increased and then decreased,the glass transition temperature(T_(g))and melting temperature(T_(m))do not changed significantly.The impact strength of composites was 9.1 kJ/m^(2) at a 5 wt%loading for L-APP,which was the highest level.When the content of L-APP was 20%,the LOI was 30.8%,the Xc was 42.3%and the UL-94 level was V-0.This research can promote the value-added utilization of lignin and the application of PLLA in the fields of flame retardant materials.

SURFACE OF GELATIN MODIFIED POLY(L-LACTIC ACID)FILM

In this paper, the surface structure of poly(L-lactic acid) (PLLA) film modified with gelatin was investigated. ThePLLA film specimens were treated directly with aqueous alkali solution to provide their surfaces with carboxyl groups, sothat these functional groups could become the reactive sites for gelatin immobilization. The functional groups of the PLLAfilms were identified by ATR-FTIR spectra and XPS spectra, the changes in surface morphology were observed by usingenvironmental scanning electron microscopy (ESEM), and the hydrophilicity of modified PLLA films was examined bywater contact angle measurement. Experimental results showed that the gelatin was immobilized with water-solublecarbodiimide (EDC) onto the PLLA film's surfaces, and the gelatin content on the polymer surface was related to carboxylicgroup formed in the controlled hydrolysis process. Rough surfaces caused by hydrolysis will predominantly favor the adhesion and growth of cell; and the hydrophilicity of these surfaces after the modification procedure is enhanced.

Biomechanical features of Poly-D,L-lactic acid (PDLLA) rods through the degradation in vitro and in vivo

Objective：To observe the changing of biomechanical features during the degradation course of poly-D,L-lactic acid （PDLLA） rods in vivo and in vitro and to evaluate its value as an internal fixation material. Methods ：PDLLA rods were emerged into PBS simultaneous body fluid with constant temperature of 37℃ and the rods were embedded into muscle tissue of 20 rabbits for degradation in vitro and in vivo . The rods were taken out in 2, 4, 6, 8 and 12 weeks. Biomechanical features of bending, shearing and axial compression strength, rigidity and elastic modulus were observed during the degradation course. Statistical method was used to test the changes of biomechanical parameters. Results： （1）There was similar changes of bending, compressive, shearing strength and bending, compressive and shearing rigidity of the PDLLA rods between in vivo and in vitro. （2）Bending, compressive, shearing strength decreased 33%, 18 % and 43 % respectively within the first stage of the degradation, and after 6 weeks of degradation, they decreased slowly. （3）Elastic modulus, bending, compressive and shearing rigidity.decreased sharply during the 6 weeks of degradation, with a drop of 22%, 39% and 30% respectively, and after 8 weeks, they decreased slowly. Even after 12 weeks of degradation, the strength of the rods was still higher than that of sponge bone. Conclusion： During the degradation of the material, the strength and rigidity of PDLLA rods can meet the need of fracture fixation of cancellous bones.

Electrospun Chitosan( CS)/Poly( L-lactic-co-ε-caprolactone)( PLCL ) Nanofibers and Their Potential as Small-Diameter Vascular Scaffold

The ideal small-diameter vascular grafts should mimic the nanostructure and mechanical properties of nature blood vessel. In this study, electrospun chitosan( CS)/poly( L-lactic-co-ε-caprolactone)( PLCL) nanofibers were developed for potential small-diameter blood vessel applications. CS is a positively charged polymer which is beneficial for cell attachment and growth,while PLCL provides favorable mechanical support due to its excellent elasticity. Typical nanofibrous structure was observed in both CS/PLCL and pure PLCL scaffolds. The optimal mechanical property could be achieved when the weight ratio of CS/PLCL was 1 ∶ 2.Compared with pure PLCL scaffolds, the CS/PLCL scaffolds showed higher hydrophilicity and markedly promoted the attachment,spreading and proliferation of human umbilical vein endothelial cells( HUVECs). Hence,CS/PLCL scaffolds can be used as potential vascular grafts.

Multi-porous electroactive poly(L-lactic acid)/ polypyrrole composite micro/nano fibrous scaffolds promote neurite outgrowth in PC12 cells

In this study, poly（L-lactic acid）/ammonium persulfate doped-polypyrrole composite fibrous scaffolds with moderate conductivity were produced by combining electrospinning with in situ polymerization. PC12 cells were cultured on these fibrous scaffolds and their growth following electrical stimulation （0-20.0 μA stimulus intensity, for 1-4 days） was observed using inverted light microscopy, and scanning electron microscopy coupled with the MTT cell viability test. The results demonstrated that the poly（L-lactic acid）/ammonium persulfate doped-polypyrrole fibrous scaffold was a dual multi-porous micro/nano fibrous scaffold. An electrical stimulation with a current intensity 5.0- 10.0 μAfor about 2 days enhanced neuronal growth and neurite outgrowth, while a high current intensity （over 15.0 μA） suppressed them. These results indicate that electrical stimulation with a moderate current intensity for an optimum time frame can promote neuronal growth and neurite outgrowth in an intensity- and time-dependent manner.

Chitosan——L-Lactic Acid Scaffold for the Regeneration of Peripheral Nerve and Its NGF Release Properties

Chitosan—L-lactic acid composite scaffold for the regeneration of peripheral nerve is obtained by grafting L-lactic acid onto the amino groups in chitosan with combined vacuum freezer drier. The composite scaffold was characterized by ATR-FTIR and SEM. The scaffold has a better graft efficiency and has a dense inner layer and a loose outer layer with porous structure, and the pore size is about 100 μm.The NGF release properties of the scaffold were investigated. The experimental results showed that, at the 1st day, 15.2 ng of NGF on average was released from the scaffold. From day 2 to day 10, the release rate obviously slowed down and 1.64 ng of NGF was released on average every day. After 10 days, the release rate was slower and 10.3 ng of NGF was released on average every day. After 60 days, NGF could also maintained a certain concentration. These properties show that the scaffold is a better carrier for NGF which can be more advantageous to the regeneration of the damaged peripheral nerve. As a result, this composite scaffold would be an ideal candidate for the regeneration of damaged peripheral nerve.

Effect of Process Parameters on Co-precipitation of Paclitaxel and Poly(L-lactic Acid) by Supercritical Antisolvent Process

Paclitaxel(PTX) is an effective anticancer drug with poor solubility in water.Recently,much effort has been devoted into alternative formulations of PTX for improving its aqueous solubility.In this study,PTX and poly(L-lactic acid)(PLLA) were co-precipitated by a supercritical antisolvent(SAS) process using dichloromethane(DCM) and the mixtures of DCM/ethanol(EtOH) or DCM/dimethyl sulfoxide(DMSO) as the solvent,with super-critical carbon dioxide as the antisolvent.The effects of solvent,solvent ratio,temperature,pressure,polymer con-centration and solution flow rate on particle morphology,mass median diameter(Dp50) and PTX loading were in-vestigated using single-factor method.The particle samples were characterized using X-ray diffraction(XRD),scanning electron microscopy(SEM),laser diffraction particle size analyzer and high pressure liquid chromatogra-phy(HPLC).XRD results indicate that the micronized PTX is dispersed into the PLLA matrix in an amorphous form.SEM indicates that the solvent and the solvent ratio have great effect on the particle morphologies,and particle morphology is good at the volume ratio of DCM/EtOH of 50/50.For the mixed DCM/EtOH solvent,Dp50 increases with the increase of the temperature,pressure,PLLA concentration and solution flow rate,and PTX loading in-creases with pressure.Suitable operating conditions for the experimental system are as follows:DCM/EtOH 50/50(by volume),35 ℃,10-12 MPa,PLLA concentration of 5 g·L-1 and solution flow rate of 0.5 ml·min-1.

Preparation of Poly ( L-lactic acid ) / Vermiculites Composites by in situ Copolymerization of Lactic Acid and Hydroxylic Vermiculites

L-lactic acid (L-LA) based copolymer/hydroxylation vermiculites composites (PLLA-co-bis A/HVMTs) were prepared by in situ reaction among L-LA, adipic acid, and hydroxylation lamellar vermiculites (HVMTs) using bisphenol-A epoxy resin as chain extending agent. HVMTs were obtained by sulfuric acid-leaching of lamellar vermiculites (VMTs). The effects of sulfuric acid leaching on the VMTs structure were characterized by X-ray diffraction (XRD), 29Si magic-angle spinning nuclear magnetic resonance(29Si NMR), Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FE-SEM), and thermogravimetric analysis (TGA). FTIR, FE-SEM, and TGA were used to characterize the reaction activity of HVMTs. The results indicated that VMTs with increased hydroxyl groups had been successfully obtained and could react with -COOH of the reaction system. The amount of L-LA based copolymer grafted on the surface of HVMTs was more than 22%. The onset decomposition temperature of L-LA based copolymer grafted on the surface of HVMTs was 30℃ higher than that of free L-LA based copolymer.

Microwave induced mutagenesis of Lactobacillus casei subsp. rhamnosus for enhancing L-lactic acid production

Mutagenesis of Lactobacillus casei subsp, rhamnosus Xl-12 after low power microwave irradiation was investigated. Under a microwave power of 400 W and irradiation length of 3 min, a mutated strain W4-3-9 with high-yield L-lactic acid was obtained by screening. Compared with the starting strain X1-12, the L-lactic acid production of W4-3-9 was increased by 58.0% at a concentration of 115.8 g/L. The strain maintained the capability of producing a high L-lactic acid level after 10 generations. Cell surface morphology and DNA structures of parental and mutated strains were observed by atomic force microscopy （ AFM ）. Amplified fragment length polymorphism （AFLP） analysis suggested the difference in AFLP band pattern between the mutated and non-mutated strains. Sequencing and BLAST analysis revealed that the catalytic site of lactate dehydrogenase （DHL） was changed due to the microwave induced mutation.

Composite Biomaterials Based on Poly(L-Lactic Acid)and Functionalized Cellulose Nanocrystals

The biocomposite films were prepared from poly(L-lactic acid)and cellulose nanocrystals.To improve interfacial compatibility of hydrophilic cellulose nanocrystals with hydrophobic matrix polymer as well as to provide the osteoconductive properties,cellulose was functionalized with poly(glutamic acid).The modified cellulose nanocrystals were better distributed and less aggregated within the matrix,which was testified by scanning electron,optical and polarized light microscopy.According to mechanical tests,composites filled with nanocrystals modified with PGlu demonstrated higher values of Young’s modulus,elongation at break and tensile strength.Incubation of composite materials in model buffer solutions for 30 weeks followed with staining of Ca^(2+)deposits with Alizarin Red S assay testified better mineralization of materials containing PGlu-modified cellulose nanocrystals as filler.As the result of in vivo experiment,the developed composite materials showed less level of inflammation in comparison with pure polymer matrix and composites filled with non-functionalized cellulose nanocrystals.

Optimization of L-lactic Acid Production of Rhizopus Oryzae Mutant RLC41-6 by Ion Beam Implantation at Low-Energy

In order to obtain an industrial strain with a higher L（＋）-lactic acid yield, the strain Rhizopus oryzae RF3608 was mutated by means of nitrogen ion beam implantation and the mutant strain RLC41-6 was isolated. Under optimal conditions the yield of L（＋）-lactic acid produced in a shake-flask reached 133 g/L - 137 g/L after 36 h cultivation, indicating that the conversion rate based on glucose was as high as 88% - 91% and the productivity was 3.75 g/L.h. It was almost a 115% increase in lactic acid production compared with the original strain RF3608.

Superior Toughened Biodegradable Poly(L-lactic acid)-based Blends with Enhanced Melt Strength and Excellent Low-temperature Toughness via In situ Reaction Compatibilization

The toughened poly(L-lactic acid)/poly(butylene succinate-butylene terephthalate)(PLLA/PBST) blend with enhanced melt strength and excellent low temperature toughness and strength was prepared by melt compounding through in situ compatibilization reaction in presence of multifunctional epoxy compound(ADR).The PLLA/PBST blend was an immiscible system,and the compatibility of the PLLA/PBST blend was improved after adding ADR.FTIR and GPC curves confirmed the formation of the PLLA-g-PBST copolymer,which improved the interfacial bonding of the blend and therefore the PLLA/PBST/ADR blend showed excellent melt strength and mechanical properties.For the PLLA/PBST/ADR blend with 70/30 PLLA/PBST content,the complex viscosity increased significantly with increasing ADR content.Moreover,the tensile strength,elongation at break and impact strength all increased obviously with increasing the ADR content.The elongation at break of the blend reached the maximum value of 392.7%,which was 93.2 times that of neat PLLA.And the impact strength of the blend reached the maximum value of 74.7 k J/m~2,which was 21.3 times that of neat PLLA.Interestingly,the PLLA/PBST/ADR blend exhibited excellent lowtemperature toughness and strength.At –20 ℃,the elongation at break of the PLLA/PBST/ADR blend was as high as 93.2%,and the impact strength reached 18.8 k J/m~2.Meanwhile,the tensile strength of the blend at low temperature was also high(64.7 MPa),which was beneficial to the application of PLA in the low temperature field.In addition,the PLLA/PBST/ADR blend maintaind good biodegradability,which was of great significance to the wide application of PLLA.

构建大肠杆菌合成生物群落利用混合糖同步发酵生产L-乳酸

目的:实现大肠杆菌混合糖发酵产L-乳酸过程中对葡萄糖-木糖的同步利用。方法:以L-乳酸工程菌大肠杆菌JH16(E.coli B,△frdBC△pflB△ackA△adhE,ldhA::ldhL)为出发菌株,通过RED同源重组技术敲除木糖转运及代谢基因xylFGH、xylE和xylA,获得不能利用木糖的菌株大肠杆菌JH16031。以大肠杆菌JH2705(E.coli JH16,△ptsG△mglB)为出发菌株,敲除葡萄糖转运及代谢基因crr、malX和galP,获得不能利用葡萄糖的菌株大肠杆菌JH27071,以构建大肠杆菌合成生物群落。通过摇瓶和5 L发酵罐试验确定该合成生物群落在混合糖发酵时较优的混合接种比例。结果:以60 g/L葡萄糖和40 g/L木糖为碳源进行发酵,当JH16031与JH27071初始接种比为1∶50,初始OD_(600nm)=0.5,混合糖的利用率最高,在84 h内消耗97%的糖,并在96 h内结束发酵。葡萄糖消耗速率为705 mg/(L·h),木糖消耗速率为435 mg/(L·h),L-乳酸产率为951 mg/(L·h),L-乳酸产量达到92 g/L,糖酸转化率为91%。结论:构建大肠杆菌合成生物群落可实现利用混合糖发酵产L-乳酸过程中葡萄糖和木糖的同步利用。研究结果为工业发酵生产中,使用低成本的木质纤维素为原料,降低发酵成本,提高混合糖利用率提供技术支持。