A STUDY OF STRUCTURE AND PROPERTY CHANGES OF BIODEGRADABLE POLYGLYCOLIDE AND POLY(GLYCOLIDE-co-LACTIDE)FIBERS DURING PROCESSING AND IN VITRO DEGRADATION

Structure and properties of bioabsorbable polyglycolide (PGA) and poly(glycolide-co-lactide) (PGA-co-PLA)fibers were investigated during several industrial processing stages and in vitro degradation by means of wide-angle X-raydiffraction (WAXD), dynamic mechanical analysis (DMA) and mechanical property tests. In the orientation stage, the PGAfibers were found to have higher degrees of crystallinity than corresponding PGA-co-PLA samples produced under similarconditions. In the hot-stretching and post-annealing stages, after fibers were braided, PGA samples were found to gain morecrystallinity and higher T_g than PGA-co-PLA samples. The higher crystallinity in PGA fibers resulted in a slower rate ofdegradation. DMA results showed that a great deal of internal stress that was built during orientation and hot-stretchingstages was released in the post-annealing stage for a1l PGA and PGA-co-PLA samples. During earlier stages of in vitrodegradation, both PGA and PGA-co-PLA samples exhibited the typical cleavage-induced crystallization mechanism. Theheat shrinkage in the glass transition area was found to disappear after 6-8 days of degradation for all PGA and PGA-co-PLAsamples, indicating the amorphous portions of the polymers lost orientation after a short period in the buffer solution, mostlikely due to relaxation of the cleaved chains.

Preparation, Characterization, and in vitro Release of Biodegradable Erythromycin-gelatin Microspheres

Blank and erythromycin-loaded gelatin microspheres were successfully fabricated via emulsion chemical- crosslinking technique. The surface morphology of the microspheres was characterized by scanning electron microscope（SEM） and optical microscope. The results show that the microspheres were spherical and smooth. The particle average size of erythromycin-loaded microspheres was found to be 20.6 μm, with a high purity of more than 90% and with a good dispersibility. The microspheres could be obtained in a high yield. Erythromycin released from the microspheres was monitored in buffer and artificial body fluid at 37 ℃. Average drug content was 27.2%, and erythromycin-loaded gelatin microspheres showed good release profiles with a nearly constant release during 4-8 h in artificial body fluid in vitro degradation studies. These gelatin microspheres are useful for studying and developing various drug-delivery systems.

Selective ligninolysis of wheat straw and wood chips by the white-rot fungus Lentinula edodes and its influence on in vitro rumen degradability

Background： The present work investigated the influence of lignin content and composition in the fungal treatment of lignocellulosic biomass in order to improve rumen degradability. Wheat straw and wood chips,differing in lignin composition, were treated with Lentinula edodes for 0, 2, 4, 8 and 12 wk and the changes occurring during fungal degradation were analyzed using pyrolysis-gas chromatography-mass spectrometry and detergent fiber analysis.Results： L. edodes preferentially degraded lignin, with only limited cellulose degradation, in wheat straw and wood chips, leaving a substrate enriched in cellulose. Syringyl（S）-lignin units were preferentially degraded than guaiacyl（G）-lignin units, resulting in a decreased S/G ratio. A decreasing S/G ratio（wheat straw： r =-0.72, wood chips： r =-0.75） and selective lignin degradation（wheat straw： r =-0.69, wood chips： r =-0.88） were correlated with in vitro gas production（IVGP）, a good indicator for rumen degradability.Conclusions： L. edodes treatment increased the IVGP of wheat straw and wood chips. Effects on IVGP were similar for wheat straw and wood chips indicating that lignin content and 3D-structure of cell walls influence in vitro rumen degradability more than lignin composition.

The environmental prospects of cultured meat in China

To deal with concerns in China about environmental degradation and a growth in population accompanied by increased consumption of livestock products, a meat alternative is required. This study compared the environmental impacts of producing different protein sources for nutrition, including crops, livestock products, and cultured meat. The results showed that cultured meat has the lowest land use per unit of protein and unit of human digestible energy. China＇s crops have the lowest energy use and greenhouse gas（GHG） emissions per unit of energy and protein. The energy use in cultured meat production is slightly higher than that of current pork production in China, whereas GHG emissions are lower. It is concluded that the overall impact of replacing livestock products with cultured meat would be beneficial for China＇s environment and would potentially improve food security because less land is needed to produce the same amount of protein and energy.

The effect of particle size and amount of inoculum on fungal treatment of wheat straw and wood chips

Background： The aim of this study was to optimize the fungal treatment of lignocellulosic biomass by stimulating the colonization. Wheat straw and wood chips were treated with Ceriporiopsis subvermispora and Lentinula edodes with various amounts of colonized millet grains（0.5, 1.5 or 3.0 % per g of wet weight of substrate） added to the substrates. Also, wheat straw and wood chips were chopped to either 0.5 or 2 cm.Effectiveness of the fungal treatment after 0, 2, 4, 6, or 8 wk of incubation was determined by changes in chemical composition, in vitro gas production（IVGP） as a measure for rumen degradability, and ergosterol content as a measure of fungal biomass.Results： Incomplete colonization was observed for C. subvermispora treated wheat straw and L. edodes treated wood chips. The different particle sizes and amounts of inoculum tested, had no significant effects on the chemical composition and the IVGP of C. subvermispora treated wood chips. Particle size did influence L.edodes treatment of wheat straw. The L. edodes treatment of 2 cm wheat straw resulted in a more selective delignification and a higher IVGP than the smaller particles. Addition of 1.5 % or 3 % L. edodes inoculum to wheat straw resulted in more selective delignification and a higher IVGP than addition of 0.5 % inoculum.Conclusion： Particle size and amount of inoculum did not have an effect on C. subvermispora treatment of wood chips. At least 1.5 % L. edodes colonized millet grains should be added to 2 cm wheat straw to result in an increased IVGP and acid detergent lignin（ADL） degradation.

High-purity Mg and Mg-1Ca alloys:Comparative assessment of the merits regarding degradation,osteogenesis,and biosafety for orthopedic applications

High-purity magnesium(HP Mg)and Mg-1Ca,as representations of Mg-matrix implants produced by purifying and alloying,are employed in biomedical applications primarily because of their bioactivity and degradability.The superiority of both degradation properties,the match between degradation and osteo-genesis in vivo,and biosafety are critical problems that will decide future purifying or alloying to construct Mg-based implants and promote clinical translation.The present study investigated the benefits and limitations of degradation behavior and biosafety of HP Mg and Mg-1Ca according to the electro-chemical experiment,hydrogen evolution test,immersion test,and in vivo bone implantation assay.The results indicated that due to its Mg 2 Ca phase,Mg-1Ca exhibited a considerably higher corrosion current density and hydrogen production than HP Mg in vitro.Furthermore,HP Mg and Mg-1Ca display a favorable match between their degradation and the surrounding osteogenesis,resulting in no significant variation in degradation in vivo during 26 weeks.Additionally,the implantation and degradation of HP Mg and Mg-1Ca do not result in major organ dysfunction or pathological abnormalities.This work is expected to lay the foundation for future clinical translation of Mg and Mg alloy orthopedic implants.

Microstructure,fracture behavior,in vitro corrosion resistance,and cytotoxicity of Zn-Mg/Mg-Zn-HAp laminated composites produced by spark plasma sintering

Ideal biodegradable materials exhibit suitable degradation rates and sufficient mechanical properties for their specific application.With these parameters in mind,Zn-Mg/Mg-Zn-hydroxyapatite(HAp) laminated composites were designed and fabricated by spark plasma sintering.This paper describes the structure,mechanical properties,in vitro corrosion resistance,and cytotoxicity of the Zn-Mg/Mg-Zn-HAp laminated composites.The compressive strength and elastic moduli of the laminated composites matched that of cortical bone and could effectively reduce the stress shielding effect as an implant with good biomechanical compatibility.Analysis of the fracture path and morphology after fracture toughness tests indicated that the Zn-Mg/Mg-Zn-HAp laminated composites exhibited significant capacity to prevent crack propagation,improving the fracture toughness.In vitro degradation experiments showed that the design of the laminated structure can provide a gradient degradation rate for the material.Furthermore,the laminated composites exhibited excellent biocompatibility and are promising candidates for orthopedic implants.

The influence of Ca and Cu additions on the microstructure,mechanical and degradation properties of Zn-Ca-Cu alloys for absorbable wound closure device applications

Novel ternary Zn-Ca-Cu alloys were studied for the development of absorbable wound closure device material due to Ca and Cu’s therapeutic values to wound healing.The influence of Ca and Cu on the microstructure,mechanical and degradation properties of Zn were investigated in the as-cast state to establish the fundamental understanding on the Zn-Ca-Cu alloy system.The microstructure of Zn-0.5Ca-0.5Cu,Zn-1.0Ca-0.5Cu,and Zn0.5Ca-1.0Cu is composed of intermetallic phase CaZn13 distributed within the Zn-Cu solid solution.The presence of CaZn13 phase and Cu as solute within the Zn matrix,on the one hand,exhibited a synergistic effect on the grain refinement of Zn,reducing the grain size of pure Zn by 96%;on the other hand,improved the mechanical properties of the ternary alloys through solid solution strengthening,second phase strengthening,and grain refinement.The degradation properties of Zn-Ca-Cu alloys are primarily influenced by the micro-galvanic corrosion between Zn-Cu matrix and CaZn13 phase,where the 0.5%and 1.0%Ca addition increased the corrosion rate of Zn from 11.5μm/y to 19.8μm/y and 29.6μm/y during 4 weeks immersion test.

Torsion properties of poly (glycolide-co-L-lactide) biodegradable braided regeneration conduits for peripheral nerve repair

BACKGROUND： Poly （glycolide-co-L-lactide） （PGLA） braided regeneration conduits have been shown to be biocompatible for the repair of damaged nerve. Mechanical properties, such as radial compression and torsion, greatly influence nerve regeneration and functional recovery. OBJECTIVE： To observe the influence of conduit parameters and coating methods on torsion properties in an in vitro-degradation environment and at normal temperature. DESIGN, TIME AND SE＇I-FING： An in vitro, comparative study using repeated measures was performed at the College of Textiles, Donghua University, China from January 2005 to December 2007. MATERIALS： PGLA fiber and yarn （Shanghai Bio-TianQing, China）, as well as torsion property testing instrument （LaiZhou Electronic Instrument, China）, were used in the present study. METHODS： A total of 16 types of conduits were constructed according to braiding structures （regular/triaxial）, angles （50°/55°/60°/65°）nd coating methods （coated/uncoated）. At normal temperature, torsion properties of all conduits were tested at a predefined constant angle of 90°. Coated and uncoated conduits, which were triaxial and 65°, were incubated in a 5% CO2 incubator at 37 ℃ to simulate an in vitro degradation environment, and then torsion properties were tested at 4, 7, 11, 14, 17, 21,24, and 28 days in culture. MAIN OUTCOME MEASURES： Maximal torsion strength and torsion strength-torsion angle curve of conduits at normal temperature, as well as torsion strength-torsion angle curve, loss of torsion strength, and change in maximal torsion strength in an in vitro degradation environment. RESULTS： At normal temperature, the torsion properties of the triaxial structure were superior to the regular structure. Coated conduits performed better than uncoated ones, and the larger braiding angles exhibited superior torsion properties （P 〈 0.05）. In the in vitro degradation environment, with degradation time, torsion strength of uncoated conduits was deceased gradually and the loss of torsion strength was increased fast. Torsion strength of coated conduits was increased first and decreased afterwards; the loss of torsion strength was decreased slowly till 14 days; both became identical after 14 days （P 〉 0.05）. CONCLUSION： Torsion properties of coated conduits with a triaxial structure and large braiding angle were superior to uncoated conduits with regular structures and small braiding angles.

Preparation and Characterization of 3D Printed Hydroxyapatite-Whisker-Strengthened Hydroxyapatite Scaffold Coated with Biphasic Calcium Phosphate

This study investigates the in vitro degradation of calcium-deficient hydroxyapatite powder after heat treatment at different temperatures and analyzes the calculated phase composition,particle size distribution,degradation rate,and bioactivity of the powder after heat treatment.A mixture of hydroxyapatite and𝛽-tricalcium phosphate(BCP)coatings was prepared on the surface of a 3D-printed hydroxyapatite-whisker-strengthened hydroxyapatite scaf-fold(HAw/HA)by vacuum impregnation and ultraviolet light curing combined with an optimized heat treatment process.The performance of the coatings under different methods was characterized.The composite scaffolds with highly interconnected pores and excellent mechanical properties were prepared,and their biodegradation performance,bioactivity,osteoconductivity,and osteoinductivity of the scaffolds were improved.The results showed that calcium-deficient hydroxyapatite began to transform into BCP between 600℃and 800℃,and the powder treated at 800℃has better bioactivity.The BCP coating prepared by light curing was more uniform,resulting in a higher interfacial bonding strength,and has better osteoconductivity and osteoinductivity than that prepared by vacuum impregnation.

INITIATOR-FREE PHOTOCROSSLINKING OF ELECTROSPUN BIODEGRADABLE POLYESTER FIBER BASED TUBULAR SCAFFOLDS AND THEIR CELL AFFINITY FOR VASCULAR TISSUE ENGINEERING

Random copolyester of poly（ε-caprolactone-co-L-lactide） （PCLA） with a 50：50 feeding molar ratio was synthesized via the ring-opening polymerization and functionalized by the end-capping reaction with acryloyl chloride. The resulting acrylated PCLA was then fabricated into small diameter tubular scaffolds by electrospinning technique and the formed scaffolds were followed by photocrosslinking under UV irradiation in the absence of photoinitiator. The mechanical strengths including tensile, suture retention and burst pressure were greatly enhanced after the photocrosslinking. The in vitro degradation data clearly revealed that the mechanical properties of the crosslinked scaffolds still remained after one month degradation in PBS solution, while those of the non-crosslinked ones lost heavily. The cytotoxicity assay on the mouse fibroblast L929 cells was conducted via MTT measurement. Furthermore, the observation on endothelial and fibroblast cell adhesion and proliferation was also made by using scanning electron microscopy （SEM）. The initiator-free photocrosslinked tubular scaffolds show the potential to be used in vascular tissue engineering.