In this study,Mg-based composites,by the addition of ZnO,Ca_(2)ZnSi_(2)O_(7),Ca_(2)MgSi_(2)O_(7),and CaSiO_(3)as bioactive agents,were fabricated using friction stir processing.The microstructure and in vitro assessme...In this study,Mg-based composites,by the addition of ZnO,Ca_(2)ZnSi_(2)O_(7),Ca_(2)MgSi_(2)O_(7),and CaSiO_(3)as bioactive agents,were fabricated using friction stir processing.The microstructure and in vitro assessment of bioactivity,biodegradation rate,and corrosion behavior of the resultant composites were investigated in simulated body fluid(SBF).The results showed that during the immersion of composites in SBF for 28 d,due to the release of Ca^(2+)and PO_(4)^(3-)ions,hydroxyapatite(HA)crystals with cauliflower shaped morphology were deposited on the surface of composites,confirming good bioactivity of composites.In addition,due to the uniform distribution of bioceramic powders throughout Mg matrix,grain refinement of the Mg matrix,and uniform redistribution of secondary phase particles,the polarization resistance increased,and the biodegradation rate of composites significantly reduced compared to monolithic Mg matrix.The polarization corrosion resistance of Mg-ZnO increased from 0.216 to 2.499 kΩ/cm^(2)compared to monolithic Mg alloy.Additionally,Mg-ZnO composite with the weight loss of 0.0217 g after 28 d immersion showed lower weight loss compared to other samples with increasing immersion time.Moreover,Mg-ZnO composite with the biodegradation rate of 37.71 mm/a exhibited lower biodegradation rate compared to other samples with increasing immersion time.展开更多
Biowaste compost can influence soil organic matter accumulation directly or indirectly. A 5-year experiment was conducted to assess the influence of biowaste compost on the process of soil aggregation and soil organic...Biowaste compost can influence soil organic matter accumulation directly or indirectly. A 5-year experiment was conducted to assess the influence of biowaste compost on the process of soil aggregation and soil organic carbon （SOC） accumulation in a Mediterranean vegetable cropping system. The study involved four treatments： biowaste compost （COM）, mineral NPK fertilizers （MIN）, biowaste compost with half-dose N fertilizer （COMN）, and unfertilized control （CK）. The SOC stocks were increased in COM, COMN, and MIN by 20.2, 14.9, and 2.4 Mg ha-1 over CK, respectively. The SOC concentration was significantly related to mean weight diameter of aggregates （MWD） （P 〈 0.05, R^2 = 0.798 4） when CK was excluded from regression analysis. Compared to CK, COM and COMN increased the SOC amount in macroaggregates （〉 250 μm） by 2.7 and 0.6 g kg-1 soil, respectively, while MIN showed a loss of 0.4 g kg-1 soil. The SOC amount in free microaggregates （53-250 ttm） increased by 0.9, 1.6, and 1.0 g kg-1 soil for COM, COMN, and MIN, respectively, while those in the free silt plus clay aggregates （~ 53 ~m） did not vary significantly. However, when separating SOC in particle-size fractions, we found that more stable organic carbon associated with mineral fraction 〈 53 μm （MOM-C） increased significantly by 3.4, 2.2, and 0.7 g kg-1 soil for COM, COMN, and MIN, respectively, over CK, while SOC amount in fine particulate organic matter （POM） fraction （53-250 μm） increased only by 0.3 g kg-1 soil for both COM and COMN, with no difference in coarse POM 〉 250 μm. Therefore, we consider that biowaste compost could be effective in improving soil structure and long-term C sequestration as more stable MOM-C.展开更多
Immediate loading(IL)increases the risk of marginal bone loss.The present study investigated the biomechanical response of peri-implant bone in rabbits after IL,aiming at optimizing load management.Ninety-six implants...Immediate loading(IL)increases the risk of marginal bone loss.The present study investigated the biomechanical response of peri-implant bone in rabbits after IL,aiming at optimizing load management.Ninety-six implants were installed bilaterally into femurs of 48 rabbits.Test implants on the left side created the maximal initial stress of 6.9 and 13.4 MPa in peri-implant bone and unloaded implants on the contralateral side were controls.Bone morphology and bone-implant interface strength were measured with histological examination and push-out testing during a 12-week observation period.Additionally,the animal data were incorporated into finite element(FE)models to calculate the bone stress distribution at different levels of osseointegration.Results showed that the stress was concentrated in the bone margin and the bone stress gradually decreased as osseointegration proceeded.A stress of about 2.0 MPa in peri-implant bone had a positive effect on new bone formation,osseointegration and bone-implant interface strength.Bone loss was observed in some specimens with stress exceeding 4.0 MPa.Data indicate that IL significantly increases bone stress during the early postoperative period,but the load-bearing capacity of peri-implant bone increases rapidly with an increase of bone-implant contact.Favorable bone responses may be continually promoted when the stress in peri-implant bone is maintained at a definite level.Accordingly,the progressive loading mode is recommended for IL implants.展开更多
文摘In this study,Mg-based composites,by the addition of ZnO,Ca_(2)ZnSi_(2)O_(7),Ca_(2)MgSi_(2)O_(7),and CaSiO_(3)as bioactive agents,were fabricated using friction stir processing.The microstructure and in vitro assessment of bioactivity,biodegradation rate,and corrosion behavior of the resultant composites were investigated in simulated body fluid(SBF).The results showed that during the immersion of composites in SBF for 28 d,due to the release of Ca^(2+)and PO_(4)^(3-)ions,hydroxyapatite(HA)crystals with cauliflower shaped morphology were deposited on the surface of composites,confirming good bioactivity of composites.In addition,due to the uniform distribution of bioceramic powders throughout Mg matrix,grain refinement of the Mg matrix,and uniform redistribution of secondary phase particles,the polarization resistance increased,and the biodegradation rate of composites significantly reduced compared to monolithic Mg matrix.The polarization corrosion resistance of Mg-ZnO increased from 0.216 to 2.499 kΩ/cm^(2)compared to monolithic Mg alloy.Additionally,Mg-ZnO composite with the weight loss of 0.0217 g after 28 d immersion showed lower weight loss compared to other samples with increasing immersion time.Moreover,Mg-ZnO composite with the biodegradation rate of 37.71 mm/a exhibited lower biodegradation rate compared to other samples with increasing immersion time.
文摘Biowaste compost can influence soil organic matter accumulation directly or indirectly. A 5-year experiment was conducted to assess the influence of biowaste compost on the process of soil aggregation and soil organic carbon （SOC） accumulation in a Mediterranean vegetable cropping system. The study involved four treatments： biowaste compost （COM）, mineral NPK fertilizers （MIN）, biowaste compost with half-dose N fertilizer （COMN）, and unfertilized control （CK）. The SOC stocks were increased in COM, COMN, and MIN by 20.2, 14.9, and 2.4 Mg ha-1 over CK, respectively. The SOC concentration was significantly related to mean weight diameter of aggregates （MWD） （P 〈 0.05, R^2 = 0.798 4） when CK was excluded from regression analysis. Compared to CK, COM and COMN increased the SOC amount in macroaggregates （〉 250 μm） by 2.7 and 0.6 g kg-1 soil, respectively, while MIN showed a loss of 0.4 g kg-1 soil. The SOC amount in free microaggregates （53-250 ttm） increased by 0.9, 1.6, and 1.0 g kg-1 soil for COM, COMN, and MIN, respectively, while those in the free silt plus clay aggregates （~ 53 ~m） did not vary significantly. However, when separating SOC in particle-size fractions, we found that more stable organic carbon associated with mineral fraction 〈 53 μm （MOM-C） increased significantly by 3.4, 2.2, and 0.7 g kg-1 soil for COM, COMN, and MIN, respectively, over CK, while SOC amount in fine particulate organic matter （POM） fraction （53-250 μm） increased only by 0.3 g kg-1 soil for both COM and COMN, with no difference in coarse POM 〉 250 μm. Therefore, we consider that biowaste compost could be effective in improving soil structure and long-term C sequestration as more stable MOM-C.
基金supported by the National Natural Science Foundation of China(10902010,11120101001)National Science&Technology Pillar Program of China(2012BAI22B02)Research Fund for the Doctoral Program of Higher Education of China(20131102130004)
文摘Immediate loading(IL)increases the risk of marginal bone loss.The present study investigated the biomechanical response of peri-implant bone in rabbits after IL,aiming at optimizing load management.Ninety-six implants were installed bilaterally into femurs of 48 rabbits.Test implants on the left side created the maximal initial stress of 6.9 and 13.4 MPa in peri-implant bone and unloaded implants on the contralateral side were controls.Bone morphology and bone-implant interface strength were measured with histological examination and push-out testing during a 12-week observation period.Additionally,the animal data were incorporated into finite element(FE)models to calculate the bone stress distribution at different levels of osseointegration.Results showed that the stress was concentrated in the bone margin and the bone stress gradually decreased as osseointegration proceeded.A stress of about 2.0 MPa in peri-implant bone had a positive effect on new bone formation,osseointegration and bone-implant interface strength.Bone loss was observed in some specimens with stress exceeding 4.0 MPa.Data indicate that IL significantly increases bone stress during the early postoperative period,but the load-bearing capacity of peri-implant bone increases rapidly with an increase of bone-implant contact.Favorable bone responses may be continually promoted when the stress in peri-implant bone is maintained at a definite level.Accordingly,the progressive loading mode is recommended for IL implants.
