Analysis of spatio-temporal evolution of droughts in Luanhe River Basin using different drought indices

Based on the monthly precipitation and air temperature from 1960 to 1989 in the Luanhe River Basin, the standardized precipitation evapotranspiration index （SPEI） and standardized precipitation index （SPI） at three- and six-month time scales and the self-calibrating Palmer drought severity index （sc-PDSI） were calculated to evaluate droughts in the study area. Temporal variations of the drought severity from 1960 to 1989 were analyzed and compared based on the results of different drought indices, and some typical drought events were identified. Spatial distributions of the drought severity according to the indices were also plotted and investigated. The results reveal the following： the performances of different drought indices are closely associated with the drought duration and the dominant factors of droughts; the SPEI is more accurate than the SPI when both evaporation and precipitation play important roles in drought events; the drought severity shown by the sc-PDSI is generally milder than the actual drought severity from 1960 to 1989; and the evolution of the droughts is usually delayed according to the scPDSI. This study provides valuable references for building drought early warning and mitigation systems in the Luanhe River Basin.

Silicified collagen scaffold induces semaphorin 3A secretion by sensory nerves to improve in-situ bone regeneration

Sensory nerves promote osteogenesis through the release of neuropeptides.However,the potential application and mechanism in which sensory nerves promote healing of bone defects in the presence of biomaterials remain elusive.The present study identified that new bone formation was more abundantly produced after implantation of silicified collagen scaffolds into defects created in the distal femur of rats.The wound sites were accompanied by extensive nerve innervation and angiogenesis.Sensory nerve dysfunction by capsaicin injection resulted in significant inhibition of silicon-induced osteogenesis in the aforementioned rodent model.Application of extracellular silicon in vitro induced axon outgrowth and increased expression of semaphorin 3 A(Sema3A)and semaphorin 4D(Sema4D)in the dorsal root ganglion(DRG),as detected by the upregulation of signaling molecules.Culture medium derived from silicon-stimulated DRG cells promoted proliferation and differentiation of bone marrow mesenchymal stem cells and endothelial progenitor cells.These effects were inhibited by the use of Sema3A neutralizing antibodies but not by Sema4D neutralizing antibodies.Knockdown of Sema3A in DRG blocked silicon-induced osteogenesis and angiogenesis almost completely in a femoral defect rat model,whereas overexpression of Sema3A promoted the silicon-induced phenomena.Activation of“mechanistic target of rapamycin”(mTOR)pathway and increase of Sema3A production were identified in the DRG of rats that were implanted with silicified collagen scaffolds.These findings support the role of silicon in inducing Sema3A production by sensory nerves,which,in turn,stimulates osteogenesis and angiogenesis.Taken together,silicon has therapeutic potential in orthopedic rehabilitation.

Polyphosphate-crosslinked collagen scaffolds for hemostasis and alveolar bone regeneration after tooth extraction

Post-extraction bleeding and alveolar bone resorption are the two frequently encountered complications after tooth extraction that result in poor healing and rehabilitation difficulties.The present study covalently bonded polyphosphate onto a collagen scaffold(P-CS)by crosslinking.The P-CS demonstrated improved hemostatic property in a healthy rat model and an anticoagulant-treated rat model.This improvement is attributed to the increase in hydrophilicity,increased thrombin generation,platelet activation and stimulation of the intrinsic coagulation pathway.In addition,the P-CS promoted the in-situ bone regeneration and alveolar ridge preservation in a rat alveolar bone defect model.The promotion is attributed to enhanced osteogenic differentiation of bone marrow stromal cells.Osteogenesis was improved by both polyphosphate and blood clots.Taken together,P-CS possesses favorable hemostasis and alveolar ridge preservation capability.It may be used as an effective treatment option for post-extraction bleeding and alveolar bone loss.Statement of significance:Collagen scaffold is commonly used for the treatment of post-extraction bleeding and alveolar bone loss after tooth extraction.However,its application is hampered by insufficient hemostatic and osteoinductive property.Crosslinking polyphosphate with collagen produces a modified collagen scaffold that possesses improved hemostatic performance and augmented bone regeneration potential.