Fabrication and Evaluation of Alginate/Bacterial Cellulose Nanocrystals–Chitosan–Gelatin Composite Scaffolds

It is common knowledge that pure alginate hydrogel is more likely to have weak mechanical strength, a lack of cell recognition sites, extensive swelling and uncontrolled degradation, and thus be unable to satisfy the demands of the ideal scaffold. To address these problems, we attempted to fabricate alginate/bacterial cellulose nanocrystals-chitosan-gelatin (Alg/BCNs-CS-GT) composite scaffolds using the combined method involving the incorporation of BCNs in the alginate matrix, internal gelation through the hydroxyapatite-d-glucono-δ-lactone (HAP-GDL) complex, and layer-by-layer (LBL) electrostatic assembly of polyelectrolytes. Meanwhile, the effect of various contents of BCNs on the scaffold morphology, porosity, mechanical properties, and swelling and degradation behavior was investigated. The experimental results showed that the fabricated Alg/BCNs-CS-GT composite scaffolds exhibited regular 3D morphologies and well-developed pore structures. With the increase in BCNs content, the pore size of Alg/BCNs-CS-GT composite scaffolds was gradually reduced from 200 μm to 70 μm. Furthermore, BCNs were fully embedded in the alginate matrix through the intermolecular hydrogen bond with alginate. Moreover, the addition of BCNs could effectively control the swelling and biodegradation of the Alg/BCNs-CS-GT composite scaffolds. Furthermore, the in vitro cytotoxicity studies indicated that the porous fiber network of BCNs could fully mimic the extracellular matrix structure, which promoted the adhesion and spreading of MG63 cells and MC3T3-E1 cells on the Alg/BCNs-CS-GT composite scaffolds. In addition, these cells could grow in the 3D-porous structure of composite scaffolds, which exhibited good proliferative viability. Based on the effect of BCNs on the cytocompatibility of composite scaffolds, the optimum BCNs content for the Alg/BCNs-CS-GT composite scaffolds was 0.2% (w/v). On the basis of good merits, such as regular 3D morphology, well-developed pore structure, controlled swelling and biodegradation behavior, and good cytocompatibility, the Alg/BCNs-CS-GT composite scaffolds may exhibit great potential as the ideal scaffold in the bone tissue engineering field

西北干旱区两种不同栽培管理措施下棉田CH4和N2O排放通量研究/CH4 AND N2O FLUXES FROM COTTON FIELDS DIFFERENT IN FARMING PRACTICES IN NORTHWESTERN CHINA[J]

采用静态箱-气相色谱法对西北干旱区当前普遍采用的膜下滴灌和传统的无膜漫灌两种栽培管理下土壤CH4和N2O通量日变化和季节变化特征进行了研究.结果表明,随时间的推移,无膜漫灌栽培管理措施下棉田土壤CH4日变化通量呈先降后升趋势,而膜下滴灌栽培处理CH4排放通量日变化则呈现先升后降趋势；在整个生长季节,无膜漫灌和膜下滴灌土壤CH4季节变化规律不太明显,前者吸收大气CH4 45.2～52.5 mgm-2 a-1,后者释放CH4通量为0.7～23.1 mg m-2 a-1.两种栽培管理措施下棉田土壤N2O通量的日变化和季节变化均随时间的推移均呈现先升后降趋势,但是,无膜漫灌日均排放N2O通量显著高于膜下滴灌.在整个生长季节,无膜漫灌土壤N2O释放量(N2O 99.3～320.0 mg m-2a-1)显著高于膜下滴灌(N2O 60.0～259.0 mgm-2a-1).以上结果说明,膜下滴灌栽培管理措施可以改变旱田传统无膜漫灌栽培土壤与大气CH4的交换方向,促进土壤CH4向大气的排放,但对N2O通量日变化和季节变化规律不产生影响,显著降低土壤N2O的排放量