2.2.1 Chitosan and PVA solution preparation
Briefly, PVA hydrogels were prepared by fully dissolving 5.0g of polymer powder without further purification in 100 ml of Milli-Q water, under magnetic stirring, at temperature of 75 ± 2℃ (solution A), as previously reported by our group [7–9]. PVA 5% solution was let to cool down to room temperature and the pH was corrected to (2.00 ± 0.05) with 1.0 M HCl (Sigma). Chitosan hydrogels (Chi) were produced in a similar procedure by fully dissolving 2.5g in 250.0ml of Milli-Q water with 2% of CH3COOH (Sigma),under magnetic stirring for 48 h (solution B).

2.2.2 Chitosan, PVA and blends films preparation
Different quantities of PVA (solution A) were added into the 1.0% chitosan solution (solution B) to obtain chitosan/PVA mass ratios of (0:1), (1:3), (1:1), (3:1), and (1:0) and pH was corrected to (4.00 ± 0.05) with 1.0 M NaOH solution. The mixture was kept under stirring for 5 min until the PVA and chitosan completely formed a clear solution. Then, the crosslinker reagent (GA) was slowly added under constant stirring. The final concentration of GA in the gel solution precursors was 1% and 5% (wt%). Further in thesequence, the solution was poured into plastic moulds and let drying for 72–120 h at room temperature, and finally dried at 40℃ for 24 h (constant weight). Chitosan/PVA samples chemically crosslinked were identified by (X:Y:Z) that is, X as chitosan content, Y as PVA content, and Z as GA (wt%). For instance, sample identified as Chi/PVA/GA (1:3:1) represents the following proportion of reagents: 25% chitosan, 75% PVA and crosslinked with 1.0% GA (wt%). The dried gel was stored in a desiccator before all sub-sequent characterization procedures.



2.2.1殼聚糖溶液和PVA溶液制備
首先，聚乙烯醇水凝膠的制備，是先稱5.0g聚乙烯醇粉末使其在100ml純凈水中進(jìn)一步完全溶解，同時(shí)在電磁攪拌下，溫度控制75±2℃（溶液A），就像我們團(tuán)隊(duì)之前的報(bào)道所示。[7-9]。5％的聚乙烯醇完全溶解后，讓其冷卻到室溫和用1.0 M鹽酸（ ）把pH值控制在（2.00±0.05）。殼聚糖水凝膠（殼聚糖）制備采用相似的步驟，稱2.5g殼聚糖在250ml 2％的醋酸溶液（ ）中，電磁攪拌48小時(shí)（溶液B）。

2.2.2殼聚糖和聚乙烯醇復(fù)合水凝膠制備
用不同量的聚乙烯醇溶液（溶液A）加入到1.0％的殼聚糖溶液（溶液B）獲得以下幾種殼聚糖/聚乙烯醇水凝膠，分別質(zhì)量比為（0:1），（1:3 ），（1:1），（3:1）和（1:0）和用1.0M氫氧化鈉溶液把pH值調(diào)節(jié)在（4.00±0.05）。將該混合物繼續(xù)攪拌5分鐘，直到聚乙烯醇和殼聚糖完全形成了清澈溶液。然后，緩慢加入交聯(lián)劑（戊二醛），并不斷攪拌。在溶液凝膠初期，戊二醛的最后濃度為1％和5％（質(zhì)量分?jǐn)?shù)％）。隨著進(jìn)一步反應(yīng)，溶液不斷塑化，接著在室溫下其讓干燥72至120 h，最后在40℃干燥24小時(shí)（恒重）。殼聚糖-聚乙烯醇復(fù)合水凝膠樣品的化學(xué)交聯(lián)反應(yīng)產(chǎn)生凹痕已確定為（X： Y： Z）三種因素，X為殼聚糖的含量，Y為聚乙烯醇的含量，Z為戊二醛（質(zhì)量分?jǐn)?shù)%）。例如，樣品組成確定為殼聚糖/聚乙烯醇/戊二醛=（1:3:1）,則：25％的殼聚糖，75％聚乙烯醇和1.0％（質(zhì)量分?jǐn)?shù)％）戊二醛。干凝膠儲(chǔ)存在干燥器之前，要記錄樣品每一個(gè)特征。