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  生物體內(nèi)承載組織，大多具有較強(qiáng)的生物力學(xué)性能，但是其弱的自修復(fù)能力導(dǎo)致其在發(fā)生損傷時(shí)，很難恢復(fù)到原來的結(jié)構(gòu)和性能，組織工程替代物是實(shí)現(xiàn)承載組織功能再生的有效措施。水凝膠作為一種軟濕材料，具有良好的生物相容性，在生物組織工程領(lǐng)域已經(jīng)得到了廣泛的應(yīng)用，然而，由于其較低的力學(xué)性能（弱的抗張強(qiáng)度，較低的楊氏模量以及較差的韌性等），以及在水環(huán)境中不穩(wěn)定的缺點(diǎn)，限制了其在生物承載組織中的應(yīng)用。近年來，高強(qiáng)水凝膠獲得了廣泛而又深入的研究，并且取得了一定的成果，然而，由于高強(qiáng)水凝膠相對(duì)較低的模量，限制了其在跟腱、半月板等高模量生物承載組織的應(yīng)用，而目前高模量水凝膠制備的復(fù)雜性、耗時(shí)性以及水環(huán)境中的不穩(wěn)定性等缺點(diǎn)，使其作為生物組織替代物的研究更是鮮有報(bào)道。因此，設(shè)計(jì)一種簡(jiǎn)單有效地制備高強(qiáng)、高模量水凝膠，并能夠在水中、PBS中保持穩(wěn)定的水凝膠的方法仍然存在很大的挑戰(zhàn)。

  基于上述考慮，天津大學(xué)劉文廣教授團(tuán)隊(duì)提出了一種力學(xué)“增強(qiáng)因子”的概念，通過一種全新的氫鍵單體NASC（只將已報(bào)道的NAGA側(cè)鏈兩個(gè)酰胺間的CH2換成NH，使NASC側(cè)鏈帶有一個(gè)酰胺鍵和一個(gè)脲基）的設(shè)計(jì)與合成，成功制備了PNASC超分子聚合物水凝膠。由于側(cè)鏈強(qiáng)的氫鍵交聯(lián)作用，溶脹平衡之后的超分子聚合物水凝膠的拉伸強(qiáng)度可達(dá)1.7-4.7 MPa，楊氏模量達(dá)48.4-100.3 MPa，斷裂應(yīng)變達(dá)341-638%，韌性可達(dá)5.66-20.35 MJ m^-3，遠(yuǎn)高于迄今為止報(bào)道的超分子聚合物水凝膠 （Fig. 1），該團(tuán)隊(duì)對(duì)于PNASC水凝膠力學(xué)增強(qiáng)機(jī)制進(jìn)行了探索。

Fig. 1. (a): Molecular structures of NAGA, NASC, PNAGA and PNASC. (b): Schematic illustration of reconstruction of hydrogen bonding of amide and urea in PNASC gels when DMSO is replaced with water. (c): Tensile stress-strain curves. (d): Tensile strength, Young’s modulus and yielding strength of PNASC hydrogels with different initial monomer concentrations (n=3). (e, f, g) Photos portraying the high stiffness of the PNASC-25 hydrogels. (e): 79 g of aluminum sheets can be lifted up by a length of hydrogel line (d=0.6 mm) without stretching, and nylon cord is threaded through a hole in a piece of PNASC-25 hydrogel sheet (3 cm × 1.5 cm × 0.2 cm) and lifts a bottle of water weighing 0.9 kg without occurrence of deformation of the hydrogel hole. The hydrogel sheet (3 cm × 2.5 cm × 0.2 cm) was able to bear self-weight (f) and 70 g of aluminum sheets without collapse (g).

  此外，值得注意的是，該單體可以與AAm，CBAA等代表性的單體共聚制備具有一定力學(xué)強(qiáng)度且在PBS中保持穩(wěn)定的超分子聚合物水凝膠。為了探索PNASC基水凝膠的應(yīng)用，該團(tuán)隊(duì)將單體NASC與接雙鍵的肝素共聚，制備P(NASC-co-HepMAm) 共聚水凝膠微管，該水凝膠在37 ℃可以保持高的模量，并且具有良好的生物相容性和血液相容性，肝素的引入提高了其抗凝血性能，使其有望作為臨時(shí)血管用于野外突發(fā)事故導(dǎo)致的血管破裂而引起的肢體缺血的救治，對(duì)于緊急情況下的受傷肢體的血液快速恢復(fù)具有潛在的應(yīng)用價(jià)值 (Fig. 2)。

Fig. 2. (a) Schematic illustration of the fabrication of P(NASC-co-HepMAm) hydrogel tubes and their application as the TIVS in vivo. (b) Sequential steps in placement of hydrogel tube for TIVS in a rabbit model: (1) The rabbit’s arteria carotis was clamped on both sides by the artery clamp; (2) Defective treatment of blood vessels located between two arterial clips; (3) One end of the trimmed hydrogel tube was inserted into the rabbit’s carotid artery (3-4 mm depth) through the defect; (4, 5) Another end of the hydrogel tube was trimmed and the rabbit carotid artery was amputated; immediately, this end of the trimmed hydrogel tube was inserted into rabbit carotid artery (3-4 mm); (6) The arterial clip was removed to restore the blood flow. (c) (1, 7), (2, 8), (3, 9), and (4, 10) are the photos of blood color change in the PNASC-25 and P(NASC-co-HepMAm)-25-15 hydrogel tubes after being implanted for 0, 1, 2, and 4 h. (5, 11) are the photos of the PNASC-25 and P(NASC-co-HepMAm)-25-15 hydrogel tubes removed from the end of arteria carotis. (6, 12) Stereomicroscopic images of the PNASC-25 and P(NASC-co-HepMAm)-25-15 hydrogel tube luminal surface.

  這項(xiàng)研究開辟了一種非常簡(jiǎn)單且通用的制備具有特定功能的高強(qiáng)度、高剛度、高韌性以及溶脹穩(wěn)定的超分子聚合物水凝膠的策略，對(duì)于其在承載組織的應(yīng)用中具有重要的意義。

  目前上述工作已發(fā)表在《Materials Horizons》上，論文第一作者為天津大學(xué)材料學(xué)院博士生范川川，通訊作者為天津大學(xué)材料學(xué)院劉文廣教授。

  論文鏈接：https://pubs.rsc.org/en/content/articlelanding/2020/mh/c9mh01844a#!divAbstract