Article pubs.acs.org/Biomac
Rapid Gelling Chitosan/Polylysine Hydrogel with Enhanced Bulk Cohesive and Interfacial Adhesive Force: Mimicking Features of Epineurial Matrix for Peripheral Nerve Anastomosis Yalin Zhou,† Jin Zhao,*,† Xiaolei Sun,‡ Sidi Li,† Xin Hou,† Xubo Yuan,† and Xiaoyan Yuan† †
School of Materials Science and Engineering, and Tianjin Key Laboratory of Composite and Functional Materials, Tianjin University, Tianjin 300072, China ‡ Department of Orthopedic Surgery, Tianjin Hospital, Tianjin 300211, China ABSTRACT: Prompt and strong reconnection of severed peripheral nerves is crucial to nerve regeneration. The development of biocompatible nerve adhesives that are stronger than commonly used fibrin glue would be extremely beneficial to this field. We designed an in situ forming nerve adhesive hydrogel composed of chitosan and ε-polylysine (PL), which mimics the polysaccharides/protein structure of natural epineurium matrices, thus, enhancing the compatibility with nerves. Michael-type addition between the maleimide and thiol group was employed as a cross-linking reaction to eliminate foreign damage to nerves and to ensure a fast hydrogel formation speed (curing speed). Gelation occurred within 10 s, quick enough to promptly seal the transected nerve. Catechol groups conjugated onto PL molecules were demonstrated to reinforce both the bulk cohesive force of the hydrogel and the interfacial adhesive force between the hydrogel and epineurium. The storage modulus of the hydrogel was elevated to more than 2400 Pa. A superior nerve adhesion property that can tolerate 0.185 N of force (8× higher than fibrin glue) was obtained. After 8 weeks, the morphology of the repaired nerve fiber coapted by our hydrogel was very close to the morphology of normal nerve, and the axon cross ratio of the regenerated nerves coapted using hydrogel (57%) was much higher than employing the suture technique (35%). Thus, the in situ rapid gelling system offers a promising approach to the repair of severed peripheral nerves. frequently reported.6,14−16 Derived from thrombin and fibrinogen, fibrin glue is proved to be more biocompatible,17 but its weak adhesion strength due to the low bulk storage modulus and the inefficient reaction with the nerve surface impedes its clinical use.18,19 Worse still, it suffers from the risk of viral and prion infections.6 Therefore, an effective all-in-one nerve adhesive is still urgently needed. In the present study, we developed a rapidly in situ forming adhesive hydrogel for nerve. Nerve anastomosis is actually the successful join and seal of epineurium.19 Therefore, as shown in Scheme 1, chitosan and ε-polylysine (PL)20,21 were chosen to form hydrogel through Michael addition reaction (Scheme 1A). Chitosan22,23 mimics the polysaccharide component of epineurium. PL, a naturally occurring biodegradable polypeptide,24,25 can mimic the hydroxylysine sequences that exist in collage protein of epineurium. In comparison to the violent polymerization procedures such as those involved in cyanoacrylates, Michael addition is a mild reaction not involving toxic agents or catalysts and avoiding exposure to
1. INTRODUCTION Transection of peripheral nerves is caused by blunt trauma, foreign object penetration, or sports injuries. The recovery of the nerve function required precise anastomosis of the divided ends.1,2 The direct end-to-end suture technique has been the standard method in the past few decades.3 However, several unavoidable disadvantages, such as being time-consuming, incomplete nerve sealing, foreign body reactions, and neuroma formation,4−6 highlight the need for an alternative approach. Adhesives provide great potential alternatives because they can avoid secondary damage and reduce operating times.7,8 An ideal bioadhesive should be nonimmunogenic and biocompatible with tissues.9 With regard to nerve coaptation, there are some special requirements: extremely fast curing of the adhesive is needed for the prompt recontact of the inside damaged axon, which is vital to nerve axon repair;10 the cohesive and adhesive force should be enhanced simultaneously with regard to the special tubular adhesive type for nerve coaptation.11 However, the current two main adhesives,6,12,13 cyanoacrylate and fibrin glue, have their own shortcomings. Cyanoacrylate-based material possesses strong adhesion strength. But severe histotoxicity, time-consuming (300−600 s for setting), limited flexibility, and necrosis have been © XXXX American Chemical Society
Received: November 16, 2015 Revised: January 6, 2016
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DOI: 10.1021/acs.biomac.5b01550 Biomacromolecules XXXX, XXX, XXX−XXX
Article
Biomacromolecules
Scheme 1. Gelation Mechanism through Michael Addition (A); Formation of Hydrogel Network (B); Schematic of Interactions inside the Adhesives (C); Schematic of Nerve Anastomosis Test (D)
Table 1. Preparation Parameter and Gelation Time (n = 3) of Hydrogela hydrogel
DScatechol (mol %)
DSmaleimide (mol %)
CSS concentration (wt %)
−MAL/−SH (mol/mol)
NaIO4 (mol/L)
gelation time (s)
H6 G1 G2 G3 G4 fibrin glue
0 5 8 11 5
20 23 20 24 23
4 4 4 4 4
1:1 1:1 1:1 1:1 1:1
0 0 0 0 0.04
5±1 6±1 6±1 7±1
