Preparation And Properties Of Physically Cross-linked Double-network Hydrogels

Polymer hydrogels,consisting of plenty of water and three-dimensional cross-linked networks with covalent or noncovalent bonds,have attracted more and more attentions for their wide use in various fields,such as the tissue scaffolds,cartilage repair,drug delivery,wearable devices and smart actuators.However,their practical applications are severely limited by the poor mechanical properties and biocompatibility.Physically cross-linked double-network hydrogels have attracted much attention in these years due to their good mechanical properties and excellent self-healing ability.However,they usually suffer from complicated preparation process and fussy performance regulation,which severely limit their applications in many fields.In this thesis,three kinds of physically cross-linked double-networks were developed by a two-step method of freezing/thawing and immersion processing.There were no organic solvents or initiators used throughout the preparation process.The obtained hydrogels had great mechanical properties and biocompatibility,which can be applied to the cartilage repair and artificial nerve.The specific contents as follows:?1?Herein,we fabricated a physically cross-linked poly?vinylalcohol?-?2-hydroxypropyltrimethyl ammonium chloride chitosan??PVA-HACC?DN hydrogels via a simple two-step method of freezing/thawing and immersion processing.In the hydrogels,the HACC network as the first network,the PVA network as the second network.The effects of immersion time and concentration of Na3Cit solution on the structures and mechanical properties of the hydrogels were investigated.The obtained hydrogels exhibited excellent mechanical properties including high elastic modulus?1.44 MPa?,high strength?a maximal tensile fracture stress of 4.14 MPa and a maximal compressive stress of over 70 MPa at 98%strain?,and superior fracture toughness?17.09 MJ/m3?.In addition,good self-recovered property and anti-fatigue performance were realized for the hydrogels owing to the reversible HACC ionic networks.?2?Hydrogels with desirable characteristics have been supposed to be potential materials for cartilage repair.However,the biomechanical,biotribological and biocompatible properties of hydrogels remain some crucial challenges.To address these challenges,we developed a dual physically cross-linked poly?vinyl alcohol?-?nano-hydroxyapatite?/?2-hydroxypropyltrimethyl ammonium chloride chitosan??PVA-HA/HACC-Cit?hydrogels with double-network?DN?through a simply freezing/thawing technique and an immersing process.The DN hydrogel with an optimized HA concentration exhibited outstanding fracture tensile stress?2.70±0.24 MPa?,toughness?14.09±2.06 MJ/m3?and compressive modulus?0.88±0.09 MPa?.In addition,the PVA-HA/HACC-Cit DN hydrogels demonstrated remarkable anti-fatigue property,extraordinary self-recovery and energy dissipation ability due to their unique dual physically cross-linked structures.Moreover,the low friction coefficient,the predominant wear resistance property,as well as the excellent cytocompatibility were realized for the DN hydrogels because of the existence of nano-hydroxyapatite.Thus,this work puts forward a new strategy in the preparation of DN hydrogels for promising applications in cartilage repair.?3?Ionic conductive hydrogels that have both high-performance in conductivity and mechanical properties have received increasing attention due to their unique potential in artificial soft electronics.Here,a dual physically cross-linked ionic conductive DN hydrogel was fabricated by pre-stretching,freezing/thawing technique and soaking process.In the hydrogels,the SA-Ca network as the first network,the PVA network as the second work,at the same time,hydroxypropyl cellulose?HPC?was added to the system to improve the strength and conductivity of the hydrogels.The obtained ionic conductive hydrogels exhibited good strength?1.4 MPa?and high conductivity(3.49 S m^-1).Furthermore,the low friction coefficient,outstanding wear resistance properties and excellent biocompatibility were achieved for the DN hydrogels.We think that the PVA-HPC_T/SA-Ca DN hydrogel had application potential as an artificial nerve material.