Construction Of Oriented Heterogeneous Biomimetic Cartilage Materials And Its Biomechanical And Tribological Properties

Traditional artificial joints with hard-hard or hard-soft friction forms have fundamental differences compared to the soft-soft friction form of natural joints,making them prone to wear and failure in the physiological environment of the human body.In order to design and manufacture of the high-reliability,long-life soft-soft frictional biomimetic joints,the development of a biomimetic cartilage material with properties similar to natural cartilage is a key aspect in solving this problem.Hydrogels have a structure and properties similar to natural cartilage and are considered an ideal biomimetic cartilage material.However,traditional hydrogels lack the ordered orientation and multilayer structure,which makes it difficult to obtain the high-load bearing and superlubricity performance of natural cartilage,greatly limiting their practical applications.Therefore,this thesis proposes an ordered orientation structure-enhanced,high load-bearing and superlubricity functional synergistic directed heterostructure biomimetic cartilage material based on the ordered orientation and multilayer structure of natural joint cartilage,laying the foundation for achieving high-reliability,long-life soft-soft frictional biomimetic artificial joints.Firstly,based on the multiple crosslinking strategies of freeze-thawing,ion crosslinking,and UV crosslinking,combined with annealing recrystallization process,a high-strength PVA-PAA-PAAm TN hydrogel with a multiple crosslinked network was constructed.This approach significantly enhanced the mechanical and tribological properties of the hydrogel by increasing the degree of crosslinking and network density.The TN hydrogel exhibited remarkable compressive strength(6.3 MPa),compressive modulus(2.68 MPa),tensile strength(7.3 MPa),tensile modulus(10.27 MPa),and toughness(15.69 MJ/m~3).Furthermore,the TN hydrogel demonstrated excellent fatigue resistance,with no signs of damage after one million cycles of dynamic loading.The hydrogel also exhibited low sliding friction coefficient(0.043)and stable torsional friction performance.Secondly,based on freeze orientation and magnetic field induction techniques,HA,CF,and GO were incorporated into TN hydrogels to enhance the ordered orientation phase,resulting in the creation of three types of biomimetic cartilage material,which are vertically oriented PVA-PAA-PAAm-HA,staggered oriented PVA-PAA-PAAm-CF,and horizontally oriented PVA-PAA-PAAm-GO.These materials mimicked the deep,middle,and superficial layers of natural articular cartilage,respectively.The PVA-PAA-PAAm-HA biomimetic cartilage material has a vertically oriented and honeycomb-like porous network structure.The vertically ordered network structure and hard HA reinforcing phase enhance the mechanical properties and load-bearing capacity of the hydrogel.Its compression strength and modulus can reach 11 MPa and 5.2 MPa,respectively,and the mechanical load-bearing performance is maintained even after one million cycles of fatigue compressions.The PVA-PAA-PAAm-CF biomimetic cartilage material in the middle layer presented a staggered orientation structure and a dense porous network.The staggered ordered molecular network structure,along with the high modulus and strength CF reinforcement,endowed excellent mechanical dissipation capability,shear resistance performance,and high load-bearing characteristics.It demonstrated a compression strength and compression modulus of10.1 MPa and 7.5 MPa,and the strain value change after one million cycles of fatigue compressions was only 1.9%(14.0-15.9%).The PVA-PAA-PAAm-GO biomimetic cartilage material in the superficial layer had a horizontally oriented sponge-like porous network structure.The synergistic effect of the horizontal orientation structure and the GO reinforcement phase resulted in excellent mechanical load-bearing and low friction characteristics,with a tensile strength of 11 MPa,tensile modulus of 16 MPa,and a sliding friction coefficient of only 0.033.Additionally,in vitro biological evaluations showed that the deep,middle,and superficial layer biomimetic cartilage materials have excellent biocompatibility.Finally,a biomimetic multi-layer cartilage material with an ordered gradient structure resembling natural cartilage was constructed layer by layer using surface fusion methods combined with temperature gradient orientation/magnetic field-induced orientation,nano/fiber reinforcement,multiple cross-linking strategies,and annealing recrystallization processes.The multi-layer heterogeneous biomimetic cartilage material exhibits a gradient ordered structure with a horizontal orientation at the superficial layer,staggered orientation at the middle layer,and vertical orientation a the deep layer.The highly entangled polymer chains between the layers show ultra-high interfacial toughness and interfacial bonding strength.The heterogeneity and layered structure endow the three-layer biomimetic cartilage material with optimal mechanical load-bearing capacity,with a compression strength of 12.6 MPa,compression modulus of 9.5 MPa,tensile strength of 13.0 MPa,and tensile modulus of 27.7 MPa.After one million cycles of fatigue compressions,the strain value changed only by 1.62%.Under the synergistic effect of high load-bearing at the deep/middle layers and self-lubrication at the superficial layer,the trilayer heterogeneous biomimetic cartilage material exhibits excellent biotribological performance.The sliding friction coefficient of the trilayer biomimetic cartilage material under the hard-soft contact form is only 0.029,while the sliding friction coefficient under the soft-soft contact form is as low as 0.023.Studies on sliding and twisting tribological behavior indicate that the multilayer heterogeneous structure is beneficial for improving the friction performance of biomimetic cartilage materials,and the soft-soft contact form helps to reduce the friction and wear between artificial joint friction pairs.