Microstructure and friction properties of PVA/PVP hydrogels for articular cartilage repair as function of polymerization degree and polymer concentration☆
Introduction
Articular cartilage, which covers the ends of the long bones in the body, plays an important role in characterizing and maintaining the delicate balance of synovial joint [1]. An acute trauma, osteoarthritis and congenital or acquired joint diseases may cause cartilage damage. However, the damaged cartilage lacks the capability of self-recovery due to its avascular and aneural nature [2]. The surgical techniques, such as microfracture [3], autologous chondrocyte implantation (ACI) [4], osteochondral autograft transfer (OAT) [5], [6] etc., have been widely taken to ease pain and regenerate tissue function. Unfortunately, the technique for microfracture may induce the cartilage defect replaced by fibrocartilage instead of hyaline, so that new cartilage could not meet the requirements of natural cartilage [3], [7]. Both ACI and OAT procedures need two surgical steps to assume a two risk of injure, and the problem of the lack of suitable donors should not be neglected [8], [9], [10]. In general, all of these options cannot reconstruct natural function to articular cartilage. Therefore, there is a push to find a permanent implant to substitute damaged cartilage and to encourage tissue regeneration.
The primary function of articular cartilage is to support and redistribute the high level of mechanical loads. It is pivotal for artificial articular cartilage to possess both mechanical and friction properties to function and load-bearing in vivo [11]. Recent years, encouraging progress has been made in mechanical properties of articular cartilage whose compressive and tensile strength is close to the level of native tissue [12], [13]. Now researchers are committed to the development of friction property of articular cartilage. Various lubrication mechanisms, including weeping lubrication [14], [15], boosted lubrication [16], boundary lubrication [17], [18] and biphasic lubrication [19], [20], [21] have been proposed to explain the low friction level in synovial joints. A consensus is that no single theory can comprehensively explain all the joint lubrication characteristics under various physiological conditions, and a mixed lubrication regime may be more convincing.
A great variety of biomaterials have been proposed as articular cartilage material to replace the damaged tissue. Lopes et al. [22] developed an unmodified bacterial cellulose (BC) pellicle, where the tribological properties of BC against bovine articular cartilage were estimated, and low friction coefficient values (∼0.05) were achieved. Freeman et al. [23] investigated the friction behavior of synthesized poly(2-hydroxyethyl)methacrylate (polyHEMA) hydrogel using an oscillating contact device. The results showed that the average friction coefficients for different conditions ranged from a low value (0.05) to a high one (1.7). In particular, PVA hydrogel is one of the most widely used polymers due to its excellent weight-bearing properties and biocompatibility [24], [25], which has been subjected to intense studies in terms of their friction properties. Li et al. [26] found the friction coefficient of PVA hydrogel decreased from 0.178 to 0.076 in 60 min under cartilage-on-PVA hydrogel. Ma et al. [27] found that the addition of PVP to PVA hydrogel would improve both mechanical and tribological properties. Katta et al. [28] investigated the effects of polymer content, load and lubricant on the friction and wear behaviors of PVA/PVP hydrogels. The results showed that the wear of hydrogel samples was remarkably reduced at higher polymer content, and a transition of the lubricating mechanism happened at the critical 125 N load. Effects of PVP content, sliding speed, load and lubrication condition on the friction properties of PVA/PVP hydrogels were preliminary discussed in our previous work [29].
In the present study, PVA/PVP hydrogels with various polymerization degree of the PVA and polymer concentration were synthesized by a repeated freezing–thawing method. The primary objective of this investigation was to determine the friction properties of PVA/PVP hydrogels in response to stainless steel ball component under different experimental conditions. The effects of polymerization degree of the PVA, polymer concentration, lubrication condition, sliding speed, and load on the friction coefficients were explored by a rotating ball-on-plate tribometer. The effects of polymerization degree of PVA and polymer concentration on the microstructure and swelling behaviors were also investigated.
Section snippets
Hydrogel and specimen preparation
PVA, saponified greater than 99% with a polymerization degree of 1700 (Kuraray Co., Japan), 2400 and 2600 (The Nippon Synthetic Chemical Industry Co., Japan), and PVP K-30 (40,000 g mol−1, Shanghai Jiuyi Chemical Reagent Co., China) were chosen as the raw materials. Both polymers were used without further purification. The required amount of polymer powders were dissolved in deionized water at 95 °C for 10 h to prepare 10%w/w, 15%w/w or 20%w/w polymer solutions. After held at a higher temperature
Microstructures of PVA/PVP hydrogel
Fig. 1 shows that PVA/PVP hydrogels exhibit an internal three-dimensional network structure with a lot of micropores on the surface, which is similar to the natural articular cartilage. The internal structure of the hydrogel samples becomes denser with higher polymer concentration and PVA polymerization. During freezing process, the polymers were expelled to create regions of concentrated polymer, while there was water loss during the process of drying. The polymer chains were pushed into close
Discussion
In 1980, Mow et al. [19], [20] proposed the biphasic theory for articular cartilage lubrication. The articular cartilage was assumed to be comprised of solid phase and fluid phase, which were incompressible and immiscible phases. The solid phase consisted of the collagen–proteoglycan network, while the fluid phase was the interstitial fluid in cartilage and the ions. This unique biphasic nature caters very well to its friction properties. Articular cartilage has a porous structure with very low
Conclusions
PVA/PVP hydrogel was synthesized by a repeated freezing–thawing method. With the increase of polymerization degree of PVA and polymer concentration, the microstructure of PVA/PVP hydrogels becomes denser and the pore size decreases, which leads to the decrease of the swelling ratio. Friction tests were carried out using a ball-on-plate friction tribometer. The variation of friction coefficient of PVA/PVP hydrogels as function of polymerization degree of PVA, polymer concentration, lubrication
Acknowledgments
This project is supported by the National Natural Science Foundation of China (Grant no. 11172142, 50975145).
References (40)
The frictional properties of animal joints
Wear
(1962)- et al.
Boundary lubricating films: formation and lubrication mechanism
Tribology International
(2005) - et al.
Lubrication mode analysis of articular cartilage using Stribeck surfaces
Journal of Biomechanics
(2008) - et al.
Experimental verification of the role of interstitial fluid pressurization in cartilage lubrication
Journal of Orthopaedic Research
(2004) - et al.
Friction and wear behaviour of bacterial cellulose against articular cartilage
Wear
(2011) - et al.
Friction, wear, and lubrication of hydrogels as synthetic articular cartilage
Wear
(2000) - et al.
Functional compressive mechanics of a PVA/PVP nucleus pulposus replacement
Biomaterials
(2006) - et al.
Novel PVP/PVA hydrogels for articular cartilage replacement
Materials Science and Engineering C
(2009) - et al.
A study on the friction properties of poly(vinyl alcohol) hydrogel as articular cartilage against titanium alloy
Wear
(2007) - et al.
Friction properties of nano-hydroxyapatite reinforced poly(vinyl alcohol) gel composites as an articular cartilage
Wear
(2009)
Cartilage interstitial fluid load support in unconfined compression
Journal of Biomechanics
Effect of sustained internal fluid pressurization under migrating contact area, and boundary lubrication by synovial fluid, on cartilage friction
Osteoarthritis Cartilage
Atomic force microscope investigation of the boundary-lubricant layer in articular cartilage
Osteoarthritis Cartilage
Current surgical options for articular cartilage repair
Journal of Agricultural and Food Chemistry
Cartilage tissue engineering and bioreactor systems for the cultivation and stimulation of chondrocytes
The European Biophysics Journal
Improvement of full-thickness chondral defect healing in the human knee after debridement and microfracture using continuous passive motion
The American Journal of Knee Surgery
Autologous chondrocyte transplantation. Biomechanics and long-term durability
The American Journal of Sports Medicine
Perichondral grafting for cartilage lesions of the knee
Journal of Bone & Joint Surgery (British Volume)
Rib perichondrial autografts in full-thickness articular cartilage defects in rabbits
Clinical Orthopaedics and Related Research
The microfracture technique for the treatment of articular cartilage lesions in the knee. A prospective cohort study
Journal of Bone and Joint Surgery, American Volume
Cited by (90)
Bioinspired multi-crosslinking and solid–liquid composite lubricating MXene/PVA hydrogel based on salting out effect
2023, Chemical Engineering JournalTribology of biodegradable polymeric systems
2022, Tribology of Polymers, Polymer Composites, and Polymer NanocompositesMOF-derived hierarchical carbon network as an extremely-high-performance supercapacitor electrode
2021, Electrochimica ActaMolecularly imprinted polymers hydrogel for the rapid risk-category-specific screening of food using SPE followed by fluorescence spectrometric detection
2020, Microchemical JournalCitation Excerpt :The hydrogel can be flexible, brittle, soft or hard, depending on the degree of crosslinking, which also affects the extraction performance of the hydrogel and thus the fluorescence sensitivity. Since the MIPs-PVA hydrogel serves as the SPE sampling medium as well as the fluorescence detection platform, a systematic investigation, including the additive amount of MIPs, PVA concentration [37] and the ratio of borate to PVA [38] were carried out to achieve the proper balance between the mechanical properties of the hydrogel and its fluorescence performance. As an example, the fluorescence performance of SMX-MIPs-PVA hydrogel with different fabrication conditions is shown in Fig. 2.
Polyacrylamide/Alginate double-network tough hydrogels for intraoral ultrasound imaging
2020, Journal of Colloid and Interface SciencePreparation and tribological properties of MAO-PVA/PTFE self-lubricating composite coating on aluminum alloy surface
2024, Journal of Coatings Technology and Research
- ☆
This paper was presented at the WOM 2013 conference, Portland, Oregon USA.