Triborheological Study under Physiological Conditions of PVA Hydrogel/HA Lubricant as Synthetic System for Soft Tissue Replacement

Abstract

In soft tissue replacement, hydrophilic, flexible, and biocompatible materials are used to reduce wear and coefficient of friction. This study aims to develop and evaluate a solid/liquid triborheological system, polyvinyl alcohol (PVA)/hyaluronic acid (HA), to mimic conditions in human synovial joints. Hydrogel specimens prepared via the freeze-thawing technique from a 10% (w/v) PVA aqueous solution were cut into disc shapes (5 ± 0.5 mm thickness). Compression tests of PVA hydrogels presented a Young's modulus of 2.26 ± 0.52 MPa. Friction tests were performed on a Discovery Hybrid Rheometer DHR-3 under physiological conditions using 4 mg/mL HA solution as lubricant at 37 °C. Contact force was applied between 1 and 20 N, highlighting a coefficient of friction change of 0.11 to 0.31 between lubricated and dry states at 3 N load (angular velocity: 40 rad/s). Thermal behavior was evaluated by differential scanning calorimetry (DSC) in the range of 25-250 °C (5 °C/min rate), showing an endothermic behavior with a melting temperature (Tm) around 231.15 °C. Scanning Electron Microscopy (SEM) tests showed a microporous network that enhanced water content absorption to 82.99 ± 1.5%. Hydrogel achieved solid/liquid lubrication, exhibiting a trapped lubricant pool that supported loads, keeping low coefficient of friction during lubricated tests. In dry tests, interstitial water evaporates continuously without countering sliding movement friction.

Keywords: coefficient of friction; hyaluronic acid lubricant; polyvinyl alcohol hydrogel; triborheology; wear.

Figure 1

Damage explanation in the joints: (A) Hip osteoarthritis (OA); (B) knee OA; (C) facet OA; (D) elbow OA.

Figure 2

Characterization in a Discovery Hybrid Rheometer DHR-3. (a) Rheological study using cone-and-plate stainless steel configuration with an angle of 0.09969°, a diameter of 60 mm, and a truncation gap of 23 um. Samples used were 4 mg/mL hyaluronic acid (HA) solution. (b) Triborheological study using plate-and-plate stainless steel configuration with a diameter of 40 mm. Samples used were 10% polyvinyl alcohol (PVA) hydrogel with 5.0 ± 0.5 mm thickness and 45 mm diameter, hydrated with 4 mg/mL HA solution.

Figure 3

SEM of PVA hydrogels. (a) Surface distribution, (b) porosity (High vacuum, 50–1000×, secondary electrons).

Figure 4

Compression tests (Up to 4500 N, compression rate 1 mm/min). (a) Linear regression of all tests; (b) exponential behavior of compression modulus in test 1; (c) test 5 deformation over time.

Figure 5

Rheological test. (a) Viscosity vs. shear rate; (b) shear stress vs. shear rate; (c) modules and complex viscosity vs. frequency (humidity, 37 °C, 0.01–100 Hz, 0.001–100 s⁻¹).

Figure 6

Coefficient of friction vs. angular velocity. (a) Dry; (b) HA lubricated; (c) coefficient of friction vs. angular velocity: Lubrication comparative; (d) coefficient of friction vs/pressure (0.1–100 rad/s, 1–20 N).

Figure 7

(a) Lubrication mechanism in PVA hydrogel under applied force in solid–solid contact. (b) Lubrication mechanisms applied to a PVA hydrogel/HA lubricant system.

Figure 8

Differential scanning calorimetry (DSC) thermal diagram of PVA samples at different weights.