A Synthetic Bottle-brush Polyelectrolyte Reduces Friction and Wear of Intact and Previously Worn Cartilage

Abstract

A poly(7-oxanorbornene-2-carboxylate) polymer containing pendent triethyleneglycol (TEG) chains of 2.8 MDa ("2.8M TEG") was synthesized and evaluated for long-term lubrication and wear reduction of ex vivo bovine cartilage as well as for synovitis in rats and dogs after intra-articular administration. Bovine cartilage surfaces were tested under torsional friction for 10,080 rotations while immersed in either saline, bovine synovial fluid (BSF), or 2.8M TEG. For each solution, coefficient of friction (μ), changes in surface roughness, and lost cartilage glycosaminoglycan were compared. To directly compare 2.8M TEG and BSF, additional samples were tested sequentially in BSF, BSF, 2.8M TEG, and then BSF. Finally, another set of samples were tested twice in saline to induce surface roughness and then tested in BSF, Synvisc, or 2.8M TEG to determine each treatment's effect on worn cartilage. Next, male Lewis rats were injected in one knee with 2.8M TEG or saline and evaluated for effects on gait, and female beagles were injected with either 2.8M TEG or saline in one knee, and their synovial tissues analyzed for inflammation by H&E staining. Treatment with 2.8M TEG lowers μ, lessens surface roughness, and minimizes glycosaminoglycan loss compared to saline. The 2.8M TEG also reduces μ compared to BSF in pairwise testing and on worn cartilage surfaces. Injection of 2.8M TEG in rat or beagle knees gives comparable effects to treatment with saline, and does not cause significant synovitis.

Keywords: CT imaging; biolubricant; chondroprotection; osteoarthritis; synovial fluid; viscosupplement.

Figure 1.

a) Graphical representation of the bottle brush 2.8M TEG lubricant. b) Chemical structure of the 2.8M TEG polymer. c) Photograph of the isolated 2.8M TEG polymer after synthesis. Scale bare = 1 cm d) Photograph of an aqueous solution of the 2w/v% 2.8M TEG ejecting from a 26G needle.

Figure 2.

Coefficients of friction (μ_mean) for bovine cartilage plug pairs (patella against femoral groove) tested in three lubricants (n=4 each) during the long-duration torsional friction regimen (>10,000 rotations) of Study 1. Error bars indicate standard deviation. *2.8M TEG vs Saline (p<0.05), #BSF vs Saline (p<0.05), ↑ indicates pause for lubricant extraction (plugs held apart for ~30 sec). Saline and BSF data reproduced with permission from ref 32. Copyright 2018 Elsevier.

Figure 3.

Total number of rings on cartilage plug surfaces from each pair tested (example photo shown in inset) following long-duration torsional friction testing in three lubricants (n=4 each) in Study 1. Error bars indicate standard deviation. *2.8M TEG vs saline (p<0.05). Scale bar is 1 mm.

Figure 4.

a) Representative CECT color maps of femoral groove plugs subjected to long-duration torsional friction testing in Study 1 using saline, BSF, and 2.8M TEG. b) Percent increase in cartilage surface roughness following long-duration torsional friction testing in three lubricants (n=4 each) during Study 1. 2.8M TEG vs Saline (p<0.05). Error bars indicate standard deviation.

Figure 5.

Mean of each long-duration friction test’s μ-values normalized to the μ-values of Test1 from Study 2 (n=3). The mean coefficient of friction of Test2 (2.8M TEG) reduced by 20.9 ± 10.5% (mean ± SD) relative to that of Test1 (BSF), while the mean coefficient of friction of Test3 (BSF) increased by 2.0 ± 7.1% relative to Test1. Error bars indicate standard deviation. *The normalized Test2 mean μ-value was significantly less than the normalized Test3 μ-value (p<0.05).

Figure 6.

Percent change in μ_mean from the day 2 “wear test” to the day 3 “lubricant test” in BSF (n=4), Synvisc (n=3) and 2.8M TEG (n=4) during Study 3. Error bars indicate standard deviation. The percent change in μ_mean values for 2.8M TEG were significantly lower than those for BSF for all time points except 800, 6080, 6240, 6400, 6560, 6720, 6880, 7040 and 8480 sec. *2.8M TEG vs BSF (p<0.05), except for the two time points indicated with # (800 and 8480 sec).

Figure 7.

Representative H&E histological sections (50x) of synovium from beagle knees injected with a) saline or b) 2 w/v% 2.8M TEG. Scale bar = 100 μm. Both knees experienced minimal papillary proliferation (PP).