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Orthopedic and Rehabilitation Engineering

Orthopedic and Rehabilitation Engineering - Poster Session D

Poster AA11 - Addressing multimodal mechanics of cartilage like materials for tissue repair

Friday, October 25, 2024
3:30 PM - 4:30 PM EST
Location: Exhibit Hall E, F & G

Introduction:  Articular cartilage(AC) microarchitectures accommodate multiaxial and multimodal loading regimens ranging from normal ambulation to extreme athletic performance1. Thus, cartilage repair materials should be able to adapt to multiple loading modes2,3. Collagen fibrils in AC's superficial zone protect against shearing, while those in the deepest zone protect against compression4. Cartilage like materials used for clinical training simulators as well as cartilage repair materials required to support the surrounding cartilage following salvage or preservation procedures can be improved by addressing multimodal loading mechanics. This study compares multi-modal loading of 1) 3D printable clinical training simulator material for the Stratasys’ J750 and 2) a potential cartilage repair material with cartilage from the ovine trochlear groove. Samples were tested under stress relaxation and rheometry, hypothesizing that materials like AC under compression than under shear4.

Materials and

Methods:  Polycondensation of 1:1 glycerol and dodecanedioic acid was conducted under vacuum at 120oC for 48 hours, 18% of free the hydroxyl groups in the prepolymer backbone were acrylated5. PGD was 3D printed using a digital light projection with an orthotopic lattice. Ovine femoral cartilage was obtained via punch biopsy. Rheometry was done with an Anton Paar rheometer, performing frequency sweeps from 0.001 rad/s to 10 rad/s at a constant 0.1% strain and 1N pinning force6.Complex shear modulus versus frequency was plotted. Confined compression was done on an Instron tester with successive 5% strain increases (50%/s ramp), each followed by a 10-minute hold, up to 20% compression2. Custom CAD-designed testing chambers were used to simulate physiological conditions (submerged in phosphate buffer solution, 37°C) (Figure 1A,B). Maximum and minimum force for each step were noted and an ANOVA was used to check for significance within and across groups.

Results, Conclusions, and Discussions: Stress relaxation under confined compression within an immersion chamber at physiological conditions revealed PGD repair materials (Figure 1E) to have similar properties to those of ovine articular cartilage (Figure 1A). Modulus and peak load at each cycle of articular cartilage and PGD materials were different from those of J750 repair materials (Figure 2A, p < 0.01). The relaxation of articular cartilage and PGD showed very similar values. Utilizing the findings form these non-destructive loading regimens, a pinning compression force was applied as was previously described. Shear rheology paired with compression reveals that J750’s storage and loss moduli are closer to poly(glycerol-dodecanedioate) than articular cartilage (Figure 1B). This indicates that testing multiple loading conditions results in different interpretation as it comes to material design. Understanding the utilization of repair or simulations materials for various applications, the specific user needs for those applications, and translating these needs to specific design requirements can improve both repair and training outcomes. Testing of compressive and shear properties utilizing a commercial grade rheometer allows for a cost effective and adaptable analysis of articular cartilage and repair materials, allowing for multiple test iterations and specimens, with industry-grade precision. Evaluating various pinning forces in conjunction with frequency sweeps, determining the impact of 3D printed architectures on shear and confined compression, and assessing the role of immersion solution composition are studies underway for addressing this multi-modal mechanics approach towards cartilage repair and mimic materials.

Acknowledgements (Optional):  Acknowledgements: Funded in part by the Georgia Research Alliance
1. Chan, D. D., et al. (2016). Scientific Reports, 6.
2. Patel, J. M., et al. (2019). In Tiss Eng-C: Methods 25(10)593–608
3. Weizel, A. et al. (2020). Acta Biomaterialia, 118, 113–128.
4. Fox S et al. (2009), Sports Health, 1(6), 461–468.
5. Ramaraju, H et al. (2020). Advanced Functional Materials, 15(2).
6. Perni et al. (2020). Sci Rep, 10(1).