C. Puttlitz (Fort Collins, US)
Colorado State Universiity Mechanical EngineeringPresenter Of 1 Presentation
16.3.2 - Comparison of Fresh and Cryopreserved ProChondrixCR® Thin Osteochondral Allograft Mechanics in Explant Conditions
Abstract
Purpose
The clinical feasibility of thin osteochondral allografts for cartilage repair can benefit from cryopreservation to extend the shelf life of the implants. It is critical to consider the effects of cryopreservation on the mechanical properties of cartilage. The purpose of this study was to compare the viscoelastic mechanics of fresh and cryopreserved allografts via indentation stress-relaxation testing.
Methods and Materials
1mm thick cartilage sheets 20mm in diameter (AlloSource, Centennial, CO, USA) were prepared from weight bearing joints of eight research consented cadaveric human donors. Fresh grafts were aseptically packaged in media and stored at 4°C for 14-25 days until tested. Donor-matched grafts were cryopreserved following a proprietary process using a common cryoprotectant and stored at -80°C until tested. Specimens were hydrated by frequent saline spray and underwent indentation testing at room temperature using a 0.8mm diameter spherical tip displaced 0.1mm into the sample at a rate of 0.1mm/s; this displacement was held for a 100s relaxation period (Figure 1). Indentation repetitions were conducted at three locations per specimen. Elastic moduli were calculated using Hertzian contact mechanics formulae.
Results
Differences between fresh and cryopreserved means fell within one standard deviation for all parameters (Table 1). There was no consistent effect of cryopreservation on the mechanical properties when comparing specimens from individual donors (Figure 2). Accordingly, there were no significant differences from paired t-tests (α=0.05) between fresh and cryopreserved groups in instantaneous modulus (P =.18), equilibrium modulus (P =.36), or percent relaxation (P =.69).
| Fresh (Mean±S.D.) | Cryopreserved (Mean±S.D.) | Percent Difference Mean (95% C.I.) | |
|---|---|---|---|
| Instantaneous elastic modulus (MPa) | 5.71±2.77 | 3.87±2.15 | -32%(-85%,+19%) |
| Equilibrium elastic modulus (MPa) | 0.75±0.26 | 0.61±0.32 | -19%(-65%,+27%) |
| Percent relaxation (%) | 85.1±6.0 | 83.2±9.2 | -2%(-15%,+10%) |
Conclusion
The data from this study indicated no significant differences in the instantaneous and time-dependent (viscoelastic) mechanical properties derived from indentation tests between fresh and cryopreserved ProChondrixCR® allografts.