Degradative enzymes of cartilage. Effects of freeze-thawing of the tissue prior to extraction, and of protease inhibitors, on proteoglycans extracted with iso-osmotic neutral salt and 4 M guanidinium chloride

The bioactivity of cartilage extracellular matrix in articular cartilage regeneration

Cartilage matrix is a promising material for cartilage regeneration given the evidence supporting its chondroinductive character. The "raw materials" of cartilage matrix can serve as building blocks and signals for tissue regeneration. These matrices can be created by chemical or physical processing: physical methods disrupt cellular membranes and nuclei but may not fully remove all cell components and DNA, whereas chemical methods combined with physical methods are effective in fully decellularizing such materials. It is important to delineate between the sources of the cartilage matrix, that is, derived from matrix in vitro or from native tissue, and then to further characterize the cartilage matrix based on the processing method, decellularization or devitalization. With these distinctions, four types of cartilage matrices exist: decellularized native cartilage (DCC), devitalized native cartilage (DVC), decellularized cell-derived matrix (DCCM), and devitalized cell-derived matrix (DVCM). One currently marketed cartilage matrix device is decellularized, although trends in patents suggest additional decellularized products may be available in the future. To identify the most relevant source and processing for cartilage matrix, testing needs to include targeting the desired application, optimizing delivery of the material, identify relevant FDA regulations, assess availability of materials, and immunogenic properties of the product.

Frozen storage affects the compressive creep behavior of the porcine intervertebral disc

STUDY DESIGN

A biomechanical study of the compressive creep behavior of the porcine intervertebral disc before and after frozen storage.

OBJECTIVE

To determine whether frozen storage alters the creep response, hydration, and nuclear swelling pressure of the intact intervertebral disc.

SUMMARY OF BACKGROUND DATA

The mechanical response of the disc is dominated by swelling and fluid flow, whose effects are time-dependent. Because fluid content, which may change during storage, plays a significant role in the disc's time-dependent behavior, changes in mechanical response due to freezing may have been missed in previous studies that focused on time-independent behavior only.

METHODS

Porcine intervertebral discs were tested in repeated cycles of compressive creep either immediately postmortem or after 3 weeks of frozen storage. Swelling pressure and nuclear hydration were also measured in fresh and frozen discs. A fluid transport model was used to analyze the creep data.

RESULTS

The creep behavior of the intact porcine intervertebral disc is dramatically affected by frozen storage. The apparent permeability of the frozen discs was 82% higher than that of the fresh discs, and the swelling pressure of frozen discs was 25% lower in frozen discs (P < 0.01). The behavior of fresh and frozen discs became more dissimilar with repeated cycles of creep.

CONCLUSIONS

In vitro tests of frozen porcine intervertebral discs do not represent fresh behavior. Frozen storage appears to permanently alter disc behavior. The precise nature of any freezing-induced damage, and whether frozen storage similarly affects human discs, remains to be seen.