Bonding of articular cartilage using a combination of biochemical degradation and surface cross-linking

After trauma, articular cartilage often does not heal due to
incomplete bonding of the fractured surfaces. In this study we
investigated the ability of chemical cross-linkers to facilitate
bonding of articular cartilage, either alone or in combination with
a pre-treatment with surface-degrading agents. Articular cartilage
blocks were harvested from the femoropatellar groove of bovine
calves. Two cartilage blocks, either after pre-treatment or
without, were assembled in a custom-designed chamber in partial
apposition and subjected to cross-linking treatment. Subsequently,
bonding of cartilage was measured as adhesive strength, that is,
the maximum force at rupture of bonded cartilage blocks divided by
the overlap area. In a first approach, bonding was investigated
after treatment with cross-linking reagents only, employing
glutaraldehyde, 1-ethyl-3diaminopropyl-carbodiimide
(EDC)/N-hydroxysuccinimide (NHS), genipin, or transglutaminase.
Experiments were conducted with or without compression of the
opposing surfaces. Compression during cross-linking strongly
enhanced bonding, especially when applying EDC/NHS and
glutaraldehyde. Therefore, all further experiments were performed
under compressive conditions. Combinations of each of the four
cross-linking agents with the degrading pretreatments, pepsin,
trypsin, and guanidine, led to distinct improvements in bonding
compared to the use of cross-linkers alone. The highest values of
adhesive strength were achieved employing combinations of pepsin or
guanidine with EDC/NHS, and guanidine with glutaraldehyde. The
release of extracellular matrix components, that is,
glycosaminoglycans and total collagen, from cartilage blocks after
pre-treatment was measured, but could not be directly correlated to
the determined adhesive strength. Cytotoxicity was determined for
all substances employed, that is, surface degrading agents and
cross-linkers, using the resazurin assay. Taking the favourable
cell vitality after treatment with pepsin and EDC/NHS and the
cytotoxic effects of guanidine and glutaraldehyde into account, the
combination of pepsin and EDC/NHS appeared to be the most
advantageous treatment in this study. In conclusion, bonding of
articular cartilage blocks was achieved by chemical fixation of
their surface components using cross-linking reagents. Application
of compressive forces and prior modulation of surface structures
enhanced cartilage bonding significantly. Enzymatic treatment in
combination with cross-linkers may represent a promising addition
to current techniques for articular cartilage repair.