SCAFFOLD CONSIDERATIONS FOR OSTEOCHONDRAL TISSUE ENGINEERING - Intelligent Scaffolds for Tissue Engineering and Regenerative Medicine - page 792

Thereareotherdistinctconsiderationswithregardtothegener-
ation of a tissue-engineered osteochondral replacement construct.
Firstly,fixationofthetissue-engineeredconstructintothedefectsite
must be taken into account for several reasons. The most obvious
is that the construct must remain in place if it is to function prop-
erly.Also,inorderforproperintegrationtooccurwiththesurround-
ing tissue, the construct must not be permitted to move excessively.
Several methods are employed to fix constructs in place, the most
common being gluing, usually using fibrin and suturing. Mechanical
properties of the construct have already been mentioned in relation
tothescaffoldmaterialandloadbearing,butthismustalsobetaken
into account for the final tissue properties required and how this
willaffectintegrationwiththesurroundingtissue.Thisisoneofthe
largest problems currently associated with repair of chondral and
osteochondral defects. In osteochondral transplantation, poor inte-
gration at the cartilage and bone levels has been reported. 66 Poor
integration prevents the structure from functioning as one biome-
chanical entity, and the high stress at the interface leads to further
degeneration in time. In contrast to mature osteochondral grafts it
isbelievedthattheimmaturetissueoftissue-engineeredconstructs
have better integration capacities. 67 Other options may be consid-
ered to improve integration upon implantation, such as enzymatic
treatment of the wound area 68 or mechanical debridement or use
of glues for initial fixation. Development of a construct with similar
mechanical properties to the surrounding cartilage and underlying
bonecan onlyimprove the chances ofgood initialintegration.
Alsotobeconsideredisthefactthatboneisahighlyvascularized
tissue,whereascartilageremainsavascularthroughoutlife.Depend-
ingonthecelltypechosenfortheosteochondralconstruct,itispos-
sible that blood vessels might invade from the lower osseous layer
to the chondral layer. This could be prevented in a number of pos-
sible ways, from the placement of a degradable impermeable mem-
brane between the two layers to allow for stabilization in vivo to the
addition of gene vectors expressing anti-angiogenic factors to pre-
ventinvasion.Thisexpressioncouldalsobeprogrammedtobetran-
sient,switchingoffoncethetissuehasfullyintegratedandmatured.
A final consideration in designing a layered scaffold for osteochon-
dral tissue repair is tailoring the degradation characteristics of the