DYNAMIC CELL CULTURE METHODS FOR FUNCTIONALIZED BIOMATERIALS - Biologically-Responsive Hybrid Biomaterials - page 394

chondrocytes promotes redifferentiation of cells to the functional phenotype
[127]. The RGD motif (in the peptide GRGDSPK) can be cross-linked to the
surface of PLLA microspheres [126], and TGF- Ȳ 1 can be incorporated by a
water/oil/water (W/O/W) double-emulsion, solvent extraction method. When
cultured in a commercially available pendulum stirred-type spinner flask at 50
rpm for 5 minutes in flow and 15 minutes in stasis, human chondrosarcoma cell
line OUMS-27 cells proliferated and aggregated on the microspheres. The size of
the aggregates grew progressively over 14 days for all microcarrier types,
polystyrene control, PLLA + RGD, PLLA + TGF- Ȳ 1, and PLLA plain. The
incorporation of the RGD motif increased aggregate size after 7 days, most likely
due to increased cell attachment to the surface of the microcarriers. The release
of TGF- Ȳ 1 also increased aggregate size after 7 days of culture, and it also
increased sulfated GAG production the most between 7 and 14 days of culture.
Both bioactive molecule incorporations resulted in increased cell attachment,
with the added benefit that the PLLA scaffold would degrade with time, leaving
only new tissue. Cartilage is a multi-faceted, highly-functional tissue featuring a
very specialized architecture, especially for articular cartilage, which can best be
engineered using both materials which have been functionalized to increase cell
attachment and differentiation as well as a dynamic system in which to provide
mechanical stimulation and nutrient resources.
3.4. Ligaments and tendons
Bioreactors for the use of mechanical stimulation have long been utilized for
ligament tissue engineering due to the beneficial effect strain can have on the
cellular phenotype [128]. In addition, growth factors can have a profound effect
upon the function of cells, notably basic fibroblast growth factor (bFGF) and
growth and differentiation factor 5 (GDF-5) along with others for ligament and
tendon tissue applications [129, 130, 131]. The McAllister et al. group has
created a 95% porous polycaprolactone (PCL) scaffold which provides an initial
burst release of growth factor followed by lower dose release. This scaffold is
coated with a combination solution of collagen and the growth factor of interest
and allowed to dry between multiple applications. In Petrigliano et al. , bFGF
coating was used on the PCL scaffolds for cultures of rat bone marrow stromal
cells (BMSC). Scaffolds were subjected to loading of 6% uniaxial cyclical strain
at a frequency of 0.125 Hz for 23 hours/day, conditions found to be previously
favorable [132,133]. A lower dose (100 ng) of bFGF or uniaxial cyclic strain
alone both proved positive mRNA expression over the control (no bFGF, no