Tissue engineering - Biomedical Engineering Desk Reference - page 660

( Fig. 7.1.4-4 B). The polymer scaffolds are loaded into
the vessel and a uniform cell suspension is added. Vessel
rotation is initiated to allow dynamic cell seeding and in-
creased to maintain a high rate of nutrient and oxygen
diffusion. Alternately, the scaffolds can be preseeded with
cells under static conditions before loading ( Goldstein
et al., 1999 ). Several configurations of RWV have been
used in microgravity tissue engineering ( Freed and Vunjak-
Novakovic, 1997 ).

optimal tissue regeneration. For instance, mechanical
stimulation plays an important role in the differentiation
of mesenchymal tissues ( Chiquet et al., 1996 ; Goodman
and Aspenberg, 1993 ). Application of well-controlled
loads may stimulate bone growth into porous scaffolds.
The degradation of the scaffolds can be affected by ap-
plied strain ( Miller and Williams, 1984 ). Transwell cul-
ture systems that allow the use of different culture media
for apical or basal sides are often employed to induce and
maintain the polarity of epithelial cells. The growth and
function of some retinal cells may be regulated by the
light-dark cycle. In some cases, a gradient substrate with
spatially controlled wettability or other properties may
be desired ( Ruardy et al. , 1995 ). Some cellular chemo-
tactic responses may require the creation of concentra-
tion gradients of growth factors. Temporal presentation
of signals is also important. For example, each phase
of the differentiation of osteoblasts (proliferation, mat-
uration of ECM, and mineralization) requires different
signals ( Lian and Stein, 1992; Peter et al. , 1998a ). Co-
culture of several types may be preferred for in vitro
organogenesis including angiogenesis.

Perfusion culture

A flow perfusion culture system has been used for
in vitro regeneration of large 3D tissues and organs
( Fig.7.1.4-4 C)( Bancroft et al. , 2002; Glowacki et al. ,
1998; Griffith et al. , 1997; Kim et al. , 1998 ). The cell-
polymer constructs are maintained in a continuous-flow
condition. The culture medium is pumped from a reser-
voir through an oxygenator and the cell-polymer con-
structs, and recirculated back to the reservoir. The flow
rate for cell survival is adjusted based on cell mass. The
entire perfusion unit is maintained in normal sterile cul-
ture conditions. Compared to static culture, medium
perfusion has been shown to significantly enhance cell
viability and matrix production ( Glowacki et al. , 1998 ).
Additionally, the medium flow rate was found to influence
ECM deposition and the timing of osteogenic differenti-
ation when marrow stromal cells were cultured on three-
dimensional scaffolds in a perfusion bioreactor ( Bancroft
et al. , 2002 ). These systems are useful for the de-
velopment of complex tissue structures as well as the
study of the effects of mechanical stimulation on cell vi-
ability, differentiation, and ECM production.

Conclusions

Significant progress has been made to optimize the en-
gineering of tissue and organ analogs. However, many
challenges remain in the engineering of 3D tissues and
organs for clinical use. Nevertheless, many advances have
been made in synthetic polymer chemistry, scaffold
processing methods, and tissue-culture techniques.
These may eventually allow the generation of long-term
functional complex cell-polymer constructs with pre-
cisely controlled local environment such as material mi-
crostructure, nutrient and growth factor concentration,
and mechanical forces.

Other culture conditions

Ideally the culture conditions should provide all neces-
sary signals that the cells normally experience in vivo for

Bibliography

Aulthouse, A. L., Beck, M., Griffey, E.,
Sanford, J., Arden, K., Machado, M. A.,
and Horton, W. A. (1989). Expression
of the human chondrocyte phenotype
in vitro. In Vitro Cell Dev. Biol. 25:
659-668.
Babensee, J. E., Anderson, J. M., McIntire,
L. V., and Mikos, A. G. (1998). Host
response to tissue engineered
devices. Adv. Drug Deliv. Rev. 33:
111-139.
Babensee, J. E., McIntire, L. A., and Mikos,
A. G. (2000). Growth factor delivery

for tissue engineering. Pharm. Res. 17:
497-504.
Bancroft, G. N., and Mikos, A. G. (2001).
Bone tissue engineering by cell
transplantation. in Tissue Engineering
for Therapeutic Use , Y. Ikada and
N. Ohshima (eds.). Vol. 5. Elsevier
Science, New York, pp. 151-163.
Bancroft, G. N., Sikavitsas, V. I., van den
Dolder, J., Sheffield, T. L., Ambrose,
C. G., Jansen, J. A., and Mikos, A. G.
(2002). Fluid flow increases
mineralized matrix deposition in 3D
perfusion culture of marrow stromal

osteoblasts in a dose-dependent
manner. Proc. Natl. Acad. Sci. USA
99: 12600-12605.
Barrera, D., Zylstra, E., Lansbury, P., and
Langer, R. (1995). Copolymerization
and degradation of poly(lactic- co -
lysine). Macromolecules 28: 425-432.
Bartels, K. A., Bovik, A. C., Crawford,
R. C., Diller, K. R., and Aggarwal, S. J.
(1993). Selective laser sintering for the
creation of solid models from 3D
microscopic images. Biomed. Sci.
Instrum. 29: 243-250.