4
Biomimetic Structured Porogen Freeform
Fabrication System for Tissue Engineering
Jack Zhou and Lin Lu
Department of Mechanical Engineering and Mechanics
Drexel University, Philadelphia,
USA- Introduction
1.1 From traditional bone scaffold replacement to tissue engineering
Non-healing bone fractures are a major health concern in the United States because of a
large aging population and increased occurrence of sport-related injuries. The rate of usage
of bone grafting is increasing dramatically. Bone substitutes are playing a major role in
repairing or replacing damaged or diseased tissues resulting from trauma, pathological
degradation, congenital deformation, cancer and cosmetics [Yang, Hillas, Baez, Nokelainen
and Balan, 2004; Cuckler, 2004 and Bock, Goode and Novartis, 2003]. It was reported that
over 1 million bone grafts implanted annually in US and Europe [Kelly, 2000] and over
500,000 bone-grafting procedures performed annually in the United States alone [Cutter and
Babak, 2006].
Two traditional ways used in bone disease treatment are autografting and allografting. The
autograft, which is a section of bone taken from a patient’s own body, has been used for
decades to supplement host repair, while an allograft is tissue harvested from one
individual and implanted into another individual of the same species, usually taken from
cadaver. Bone graft provides the structural stability and natural osteogenic behavior for
patients, but both autograft and allograft failed to provide the optimum therapy and they
have limitations [Giannoudis, Dinopoulos and Tsiridis, 2005 and Laurencin and Ambrosio,
1999]. Autograft is expensive and the remaining tissue at the harvest site is damaged by the
removal of the graft, which often leads to donor site morbidity and raises problems of
restricted availability [Silber, Anderson and Duffner, 2003]. Furthermore there is limited
amount of bone available for harvesting, besides that the characteristics in resorption of the
graft cannot be easily predicted. Allograft often provokes an immunogenic response, can be
rejected by the host and often needs autograft tissue to initiate osteogenesis. Furthermore it
may transmit disease. Although these methods are successful in some aspects, shortcomings
are encountered with their usage [Gadzag, Lane, Glaster and Forster, 1995]. The main
problem when using those traditional treatments is the shortage of donor tissue that limits
the number of people receiving bone transplantations.
To overcome the limitations, alternative methods have been developed to fabricate synthetic
bone graft substituates to promote regeneration of feasible healthy bone, however till now,
no method has yet provided a satisfactory solution. As a result, researchers are turning
toward a promising field of tissue engineering to develop new methods of bone