Hybrid, combination, and replant materials - Orthopaedic Biomaterials in Research and Practice - page 245

CHaPTer TeN
Hybrid, combination,
and replant materials
As described in Chapter 9, the field of tissue engineering has proliferated
over the past few decades. The confluence of engineering, biology, and
medical devices has led to the development of many so-called tissue-
engineered products, some of which are now considered to be standard
of care. Tissue engineering , as understood most generally, is the use of
a combination of cells, engineering and materials methods, and suitable
biochemical and physiochemical factors to improve or replace biological
functions. A major component of tissue engineering is the development
of substrates or scaffolds for cell adhesion. The ultimate goal of this
development is to allow controlled degradation of the substrate so that
the engineered tissue can support itself. These degradable materials that
are used as substrates can be categorized as natural, synthetic, or hybrid
materials. Natural materials may include collagen and other naturally
derived polymers. However, natural substrates in their current form suf-
fer from the lack of necessary mechanical integrity for fabrication into
scaffolds. Natural materials also tend to be limited by supply and suffer
from variation based on the source. Naturally derived polymers may also
be immunogenic.
Synthetic materials include poly(glycolic acid), poly(lactic acid), and
poly(d,l-lactide-co-glycolide) copolymer. The benefit of synthetic mate-
rials is the ability to adjust their physical properties so that they can be
constructed to a specified size, shape, and morphology. There is also
more control over their degradation characteristics.
The use of such cell or tissue scaffolds, either seeded with cells before
implantation or attractive to cells after implantation, produces a new
class of biomaterials: hybrid (sometimes biohybrid ) materials . Although
some scaffolds are not resorbable, the overall goal of the engineering
designer is to produce hybrid materials that will eventually be remodeled
and replaced by normal host tissue. However, the host response between
the synthetic scaffold and seeded cells presents a great challenge.
Therefore, multiphase materials, which combine the characteristics of
both natural and synthetic materials, are commonly used. Multiphase