Biomedical Engineering Reference
In-Depth Information
material with desired porous architecture for specific biomedical application is still
awaiting. Regardless of the type of porous scaffold (ceramic or polymer based), all
tissue engineering scaffolds should meet the following requirements:
1. Surface wettability properties to promote cell adhesion, proliferation, and
differentiation.
2. Mechanical properties to withstand stress.
3. Large ratio of surface area to volume to allow tissue ingrowth.
4. Controlled rate of degradation (particularly for polymer scaffolds).
In this chapter, emphasis has also been placed on the design of polymeric scaffold
materials that obtain specific, desired, and timely responses from surrounding cells
and tissues. The overall challenges concerning critical scaffold design parameters
include polymer assembly, surface properties, nano- or macrostructure, bio-
compatibility, biodegradability, and mechanical properties.
From the discussion on porous scaffolds, it should be clear that multiscale
porous scaffolds would be an interesting material to be developed and investigated
in the future. It is known that microporosity with pore sizes of less than 1
mhelps
m
in initial protein adsorption, and pore sizes of 1-20
m aid in cell attachment as
well as oriented cellular growth at the initial stage of cell proliferation and growth.
Also, macroporosity with pore sizes of 100-1000
m
m facilitates tissue or bone
ingrowth in vivo. It would be therefore ideal to produce a porous scaffold with top
surface of less than 1
m
m pore size and of bioresorbable material followed by pores
m
of 1-20
morlargerwithatop-down
approach. Although the fabrication of scaffolds with such a controlled or gradient
pore size could be a major challenge in terms of processing, one can use 3D
printing method to produce such gradient porosity in HA-TCP or TCP-Ti system.
As mentioned earlier, the type and amount of binder as well as postprinting heat
treatment would be related challenges.
The potential for improving the mechanical properties of bioceramics or polymer
composite scaffolds with a fabrication approach has been demonstrated in several
systems with limited success to achieve mechanical properties, particularly com-
pression strength, or modulus in the range of values for cancellous bone. All of the
processing approaches can be conveniently classified into two categories: (1)
chemical precursor-based routes and (2) engineering-based approaches. Although
the first category largely results in uncontrolled porosity with heterogeneous or
untailored pore sizes, the second category (i.e., 3D printing or other rapid proto-
typing routes) produces porous scaffolds with tailored porosity. More emphasize
should be placed in the future to develop porous scaffolds with properties compara-
ble to those of cancellous bone.
Another key question that needs to be addressed in future research is whether
porosity in inherently bioinert scaffold material can induce bioactivity. To illustrate
this issue, one can do in vitro or in vivo experiments on porous Ti and porous HA
under identical conditions with similar porous architecture.
m
m size and subsequently pores of 100
m
Search WWH ::
Custom Search