The use of 3d printed Scaffold Models in Medical and Biomedical Engineering Education. Abstract

Bioactive glass scaffolds

Bioactive glasses form a bond to bone much faster than bioceramic materials. This is due to them being amorphous. Dissolution of a random amorphous network begins much earlier than that of a crystalline ceramic; therefore, the HA forms more quickly on the glass than on synthetic HA. Bioactive glasses
can be made via two routes: traditional melt-processing and the sol–gel
process. Sol–gel-derived bioactive glasses have a porous texture in the
nanometre range, giving them a surface area of 150–600 m²g^–1, which is two
orders of magnitude higher than melt-derived glasses. Dissolution is therefore,
more rapid than for melt-derived bioactive glasses of similar composition.
Along this surface there are many silanol groups that act as nucleation sites
for HA layer formation, also making sol–gel-derived glasses more bioactive.
The dissolution of sol–gel-derived bioactive glasses is large enough for bioactive
glasses to be considered resorbable and the rate of resorption can be controlled
by altering the textural porosity. The foaming of sol–gelderived bioactive glasses is the most successful way for producing bioactive glass scaffolds with a structure similar to trabecular bone mineral. Polymer reactions of glass precursors in a solution are involved in the sol–gel process (sol). The sol is a solution of silica species that cross-links together to form a silica network and forms a gel.
3.1 Composites
Bone is consisted of collagen (polymer) and mineralized bone (ceramic). Collagen fibres create a framework for the bone and have excellent tensile and flexural strength. Bone mineral is an apatite that gives the bone its rigidity and strong compressive strength. A porous scaffold made of a composite material would be an apparent way to emulate the structure of bone.
Composites are generally a polymer matrix with ceramic or glass fibres or particles reinforcing the matrix. Attempts to produce an ideal scaffold from
composite materials has led to the use of the PGA/PLLA and poly(caprolactone)
resorbable polymers as described in Section 1.2. Filler materials of bioactive
ceramics such as synthetic HA and tricalcium phosphate have been added to
impart not only increased strength and stiffness but also bioactivity to the
polymer matrix. Bioactive glass particles have been incorporated into PLGA
foam scaffolds shown in this Fig 3.1.

Fig 3.1. Electron micrograph of a PGLA scaffold made by freeze–drying.
to provide not only bioactivity but also
delivery of gene activating ions to the scaffold (CD Fig. 3.2). It is still very
difficult to maintain the resorbability and maintain the mechanical properties
of the scaffold during resorbtion, so the quest for an ideal scaffold continues.


Fig.3.2. A polymer scaffold that has been created by fused deposition
modelling.
a layer-by-layer process through a nozzle, the movements of which are dictated
by a CAD file.