Barbieri Thesis - BioMedical Materials program (BMM)

Chapter 5 – Alkali surface treatment effects
5.3.8. Animal experiments
A total of six samples per material were intramuscularly implanted in six dogs. After
12 weeks, all samples were retrieved and they were surrounded by a thin layer of
connective tissue and then muscle tissue. As shown in the histological overviews
(Figure 9), after 12 weeks of implantation all specimens retained the initial shape and
size of the granules. However, no bone was observed in any of the composites.
Observations at BSEM showed that, as compared to the starting materials, average
thicker apatite layers surrounding M1 and M2 granules could be seen. However, their
increase compared to their starting counterparts was not significant (t–test, p>0.31 for
M1, and p>0.1 for M2) (Table 4, Figure 9). The resulting apatite layers had
significantly different thickness amongst the three materials (ANOVA, p0.2).
5.4. Discussion
We prepared three composites of apatite and 96%mol. L–lactide/4%mol. D–lactide
copolymer having three different levels of surface roughness, which was directly
linked to the topographical disorder. Clashing with our expectances, none of them
supported heterotopic bone formation after twelve weeks intramuscular
implantation in dogs. In fact, we expected that the rougher and topographically more
disordered surfaces (i.e. M2) would have triggered the osteoinduction process
because, consistently with literature, [195, 363] they diminished human bone marrow
stromal stem cell osteoblastic proliferation but increased their osteogenic
differentiation compared to their smoother counterparts (Figure 8). It is suggested that
osteogenic stem cells are anchorage–dependent and they adhere well on nano–
rough surfaces able to adsorb proteins, [153, 362, 367] including fibronectin and vitronectin
that facilitate focal adhesion [371–373] and cytoskeleton reorganization. [374] At the same
time, increased surface roughness is reported to enhance osteogenic
differentiation, [363] probably because such nano–texture can adsorb higher amounts of
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