New Trends in Polymers - Progress in Organic and Physical Chemistry: Structures and Mechanisms - page 208

It was shown also that cultured cells produced collagen II and glycosaminogly-
can, the speci¿ c structural biopolymers formed the extracellular matrix [77, 80, 81].
A good viability and proliferation level of macrophages and ¿ broblasts cell lines was
obtained under culturing in presence of particles from short-chain low-molecular PHB
[61]. However it was shown that cell growth on the PHB ¿ lms was relatively poor: the
viable cell number ranged from 1×10 3 to 2×10 5 [34, 73, 81]. An impaired interaction
between PHB matrix and cytoskeleton of cultured cells was also demonstrated [77].
It was reported that a number of polymer properties including chemical composition,
surface morphology, surface chemistry, surface energy, and hydrophobicity play im-
portant roles in regulating cell viability and growth [84]. The investigation showed
that this biomaterial can be used to make scaffolds for in vitro proliferous cells [34,
76, 80].
The most widespread methods to manufacture the PHB scaffolds for tissue engi-
neering by means of improvement of cell adhesion and growth on polymer surface
are change of PHB surface properties and microstructure by salt leaching methods
and enzymatic/chemical/physical treatment of polymer surface [34, 76, 80, 85]. Ad-
hesion to polymer substrates is one of the key issues in tissue engineering, because
adhesive interactions control cell physiology. One of the most effective techniques to
improve adhesion and growth of cells on PHB ¿ lms is treatment of polymer surface
with enzymes, alkali, or low pressure plasma [34, 85]. Lipase treatment increases the
viable cell number on the PHB ¿ lm from 100 to 200 times compare to the untreated
PHB ¿ lm. The NaOH treatment on PHB ¿ lm also indicated an increase of 25 times on
the viable cell number compared with the untreated PHB ¿ lm [34]. It was shown that
treatment of PHB ¿ lm surface with low pressure ammonia plasma improved growth
of human ¿ broblasts and epithelial cells of respiratory mucosa due to increased hydro-
phylicity (but with no change of microstructure) of polymer surface [74]. It was sug-
gested that the improved hydrophilicity of the ¿ lms after PHB treatment with lipases,
alkali and plasma allowed cells in its suspension to easily attach on the polymer ¿ lms
compared to that on the untreated ones. The inÀ uence of hydrophilicity of biomaterial
surface on cell adhesion was demonstrated earlier [86].
But a microstructure of PHB ¿ lm surface can be also responsible for cell adhe-
sion and cell growth [87-89]. Therefore, modi¿ cation of polymer ¿ lm surface after
enzymatic and chemical treatment (in particular, reduced pore size, and a surface
smoothing) is expected to play an important role for enhanced cell growth on the poly-
mer ¿ lms [34]. Different cells prefer different surface. For example, osteoblasts pre-
ferred rougher surfaces with appropriate size of pores [87, 88] while ¿ broblast prefer
smoother surface, yet epithelial cells only attached to the smoothest surface [89]. This
appropriate roughness affects cell attachment as it provides the right space for osteo-
blast growth, or supplies solid anchors for ¿ lapodia. A scaffold with appropriate size
of pores provided better surface properties for anchoring type II collagen ¿ laments and
for their penetration into internal layers of the scaffolds implanted with chondrocytes.
This could be illuminated by the interaction of extracellular matrix proteins with the
material surface. The right surface properties may also promote cell attachment and
proliferation by providing more spaces for better gas/nutrients exchange or more se-
rum protein adsorption. [30, 76, 80]. Additionally, Sevastianov et al. found that PHB