Page 243 - Biodegradable Polyesters

9.2 MFC Concept and its Potential for Biomedical Applications 221

nanofibrillar single-polymer composites (SPCs) demonstrating superior mechan-
ical performance [20]. The same approach has been also applied to other polymers
[20, 21].
In this way, exploring the experience gained during the MFC and NFC devel-
opment, neat nano- and microfibrils of many polymers were manufactured. They
meet important demands of scaffolds for regenerative medicine and specifically
extend the current options of stem cell bioengineering. Advantages of the fibril-
lar matrices, particularly combined with their high porosity, will comprise their
microstructural adaptability, dedicated bioactive characteristics, and fine-tuned
degradability; finally, there is the important fact that the biodegradable compo-
nent is produced without any contact with organic solvents and/or long high-
temperature treatments.
The most frequently used technique for achieving high porosity is the manu-
facturing of ultrathin fibers by electrospinning [22, 23]. With the exception of a
few cases, electrospinning is performed using a polymer solution in organic sol-
vents, themajorityofwhich aretoxic.Eventracesofthe latter negatively affect
the growth and the overall behavior of the living cells on the scaffolds, as out-
lined above. For this reason, a question of paramount importance is how to make
scaffolds free of organic solvents.
Since in some cases the use of organic solvent was unavoidable, it was of
interest to measure the amount of organic solvent (xylene) in nano- and microfib-
rillar scaffolds after drying them at elevated temperature in a vacuum. The
measurements have been performed by means of gas chromatography coupled
to mass spectrometry (GC-MS) [24]. For this purpose, model scaffolds of PET
comprised of microfibrils with diameters of ∼1 μm or nanofibrils with diameters
of 50–150 nm as well as microfibrillar scaffolds of PGA have been used. As can
be concluded from Table 9.1, an extremely low initial amount of xylene has been
found (<20 ppm). The xylene amount dropped below 2 ppm after drying for 24 h
∘
in a vacuum at 80 C. The microfibrillar PGA scaffolds, initially containing more
xylene (23.4 ppm), retained only 3.6 ppm after drying for 24 h. After drying for
48 h, the amount of xylene in all the scaffolds studied reached the detection limits
of the GC-MS apparatus (<0.5 ppm).

Table 9.1 Room storage conditions, amount of xylene, BET specific surface area, and fibril
diameters of fibrillar scaffold samples [24].

Sample Room Xylene (ppm) after treatment in vacuum at Surface Diameter
∘
−1
2
storage 80 C for (h) (m g ) ( m)
(month)
6 24 48 90 115
PET-Micro 1 8 0.5 0.4 0.2 — 0.2 — 0.98
PET-Micro 2 3 1.3 0.8 0.3 — 0.3 4.0 0.86
PET-Nano 1 21.0 2.0 — 1.1 — 18.8 0.05–0.16
PGA 1 23.4 3.6 — 0.5 — 8.9 1.24