Page 218 - Biodegradable Polyesters

196 8 Systematic Development of Electrospun PLA/PCL Fiber Hybrid Mats
∘
speed: 100 rpm) at 37 C in a 20 ml PBS (pH = 7.4). When the required incuba-
tion time was reached for the designated drug release, the mat sample was further
transferred to a 20 ml fresh buffer solution. Subsequently, the drug release rate
was calculated from the initial TCH amount by weight loaded in the fiber mats.
The corresponding cumulative drug release rate was calculated in Eq. (8.1):
M t
Cumulative drug release rate (%) = × 100% (8.1)
M ∞
where M and M are the amounts of drugs released from electrospun fiber mats
∞
t
at time t and infinite time when drugs are fully released, respectively. Three drug
release tests were conducted for each type of electrospun fiber mats and the aver-
age data were recorded accordingly.
The fiber mats of the same size were measured to have the initial mass m and
were transferred to a 15 ml PBS (pH = 7.4). They were further subjected to the
rotary shaker incubation at a rotor speed of 100 rpm for the biodegradation study.
The fiber mats were removed at each given incubation period and further washed
in deionized water. The final mass m of the fiber mats was obtained after they
1
∘
were dried under vacuum at 37 C. The total mass loss m% was determined from
Eq. (8.2):
m − m
m%= 1 × 100% (8.2)
m
Solution viscosity was measured by using a Visco 88 portable viscometer from
Malvern Instruments (UK). The morphology of electrospun fiber mats was studied
via an EVO 40XVP scanning electron microscope (SEM) (Germany) at an acceler-
ating voltage of 5 kV. Before the SEM observation, the samples were sputter-coated
with platinum. Fiber diameters were calculated from SEM images by using an
image analysis tool incorporated in the Zeiss Smart SEM software. For each sam-
ple, measurements were made for a minimum of 150 fibers from multiple scanned
SEM images at a rate of 15 fibers per image. Researchers working in electrospun
fibers have an ambiguous definition of nanofibers based on the fiber diameter
(normally any fibers less than 1 μm). To be more precise, we assume in this study
that fibers with a diameter less than 500 nm are called nanofibers while those
larger than 500 nm in diameter are categorized as microfibers for imaging analysis.
X-ray diffraction (XRD) measurements of prepared samples were performed
in a Bruker Discover 8 X-ray diffractometer (Germany) operated at 40 kV and
40 mA using Cu-Kα radiation that was monochromatized with graphite sample
∘
monochromators in a 2 range from 7.5 to 40 with a scanning rate of 0.016 to
∘
0.02 per s.
Thermal analysis was undertaken using a DSC6000 Perkin Elmer (USA) with
cryofill liquid nitrogen cooling system. Approximately 10 mg of cut fiber mat was
sealed in an aluminum pan. The thermal behavior was analyzed during the first
∘
∘
−1
heating scan from 90 to 200 C with a ramp rate of 10 Cmin . The DSC ther-
mograms and associated thermal parameters such as glass transition tempera-
ture (T ), crystallization temperature (T ), and melting temperature (T )were
g c m
obtained.