Page 589 - IJB-10-3

International Journal of Bioprinting 4D printing & simulation for biomedicine

the utilized SMP exhibits no cytotoxicity, indicating its changes to the glass phase during the cooling process. In
potential suitability for use in biomedical devices. This this process, the strain is stored in the SMP material, while
trend was also evident in cell proliferation experiments the stored strain is returned during the heating process. The
using WST-1 (Figure 4c). stress–strain relation of the SMP is expressed as follows: 40
The biocompatibility of polymers is closely related to
−1
cell adhesion, as cells interact with the polymer surface σ = (S r + η (S g − S r )) ( ε − ε − ε ) (VII)
g
in
th
to which they adhere. In the presence of a biocompatible
polymer, protein adsorption occurs on the polymer where σ represents stress, and S and S represent
surface, facilitating cell adhesion in the cytoskeleton. This the rubber phase and glass phase compliance matrix,
g
r
interaction directly influences receptors, such as integrin, respectively. S is expressed as follows: 22
and plays a crucial role in cell survival and proliferation i
by impacting extracellular matrix (ECM) deposition,
cell movement, and proliferation. 33-36 SEM was used to   1 v − i v − i 0 0 0  
verify the morphology of adherent cells on the developed  E i E i E i 
polymer (Figure 4d). The results confirmed that cells grew  v − i 1 v − i 0 0 0 
and formed a confluent layer that covered the surface of   E i E i E i   
the polymer. In addition, microextensions were observed  v − i v − i 1 
between adjacent cells, connecting them and forming   E E E 0 0 0  
a spindle shape. 37,38 These observations indicated that S =  i i i 21( + vv )  (VIII)
i
cell adhesion occurred smoothly on the surface of the  0 0 0 E i 
developed polymer, thus confirming the biocompatibility   i  
of the developed SMP.  0 0 0 0 ( 21 + v ) 
i
 E i 
3.5. Shape-memory effect   ( 21 + v )  
i
To explain the thermodynamic behavior of the SMP   0 0 0 0 0 E  
mathematically, a two-phase model consisting of a rubber i
phase and a glass phase was used as a phenomenological where subscript i = g represents the glass phase,
constitutive model. 22,39,40 The two phases, the so-called and i = r represents the rubber phase. Measurement of
glass phase and rubber phase, in the SMP were stable at temperature-dependent Young’s modulus revealed E and
temperatures above and below T , respectively. As the E values of 1880 and 5.63 MPa, respectively, and Poisson’s
g
g
SMP is a mixture of the glass and rubber phases during ratios ν and ν were 0.35 and 0.4, respectively.
r
the transition process, the volume fraction (η ) of the g r
g
rubber phase and the glass phase represents the state of From a numerical perspective, nonlinear SMP behavior
the SMP. Considering the experimental results of the can be handled in an explicit time-discrete stress–strain
40
DMA test of PLA+PEG 20 phr, the η of the glass phase temperature-based framework. For the infinitesimal time
g
can be expressed approximately as a hyperbolic function, domain [t , t ], the evolution equation of SMP in an n+1
n
n+1
as described previously. The values of a and a of the step is expressed as follows: 40
40
1
2
hyperbolic function, obtained by fitting the DMA curve,
were 0.0956 and 0.0968, respectively. The changes in n+1 n+1 n+1 e ) ( n+1 n+1 n+1 ε ( n+1 ε ))
−1
n+1
n n+1
=
n
the glass and rubber phases of SMPs are generally only ε in ( I + ∆ η g S r C ε +∆ η g S r C e − th
in
a function of temperature, and the total strain rate (ε) is (IX)
−1
expressed as follows: 40 ε in ( I + ∆ η n+1 S n+1 C e ) ( ε +∆ η n+1 S n+1 C n+1 ε ( n+1 − ε ))
n
n n+1
n+1
n+1
=
g
r
g
th
e
r
in
ε = η ε + (1 − η ε +) r ε + ε th (VI) where the superscript n+1 represents the current step,
g
g
g
in
the superscript n represents the previous step, ∆η n g +1 is
where ε and ε are the strains of the glass and rubber
r
g
phases, respectively, and ε and ε represent the inelastic η n+1 − η , and C is the overall equivalent stiffness. 22,40
n
th
in
strain due to SMP phase transformation and thermal g g e
strain, respectively. 40 Calculation of the inelastic strain (ε ) due to the SMP
in
The phase transformation mechanism between the phase transformation from the evolution equation of SMP
glass and the rubber phases indicates that the rubber phase was implemented using MATLAB software (MathWorks,
Volume 10 Issue 3 (2024) 581 doi: 10.36922/ijb.3035