Substrates with Changing Properties for Extracellular Matrix Mimicry - Advances in Biomaterials Science and Biomedical Applications - page 94

Figure 3. Substrates with dynamic mechanical stiffness and their application in cell culture studies. (A) Live/deal cell
staining of human mesenchymal stem cells (hMSCs) in a hyaluronic acid hydrogel (A1) and the analysis of gene expres‐
sion of type I/II collagen and aggrecan revealed that aside from type I collagen, both type II collagen and aggrecan
exhibited an elevated level of expression on dynamic gels from the static ones. Extracted from [78]. With permission
from publisher. (B) L929 fibroblast growth in a DNA crosslinked hydrogel with dynamic stiffness from crosslinking den‐
sity change (B1) and the quantification of spreading area and aspect ratio (B2) showed that dynamic gels are signifi‐
cantly different from their static counterparts. Extracted from [81].
3.3. Other types of materials
The approach of employing polymeric hydrogel to study dynamic changes has certain limi‐
tations, one of which is the coupling of mechanical stiffness and forces (e.g., [83]). To ad‐
dress this concern and others, different from the approach by using SAM or polymeric
hydrogel, AFM based method put forth by Webster and co-workers [84] probed cellular re‐
sponse to instant step change in stiffness excluding influence from stress or strain in the sub‐
strates (Table 1). It has been confirmed that indeed individual 3T3 fibroblasts are able to
sense and respond to the stiffness in a scale of seconds as demonstrated in traction rate and
contraction velocity [84]. However, this approach is most likely with inherent limitation in
mimicking natural cell environment while remains an interesting tool in probing cellular re‐
sponses to instantaneously change in stiffness. Additionally, this approach is applicable
mostly to cells with dynamic morphology.
Common cell culture substrates (e.g., glass coverslip) modified with common photo-cleava‐
ble agents (NPE-TCSP) were shown to be useful for controlling cell adhesion selectively and
temporally [62]. In this method, target areas were first irradiated to remove BSA known to