Biomedical Engineering Reference
In-Depth Information
via DNA hybridization (Bb). Upon delivery of the ssDNA complementary to strand A,
thrombin is released. Extracted from (Wei et al. 2008) with publisher's permission. (
C
) For a
DNA crosslinked hydrogel (Jiang et al. 2010b), delivery of the 'removal' DNA strand
complementary to the crosslinker DNA leads to de-crosslinking.
Dynamic materials can be used to manipulate cell behavior. In studies performed by
Langrana and colleagues, DNA-crosslinked hydrogels (DNA hydrogels) were used as the
underlying substrate to study the effects of dynamic mechanical cues on fibroblast behavior
(Jiang et al. 2010c, Previtera et al. 2011). The DNA hydrogels have the ability to temporally
change stiffness (Jiang et al. 2008a, Jiang et al. 2010c, Lin 2005, Lin et al. 2004a, Lin et al. 2005,
Previtera et al. 2011). Upon a decrease or increase in DNA hydrogel stiffness, expansion or
contraction forces are generated, respectively. The two properties cannot be decoupled (data
unpublished). When grown on these dynamic hydrogels, fibroblast morphology is
noticeably different compared to static hydrogels, which do not change in stiffness and thus
do not generate forces (Jiang et al. 2010c, Previtera et al. 2011). GFP fibroblast became larger
and more circular, compared to static conditions, when grown on DNA hydrogels that
became softer and expanded (Previtera et al. 2011). Therefore, as the underlying substrate
expands and softens, the GFP fibroblasts expand and become rounder morphology. This is
in contrast to GFP fibroblast grown on dynamic hydrogels with increasing stiffness and
contraction forces (Jiang et al. 2010c). These GFP fibroblasts became smaller and/or longer
when compared to static hydrogels. However, these results depended on magnitude of
hydrogel stiffness change (Jiang et al. 2010c).
3.2 Potential application of DNA based macro-materials
Three main areas of application are being explored by using these DNA based
macromaterials (
Table 1
).
3.2.1 Biosensor| Actuator| Bioelectronics
Hydrogels synthesized from DNA nanostructures hold promises as biosensor (Cheng et al.
2009, Lin et al. 2004b), Simmel and Yurke designed a DNA-based actuator capable of
switching between two physical states, which can potentially be used as motor to drive the
nano-robot (
Figure 1
) (Simmel & Yurke 2001). This approach, together with others
(Knoblauch & Peters 2004), can be adopted in hydrogel formation, giving rise to novel
materials with changing properties upon 'fuel strand' delivery. Besides the potential uses of
DNA based macromaterials in sensors and actuators, DNA's electronic properties and
molecular recognition, feasibility of DNA manipulation at nano-scale, and the trend of
miniaturization are driving the synergy between DNA and electronics. Braun and Keren
(Braun & Keren 2004) put forth a scheme of constructing DNA based transistors, in which
DNA is metallized and serves as a template for electronic circuit, which exemplifies DNA's
impressive capability of information storage and molecular recognition mechanism.
Incorporation of grafted oligonucleotides also leads to novel materials with high optical
resolution, and can be potentially used in biosensing (Tierney & Stokke 2009) (
Figure 6A
).
3.2.2 Drug delivery vehicle
In response to various environmental factors, DNA may alter its secondary and tertiary
structures, resulting in alterations in the bulk materials that are built upon them. Aiming at
drug delivery application for cancer therapy, a great deal of effort has been made in
