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International Journal of Bioprinting DNA-functionalized hyaluronic acid bioink

shear. Jin et al. encapsulated single cells in DNA hydrogel Apt19S exhibited a strong binding affinity toward the
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caps within PDMS (polydimethylsiloxane) microwells. ALPL protein on the surface of BMSCs, achieving specific
After 24 h of culture, 98% of the cells remained viable. anchoring of BMSCs. By digesting the DNA network into
Using the restriction enzyme EcoR I could open the DNA fragments with the nucleic acid enzyme DNase I, BMSCs
hydrogel caps to release the encapsulated single cells on can be released in a concentration-dependent manner
demand. Strategically, using specific restriction enzymes within tens of minutes. Moreover, Hu et al. employed DNA
and digesting DNA hydrogel could precisely control the aptamer Apt19S was immobilized on the bilayer scaffold to
release of cells (Figure 7d). In addition, researchers also recruit MSCs for articular cartilage and subchondral bone
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prepared biostable and non-biodegradable DNA hydrogel regeneration. The inclusion of the stimulatory factor
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networks by replacing natural D-type DNA with L-type kartogenin (KGN) within the aptamer-functionalized gel
DNA, which had better biostability and low inflammation layer enhanced the process of chondrogenic differentiation,
response. In 3D cell culture and tissue engineering, L-DNA guiding MSCs toward adopting a chondrocyte phenotype.
hydrogels can maintain uniform cell distribution, prevent In parallel, the aptamer-functionalized 3D graphene
degradation and remodeling of ECM, and provide an inert oxide-based biomineral framework (GBF) layer expedited
mechanical stimulation platform 74,75 (Figure 7e). the osteoblastic differentiation of MSCs, facilitating
their transformation into osteoblasts (Figure 8b).
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4.2. Drug delivery Except aptamer Apt19S, aptamer HM69 was also used to
The structure of DNA hydrogels can form hollow specifically recruit MSC. Yang et al. chemically combined
internal spaces, which provide a favorable environment the aptamer HM69 with decellularized cartilage ECM
for drug molecule encapsulation. Under electrostatic and subsequently blended it with gelatin methacrylate
attraction, positively charged subunits can bind to DNA (GelMA) to produce a photo-crosslinkable bioink.
nanostructures. These characteristics are the prime factors The 3D-bioprinted scaffold can guide MSCs to move
prompting researchers to use nucleic acid nanostructures directionally to the site of cartilage injury in situ (Figure
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as carriers to deliver drugs to target cells. Notably, Chen et 8c and d). Apart from cells, DNA hydrogels can also bind
al. developed an injectable DNA hydrogel that could deliver to and recruit exosomes. An exosome separation strategy
dexamethasone and induce macrophages to polarize to M2 based on a DNA network of polyvalent adaptors has been
phenotype, in order to promote bone formation. Li et al. developed. A DNA ultra-long single strand containing
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also developed a physically crosslinked DNA hydrogel polyvalent adaptors was synthesized by enzyme-catalyzed
loaded with interleukin-10 as a soft bioscaffold, which RCA reaction. The DNA single strand was added to the
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could gradually degrade or hydrolyze under physiological biological system. The DNA chain containing polyvalent
conditions, thereby continuously releasing cytokines for a adaptors could capture exosomes through specific
long time (Figure 7f). In addition, Borum et al. effectively recognition of CD63 protein on exosomes.
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encapsulated MB-Dox conjugates within specific regions of
DNA hydrogels. Upon in vivo injection, these hydrogels 4.4. Gene transfection
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undergo degradation initiated by nucleases present in Hydrogels can serve as an effective gene carrier for
bodily fluids, resulting in the gradual release of MB-Dox encapsulating and delivering different types of DNA
conjugates. Importantly, the rate of this release can be molecules, such as plasmid DNA and siRNA, to damaged
finely controlled by modulating the weight percentage of tissues. 55,56 Hydrogels can prevent plasmid DNA from
the hydrogel. 78 being degraded or cleared by nucleases or the immune
system and enhance the transfection efficiency of DNA
4.3. Cell recruitment molecules. 55,56 These functionalized hydrogels can
Unlike inherent ECMs, traditional hydrogels generally also achieve long-term and sustained release of DNA
lack bioactive groups serving as “baits” to attract cells. The molecules through the addition of degradable or cleavable
integration of bait molecules into DNA-based hydrogels crosslinkers or functional units, which enable the hydrogel
enables precise interactions between cell and matrices, thus to undergo structural changes or degradation according to
verifying the presence of requisite cell surface markers. environmental conditions or target molecules to release
Mimicking the ECM requires the ability of the hydrogels active DNA molecules.
to recognize specific cell types, which is the fundamental
of tissue engineering. 51,79 Yao et al. constructed a DNA 4.5. Reversible mechanical regulation
hydrogel using the double rolling circle amplification (RCA) One of the enduring challenges in tissue engineering is to
method to achieve effective capture and enzymatically construct artificial tissues with 3D arrangement of different
triggered release of bone marrow mesenchymal stem types of living cells. Li et al. showed that these hydrogels
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cells (BMSCs) (Figure 8a). The introduced aptamer can be used for in situ multilayer 3D cell printing, which
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Volume 10 Issue 2 (2024) 37 doi: 10.36922/ijb.1814