Remote Controlling DNA Hydrogel by Magnetic Field - ACS Publications

Letter www.acsami.org

Remote Controlling DNA Hydrogel by Magnetic Field Xiaozhou Ma,†,‡ Zhongqiang Yang,*,‡ Yijie Wang,‡ Guoliang Zhang,‡ Yu Shao,‡ Haoyang Jia,‡ Tianyang Cao,‡ Rui Wang,*,† and Dongsheng Liu*,‡ †

School of Basic Medical Sciences, Lanzhou University, Lanzhou, Gansu 730000, China Key Laboratory of Organic Optoelectronics and Molecular Engineering of the Ministry of Education, Department of Chemistry, Tsinghua University, Beijing 100084, China

‡

S Supporting Information *

ABSTRACT: DNA hydrogel has aroused widespread attention because of its unique properties. In this work, the DNA-modified magnetic nanoparticles were integrated into the mainframe of DNA hydrogel, resulting in DNA-MNP hydrogel. Under the magnetic field, this hydrogel can be remotely deformed into various shapes, driven to jump between two planes and even climb the hill. By applying various triggers, such as temperature, enzyme, and magnetic field, DNA-MNP hydrogel can specifically undergo sol−gel transition. This work not only imparts DNA hydrogel with a new fold of property but also opens a unique platform of such smart materials for its further applications. KEYWORDS: magnetic nanoparticle, DNA hydrogel, DNA conjugation, remote controlling, hydrogel movement

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forming a hybrid DNA-MNP hydrogel. Note that the MNPs are introduced into DNA hydrogel via hybridization instead of physical mixing. Such design ensures that MNPs are part of the network, improving the stability of the particles in the gel. We first prepared DNA modified MNPs by four steps reactions. The hydrophilic MNPs were synthesized with a diameter about 20 nm.18−20 The amino groups were modified onto MNPs by reacting the obtained MNPs with (3-aminopropy)triethoxysilane (APTES).19 The one side of N-ε-maleimidocaproyl-succinimide ester (EMCS) reacted with amino groups on MNPs and another side reacted with thiolated DNA, therefore, the DNA strands were covalently attached to MNPs (Scheme S2, Figure S3).21 To test whether the DNA strands were attached to MNPs, we used two kinds of DNA linkers: one was complementary to the DNA strands on the MNPs while the other was not (Figure 1a). It turned out that in the presence of DNA linkers that can hybridize with MNPs, the precipitant appeared in 10 min (Figure 1b). In contrast, the addition of noncomplementary DNA linkers did not cause any changes (Figure 1c). This result concludes that MNPs were indeed modified with a layer of DNA strands, which can further hybridize with DNA. Next, we employed the DNA modified MNPs to form hydrogel. In a typical experiment, DNA-MNPs mixed with Yscaffold first, as both sticky ends were noncomplementary to each other, the mixing went well and did not cause any

n recent years, the DNA hydrogel has been widely studied because of its rational design and smart responsiveness to various stimuli.1−7 The most important property of DNA hydrogel is that by programmable designing, the microscopic structure of the hydrogel can be constructed from bottom up.8,9 Combined with 3D printing and molding technique, we can further customize the hydrogel from top down.10−12 It is worth mentioning that current established techniques are more suitable to shape DNA hydrogel before and whist its formation13,14 In addition, the DNA hydrogel is usually weak, which brings another fold of difficulty of handling3,15 However, in practical applications, it is desirable that DNA hydrogel can be further manipulated without physical touch, such as killing tumor cells in a specific area. Though light can remotely trigger DNA hydrogel undergoing a transition, which only promised a change between sol and gel state, instead of manipulating the DNA hydrogel in its gel form.16,17 To this end, we introduced magnetic nanoparticles (MNPs) to DNA hydrogel frame, so as to exploit magnetic field to control DNA hydrogel to from a certain shape, move toward a desirable direction and even jump overcoming the gravity. More importantly, the DNA-MNP hydrogel can further respond to temperature, enzyme and magnetic field, exhibiting a gel-to-sol transition. Those combined characters are well-needed in drug delivery and cancer therapy, to remotely move the gel to a certain place and release cargos. Our strategy of forming magnetic DNA hydrogel is shown in Scheme 1. MNPs are modified with a layer of single stranded DNA, after adding DNA Y-scaffold and DNA linker, the MNPs are connected with DNA linker associated with Y-scaffold, © 2017 American Chemical Society

Received: September 28, 2016 Accepted: January 5, 2017 Published: January 5, 2017 1995

DOI: 10.1021/acsami.6b12327 ACS Appl. Mater. Interfaces 2017, 9, 1995−2000

Letter

ACS Applied Materials & Interfaces

Scheme 1. Schematic Illustration of the Formation of DNA-MNP Hydrogel: (a) DNA was Modified onto the MNPs Surface, and (b) Formation of Three-Component Hydrogel by Y-Scaffolds, DNA Linker, and DNA-MNPs

Figure 1. Schematic illustration of (a) DNA-MNPs after adding (b) complementary or (c) noncomplementary linker, respectively.

aggregation. Then the double stranded DNA linkers were added, followed by quick stirring, resulting in hydrogel formation in 30 s. SEM images suggested that the DNAMNP hydrogel surface at dry state was obviously rougher than pure DNA hydrogel, indicating the MNPs were embedded in the hydrogel network (Figure S9). TEM characterization of the DNA-MNP hydrogel further confirmed that the MNPs dispersed in the gel instead of forming big aggregates (Figure S9). We carried out a series of experiments to optimize the concentration of DNA-MNPs in the hydrogel (Figure S7). It was found that when the concentration of the DNA-MNPs in the hydrogel was above 70 mg/mL, the hydrogel could easily respond to the magnet and move toward the magnet, which means that the amount of the DNA-MNPs was enough to generate an appropriate magnetic force.22,23 Meanwhile, the DNA-MNP hydrogel possessing a certain mechanical strength with the DNA content no less than 1.8 wt % can respond external magnetic field as a whole instead of flowing as a viscous liquid. Combined above two factors, it concludes that when the concentration of the DNA-MNPs was 70 mg/mL, the molar

ratio between Y-scaffold and linker was 2:3.6, the DNA content was 1.8 w.t.%, for the number of DNA loaded on MNP was 1.07 nmol/mg. (Figure S6) under this DNA content, the DNAMNP hydrogel with a mechanical strength hard enough for later handling and responding to a magnet (Figure 2a). We carried out rheological tests to further characterize DNAMNP hydrogel and compare it with pure DNA hydrogel. As shown in Figure 2, the shear-storage modulus (G′) of three hydrogels was obviously higher than the shear-loss modulus (G″) at 50% shear strain at a fixed angular frequency of 1 Hz at 25 °C, confirming the gel-like state. DNA-MNP hydrogel exhibited very similar mechanical strength. It is noted that the G′ value of pure DNA hydrogel and DNA-MNP hydrogel rapidly decreased upon reaching 100% strain and had a crossing point with G″ at 200% strain, i.e., the gel-to-sol transition point, indicating a collapse of the gel state to a quasi-liquid sol state. All these data proved that the integration of DNA-MNPs into DNA hydrogel did not cause detectable the mechanical change of the hydrogel. 1996


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Figure 2. Rheological properties of DNA hydrogel and DNA-MNP hydrogel. (a) Time scan tests were performed with a strain of 50% with a fixed frequency (1 Hz) at 25 °C. (b) Rheological strain sweep was performed from 1% to 1000% at 25 °C with a fixed frequency of 1 Hz. MNP loaded hydrogel was added on top of pure DNA hydrogel with (c, d) and without (e, f) a magnet for 48 h at 34 °C. (g, h) DNA-MNP hydrogel was added on top of pure DNA hydrogel with a magnet.

Figure 3. Remote controlling of the DNA-MNP hydrogel. (a−d) Shape of the DNA-MNP hydrogel was controlled by a magnet, scale bar = 5 mm; (e−g) DNA-MNP hydrogel was dragged uphill by a magnet, scale bar = 1 cm; (h−l) DNA-MNP hydrogel was controlled by the magnet to jump between two plates, scale bar = 5 mm.

and the bilayer hydrogel turned to homogeneous black. However, MNPs in DNA-MNP hydrogel hardly moved to the bottom of pure DNA hydrogel under the magnetic field, which suggested that MNPs hybridized in the framework of DNA hydrogel, thus lacking diffusion freedom. This result demonstrated that DNA-MNPs were much stable than bare MNPs in DNA hydrogel and were mainly focused in the rest of the study. In practical applications, it requires the hydrogel which can be directed and moved to a certain place, and release cargos as desired. Therefore, we first tested whether we can apply magnetic field to distort the shape of the DNA-MNP hydrogel. A piece of DNA-MNP hydrogel was placed on a parafilm which has hydrophobic and nonsticky surface. Figure 3a−d showed that the hydrogel with an initial spherical shape could be tuned to an ellipsoidal shape with the magnet (52 N NdFeB)

In addition, we compared the stability of MNPs in the hydrogel, i.e., MNPs were loaded either through physical mixing or through DNA hybridization. Bilayer DNA hydrogel was made as follows: 50 μL 250 μM Y-scaffold and 50 μL 375 μM DNA linker were mixed and held under 4 °C for 30 min to form the pure DNA hydrogel at the bottom layer of EP tube. Then, 50 μL 375 μM DNA linker was added slowly on top of the first layer, followed by adding 50 μL 250 μM Y-scaffold containing 140 mg/mL DNA-MNPs (or MNPs) to form the DNA hybrid hydrogel at the top layer of EP tube. The bilayer hydrogel was incubated under 4 °C overnight and heated gently to 34 °C. 52 N magnet was applied for 48 h. As shown in Figure 2c, d, MNP loaded hydrogel on top of the pure DNA hydrogel after 48 h at 34 °C, the boundary in the middle of bilayers remained unchanged. In contrast, MNPs migrated and diffused into pure DNA hydrogel under the magnetic effect, 1997


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Figure 4. (a) Temperature-ramp rheological test of DNA-MNP hydrogel was carried out from 25 to 60 °C at a rate of 2 °C min−1 at a fixed frequency (1 Hz) and strain (1%). (b) DNA-MNP hydrogel was prepared from 500 μM of Y-scaffold and 750 μM of linker with 70 mg/mL MNPs, and (c) was heated to 50 °C, undergoing a gel-to-sol transition. (d) Scheme of linker DNA with restriction site treated with EcoR I restriction enzyme. DNA-MNP hydrogel was incubated with buffer (e, g) without EcoR I and (f, h) with 45 U EcoR I for 48 h at room temperature.

Figure 5. Magnetic field sensitivity of DNA-MNP hydrogel. (a) B−H loop of bare MNP, MNP-NH2, MNP-EMCS and DNA-MNP. (b) Temperature of DNA-MNP hydrogel as a function of time under AMF (390 kHz, excitation current 10 A). (c) Temperature of DNA-MNP hydrogel under different excitation currents. (d) DNA-MNP hydrogel heated under AMF to 40 °C (left) and 50 °C (right).

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into one piece, further dragging the DNA hydrogel to move. Furthermore, DNA-MNP hydrogel reported here not only possesses all properties of conventional DNA hydrogel but also for the first time imparts DNA hydrogel magnetic responsiveness. It can be envisioned that DNA-MNP hydrogel provides a new class of material for cell culture,24,25 tissue engineering,26,27 and biomedical applications.28−30

underneath the parafilm. The shape of the hydrogel can be further distorted into elongated ellipsoids to rectangles with four right angles. Furthermore, we investigated how to apply magnetic field to direct DNA-MNP hydrogel performing more challenging tasks. A parafilm with a piece of DNA-MNP hydrogel on top was tilted with an angle of 18° (Figure 3e−g). After putting the magnet under the film, the movement of the magnet can drag the hydrogel climbed uphill over 1.5 cm in 12 s. More interestingly, the magnet on the top can even lift the DNA-MNP hydrogel between two parafilms with a distance of 4 mm, Figure 3h-l. Putting the magnet underneath the parafilm can drag the DNA-MNP hydrogel down, the cycle of putting magnet up and down would cause the DNA-MNP hydrogel jump back and forth. The last demonstration is to move DNAMNP hydrogel to cover and pack a DNA hydrogel not containing MNPs by using a magnet. The combined hydrogel formed an integrated piece with an advantage of self-healing property of DNA hydrogel, and can be further dragged to a certain place under the magnetic field. We further determine how to switch DNA hydrogel from gel to sol state in order to satisfy the practical need of release of cargos for medical applications, e.g., cancer therapy. It is known that DNA hydrogel can respond to temperature. We first checked the melting temperature (Tm) of the DNA-MNP hydrogel by a rheometer, and Figure 4a indicated that the Tm of DNA-MNP hydrogel was about 40 °C, and the bulk DNAMNP hydrogel collapsed to solution at 50 °C, Figure 4b, c. We also tried to use DNA endonuclease to degrade the hydrogel. EcoR I specific sequences were designed in the DNA linker (Figure 4d), and the DNA-MNP hydrogel turned to solution after digestion by 45 U EcoR I for 48 h at room temperature, Figure 4e-h. Moreover, the unique property of DNA-MNP hydrogel is the magnetic responsiveness due to the presence of MNPs. For example, an alternative magnetic field (AMF) was applied to heat the MNPs, and the B−H loop in Figure 5a indicated that four kinds of particles (bare MNPs, amino modified MNPs, EMCS modified MNPs and DNA-MNPs) still possessed the paramagnetism. The magnetic induction strength was obviously decreased after modification of amino group and DNA molecules, but only slightly decreased after attaching the EMCS. It might be attributed to the size of the EMCS which is relatively smaller comparing to APTES and DNA strand. After putting the DNA-MNP hydrogel into AMF (390 kHz, excitation current 10 A), the hydrogel could be heated quickly to 60 °C in about 2 min, Figure 5b. As the increase of the excitation current, the heating speed was also increased, Figure 5c. It was demonstrated that the DNA-MNP hydrogel can be triggered to sol state under the AMF (390 kHz, 10 A) for 74 s (heated to 50 °C), but remained in gel at 40 °C, Figure 5d. All these result indicated that DNA-MNP hydrogel remained all important properties of DNA hydrogel, such as thermal and enzymatic responsiveness, in addition, DNA-MNP hydrogel demonstrated the first example that DNA hydrogel can respond to magnetic field. In conclusion, by integrating DNA-modified MNPs into the mainframe of the DNA hydrogel, we built a DNA-MNP hydrogel which could be remotely controlled by the magnetic field or respond to temperature, enzyme and AMF. The MNPs in the frame of DNA hydrogel allowed external untouched stimuli, such as magnetic field to manipulate DNA-MNP hydrogel to deform into various shapes, move toward a certain direction and even jump off the surface. The DNA-MNP hydrogel can also adhere with pure DNA hydrogel and heal

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ASSOCIATED CONTENT

* Supporting Information S

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsami.6b12327. Experimental details, NMR data of EMCS, information on DNA sequences, TEM photos of MNPs, strength of DNA-MNP hydrogel, and TEM and SEM photos of DNA-MNP hydrogel (PDF)

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. *E-mail: [email protected]. *E-mail: [email protected]. ORCID

Dongsheng Liu: 0000-0002-2583-818X Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We thank Professor Gu’s group in Southeast University for their assistant. We also thank National Basic Research Program of China (973 program, 2013CB932803), the National Natural Science Foundation of China (21534007, 91427302, 21421064).

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Remote Controlling DNA Hydrogel by Magnetic Field - ACS Publications

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