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Adhesive curing through low-voltage activation.

Ping J, Gao F, Chen JL, Webster RD, Steele TW - Nat Commun (2015)

Bottom Line: As the applied voltage discontinued, crosslinking immediately terminated.Thus, crosslinking initiation and propagation are observed to be voltage and time dependent, enabling tuning of both material properties and adhesive strength.The electrocuring adhesive has immediate implications in manufacturing and development of implantable bioadhesives.

View Article: PubMed Central - PubMed

Affiliation: 1] School of Materials Science and Engineering, College of Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Singapore [2] School of Biosystems Engineering and Food Science, Zhejiang University, 866 Yuhangtang Road, Hangzhou 310058, China.

ABSTRACT
Instant curing adhesives typically fall within three categories, being activated by either light (photocuring), heat (thermocuring) or chemical means. These curing strategies limit applications to specific substrates and can only be activated under certain conditions. Here we present the development of an instant curing adhesive through low-voltage activation. The electrocuring adhesive is synthesized by grafting carbene precursors on polyamidoamine dendrimers and dissolving in aqueous solvents to form viscous gels. The electrocuring adhesives are activated at -2 V versus Ag/AgCl, allowing tunable crosslinking within the dendrimer matrix and on both electrode surfaces. As the applied voltage discontinued, crosslinking immediately terminated. Thus, crosslinking initiation and propagation are observed to be voltage and time dependent, enabling tuning of both material properties and adhesive strength. The electrocuring adhesive has immediate implications in manufacturing and development of implantable bioadhesives.

No MeSH data available.


Related in: MedlinePlus

Electrorheological properties of PAMAM-g-diazirine solutions.(a) Scheme of real-time oscillatory dynamic rheometry of electro-activated adhesives. (b) Storage modulus (G′) with respect to time before and after an applied voltage of −2.0 V versus Ag/AgCl on the disposable Zensor chip. PAMAM-g-diazirine solutions (25 wt% in PBS in all figures) with different conjugation degrees (5, 10 and 15%) were electrocured for 20 min. (c) Kinetics of storage modulus (G′) and loss modulus (G″) with respect to magnitude of applied potential versus Ag/AgCl. Gelation point is defined where G′=G″. (d) Kinetics of storage modulus with respect to temporal activation of a −2.0 V applied to PAMAM-g-diazirine (15%).
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f4: Electrorheological properties of PAMAM-g-diazirine solutions.(a) Scheme of real-time oscillatory dynamic rheometry of electro-activated adhesives. (b) Storage modulus (G′) with respect to time before and after an applied voltage of −2.0 V versus Ag/AgCl on the disposable Zensor chip. PAMAM-g-diazirine solutions (25 wt% in PBS in all figures) with different conjugation degrees (5, 10 and 15%) were electrocured for 20 min. (c) Kinetics of storage modulus (G′) and loss modulus (G″) with respect to magnitude of applied potential versus Ag/AgCl. Gelation point is defined where G′=G″. (d) Kinetics of storage modulus with respect to temporal activation of a −2.0 V applied to PAMAM-g-diazirine (15%).

Mentions: The rheology performance of PAMAM-g-diazirine under −2 V applied potential was investigated with respect to electrochemical activation. This allowed the characterization of the hydrogel mechanical properties in real time via oscillatory dynamic rheometry through parallel-plate geometry. The experimental set-up is demonstrated in Fig. 4a, where PAMAM-g-diazirine rheological analysis is followed through the electrochemical activation (electrocuring) on a disposable Zensor chip with three screen printed electrodes. The storage modulus (G′) and loss modulus (G″) in amplitude tests (Supplementary Fig. 1) were almost stable when the deformation (strain) is 1%. Thus the oscillatory rheometry (1 Hz, 1%) of electrochemically activated PAMAM-g-diazirine conjugate is performed in linear-viscoelastic range. The PAMAM-g-diazirine storage modulus with various diazirine conjugation degrees was measured under ‘OFF' (control) and ‘ON' −2 V activation, as seen in Fig. 4b. Under no voltage activation (‘OFF' region in Fig. 4b), the G′ or storage modulus is stable, hence no crosslinking is initiated or observed (see first 2 min). On an applied voltage, an immediate increase in storage modulus is observed, that displays a logarithmic growth function—a large increase in G′/time (slope) at the onset that quickly decays but never reaches zero. PAMAM-g-diazirine conjugates with higher amounts of grafted diazirine undergo faster changes in G′/time and obtain higher storage modulus with respect to a given amount of time. PAMAM-g-diazirine at 5%, 10% and 15% conjugation in 25% w/v PBS displays a storage modulus of 0.5, 0.7 and 1 kPa after 20-min activation, respectively. In comparison, the storage modulus is comparable to gelatin or liver tissue1819. Note that these storage moduli are relatively small only because of the small deformations (1% amplitude) that are applied to the anisotropic hydrogel, as explained in the next section. Gelation time, the point where storage modulus and the loss modulus have equal values (as seen in Fig. 4b), decreases with the increase of grafted diazirine on PAMAM. Using Ohm's law, the resistance of the hydrogel was measured to be 76, 6.9 and 2.9 kΩ for the 5%, 10% and 15% conjugated PAMAM-g-diazirine, respectively, suggesting a percolation threshold is crossed from 5 to 10%. To exclude competing side reactions to the PAMAM-g-diazirine crosslinking mechanism, PAMAM-g-diazirine (15%) was activated in −0.5 V increments, up to −2 V, as displayed in Fig. 4c. No change in properties was seen under −1 V. At −1.5 V, where water electrolysis is applicable, modulus values are slightly shifted, but no crosslinking or increase in modulus is observed. This signal change in modulus within this region is likely due to changes in surface chemistry on the three electrodes. When the voltage exceeds the −1.6 V required (Fig. 3c, inset) for diazirine activation, instantaneous crosslinking is observed as measured by the sharp increase in storage modulus. A simple cyclic power switch is performed to assess the mechanical properties before and after electrochemical activation. At 2-min intervals, −2 V is switched ‘ON' and ‘OFF' for four cycles with the results displayed in Fig. 4d. After the first cycle, the storage modulus is regarded as stable and the crosslinking deemed irreversible (under these limited conditions). This suggests chemical crosslinking by electrochemical activation of diazirine and the change in storage modulus was not subject to other events, for example, PAMAM polarization by electric fields, resistive heating. Note that both crosslinking initiation and propagation were controlled by the electrochemical activation—crosslinking halted under the ‘OFF' conditions. Most on-demand (that is, photocuring) adhesives only control initiation, while propagation continues uncontrollably. The combined data demonstrate that the adhesive mechanical properties (G′, G″ and gelation point) may be tuned by varying stimulation time and diazirine conjugation degree.


Adhesive curing through low-voltage activation.

Ping J, Gao F, Chen JL, Webster RD, Steele TW - Nat Commun (2015)

Electrorheological properties of PAMAM-g-diazirine solutions.(a) Scheme of real-time oscillatory dynamic rheometry of electro-activated adhesives. (b) Storage modulus (G′) with respect to time before and after an applied voltage of −2.0 V versus Ag/AgCl on the disposable Zensor chip. PAMAM-g-diazirine solutions (25 wt% in PBS in all figures) with different conjugation degrees (5, 10 and 15%) were electrocured for 20 min. (c) Kinetics of storage modulus (G′) and loss modulus (G″) with respect to magnitude of applied potential versus Ag/AgCl. Gelation point is defined where G′=G″. (d) Kinetics of storage modulus with respect to temporal activation of a −2.0 V applied to PAMAM-g-diazirine (15%).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4557340&req=5

f4: Electrorheological properties of PAMAM-g-diazirine solutions.(a) Scheme of real-time oscillatory dynamic rheometry of electro-activated adhesives. (b) Storage modulus (G′) with respect to time before and after an applied voltage of −2.0 V versus Ag/AgCl on the disposable Zensor chip. PAMAM-g-diazirine solutions (25 wt% in PBS in all figures) with different conjugation degrees (5, 10 and 15%) were electrocured for 20 min. (c) Kinetics of storage modulus (G′) and loss modulus (G″) with respect to magnitude of applied potential versus Ag/AgCl. Gelation point is defined where G′=G″. (d) Kinetics of storage modulus with respect to temporal activation of a −2.0 V applied to PAMAM-g-diazirine (15%).
Mentions: The rheology performance of PAMAM-g-diazirine under −2 V applied potential was investigated with respect to electrochemical activation. This allowed the characterization of the hydrogel mechanical properties in real time via oscillatory dynamic rheometry through parallel-plate geometry. The experimental set-up is demonstrated in Fig. 4a, where PAMAM-g-diazirine rheological analysis is followed through the electrochemical activation (electrocuring) on a disposable Zensor chip with three screen printed electrodes. The storage modulus (G′) and loss modulus (G″) in amplitude tests (Supplementary Fig. 1) were almost stable when the deformation (strain) is 1%. Thus the oscillatory rheometry (1 Hz, 1%) of electrochemically activated PAMAM-g-diazirine conjugate is performed in linear-viscoelastic range. The PAMAM-g-diazirine storage modulus with various diazirine conjugation degrees was measured under ‘OFF' (control) and ‘ON' −2 V activation, as seen in Fig. 4b. Under no voltage activation (‘OFF' region in Fig. 4b), the G′ or storage modulus is stable, hence no crosslinking is initiated or observed (see first 2 min). On an applied voltage, an immediate increase in storage modulus is observed, that displays a logarithmic growth function—a large increase in G′/time (slope) at the onset that quickly decays but never reaches zero. PAMAM-g-diazirine conjugates with higher amounts of grafted diazirine undergo faster changes in G′/time and obtain higher storage modulus with respect to a given amount of time. PAMAM-g-diazirine at 5%, 10% and 15% conjugation in 25% w/v PBS displays a storage modulus of 0.5, 0.7 and 1 kPa after 20-min activation, respectively. In comparison, the storage modulus is comparable to gelatin or liver tissue1819. Note that these storage moduli are relatively small only because of the small deformations (1% amplitude) that are applied to the anisotropic hydrogel, as explained in the next section. Gelation time, the point where storage modulus and the loss modulus have equal values (as seen in Fig. 4b), decreases with the increase of grafted diazirine on PAMAM. Using Ohm's law, the resistance of the hydrogel was measured to be 76, 6.9 and 2.9 kΩ for the 5%, 10% and 15% conjugated PAMAM-g-diazirine, respectively, suggesting a percolation threshold is crossed from 5 to 10%. To exclude competing side reactions to the PAMAM-g-diazirine crosslinking mechanism, PAMAM-g-diazirine (15%) was activated in −0.5 V increments, up to −2 V, as displayed in Fig. 4c. No change in properties was seen under −1 V. At −1.5 V, where water electrolysis is applicable, modulus values are slightly shifted, but no crosslinking or increase in modulus is observed. This signal change in modulus within this region is likely due to changes in surface chemistry on the three electrodes. When the voltage exceeds the −1.6 V required (Fig. 3c, inset) for diazirine activation, instantaneous crosslinking is observed as measured by the sharp increase in storage modulus. A simple cyclic power switch is performed to assess the mechanical properties before and after electrochemical activation. At 2-min intervals, −2 V is switched ‘ON' and ‘OFF' for four cycles with the results displayed in Fig. 4d. After the first cycle, the storage modulus is regarded as stable and the crosslinking deemed irreversible (under these limited conditions). This suggests chemical crosslinking by electrochemical activation of diazirine and the change in storage modulus was not subject to other events, for example, PAMAM polarization by electric fields, resistive heating. Note that both crosslinking initiation and propagation were controlled by the electrochemical activation—crosslinking halted under the ‘OFF' conditions. Most on-demand (that is, photocuring) adhesives only control initiation, while propagation continues uncontrollably. The combined data demonstrate that the adhesive mechanical properties (G′, G″ and gelation point) may be tuned by varying stimulation time and diazirine conjugation degree.

Bottom Line: As the applied voltage discontinued, crosslinking immediately terminated.Thus, crosslinking initiation and propagation are observed to be voltage and time dependent, enabling tuning of both material properties and adhesive strength.The electrocuring adhesive has immediate implications in manufacturing and development of implantable bioadhesives.

View Article: PubMed Central - PubMed

Affiliation: 1] School of Materials Science and Engineering, College of Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Singapore [2] School of Biosystems Engineering and Food Science, Zhejiang University, 866 Yuhangtang Road, Hangzhou 310058, China.

ABSTRACT
Instant curing adhesives typically fall within three categories, being activated by either light (photocuring), heat (thermocuring) or chemical means. These curing strategies limit applications to specific substrates and can only be activated under certain conditions. Here we present the development of an instant curing adhesive through low-voltage activation. The electrocuring adhesive is synthesized by grafting carbene precursors on polyamidoamine dendrimers and dissolving in aqueous solvents to form viscous gels. The electrocuring adhesives are activated at -2 V versus Ag/AgCl, allowing tunable crosslinking within the dendrimer matrix and on both electrode surfaces. As the applied voltage discontinued, crosslinking immediately terminated. Thus, crosslinking initiation and propagation are observed to be voltage and time dependent, enabling tuning of both material properties and adhesive strength. The electrocuring adhesive has immediate implications in manufacturing and development of implantable bioadhesives.

No MeSH data available.


Related in: MedlinePlus