- Email: [email protected]
Injectable, strongly compressible hyaluronic acid hydrogels via incorporation of Pluronic F127 diacrylate nanomicelles
Accepted Manuscript Injectable, strongly compressible hyaluronic acid hydrogels via incorporation of Pluronic F127 diacrylate nanomicelles Hua Zhang, Penggang Ren, Yanling Jin, Fang Ren PII: DOI: Reference:
S0167-577X(19)30212-5 https://doi.org/10.1016/j.matlet.2019.01.159 MLBLUE 25708
To appear in:
Materials Letters
Received Date: Revised Date: Accepted Date:
8 December 2018 20 January 2019 31 January 2019
Please cite this article as: H. Zhang, P. Ren, Y. Jin, F. Ren, Injectable, strongly compressible hyaluronic acid hydrogels via incorporation of Pluronic F127 diacrylate nanomicelles, Materials Letters (2019), doi: https://doi.org/ 10.1016/j.matlet.2019.01.159
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Injectable, strongly compressible hyaluronic acid hydrogels via incorporation of Pluronic F127 diacrylate nanomicelles Hua Zhanga, Penggang Ren*ab, Yanling Jinb, Fang Renb* a. School of Materials Science and Engineering, Xi’an University of Technology, Xi’an 710048, China b. Faculty of Printing, Packaging Engineering and Digital media Technology, Xi’an University of Technology, Xi’an, Shaanxi 710048, PR China
*E-mail: [email protected]; [email protected]
Abstract: Injectable, strongly compressible nanomicelle hydrogels (NMgels) were prepared by photo-initiated free radical copolymerization of methacrylated hyaluronate acid (MeHA) and Pluronic F127 diacrylate (F127DA) micelles. The gelation of precursor solutions occurred with short irradiation times of 25 s and hardened within 120 s. The obtained NMgels display outstanding mechanical properties with compressive strength, modulus and fracture energy up to about 3.44 MPa, 0.31 MPa and 1204 J/m2, respectively. The hydrogels also showed excellent anti-fragility and self-recovery capability due to the dense and strong micelle networks. In addition, the prepared NMgels exhibited low swelling ratios and a well-maintained network even after 90 days in pH=7.4 phosphate buffer saline. This study presents a tough biocompatible hydrogel that has promising applications especially in load-bearing tissue systems. Keywords: Biomaterials; Polymer; Injectability; Strong compression; Hydrogels; Nanomicelles
Introduction Injectable hydrogels are widely pursued as “soft and wet” biomaterials for biological scaffolds in tissue engineering, including structurally and functionally optimized natural polymers (e.g., alginate, gelatin, hyaluronic acid, chitosan) and synthetic polymers (e.g., 1
poly(ethylene oxide/glycol), Pluronic F127, polyvinyl alcohol) [1]. However, most of these hydrogel scaffolds are usually weak and prone to fracture at low deformations due to the lack of efficient energy dissipation mechanism, with the fracture energies of only about 10 J/m2, as compared with 1,000 J/m2 for cartilage [2], which has severely restrained their applications in loading-bearing tissues. Introducing of sacrificial bonds in hydrogels for energy dissipation provides a robust pathway to achieve outstanding strength and tough hydrogels, such as double network hydrogels, nanocomposite hydrogels and micelle crosslinked hydrogels [3, 4]. In particularly, it has demonstrated that the amphiphilic block copolymer assembly structures including micelles, cylinders, and vesicles can be as macro-crosslinkers to effectively toughen hydrogels and excellently dissipate energy due to their viscoelasticity and deformation under loadings, and fully self-recovery after load release [5-8]. Unfortunately, these hydrogels are often un-injectable and usually do not provide a safety environment for cells due to some potential risk components, although the fracture toughness of them are higher than that of articular cartilage [9, 10]. Here, we developed a novel injectable hydrogel by photo-crosslinking methacrylated hyaluronic acid (MeHA) in the presence of PEO99-PPO65-PEO99 triblock copolymer diacrylates (Pluronic F127 diacrylate, F127DA). Both of hyaluronic acid and F127 are established biomaterials with FDA-approved uses, and therefore, is suitable for biocompatible hydrogels. The hydrophobic PPO block drives self-assembling of the copolymer chains into micelles in an aqueous solution. The highly entangled assemblies of F127DA was used as physical network to host the crosslinking copolymerization of MeHA, yielding nanomicelle hydrogel (NMgel) with extraordinary compressive properties and excellent network stability.
2. Materials and methods 2.1. Materials Pluronic F127 (PEO99-PPO65-PEO99), sodium hyaluronate (50~70 kDa) molecular sieves (3 Å, 4-8 mesh) and other reagents are shown in supporting information. 2
2.2. Hydrogel preparation MeHA and F127DA were first synthesized according to a well-established literature procedure, respectively [11, 12]. To evaluate the influence of solid content, NMgels with varying percentages of F127DA were prepared by photo-initiated free radical copolymerization. The details were shown in supporting information. 2.3. Characterizations The synthesized MeHA and F127DA were analyzed by 1H NMR spectrometer. The gelation kinetics and compressive measurements of NMgels were assessed by using a rheometer and universal testing machine. The abundant details were shown in supporting information.
3. Results and discussion 3.1. Synthesis of compressible hydrogels The nanomicelle hydrogels (NMgel) were prepared by photo-initiated free radical copolymerization of biocompatible methacrylated hyaluronate acid (MeHA) and Pluronic F127 diacrylate (F127DA) micelles. The MeHA were synthesized by conjugating methacrylate groups to hydroxyl groups of sodium hyaluronate. The degree of methacrylation substitution is ~46.9% according to 1H NMR results (Fig. S1a). The F127DA was synthesized with ~90% acylation modification by coupling of the end hydroxyl groups of F127 with acryloyl chloride (Fig. S1b). The obtained F127DA chains self-assembled into micelles with around 30~400 nm diameters in aqueous solution (Fig. S1c, Table S1). In presence of MeHA, the micelle size and shape may be changed due to the interactions between F127DA micelles and MeHA (Fig. S2). These double acrylate-terminated micelles acted as dynamic macro-crosslinkers were copolymerized with MeHA chains to form a dense micellization hydrogels by 405 nm light with cytocompatible LAP initiator (Fig. 1a) [13]. To determine the gelling speed, the storage modulus (G’) and the loss modulus (G’’) of 15 wt% of NMgel precursors were firstly monitored with an oscillatory time sweep at 25 ºC (Fig. 1b). An injectable liquid-like property of the precursor was shown from the 3
larger G’’ than G’. When irradiated by light at 100 s, the injectable precursor was rapidly converted into hydrogel (< 25 s), as reflected by the increase in G’ over the G’’. Allowing crosslinking to proceed to completion, the G’ of NMgels reached as high as ~15 kPa at about 120 s irradiation, which is much higher than most comparable systems (~1-10 kPa) [14-16]. Unconfined compression testing also showed that the mechanical strengths were maximal when the crosslinking time is more than 120 s (Fig. 1c). Two minutes was chosen in all subsequent studies, unless otherwise specified.
Fig. 1. (a) Schematic illustration of the preparation of F127DA/MeHA hydrogels based on covalent crosslinking and physical micellization.
(b) Real-time rheological
observation of the 15 wt% NMgels with 0.1% LAP irradiated by 405 nm blue-light (10 mW/cm2).
Compressive stress-strain curves of the 15 wt% NMgels with different
crosslinking times.
3.2 Compression properties of hydrogels Fig. 2a shows the representative compression stress-strain curves of NMgels with various F127DA contents. As the F127DA content increased from 1 wt% to 15 wt%, the corresponding fracture strength (δf), Young's modulus (E) and the fracture energy (Γ) monotonically increased from 0.11 MPa, 0.03 MPa and 35 J/m2 to 3.44 MPa, 0.31 MPa 4
and 1204 J/m2, respectively (Fig. 2a-c), which match that of the human knee meniscus (E = 0.17-0.35 MPa, Γ = ~1000 J/m2) [17]. The increased strength, modulus and toughness indicate the formation of dense networks in NMgels. It is noteworthy that the fracture strain of the NMgels improved from 57% to 81% with the increasing F127DA concentration from 1 wt% to 10 wt%. However, at a high F127DA concentration of 15 wt%, the fracture strain of NMgels was decreased to 75%, suggesting forming more covalent crosslinks. The denser covalent network may be more prone to fracture under loading, causing the fracture strain of the NMgels decreases [7]. The recovery and anti-fatigue properties of the NMgels were shown in Fig. 2d. For five immediate loading-unloading cycles without waiting at 60% strain, neither residual strains nor strength decrease occurred in the 15 wt% NMgels, indicating their good robustness and resilience property. The variation of the compressive stress over time upon cyclic loading-unloading tests demonstrates the fast recovery of the NMgels after unloading (Fig. 2e). Although the energy dissipation ∆U (the area of the hysteresis loop) of the second cycling is smaller than that of the first cycling due to a few covalent-bonding rupture, the differences between them diminish with further testing, confirming the excellent anti-fragility and self-recovery capability of the 15 wt% NMgels, and also suggesting that the energy dissipation of the NMgels primarily bases on the reversible micelle networks (Fig. 2f). Fig. 2g displays good reversibility of the NMgels during compression and relaxation with 60% strain. It is likely that the excellent reversibility and significant energy dissipation of NMgels attributed to the directional deformation of the soft micelles, which fully recovered to spheres after load release [7, 18, 19]. Additionally, the hydrophobic association in the micelle core may be not strong enough to offer upon loadings [20].
5
Fig. 2. (a) Compressive stress-strain (δ-ɛ) curves, (b) the fracture stress (δf) and Young’s modulus (E), and (c) fracture energy (Γ) of the NMgels with different F127DA contents. (d) Representative cyclic loading-unloading curves of 15 wt% NMgels. (e) Stress-time curves at 60% strain. (f) The energy dissipation for 15 wt% NMgels with increasing cycle numbers. (g) Photographs of compression and release process of NMgels with 60% strain.
3.3 Swelling property Fig. 3a compares the equilibrated swelling ratios (ESR) of scaffolds with increasing 6
F127DA contents. NMgels of 1 wt% shows a higher ESR around 45, suggesting its low crosslinking density. As the increasing of the F127DA ratio to 15 wt%, the ESR of hydrogels dramatically decrease to 9, which indicated the formation of the dense micellization networks. It is consistent with the results in Fig. 2. In addition, the ESR of the 15 wt% NMgels was similarly constant in 10 days (Fig. 3b). And these hydrogels have well-maintained network even after 90 days in phosphate buffer saline of pH=7.4 at 37 °C, which is important for the tissue repair in vivo. These observations demonstrate the important contribution from the covalent crosslinking of MeHA to the micelle networks.
Fig. 3. (a) The effect of F127DA content on the equilibrium swelling ratio (ESR) of the NMgels. (b) The ESR of the 15 wt% NMgels in 10 days, photo-images of the immersed hydrogels at day 10 and 90 were shown in insert.
4. Conclusions In summary, a novel injectable and strongly compressive hydrogel have been successfully synthesized by using biocompatible methacrylated hyaluronic acid and Pluronic F127 diacrylate micelles as macro-crosslinkers. The hydrogels showed strong compressive toughness, fatigue resistance and recovery capability. Moreover, the moduli and fracture energy of these hydrogels could be up to about 0.31 MPa and 1204 J/m2, respectively. Because of the dense micellization networks crosslinked by covalent bonding, these hydrogels exhibit a stable and well-maintained network. We envision that NMgels would be ideal candidates in tissue engineering, especially in various 7
load-bearing tissue systems.
Acknowledgements This work was funded by the Natural Science Foundation of China (Grant No. 21706208, 51573147, 51773167).
References [1] M. Liu, X. Zeng, C. Ma, H. Yi, Z. Ali, X. Mou, S. Li, Y. Deng, N. He, Bone Res 5 (2017) 17014. [2] J.-Y. Sun, X. Zhao, W.R.K. Illeperuma, O. Chaudhuri, K.H. Oh, D.J. Mooney, J.J. Vlassak, Z. Suo, Nature 489 (2012) 133. [3] X. Zhao, Proceedings of the Natl. Acad. Sci. 114(31) (2017) 8138-8140. [4] Y.S. Zhang, A. Khademhosseini, Science 356(6337) (2017) 3627. [5] T. Baskan, D.C. Tuncaboylu, O. Okay, Polymer 54(12) (2013) 2979-2987. [6] C.-J. Wu, A.K. Gaharwar, B.K. Chan, G. Schmidt, Macromolecules 44(20) (2011) 8215-8224. [7] Z. Xu, J. Li, G. Gao, Z. Wang, Y. Cong, J. Chen, J. Yin, L. Nie, J. Fu, J. Polym. Sci. Pol. Phys. 56(11) (2018) 865-876. [8] J. Fu, J. Polym. Sci. Pol. Phys. 56(19) (2018) 1279-1280. [9] Y. Sun, N. Xiang, X. Jiang, L. Hou, Mater. Lett. 194 (2017) 34-37. [10] B. Xu, L. Wang, Y. Liu, H. Zhu, Q. Wang, Mater. Lett. 228 (2018) 104-107. [11] F. Cellesi, N. Tirelli, J.A. Hubbell, Macromol. Chem. and Phys. 203(10-11) (2002) 1466-1472. [12] S. Khetan, M. Guvendiren, W.R. Legant, D.M. Cohen, C.S. Chen, J.A. Burdick, Nature Materials 12 (2013) 458. [13] B.D. Fairbanks, M.P. Schwartz, C.N. Bowman, K.S. Anseth, Biomaterials 30(35) (2009) 6702-6707. [14] R. Wieduwild, M. Howarth, Biomaterials 180 (2018) 253-264. [15] C.B. Rodell, J.W. MacArthur Jr, S.M. Dorsey, R.J. Wade, L.L. Wang, Y.J. Woo, J.A. Burdick, Adv. Funct. Mate. 25(4) (2015) 636-644. [16] J. Lou, F. Liu, C.D. Lindsay, O. Chaudhuri, S.C. Heilshorn, Y. Xia, Adv. Mater. 30(22) (2018) 1705215. [17] M. Sweigart, K. Athanasiou, Proc. Inst. Mech. Eng., Part H, 219(1) (2005) 53-62. [18] L. Xiao, J. Zhu, J.D. Londono, D.J. Pochan, X. Jia, Soft Matter 8(40) (2012) 10233-10237. [19] L.-W. Xia, R. Xie, X.-J. Ju, W. Wang, Q. Chen, L.-Y. Chu, Nat. Commun. 4 (2013) 2226. [20] M. Tan, T. Zhao, H. Huang, M. Guo, Poly. Chem. 4(22) (2013) 5570-5576.
8
Highlights: Injectable and strongly compressible nanomicelle hydrogels were prepared from biomaterials. The hydrogels exhibited fast gelation with short irradiation times of 25 s. The obtained hydrogels displayed outstanding compressive strength, modulus and fracture energy. The hydrogel possessed a stable and well-maintained network.
9
S0167-577X(19)30212-5 https://doi.org/10.1016/j.matlet.2019.01.159 MLBLUE 25708
To appear in:
Materials Letters
Received Date: Revised Date: Accepted Date:
8 December 2018 20 January 2019 31 January 2019
Please cite this article as: H. Zhang, P. Ren, Y. Jin, F. Ren, Injectable, strongly compressible hyaluronic acid hydrogels via incorporation of Pluronic F127 diacrylate nanomicelles, Materials Letters (2019), doi: https://doi.org/ 10.1016/j.matlet.2019.01.159
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Injectable, strongly compressible hyaluronic acid hydrogels via incorporation of Pluronic F127 diacrylate nanomicelles Hua Zhanga, Penggang Ren*ab, Yanling Jinb, Fang Renb* a. School of Materials Science and Engineering, Xi’an University of Technology, Xi’an 710048, China b. Faculty of Printing, Packaging Engineering and Digital media Technology, Xi’an University of Technology, Xi’an, Shaanxi 710048, PR China
*E-mail: [email protected]; [email protected]
Abstract: Injectable, strongly compressible nanomicelle hydrogels (NMgels) were prepared by photo-initiated free radical copolymerization of methacrylated hyaluronate acid (MeHA) and Pluronic F127 diacrylate (F127DA) micelles. The gelation of precursor solutions occurred with short irradiation times of 25 s and hardened within 120 s. The obtained NMgels display outstanding mechanical properties with compressive strength, modulus and fracture energy up to about 3.44 MPa, 0.31 MPa and 1204 J/m2, respectively. The hydrogels also showed excellent anti-fragility and self-recovery capability due to the dense and strong micelle networks. In addition, the prepared NMgels exhibited low swelling ratios and a well-maintained network even after 90 days in pH=7.4 phosphate buffer saline. This study presents a tough biocompatible hydrogel that has promising applications especially in load-bearing tissue systems. Keywords: Biomaterials; Polymer; Injectability; Strong compression; Hydrogels; Nanomicelles
Introduction Injectable hydrogels are widely pursued as “soft and wet” biomaterials for biological scaffolds in tissue engineering, including structurally and functionally optimized natural polymers (e.g., alginate, gelatin, hyaluronic acid, chitosan) and synthetic polymers (e.g., 1
poly(ethylene oxide/glycol), Pluronic F127, polyvinyl alcohol) [1]. However, most of these hydrogel scaffolds are usually weak and prone to fracture at low deformations due to the lack of efficient energy dissipation mechanism, with the fracture energies of only about 10 J/m2, as compared with 1,000 J/m2 for cartilage [2], which has severely restrained their applications in loading-bearing tissues. Introducing of sacrificial bonds in hydrogels for energy dissipation provides a robust pathway to achieve outstanding strength and tough hydrogels, such as double network hydrogels, nanocomposite hydrogels and micelle crosslinked hydrogels [3, 4]. In particularly, it has demonstrated that the amphiphilic block copolymer assembly structures including micelles, cylinders, and vesicles can be as macro-crosslinkers to effectively toughen hydrogels and excellently dissipate energy due to their viscoelasticity and deformation under loadings, and fully self-recovery after load release [5-8]. Unfortunately, these hydrogels are often un-injectable and usually do not provide a safety environment for cells due to some potential risk components, although the fracture toughness of them are higher than that of articular cartilage [9, 10]. Here, we developed a novel injectable hydrogel by photo-crosslinking methacrylated hyaluronic acid (MeHA) in the presence of PEO99-PPO65-PEO99 triblock copolymer diacrylates (Pluronic F127 diacrylate, F127DA). Both of hyaluronic acid and F127 are established biomaterials with FDA-approved uses, and therefore, is suitable for biocompatible hydrogels. The hydrophobic PPO block drives self-assembling of the copolymer chains into micelles in an aqueous solution. The highly entangled assemblies of F127DA was used as physical network to host the crosslinking copolymerization of MeHA, yielding nanomicelle hydrogel (NMgel) with extraordinary compressive properties and excellent network stability.
2. Materials and methods 2.1. Materials Pluronic F127 (PEO99-PPO65-PEO99), sodium hyaluronate (50~70 kDa) molecular sieves (3 Å, 4-8 mesh) and other reagents are shown in supporting information. 2
2.2. Hydrogel preparation MeHA and F127DA were first synthesized according to a well-established literature procedure, respectively [11, 12]. To evaluate the influence of solid content, NMgels with varying percentages of F127DA were prepared by photo-initiated free radical copolymerization. The details were shown in supporting information. 2.3. Characterizations The synthesized MeHA and F127DA were analyzed by 1H NMR spectrometer. The gelation kinetics and compressive measurements of NMgels were assessed by using a rheometer and universal testing machine. The abundant details were shown in supporting information.
3. Results and discussion 3.1. Synthesis of compressible hydrogels The nanomicelle hydrogels (NMgel) were prepared by photo-initiated free radical copolymerization of biocompatible methacrylated hyaluronate acid (MeHA) and Pluronic F127 diacrylate (F127DA) micelles. The MeHA were synthesized by conjugating methacrylate groups to hydroxyl groups of sodium hyaluronate. The degree of methacrylation substitution is ~46.9% according to 1H NMR results (Fig. S1a). The F127DA was synthesized with ~90% acylation modification by coupling of the end hydroxyl groups of F127 with acryloyl chloride (Fig. S1b). The obtained F127DA chains self-assembled into micelles with around 30~400 nm diameters in aqueous solution (Fig. S1c, Table S1). In presence of MeHA, the micelle size and shape may be changed due to the interactions between F127DA micelles and MeHA (Fig. S2). These double acrylate-terminated micelles acted as dynamic macro-crosslinkers were copolymerized with MeHA chains to form a dense micellization hydrogels by 405 nm light with cytocompatible LAP initiator (Fig. 1a) [13]. To determine the gelling speed, the storage modulus (G’) and the loss modulus (G’’) of 15 wt% of NMgel precursors were firstly monitored with an oscillatory time sweep at 25 ºC (Fig. 1b). An injectable liquid-like property of the precursor was shown from the 3
larger G’’ than G’. When irradiated by light at 100 s, the injectable precursor was rapidly converted into hydrogel (< 25 s), as reflected by the increase in G’ over the G’’. Allowing crosslinking to proceed to completion, the G’ of NMgels reached as high as ~15 kPa at about 120 s irradiation, which is much higher than most comparable systems (~1-10 kPa) [14-16]. Unconfined compression testing also showed that the mechanical strengths were maximal when the crosslinking time is more than 120 s (Fig. 1c). Two minutes was chosen in all subsequent studies, unless otherwise specified.
Fig. 1. (a) Schematic illustration of the preparation of F127DA/MeHA hydrogels based on covalent crosslinking and physical micellization.
(b) Real-time rheological
observation of the 15 wt% NMgels with 0.1% LAP irradiated by 405 nm blue-light (10 mW/cm2).
Compressive stress-strain curves of the 15 wt% NMgels with different
crosslinking times.
3.2 Compression properties of hydrogels Fig. 2a shows the representative compression stress-strain curves of NMgels with various F127DA contents. As the F127DA content increased from 1 wt% to 15 wt%, the corresponding fracture strength (δf), Young's modulus (E) and the fracture energy (Γ) monotonically increased from 0.11 MPa, 0.03 MPa and 35 J/m2 to 3.44 MPa, 0.31 MPa 4
and 1204 J/m2, respectively (Fig. 2a-c), which match that of the human knee meniscus (E = 0.17-0.35 MPa, Γ = ~1000 J/m2) [17]. The increased strength, modulus and toughness indicate the formation of dense networks in NMgels. It is noteworthy that the fracture strain of the NMgels improved from 57% to 81% with the increasing F127DA concentration from 1 wt% to 10 wt%. However, at a high F127DA concentration of 15 wt%, the fracture strain of NMgels was decreased to 75%, suggesting forming more covalent crosslinks. The denser covalent network may be more prone to fracture under loading, causing the fracture strain of the NMgels decreases [7]. The recovery and anti-fatigue properties of the NMgels were shown in Fig. 2d. For five immediate loading-unloading cycles without waiting at 60% strain, neither residual strains nor strength decrease occurred in the 15 wt% NMgels, indicating their good robustness and resilience property. The variation of the compressive stress over time upon cyclic loading-unloading tests demonstrates the fast recovery of the NMgels after unloading (Fig. 2e). Although the energy dissipation ∆U (the area of the hysteresis loop) of the second cycling is smaller than that of the first cycling due to a few covalent-bonding rupture, the differences between them diminish with further testing, confirming the excellent anti-fragility and self-recovery capability of the 15 wt% NMgels, and also suggesting that the energy dissipation of the NMgels primarily bases on the reversible micelle networks (Fig. 2f). Fig. 2g displays good reversibility of the NMgels during compression and relaxation with 60% strain. It is likely that the excellent reversibility and significant energy dissipation of NMgels attributed to the directional deformation of the soft micelles, which fully recovered to spheres after load release [7, 18, 19]. Additionally, the hydrophobic association in the micelle core may be not strong enough to offer upon loadings [20].
5
Fig. 2. (a) Compressive stress-strain (δ-ɛ) curves, (b) the fracture stress (δf) and Young’s modulus (E), and (c) fracture energy (Γ) of the NMgels with different F127DA contents. (d) Representative cyclic loading-unloading curves of 15 wt% NMgels. (e) Stress-time curves at 60% strain. (f) The energy dissipation for 15 wt% NMgels with increasing cycle numbers. (g) Photographs of compression and release process of NMgels with 60% strain.
3.3 Swelling property Fig. 3a compares the equilibrated swelling ratios (ESR) of scaffolds with increasing 6
F127DA contents. NMgels of 1 wt% shows a higher ESR around 45, suggesting its low crosslinking density. As the increasing of the F127DA ratio to 15 wt%, the ESR of hydrogels dramatically decrease to 9, which indicated the formation of the dense micellization networks. It is consistent with the results in Fig. 2. In addition, the ESR of the 15 wt% NMgels was similarly constant in 10 days (Fig. 3b). And these hydrogels have well-maintained network even after 90 days in phosphate buffer saline of pH=7.4 at 37 °C, which is important for the tissue repair in vivo. These observations demonstrate the important contribution from the covalent crosslinking of MeHA to the micelle networks.
Fig. 3. (a) The effect of F127DA content on the equilibrium swelling ratio (ESR) of the NMgels. (b) The ESR of the 15 wt% NMgels in 10 days, photo-images of the immersed hydrogels at day 10 and 90 were shown in insert.
4. Conclusions In summary, a novel injectable and strongly compressive hydrogel have been successfully synthesized by using biocompatible methacrylated hyaluronic acid and Pluronic F127 diacrylate micelles as macro-crosslinkers. The hydrogels showed strong compressive toughness, fatigue resistance and recovery capability. Moreover, the moduli and fracture energy of these hydrogels could be up to about 0.31 MPa and 1204 J/m2, respectively. Because of the dense micellization networks crosslinked by covalent bonding, these hydrogels exhibit a stable and well-maintained network. We envision that NMgels would be ideal candidates in tissue engineering, especially in various 7
load-bearing tissue systems.
Acknowledgements This work was funded by the Natural Science Foundation of China (Grant No. 21706208, 51573147, 51773167).
References [1] M. Liu, X. Zeng, C. Ma, H. Yi, Z. Ali, X. Mou, S. Li, Y. Deng, N. He, Bone Res 5 (2017) 17014. [2] J.-Y. Sun, X. Zhao, W.R.K. Illeperuma, O. Chaudhuri, K.H. Oh, D.J. Mooney, J.J. Vlassak, Z. Suo, Nature 489 (2012) 133. [3] X. Zhao, Proceedings of the Natl. Acad. Sci. 114(31) (2017) 8138-8140. [4] Y.S. Zhang, A. Khademhosseini, Science 356(6337) (2017) 3627. [5] T. Baskan, D.C. Tuncaboylu, O. Okay, Polymer 54(12) (2013) 2979-2987. [6] C.-J. Wu, A.K. Gaharwar, B.K. Chan, G. Schmidt, Macromolecules 44(20) (2011) 8215-8224. [7] Z. Xu, J. Li, G. Gao, Z. Wang, Y. Cong, J. Chen, J. Yin, L. Nie, J. Fu, J. Polym. Sci. Pol. Phys. 56(11) (2018) 865-876. [8] J. Fu, J. Polym. Sci. Pol. Phys. 56(19) (2018) 1279-1280. [9] Y. Sun, N. Xiang, X. Jiang, L. Hou, Mater. Lett. 194 (2017) 34-37. [10] B. Xu, L. Wang, Y. Liu, H. Zhu, Q. Wang, Mater. Lett. 228 (2018) 104-107. [11] F. Cellesi, N. Tirelli, J.A. Hubbell, Macromol. Chem. and Phys. 203(10-11) (2002) 1466-1472. [12] S. Khetan, M. Guvendiren, W.R. Legant, D.M. Cohen, C.S. Chen, J.A. Burdick, Nature Materials 12 (2013) 458. [13] B.D. Fairbanks, M.P. Schwartz, C.N. Bowman, K.S. Anseth, Biomaterials 30(35) (2009) 6702-6707. [14] R. Wieduwild, M. Howarth, Biomaterials 180 (2018) 253-264. [15] C.B. Rodell, J.W. MacArthur Jr, S.M. Dorsey, R.J. Wade, L.L. Wang, Y.J. Woo, J.A. Burdick, Adv. Funct. Mate. 25(4) (2015) 636-644. [16] J. Lou, F. Liu, C.D. Lindsay, O. Chaudhuri, S.C. Heilshorn, Y. Xia, Adv. Mater. 30(22) (2018) 1705215. [17] M. Sweigart, K. Athanasiou, Proc. Inst. Mech. Eng., Part H, 219(1) (2005) 53-62. [18] L. Xiao, J. Zhu, J.D. Londono, D.J. Pochan, X. Jia, Soft Matter 8(40) (2012) 10233-10237. [19] L.-W. Xia, R. Xie, X.-J. Ju, W. Wang, Q. Chen, L.-Y. Chu, Nat. Commun. 4 (2013) 2226. [20] M. Tan, T. Zhao, H. Huang, M. Guo, Poly. Chem. 4(22) (2013) 5570-5576.
8
Highlights: Injectable and strongly compressible nanomicelle hydrogels were prepared from biomaterials. The hydrogels exhibited fast gelation with short irradiation times of 25 s. The obtained hydrogels displayed outstanding compressive strength, modulus and fracture energy. The hydrogel possessed a stable and well-maintained network.
9