Due to the soft and wet characteristics of hydrogels that acquire high mechanical strength by toughening strategies, tough and robust hydrogels are attractive as next-generation structural ...biomaterials, especially for the substitution of soft connective tissues such as cartilage, tendons, and ligaments. Firm fixation of the gels to bone in vivo is an indispensable technology in clinical applications. However, since the surface of the hydrogel is very watery, current medical adhesives cannot fix the gels at all. In this review, first, the double network (DN) strategy, a universal method to toughen hydrogels, is presented. Second, by combining hydroxyapatite (HAp) of a main bony inorganic component with a high-strength DN gel, a biocompatible adhesion method accompanied by spontaneous osteogenesis penetration into the gel matrix is introduced. In addition, the HAp-gel composite can be used as a simplified model of bone tissues because of their similarity in terms of components. Third, HAp formation spatially confined by the polymer network of gel is shown as a model of the earliest stage of biomineralization in vivo. These studies on biomineral–hydrogel composites have great potential to contribute not only basic research on osteogenesis mechanisms but also clinical applications of tough hydrogels.Double network (DN) gel - hydroxyapatite (HAp) composite achieves robust fixation to bone tissue accompanied by spontaneous osteogenesis penetration into the gel matrix. In addition, the HAp-DN gel composite can be used as a simplified model of bone tissues because of their similarity in terms of components. The HAp orientation is regulated by the anisotropy of the polymer network of gel, implying that the collagen matrix is oriented in the earliest stage of biomineralization in vivo.
Bones are an absolutely essential organ for our body on chemical, biological and mechanical aspects, while the discovering of their hidden functions is challenging because bones, consisting of ...biominerals and biopolymers, have complicated hierarchical structure. In this review, bioceramics-soft material hybrid materials are introduced as a simplified model material to estimate the functions of bones. The design of polymer is important because it has been considered that such polymer regulates bioceramics formation in the early stage of bone formation. The polypeptide, self-assembling to fine structure, was employed to investigate the effect of functional group pattern in angstrom scale on hydroxyapatite (HAp) mineralization. Also, polymeric gels were applied to investigate the energy dissipation coming from mineral deformation and the effect of anisotropic space of polymer on HAp mineralization because the polymer network in gel can be deformed by macroscopic deformation. Furthermore, the bioceramics-tough gel system itself can be used as biomaterials bondable to bones. The hybridization of bioceramics and soft material has great potential to estimate various functions and mechanisms of bones up to material design.
Proteins of thermophiles are thermally stable in a high‐temperature environment, adopting a strategy of enhancing the electrostatic interaction in hydrophobic media at high temperature. Herein, ...inspired by the molecular mechanism of thermally stable proteins, the synthesis of novel polymer materials that undergo ultrarapid, isochoric, and reversible switching from soft hydrogels to rigid plastics at elevated temperature is reported. The materials are developed from versatile, inexpensive, and nontoxic poly(acrylic acid) hydrogels containing calcium acetate. By the cooperative effects of hydrophobic interaction and ionic interaction, the hydrogels undergo significant spinodal decomposition and subsequent rubbery‐to‐glassy transition when heated to an elevated temperature. As a result, the gels exhibit super‐rapid and significant hikes in stiffness, strength, and toughness by up to 1800‐, 80‐, and 20‐folds, respectively, when the temperature is raised from 25 to 70 °C, while the volumes of the gels are almost unchanged. As a potential application, the performance of the materials as athletic protective gear is demonstrated. This work provides a pathway for developing thermally stiffened materials and may significantly broaden the scope of polymer applications.
Thermal softening at the glass transition temperature is an intrinsic property of polymers, and it is observable in plastics that melt and even flow when heated. Polymers possessing a rubbery‐to‐glassy transition at elevated temperatures contrary to the intrinsic property are reported, and super‐rapid and reversible thermal hardening, which is a process opposite to thermal softening in general polymers, is demonstrated.
Double-network hydrogels are one of the most promising candidates as artificial soft supporting tissues owing to their excellent mechanical performance, water storage capability, and ...biocompatibility. A double-network hydrogel consists of two contrasting polymer networks: rigid and brittle first network and soft and ductile second network. To satisfy this double-network requirement, polyelectrolyte and neutral polymer are suitable as the first and the second networks, respectively. Combination of these two networks gives rise to extraordinarily tough double-network hydrogel as a result of substantial internal fracture of the brittle first network at large deformation, which contributes to the energy dissipation. Therefore, the first network serves as the sacrificial bonds to toughen the material. The double-network principle is universal and many kinds of double-network hydrogels composed of various chemical species have been developed. Moreover, a molecular stent technology has been developed to synthesize the double-network hydrogels using neutral polymer network as the brittle first network. The sulfonic double-network hydrogel was found to induce spontaneous hyaline cartilage regeneration in vivo.
Living organisms share the ability to grow various microstructures on their surface to achieve functions. Here we present a force stamp method to grow microstructures on the surface of hydrogels ...based on a force-triggered polymerisation mechanism of double-network hydrogels. This method allows fast spatial modulation of the morphology and chemistry of the hydrogel surface within seconds for on-demand functions. We demonstrate the oriented growth of cells and directional transportation of water droplets on the engineered hydrogel surfaces. This force-triggered method to chemically engineer the hydrogel surfaces provides a new tool in addition to the conventional methods using light or heat, and will promote the wide application of hydrogels in various fields.
Abstract Soft supporting tissues in the human body, such as cartilages and ligaments, are tough materials firmly fixed to bones. These soft tissues, once injured, cannot regenerate spontaneously in ...vivo . Developing tough and biocompatible hydrogels as artificial soft supporting tissues would substantially improve outcomes after soft tissue injury. Collagen is the main rigid component in soft connective tissues which is organized in various hierarchical arrays. We have successfully developed a novel class of collagen fibril-based tough hydrogels based on the double network concept using swim bladder collagen (SBC) extracted from Bester sturgeon fish. The DN hydrogels, SBC/PDMAAm, are composed of physically/chemically crosslinked anisotropic SBC fibril as the first network and neutral biocompatible poly(N,N′-dimethylacrylamide) (PDMAAm) as the second network. The anisotropic structure of SBC fibril, which is well retained in the DN hydrogels, is formed by free injection method, taking advantage of the excellent fibrillogenesis capacity of SBC. The denaturation temperature of collagen is improved in the DN hydrogels. These DN gels possess anisotropic swelling behavior, exhibiting excellent mechanical properties comparable to natural cartilage. The 4 weeks implantation of the gels in the osteochondral defect of rabbit knee also shows excellent biomechanical performance in vivo . Furthermore, the hydroxyapatite (HAp) coated DN gels, HAp/SBC/PDMAAm gels, strongly bond to bone after 4 weeks. This new class of collagen-based hybrid DN gels, as soft and elastic ceramics, having good biomechanical performance and strong bonding ability with bone would expand the choice for designing next-generation orthopedic implants such as artificial cartilage, bone defect repair material in the load-bearing region in the body.
Bone tissues possess excellent mechanical properties such as compatibility between strength and flexibility and load bearing owing to the hybridization of organic/inorganic matters with anisotropic ...structure. To synthetically mimic such an anisotropic structure of natural organic/inorganic hybrid materials, we carried out hydroxyapatite (HAp) mineralization in stretched tough double network (DN) hydrogels. Anisotropic mineralization of HAp took place in stretched hydrogels, as revealed by high brightness synchrotron X-ray scattering and transmission electron microscopic observation. The c-axis of mineralized HAp aligned along the stretching direction, and the orientation degree S calculated from scattering profiles increased with increasing in the elongation ratio λ of the DN gel, and S at λ = 4 became comparable to that of rabbit tibial bones. The morphology of HAp polycrystal gradually changed from spherical to unidirectional rod-like shape with increased elongation ratio. A possible mechanism for the anisotropic mineralization is proposed, which would be one of the keys to develop mechanically anisotropic organic/inorganic hybrid materials.
Background:
Ultrapurified alginate (UPAL) gel implantation has been demonstrated as effective in cartilage repair for osteochondral defects; however, cell transplantation within UPAL gels would be ...required to treat larger defects.
Hypothesis:
The combination of UPAL gel and bone marrow aspirate concentrate (BMAC) would enhance cartilage repair and subchondral bone repair for large osteochondral defects.
Study Design:
Controlled laboratory study.
Methods:
A total of 104 osteochondral defects (1 defect per knee) of 52 rabbits were randomly divided into 4 groups (26 defects per group): defects without any treatment (Defect group), defects treated using UPAL gel alone (UPAL group), defects treated using UPAL gel containing allogenic bone marrow mesenchymal stromal cells (UPAL-MSC group), and defects treated using UPAL gel containing BMAC (UPAL-BMAC group). At 4 and 16 weeks postoperatively, macroscopic and histologic evaluations and measurements of repaired subchondral bone volumes of reparative tissues were performed. Collagen orientation and mechanical properties of the reparative tissue were assessed at 16 weeks.
Results:
The defects in the UPAL-BMAC group were repaired with hyaline-like cartilage with well-organized collagen structures. The histologic scores at 4 weeks were significantly higher in the UPAL-BMAC group (16.9 ± 2.0) than in the Defect group (4.7 ± 1.9; P < .05), the UPAL group (10.0 ± 3.3; P < .05), and the UPAL-MSC group (12.2 ± 2.9; P < .05). At 16 weeks, the score in the UPAL-BMAC group (24.4 ± 1.7) was significantly higher than those in the Defect group (9.0 ± 3.7; P < .05), the UPAL group (14.2 ± 3.9; P < .05), and the UPAL-MSC group (16.3 ± 3.6; P < .05). At 4 and 16 weeks, the macroscopic evaluations were significantly superior in the UPAL-BMAC group compared with the other groups, and the values of repaired subchondral bone volumes in the UPAL-BMAC group were significantly higher than those in the Defect and UPAL groups. The mechanical properties of the reparative tissues were significantly better in the UPAL-BMAC group than in the other groups.
Conclusion:
The implantation of UPAL gel containing BMAC-enhanced hyaline-like cartilage repair and subchondral bone repair of osteochondral defects in a rabbit knee model.
Clinical Relevance:
These data support the potential clinical application of 1-step treatment for large osteochondral defects using biomaterial implantation with cell transplantation.
Hydroxyapatite is mineralized along the long axis of collagen fiber during osteogenesis. Mimicking such biomineralization has great potential to control inorganic structures and is fast becoming an ...important next-generation inorganic synthesis method. Inorganic matter synthesized by biomineralization can have beautiful and functional structures that cannot be created artificially. In this study, we applied biomineralization to the synthesis of the only photocatalyst in practical use today, titanium dioxide (TiO2). The photocatalytic activity of TiO2 mainly relates to three properties: morphology, crystal phase, and light-use efficiency. To optimize TiO2 morphology, we used a simple sequential peptide as an organic template. TiO2 mineralized by a β-sheet peptide nanofiber template forms fiber-like shapes that are not observed for mineralization by peptides in the shape of random coils. To optimize TiO2 crystal phase, we mineralized TiO2 with the template at 400 °C to transform it into the rutile phase and at 700 °C to transform it into a mixed phase of anatase and rutile. To optimize light-use efficiency, we introduced nitrogen atoms of the peptide into the TiO2 structure as doped elemental material during sintering. Thus, this biomineralization method enables control of inorganic morphology, crystal phase, and light-use efficiency in a single process.
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