Enzyme‐Induced Ferrification of Hydrogels for Toughening of Functional Inorganic Compounds

Abstract

Enzyme-induced mineralization (EIM) has been shown to greatly enhance the mechanical properties of hydrogels by precipitation of calcium salts. Another feature of such hydrogels is their high toughness even when containing finely nanostructured mineral content of ≈75 wt%. This might be useful for bendable materials with high content of functional inorganic nanostructures. The present study demonstrates that EIM can form homogeneous nanostructures of water-insoluble iron salts within hydrogels. Crystalline iron(II) carbonate precipitates urease-induced within polyacrylate-based hydrogels and forms platelet structures that have the potential of forming self-organized nacre-like architectures. The platelet structure can be influenced by chemical composition of the hydrogel. Further, amorphous iron(II) phosphate precipitates within hydrogels with alkaline phosphatase, forming a nanostructured porous inorganic phase, homogeneously distributed within the double network hydrogel. The high amount of iron phosphate (more than 80 wt%) affords a stiffness of ≈100 MPa. The composite is still bendable with considerable toughness of 400 J m −2 and strength of 1 MPa. The high water content (>50%) may allow fast diffusion processes within the material. This makes the iron phosphate-based composite an interesting candidate for flexible electrodes and demonstrates that EIM can be used to deliberately soften ceramic materials, rendering them bendable.

Ultrastrong Poly(2‐Oxazoline)/Poly(Acrylic Acid) Double‐Network Hydrogels with Cartilage‐Like Mechanical Properties

“…The determination of the fracture of energy was determined based on previous works of Tiller et al [61,66] Three additional samples, with the same dimensions as mentioned above, were notched in the center. The notch length corresponds to one-third of the sample's width.…”

Enzyme-Mineralized PVASA Hydrogels with Combined Toughness and Strength for Bone Tissue Engineering

“…Enzymatic mineralization is a promising approach to enhancing the stiffness and strength of the hydrogel, by introducing uniformly distributed mineralized products at nanoscale. , One limitation of the enzymatic mineralization process is that the mineralized hydrogel is brittle, often with a poor elongation rate of about 10% or less. ,, Moreover, a dense and rigid network is generally required to ensure the entrapment of enzymes and uniform nucleation within the hydrogel network. , The usually selected systems like poly- N , N -dimethyl acrylamide and polyacrylamide , are generally not desired candidates for tissue engineering applications, despite with dramatic increase of stiffness.…”

“…In particular, enzymatic mineralization greatly compromised the toughness while achieving dramatic enhancement in stiffness, with most of the existing work having an elongation at a break of about 10% or less. [22][23][24]26 alginate into the polyacrylamide mineralized networks, and a 140% elongation at break was achieved. 27 Despite these efforts, most of the existing studies have focused on the optimization of the mechanical properties of the material, and the hydrogels currently used for enzymatic mineralization are in general not ideal hydrogels for bone tissue engineering.…”

“…27 Despite these efforts, most of the existing studies have focused on the optimization of the mechanical properties of the material, and the hydrogels currently used for enzymatic mineralization are in general not ideal hydrogels for bone tissue engineering. [21][22][23]26 For instance, polyacrylamide, poly-2-hydroxyethyl acrylate, and poly-N,N-dimethyl acrylamide were used to allow for the formation of a dense network for enzymatic mineralization and hydrogels with high stiffness, but with limited biocompatibility. 21,24,27 Due to its hydrophilic properties and biocompatibility, 28−30 poly(vinyl alcohol) (PVA) has been widely used for medical applications such as wound dressing, 30 artificial vessels, 31 and bone repair.…”

“…Mineralization usually results in the loss of toughness and makes the material more brittle, − which is not desired for the repair of bone defective sites. In particular, enzymatic mineralization greatly compromised the toughness while achieving dramatic enhancement in stiffness, with most of the existing work having an elongation at a break of about 10% or less. − , Progress has been made by incorporating the ionic cross-linking of sodium alginate into the polyacrylamide mineralized networks, and a 140% elongation at break was achieved . Despite these efforts, most of the existing studies have focused on the optimization of the mechanical properties of the material, and the hydrogels currently used for enzymatic mineralization are in general not ideal hydrogels for bone tissue engineering. − , For instance, polyacrylamide, poly-2-hydroxyethyl acrylate, and poly- N , N -dimethyl acrylamide were used to allow for the formation of a dense network for enzymatic mineralization and hydrogels with high stiffness, but with limited biocompatibility. ,, …”