Programming the shape and deformation of the protein hydrogel methods Breakthrough!
Dynamic biological material is a class of artificial tissue material can simulate the morphology can be converted to conformational changes which can be made to be utilized to react to the environment and the robot simulation software changes. The most common shape of the deformable material is currently based crosslinked polymer material, and the need to switch between the hard and soft hardness. These materials typically rely on two or more backbone networks and share the same three-dimensional (3D) space, has small ions or chemical reaction. However, the recovery of the original shape class of materials is the need to convert from hard phase soft phase, and this transformation requires compromise the integrity of the secondary network through the By changing the temperature, pH or solvent type or light regulatory catalytic secondary crosslinking polymer network is achieved. Protein-basedin a water-rich environment protein as a component thereof constituting the primary network, so these hydrogel retains many characteristics of the polymer-based material, but can be more diverse biological functions from library obtained. Proteins perform many life-sustaining functions, for example, a metabolic and enzymatic reactions of the living body tissue structure, and their function is directly related to their 3D fold structure in most cases. Despite the great diversity of the starting material, but the protein material within a narrower temperature, pH or salt conditions are stable and functional range and requires a water-based environment. Since the mechanical response of the material is directly dependent on the concentration of the composition of a network node, a protein-based hydrogels obtainable hardness range is extremely limited: the critical gelling concentration is higher than the required protein can be transformed into a biological material and below its solubility limit specific , and most protein gel material hardness change only from about 10% to 30% in this narrow range. Globular protein having a clear three-dimensional structures, like hard spheres, which provides an excellent structural integrity of the control point and the crosslinking density while maintaining the tertiary structure of the network node. It has been found in various applications of shape memory and shape deformation based hydrogel polymer, although these methods may be biocompatible deformable material, but the polymer and the protein can not achieve the same diversity of structure and a control sequence . Thus, University of Wisconsin-Milwaukee Ionel Popa TF in the Science Advance issued description An innovative approach to programming a , and induce shape change and the aqueous solution at room temperature.
Here, as used herein, is obtained by the photoactive [Ru (bpy) 3] 2+ in bovine serum albumin (BSA) made of a hydrogel-based(FIG. 1). The reaction is shown in covalent carbon tyrosine amino acid positions between the protein domains exposed adjacent – carbon bond. The advantage of using light crosslinking reaction, this method allows the reaction mixture was loaded a desired shape and no change in viscosity before illumination.
The first step is to explore herein, two positively charged ion concentration may increase the hardness range of protein hydrogels, and protein levels allow hydrogel programmed shape. First, an inner diameter of 0.56 mm Teflon tube as a mold to synthesize bovine serum albumin cylindrical hydrogel. These gels are then respectively connected by two metal hook to the voice coil motor and the force sensor (2) and attached to the clamp rheometer. After incubation at the desired cation concentration in phosphate buffered saline for 30 minutes at 0- 4- one thousand mechanical response to bovine serum albumin hydrogel treated within the measurement range Pa (FIG. 2). When the applied force increases linearly with time, changes in stress with strain it may be used to evaluate the stiffness of the material, because of the rising slope of the trace portion directly reflect the dynamic Young\’s modulus. Typically, the hydrogel of globular proteins such as bovine serum albumin produced in the stress – strain curve also shows hysteresis (FIG. 2A). When exposed to a chemical denaturant, such BSA hydrogel hysteresis disappears, a chemical denaturant destroy the tertiary structure of the protein domains to form a hydrogel network. When treated with a Cu 2+ , BSA hydrogel showed an increase up to five times the stiffness, the stiffness exhibited 17-fold increase (FIG. 2B) when the Zn 2+ is present . When the polyelectrolyte treated, BSA hydrogel 2 M Zn 2+ hardness is orders of magnitude larger than the hardness of the same gel should be reported and allows more complex shapes programmed. Thus, hardening effect seems to be more dependent on the cation concentration of the solution rather than their properties (FIG. 2B). Compared with Cu 2+ , Zn 2+ The main advantage lies in its greater solubility in water, which makes it possible to prepare a solution of higher concentration in the study, and observed greater hardness.
In addition to hardening effect, the protein was incubated in a high hydrogel concentration of the cationic solution to improve their properties of mechanical failure. For these tests, we used the typical shape of the bones, which is extended BSA hydrogel, until we reach the force sensor failure or maximum force range (Figure 3A). BSA-based hydrogels exhibited with increasing concentrations of cations, have increased toughness and fracture stress. Represents measured toughness and deformation ability of material to absorb energy without breaking, a tensile stress – strain curve obtained in the area (FIGS. 3B and 3C, the left), as the cation concentration from 1 kJ / mol increased to 2.8 kJ / mol. Failure stress from 15 kPa to 33 kPa. The maximum elongation does not show a significant change with cation concentration. This shows that, although the stiffness may increase the mechanical stability of the connection at about 120% and a protein domain given by non-covalent, but the primary network BSA hydrogel is subjected to an irreversible covalent bond breakage starts after failure . Thus, the geometry of the crosslinked gel is the limiting factor of stretching, the hydrogel networks need to refine the primary increasing the maximum elongation.
The results demonstrate that the foregoing 2+ BSA hydrogel great hardness change caused by the solution immersed in a Zn 2+ and Cu, followed by herein programming biological material cast cylindrical spring shape, the programming material is cast annular flowers (FIG. 4). About 6.5-fold increase in stiffness sufficient to BSA hydrogel has programmed a spring shape, Zn 2+ , and Cu 2+ induced a strong rigid enough (up to about 17-fold). Compared with the polyelectrolyte, the main advantage is their small ion diffusion speed is relatively fast (< 5分钟)。此外，在本例中，形状变形是由简单的扩散驱动的并且不需要借助化学变性剂来破坏初级蛋白质网络。在阳离子存在下，BSA水凝胶杨氏模量增加的另一个优点是可以获得更复杂的形状。例如，我们演示了从环形到花朵形状的变形(图4，底部)。为了获得这种复杂的形状变形，我们首先使用硅树脂模具将水凝胶铸造成花状。在光活化交联反应之后，我们通过将水凝胶安装在塑料管上将其编程为环形，然后将其浸入阳离子溶液中30分钟。当从塑料管移至相同浓度的Zn 2+ in the solution, the hydrogel retention ring (Figure 4B, bottom left). However, when immersed in a conventional Tris buffered when the liquid is in a ring shape quickly deformed to the original flower shape (FIG. 4B)
summary and Outlook:
1, the present study shows a method can be based on protein hydrogel shape deformation achieved, this method relies on the Zn 2+ , and Cu 2+ induced hardening permanently programmed to a new temporary shape configuration, and diffusing the ions of the outer material makes it possible to restore the original shape .Zn 2+ to achieve more biologically relevant applications, because it is more than Cu 2+ much less toxic. 2, the main advantages of the procedure cationic protein hydrogel obtainable hardness is much lower (about 17 times) than conventional high buffer, the program can be designed in a complicated shape and a small quick diffusion of ions results in a rapid irreversible deformation ([123 ]