ABSTRACT: Hydrogels are formed using various triggers, including light irradiation, pH adjustment, heating, cooling, or chemical addition. Here, a new method for forming hydrogels is introduced: ultrasound-triggered enzymatic gelation. Specifically, ultrasound is used as a stimulus to liberate liposomal calcium ions, which then trigger the enzymatic activity of transglutaminase. The activated enzyme catalyzes the formation of fibrinogen hydrogels through covalent intermolecular crosslinking. The catalysis and gelation processes are monitored in real time and both the enzyme kinetics and final hydrogel properties are controlled by varying the initial ultrasound exposure time. This technology is extended to microbubble-liposome conjugates, which exhibit a stronger response to the applied acoustic field and are also used for ultrasound-triggered enzymatic hydrogelation. To the best of the knowledge, these results are the first instance in which ultrasound is used as a trigger for either enzyme catalysis or enzymatic hydrogelation. This approach is highly versatile and can be readily applied to different ion-dependent enzymes or gelation systems. Moreover, this work paves the way for the use of ultrasound as a remote trigger for in vivo hydrogelation.
Project description:Enzymatic supramolecular hydrogelation is a simple, controllable, and novel strategy for preparation of soft colloidal materials, which allows the integration of self-assembly with enzyme associated biological processes. The development of more enzymes involve in hydrogelation is a subject of developing useful soft colloids. In this work, an ectoenzyme, CD73, was found to trigger the formation of nanofibers as matrices of hydrogels. CD73 is an important cell surface enzyme which converts extracellular adenosine monophosphate (AMP) to adenosine. It is broadly expressed in many cancer cells and participates in tumor growth. The successful application of CD73 in self-assembly and hydrogelation may provide new strategies for CD73-guided materials and therapies.
Project description:A modular system for detecting protease activity via enzyme-triggered gel formation is described. Protease-specific recognition sequences are utilized to achieve enzyme specificity. Artificial blood clotting is demonstrated by activating endogenous thrombin to trigger gelation in fibrinogen-deficient blood plasma.
Project description:Anisotropy or alignment is a critical feature of functional soft materials in living organisms, but it remains a challenge for spontaneously generating anisotropic gel materials. Here we report a molecular design that increases intermolecular aromatic-aromatic interactions of hydrogelators during enzymatic hydrogelation for spontaneously forming an anisotropic hydrogel. This process, relying on both aromatic-aromatic interactions and enzyme catalysis, results in spontaneously aligned supramolecular nanofibers as the matrices of a monodomain hydrogel that exhibits significant birefringence. This work, as the first example of monodomain hydrogels formed via an enzymatic reaction, illustrates a new biomimetic approach for generating aligned anisotropic soft materials.
Project description:The diverse requirements of hydrogels for tissue engineering motivate the development of cross-linking reactions to fabricate hydrogel networks with specific features, particularly those amenable to the activity of biological materials (e.g., cells, proteins) that do not require exposure to UV light. We describe gelation kinetics for a library of thiolated poly(ethylene glycol) sulfhydryl hydrogels undergoing enzymatic cross-linking via horseradish peroxidase, a catalyst-driven reaction activated by hydrogen peroxide. We report the use of small-amplitude oscillatory shear (SAOS) to quantify gelation kinetics as a function of reaction conditions (hydrogen peroxide and polymer concentrations). We employ a novel approach to monitor the change of viscoelastic properties of hydrogels over the course of gelation (? tgel) via the time derivative of the storage modulus (d G'/d t). This approach, fundamentally distinct from traditional methods for defining a gel point, quantifies the time interval over which gelation events occur. We report that gelation depends on peroxide and polymer concentrations as well as system temperature, where the effects of hydrogen peroxide tend to saturate over a critical concentration. Further, this cross-linking reaction can be reversed using l-cysteine for rapid cell isolation, and the rate of hydrogel dissolution can be monitored using SAOS.
Project description:Silk fibroin (SF) hydrogels find wide applications in tissue engineering. However, their scope has been limited due to the long gelation time in ambient conditions. This paper shows the reduction in gelation time of silk fibroin to minutes upon doping with a newly synthesized lauric acid sophorolipid (LASL). LASL comprises a fatty acid, lauric acid (with a 12-carbon aliphatic chain), that is derivatized by glucose molecules using a non-pathogenic yeast Candida bombicola. LASL was characterized using spectroscopic (Fourier transform infrared spectroscopy) and chromatographic (high-performance liquid chromatography, thin-layer chromatography, and high-resolution mass spectrometry) methods. This gelation of SF is comparable to the effect of an anionic surfactant, sodium dodecyl sulfate (SDS). The microstructure of SF-LASL hydrogels was investigated by small-angle neutron scattering (SANS) measurements and exhibited the beads-on-a-necklace model. The rheological properties of these hydrogels show similarity to SF-SDS hydrogels, therefore presenting a greener alternative for tissue engineering applications.
Project description:Gelation kinetics of hydrogels is closely linked to many applications such as the development of injectable and printable hydrogels. However, the control of gelation kinetics without compromising the structure and other properties of the hydrogels, remains a challenge. Here, we demonstrate a method to control the gelation kinetics of cucurbituril-adamantane (CB-AD) cross-linked supramolecular hydrogels by using competing guest molecules. The association between CB and AD moieties on the polymer backbone was impeded by pre-occupying the CB cavity with competing guest molecules. By using various guest molecules and concentrations, the gelation of the hydrogels could be varied from seconds to hours. The strong interaction of CB-AD pair endue the hydrogels good mechanical properties and stability. Moreover, the binding of functionalized guest molecules of CB moieties offers a facile approach for tailoring of the hydrogels' scaffold. Combined with hydrogel injection and printing technology, this method offers an approach for the development of hydrogels with advanced temporal and spatial complexity.
Project description:Small-angle X-ray scattering (SAXS) was used to monitor peptide hydrogelation with and without the MRI contrast agent gadolinium chelate (Gd(III)-chelate). The gelators are a pair of decapeptides that are self-repulsive but mutually attractive. Gd(III)-chelate was either free or covalently bound to one of the decapeptides. Free and conjugated Gd(III)-chelate have the opposite effects on peptide gelation: free Gd(III)-chelate slows down gelation while having little effect on the cross-sectional area of peptide fibers; covalently conjugated Gd(III)-chelate speeds up gelation and results in peptide fibers with significantly greater cross-sectional area. After 24 h of gelation, the cross-sectional areas of hydrogels with no Gd(III)-chelate, with free Gd(III)-chelate and with conjugated Gd(III) chelate are 3700, 3800, and 6300 Å(2), respectively. Free Gd(III)-chelate is not incorporated into peptide fibers and remains in solution with little effect on MRI intensity upon gelation. In contrast, covalently conjugated Gd(III)-chelate is not only incorporated into peptide fibers, but further aggregates toward the center of the peptide fibers. In conclusion, to visualize hydrogelation using (1)H MRI, it is necessary to conjugate Gd(III)-chelate to the material covalently and use T(2)-weighted imaging.
Project description:We demonstrate the formation of polyethylene glycol (PEG) based hydrogels via oxime ligation and the photoinitiated thiol-ene 3D patterning of peptides within the hydrogel matrix postgelation. The gelation process and final mechanical strength of the hydrogels can be tuned using pH and the catalyst concentration. The time scale to reach the gel point and complete gelation can be shortened from hours to seconds using both pH and aniline catalyst, which facilitates the tuning of the storage modulus from 0.3 to over 15 kPa. Azide- and alkene-functionalized hydrogels were also synthesized, and we have shown the post gelation "click"-type Huisgen 1,3 cycloaddition and thiolene-based radical reactions for spatially defined peptide incorporation. These materials are the initial demonstration for translationally relevant hydrogel materials that possess tunable mechanical regimes attractive to soft tissue engineering and possess atom neutral chemistries attractive for post gelation patterning in the presence or absence of cells.
Project description:Composite hydrogels of hyaluronic acid and gelatin attract great attention in biomedical fields. In particular, the composite hydrogels obtained through processes that are mild for cells are useful in tissue engineering. In this study, hyaluronic acid/gelatin composite hydrogels obtained through a blue light-induced gelation that is mild for mammalian cells were studied for the effect of the content of each polymer in the precursor solution on gelation, properties of resultant hydrogels, and behaviors of human adipose stem cells laden in the hydrogels. Control of the content enabled gelation in less than 20 s, and also enabled hydrogels to be obtained with 0.5-1.2 kPa Young's modulus. Human adipose stem cells were more elongated in hydrogels with a higher rather than lower content of hyaluronic acid. Stem cell marker genes, Nanog, Oct4, and Sox2, were expressed more in the cells in the composite hydrogels with a higher content of hyaluronic acid compared with those in the hydrogel composed of gelatin alone and on tissue culture dishes. These results are useful for designing conditions for using gelatin/hyaluronic acid composite hydrogels obtained through blue light-induced gelation suitable for tissue engineering applications.
Project description:In this work, poly(ethylene glycol) diacrylate (PEGDA) molecules were grafted to silk fibroin (SF) molecules via a thiol-ene click reaction under 405 nm UV illumination for the fabrication of a PEGDA/SF composite hydrogel. The composite hydrogels could be prepared in a short and controllable gelation time without the use of a photoinitiator. Features relevant to the drug delivery of the PEGDA/SF hydrogels were assessed, and the hydrogels were characterized by various techniques. The results showed that the prepared PEGDA/SF hydrogels demonstrated a good sustained-release performance with limited swelling behavior. It was found that a prior cooling step can improve the compressive strength of the hydrogels effectively. Additionally, the MTT assay indicated the prepared PEGDA/SF hydrogel is non-cytotoxic. Subcutaneous implantation of the PEGDA/SF hydrogel in Kunming mice did not induce an obvious inflammation, which revealed that the prepared PEGDA/SF hydrogel possessed good biocompatibility. Furthermore, the mechanism of the gelation process was discussed.