Dynamic ligand presentation in biomaterials - Bioconjugate Chemistry

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Dynamic ligand presentation in biomaterials Joshua Hammer, and Jennifer L. West Bioconjugate Chem., Just Accepted Manuscript • DOI: 10.1021/acs.bioconjchem.8b00288 • Publication Date (Web): 23 May 2018 Downloaded from http://pubs.acs.org on May 23, 2018

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Bioconjugate Chemistry

Dynamic ligand presentation in biomaterials Joshua A. Hammer and Jennifer L. West*

Joshua A. Hammer Department of Biomedical Engineering Duke University 101 Science Drive Campus Box 90281 Durham, NC 27708-0281, USA E-mail: [email protected]

*: Corresponding author Prof. Jennifer L. West Department of Biomedical Engineering Duke University 101 Science Drive Campus Box 90281 Durham, NC 27708-0281, USA E-mail: [email protected] Phone: 919-660-5229

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Abstract The native cell microenvironment is extraordinarily dynamic, with reciprocal regulation pathways between cells and the extracellular matrix guiding many physiological processes, such as cell migration, stem cell differentiation, and tissue formation. Providing the correct sequence of biochemical cues to cells, both in vivo and in vitro, is critical for triggering specific biological outcomes. There has been a diversity of methods developed for exposing cells in culture to spatiotemporally varying cues, many of which have centered on dynamic control over cellmaterial interactions in an attempt to recapitulate the role of the extracellular matrix in cell signaling. This review highlights several mechanisms that have been employed to control bioactive ligand presentation in biomaterials, and looks ahead toward the potential for genetically encoded approaches to dynamically regulate material bioactivity using light. Introduction Cells exist within a remarkably complex microenvironment where a multitude of different cell types act in concert to form the structural and biochemical fabric of tissues. Cellular responses to chemokines and other biomolecular signals are influenced by both their spatial presentation (e.g., as gradients which guide migration) and their temporal presentation (e.g., as transient signaling to trigger tissue repair after injury) 1, 2. Indeed, aberrant signaling dynamics from a cell’s microenvironment will oftentimes push the cell to respond pathologically, rather than physiologically, to the cue in question. One such example is tumor angiogenesis, where persistent displays of vascular endothelial growth factor (VEGF) gradients and other angiogenic cues are crucial for rapid formation of new vasculature to nourish the growing tumor but result in leaky, tortuous microvasculature characteristically distinct from healthy capillary beds 3, 4. In addition, the stiffness, dimensionality, biochemical makeup, porosity, and organization of the 2 ACS Paragon Plus Environment

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extracellular matrix (ECM) all play a role in regulating the behavior and phenotype of embedded cells, often by affecting the spatiotemporal presentation of biomolecular cues 1, 2. Many biological processes, including organogenesis 5, 6, immune response 7, wound healing 8, and others, are dependent on a sequence of precisely coordinated biochemical signals to guide cells toward the proper physiological outcomes. It follows that to truly recapitulate the native cell microenvironment in the lab, we must have exquisite control over both the spatial and temporal presentation of biochemical cues to cells in culture. The importance of environmental cues on the biological output of cells has been understood for some time 9-11. Because of this, researchers have explored many cell culture systems and substrates in an attempt to more closely replicate key aspects of the cell microenvironment and in doing so produce more physiologically relevant experimental outputs. Hydrogels have proven to be a highly versatile and effective class of material for cell culture, particularly because hydrogels can be engineered to match the stiffness and hydration of native tissue 10, 12, 13. Many hydrogel materials, especially those that can be remodeled by cells, are suitable for 3D cell culture. This is an important consideration, as cells cultured in traditional 2D systems do not receive cues in the same context or with the same dimensionality as cells grown in 3D, resulting in differences in phenotype, morphology, and responses to drugs or other therapeutics compared to 3D cultured cells 14-16. Numerous natural and synthetic polymers have been used to form hydrogels, and in many cases the bioactivity of these hydrogel materials have been precisely tuned to present specific environmental cues to cultured cells (reviewed in ref. 17). However, in most cases cell-instructive cues presented by the hydrogel are engineered into the material at the start of a particular experiment, and then remain static for the duration of the study. While biochemically static materials are quite experimentally powerful, they cannot



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recapitulate the dynamics of the in vivo cell microenvironment, making it difficult to study clinically relevant biological phenomena which are driven by biochemical dynamics in vitro. Mechanisms to dynamically present bioactive ligands to cultured cells Because of the importance of dynamic signaling in the native microenvironment, researchers have begun to explore ways to dynamically change the biochemical characteristics of cell culture substrates in the presence of cells. There have been a variety of strategies employed that rely on competitive binding or affinity-based swapping of bound biomolecules, as well as some systems which use enzymes to mediate biomolecule presentation (Figure 1). One method is to use competitive binding to modulate the bioavailability of noncovalently immobilized molecules on a substrate. For example, Liu et al. demonstrated this approach using leucine zippers of varying binding affinity to control the availability of the adhesion ligand Arg-Gly-Asp (RGD) on a surface (Figure 1a) 18. The investigators created two leucine zippers, one acidic (zipper A) and one basic (zipper B), that were engineered to have greater heterotypic (AB) binding affinity than homotypic binding affinity (AA or BB). Zipper A included an N-terminal cysteine for thiol-mediated attachment to a gold surface, and a Cterminal RGD sequence for cell adhesion. Zipper B contained a C-terminal cysteine which was used to conjugate zipper B to either a terminal acrylate or maleimide group on a poly(ethylene glycol) (PEG) molecule. Zipper A alone on a gold-coated surface presented RGD groups to which NIH 3T3 fibroblasts were able to attach. PEG-conjugated zipper B (10 kDa PEG) was added to the surface, allowing an AB zipper interaction that resulted in the formation of a PEG brush that sterically blocked the RGD sites on the surface. This modification made the surface unable to support fibroblast attachment. By adding an excess of cysteine-free zipper A, PEGconjugated zipper B was displaced from the surface as free zipper A competed for the AB 4 ACS Paragon Plus Environment

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interaction, thereby revealing the bound RGD sites and allowing cell adhesion to occur once more.

Figure 1: Highlighted strategies for modulating the biochemical environment of cells in culture. A) Two leucine zippers with a higher heterotypic than homotypic affinity are used to regulate the availability of cell adhesion sites on a surface. B) “Hostguest” interactions between cyclodextrin and guest molecule-linked peptides are used to transiently display adhesion sites to cells. C) A biomolecule linked to the substrate via a protease-degradable linker is removed using plasmin. D) Sortase is used to reversibly ligate a biomolecule to sortase recognition sites within a biomaterial.



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Sterically blocking adhesion sites using PEG chains as described in the aforementioned implementation of leucine zippers would be difficult to adapt to 3D cell culture. Boekhoven et al. described an affinity-based “host-guest” system that would be more straightforward to bring into 3D 19. Instead of adding or removing blocking groups, a matrix-bound adhesion ligand is directly swapped for a non-adhesive peptide (Figure 1b). Cyclodextrin-conjugated alginate was first coated onto a glass surface. Cell-adhesive Arg-Gly-Asp-Ser (RGDS) peptide with an attached hydrophobic “guest” molecule (both 1-adamantanecarboxylic acid and 1-naphthoic acid were used as guests) was then topically applied, allowing the RGDS to dock with “host” cyclodextrin sites by insertion of the guest region into the hydrophobic interior of the host cyclodextrins. RGDS presented to cells in this way supported attachment and stress fiber formation. As 1naphthoic acid has lower affinity for cyclodextrin of the two guest molecules used, naphthoic acid-conjugation RGDS was displaced from the alginate gel upon application of adamantanecarboxylic acid-conjugated non-adhesive peptide Arg-Gly-Glu-Ser, resulting in a reduction of cell spreading to a level comparable to their non-specific adhesion control. Affinity-based manipulation of RGDS presentation was also demonstrated by Lambert et al. using streptavidin-mediated binding to an agarose gel 20. The researchers created an agarose gel containing desthiobiotin sites which were able to bind streptavidin-conjugated RGDS. Applying soluble biotin displaced the streptavidin-RGDS molecules because biotin has a higher binding affinity with streptavidin than desthiobiotin (KD = 10-15 M for biotin vs. 10-11 M for desthiobiotin). Thus freed of bound RGDS, the desthiobiotin sites were again available to bind additional streptavidin-conjugated biomolecules. Another strategy to modulate bioactive ligand presentation in hydrogels has been to add or remove biomolecules from the gel network using substrate-specific enzymes. Sakiyama-Elbert 6 ACS Paragon Plus Environment

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et al. incorporated recombinant beta nerve growth factor (β-NGF) into fibrin gels by tagging the N-terminus of β-NGF with the transglutaminase recognition sequence NQEQVSPL, allowing it to be incorporated into the fibrin matrix during factor XIII-mediated crosslinking 21. Further, by incorporating a plasmin-labile sequence between the transglutaminase recognition domain and the β-NGF domain, covalently immobilized β-NGF could be cleaved from the fibrin matrix via plasmin activity and released (Figure 1c). This dual strategy of enzymatic incorporation and release was framed as a cell-driven growth factor delivery mechanism. However, employing enzyme-mediated attachment and release of biomolecules adds a layer of spatiotemporal specificity to binding and dissociation events occurring within the hydrogel and facilitates the deployment of multiple orthogonal reactions within the same gel. Enzymatic labeling of hydrogels has also been demonstrated by Cambria et al. using sortase A 22. Sortase A ligates an N-terminal glycine-bearing molecule (this can be an N-terminal poly-glycine sequence to improve the accessibility of the terminal glycine) to the peptide sequence LPXTG where “X” is any amino acid except proline 23, 24. The ligation is directionally dependent and the LPXTG recognition sequence is uncommon in mammalian cells, making sortase a particularly attractive orthogonal, site-specific conjugation chemistry. Cambria et al. created PEG hydrogels containing covalently immobilized LPRTG, and then used soluble sortase to ligate polyglycine-terminated epidermal growth factor (GGG-EGF) to the LPRTG sites within the gel (Figure 1d). Because sortase recognizes the LPXTG sequence even if it is not terminal, reversal of the EGF labeling reaction was also demonstrated. GGG-EGF was removed from the hydrogel by adding additional sortase and an excess of GGG peptide, allowing sortase to swap GGG into sites which contained GGG-EGF. The reversibility of this system is advantageous for creating a dynamic biochemical microenvironment, and the fact that both sides of the



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conjugation reaction (the LPXTG and poly-glycine sequences) can be genetically encoded potentially eases the complexity of assembling this system. As with affinity-based labeling systems, sortase requires large molar excesses of label to substrate (on the order of 20:1), leading to potential bottlenecks in hydrogel labeling efficiency created by solubility constraints of label molecules or even cytotoxicity should the label be applied in the presence of cells. Theoretical limitations aside, one broad drawback of employing bulk switches in biochemical environment is the lack of patterning ability within hydrogels. By simply applying topical agents onto a gel in a dish, it is difficult to spatially constrain where these biochemical changes are taking place. To achieve not just temporal control over bioactivity within the hydrogel niche, but spatial control as well, more precise initiation of these association/dissociation events is needed. Achieving spatiotemporal control using light By taking advantage of photochemical reactions, light can be used as a trigger of binding or dissociation events with precise temporal control within cell culture hydrogels. There have been many techniques developed to control light exposure in order to use photochemistry as a patterning strategy. Many photolithographic techniques have been developed to pattern biomaterials in 2D, such as photomasks which block light from discrete regions of the surface 25, 26

, laser scanning lithography which uses focused light to constrain the exposure area 27, and

microscope projection photolithography, a method of photomask-based lithography which uses microscope optics to reduce feature size 28. More sophisticated experiments necessitate the ability to pattern photochemical reactions in 3D, and this functionality has been achieved using a technique called multiphoton lithography (MPL). In MPL, photons carrying a fraction of the energy necessary to drive the photochemical reaction (most typically they are at half energy, or twice the peak absorption wavelength of the photoabsorptive compound) are focused within the 8 ACS Paragon Plus Environment

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material such that the reaction only proceeds when multiple photons are absorbed at the same time 29, 30. In this way the photochemistry, and by extension any pattern generated through driving a photochemical reaction, is restricted to the focal volume of the light beam. Using MPL and other photolithographic techniques, researchers have attained exquisite spatiotemporal control over biochemical cue presentation to encapsulated cells (several examples of 3D spatial patterning of light-driven reactions will be presented in the following sections). There have been efforts to develop photosensitive host/guest supramolecular hydrogels based on photoswitchable groups such as azobenzene or spiropyran, but these systems have most commonly been used for tuning hydrogel mechanical properties or, in the case of spiropyran, controlling molecular release from hydrogels via photoswitchable static interactions 31-38. Generally, light-driven reactions

Figure 2: Three methods of modifying the biochemistry of hydrogels using light. A) Photodegradation of the hydrogel network leads to reduced crosslinking density and release of molecules bound via photolabile linker. B) A hydrogel network formed from either acrylate or methacrylate photopolymerization contains unreacted sites which can be conjugated to acrylate or methacrylate-linked biomolecules during another round of photopolymerization. C) Active sites, either biomolecules or reactive groups, are present in the material but inaccessible until the photocage is removed using light.



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used to modify the biochemical microenvironment of hydrogels tend to fall within three broad categories: photodegradation of the hydrogel network, photoinduction of covalent linkages, and photoscission of caging groups (Figure 2). In many cases, these reaction strategies have been multiplexed to achieve a degree of biochemical tunability not possible using one mechanism alone. Photodegradation of the hydrogel network Breaking linkages within hydrogels using light can be used to either degrade the hydrogel, thereby reducing crosslinking density, or release biomolecules bound via a photodegradable linker. Kloxin et al. created a photodegradable PEG hydrogel capable of supporting encapsulated cells in culture, and used this system to dynamically change the biochemical microenvironment of human mesenchymal stem cells (hMSCs), influencing the efficiency of hMSC differentiation into chondrocytes 39. Their system relied on a photocleavable nitrobenzyl ester derivative, ethyl 4-(4-(1-hydroxyethyl)-2-methoxy-5-nitrophenoxy)butanoic acid, which breaks upon absorbing near ultraviolet light (λ = 300-400 nm). RGDS was tethered to a PEG hydrogel network via a linker molecule containing the photolabile nitrobenzyl ester group. Encapsulated hMSCs were able to form adhesions with pendant RGDS groups until the researchers dosed the gel with light, thereby cleaving the RGDS linker and releasing the adhesion moiety from the cell microenvironment. After 21 days in culture, the hMSC population presented with persistent RGDS was approximately 50% positive for the hMSC marker CD105, and 50% positive for the chondrocyte marker COLII. In contrast, when RGDS was removed from the culture at day 10, the population shifted to 75% COLII-positive cells and 25% CD105positive cells. These results indicated that dynamically presenting RGDS in this hydrogel material pushed the hMSC population toward a chondrogenic phenotype more efficiently than 10 ACS Paragon Plus Environment

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presenting RGDS continuously during the culture period. The same photolabile nitrobenzyl ester group was also incorporated into the hydrogel backbone and used to degrade the gel in discrete regions using MPL, indicating that bioactive ligands could also be patterned in 3D using this photodegradable linker (though this functionality was not explicitly demonstrated). One interesting application of photodegradable hydrogels was presented by Käpylä et al. in which composite gel sheets containing both photodegradable and non-photodegradable PEG derivatives were folded into 3D shapes using patterned near ultraviolet light 40. By controlling the direction and intensity of light exposure, the researchers created heterogeneous crosslinking densities within the material that resulting in predictable bending moments upon swelling. Of note, the researchers were able to create tube-shaped hydrogels with C2C12 myoblasts present, and retain 60-70% cell viability after completing the exposure protocol. It would be interesting to combine this method of hydrogel tube fabrication with the RGDS removal strategy discussed in the Kloxin paper above, as both groups form their PEG network via radical-mediated acrylate polymerization and both systems utilize the same photodegradation sites. RGDS or other biomolecules could be crosslinked into the polyacrylate centers of the hydrogel via a photolabile linker so that the spatial patterning of the bioactive moiety would follow the 3D structures generated through crosslink breakdown and uneven swelling. In this way tube-shaped hydrogels could be fabricated which contain different concentrations of a tethered biomolecule of interest on the interior surface vs the exterior surface. This dual action of biochemical patterning and structural folding may have utility for guiding tissue formation, as variations in ligand presentation are critical for hierarchical tissue development.



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Photoinduction of covalent linkages PEG hydrogel networks can be formed by driving polymerization of C=C containing groups such as acrylates or methacrylates using photoinitiators that generate free radicals. Gel networks formed in this way contain a small amount of unreacted acrylate or methacrylate groups 41, which can then be used as conjugation sites for biomolecules bearing acrylates or methacrylates by inducing a second round of photopolymerization. This approach has been used to pattern bioactive ligands into PEG hydrogels. Hahn et al. patterned RGDS into a PEG hydrogel in 2D using a photomask 25, and, critically, in 3D using MPL 30, resulting in cells closely following the patterned adhesion sites (Figure 3). The versatility of using free acrylate

Figure 3: Fluorescently labeled RGDS-acrylate was patterned into PEG-diacrylate hydrogels by photoinduction of covalent linkages. A) Fluorescently labeled RGDS was patterned onto 2D PEG hydrogels using a photomask (1,2), thereby controlling human dermal fibroblast attachment to the surface of the gel (3,4). 1,2: scale bar = 250 µm. 3,4: scale bar = 200 µm. B) Fluorescently labeled RGDS was patterned in 3D into PEG hydrogels using two-photon lithography. Panel A: adapted with permission from ref 25. Copyright 2006, Elsiver. Panel B: adapted with permission from ref 30. Copyright 2006, John Wiley and Sons.


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groups to pattern ligands in 3D with MPL was further demonstrated by Hoffman and West who patterned multiple fluorescently labeled RGDS molecules into the same gel, creating complex 3D patterns and achieving precise control over both spatial resolution and ligand concentration 42

. MPL has also been used to recreate the spatial geometry of tissue-specific microvasculature

using image guided lithography in pro-vasculogenic PEG hydrogels (Figure 4) 43. ROI masks were created digitally from images of endogenous capillary networks, and then used to guide the patterning of RGDS in 3D using a scanning laser confocal microscope. Human umbilical vein endothelial cells (HUVEC) and mesenchymal precursor cells (10T1/2) encapsulated in these patterned gels formed themselves into vascular networks 44 that followed the patterned adhesion ligand.

Figure 4. Image-guided two photon laser scanning lithography was used to create tissue-derived vascular patterns in vitro. A) Tissue-specific vasculature was imaged (1), converted into a digital mosaic of simple geometric shapes using MatLab (2,3), and then patterned into PEG-diacrylate hydrogels using the mosaic as a laser guide (4,5) by linking fluorescent monoacrylate-RGDS into unreacted acrylate sites via photoinduced free radicals. Scale bar = 100 µm. B) Encapsulated vascular progenitor cells (human umbilical vein endothelial cells (HUVEC) and 10T1/2 support cells) formed tubule networks which closely aligned with patterned fluorescent RGDS. Scale bar = 50 µm. Adapted with permission from ref 43. Copyright 2012, John Wiley and Sons.



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Using photochemistry to link biomolecules into a PEG hydrogel can also be accomplished independent of hydrogel crosslinking chemistry. DeForest et al. demonstrated this by fabricating hydrogels using four-arm PEG-azide with a bis(cyclooctyne)-functionalized peptide crosslinker to form hydrogels using strain-promoted alkyne azide click (SPAAC) chemistry 45. The peptide crosslinker contained a vinyl group which allowed the researchers to conjugate thiol-tagged fluorophores or thiol-tagged RGDS to the network using a photoinitiated

Figure 5. A dual-function photosensitive crosslinker enables two orthogonal reactions to be driven by light after hydrogel formation. A) Schematic showing a photoinduced thiol-ene linkage triggered by 490-650 nm light (single photon) or 860 nm light (two photon) and photoscission of the crosslinker using 365 nm light (single photon) or 740 nm light (two photon). The two reactions are orthogonal and therefore the order shown is arbitrary. B) 3T3 fibroblast-laden fibrin clots were encapsulated within the bifunctional photoreactive hydrogel. Cell outgrowth was confined to physical channels created in 3D using photodegradation that were also functionalized with RGDS (denoted by dashed line). Channels without RGDS functionalization did not support fibroblast outgrowth. Scale bar = 100 µm. Adapted with permission from ref 46. Copyright 2011, Springer Nature.

thiol-ene reaction. One advantage gained by using a crosslinking reaction that does not depend on photochemistry in a bioconjugation system like this is that multiple orthogonal photochemical reactions can be used to modify the same hydrogel. DeForest and Anseth created a similar hydrogel system using the same SPAAC crosslinking chemistry, but modified the crosslinker such that it contained both a vinyl group for biomolecular labeling using visible light (upon inclusion of the green light photosensitizer eosin Y into the labeling solution) and a nitrobenzyl ester group that could be used to degrade the gel using UV light 46. These two photochemistries 14 ACS Paragon Plus Environment

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were multiplexed to guide fibroblast migration through 3D RGDS-functionalized channels within the gel (Figure 5). Photolabile molecular cages Photolabile cages are a versatile method for controlling the bioactivity of cell substrates. Often based around a nitrobenzyl derivative that can be broken upon UV light exposure (though there has been several demonstrations of coumarin-derived photolabile groups for biomaterialbased drug delivery 47-52) , photocages can either restrict cellular interaction with a bioactive moiety present in the material or restrict the availability of a conjugation site such that biomolecules can be added into the substrate only where the molecular cage was previously removed. Luo et al. notably published a study whereby agarose gel was prepared containing 2nitrobenzyl-protected cysteine groups that could be revealed upon UV light exposure 53. By revealing the thiol-containing cysteine groups with patterned UV light, maleimide-tagged RDGS was added into irradiated areas via Michael-type addition and used to guide rat dorsal root ganglia cells. Photocages were also used to control cell adhesion to a material by restricting

Figure 6. HeLa cells were patterned onto a surface by selectively de-caging immobilized RGDS groups using UV light, thereby restricting cell adhesion to regions of light exposure. Adapted with permission from ref 54. Copyright 2008, John Wiley and Sons.



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access to RGDS groups presented on surfaces. Ohmuro-Matsuyama and Tatsu patterned HeLa cells by coating a cell culture dish in 2-nitrobenzyl-caged RGDS bound to poly-L-lysine, and then exposing regions of the dish to UV light (Figure 6) 54. Petersen et al. achieved similar results by photocaging cyclic RGD with 3-(4,5-dimethoxy-2-nitrophenyl)-2-butyl ester presented on a silica surface via a triethoxysilane anchor 55. Caged cyclic RGD affixed to a surface was later used by Weis et al. to dynamically control both concentration and availability of cell adhesion sites in order to influence the proliferation and differentiation of C2C12 myoblasts 56. Caged cyclic RGD was then used by Lee et al. in PEG hydrogels to examine the influence of dynamic RGD presentation on both in vivo vascularization and fibrotic capsule formation 57. Using transdermal irradiation with UV light, the researchers de-caged cyclic RGD groups within implanted hydrogels at various time points after implantation and found that by de-caging 7 days after implantation they could reduce fibrotic capsule thickness down to non-adhesive control gel levels while improving vessel density compared to non-adhesive controls. One interesting dual-function example of photocaging was employed by Gu and Tang as part of a technique they called “enzyme-assisted photolithograpy” (Figure 7a) 58. In this approach, a caspase-degradable peptide crosslinker VDEVDTK was synthesized with a nitrobenzyl ester-caged Asp residue (underlined) such that it could not be enzymatically degraded without UV light exposure. This crosslinker was used to form a thin film PEG hydrogel which was then exposed to UV light through a photomask to de-cage the enzymatically degradable crosslinker in defined regions. By applying caspase 3, two patterning aims were achieved. First, the hydrogel was removed in areas of enzymatic degradation, resulting in topographical patterning of the gel. Second, free amines were exposed in areas of degradation as


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a consequence of caspase acting on the peptide crosslinks, and were used for later chemical conjugation of RGD and other relevant molecules.

Figure 7. Two examples of enzyme-assisted photolithography are shown. A) Photocages are used to restrict access of a protease to its site of action. Patterned light can be used to de-cage select regions, thereby allowing the protease to degrade the material only in regions of light exposure. In this example, caspase-3 degradation revealed amine groups at the site of degradation, which were then used to link biomolecules into the material only in light-exposed regions. B) In this example, enzyme-mediated ligation was restricted to sites of light exposure. Photocaged FXIIIa recognition sites were incorporated into the hydrogel, and then selectively de-caged using patterned light. Subsequent addition of FXIIIa and a biomolecule tagged with a complementary FXIIIa substrate resulted in biomolecular labeling of photoirradiated regions.

Another example of using photocaged enzyme recognition sites was developed by Mosiewicz et al. who created a PEG hydrogel containing ea nitrobenzyl ester-caged peptide substrate for transglutaminase factor XIIIa (FXIIIa) 59. UV irradiation using a laser scanning confocal microscope exposed the amine present on a lysine residue in the peptide substrate, making it available for FXIIIa-mediated conjugation to biomolecules tagged with the amineaccepting peptide sequence NQEQVSPL (Figure 7b). Using this technique, the researchers were able to create high fidelity spatial patterns and concentration gradients within the hydrogel using several biomolecules, including RGD peptide, VEGF121, protein A, protein G, the recombinant fibronectin fragment FN9-10, and platelet-derived growth factor B (PDGF-BB). Interestingly, the researchers were able to induce and direct the migration of encapsulated MSCs by patterning 17 ACS Paragon Plus Environment


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regions containing either adhesion sites (RGD, FN9-10) or PDGF-BB in the proximity of MSC clusters, illustrating that this method of dynamic biomolecule display can be used in the presence of cells to trigger relevant biological events. Nitrobenzyl esters can be used not only to photocage chemical reactive sites and cellular recognition sites, but can also be used to disrupt recognition sequences for non-covalent interactions. Li et al. used this strategy to create a photopatterning modality that took advantage of a collagen mimetic peptide (CMP) which will spontaneously hybridize with unfolded gelatin chains 60. By incorporating an o-nitrobenzyl group into the CMP backbone which sterically hindered hybridization until it was cleaved, biomolecules conjugated to the caged CMP were

Figure 8. Photocaged fluorescent collagen mimetic peptide (CMP) was patterned into various substrates by applying photocaged CMP to the material and then exposing the material to patterned UV light. From left to right: gelatin-containing zymogram (0.4 mm bands separated by 4 mm spaces), gelatin methacrylate hydrogel film (scale bar = 500 µm), bovine cortical tissue (arrows indicate patterned lines; scale bar = 4 mm). Adapted with permission from ref 61. Copyright 2014, John Wiley and Sons.

patterned into thin gelatin films, methacrylated gelatin hydrogel, a gelatin-containing zymogram polyacrylamide gel, or heat-damaged bovine corneal stroma tissue only in regions of UV light exposure (Figure 8). The power of this strategy of biochemical modification is that the substrate need not be chemically modified to receive a light-patterned biomolecular tag. Even natural tissue can be patterned directly, though for efficient patterning it must be an area of significant collagen denaturation as was induced using heat in the cortical tissue tested 60. Photodegradable nitrobenzyl esters form the basis of many strategies for dynamic photopatterning of biochemistry within hydrogels. DeForest and colleagues have multiplexed the 18 ACS Paragon Plus Environment

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photocission of nitrobenzyl esters with several other reactions to create sophisticated systems which allow for the reversible patterning of ligands within PEG gels. Utilizing green light photoinduced thiol-ene conjugation within a SPAAC-crosslinked PEG gel, DeForest and Anseth patterned either fluorophores or RGDS peptide into the network via a nitrobenzyl ester-

Figure 9. Photoreversible patterning of vitronectin in a PEG hydrogel was used to reversibly differentiate hMSCs. A) Schematic for achieving reversible patterning using irreversible photochemical reactions. Oxime ligation sites are de-caged using patterned 365 nm (single photon) or 740 nm (two photon) light thereby allowing proteins tagged with an aldehydefunctionalize photolabile linker to be bound to the gel in spatially defined regions. Subsequent exposure to 365 nm (single photon) or 740 nm (two photon) light breaks the linker and releases the bound protein. B) Encapsulated hMSCs labeled with CellTracker Red (1) showed positive osteocalcin staining (green) in regions of patterned vitronectin (delineated by dashed line; (2)). Subsequent patterned removal of vitronectin resulted in osteocalcin staining only in regions where vitronectin remained (3). Scale bar = 200 µm. Adapted with permission from ref 63. Copyright 2015 Springer Nature.

containing linker which terminated in a thiol 61. Biomolecules patterned into the gel network using either a photomask or MPL could then be patterned out using UV light to break the photolabile linker. This system was later evolved by DeForest and Tirrell such that the



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biomolecule conjugation to the hydrogel network was mediated by 2-(2-nitrophenyl) propyloxycarbonyl (NPPOC)-caged alcoxyamine groups distributed throughout the PEG gel 62. In this system, alcoxyamine groups were de-caged using UV light, and then biomolecules functionalized with an o-nitrobenzyl ester-containing linker with a terminal aldehyde group were snapped into the network via oxime ligation (Figure 9a). Biomolecules patterned into the hydrogel in this way could then be patterned out using UV light to cleave the linker. The researchers used this reversible patterning technique with several biomolecules, including vitronectin which was successfully used to transiently direct human MSCs down an osteogenic lineage in areas of vitronectin patterning, as shown by osteocalcin immunocytochemical staining and temporally varying levels of alkaline phosphatase expression correlating to time points when vitronectin was present in the hydrogel (Figure 9b). More recently, Farahani et al. have broadened the utility of the photomediated oxime ligation system described previously by using it to modulate either the mechanical properties or biochemical environment within an 8-arm PEG gel, depending simply on the stoichiometry of the hydrogel components 63. Looking ahead toward genetically encoded strategies for reversible ligand patterning in hydrogels Current techniques for dynamically modulating the biochemical microenvironment of hydrogels are powerful, and have been successfully used to control biologically relevant cellmatrix interactions such as adhesion, migration, and material-mediated differentiation. However, there is as yet no reaction modality which can offer true, repeatable reversibility using a gentle light stimulus to rapidly generate dynamic, high-fidelity patterns and gradients without perturbing sensitive cell types. There may be a way to achieve this goal using photoresponsive proteins more commonly used in the field of optogenetics 64-67. In optogenetics work, proteins 20 ACS Paragon Plus Environment

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which control light-regulated biological processes in plants, algae, bacteria, and other organisms (one example is the red light-sensing phytochrome B (PhyB) which regulates de-etiolation in Arbidopsis thaliana) are fused to proteins of interest within living cells or whole animals using gene editing techniques. Those proteins of interest can then be controlled using light which is specifically absorbed by the light-sensing protein (LSP). Many LSP tools have been developed

Figure 10. Several mechanisms by which light-sensing proteins can be made to induce a biological response in cells (specific light-sensing proteins used in these approaches are listed in the right-most column). Depending on the photosensitive proteins used, light stimulus can induce binding (A, B, and C), dissociation (D), or unfolding (E), all of which are reversible either through thermal relaxation (Cry2, LOV) or upon irradiation with a second wavelength of light (PhyB, DRONPA).

which can force proteins of interest to become active, inactive, cluster, or interact with another protein of interest upon light exposure (Figure 10) 64. Interestingly, LSPs have very attractive commonalities that might make these proteins a rich source for developing tools for regulating biomaterial bioactivity. Most LSPs absorb light in the visible spectrum and are typically sensitive to low levels of light in the 10-20 mW/cm2 range. When LSPs absorb light and become excited, they change conformation, which is the core of what optogenetic techniques leverage. Critically, this conformational change is reversible upon either stimulation with a second wavelength of light (as with PhyB 66, 68 and DRONPA 69, 70) or upon thermal relaxation of the LSP (as with LOV 65, 71, cryptochrome 2 67, 72, and others), and this reversion can happen in some cases 10s to 21 ACS Paragon Plus Environment


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over 100 times with no apparent degradation of LSP function. It is possible that LSPs could be translated into synthetic biomaterials through recombinant expression and conjugation to hydrogel polymers such as PEG. Lyu et al. has recently demonstrated that DRONPA can be translated into a reversible crosslinking chemistry within a protein hydrogel 73, but was not able to initiate gelation of the material a second time. Even so, this paper represents a promising first step in adapting LSPs into light-mediated reversible conjugation chemistries within biomaterials. Acknowledgements This work was supported by the National Science Foundation Graduate Research Fellowship under grant number DGE-1644868.

References (1)

Schultz, G. S., Davidson, J. M., Kirsner, R. S., Bornstein, P., and Herman, I. M. (2011) Dynamic reciprocity in the wound microenvironment. Wound Repair Regen 19, 134-48.


Page 23 of 28 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(2)

(3) (4) (5) (6)

(7) (8) (9) (10) (11) (12) (13)

(14) (15)

(16) (17) (18)

(19)

(20) (21)

Barthes, J., Ozcelik, H., Hindie, M., Ndreu-Halili, A., Hasan, A., and Vrana, N. E. (2014) Cell microenvironment engineering and monitoring for tissue engineering and regenerative medicine: the recent advances. Biomed Res Int 2014, 921905. Weis, S. M., and Cheresh, D. A. (2011) Tumor angiogenesis: molecular pathways and therapeutic targets. Nat Med 17, 1359-70. Carmeliet, P., and Jain, R. K. (2011) Molecular mechanisms and clinical applications of angiogenesis. Nature 473, 298-307. Si-Tayeb, K., Lemaigre, F. P., and Duncan, S. A. (2010) Organogenesis and development of the liver. Dev Cell 18, 175-89. Inman, J. L., Robertson, C., Mott, J. D., and Bissell, M. J. (2015) Mammary gland development: cell fate specification, stem cells and the microenvironment. Development 142, 1028-42. Iwasaki, A., and Medzhitov, R. (2015) Control of adaptive immunity by the innate immune system. Nat Immunol 16, 343-53. Sinno, H., and Prakash, S. (2013) Complements and the wound healing cascade: an updated review. Plast Surg Int 2013, 146764. Bissell, M. J., Hall, H. G., and Parry, G. (1982) How does the extracellular matrix direct gene expression? J Theor Biol 99, 31-68. Adam J. Engler, S. S., H. Lee Sweeney, Dennis E. Discher. (2006) Matrix elasticity directs stem cell lineage specification. Cell 126, 677–689. Cukierman, E., Pankov, R., Stevens, D. R., and Yamada, K. M. (2001) Taking cell-matrix adhesions to the third dimension. Science 294, 1708-12. Nemir, S., and West, J. L. (2010) Synthetic materials in the study of cell response to substrate rigidity. Ann Biomed Eng 38, 2-20. Nemir, S., Hayenga, H. N., and West, J. L. (2010) PEGDA Hydrogels With Patterned Elasticity: Novel Tools for the Study of Cell Response to Substrate Rigidity. Biotechnol Bioeng 105, 636-644. Yamada, K. M., and Cukierman, E. (2007) Modeling tissue morphogenesis and cancer in 3D. Cell 130, 601-610. Imamura, Y., Mukohara, T., Shimono, Y., Funakoshi, Y., Chayahara, N., Toyoda, M., Kiyota, N., Takao, S., Kono, S., Nakatsura, T., et al. (2015) Comparison of 2D-and 3Dculture models as drug-testing platforms in breast cancer. Cancer Res 75. Elliott, N. T., and Yuan, F. (2011) A Review of Three-Dimensional In Vitro Tissue Models for Drug Discovery and Transport Studies. J Pharm Sci-Us 100, 59-74. Zhu, J., and Marchant, R. E. (2011) Design properties of hydrogel tissue-engineering scaffolds. Expert Rev Med Devices 8, 607-26. Liu, B., Liu, Y., Riesberg, J. J., and Shen, W. (2010) Dynamic Presentation of Immobilized Ligands Regulated through Biomolecular Recognition. J Am Chem Soc 132, 13630-13632. Boekhoven, J., Perez, C. M. R., Sur, S., Worthy, A., and Stupp, S. I. (2013) Dynamic Display of Bioactivity through Host-Guest Chemistry. Angew Chem Int Edit 52, 1207712080. Lambert, C., Nijsure, D., Huynh, V., and Wylie, R. (2018) Hydrogels with reversible chemical environments for in vitro cell culture. Biomed Mater 13, 1-11. Sakiyama-Elbert, S. E., Panitch, A., and Hubbell, J. A. (2001) Development of growth factor fusion proteins for cell-triggered drug delivery. Faseb J 15, 1300-2. 23 ACS Paragon Plus Environment


(22)

(23)

(24)

(25)

(26)

(27)

(28)

(29) (30)

(31)

(32)

(33)

(34) (35)

(36)

(37)

Page 24 of 28

Cambria, E., Renggli, K., Ahrens, C. C., Cook, C. D., Kroll, C., Krueger, A. T., Imperiali, B., and Griffith, L. G. (2015) Covalent Modification of Synthetic Hydrogels with Bioactive Proteins via Sortase-Mediated Ligation. Biomacromolecules 16, 2316-26. Guimaraes, C. P., Witte, M. D., Theile, C. S., Bozkurt, G., Kundrat, L., Blom, A. E., and Ploegh, H. L. (2013) Site-specific C-terminal and internal loop labeling of proteins using sortase-mediated reactions. Nat Protoc 8, 1787-99. Theile, C. S., Witte, M. D., Blom, A. E., Kundrat, L., Ploegh, H. L., and Guimaraes, C. P. (2013) Site-specific N-terminal labeling of proteins using sortase-mediated reactions. Nat Protoc 8, 1800-7. Hahn, M. S., Taite, L. J., Moon, J. J., Rowland, M. C., Ruffino, K. A., and West, J. L. (2006) Photolithographic patterning of polyethylene glycol hydrogels. Biomaterials 27, 2519-24. Revzin, A., Russell, R. J., Yadavalli, V. K., Koh, W. G., Deister, C., Hile, D. D., Mellott, M. B., and Pishko, M. V. (2001) Fabrication of poly(ethylene glycol) hydrogel microstructures using photolithography. Langmuir 17, 5440-5447. Miller, J. S., Bethencourt, M. I., Hahn, M., Lee, T. R., and West, J. L. (2006) Laserscanning lithography (LSL) for the soft lithographic patterning of cell-adhesive selfassembled monolayers. Biotechnol Bioeng 93, 1060-8. Love, J. C., Wolfe, D. B., Jacobs, H. O., and Whitesides, G. M. (2001) Microscope projection photolithography for rapid prototyping of masters with micron-scale features for use in soft lithography. Langmuir 17, 6005-6012. Wylie, R. G., and Shoichet, M. S. (2008) Two-photon micropatterning of amines within an agarose hydrogel. J Mater Chem 18, 2716-2721. Hahn, M. S., Miller, J. S., and West, J. L. (2006) Three-dimensional biochemical and biomechanical patterning of hydrogels for guiding cell behavior. Adv Mater 18, 26792684. Tamesue, S., Takashima, Y., Yamaguchi, H., Shinkai, S., and Harada, A. (2010) Photoswitchable Supramolecular Hydrogels Formed by Cyclodextrins and Azobenzene Polymers. Angew Chem Int Edit 49, 7461-7464. Wang, J., Li, Q. T., Yi, S. J., and Chen, X. (2017) Visible-light/temperature dualresponsive hydrogel constructed by alpha-cyclodextrin and an azobenzene linked surfactant. Soft Matter 13, 6490-6498. Wang, D. S., Wagner, M., Butt, H. J., and Wu, S. (2015) Supramolecular hydrogels constructed by red-light-responsive host-guest interactions for photo-controlled protein release in deep tissue. Soft Matter 11, 7656-7662. Tomatsu, I., Hashidzume, A., and Harada, A. (2005) Photoresponsive hydrogel system using molecular recognition of alpha-cyclodextrin. Macromolecules 38, 5223-5227. Qiu, Z. J., Yu, H. T., Li, J. B., Wang, Y., and Zhang, Y. (2009) Spiropyran-linked dipeptide forms supramolecular hydrogel with dual responses to light and to ligandreceptor interaction. Chem Commun (Camb), 3342-3344. Wang, N., Li, Y. M., Zhang, Y. Y., Liao, Y., and Liu, W. G. (2014) High-Strength Photoresponsive Hydrogels Enable Surface-Mediated Gene Delivery and Light-Induced Reversible Cell Adhesion/Detachment. Langmuir 30, 11823-11832. Sun, Z. Q., Liu, S. L., Li, K. W., Tan, L. H., Cen, L., and Fu, G. D. (2016) Well-defined and biocompatible hydrogels with toughening and reversible photoresponsive properties. Soft Matter 12, 2192-2199. 24 ACS Paragon Plus Environment

Page 25 of 28 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(38)

(39) (40) (41)

(42)

(43)

(44)

(45)

(46)

(47)

(48)

(49)

(50)

(51)

(52) (53)

Rosales, A. M., Rodell, C. B., Chen, M. H., Morrow, M. G., Anseth, K. S., and Burdick, J. A. (2018) Reversible Control of Network Properties in Azobenzene-Containing Hyaluronic Acid-Based Hydrogels. Bioconjug Chem 29, 905–913. Kloxin, A. M., Kasko, A. M., Salinas, C. N., and Anseth, K. S. (2009) Photodegradable Hydrogels for Dynamic Tuning of Physical and Chemical Properties. Science 324, 59-63. Kapyla, E., Delgado, S. M., and Kasko, A. M. (2016) Shape-Changing Photodegradable Hydrogels for Dynamic 3D Cell Culture. ACS Appl Mater Interfaces 8, 17885-93. Beamish, J. A., Zhu, J., Kottke-Marchant, K., and Marchant, R. E. (2010) The effects of monoacrylated poly(ethylene glycol) on the properties of poly(ethylene glycol) diacrylate hydrogels used for tissue engineering. J Biomed Mater Res A 92, 441-50. Hoffmann, J. C., and West, J. L. (2010) Three-dimensional photolithographic patterning of multiple bioactive ligands in poly(ethylene glycol) hydrogels. Soft Matter 6, 50565063. Culver, J. C., Hoffmann, J. C., Poche, R. A., Slater, J. H., West, J. L., and Dickinson, M. E. (2012) Three-dimensional biomimetic patterning in hydrogels to guide cellular organization. Adv Mater 24, 2344-8. Moon, J. J., Saik, J. E., Poche, R. A., Leslie-Barbick, J. E., Lee, S. H., Smith, A. A., Dickinson, M. E., and West, J. L. (2010) Biomimetic hydrogels with pro-angiogenic properties. Biomaterials 31, 3840-3847. DeForest, C. A., Polizzotti, B. D., and Anseth, K. S. (2009) Sequential click reactions for synthesizing and patterning three-dimensional cell microenvironments. Nat Mater 8, 659664. DeForest, C. A., and Anseth, K. S. (2011) Cytocompatible click-based hydrogels with dynamically tunable properties through orthogonal photoconjugation and photocleavage reactions. Nat Chem 3, 925-931. Lin, Q. N., Bao, C. Y., Yang, Y. L., Liang, Q. N., Zhang, D. S., Cheng, S. Y., and Zhu, L. Y. (2013) Highly Discriminating Photorelease of Anticancer Drugs Based on Hypoxia Activatable Phototrigger Conjugated Chitosan Nanoparticles. Adv Mater 25, 1981-1986. Lin, Q. N., Huang, Q., Li, C. Y., Bao, C. Y., Liu, Z. Z., Li, F. Y., and Zhu, L. Y. (2010) Anticancer Drug Release from a Mesoporous Silica Based Nanophotocage Regulated by Either a One- or Two-Photon Process. J Am Chem Soc 132, 10645-10647. Mal, N. K., Fujiwara, M., Tanaka, Y., Taguchi, T., and Matsukata, M. (2003) Photoswitched storage and release of guest molecules in the pore void of coumarin-modified MCM-41. Chemistry of Materials 15, 3385-3394. Azagarsamy, M. A., and Anseth, K. S. (2013) Wavelength-Controlled Photocleavage for the Orthogonal and Sequential Release of Multiple Proteins. Angew Chem Int Edit 52, 13803-13807. Seo, H. J., and Kim, J. C. (2014) 7-acetoxycoumarin dimer-incorporated and folatedecorated liposomes: photoresponsive release and in vitro targeting and efficacy. Bioconjug Chem 25, 533-42. Jin, Q., Mitschang, F., and Agarwal, S. (2011) Biocompatible drug delivery system for photo-triggered controlled release of 5-Fluorouracil. Biomacromolecules 12, 3684-91. Luo, Y., and Shoichet, M. S. (2004) A photolabile hydrogel for guided three-dimensional cell growth and migration. Nat Mater 3, 249-53.



(54)

(55)

(56)

(57)

(58) (59)

(60)

(61) (62) (63)

(64) (65) (66) (67)

(68) (69)

(70)

Page 26 of 28

Ohmuro-Matsuyama, Y., and Tatsu, Y. (2008) Photocontrolled cell adhesion on a surface functionalized with a caged arginine-glycine-aspartate peptide. Angew Chem Int Edit 47, 7527-7529. Petersen, S., Alonso, J. M., Specht, A., Duodu, P., Goeldner, M., and del Campo, A. (2008) Phototriggering of cell adhesion by caged cyclic RGD peptides. Angew Chem Int Edit 47, 3192-3195. Weis, S., Lee, T. T., del Campo, A., and Garcia, A. J. (2013) Dynamic cell-adhesive microenvironments and their effect on myogenic differentiation. Acta Biomater 9, 80598066. Lee, T. T., Garcia, J. R., Paez, J. I., Singh, A., Phelps, E. A., Weis, S., Shafiq, Z., Shekaran, A., del Campo, A., and Garcia, A. J. (2015) Light-triggered in vivo activation of adhesive peptides regulates cell adhesion, inflammation and vascularization of biomaterials. Nat Mater 14, 352-360. Gu, Z., and Tang, Y. (2010) Enzyme-assisted photolithography for spatial functionalization of hydrogels. Lab Chip 10, 1946-1951. Mosiewicz, K. A., Kolb, L., van der Vlies, A. J., Martino, M. M., Lienemann, P. S., Hubbell, J. A., Ehrbar, M., and Lutolf, M. P. (2013) In situ cell manipulation through enzymatic hydrogel photopatterning. Nat Mater 12, 1072-8. Li, Y., San, B. H., Kessler, J. L., Kim, J. H., Xu, Q. G., Hanes, J., and Yu, S. M. (2015) Non-Covalent Photo-Patterning of Gelatin Matrices Using Caged Collagen Mimetic Peptides. Macromolecular bioscience 15, 52-62. DeForest, C. A., and Anseth, K. S. (2012) Photoreversible Patterning of Biomolecules within Click-Based Hydrogels. Angew Chem Int Edit 51, 1816-1819. DeForest, C. A., and Tirrell, D. A. (2015) A photoreversible protein-patterning approach for guiding stem cell fate in three-dimensional gels. Nat Mater 14, 523-31. Farahani, P. E., Adelmund, S. M., Shadish, J. A., and DeForest, C. A. (2017) Photomediated oxime ligation as a bioorthogonal tool for spatiotemporally-controlled hydrogel formation and modification. J Mater Chem B 5, 4435-4442. Tischer, D., and Weiner, O. D. (2014) Illuminating cell signalling with optogenetic tools. Nat Rev Mol Cell Biol 15, 551-8. Hahn, K. M., and Kuhlman, B. (2010) Hold me tightly LOV. Nat Methods 7, 595, 597. Levskaya, A., Weiner, O. D., Lim, W. A., and Voigt, C. A. (2009) Spatiotemporal control of cell signalling using a light-switchable protein interaction. Nature 461, 997-1001. Kennedy, M. J., Hughes, R. M., Peteya, L. A., Schwartz, J. W., Ehlers, M. D., and Tucker, C. L. (2010) Rapid blue-light-mediated induction of protein interactions in living cells. Nat Methods 7, 973-5. Ni, M., Tepperman, J. M., and Quail, P. H. (1999) Binding of phytochrome B to its nuclear signalling partner PIF3 is reversibly induced by light. Nature 400. Mizuno, H., Mal, T. K., Walchli, M., Kikuchi, A., Fukano, T., Ando, R., Jeyakanthan, J., Taka, J., Shiro, Y., Ikura, M., et al. (2008) Light-dependent regulation of structural flexibility in a photochromic fluorescent protein. Proc Natl Acad Sci U S A 105, 92279232. Zhou, X. X. (2013) Optical Control of Protein Activity by Fluorescent Protein Domains. Biophys J 104, 680a-680a.


Page 27 of 28 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(71)

(72)

(73)

Wang, H., Vilela, M., Winkler, A., Tarnawski, M., Schlichting, I., Yumerefendi, H., Kuhlman, B., Liu, R., Danuser, G., and Hahn, K. M. (2016) LOVTRAP: an optogenetic system for photoinduced protein dissociation. Nat Methods 13, 755–758. Liu, H., Yu, X., Li, K., Klejnot, J., Yang, H., Lisiero, D., and Lin, C. (2008) Photoexcited CRY2 Interacts with CIB1 to Regulate Transcription and Floral Initiation in Arabidopsis. Science 322. Lyu, S. S., Fang, J., Duan, T. Y., Fu, L. L., Liu, J. Q., and Li, H. B. (2017) Optically controlled reversible protein hydrogels based on photoswitchable fluorescent protein Dronpa. Chem Commun (Camb) 53, 13375-13378.

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Dynamic ligand presentation in biomaterials - Bioconjugate Chemistry

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