Tricolor visible wavelength-selective photodegradable hydrogel biomaterials

Bioluminescence Resonance Energy Transfer (BRET)-Mediated Protein Release from Self-Illuminating Photoresponsive Biomaterials

Phototriggered release of various cargos, including soluble protein factors and small molecules, has the potential to correct aberrant biological events by offering spatiotemporal control over local therapeutic levels. However, the poor penetration depth of light historically limits implementation to subdermal regions, necessitating alternative methods of light delivery to achieve the full potential of photodynamic therapeutic release. Here, we introduce a strategy exploiting bioluminescence resonance energy transfer (BRET)-an energy transfer process between light-emitting Nanoluciferase (NLuc) and a photosensitive acceptor molecule-to drive biomolecule release from hydrogel biomaterials. Through a facile, one-pot, and high-yielding synthesis (60-70%), we synthesized a heterobifunctional ruthenium cross-linker bearing an aldehyde and an azide (CHO-Ru-N3), a compound that we demonstrate undergoes predictable exchange of the azide-bearing ligand under blue-green light irradiation (>550 nm). Following site-specific conjugation to NLuc via sortase-tag enhanced protein ligation (STEPL), the modified protein was covalently attached to a poly(ethylene glycol) (PEG)-based hydrogel via strain-promoted azide-alkyne cycloaddition (SPAAC). Leveraging the high photosensitivity of Ru compounds, we demonstrate rapid and equivalent release of epidermal growth factor (EGF) via either direct illumination or via BRET-based bioluminolysis. As NLuc-originated luminescence can be controlled equivalently throughout the body, we anticipate that this unique protein release strategy will find use for locally triggered drug delivery following systemic administration of a small molecule.

Controllable Contact-Destructive Hydrogel Actuators

Constructing hydrogels with spatially heterogeneous structures are crucial for unlocking novel applications. To this end, selectively removing a specific portion of hydrogels by facile and intricate destructive strategies is worth exploring. Herein, a "contact-destructive" hydrogel actuator is presented, composed of a dynamic hydrogel network doped with hydrophilic polyethylene glycol (PEG). The destructive behavior of the hydrogel actuator is attributed to the surface tension-induced spreading effect and the enhanced water absorption due to the additive PEG. Parameters that act on these mechanisms are used to control the destruction of the hydrogel. During the destructive process, the hydrogel actuator exhibits locomotion routes predetermined by the graphic pattern with the aid of 3D printing. Additionally, such self-destructive behavior can be terminated by UV light irradiation when PEG is replaced with poly(ethylene glycol) diacrylate (PEGDA). Significantly, diverse applications including controllable 3D structures collapse, self-erasing, and on-demand cell release, are realized with such self-destructive hydrogel. These results demonstrate that the present hydrogel has great values in soft robotics, anti-counterfeiting, controlled drug delivery, and other related fields.

Engineered Protein Hydrogels as Biomimetic Cellular Scaffolds

The biochemical and biophysical properties of the extracellular matrix (ECM) play a pivotal role in regulating cellular behaviors such as proliferation, migration, and differentiation. Engineered protein-based hydrogels, with highly tunable multifunctional properties, have the potential to replicate key features of the native ECM. Formed by self-assembly or crosslinking, engineered protein-based hydrogels can induce a range of cell behaviors through bioactive and functional domains incorporated into the polymer backbone. Using recombinant techniques, the amino acid sequence of the protein backbone can be designed with precise control over the chain-length, folded structure, and cell-interaction sites. In this review, the modular design of engineered protein-based hydrogels from both a molecular- and network-level perspective are discussed, and summarize recent progress and case studies to highlight the diverse strategies used to construct biomimetic scaffolds. This review focuses on amino acid sequences that form structural blocks, bioactive blocks, and stimuli-responsive blocks designed into the protein backbone for highly precise and tunable control of scaffold properties. Both physical and chemical methods to stabilize dynamic protein networks with defined structure and bioactivity for cell culture applications are discussed. Finally, a discussion of future directions of engineered protein-based hydrogels as biomimetic cellular scaffolds is concluded.

Wavelength-Selective Xanthene-Based Monochromophoric Photoremovable Protecting Groups for Tuning Soft Matter Material Properties

Photocontrolled deprotection of specific functional groups has garnered significant interest over the past two decades. Notably, the selective deprotection of distinct groups based on wavelength has emerged as a prominent focus in recent research. The achievement of this objective has primarily involved the utilization of linker-based bichromophoric systems and diverse cocktail mixtures of photoresponsive protecting groups (PRPGs), each responsive to varying wavelengths of light. Herein, we present the first wavelength-selective monochromophoric system based on a hydroxanthene moiety, enabling the wavelength-selective release of two distinct functionalities under 450 and 600 nm light, respectively. The mechanism of the wavelength-selective photodegradation was thoroughly investigated by 1H NMR, UV-vis, and fluorescence spectroscopy, suggesting a proton-coupled electron transfer mechanism in the first photorelease step and electron transfer based arylmethyl type of photorelease in the second step. The utility of the xanthene-based wavelength-selective PRPGs was demonstrated in the multistep degradation of microparticles and dual-color tuning of polymer chain architecture, thus opening an avenue to design advanced photoreactive wavelength-controlled systems for applications in soft matter materials.

Photochemical Action Plots Map Orthogonal Reactivity in Photochemical Release Systems

The wavelength-by-wavelength resolved photoreactivity of two photo-caged carboxylic acids, i. e. 7-(diethylamino)-coumarin- and 3-perylene-modified substrates, is investigated via photochemical action plots. The observed wavelength-dependent reactivity of the chromophores is contrasted with their absorption profile. The photochemical action plots reveal a remarkable mismatch between the maximum reactivity and the absorbance. Through the action plot data, the study is able to uncover photochemical reactivity maxima at longer and shorter wavelengths, where the molar absorptivity of the chromophores is strongly reduced. Finally, the laser experiments are translated to light emitting diode (LED) irradiation and show efficient visible-light-induced release in a near fully wavelength-orthogonal, sequence-independent fashion (λLED1 = 405 nm, λLED2 = 505 nm) with both chromophores in the same reaction solution. The herein pioneered wavelength orthogonal release systems open an avenue for releasing two different molecular cargos with visible light in a fully orthogonal fashion.

Coumarin-Based Photodegradable Hydrogels Enable Two-Photon Subtractive Biofabrication at 300 mm s-1

Spatiotemporally controlled two-photon photodegradation of hydrogels has gained increasing attention for high-precision subtractive tissue engineering. However, conventional photolabile hydrogels often have poor efficiency upon two-photon excitation in the near-infrared (NIR) region and thus require high laser dosage that may compromise cell activity. As a result, high-speed two-photon hydrogel erosion in the presence of cells remains challenging. Here we introduce the design and synthesis of efficient coumarin-based photodegradable hydrogels to overcome these limitations. A set of photolabile coumarin-functionalized polyethylene glycol linkers are synthesized through a Passerini multicomponent reaction. After mixing these linkers with thiolated hyaluronic acid, semi-synthetic photodegradable hydrogels are formed in situ via Michael addition crosslinking. The efficiency of photodegradation in these hydrogels is significantly higher than that in nitrobenzyl counterparts upon two-photon irradiation at 780 nm. A complex microfluidic network mimicking the bone microarchitecture is successfully fabricated in preformed coumarin hydrogels at high speeds of up to 300 mm s-1 and low laser dosage down to 10 mW. Further, we demonstrate fast two-photon printing of hollow microchannels inside a hydrogel to spatiotemporally direct cell migration in 3D. Collectively, these hydrogels may open new avenues for fast laser-guided tissue fabrication at high spatial resolution.

The Role of Biophysical Factors in Organ Development: Insights from Current Organoid Models

Biophysical factors play a fundamental role in human embryonic development. Traditional in vitro models of organogenesis focused on the biochemical environment and did not consider the effects of mechanical forces on developing tissue. While most human tissue has a Young's modulus in the low kilopascal range, the standard cell culture substrate, plasma-treated polystyrene, has a Young's modulus of 3 gigapascals, making it 10,000-100,000 times stiffer than native tissues. Modern in vitro approaches attempt to recapitulate the biophysical niche of native organs and have yielded more clinically relevant models of human tissues. Since Clevers' conception of intestinal organoids in 2009, the field has expanded rapidly, generating stem-cell derived structures, which are transcriptionally similar to fetal tissues, for nearly every organ system in the human body. For this reason, we conjecture that organoids will make their first clinical impact in fetal regenerative medicine as the structures generated ex vivo will better match native fetal tissues. Moreover, autologously sourced transplanted tissues would be able to grow with the developing embryo in a dynamic, fetal environment. As organoid technologies evolve, the resultant tissues will approach the structure and function of adult human organs and may help bridge the gap between preclinical drug candidates and clinically approved therapeutics. In this review, we discuss roles of tissue stiffness, viscoelasticity, and shear forces in organ formation and disease development, suggesting that these physical parameters should be further integrated into organoid models to improve their physiological relevance and therapeutic applicability. It also points to the mechanotransductive Hippo-YAP/TAZ signaling pathway as a key player in the interplay between extracellular matrix stiffness, cellular mechanics, and biochemical pathways. We conclude by highlighting how frontiers in physics can be applied to biology, for example, how quantum entanglement may be applied to better predict spontaneous DNA mutations. In the future, contemporary physical theories may be leveraged to better understand seemingly stochastic events during organogenesis.

Advanced Multifunctional Hydrogels for Enhanced Wound Healing through Ultra-Fast Selenol-SNAr Chemistry

Fabrication of versatile hydrogels in a facile and effective manner represents a pivotal challenge in the field of biomaterials. Herein, a novel strategy is presented for preparing on-demand degradable hydrogels with multilevel responsiveness. By employing selenol-dichlorotetrazine nucleophilic aromatic substitution (SNAr) to synthesize hydrogels under mild conditions in a buffer solution, the necessity of additives or posttreatments can be obviated. The nucleophilic and redox reactions between selenol and tetrazine culminate in the formation of three degradable chemical bonds-diselenide, aryl selenide, and dearomatized selenide-in a single, expeditious step. The resultant hydrogel manifests exceptional adaptability to intricate environments in conjunction with self-healing and on-demand degradation properties. Furthermore, the resulting material demonstrated light-triggered antibacterial activity. Animal studies further underscore the potential of integrating metformin into Se-Tz hydrogels under green light irradiation, as it effectively stimulates angiogenesis and collagen deposition, thereby fostering efficient wound healing. In comparison to previously documented hydrogels, Se-Tz hydrogels exhibit controlled degradation and drug release, outstanding antibacterial activity, mechanical robustness, and bioactivity, all without the need for costly and intricate preparation procedures. These findings underscore Se-Tz hydrogels as a safe and effective therapeutic option for diabetic wound dressings.

Biomaterial strategies for regulating the neuroinflammatory response

Injury and disease in the central nervous system (CNS) can result in a dysregulated inflammatory environment that inhibits the repair of functional tissue. Biomaterials present a promising approach to tackle this complex inhibitory environment and modulate the mechanisms involved in neuroinflammation to halt the progression of secondary injury and promote the repair of functional tissue. In this review, we will cover recent advances in biomaterial strategies, including nanoparticles, hydrogels, implantable scaffolds, and neural probe coatings, that have been used to modulate the innate immune response to injury and disease within the CNS. The stages of inflammation following CNS injury and the main inflammatory contributors involved in common neurodegenerative diseases will be discussed, as understanding the inflammatory response to injury and disease is critical for identifying therapeutic targets and designing effective biomaterial-based treatment strategies. Biomaterials and novel composites will then be discussed with an emphasis on strategies that deliver immunomodulatory agents or utilize cell-material interactions to modulate inflammation and promote functional tissue repair. We will explore the application of these biomaterial-based strategies in the context of nanoparticle- and hydrogel-mediated delivery of small molecule drugs and therapeutic proteins to inflamed nervous tissue, implantation of hydrogels and scaffolds to modulate immune cell behavior and guide axon elongation, and neural probe coatings to mitigate glial scarring and enhance signaling at the tissue-device interface. Finally, we will present a future outlook on the growing role of biomaterial-based strategies for immunomodulation in regenerative medicine and neuroengineering applications in the CNS.

Chemical and Biological Engineering Strategies to Make and Modify Next-Generation Hydrogel Biomaterials

There is a growing interest in the development of technologies to probe and direct in vitro cellular function for fundamental organoid and stem cell biology, functional tissue and metabolic engineering, and biotherapeutic formulation. Recapitulating many critical aspects of the native cellular niche, hydrogel biomaterials have proven to be a defining platform technology in this space, catapulting biological investigation from traditional two-dimensional (2D) culture into the 3D world. Seeking to better emulate the dynamic heterogeneity characteristic of all living tissues, global efforts over the last several years have centered around upgrading hydrogel design from relatively simple and static architectures into stimuli-responsive and spatiotemporally evolvable niches. Towards this end, advances from traditionally disparate fields including bioorthogonal click chemistry, chemoenzymatic synthesis, and DNA nanotechnology have been co-opted and integrated to construct 4D-tunable systems that undergo preprogrammed functional changes in response to user-defined inputs. In this Review, we highlight how advances in synthetic, semisynthetic, and bio-based chemistries have played a critical role in the triggered creation and customization of next-generation hydrogel biomaterials. We also chart how these advances stand to energize the translational pipeline of hydrogels from bench to market and close with an outlook on outstanding opportunities and challenges that lay ahead.