Light guiding and manipulation in photonics have become ubiquitous in events ranging from everyday communications to complex robotics and nanomedicine. The speed and sensitivity of light–matter interactions offer unprecedented advantages in biomedical optics, data transmission, photomedicine, and detection of multi‐scale phenomena. Recently, hydrogels have emerged as a promising candidate for interfacing photonics and bioengineering by combining their light‐guiding properties with live tissue compatibility in optical, chemical, physiological, and mechanical dimensions. Herein, the latest progress over hydrogel photonics and its applications in guidance and manipulation of light is reviewed. Physics of guiding light through hydrogels and living tissues, and existing technical challenges in translating these tools into biomedical settings are discussed. A comprehensive and thorough overview of materials, fabrication protocols, and design architectures used in hydrogel photonics is provided. Finally, recent examples of applying structures such as hydrogel optical fibers, living photonic constructs, and their use as light‐driven hydrogel robots, photomedicine tools, and organ‐on‐a‐chip models are described. By providing a critical and selective evaluation of the field's status, this work sets a foundation for the next generation of hydrogel photonic research.

Impaired skin wound healing due to severe injury often leads to dysfunctional scar tissue formation as a result of excessive and persistent myofibroblast activation, characterised by the increased expression of α-smooth muscle actin (αSMA) and extracellular matrix (ECM) proteins. Yet, despite extensive research on impaired wound healing and the advancement in tissue-engineered skin substitutes, scar formation remains a significant clinical challenge. This study aimed to first investigate the effect of methacrylate gelatin (GelMA) biomaterial stiffness on human dermal fibroblast behaviour in order to then design a range of 3D-printed GelMA scaffolds with tuneable structural and mechanical properties and understand whether the introduction of pores and porosity would support fibroblast activity, while inhibiting myofibroblast-related gene and protein expression. Results demonstrated that increasing GelMA stiffness promotes myofibroblast activation through increased fibrosis-related gene and protein expression. However, the introduction of a porous architecture by 3D printing facilitated healthy fibroblast activity, while inhibiting myofibroblast activation. A significant reduction was observed in the gene and protein production of αSMA and the expression of ECM-related proteins, including fibronectin I and collagen III, across the range of porous 3D-printed GelMA scaffolds. These results show that the 3D-printed GelMA scaffolds have the potential to improve dermal skin healing, whilst inhibiting fibrosis and scar formation, therefore potentially offering a new treatment for skin repair.

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and shown able to integrate the organism and maintain physiological function for many years after implantation. Even though these are examples of success, they represent mostly nonvital organs generally simpler in terms of morphology and cellular complexity. On the other hand, vital organs like the kidney, heart, liver, or lungs top the list of transplant requirements worldwide. [4] Yet, there are no TE equivalents of these organs so far, resulting from their complex cellular function and architecture, which are extremely hard to engineer, leading to a continuous effort to better organ recovery and transplantation. [5] Biomaterials have been faithful companions of cells in TE strategies, physically supporting them and allowing the maintenance of their phenotype in distinct environments. In fact, with the recent advances in the field of 3D printing, biomaterial-based 3D structures can now be manipulated to approach the architecture of complex tissues and organs, such as vascular beds and cardiac components. [6,7] However, shape and architecture alone cannot assure the ultimate TE challenge: recapitulation of physiological cellular and tissue function. As such, there is one additional burden for biomaterials to carry-the control of cellular behavior. These requirements force upon biomaterials the need to be intelligent and dynamic, supporting and efficiently directing the behavior of cells toward specific outcomes.Natural-origin materials have been continuously derived from different animal and plant components, gathering attention as biomaterials due to their original role in biological environments. [8] However, their bioactivity and biodegradability can be just as limited as that of synthetic components. Thus, this review explores some of the leading natural materials that have been used in TE approaches, looking at their typical applications, degradability properties, and ability to interact with and be modified by the action of cells-a biomimetic, extracellular matrix (ECM)-like behavior. Furthermore, we explore the progress on the use of adhesive sequences and growth factors and their combinatorial applications with emerging synergistic results and novel biological outcomes. Likewise, as force and shape establish themselves as fair opponents to classical biochemical cues, [9,10] we review the recent progress in manipulating stiffness and topography within 3D natural materials and how they can further boost cellular responses.The engineering of fully functional, biological-like tissues requires biomaterials to direct cellular events to a near-native, 3D niche extent. Natural biomaterials are generally seen as a safe option for cell support, but their biocompatibility and biodegradability can be just as limited as their bioactive/ biomimetic performance. Furthermore, integrating different biomaterial cues and their final impact on cellular behavior is a complex equation where the outcome might be very different from the sum of individual parts. This review critically analyses recent progress on biomaterial-indu...

Solid‐state optics has been the pillar of modern digital age. Integrating soft hydrogel materials with micro/nanooptics could expand the horizons of photonics for bioengineering. Here, wet‐spun multilayer hydrogel fibers are engineered through ionic‐crosslinked natural polysaccharides that serve as multifunctional platforms. The resulting flexible hydrogel structure and reversible crosslinking provide tunable design properties such as adjustable refractive index and fusion splicing. Modulation of the optical readout via physical stimuli, including shape, compression, and multiple optical inputs/outputs is demonstrated. The unique permeability of the hydrogels is also combined with plasmonic nanoparticles for molecular detection of SARS‐CoV‐2 in fiber‐coupled biomedical swabs. A tricoaxial 3D printing nozzle is then employed for the continuous fabrication of living optical fibers. Light interaction with living cells enables the quantification and digitalization of complex biological phenomena such as 3D cancer progression and drug susceptibility. These fibers pave the way for advances in biomaterial‐based photonics and biosensing platforms.