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Hydrogels with tailor‐made swelling‐shrinkable properties have aroused considerable interest in numerous biomedical domains. For example, as swelling is a key issue for blood and wound extrudates absorption, the transference of nutrients and metabolites, as well as drug diffusion and release, hydrogels with high swelling capacity have been widely applicated in full‐thickness skin wound healing and tissue regeneration, and drug delivery. Nevertheless, in the fields of tissue adhesives and internal soft‐tissue wound healing, and bioelectronics, non‐swelling hydrogels play very important functions owing to their stable macroscopic dimension and physical performance in physiological environment. Moreover, the negative swelling behavior (i.e., shrinkage) of hydrogels can be exploited to drive noninvasive wound closure, and achieve resolution enhancement of hydrogel scaffolds. In addition, it can help push out the entrapped drugs, thus promote drug release. However, there still has not been a general review of the constructions and biomedical applications of hydrogels from the viewpoint of swelling‐shrinkable properties. Therefore, this review summarizes the tactics employed so far in tailoring the swelling‐shrinkable properties of hydrogels and their biomedical applications. And a relatively comprehensive understanding of the current progress and future challenge of the hydrogels with different swelling‐shrinkable features is provided for potential clinical translations.

Since the last few decades, the development of smart hydrogels, which can respond to stimuli and adapt their responses based on external cues from their environments, has become a thriving research frontier in the biomedical engineering field. Nowadays, drug delivery systems have received great attention and smart hydrogels can be potentially used in these systems due to their high stability, physicochemical properties, and biocompatibility. Smart hydrogels can change their hydrophilicity, swelling ability, physical properties, and molecules permeability, influenced by external stimuli such as pH, temperature, electrical and magnetic fields, light, and the biomolecules’ concentration, thus resulting in the controlled release of the loaded drugs. Herein, this review encompasses the latest investigations in the field of stimuli-responsive drug-loaded hydrogels and our contribution to this matter.

[This corrects the article DOI: 10.1371/journal.pone.0155625.].

Fast advances in polymer science have provided new hydrogels for applications in drug delivery. Among modern drug formulations, polymeric type stimuli-responsive hydrogels (SRHs), also called smart hydrogels, deserve special attention as they revealed to be a promising tool useful for a variety of pharmaceutical and biomedical applications. In fact, the basic feature of these systems is the ability to change their mechanical properties, swelling ability, hydrophilicity, or bioactive molecules permeability, which are influenced by various stimuli, particularly enzymes. Indeed, among a great number of SHRs, enzyme-responsive hydrogels (ERHs) gain much interest as they possess several potential biomedical applications (e.g., in controlled release, drug delivery, etc.). Such a new type of SHRs directly respond to many different enzymes even under mild conditions. Therefore, they show either reversible or irreversible enzyme-induced changes both in chemical and physical properties. This article reviews the state-of-the art in ERHs designed for controlled drug delivery systems (DDSs). Principal enzymes used for biomedical hydrogel preparation were presented and different ERHs were further characterized focusing mainly on glucose oxidase-, β-galactosidase- and metalloproteinases-based catalyzed reactions. Additionally, strategies employed to produce ERHs were described. The current state of knowledge and the discussion were made on successful applications and prospects for further development of effective methods used to obtain ERH as DDSs.

Programmable hydrogels are an emerging class of intelligent materials engineered to respond precisely to specific stimuli, offering tailored functionalities with significant potential for biomedical applications, including drug delivery, tissue engineering, and wound healing. This review comprehensively explores various programmable hydrogels responsive to diverse triggers, including temperature, gene expression, color, shape, and mechanical force. The design and fabrication methods underlying these systems are detailed, highlighting the roles of crosslinkers, adhesion groups, and photosensitive functional groups. Furthermore, the key physical, chemical, and biological properties that govern the performance and functionality of hydrogels are analyzed. The review further examines the mechanisms and recent advancements in self‐executing hydrogels, such as self‐activated, self‐oxygenated, self‐expandable, and self‐powered systems, demonstrating how these innovative designs drive the development of next‐generation programmable hydrogels. The main challenges in hydrogel design, including complexity, reproducibility, and clinical translation, are also addressed. Finally, a perspective on future research directions, highlighting the integration of the latest technologies to realize programmable hydrogels with dynamic closed‐loop responsiveness, bionic synergy, and robust clinical applicability, is offered. This review summarizes the design principles and key features of programmable hydrogels that respond to multiple stimuli. It then delves into the cutting‐edge mechanisms of self‐executing systems, highlighting their role as the cornerstone of next‐generation programmable hydrogels (NGPHs). Finally, by addressing critical challenges in complexity and translation, the review looks to the future of NGPHs, emphasizing their evolution toward dynamic closed‐loop control, biomimetic intelligence, and successful clinical integration.

The design of new hemostatic materials to mitigate uncontrolled bleeding in emergencies is challenging. Chitosan-based hemostatic hydrogels have frequently been used for hemostasis due to their unique biocompatibility, tunable mechanical properties, injectability, and ease of handling. Moreover, chitosan (CS) absorbs red blood cells and activates platelets to promote hemostasis. Benefiting from these desired properties, the hemostatic application of CS hydrogels is attracting ever-increasing research attention. This paper reviews the recent research progress of CS-based hemostatic hydrogels and their advantageous characteristics compared to traditional hemostatic materials. The effects of the hemostatic mechanism, effects of deacetylation degree, relative molecular mass, and chemical modification on the hemostatic performance of CS hydrogels are summarized. Meanwhile, some typical applications of CS hydrogels are introduced to provide references for the preparation of efficient hemostatic hydrogels. Finally, the future perspectives of CS-based hemostatic hydrogels are presented.

Gelatin methacryloyl (GelMA) is a versatile material for a wide range of bioapplications. There is an intense interest in developing effective chemical strategies to prepare GelMA with a high degree of batch-to-batch consistency and controllability in terms of methacryloyl functionalization and physiochemical properties. Herein, we systematically investigated the batch-to-batch reproducibility and controllability of producing GelMA (target highly and lowly substituted versions) via a one-pot strategy. To assess the GelMA product, several parameters were evaluated, including the degree of methacryloylation, secondary structure, and enzymatic degradation, along with the mechanical properties and cell viability of GelMA hydrogels. The results showed that two types of target GelMA with five batches exhibited a high degree of controllability and reproducibility in compositional, structural, and functional properties owing to the highly controllable one-pot strategy.

Among modern drug formulations, stimuli-responsive hydrogels also called \"smart hydrogels\" deserve a special attention. The basic feature of this system is the ability to change their mechanical properties, swelling ability, hydrophilicity, bioactive molecules permeability, etc., influenced by various stimuli, such as temperature, pH, electromagnetic radiation, magnetic field and biological factors. Therefore, stimuli-responsive matrices can be potentially used in tissue engineering, cell cultures and technology of innovative drug delivery systems (DDSs), releasing the active substances under the control of internal or external stimuli. Moreover, smart hydrogels can be used as injectable DDSs, due to gel-sol transition connected with in situ cross-linking process. Innovative smart hydrogel DDSs can be utilized as matrices for targeted therapy, which enhances the effectiveness of tumor chemotherapy and subsequently limits systemic toxicity. External stimulus sensitivity allows remote control over the drug release profile and gel formation. On the other hand, internal factors provide drg accumulation in tumor tissue and reduce the concentration of active drug form in healthy tissue. In this report, we summarise the basic knowledge and chemical strategies for the synthetic smart hydrogel DDSs applied in antitumor therapy.

Los liposomas son vesículas nanométricas capaces de incluir moléculas hidrófilas o lipófilas como es el resveratrol, agente antioxidante y antitumoral de baja solubilidad y estabilidad que limita su utilidad clínica. La administración bucal evita estos inconvenientes y facilita su uso. El objetivo de este trabajo fue desarrollar liposomas con resveratrol incluidos en hidrogeles y películas bucales para su aplicación en la mucosa oral. Se probaron diferentes cantidades de alginato y glicerina y se seleccionaron las condiciones óptimas para los films con liposomas, que se obtuvieron por secado de los geles. Alginato al 3 % y glicerina al 2 % fueron las condiciones más favorables. Los hidrogeles exhibieron fácil extensibilidad, y los films elevada resistencia al plegado. El resveratrol se cuantificó mediante HPLC para estimar la eficacia de encapsulación en los liposomas y para establecer su perfil de liberación. Se produce una cinética de liberación controlada desde los hidrogeles y los films, sin diferencias significativas entre el alginato de algas y el alginato sódico para los films. Se concluye que los films con liposomas cargados de resveratrol constituyen una alternativa viable para el uso clínico de este polifenol, tanto para su aplicación tópica como sistémica a través de las mucosas.