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Open research questions in Hydrogels: synthesis, properties, applications

32 unresolved questions extracted from the limitations and future-work sections of 370 Hydrogels: synthesis, properties, applications papers in our library. Each links back to the study that raised it.

What the literature leaves open

  • Lignin is an abundant by-product of the pulp and paper industry, driving strong interest in lignin-based materials. Lignin-based hydrogels show promise in sensors and flexible energy storage. However, commercialization remains limited due to processing and performance challenges. Advances in scalable synthesis, functionalization, and interdisciplinary research are essential. The transition of lignin-based hydrogels from laboratory research to industrial production presents significant challenges alongside their promising potential. Large-scale manufacturing is hindered by reliance on batch polymerization processes that require precise control of parameters such as temperature, pH, and radical initiation, which are difficult to replicate consistently at scale. Additionally, variability in lignin feedstocks from different industrial sources complicates reproducibility, highlighting the need for standardized processing methods. Economic feasibility is another key concern, as lignin hydrogels must compete with petroleum-based materials by leveraging lignin’s low-cost and abundant availability. Regulatory requirements further add complexity, particularly for biomedical applications such as drug delivery, wound healing, and tissue engineering. Compliance with strict safety standards necessitates extensive evaluation of biocompatibility, cytotoxicity, degradation behavior, and long-term stability, along with assurance of batch-to-batch consistency and safe degradation products. Even environmental applications require validation of biodegradability and absence of ecotoxicity. Despite these barriers, lignin hydrogels remain highly promising due to advances in chemical modifications (e.g., esterification, sulfonation, etherification) and the development of hybrid and nanocomposite systems with materials like chitosan, cellulose nanofibers, graphene oxide, and metal nanoparticles. These strategies enhance mechanical, functional, and antibacterial properties, enabling applications in biosensing, soft electronics, and biomedical scaffolds. Furthermore, stimuli-responsive lignin hydrogels offer innovative opportunities in smart drug delivery and responsive biomedical devices. Overall, the future of lignin-based hydrogels depends on integrating advancements in material design, scalable processing technologies, regulatory compliance, and cost optimization, enabling their transformation into sustainable and commercially viable materials for diverse environmental and biomedical applications.

    Functional lignin hydrogels for biosensors and biomedical therapy · 2026 · DOI

  • 1 Limitation of the study Although present gel matrix provide a structural and synthetic roadmap for polyphenol integrated self cross-linked gel matrix useful for in vitro drug release study with sup- ported experimental and characterization results but there are certain limitations such as mechanical/tensile strength evaluation, in vivo cytotoxicity/cytocompatibility and in vivo drug release behaviour have not been studied.

    Synthesis, characterization and in vitro release kinetics of methotrexate from oxidized fenugreek gum/chitosan-catechin bionanocomposite hydrogel matrix · 2026 · DOI

  • Alginate-based hydrogels have emerged as promising multifunctional materials, particularly in antimicrobial applications, due to their excellent biocompatibility, biodegradability, and ability to form hydrogels under mild conditions. Their high water content, tunable mechanical strength, and structural flexibility enable efficient incorporation of various antimicrobial agents such as AgNPs, antimicrobial peptides, and essential oils. Among the different strategies reported, nanomaterial-based and hybrid composite systems have generally shown excellent antimicrobial performance and enhanced biofilm disruption compared to conventional formulations. These com- posite hydrogels not only inhibit microbial growth but also effectively disrupt resis- tant biofilms, addressing a major challenge in infection control. In comparison with single-component systems, multifunctional alginate-based composites demonstrate improved stability, sustained release behavior, and broader antimicrobial efficacy. Their versatility has been successfully translated into practical applications, including wound dressings that promote healing and prevent infection, drug delivery systems for controlled therapeutic release, and food packaging materials that enhance shelf 1 3Polymer Bulletin (2026) 83:422 422 Page 24 of 29 life and safety. Overall, the most promising developments reported in recent stud- ies involve synergistic combinations of alginate with nanomaterials, bioactive com- pounds, and stimuli-responsive systems, which significantly enhance antimicrobial efficiency and functional performance. Looking forward, the development of next- generation alginate-based hydrogels will likely focus on enhancing targeted delivery, responsiveness to environmental stimuli, and long-term stability. Research should also explore the synergy between alginate and emerging antimicrobial agents, includ- ing nanomaterials and plant-derived compounds, to overcome microbial resistance. Furthermore, large-scale manufacturing techniques and regulatory considerations must be addressed to facilitate clinical and commercial translation. The integration of alginate hydrogels with smart technologies, such as sensors or stimuli-responsive systems, may open new frontiers in real-time infection monitoring and treatment. Author contributions Dr. Muhanad Alhujaily: Writing-review & editing, Critical revision & Validation. Prof. Alaa Shafie: Supervision, Validation & Critical revision. Mohammed Sanad Alhussaini: Supervision & Writing original draft. AbdulRahman Abdulla Ibrahim Alyahya: Investigation & Visualization. Funding This work was supported and funded by the Deanship of Scientific Research at Imam Moham- mad Ibn Saud Islamic University (IMSIU) (grant number IMSIU-DDRSP2601). Data availability No datasets were generated or analysed during the current study.

    Multifunctional alginate-based hydrogels with antimicrobial activity and applications: a comprehensive review · 2026 · DOI

  • Living character enables predictable molar mass; narrow dispersity (Ð ≈ 1.02–1.22); broad monomer scope including chiral and substituted oxazolines; end-group functionalization possible; reproducible homopolymer…

    Poly(2-oxazoline)s: a versatile polymers shaping the future of biomedical innovations · 2026 · DOI

  • Linear polymers with amidecontaining backbone; tunable properties via 2-substitution; good thermal and chemical stability; suitable for films and coatings Simple catalystfree route; strong adhesion and film-forming properties; high chemical and thermal resistance Efficient formation of longchain polymers; good mechanical strength and thermal stability; useful for resins…

    Poly(2-oxazoline)s: a versatile polymers shaping the future of biomedical innovations · 2026 · DOI

  • Biodegradation pathways and degradation kinetics of eutectogels, particularly those containing functionalized DES components or hybrid polymeric networks, have not been thoroughly characterized for biomedical applications requiring controlled dissolution.

    Eutectogel-Based Drug Delivery Systems: Recent Advancements and Pharmaceutical Applications · 2026 · DOI

  • Trade-offs between mechanical properties and ionic conductivity in eutectogels have been identified but not systematically characterized; quantitative structure-property relationship studies are needed to predict how DES composition affects both mechanical robustness and functionality in drug delivery applications.

    Eutectogel-Based Drug Delivery Systems: Recent Advancements and Pharmaceutical Applications · 2026 · DOI

  • Regulatory pathways for novel hybrid eutectogel systems combining DES with polymeric, inorganic, or supramolecular components remain undefined; case-by-case regulatory assessment approaches increase approval time and costs for these hybrid drug delivery platforms.

    Eutectogel-Based Drug Delivery Systems: Recent Advancements and Pharmaceutical Applications · 2026 · DOI

  • Continuous, solvent-free, or standardized production methods for eutectogels have not been developed at scale; upscaling processes such as 3D printing and electrospinning for eutectogel drug delivery systems require validation to maintain consistent composition, mechanical strength, and solvent retention.

    Eutectogel-Based Drug Delivery Systems: Recent Advancements and Pharmaceutical Applications · 2026 · DOI

  • Long-term aging and storage stability data for eutectogels are scarce; systematic investigations tracking phase separation, syneresis, and solvent evaporation mechanisms over extended periods are needed to guide material optimization for drug delivery applications.

    Eutectogel-Based Drug Delivery Systems: Recent Advancements and Pharmaceutical Applications · 2026 · DOI

  • Comprehensive cytotoxicity and hemocompatibility studies are needed to characterize the interactions between specific DES components (hydrogen-bond donors/acceptors) and blood components, as current research shows variable toxicity profiles across different DES formulations used in eutectogels.

    Eutectogel-Based Drug Delivery Systems: Recent Advancements and Pharmaceutical Applications · 2026 · DOI

  • The paper demonstrates that understanding gel-confinement contact pressure and contact area evolution is fundamental for tuning and designing of gel-based smart and active devices, but specific applications in chemo-mechanical sensing, drug delivery, tissue engineering, soft robotics, and cultural heritage conservation require further development.

    Mechanics of confined swelling in hydrogels · 2026 · DOI

  • Alternative gelation methods beyond ionic gelation, including cryogelation, non-solvent phase separation, CO2 induced crosslinking, and photo induced crosslinking, offer potential for customized drug delivery systems and scaffolds, but their optimization and comparative efficacy require further investigation.

    Alginate-Based Hydrogels and Particulate Systems: Preparation Techniques, Adaptations, and Utilizations in Pharmaceutical Delivery and Biomedical Research · 2026 · DOI

  • The evolution of smart polymer systems is moving rapidly from proof-of-concept lab studies to real-world biomedical applications, driven by cross-disciplinary innovation in materials science, biotechnology, and data intelligence. The next generation of smart polymers goes beyond single- trigger responses. Logic-based systems are being engineered to react to combinations of physiological signals—such as pH, temperature, enzymes, or redox gradients—allowing precise “AND/OR” gate-style control over drug release 85. This mimics the body’s own regulatory mechanisms, opening doors to more personalized and adaptive therapies. Artificial intelligence (AI) and machine learning are set to become core design tools for smart polymer development. Predictive modeling enables rapid optimization of polymer composition, crosslinking density, and stimulus-response kinetics 86. This shortens development timelines, reduces trial-and-error experimentation, and guides formulation toward clinically relevant endpoints. Smart hydrogels are transforming tissue engineering and regenerative medicine. By responding to cellular activity or microenvironmental cues, they can release growth factors and bioactive molecules in situ, creating dynamic scaffolds that support tissue growth, repair, and vascularization. 3D bioprinting technologies further enable customizable architectures for patient-specific implants 87. The focus of translational research is shifting toward long-acting injectables, implantable depots, and stimulus-sensitive devices. Early-stage human trials are already underway for smart insulin delivery systems, tumor-targeted nanocarriers, and adaptive wound dressings. Regulatory engagement, manufacturing scale-up, and robust safety profiling will be key to bridging the gap from bench to bedside 88.

    Smart Polymers in Pharmaceutical Sciences: Stimuli-Responsive Systems for Targeted Drug Release · 2026 · DOI

  • We further discuss practical hurdles facing clinical translation, noting that sterilization often degrades these materials, mechanical properties may prove inadequate under masticatory loads, and long-term biosafety data remains limited.

    Smart Thermosensitive Hydrogel Coatings for Oral Biomedicine: A Review from Environmental Adaptation to Therapy · 2026 · DOI

  • The evidence base at present is largely derived from in vitro and short-term small animal studies, which are insufficient to predict clinical safety or efficacy.

    Hydrogel-based strategies for dentin–pulp complex regeneration: a comprehensive review · 2026 · DOI

  • 5 g of Stockosorb® 400K is an effective tool for improving the biomass, it is insufficient as a standalone drought- mitigation tool for extreme moisture-deficit events.

    Evaluating hydrogel efficacy on biomass and survival of Casuarina equisetifolia L. and Grevillea robusta A. Cunn. ex R. Br. seedlings · 2026 · DOI

  • Moreover, the precise matching principles between crosslinking mechanisms and repair scenarios remain unclear, leading to trial-and-error-based material selection and hindering clinical translation.

    Comparative Review on Crosslinking Mechanisms of Injectable Hydrogels and Their Research Progress in Minimally Invasive Tissue Repair · 2026 · DOI

  • A more refined theoretical model is needed that accounts for non-homogeneous stress distribution within the gel, particularly for cases with limited contact area extension.

    Mechanics of confined swelling in hydrogels · 2026 · DOI

  • The main source of inaccuracy of the proposed model is due to the lack of homogeneity in the stress state within the gel, which causes the model to overestimate contact stress when the contact area has limited extension compared to the transversal cross section.

    Mechanics of confined swelling in hydrogels · 2026 · DOI

  • The difference between theoretical results and experimental contact stress is quite large, especially when the contact area has limited extension, since it is not correct to assume the contact stress to be homogeneously distributed inside the gel.

    Mechanics of confined swelling in hydrogels · 2026 · DOI

  • Alginate-based composites for intelligent and active packaging in the food industry, and for environmental cleanup of heavy metals from wastewater, represent emerging applications that require further development and validation.

    Alginate-Based Hydrogels and Particulate Systems: Preparation Techniques, Adaptations, and Utilizations in Pharmaceutical Delivery and Biomedical Research · 2026 · DOI

  • Sodium alginate beads exhibit pH-dependent stability with decreased resistance in alkaline conditions and vulnerability to structural changes in both acidic and neutral settings, indicating a need for improved stability formulations.

    Alginate-Based Hydrogels and Particulate Systems: Preparation Techniques, Adaptations, and Utilizations in Pharmaceutical Delivery and Biomedical Research · 2026 · DOI

  • Hydrogel from cassava peel and chitosan shows promise as a bioadsorbent for domestic wastewater treatment, but its capacity and optimal production temperature have not been fully studied.

    UTILIZATION OF CASSAVA PEEL AND CHITOSAN FOR THE PRODUCTION OF HYDROGEL AS A SUSTAINABLE SOLUTION FOR DOMESTIC WASTEWATER TREATMENT · 2024 · DOI

  • The relevance of such study is due to the fact that the kinetics of swelling and contraction of hydrogels in various media has been studied in many works, however, this question remains insufficiently studied.

    Some peculiarities of the kinetics of interaction of cationic hydrogels based on copolymers of vinyl esters of monoethanolamine and ethylene glycol with copper ions · 2021 · DOI

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32 open questions have been extracted from the limitations and future-work passages of 370 Hydrogels: synthesis, properties, applications papers in our library. Each one below links back to the study that raised it, so you can read the original claim in context.

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