Tough Composite Hydrogels with High Loading and Local Release of Biological Drugs

Penetration enhancers strengthen tough hydrogel bioadhesion and modulate locoregional drug delivery

The human body possesses natural barriers, such as skin and mucosa, which limit the effective delivery of therapeutics and integration of medical devices to target tissues. Various strategies have been deployed to breach these barriers mechanically, chemically, or electronically. The development of various penetration enhancers (PEs) offers a promising solution due to their ability to increase tissue permeability using readily available reagents. However, existing PE-mediated delivery methods often rely on weak gel or liquid drug formulations, which are not ideal for sustained local delivery. Hydrogel adhesives that can seamlessly interface biological tissues with controlled drug delivery could potentially resolve these issues. Here, we demonstrate that tough adhesion between drug-laden hydrogels and biological tissue (e.g. skin and tumours) can lead to effective local delivery of drugs deep into targeted tissues by leveraging the enhanced tissue penetration mediated by PEs. The drug release profile of the hydrogel adhesives can be fine-tuned by further engineering the nanocomposite hydrogel matrix to elute chemotherapeutics from 2 weeks to 2 months. Using a 3D tumour spheroid model, we demonstrated that PEs increased the cancer-killing effectiveness of doxorubicin by facilitating its delivery into tumour microtissues. Therefore, the proposed tough bioadhesion and drug delivery strategy modulated by PEs holds promise as a platform technique to develop next-generation wearable and implantable devices for cancer management and regenerative medicine.

Laponite nanoclays for the sustained delivery of therapeutic proteins

Protein therapeutics hold immense promise for treating a wide array of diseases. However, their efficacy is often compromised by rapid degradation and clearance. The synthetic smectite clay Laponite emerges as a promising candidate for their sustained delivery. Despite its unique properties allow to load and release proteins mitigating burst release and extending their effects, precise control over Laponite-protein interactions remains challenging since it depends on a complex interplay of factors whose implication is not fully understood yet. The aim of this review article is to shed light on this issue, providing a comprehensive discussion of the factors influencing protein loading and release, including the physicochemical properties of the nanoclay and proteins, pH, dispersion buffer, clay/protein concentration and Laponite degradation. Furthermore, we thoroughly revise the array of bioactive proteins that have been delivered from formulations containing the nanoclay, highlighting Laponite-polymer nanocomposite hydrogels, a promising avenue currently under extensive investigation.

Development of dual-crosslinked Pluronic F127/Chitosan injectable hydrogels incorporating graphene nanosystems for breast cancer photothermal therapy and antibacterial applications

Nanomaterials with responsiveness to near-infrared light can mediate the photoablation of cancer cells with an exceptional spatio-temporal resolution. However, the therapeutic outcome of this modality is limited by the nanostructures' poor tumor uptake. To address this bottleneck, it is appealing to develop injectable in situ forming hydrogels due to their capacity to perform a tumor-confined delivery of the nanomaterials with minimal off-target leakage. In particular, injectable in situ forming hydrogels based on Pluronic F127 have been emerging due to their FDA-approval status, biocompatibility, and thermosensitive sol-gel transition. Nevertheless, the application of Pluronic F127 hydrogels has been limited due to their fast dissociation in aqueous media. Such limitation may be addressed by combining the thermoresponsive sol-gel transition of Pluronic F127 with other polymers with crosslinking capabilities. In this work, a novel dual-crosslinked injectable in situ forming hydrogel based on Pluronic F127 (thermosensitive gelation) and Chitosan (ionotropic gelation in the presence of NaHCO3), loaded with Dopamine-reduced graphene oxide (DOPA-rGO; photothermal nanoagent), was developed for application in breast cancer photothermal therapy. The dual-crosslinked hydrogel incorporating DOPA-rGO showed a good injectability (through 21 G needles), in situ gelation capacity and cytocompatibility (viability > 73 %). As importantly, the dual-crosslinking improved the hydrogel's porosity and prevented its premature degradation. After irradiation with near-infrared light, the dual-crosslinked hydrogel incorporating DOPA-rGO produced a photothermal heating (ΔT ≈ 22 °C) that reduced the breast cancer cells' viability to just 32 %. In addition, this formulation also demonstrated a good antibacterial activity by reducing the viability of S. aureus and E. coli to 24 and 33 %, respectively. Overall, the dual-crosslinked hydrogel incorporating DOPA-rGO is a promising macroscale technology for breast cancer photothermal therapy and antimicrobial applications.

Immunomodulatory hydrogel orchestrates pro-regenerative response of macrophages and angiogenesis for chronic wound healing

Chronic wound healing often encounters challenges characterized by prolonged inflammation and impaired angiogenesis. While the immune response plays a pivotal role in orchestrating the intricate process of wound healing, excessive inflammation can hinder tissue repair. In this study, a bilayer alginate hydrogel system encapsulating polyelectrolyte complex nanoparticles (PCNs) loaded with anti-inflammatory cytokines and angiogenic growth factors is developed to address the challenges of chronic wound healing. The alginate hydrogel is designed using two distinct crosslinking methods to achieve differential degradation, thereby enabling precise spatial and temporal controlled release of PCNs. Initially, interleukin-10 (IL-10) is released to mitigate inflammation, while unsaturated PCNs bind and remove accumulated pro-inflammatory cytokines at the wound site. Subsequently, angiogenic growth factors, including vascular endothelial growth factor and platelet-derived growth factor, are released to promote vascularization and vessel maturation. Our results demonstrate that the bilayer hydrogel exhibits distinct degradation kinetics between the two layers, facilitating the staged release of multiple signaling molecules. In vitro experiments reveal that IL-10 can activate the Jak1/STAT3 pathway, thereby suppressing pro-inflammatory cytokines and chemokines while down-regulating inflammation-related genes. In vivo studies demonstrate that application of the hydrogel in chronic wounds using diabetic murine model promotes healing by positively modulating multiple integral reparative mechanisms. These include reducing inflammation, promoting macrophage polarization towards a pro-regenerative phenotype, enhancing keratinocyte migration, stimulating angiogenesis, and expediting wound closure. In conclusion, our hydrogel system effectively mitigates inflammatory responses and provides essential physiological cues by inducing a synergistic angiogenic effect, thus offering a promising approach for the treatment of chronic wounds.

Hybrid Nanoparticle-Hydrogel Systems for Drug Delivery Depots and Other Biomedical Applications

Hydrogel-based depots typically tend to remain where injected and have excellent biocompatibility but are relatively poor at controlling drug release. Nanoparticles (NPs) typically have the opposite properties. The smaller the NPs are, the more likely they are to leave the site of injection. Their biocompatibility is variable depending on the material but can be poor. However, NPs can be good at controlling drug release. In these and other properties, combining NPs and hydrogels can leverage their advantages and negate their disadvantages. This review highlights the rationale for hybrid NP-hydrogel systems in drug delivery, the basic methods of producing them, and examples where combining the two systems addressed specific problems.

Nanoclay-Composite Hydrogels for Bone Tissue Engineering

Nanoclay-composite hydrogels represent a promising avenue for advancing bone tissue engineering. Traditional hydrogels face challenges in providing mechanical strength, biocompatibility, and bioactivity necessary for successful bone regeneration. The incorporation of nanoclay into hydrogel matrices offers a potential unique solution to these challenges. This review provides a comprehensive overview of the fabrication, physico-chemical/biological performance, and applications of nanoclay-composite hydrogels in bone tissue engineering. Various fabrication techniques, including in situ polymerization, physical blending, and 3D printing, are discussed. In vitro and in vivo studies evaluating biocompatibility and bioactivity have demonstrated the potential of these hydrogels for promoting cell adhesion, proliferation, and differentiation. Their applications in bone defect repair, osteochondral tissue engineering and drug delivery are also explored. Despite their potential in bone tissue engineering, nanoclay-composite hydrogels face challenges such as optimal dispersion, scalability, biocompatibility, long-term stability, regulatory approval, and integration with emerging technologies to achieve clinical application. Future research directions need to focus on refining fabrication techniques, enhancing understanding of biological interactions, and advancing towards clinical translation and commercialization. Overall, nanoclay-composite hydrogels offer exciting opportunities for improving bone regeneration strategies.

Progress of polysaccharide-based tissue adhesives

Recently, polymer-based tissue adhesives (TAs) have gained the attention of scientists and industries as alternatives to sutures for sealing and closing wounds or incisions because of their ease of use, low cost, minimal tissue damage, and short application time. However, poor mechanical properties and weak adhesion strength limit the application of TAs, although numerous studies have attempted to develop new TAs with enhanced performance. Therefore, next-generation TAs with improved multifunctional properties are required. In this review, we address the requirements of polymeric TAs, adhesive characteristics, adhesion strength assessment methods, adhesion mechanisms, applications, advantages and disadvantages, and commercial products of polysaccharide (PS)-based TAs, including chitosan (CS), alginate (AL), dextran (DE), and hyaluronic acid (HA). Additionally, future perspectives are discussed.

Laponite for biomedical applications: An ophthalmological perspective

Clay minerals have been applied in biomedicine for thousands of years. Laponite is a nanostructured synthetic clay with the capacity to retain and progressively release drugs. In recent years there has been a resurgence of interest in Laponite application in various biomedical areas. This is the first paper to review the potential biomedical applications of Laponite in ophthalmology. The introduction briefly covers the physical, chemical, rheological, and biocompatibility features of different routes of administration. After that, emphasis is placed on 1) drug delivery for antibiotics, anti-inflammatories, growth factors, other proteins, and cancer treatment; 2) bleeding prevention or treatment; and 3) tissue engineering through regenerative medicine using scaffolds in intraocular and extraocular tissue. Although most scientific research is not performed on the eye, both the findings and the new treatments resulting from that research are potentially applicable in ophthalmology since many of the drugs used are the same, the tissue evaluated in vitro or in vivo is also present in the eye, and the pathologies treated also occur in the eye. Finally, future prospects for this emerging field are discussed.

pH-responsive scaffolds for tissue regeneration: In vivo performance

A myriad of pH-sensitive scaffolds has been reported in recent decades. Information on their behaviour in vitro under conditions that mimic the pH changes that occur during tissue regeneration is abundant. Differently, the in vivo demonstration of the advantages of pH-responsive systems in comparison with non-responders is more limited. The in vivo scenario is very complex and the intricate relationship between the host response, the overall pathological conditions of the patient, and the risk of colonization by microorganisms is very difficult to imitate in in vitro tests. This review aims to shed light on how the changes in pH between healthy and damaged states and also during the healing process have been exploited so far to develop polymer-based scaffolds that actively contribute in vivo to the healing process avoiding chronification. The main strategies so far tested to prepare pH-responsive scaffolds rely on (i) changes in ionization of natural polymers, ionizable monomers and clays, (ii) reversible cross-linkers, (iii) coatings, and (iv) production of CO2 gas. These strategies are analysed in detail in this review with the description of relevant examples of their performance on specific animal models. The versatility of the techniques used to prepare biocompatible and environment-friendly pH-responsive scaffolds that have been implemented in the last decade may pave the way for a successful translation to the clinic. STATEMENT OF SIGNIFICANCE: We report here on the most recent advances in pH-responsive polymer-based scaffolds that have been demonstrated in vivo to be suitable for wound and bone healing. pH is a critical variable in the tissue regeneration process, and small changes can speed up or completely stop the process. Although there is still a paucity of information on the performance in the complex in vivo environment, recently reported achievements using scaffolds endowed with pH-responsiveness through ionic natural polymers, ionizable monomers and clays, reversible cross-linkers, coatings, or formation of CO2 ensure a promising future towards clinical translation.

Novel HALO® image analysis to determine cell phenotype in porous precision-templated scaffolds

Image analysis platforms have gained increasing popularity in the last decade for the ability to automate and conduct high-throughput, multiplex, and quantitative analyses of a broad range of pathological tissues. However, imaging tissues with unique morphology or tissues containing implanted biomaterial scaffolds remain a challenge. Using HALO®, an image analysis platform specialized in quantitative tissue analysis, we have developed a novel method to determine multiple cell phenotypes in porous precision-templated scaffolds (PTS). PTS with uniform spherical pores between 30 and 40 μm in diameter have previously exhibited a specific immunomodulation of macrophages toward a pro-healing phenotype and an overall diminished foreign body response (FBR) compared to PTS with larger or smaller pore sizes. However, signaling pathways orchestrating this pro-healing in 40 μm PTS remain unclear. Here, we use HALO® to phenotype PTS resident cells and found a decrease in pro-inflammatory CD86 and an increase in pro-healing CD206 expression in 40 μm PTS compared to 100 μm PTS. To understand the mechanisms that drive these outcomes, we investigated the role of myeloid-differentiation-primary-response gene 88 (MyD88) in regulating the pro-healing phenomenon observed only in 40 μm PTS. When subcutaneously implanted in MyD88KO mice, 40 μm PTS reduced the expression of CD206, and the scaffold resident cells displayed an average larger nuclear size compared to 40 μm PTS implanted in mice expressing MyD88. Overall, this study demonstrates a novel image analysis method for phenotyping cells within PTS and identifies MyD88 as a critical mediator in the pore-size-dependent regenerative healing and host immune response to PTS.

Drug Delivery Approaches to Improve Tendon Healing

Tendon injuries disrupt the transmission of forces from muscle to bone, leading to chronic pain, disability, and a large socioeconomic burden. Tendon injuries are prevalent; there are over 300,000 tendon repair procedures a year in the United States to address acute trauma or chronic tendinopathy. Successful restoration of function after tendon injury remains challenging clinically. Despite improvements in surgical and physical therapy techniques, the high complication rate of tendon repair procedures motivates the use of therapeutic interventions to augment healing. While many biological and tissue engineering approaches have attempted to promote scarless tendon healing, there is currently no standard clinical treatment to improve tendon healing. Moreover, the limited efficacy of systemic delivery of several promising therapeutic candidates highlights the need for tendon-specific drug delivery approaches to facilitate translation. This review article will synthesize the current state-of-the-art methods that have been used for tendon-targeted delivery through both systemic and local treatments, highlight emerging technologies used for tissue-specific drug delivery in other tissue systems, and outline future challenges and opportunities to enhance tendon healing through targeted drug delivery.

Bioactive and Elastic Emulsion Electrospun DegraPol Tubes Delivering IGF-1 for Tendon Rupture Repair

Tendon injuries can result in two major drawbacks. Adhesions to the surrounding tissue may limit the range of motion, while fibrovascular scar formation can lead to poor biomechanical outcomes. Prosthetic devices may help to mitigate those problems. Emulsion electrospinning was used to develop a novel three-layer tube based on the polymer DegraPol (DP), with incorporated insulin-like growth factor-1 (IGF-1) in the middle layer. Scanning electron microscopy was utilized to assess the fiber diameter in IGF-1 containing pure DP meshes. Further characterization was performed with Fourier Transformed Infrared Spectroscopy, Differential Scanning Calorimetry, and water contact angle, as well as through the assessment of mechanical properties and release kinetics from ELISA, and the bioactivity of IGF-1 by qPCR of collagen I, ki67, and tenomodulin in rabbit Achilles tenocytes. The IGF-1-containing tubes exhibited a sustained release of the growth factor up to 4 days and showed bioactivity by significantly upregulated ki67 and tenomodulin gene expression. Moreover, they proved to be mechanically superior to pure DP tubes (significantly higher fracture strain, failure stress, and elastic modulus). The novel three-layer tubes intended to be applied over conventionally sutured tendons after a rupture may help accelerate the healing process. The release of IGF-1 stimulates proliferation and matrix synthesis of cells at the repair site. In addition, adhesion formation to surrounding tissue can be reduced due to the physical barrier.

Laponite-Based Nanocomposite Hydrogels for Drug Delivery Applications

Hydrogels are widely used for therapeutic delivery applications due to their biocompatibility, biodegradability, and ability to control release kinetics by tuning swelling and mechanical properties. However, their clinical utility is hampered by unfavorable pharmacokinetic properties, including high initial burst release and difficulty in achieving prolonged release, especially for small molecules (<500 Da). The incorporation of nanomaterials within hydrogels has emerged as viable option as a method to trap therapeutics within the hydrogel and sustain release kinetics. Specifically, two-dimensional nanosilicate particles offer a plethora of beneficial characteristics, including dually charged surfaces, degradability, and enhanced mechanical properties within hydrogels. The nanosilicate-hydrogel composite system offers benefits not obtainable by just one component, highlighting the need for detail characterization of these nanocomposite hydrogels. This review focuses on Laponite, a disc-shaped nanosilicate with diameter of 30 nm and thickness of 1 nm. The benefits of using Laponite within hydrogels are explored, as well as examples of Laponite-hydrogel composites currently being investigated for their ability to prolong the release of small molecules and macromolecules such as proteins. Future work will further characterize the interplay between nanosilicates, hydrogel polymer, and encapsulated therapeutics, and how each of these components affect release kinetics and mechanical properties.

Fibrous dressing containing bioactive glass with combined chemotherapy and wound healing promotion for post-surgical treatment of melanoma

Surgery is the mainstream treatment for melanoma. However, inappropriate post-surgical treatment could result in the tumor recurrence and sever tissue damage, which ultimately leads to the failure of therapy and significantly compromises the therapeutic outcome of surgery. Herein, taking advantages of the co-axial electrospinning technology, we construct a dual-function nanofibrous wound dressing for the post-surgical treatment of melanoma. Si-Ca-P-based mesoporous bioactive glass (MBG) was prepared by the template-sol-gel process, with the compositions being set as 60 SiO₂: 36 CaO: 4 P₂O₅ in mol%. Through rational design, 5-fluorouracil (5-FU)-loaded MBG nanoparticles (MBG-U) are successfully incorporated into the fiber core with biodegradable poly(lactic-co-glycolic acid) (PLGA) as the cladding layer to form the core-shell nanofibers (MBG-U CSF), which achieves sustained releases of chemotherapeutic drug (i.e.,5-FU) and wound healing promotion function. Thereafter, the post-surgical melanoma model was established to evaluate the in-situ anti-cancer and wound healing effect of MBG-U CSF. Thereafter, the post-surgical melanoma model was established to evaluate the anti-cancer and wound healing effect. The results demonstrated that the core-shell nanofibrous dressing almost complete suppressed tumor growth, and simultaneously promoted skin regeneration, which provides a promising strategy for the post-surgical treatment for melanoma.

Applications of functionally-adapted hydrogels in tendon repair

Despite all the efforts made in tissue engineering for tendon repair, the management of tendon injuries still poses a challenge, as current treatments are unable to restore the function of tendons following injuries. Hydrogels, due to their exceptional biocompatibility and plasticity, have been extensively applied and regarded as promising candidate biomaterials in tissue regeneration. Varieties of approaches have designed functionally-adapted hydrogels and combined hydrogels with other factors (e.g., bioactive molecules or drugs) or materials for the enhancement of tendon repair. This review first summarized the current state of knowledge on the mechanisms underlying the process of tendon healing. Afterward, we discussed novel strategies in fabricating hydrogels to overcome the issues frequently encountered during the applications in tendon repair, including poor mechanical properties and undesirable degradation. In addition, we comprehensively summarized the rational design of hydrogels for promoting stem-cell-based tendon tissue engineering via altering biophysical and biochemical factors. Finally, the role of macrophages in tendon repair and how they respond to immunomodulatory hydrogels were highlighted.

Controlled Delivery of Corticosteroids Using Tunable Tough Adhesives

Hydrogel-based drug delivery systems typically aim to release drugs locally to tissue in an extended manner. Tissue adhesive alginate-polyacrylamide tough hydrogels are recently demonstrated to serve as an extended-release system for the corticosteroid triamcinolone acetonide. Here, the stimuli-responsive controlled release of triamcinolone acetonide from the alginate-polyacrylamide tough hydrogel drug delivery systems (TADDS) and evolving new approaches to combine alginate-polyacrylamide tough hydrogel with drug-loaded nano and microparticles, generating composite TADDS is described. Stimulation with ultrasound pulses or temperature changes is demonstrated to control the release of triamcinolone acetonide from the TADDS. The incorporation of laponite nanoparticles or PLGA microparticles into the tough hydrogel is shown to further enhance the versatility to control and modulate the release of triamcinolone acetonide. A first technical exploration of a TADDS shelf-life concept is performed using lyophilization, where lyophilized TADDS are physically stable and the bioactive integrity of released triamcinolone acetonide is demonstrated. Given the tunability of properties, the TADDS are a suggested technology platform for controlled drug delivery.

Enhanced tendon healing by a tough hydrogel with an adhesive side and high drug-loading capacity

Hydrogels that provide mechanical support and sustainably release therapeutics have been used to treat tendon injuries. However, most hydrogels are insufficiently tough, release drugs in bursts, and require cell infiltration or suturing to integrate with surrounding tissue. Here we report that a hydrogel serving as a high-capacity drug depot and combining a dissipative tough matrix on one side and a chitosan adhesive surface on the other side supports tendon gliding and strong adhesion (larger than 1,000 J m-2) to tendon on opposite surfaces of the hydrogel, as we show with porcine and human tendon preparations during cyclic-friction loadings. The hydrogel is biocompatible, strongly adheres to patellar, supraspinatus and Achilles tendons of live rats, boosted healing and reduced scar formation in a rat model of Achilles-tendon rupture, and sustainably released the corticosteroid triamcinolone acetonide in a rat model of patellar tendon injury, reducing inflammation, modulating chemokine secretion, recruiting tendon stem and progenitor cells, and promoting macrophage polarization to the M2 phenotype. Hydrogels with 'Janus' surfaces and sustained-drug-release functionality could be designed for a range of biomedical applications.

Clay-Based Nanocomposite Hydrogels for Biomedical Applications: A Review

In recent decades, new and improved materials have been developed with a significant interest in three-dimensional (3D) scaffolds that can cope with the diverse needs of the expanding biomedical field and promote the required biological response in multiple applications. Due to their biocompatibility, ability to encapsulate and deliver drugs, and capacity to mimic the extracellular matrix (ECM), typical hydrogels have been extensively investigated in the biomedical and biotechnological fields. The major limitations of hydrogels include poor mechanical integrity and limited cell interaction, restricting their broad applicability. To overcome these limitations, an emerging approach, aimed at the generation of hybrid materials with synergistic effects, is focused on incorporating nanoparticles (NPs) within polymeric gels to achieve nanocomposites with tailored functionality and improved properties. This review focuses on the unique contributions of clay nanoparticles, regarding the recent developments of clay-based nanocomposite hydrogels, with an emphasis on biomedical applications.

Acetic Acid Enables Precise Tailoring of the Mechanical Behavior of Protein-Based Hydrogels

Engineering viscoelastic and biocompatible materials with tailored mechanical and microstructure properties capable of mimicking the biological stiffness (<17 kPa) or serving as bioimplants will bring protein-based hydrogels to the forefront in the biomaterials field. Here, we introduce a method that uses different concentrations of acetic acid (AA) to control the covalent tyrosine-tyrosine cross-linking interactions at the nanoscale level during protein-based hydrogel synthesis and manipulates their mechanical and microstructure properties without affecting protein concentration and (un)folding nanomechanics. We demonstrated this approach by adding AA as a precursor to the preparation buffer of a photoactivated protein-based hydrogel mixture. This strategy allowed us to synthesize hydrogels made from bovine serum albumin (BSA) and eight repeats protein L structure, with a fine-tailored wide range of stiffness (2-35 kPa). Together with protein engineering technologies, this method will open new routes in developing and investigating tunable protein-based hydrogels and extend their application toward new horizons.

Advances toward transformative therapies for tendon diseases

Approved therapies for tendon diseases have not yet changed the clinical practice of symptomatic pain treatment and physiotherapy. This review article summarizes advances in the development of novel drugs, biologic products, and biomaterial therapies for tendon diseases with perspectives for translation of integrated therapies. Shifting from targeting symptom relief toward disease modification and prevention of disease progression may open new avenues for therapies. Deep evidence-based clinical, cellular, and molecular characterization of the underlying pathology of tendon diseases, as well as therapeutic delivery optimization and establishment of multidiscipline interorganizational collaboration platforms, may accelerate the discovery and translation of transformative therapies for tendon diseases.

Laponite-Based Nanomaterials for Drug Delivery

Laponite is a clay-based material composed of synthetic disk-shaped crystalline nanoparticles with highly ionic, large surface area. These characteristics enable the intercalation and dissolution of biomolecules in Laponite-based drug delivery systems. Furthermore, Laponite's innate physicochemical properties and architecture enable the development of tunable pH-responsive drug delivery systems. Laponite's coagulation capacity and cation exchangeability determine its exchange capabilities, drug encapsulation efficiency, and release profile. These parameters are exploited to design highly controlled and efficacious drug delivery platforms for sustained drug release. In this review, they provide an overview of how to design efficient delivery of therapeutics by leveraging the properties and specific interactions of various Laponite-polymer composites and drug moieties.

The role of the tendon ECM in mechanotransduction: disruption and repair following overuse

Purpose: Tendon overuse injuries are prevalent conditions with limited therapeutic options to halt disease progression. The specialized extracellular matrix (ECM) both enables joint function and mediates mechanical signals to tendon cells, driving biological responses to exercise or injury. With overuse, tendon ECM composition and structure changes at multiple scales, disrupting mechanotransduction and resulting in inadequate repair and disease progression. This review highlights the multiscale ECM changes that occur with tendon overuse and corresponding effects on cell-matrix interactions and cellular response to load.Results: Different functional joint requirements and tendon types experience a wide range of loading profiles, creating varied downstream mechanical stimuli. Distinct ECM structure and mechanical properties within the fascicle matrix, interfascicle matrix, and enthesis and their varied disruption with overuse are considered. The pericellular matrix (PCM) comprising the microscale tendon cell environment has a unique composition that changes with overuse injury and exercise, suggesting an important role in mechanotransduction and promoting repair. Cell-matrix interactions are mediated by structures including cilia, integrins, connexins and cytoskeleton that signal downstream homeostasis, adaptation, or repair. ECM disruption with tendon overuse may cause altered mechanical loading and cell-matrix interactions, resulting in mechanobiological understimulation, apoptosis, and ineffective repair. Current interventions to promote repair of tendon overuse injuries including exercise, targeting cell signaling, and modulating inflammation are considered.Conclusion: Future therapeutics should be assessed with regard of their effects on multiscale mechanotransduction in addition to joint function, with consideration of the central role of ECM.

Nanoclay Reinforced Biomaterials for Mending Musculoskeletal Tissue Disorders

Nanoclay-reinforced biomaterials have sparked a new avenue in advanced healthcare materials that can potentially revolutionize treatment of musculoskeletal defects. Native tissues display many important chemical, mechanical, biological, and physical properties that engineered biomaterials need to mimic for optimal tissue integration and regeneration. However, it is time-consuming and difficult to endow such combinatorial properties on materials via feasible and nontoxic procedures. Fortunately, a number of nanomaterials such as graphene, carbon nanotubes, MXenes, and nanoclays already display a plethora of material properties that can be transferred to biomaterials through a simple incorporation procedure. In this direction, the members of the nanoclay family are easy to functionalize chemically, they can significantly reinforce the mechanical performance of biomaterials, and can provide bioactive properties by ionic dissolution products to upregulate cartilage and bone tissue formation. For this reason, nanoclays can become a key component for future orthopedic biomaterials. In this review, we specifically focus on the rapidly decreasing gap between clinic and laboratory by highlighting their application in a number of promising in vivo studies.

Polyacrylamide/Chitosan-Based Conductive Double Network Hydrogels with Outstanding Electrical and Mechanical Performance at Low Temperatures

Hydrogel-based electronics have received growing attention because of their great flexibility and stretchability. However, the fabrication of conductive hydrogels with high stretchability, excellent toughness, outstanding sensitivity, and low-temperature stability still remains a great challenge. In this study, a type of conductive hydrogels consisting of a double network (DN) structure is synthesized. The dynamically cross-linked chitosan (CS) and the flexible polyacrylamide network doped with polyaniline constitute the DN through the hydrogen bonds between the hydroxyl, amide, and aniline groups. This type of hydrogels displays excellent mechanical performance, striking conductivity, and remarkable freezing tolerance. The flexible electronic sensors based on the double-network hydrogels demonstrate superior strain sensitivity and linear response on various deformations. Additionally, the good antifreezing property of the hydrogels allows the sensors to exhibit excellent performance at -20 °C.

Dopamine/zinc oxide doped poly(N-hydroxyethyl acrylamide)/agar dual network hydrogel with super self-healing, antibacterial and tissue adhesion functions designed for transdermal patch

Dual network (DN) hydrogels with excellent mechanical strength and controllable component adjustment characteristics have a broad application range in the field of biomedicine. However, the tissue adhesion, skin affinity, self-healing, and antibacterial properties of DN hydrogels are inadequate for their application as skin patches. In this work, we prepared dopamine/zinc oxide (DOPA/ZnO) doped poly(N-hydroxyethyl acrylamide) (p(HEAA))/agar DN hydrogels and combined them to obtain a bilayer hydrogel (two-layer gel) with moisturizing properties. Upon incorporating 0.86 wt% of dopamine (DOPA), the resultant DOPA/p(HEAA))/agar DN hydrogel (DOPA@DNG) exhibited high tensile strain (up to 1600%), excellent self-repair ability, and tissue adhesion. ZnO/p(HEAA))/agar DN hydrogel (ZnO NG) obtained by incorporating 2 w/v ZnO nanoparticles (ZnO NPs) achieved high tensile strength (1.2 MPa), good antibacterial ability, and low charge transfer resistance. Moreover, ZnO NG, which has a tight structure, was employed as a protective layer for the two-layer gel, which can effectively slow down the excessive evaporation of water to protect the DOPA@DNG stability as a skin patch. Evidence showed that the two-layer hydrogel has water retention. Water retention still remains at over 50% after keeping the hydrogel in air for 3 days. These properties mean the two-layer gel based on the DOPA/ZnO doped DN hydrogels could be used as a transdermal patch for numerous applications in drug delivery, wearable devices, and electronic skin.

In Silico Factorial Screening and Optimization of Chitosan Based Gel for Urapidil Loaded Microparticle using Reduced Factorial Design

OBJECTIVE

Literature study revealed the poor mechanical strength of chitosan-based microparticles. Our research aimed at developing sufficient strength of microparticle with a suitable concentration of chitosan and non-ionic surfactants such as poloxamer-188 (pluronic). It also aimed to develop and study the effect of variables for prepared microparticles utilizing insilico screening methodology, such as reduced factorial design, followed by optimization.

METHODS

Preliminary trial batches were prepared with variable concentration of chitosan and poloxamer-188 utilizing cross-linked ion-gelation technique. A 20% w/v sodium citrate solution was used as a cross-linking solution. The resolution-IV of 24-1 reduced factorial design was selected to screen the possible and significant independent variables or factors in the dosage form design. A total number of eight runs were suggested by statistical software and responses were recorded. The responses such as spreadability, pH, viscosity and percentage of drug released at 12 h were considered in the screening study. Based on the result, selected factors were included in the optimization technique, including graphical and numerical methods.

RESULTS

The signified factors based on reduced two-level factorial screening design with randomized subtype, were identified by Half-normal and Pareto chart. Mathematical fitting and analysis were performed by the factorial equation during the optimization process. The validation and fitting of models were suggested and evaluated by p-value, adjusted R2, and predicted R2 values. The significant and non-significant terms were evaluated, followed by finding the optimal concentration and region with yellow color highlighted in an overlay plot. Based on the data obtained by the overlay study, the final formulation batch was prepared and the observed value was found to be pretty much nearer as compared to predicted values. Drug-polymer interaction study included attenuated total reflectance, differential scanning calorimetry, and X-Ray diffraction study.

CONCLUSION

The principal of the study design was based on finding the prefixed set parameter values utilizing the concept of in-silico screening technique and optimization with a minimal number of trials and study expenses. It concluded that Poloxamer-188 (0.94%), chitosan (2.38%), swelling time (1.81 h), and parts of chitosan (78.51%) in a formulation batch would fulfill the predetermined parameter with specific values.

Harnessing the physicochemical properties of DNA as a multifunctional biomaterial for biomedical and other applications

The biological purpose of DNA is to store, replicate, and convey genetic information in cells. Progress in molecular genetics have led to its widespread applications in gene editing, gene therapy, and forensic science. However, in addition to its role as a genetic material, DNA has also emerged as a nongenetic, generic material for diverse biomedical applications. DNA is essentially a natural biopolymer that can be precisely programed by simple chemical modifications to construct materials with desired mechanical, biological, and structural properties. This review critically deciphers the chemical tools and strategies that are currently being employed to harness the nongenetic functions of DNA. Here, the primary product of interest has been crosslinked, hydrated polymers, or hydrogels. State-of-the-art applications of macroscopic, DNA-based hydrogels in the fields of environment, electrochemistry, biologics delivery, and regenerative therapy have been extensively reviewed. Additionally, the review encompasses the status of DNA as a clinically and commercially viable material and provides insight into future possibilities.

Therapeutic vaccination against leukaemia via the sustained release of co-encapsulated anti-PD-1 and a leukaemia-associated antigen

Therapeutic leukaemia vaccines have shown modest potency. Here, we show that the co-encapsulation of a leukaemia-associated epitope peptide highly expressed in leukaemia patients and of the immune checkpoint inhibitor anti-programmed-cell-death-protein-1 (anti-PD-1) in degradable poly(lactic acid) microcapsules resulted in the sustained release of the peptide and of the antibody, which led to the recruitment of activated antigen-presenting cells to the injection site, their uptake of the peptide and the transportation of the anti-PD-1 antibody to lymph nodes, enhancing the expansion of epitope-specific T cells and the activation of cytotoxic T cells. After single subcutaneous injections of vaccine formulations with different epitope peptides, mice bearing leukaemia xenografts derived from humanized cell lines or from primary cells from patients showed better therapeutic outcomes than mice receiving repeated injections of free antigen, antibody and a commercial adjuvant. The sustained release of a tumour-associated peptide and of anti-PD-1 may represent a generalizable strategy for boosting antitumour immune responses to leukaemia.

Coaxial mussel-inspired biofibers: making of a robust and efficacious depot for cancer drug delivery

Biopolymer-based hydrogels have emerged as promising platforms for drug delivery systems (DDSs) due to their inherent biocompatibility, tunable physical properties and controllable degradability. Yet, drug release in majority of these systems is solely contingent on diffusion of drug molecules through the hydrogel, which often leads to burst release of drugs from these systems. Herein, inspired by the chemistry of mussel adhesive proteins, a new generation of coaxial hydrogel fibers was developed that could simultaneously exert both affinity and diffusion control over the release of chemotherapeutic drugs. Specifically, dopamine-modified alginate hydrogel along with chemotherapeutic drugs (doxorubicin or gemcitabine) was used as the main core component to confer affinity-controlled release, while a methacrylated-alginate hydrogel was used as the shell composition to provide the controlled diffusion barrier. It was shown that our coaxial mussel-inspired biofibers yielded biocompatible hydrogel fibers (as indicated by comprehensive in vitro and in vivo experiments) with favourable properties including controlled swelling, and enhanced mechanical properties, when compared against single fibers made from unmodified alginate. Notably, it was observed that these coaxial fibers were capable of releasing the two drugs in a slower manner, when compared to single fibers made from pure alginate, which was partly attributed to stronger interactions of drugs with dopamine-modified alginate (the core element of coaxial fibers) as observed from zeta-potential measurements. It was further shown that these drug-loaded coaxial fibers had optimal anticancer activity both in vitro and in vivo using various pancreatic cancer cell lines. Most remarkably, drug loaded coaxial fibers, particularly doxorubicin-containing fibers, had higher anticancer effect in vivo compared to systemic injection of equivalent dosage of the drugs. Altogether, these biocompatible and robust hydrogel fibers may be further used as neoadjuvant or adjuvant therapies for controlled delivery of chemotherapeutic drugs locally to the tumor sites.

Bisphosphonate nanoclay edge-site interactions facilitate hydrogel self-assembly and sustained growth factor localization

Nanoclays have generated interest in biomaterial design for their ability to enhance the mechanics of polymeric materials and impart biological function. As well as their utility as physical cross-linkers, clays have been explored for sustained localization of biomolecules to promote in vivo tissue regeneration. To date, both biomolecule-clay and polymer-clay nanocomposite strategies have utilised the negatively charged clay particle surface. As such, biomolecule-clay and polymer-clay interactions are set in competition, potentially limiting the functional enhancements achieved. Here, we apply specific bisphosphonate interactions with the positively charged clay particle edge to develop self-assembling hydrogels and functionalized clay nanoparticles with preserved surface exchange capacity. Low concentrations of nanoclay are applied to cross-link hyaluronic acid polymers derivatised with a pendant bisphosphonate to generate hydrogels with enhanced mechanical properties and preserved protein binding able to sustain, for over six weeks in vivo, the localized activity of the clinically licensed growth factor BMP-2.

Nanoclays have been used in composites and for drug delivery but have suffered from a trade-off in properties when used for both. Here the authors report on the use of bisphosphonate interactions with nanoclay edges to made drug loaded composites without compromising materials properties or drug loading.

Specialty Tough Hydrogels and Their Biomedical Applications

Hydrogels have long been explored as attractive materials for biomedical applications given their outstanding biocompatibility, high water content, and versatile fabrication platforms into materials with different physiochemical properties and geometries. Nonetheless, conventional hydrogels suffer from weak mechanical properties, restricting their use in persistent load-bearing applications often required of materials used in medical settings. Thus, the fabrication of mechanically robust hydrogels that can prolong the lifetime of clinically suitable materials under uncompromising in vivo conditions is of great interest. This review focuses on design considerations and strategies to construct such tough hydrogels. Several promising advances in the proposed use of specialty tough hydrogels for soft actuators, drug delivery vehicles, adhesives, coatings, and in tissue engineering settings are highlighted. While challenges remain before these specialty tough hydrogels will be deemed translationally acceptable for clinical applications, promising preliminary results undoubtedly spur great hope in the potential impact this embryonic research field can have on the biomedical community.

Versatile composite hydrogels for drug delivery and beyond

Albumin–organosilane composite hydrogels were prepared and characterized in both their wet and dry states. The wet gels were evaluated using an all-in-one-plate method for drug-delivery applications. Besides, the dry gels can withstand and absorb polar and nonpolar solvents.

Mechano-chromic protein-polymer hybrid hydrogel to visualize mechanical strain

In a proof-of-concept study, a mechano-chromic hydrogel was synthesized here, via chemoenzymatic click conjugation of fluorophore-labeled fibronectin into a synthetic hydrogel co-polymers (i.e., poly-N-isopropylacrylamide/polyethylene glycol). The optical FRET response could be tuned by macroscopic stretch.

Nucleic Acid-Based Dual Cross-Linked Hydrogels for in Situ Tissue Repair via Directional Stem Cell Migration

In situ tissue repair holds great potential as a cell-free regenerative strategy. A critical aspect of this approach is the selection of cell instructive materials that can efficiently regulate the defect microenvironment via the release of chemoattractant factors to mobilize and recruit endogenous stem cells toward the site of implantation. Here we report the design of a DNA-based hydrogel as a drug delivery platform for the sustained release of a promising chemoattractant, SDF-1α. The hydrogel is composed of chemically cross-linked DNA strands, which are bridged via silicate nanodisks (nSi). Silicate nanodisks electrostatically interact with the negatively charged DNA backbone resulting in the formation of a dual cross-linked nanocomposite hydrogel with a combination of chemical and physical cross-link points. The formulated nanocomposites display enhanced elasticity and mechanical toughness as compared to their nonsilicate containing counterparts. Moreover, the electrostatic interaction between nSi and SDF-1α leads to sustained release of the chemokine from the hydrogels. The in vitro bioactivity assays confirm the retention of chemotactic properties of the protein after its release. Overall, the dual cross-linked DNA-based hydrogel platform could be potentially used as a cell-instructive material for the recruitment of host stem cells to guide the process of in situ tissue repair.

Biomaterials to Mimic and Heal Connective Tissues

Connective tissue is one of the four major types of animal tissue and plays essential roles throughout the human body. Genetic factors, aging, and trauma all contribute to connective tissue dysfunction and motivate the need for strategies to promote healing and regeneration. The goal here is to link a fundamental understanding of connective tissues and their multiscale properties to better inform the design and translation of novel biomaterials to promote their regeneration. Major clinical problems in adipose tissue, cartilage, dermis, and tendon are discussed that inspire the need to replace native connective tissue with biomaterials. Then, multiscale structure-function relationships in native soft connective tissues that may be used to guide material design are detailed. Several biomaterials strategies to improve healing of these tissues that incorporate biologics and are biologic-free are reviewed. Finally, important guidance documents and standards (ASTM, FDA, and EMA) that are important to consider for translating new biomaterials into clinical practice are highligted.

A 3D Macroporous Alginate Graphene Scaffold with an Extremely Slow Release of a Loaded Cargo for In Situ Long-Term Activation of Dendritic Cells

Ex vivo manipulation of autologous antigen-presenting cells and their subsequent infusion back into the patient to dictate immune response is one of the promising strategies in cancer immunotherapy. Here, a 3D alginate scaffold embedded with reduced graphene oxide (rGO) is proposed as a vaccine delivery platform for in situ long-term activation of antigen-presenting dendritic cells (DCs). High surface area and hydrophobic surface of the rGO component of the scaffold provide high loading and a very slow release of a loaded antigen, danger signal, and/or chemoattractant from the scaffold. This approach offers long-term bioavailability of the loaded cargo inside the scaffold for manipulation of recruited DCs. After mice are subcutaneously vaccinated with the macroporous alginate graphene scaffold (MAGS) loaded with ovalbumin (OVA) and granulocyte-macrophage colony-stimulating factor (GM-CSF), this scaffold recruits a significantly high number of DCs, which present antigenic information via major histocompatibility complex class I for a long period. Furthermore, an MAGS loaded with OVA, GM-CSF, and CpG promotes production of activated T cells and memory T cells, leading to the suppression of OVA-expressing B16 melanoma tumor growth in a prophylactic vaccination experiment. This study indicates that an MAGS can be a strong candidate for long-term programming and modulating immune cells in vivo.

Environmentally benign pH-responsive cytidine-5′-monophosphate molecule-mediated akaganeite (5′-CMP-β-FeOOH) soft supramolecular hydrogels induced by the puckering of ribose sugar with efficient loading/release capabilities

A novel synthetic protocol for environmentally benign 5′-CMP-β-FeOOH soft hydrogels exhibiting a rapid pH-responsive reversible sol–gel transition, efficient adsorption and slow release capabilities is reported.

Application of Composite Hydrogels to Control Physical Properties in Tissue Engineering and Regenerative Medicine

The development of biomaterials for the restoration of the normal tissue structure⁻function relationship in pathological conditions as well as acute and chronic injury is an area of intense investigation. More recently, the use of tailored or composite hydrogels for tissue engineering and regenerative medicine has sought to bridge the gap between natural tissues and applied biomaterials more clearly. By applying traditional concepts in engineering composites, these hydrogels represent hierarchical structured materials that translate more closely the key guiding principles required for improved recovery of tissue architecture and functional behavior, including physical, mass transport, and biological properties. For tissue-engineering scaffolds in general, and more specifically in composite hydrogel materials, each of these properties provide unique qualities that are essential for proper augmentation and repair following disease and injury. The broad focus of this review is on physical properties in particular, static and dynamic mechanical properties provided by composite hydrogel materials and their link to native tissue architecture and, ultimately, tissue-specific applications for composite hydrogels.