Comprehensive Evaluation of Injectability Attributes in OxiFree™ Dermal Fillers: MaiLi® Product Variants and Clinical Case Reports

Dermal filler injectability is a critical factor for commercial product adoption by medical aesthetic professionals and for successful clinical administration. We have previously reported (in vitro and ex vivo) cross-linked hyaluronic acid (HA)-based dermal filler benchmarking in terms of manual and automated injectability requirements. To further enhance the function-oriented product characterization workflows and the clinical relevance of dermal filler injectability assessments, the aim of this study was to perform in vivo evaluations. Therefore, several variants of the MaiLi® product range (OxiFree™ technology) were characterized in vitro and in vivo in terms of injectability attributes, with a focus on hydrogel system homogeneity and ease of injection. Firstly, standardized in vitro assays were performed in SimSkin® cutaneous equivalents, with variations of the clinical injector, injection site, and injection technique. Then, automated injections in SimSkin® cutaneous equivalents were comparatively performed in a texture analysis setup to obtain fine-granulometry injection force profile results. Finally, five female participants were recruited for the in vivo arm of the study (case reports), with variations of the clinical injector, injection site, and injection technique. Generally, the obtained quantitative force values and injection force profiles were critically appraised from a translational viewpoint, based on discussions around the OxiFree™ manufacturing technology and on in-use specialized clinician feedback. Overall, the present study outlined a notable level of homogeneity across the MaiLi® product range in terms of injectability attributes, as well as consistently high ease of administration by medical aesthetic clinicians.

Clinical Perspectives on the Injectability of Cross-Linked Hyaluronic Acid Dermal Fillers: A Standardized Methodology for Commercial Product Benchmarking with Inter-Injector Assessments

The injectability of cross-linked hyaluronic acid (HA) dermal fillers is influenced by polymer concentration, polymer cross-linking type and degree, the presence of lidocaine or other functional excipients, types of syringes, and injection techniques. Finished product injectability constitutes a critical quality attribute for clinical injectors, as it strongly influences product applicability and ease of use in aesthetic medicine. While injectable product extrusion force specifications are provided by the respective device manufacturers, the qualitative informative value of such datasets is low for injectors wishing to compare product brands and technologies from an injectability standpoint. Therefore, the present study comparatively assessed 28 cross-linked HA dermal fillers (JUVÉDERM®, Restylane®, BELOTERO®, TEOSYAL RHA®, and STYLAGE® brands) using various injectability benchmarking setups for enhanced clinical-oriented relevance. Manual product injections were performed by three specialized and experienced clinicians, whereas automatic product extrusion was performed using a Texture Analyzer instrument. The various hydrogel products were injected into ex vivo human skin and into SimSkin® cutaneous equivalents to appropriately account for injection-related counterpressure. The injectability results revealed important variability between and within product brands, with a strong influence of the local anesthetic lidocaine, HA contents, and needle gauge size. Critical appraisals of the investigated products were performed, notably from manufacturing process-based and clinical ease of application-based standpoints, centered on respective experimental injectability quality levels. Generally, it was confirmed that each HA-based dermal filler product requires specific expertise for optimal injection, mainly due to differing viscoelastic characteristics and injectability attributes. Overall, the present study set forth evidence-based and clinical-oriented rationale elements confirming the importance for injectors to work with injectable products with which they are experienced and comfortable to optimize clinical results.

Injectable Conductive Hydrogel with Self-Healing, Motion Monitoring, and Bacteria Theranostics for Bioelectronic Wound Dressing

Wounds at joints are difficult to treat and tend to recover more slowly due to the frequent motions. When using traditional hydrogel dressings, they are easy to crack and undergo bacterial infection, difficult to match and monitor the irregular wounds. Integrating multiple functions within a hydrogel dressing to achieve intelligent wound monitoring and healing remains a significant challenge. In this research, a multifunctional hydrogel is developed based on polysaccharide biopolymer, poly(vinyl alcohol), and hydroxylated graphene through dynamic borate ester bonding and supramolecular interaction. The prepared hydrogel not only exhibits rapid self-healing (within 60 s), injectable, conductive and motion monitoring properties, but also realizes in situ bacterial sensing and killing functions. It shows excellent bacterial sensitivity (within 15 min) and killing ability via the changes of electrical signals and photothermal therapy, avoiding the emergence of drug-resistant bacteria. In vivo experiments prove that the hydrogel can promote wound healing effectively. In addition, it displays great electromechanical performance to achieve real-time monitoring and prevent re-tearing of the wound at human joints. The injectable pH-responsive hydrogel with good biocompatibility demonstrates considerable potential as multifunctional bioelectronic dressing for the detection, treatment, management, and healing of infected joint wounds.

Injectable Mesh-Like Conductive Hydrogel Patch for Elimination of Atrial Fibrillation

Irregular electrical impulses in atrium are the leading cause of atrial fibrillation (AF), resulting in fatal arrhythmia and sudden cardiac death. Traditional medication and physical therapies are widely used, but generally suffer problems in serious physical damage and high surgical risks. Flexible and soft implants have great potential to be a novel approach for heart diseases therapy. A conductive hydrogel-based mesh cardiac patch is developed for application in AF elimination. The designed mesh patch with rhombic-shaped structure exhibits excellent flexibility, surface conformability, and deformation compliance, making it fit well with heart surface and accommodate to the deformation during heart beating. Moreover, the mechanical elastic and shape-memory properties of the mesh patch enable a minimally invasive injection of the patch into living animals. The mesh patch is implanted on the atrium surface for one month, indicating good biocompatibility and stability. Furthermore, the conductive patch can effectively eliminate AF owing to the conductivity and high charge storage capability (CSC) of the hydrogel. The proposed scheme of cardiac bioelectric signal modulation using conductive hydrogel brings new possibility for the treatment of arrhythmia diseases.

Gelatin Methacryloyl Based Injectable Cryogels with Tunable Degradability for Cell Delivery

Scaffold-based cell delivery can improve therapeutic effects of transplanted cells in cell therapy. Biomaterial scaffolds serveas niche for cell growth and proliferation which improves cell survival and overall function post cell delivery. In this study, gelatin methacryloyl based injectable scaffolds made using poly(ethylene)glycol as a sacrificial polymer and cryogelation as a technique, are demonstrated to have tunable degradability and porosity that is required for cell and drug delivery applications. The pore size (10-142 µm) of these gels makes them suitable for loading different cell types as per the application. In vitro studies using mammalian cells confirm that these cryogels are cytocompatible. These cell-laden scaffolds are injectable and have a cell retention ability of up to 90% after injection. Rheology is done to evaluate stiffness and shape recovery property, and it is found that these gels can maintain their original shape even after applying 7 cycles of strain from 0.1% to 20%. Furthermore, their degradability can be modulated between 6 and 10 days by changing the overall polymer composition. Thus, injectability and degradability of these cryogels can circumvent invasive surgical procedures, thereby making them useful for a variety of applications including delivery of cells and bioactive factors.

Development of a Fully Synthetic Corneal Stromal Construct via Supramolecular Hydrogel Engineering

Recent advances in the field of ophthalmology show great potential in the design of bioengineered constructs to mimic the corneal stroma. Hydrogels based on synthetic supramolecular polymers, are attractive synthetic mimics of the natural highly hydrated corneal stroma. Here, a fully synthetic corneal stromal construct is developed via engineering of an injectable supramolecular hydrogel based on ureido-pyrimidinone (UPy) moieties. The hydrogel displays a dynamic and tunable behavior, which allows for control of biochemical and mechanical cues. Two hydrogels are developed, a fully synthetic hydrogel functionalized with a bioactive cyclic arginine-glycine-aspartate UPy (UPy-cRGD) additive, and a hybrid hydrogel based on UPy-moieties mixed with collagen type I fibers. Both hydrogels supported cell encapsulation and associated cellular deposition of extracellular matrix (ECM) proteins after 21 days. Excitingly, the hydrogels support the activation of isolated primary keratocytes into stromal fibroblasts as well as the differentiation toward more quiescent corneal stromal keratocytes, demonstrated by their characteristic long dendritic protrusions and a substantially diminished cytokine secretion. Furthermore, cells survive shear stresses during an injectability test. Together, these findings highlight the development of an injectable supramolecular hydrogel as a synthetic corneal stromal microenvironment able to host primary keratocytes.

Long-termin vitroculture of 3D brain tissue model based on chitosan thermogel

Methods for studying brain function and disease heavily rely onin vivoanimal models,ex-vivotissue slices, and 2D cell culture platforms. These methods all have limitations that significantly impact the clinical translatability of results. Consequently, models able to better recapitulate some aspects ofin vivohuman brain are needed as additional preclinical tools. In this context, 3D hydrogel-basedin vitromodels of the brain are considered promising tools. To create a 3D brain-on-a-chip model, a hydrogel capable of sustaining neuronal maturation over extended culture periods is required. Among biopolymeric hydrogels, chitosan-β-glycerophosphate (CHITO-β-GP) thermogels have demonstrated their versatility and applicability in the biomedical field over the years. In this study, we investigated the ability of this thermogel to encapsulate neuronal cells and support the functional maturation of a 3D neuronal network in long-term cultures. To the best of our knowledge, we demonstrated for the first time that CHITO-β-GP thermogel possesses optimal characteristics for promoting neuronal growth and the development of an electrophysiologically functional neuronal network derived from both primary rat neurons and neurons differentiated from human induced pluripotent stem cells (h-iPSCs) co-cultured with astrocytes. Specifically, two different formulations were firstly characterized by rheological, mechanical and injectability tests. Primary nervous cells and neurons differentiated from h-iPSCs were embedded into the two thermogel formulations. The 3D cultures were then deeply characterized by immunocytochemistry, confocal microscopy, and electrophysiological recordings, employing both 2D and 3D micro-electrode arrays. The thermogels supported the long-term culture of neuronal networks for up to 100 d. In conclusion, CHITO-β-GP thermogels exhibit excellent mechanical properties, stability over time under culture conditions, and bioactivity toward nervous cells. Therefore, they are excellent candidates as artificial extracellular matrices in brain-on-a-chip models, with applications in neurodegenerative disease modeling, drug screening, and neurotoxicity evaluation.

Connections between cohesion and properties that related to safety and effectiveness of the hyaluronic acid dermal fillers: A comparative study of the cohesive and non-cohesive gels

BACKGROUND

Although the importance of the cohesion of a hyaluronic acid (HA) filler has been recognized, the relationship between the cohesion and the other performance that related to safety and effectiveness, as well as the underlying mechanism is barely studied. Much efforts need to be made on this subject to provide guidance for clinical practice.

MATERIALS AND METHODS

Two types of the HA fillers (cohesive and particulate gels) were selected for the comparison of the cohesion and the other key physicochemical properties.

RESULTS

Hyalumatrix, with significantly higher cohesion, was homogeneously smooth and showed a linearly oriented morphology, whereas Matrifill and Restylane were particulate and showed obvious boundaries between particles. The high cohesion of Hyalumatrix is beneficial to the properties that related to safety and effectiveness, including recovery under shear stress, injectability, tissue integration and in vitro resistance to enzymolysis. The underlying reason was that the strong internal interactions of the cohesive gel protect the network structure from collapse and keep the gel as an intact whole when the gel was subjected to the stress. The homogeneously smooth morphology further improved the tissue compliance and injectability. The G' of Hyalumatrix is in the middle level of the commercially available HA fillers.

CONCLUSION

Hyalumatrix is a rare HA filler product to possess good cohesion and intermediate G' simultaneously. More clinical practice is needed to verify the connection between the cohesion of Hyalumatrix and the clinical performance.

Novel Double Hybrid-Type Bone Cements Based on Calcium Phosphates, Chitosan and Citrus Pectin

In this work, the influence of the liquid phase composition on the physicochemical properties of double hybrid-type bone substitutes was investigated. The solid phase of obtained biomicroconcretes was composed of highly reactive α-tricalcium phosphate powder (α-TCP) and hybrid hydroxyapatite/chitosan granules (HA/CTS). Various combinations of disodium phosphate (Na2HPO4) solution and citrus pectin gel were used as liquid phases. The novelty of this study is the development of double-hybrid materials with a dual setting system. The double hybrid phenomenon is due to the interactions between polycationic polymer (chitosan in hybrid granules) and polyanionic polymer (citrus pectin). The chemical and phase composition (FTIR, XRD), setting times (Gillmore needles), injectability, mechanical strength, microstructure (SEM) and chemical stability in vitro were studied. The setting times of obtained materials ranged from 4.5 to 30.5 min for initial and from 7.5 to 55.5 min for final setting times. The compressive strength varied from 5.75 to 13.24 MPa. By incorporating citrus pectin into the liquid phase of the materials, not only did it enhance their physicochemical properties, but it also resulted in the development of fully injectable materials featuring a dual setting system. It has been shown that the properties of materials can be controlled by using the appropriate ratio of citrus pectin in the liquid phase.

An Overview of Magnesium-Phosphate-Based Cements as Bone Repair Materials

In the search for effective biomaterials for bone repair, magnesium phosphate cements (MPCs) are nowadays gaining importance as bone void fillers thanks to their many attractive features that overcome some of the limitations of the well-investigated calcium-phosphate-based cements. The goal of this review was to highlight the main properties and applications of MPCs in the orthopedic field, focusing on the different types of formulations that have been described in the literature, their main features, and the in vivo and in vitro response towards them. The presented results will be useful to showcase the potential of MPCs in the orthopedic field and will suggest novel strategies to further boost their clinical application.

Injectable Pectin-Alginate Hydrogels for Improving Vascularization and Adipogenesis of Human Fat Graft

Autologous fat grafting (AFG) is the most prevailing tool for soft tissue regeneration in clinics, although efficiency is limited to unpredictable volume resorption due to poor vascularization and eventual necrosis. This study sought to improve the AFG efficiency using a hydrogel as a carrier for human fat graft (F) with and without platelet-rich plasma (PRP). PRP is clinically well known for the local release of several endogenous growth factors and has been in clinical use already. A human-fat-graft-encapsulated pectin-alginate hydrogel (FG) was developed and characterized. PRP was added to F to develop a human fat graft with PRP (FP). FP was admixed with a pectin-alginate hydrogel to develop FGP. FG and FGP showed the smooth injectable, elastic, and shear-thinning properties. FG and FGP groups showed enhanced cell viability and proliferation compared to the control F in vitro. We also investigated the in vivo angiogenesis and neo-adipogenesis ability of F, FG, FGP, and FP in nude mice after subcutaneous injection. After 2 and 4 weeks, an MRI of the mice was conducted, followed by graft explantation. The explanted grafts were also assessed histologically and with immunohistochemistry (IHC) studies. MRI and histology results revealed better vascularity of the FG and FGP system compared to fat graft alone. Further, the IHC studies, CD 31, and perilipin staining also revealed better vasculature and adipogenesis of FG and FGP systems. These results indicate the enhanced angiogenesis and adipogenesis of FG and FGP. Thus, developed pectin-alginate hydrogel-based fat graft systems FG and FGP replenish the native microenvironment by mediating angiogenesis and adipogenesis, thereby maximizing the clinical outcomes of autologous fat grafting.

Fabrication of Injectable Kartogenin-Conjugated Composite Hydrogel with a Sustained Drug Release for Cartilage Repair

Cartilage tissue engineering has attracted great attention in defect repair and regeneration. The utilization of bioactive scaffolds to effectively regulate the phenotype and proliferation of chondrocytes has become an elemental means for cartilage tissue regeneration. On account of the simultaneous requirement of mechanical and biological performances for tissue-engineered scaffolds, in this work we prepared a naturally derived hydrogel composed of a bioactive kartogenin (KGN)-linked chitosan (CS-KGN) and an aldehyde-modified oxidized alginate (OSA) via the highly efficient Schiff base reaction and multifarious physical interactions in mild conditions. On the basis of the rigid backbones and excellent biocompatibility of these two natural polysaccharides, the composite hydrogel demonstrated favorable morphology, easy injectability, good mechanical strength and tissue adhesiveness, low swelling ratio, long-term sustainable KGN release, and facilitated bone marrow mesenchymal stem cell activity, which could simultaneously provide the mechanical and biological supports to promote chondrogenic differentiation and repair the articular cartilage defects. Therefore, we believe this work can offer a designable consideration and potential alternative candidate for cartilage and other soft tissue implants.

Injectable, Tough, and Thermoplastic Supramolecular Hydrogel Coatings with Controllable Adhesion for Touch Sensing

Soft tissues in nature are anchored on the load-bearing structures of creatures, such as tendons, ligaments, and cartilages. However, mimetic hydrogel coatings that combine the unique properties of hydrogels (e.g., in situ formability, stimulus-responsiveness, strength controllability, environmental friendliness, and small molecular encapsulation) with the superior properties of substrates such as high elastic modulus and high tensile strength still require further exploration to achieve an adequately comprehensive performance. Herein, we report an approach for fabricating hydrogel coatings using an injectable, tough, and thermoplastic κ-carrageenan (κ-car)/poly(N-acryloyl glycinamide (NAGA)-co-vinyl imidazole (VI)) supramolecular hydrogel (κ-car/PNV hydrogel) with temperature-controlled adhesion by adjusting the contact at the hydrogel-substrate interface. The κ-car/PNV hydrogel with a mass ratio of NAGA to VI of 9:1 shows a sol-gel transition temperature of 85 °C, a compressive strain of 99%, a tensile strain of 1045%, fast self-recovery, durability, and the adhesive ability to handle irregular substrates. Furthermore, this supramolecular hydrogel coating forms strips and panels with slide rheostat-based touch sensing, which is minimally affected by water evaporation. This work facilitates the fabrication and application of hydrogel coatings as touch sensing devices to combine functional supramolecular hydrogels, surface coatings, and ionotronics.

"Smart" Stimuli-responsive Injectable Gels for Bone Tissue Engineering Application

Bone grafting, as the current gold-standard for large scaled bone damage of various causes, has faced challenges from both the source and appliance. Emerging new tissue engineering substitutes are demonstrating more options and possibilities, with their improved biocompatibility, accessibility, and customizable function. Amongst them, injectable gels (IGs) are a class of gel material displaying astonishing non-invasive properties and surgical viability. While possessing responsiveness toward specific stimuli, they change their physical form in vivo, thus serving as wonderful biomaterials and drug delivery systems. In this review, the mechanics of stimuli-responsive IGs developed during the past decade are illustrated. Two branches of crosslinked gels - co-valent and non-covalent crosslinked IGs and their composition and customization are introduced. In conclusion, the present trend in bone tissue engineering research is summarized and made an outlook for future. It is hoped that this comprehensive review can provide a proper reference for the development of new IGs.

Fabrication of macroporous apatite bone cements for non-load bearing orthopedic applications

Calcium deficient hydroxyapatite (CDHA)-based apatite forming bone cements are well known for their bioactivity and bioresorbability. The formulation of CDHA-based cements with improved macroporosity, injectability, and resorbability has been investigated. The solid phase consists of nanocrystalline hydroxyapatite (HA) and tricalcium phosphate (β-TCP). The liquid phase is diluted acetic acid with disodium hydrogen phosphate as binding accelerator along with gelatin and chitosan to improve the injectability. A porogen agent either mannitol (as solid porogen) or polysorbate (as liquid porogen) is also used to improve the porosity. All combined in fine-tuned composition results in optimal bone cements. The cement sets within the clinically preferred setting time (≤20 min) and injectability (>70%) and also stable at physiological pH (i.e., ~7.3-7.4). The XRD and FT-IR analysis confirmed the formation of CDHA phase on day 7 when the after-set cement immersed under phosphate buffer solution (PBS) at physiological conditions. The cements were found to have acceptable compressive strength for trabecular bone substitute. The cements were macroporous in nature with average pore size between 50 and 150 μm and were interconnected as confirmed by SEM, micro-CT and MIP analysis. The prepared cements are degradable up to 22% and 19% in simulated body fluid and PBS respectively within 10 weeks of immersion at physiological conditions. The cements exhibit higher viability (%) (>110%) with L929 and MG63 cells compared to the control after 3 days of incubation. They also show increased proliferation, well spreading and extended filopodia with MG63 cells. Overall, the developed apatite forming bone cements seems to be suitable for low or non-load bearing orthopedic applications.

Thermosensitive Injectable Gradient Hydrogel-Induced Bidirectional Differentiation of BMSCs

Osteochondral defects threaten the quality of life of patients to a great extent. To simulate gradient changes in osteochondral tissue, a gradient-mixing injection device consisting of a controller and injection pumps is design. Bioactive glass (BG) and gellan gum (GG) are used to prepare thermosensitive injectable gradient hydrogels (B_0.5 G, B₁ G) with an upper critical solution temperature (UCST) range of 37.7-40.2 °C using this device for the first time. The mechanical properties of gradient hydrogels are significantly better than those of pure GG hydrogels. The gradients in the composition, structure, and morphology of gradient hydrogels are confirmed via physicochemical characterization. Cytocompatibility tests show that hydrogels, especially B_0.5 G gradient hydrogels, promote the proliferation of bone marrow mesenchymal stem cells (BMSCs). Most importantly, qRT-PCR shows that the different components in B_0.5 G gradient hydrogels simultaneously induce the osteogenic and chondrogenic differentiation of BMSCs. Experimental injection in porcine osteochondral defects indicates that the B_0.5 G gradient hydrogel seamlessly fills irregular osteochondral defects in a less invasive manner by controlling the temperature to avoid cellular and tissue damage arising from crosslinkers or other conditions. These results show that thermosensitive injectable B_0.5 G gradient hydrogels have the potential for less invasive integrated osteochondral repair.

Synthesis of a novel injectable alginate impression material and impression accuracy evaluation

OBJECTIVES

This work aimed to synthesize a novel injectable alginate impression material and evaluate its accuracy.

METHODS

Certain proportions of sodium alginate, trisodium phosphate dodecahydrate, potassium fluorotitanate, diatomaceous earth, and other ingredients were dissolved in water and mixed evenly with a planetary centrifugal mixer to obtain a certain viscosity base paste. Certain proportions of calcium sulfate hemihydrate, magnesium oxide, glycerin, and polyethylene glycol (PEG) 400 were mixed evenly with a planetary centrifugal mixer to obtain the reactor paste with the same viscosity as the base paste. The base and reactor pastes were poured into a two-cylinder cartridge at a 2∶1 volume ratio. A gun device was used to accomplish mixing by compressing materials into a mixing tip. The samples were divided into three groups: injectable alginate impression materials (IA group) as the experimental group, and Jeltrate alginate impression materials (JA group) and Silagum-putty/light addition silicone rubber impression materials (SI group) as the two control groups.

RESULTS

Scanning electron microscopy (SEM) showed that the injectable alginate impression materials had a denser structure and fewer bubbles than the commercial alginate impression material. The accuracy of the three kinds of impression materials was evaluated by 3D image superposition. The deviations between the three test group models and the standard model (trueness) were 49.58 μm±1.453 μm (IA group), 54.75 μm±7.264 μm (JA group), and 30.92 μm±1.013 μm (SI group). The deviations of the models within each test group (precision) were 85.79 μm±8.191 μm (IA group), 97.65 μm±11.060 μm (JA group), and 56.51 μm±4.995 μm (SI group). Significant differences in trueness and precision were found among the three kinds of impression materials (P<0.05).

CONCLUSIONS

The accuracy of the new injectable alginate impression material was better than that of the traditional powder-type alginate impression material but worse than that of the addition silicone rubber impression materials. The novel injec-table alginate impression material demonstrated good operation performance and impression accuracy, showing broad application prospect.

Facile Construction of Hybrid Hydrogels with High Strength and Biocompatibility for Cranial Bone Regeneration

The significant efforts being made towards the utilization of artificial soft materials holds considerable promise for developing tissue engineering scaffolds for bone-related diseases in clinics. However, most of these biomaterials cannot simultaneously satisfy the multiple requirements of high mechanics, good compatibility, and biological osteogenesis. In this study, an osteogenic hybrid hydrogel between the amine-functionalized bioactive glass (ABG) and 4-armed poly(ethylene glycol) succinimidyl glutarate-gelatin network (SGgel) is introduced to flexibly adhere onto the defective tissue and to subsequently guide bone regeneration. Relying on the rapid ammonolysis reaction between amine groups (-NH₂) of gelatin and ABG components and N-hydroxysuccinimide (NHS)-ester of tetra-PEG-SG polymer, the hydrogel networks were formed within seconds, offering a multifunctional performance, including easy injection, favorable biocompatibility, biological and mechanical properties (compressive strength: 4.2 MPa; storage modulus: 10⁴ kPa; adhesive strength: 56 kPa), which could facilitate the stem cell viability, proliferation, migration and differentiation into osteocytes. In addition, the integration between the SGgel network and ABG moieties within a nano-scale level enabled the hybrid hydrogel to form adhesion to tissue, maintain the durable osteogenesis and accelerate bone regeneration. Therefore, a robust approach to the simultaneously satisfying tough adhesion onto the tissue defects and high efficiency for bone regeneration on a mouse skull was achieved, which may represent a promising strategy to design therapeutic scaffolds for tissue engineering in clinical applications.

Construction of Sol-Gel Phase-Reversible Hydrogels with Tunable Properties with Native Nanofibrous Protein as Building Blocks

Reversible sol-gel transforming behaviors combined with tunable mechanical properties are vital demands for developing biomaterials. However, it remains challenging to correlate these properties with the hydrogels constructed by denatured protein as building blocks. Herein, taking advantage of naturally high-affinity coordination environments consisting of i, i + 4 His-Glu motifs offered by paramyosin, a ubiquitous nanofibrous protein, we found that Zn²⁺ rather than Ca²⁺ or Mg²⁺ has the ability to trigger the self-assembly of native abalone paramyosin (AbPM) into protein hydrogels under benign conditions, while the addition of EDTA induces the hydrogels back into protein monomers, indicative of a reversible process. By using such sol-gel reversible property, the AbPM gels can serve as a vehicle to encapsulate bioactive molecules such as curcumin, thereby protecting it from degradation from thermal and photo treatment. Notably, based on the high conserved structure of native AbPM, the mechanical property and biological activity of the fabricated AbPM hydrogels can be fined-tuned by its noncovalent interaction with small molecules. All these findings raise the possibility that native paramyosin can be explored as a new class of protein hydrogels which exhibit favorable properties that the traditional hydrogels constructed by denatured protein building blocks do not have.

Silencing Gene-Engineered Injectable Hydrogel Microsphere for Regulation of Extracellular Matrix Metabolism Balance

Extracellular matrix (ECM) metabolism balance is essential for maintaining tissue structure and function. However, the complex crosstalk between the ECM, resident cellular, and tissue microenvironment makes long-term maintenance of ECM metabolism balance in an abnormal microenvironment difficult to achieve. Herein, an injectable circRNA silencing-hydrogel microsphere (psh-circSTC2-lipo@MS) is constructed by grafting circSTC2 silencing genes-loaded 1,2-dioleoyl-3-trimethylammonium-propane/cholesterol/1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOTAP/Chol/DOPE) cationic liposomes on methacrylated hyaluronic acid (HAMA) microspheres via amide bonds, which could silence pathological genes in nucleus pulposus (NP) cells to regulate ECM metabolism balance in the nutrient-restricted microenvironment, thereby inhibiting intervertebral disc (IVD) degeneration. HAMA microspheres prepared by microfluidics displayed good degradability, swellability, and injectability. And lipoplexes can be efficiently loaded and released for 27 d through chemical grafting. Cocultured under nutrient-restricted conditions for 72 h, psh-circSTC2-lipo@MS significantly promotes the synthesis of ECM-related proteins and inhibits the secretion of ECM catabolism-related proteases in NP cells. In the rat IVD nutrient-restricted model, local injection of psh-circSTC2-lipo@MS promotes ECM synthesis and restored NP tissue after 8 weeks. In summary, this study confirms that psh-circSTC2-lipo@MS as a safe and controllable targeted gene delivery system has great potential in regulating the ECM metabolism balance under an abnormal microenvironment.

Multifunctional Injectable Hydrogel for In Vivo Diagnostic and Therapeutic Applications

Injectable hydrogels show high potential for in vivo biomedical applications owing to their distinctive mode of administration into the human body. In this study, we propose a material design strategy for developing a multifunctional injectable hydrogel with good adhesiveness, stretchability, and bioresorbability. Its multifunctionality, whereupon multiple reactions occur simultaneously during its injection into the body without requiring energy stimuli and/or additives, was realized through meticulous engineering of bioresorbable precursors based on hydrogel chemistry. The multifunctional injectable hydrogel can be administered through a minimally invasive procedure, form a conformal adhesive interface with the target tissue, dynamically stretch along with the organ motions with minimal mechanical constraints, and be resorbed in vivo after a specific period. Further, the incorporation of functional nanomaterials into the hydrogel allows for various in vivo diagnostic and therapeutic applications, without compromising the original multifunctionality of the hydrogel. These features are verified through theranostic case studies on representative organs, including the skin, liver, heart, and bladder.

A Sequential Therapeutic Hydrogel With Injectability and Antibacterial Activity for Deep Burn Wounds' Cleaning and Healing

As a severe clinical challenge, escharotomy and infection are always the core concerns of deep burn injuries. However, a usual dressing without multifunctionality leads to intractable treatment on deep burn wounds. Herein, we fabricated a sequential therapeutic hydrogel to solve this problem. Cross-linked by modified polyvinyl alcohol (PVA-SH/ε-PL) and benzaldehyde-terminated F127 triblock copolymers (PF127-CHO), the hydrogel demonstrated excellent mechanical properties, injectability, tissue adhesiveness, antibacterial activity, biocompatibility, and satisfactory wound cleaning through both in vitro and in vivo assays. Additionally, based on the conception of “sequential therapy,” we proposed for the first time to load bromelain and EGF into the same hydrogel in stages for wound cleaning and healing. This work provides a strategy to fabricate a promising wound dressing for the treatment of deep burn wounds with injectability and improved patients’ compliance as it simplified the process of treatment due to its “three in one” characteristic (antibacterial activity, wound cleaning, and healing effects); therefore, it has great potential in wound dressing development and clinical application.

Ultrastretchable, Adhesive, and Antibacterial Hydrogel with Robust Spinnability for Manufacturing Strong Hydrogel Micro/Nanofibers

The ultrastretchable (over 12 400%) hydrogel with long-lasting adhesion, strong antibacterial activity, and robust spinnability is developed based on the oxidative decarboxylation and quinone-catechol reversible redox reaction induced by Ag-lignin nanoparticles in a precursor solution containing citric acid (CA), acrylic acid (AA), and poly (acrylamide-co-acrylic acid) (P(AAm-co-AA)). With massive reversible interactions including hydrogen bonds and electrostatic forces, such hydrogel exhibits promising injectability and is facilely spun via manual drawing, draw-spinning, and electrospinning for manufacturing strong hydrogel micro/nanofibers. The resulting fibers exhibit excellent mechanical properties, including tensile stress of 422.0 MPa, strain of 86.5%, Young's modulus of 8.7 GPa, and toughness of 281.6 MJ m^-3 . The hydrogel microfibers obtained from a house-built spinner are scaled-up fabricated while retaining promising mechanical properties, as evidenced by lifting a load (317.2 g) using the spun fibers of ≈33 000 times lighter weight (9.5 mg), indicating their great potentials in the applications such as net and safety cord which require robust mechanical properties. Moreover, assisted by a commercial electrospinning machine, nanosized hydrogel fibers are facilely spun on personal protective equipment such as a mask to offer an antiseptic coating with near 100% killing efficiency against airborne bacteria aerosols, demonstrating the capability of spun hydrogel fibers on disinfection-related applications.

Antifreeze and Rheological Properties of Injectable Triblock Copolymer Hydrogels with Supramolecular Junctions

ABC triblock copolymers composed of hydrophobic poly(ε-caprolactone) (PCL), zwitterionic poly(carboxybetaine methacrylate) midblock, and P(PEGMA-UPy_0.15 ) containing supramolecular ureidopyrimidinone moieties, poly(ε-caprolactone-block-carboxybetaine methacrylate-block-[poly(ethylene glycol) methyl ether methacrylate-co-(α-methacryloyl-ω-(6-(3-(6-methyl-4-oxo-1,4-dihydropyrimidin-2-yl)ureido)hexylcarbamoyloxy)poly(ethylene glycol))]), are investigated to achieve multifunctional antifreeze hydrogels. The PCL and P(PEGMA-UPy_0.15 ) blocks induce the formation of physical network with a hierarchical nanostructure comprising hydrophobic PCL cores and supramolecular junctions, respectively. The super-hydrophilic nature of polyzwitterion midblocks and the confinement effect of the supramolecular junctions enhance the antifreeze performance, where the majority of water molecules remains supercooled below sub-zero temperature. The hydrogel relaxation characterized over a wide range of timescale reveals that the facile dynamics of the supramolecular junctions lead to the self-healing and injectability of the hydrogels. In conjunction with the biodegradable PCL cores, the antifreeze and rheological characteristics of the triblock copolymer hydrogels provide significant potential to use for cryo-preservable and bio-injectable drug storage and delivery.

An Intrinsically-Adhesive Family of Injectable and Photo-Curable Hydrogels with Functional Physicochemical Performance for Regenerative Medicine

Attaching hydrogels to soft internal tissues is crucial for the development of various biomedical devices. Tough sticky hydrogel patches present high adhesion, yet with lack of injectability and the need for treatment of contacting surface. On the contrary, injectable and photo-curable hydrogels are highly attractive owing to their ease of use, flexibility of filling any shape, and their minimally invasive character, compared to their conventional preformed counterparts. Despite recent advances in material developments, a hydrogel that exhibits both proper injectability and sufficient intrinsic adhesion is yet to be demonstrated. Herein, a paradigm shift is proposed toward the design of intrinsically adhesive networks for injectable and photo-curable hydrogels. The bioinspired design strategy not only provides strong adhesive contact, but also results in a wide window of physicochemical properties. The adhesive networks are based on a family of polymeric backbones where chains are modified to be intrinsically adhesive to host tissue and simultaneously form a hydrogel network via a hybrid cross-linking mechanism. With this strategy, adhesion is achieved through a controlled synergy between the interfacial chemistry and bulk mechanical properties. The functionalities of the bioadhesives are demonstrated for various applications, such as tissue adhesives, surgical sealants, or injectable scaffolds.

Alginate-g-PNIPAM-Based Thermo/Shear-Responsive Injectable Hydrogels: Tailoring the Rheological Properties by Adjusting the LCST of the Grafting Chains

Graft copolymers of alginate backbone and N-isopropylacrylamide/N-tert-butylacrylamide random copolymer, P(NIPAMx-co-NtBAMy), side chains (stickers) with various NtBAM content were designed and explored in aqueous media. Self-assembling thermoresponsive hydrogels are formed upon heating, in all cases, through the hydrophobic association of the P(NIPAMx-co-NtBAMy) sticky pendant chains. The rheological properties of the formulations depend remarkably on the NtBAM hydrophobic content, which regulates the lower critical solution temperature (LCST) and, in turn, the stickers' thermo-responsiveness. The gelation point, Tgel, was shifted to lower temperatures from 38 to 20 °C by enriching the PNIPAM chains with 20 mol % NtBAM, shifting accordingly to the gelation temperature window. The consequences of the Tgel shift to the hydrogels' rheological properties are significant at room and body temperature. For instance, at 37 °C, the storage modulus increases about two orders of magnitude and the terminal relaxation time increase about 10 orders of magnitude by enriching the stickers with 20 mol % hydrophobic moieties. Two main thermo-induced behaviors were revealed, characterized by a sol-gel and a weak gel-stiff gel transition for the copolymer with stickers of low (0.6 mol %) and high (14, 20 mol %) NtBAM content, respectively. The first type of hydrogels is easily injectable, while for the second one, the injectability is provided by shear-thinning effects. The influence of the type of media (phosphate buffer (PB), phosphate-buffered saline (PBS), Dulbecco's modified Eagle's medium (DMEM)) on the hydrogel properties was also explored and discussed. The 4 wt % NaALG-g-P(NIPAM80-co-NtBAM20)/DMEM formulation showed excellent shear-induced injectability at room temperature and instantaneous thermo-induced gel stiffening at body temperature, rendering it a good candidate for cell transplantation potential applications.

Engineering an Injectable Electroactive Nanohybrid Hydrogel for Boosting Peripheral Nerve Growth and Myelination in Combination with Electrical Stimulation

Electrical stimulation (ES) can be used to manipulate recovery after peripheral nerve injuries. Although biomaterial-based strategies have already been implemented to gain momentum for ES and engineer permissive microenvironments for neural regeneration, the development of biomaterials for specific stimuli-responsive modulation of neural cell properties remains a challenge. Herein, we homogeneously incorporate pristine carbon nanotubes into a functional self-assembling peptide to prepare a hybrid hydrogel with good injectability and conductivity. Two-dimensional (on the surface) and three-dimensional (within the hybrid hydrogel) culturing experiments demonstrate that ES promotes axon outgrowth and Schwann cell (SC) migration away from dorsal root ganglia spheres, further revealing that ES-enhanced interactions between SCs and axons result in improved myelination. Thus, our study not only advances the development of tailor-made materials but also provides useful insights into comprehensive approaches for promoting nerve growth and presents a practical strategy of repairing peripheral nerve injuries.

Poly-tetrahydropyrimidine Antibacterial Hydrogel with Injectability and Self-Healing Ability for Curing the Purulent Subcutaneous Infection

Infections caused by pathogenic microorganisms have always been the Achilles heel in the clinic. In this work, to overcome this conundrum, we proposed an injectable multifunctional hydrogel material with outstanding antibacterial properties and self-healing properties and no adverse effects on health. The cross-linked hydrogel with three-dimensional (3D) networks was quickly formed via the dynamic Schiff base between amino-modified poly-tetrahydropyrimidine (PTHP-NH₂) and multiple vanillin polymer P(DMA-VA) in 30 s. This hydrogel composite presents effective defense against both Gram-positive and Gram-negative bacteria, especially for the pyogenic Staphylococcus aureus. Moreover, the hydrogel showed almost no hemolysis and cytotoxicity. In vivo investigations indicated that hydrogels effectively killed S. aureus and protected against deterioration of inflammation. Besides, bioimaging of mice demonstrated that the hydrogel could be completely metabolized within 16 h. In a nutshell, given its outstanding antibacterial property and biocompatibility, the novel hydrogel could be an ideal candidate for the subcutaneous infection application.

Polysaccharide-Based In Situ Self-Healing Hydrogels for Tissue Engineering Applications

In situ hydrogels have attracted increasing interest in recent years due to the need to develop effective and practical implantable platforms. Traditional hydrogels require surgical interventions to be implanted and are far from providing personalized medicine applications. However, in situ hydrogels offer a wide variety of advantages, such as a non-invasive nature due to their localized action or the ability to perfectly adapt to the place to be replaced regardless the size, shape or irregularities. In recent years, research has particularly focused on in situ hydrogels based on natural polysaccharides due to their promising properties such as biocompatibility, biodegradability and their ability to self-repair. This last property inspired in nature gives them the possibility of maintaining their integrity even after damage, owing to specific physical interactions or dynamic covalent bonds that provide reversible linkages. In this review, the different self-healing mechanisms, as well as the latest research on in situ self-healing hydrogels, is presented, together with the potential applications of these materials in tissue regeneration.

[Research on Gliding and Discharge Performance of Suspended Injection from Syringe -Effect of Diameter Ratio of Suspending Particle against Needle Hole on Needle Passageability]

Suspended injectable formulations such as sustained-release luteinizing hormone-releasing hormone (LH-RH) analogue loaded in polylactic acid-glycolic acid copolymer (PLGA) particles have been developed on market. Such formulations have potential issue of suspended particles blocking the injection needle. In this research, two types of injectability tests (gliding force, particles discharge) were developed to evaluate the needle passageability of suspended particles. The model suspension was newly designed using mono-dispersed polyethylene (PE) spheres and qualified dispersing fluid to enhance universality and validity of the test. The suspension-filled syringe, in which three sizes of spheres (L, M, S) were dispersed, was vertically fixed and pushed by auto-compression/tensile tester. The gliding force was continuously detected during testing time and all discharged PE spheres were collected and weighed. The combination of sphere (L, M, S) and injection needle were varied to evaluate the effect of the diameter ratio of sphere against needle hole (D/W) on passageability through needle. These injectability tests revealed that the blockage of a needle hole was occasionally observed when the D/W value increased up to 0.35-0.5, which was detected by jump-up of gliding force and drastic decrease of discharged sphere. In addition, the effect of the formulation properties (concentration of suspended spheres, viscosity of dispersing fluid) and operational factor (injection speed) on injectability was also investigated. The results from this study would be valuable in developing suspended injections and predicting injection trouble at the medical scene.

Complexation of Injectable Biphasic Calcium Phosphate with Phosphoserine-Presenting Dendrons with Enhanced Osteoregenerative Properties

Injectable biphasic calcium phosphates have been proposed as a solution in the treatment of a range of clinical applications including as fillers in the augmentation of osteoporotic bone. To date, various biodegradable natural or synthetic organics have been used as a polymer component of bone materials to increase their cohesiveness. Herein, a novel bone material was developed combining osteoconductive biphasic calcium phosphate (BCP) nanoparticles with phosphoserine-tethered generation 3 poly(epsilon-lysine) dendron (G3-K PS), a class of hyperbranched peptides previously shown to induce biomineralization and stem cell osteogenic differentiation. Strontium was also incorporated into the BCP nanocrystals (SrBCP) to prevent bone resorption. Within 24 h, an antiwashout behavior was observed in G3-K PS-integrated pure BCP group (BCPG3). Moreover, both in vitro tests by relevant cell phenotypes and an in vivo tissue regeneration study by an osteoporotic animal bone implantation showed that the integration of G3-K PS would downregulate Cxcl9 gene and protein expressions, thus enhancing bone regeneration measured as bone mineral density, new bone volume ratio, and trabecular microarchitectural parameters. However, no synergistic effect was found when Sr was incorporated into the BCPG3 bone pastes. Notably, results indicated a concomitant reduction of bone regeneration potential assessed as reduced Runx2 and PINP expression when bone resorptive RANKL and CTX-I levels were reduced by Sr supplementation. Altogether, the results suggest the potential of injectable BCPG3 bone materials in the treatment of osteoporotic bone defects.

Synthesis of Injectable Shear-Thinning Biomaterials of Various Compositions of Gelatin and Synthetic Silicate Nanoplatelet

Injectable shear-thinning biomaterials (iSTBs) have great potential for in situ tissue regeneration through minimally invasive therapeutics. Previously, an iSTB was developed by combining gelatin with synthetic silicate nanoplatelets (SNPs) for potential application to hemostasis and endovascular embolization. Hence, iSTBs are synthesized by varying compositions of gelatin and SNPs to navigate their material, mechanical, rheological, and bioactive properties. All compositions (each component percentage; 1.5-4.5%/total solid ranges; 3-9%) tested are injectable through both 5 Fr general catheter and 2.4 Fr microcatheter by manual pressure. In the results, an increase in gelatin contents causes decrease in swellability, increase in freeze-dried hydrogel scaffold porosity, increase in degradability and injection force during iSTB fabrication. Meanwhile, the amount of SNPs in composite hydrogels is mainly required to decrease degradability and increase shear thinning properties of iSTB. Finally, in vitro and in vivo biocompatibility tests show that the 1.5-4.5% range gelatin-SNP iSTBs are not toxic to the cells and animals. All results demonstrate that the iSTB can be modulated with specific properties for unmet clinical needs. Understanding of mechanical and biological consequences of the changing gelatin-SNP ratios through this study will shed light on the biomedical applications of iSTB on specific diseases.

Combination of Polymeric Superplasticizers, Water Repellents and Pozzolanic Agents to Improve Air Lime-Based Grouts for Historic Masonry Repair

This paper presents the experimental procedure to develop air lime-based injection grouts, including polymeric superplasticizers, a water repellent agent and pozzolanic agents as additives. Our research focuses on the development of grouts to improve various characteristics simultaneously by combining different additions and admixtures. Aiming to improve the injectability of the grouts, in this study, different polymeric superplasticizers were added, namely polycarboxylated-ether derivative (PCE), polynaphthalene sulfonate (PNS) and condensate of melamine-formaldehyde sulfonate (SMFC). As a water-repellent agent, sodium oleate was used to reduce the water absorption. The enhancement of the strength and setting time was intended by using microsilica and metakaolin as pozzolanic mineral additions. Compatibility between the different admixtures and action mechanism of the different polymers were studied by means of zeta potential and adsorption isotherms measurements. Diverse grout mixtures were produced and investigated by assessing their injectability, fluidity, stability, compressive strength, hydrophobicity and durability. This research led to several suitable mixtures produced by using more than one component, to enhance efficiency and to provide better performance of grouts. According to the results, the grout composed of air lime, metakaolin, sodium oleate and PCE was found to be the most effective composition, improving the mechanical strength, injectability and hydrophobicity.

Filling the Gap: A Correlation between Objective and Subjective Measures of Injectability

Various injectable biomaterials are developed for the minimally invasive delivery of therapeutics. Typically, a mechanical tester is used to ascertain the force required to inject these biomaterials through a given syringe-needle system. However, currently there is no method to correlate the force measured in the laboratory to the perceived effort required to perform that injection by the end user. In this article, the injection force (F) for a variety of biomaterials, displaying a range of rheological properties, is compared with the effort scores from a 50 person panel study. The maximum injection force measured at crosshead speed 1 mm s^-1 is a good proxy for injection effort, with an R² of 0.89. This correlation leads to the following conclusions: participants can easily inject 5 mL of substance for F < 12 N; considerable effort is required to inject 5 mL for 12 N < F < 38 N; great effort is required and <5 mL can be injected for 38 N < F < 64 N; and materials are entirely non-injectable for F > 64 N. These values may be used by developers of injectable biomaterials to make decisions about formulations and needle sizes early in the translational process.

In-Situ Forming pH and Thermosensitive Injectable Hydrogels to Stimulate Angiogenesis: Potential Candidates for Fast Bone Regeneration Applications

Biomaterials that promote angiogenesis are required for repair and regeneration of bone. In-situ formed injectable hydrogels functionalised with bioactive agents, facilitating angiogenesis have high demand for bone regeneration. In this study, pH and thermosensitive hydrogels based on chitosan (CS) and hydroxyapatite (HA) composite materials loaded with heparin (Hep) were investigated for their pro-angiogenic potential. Hydrogel formulations with varying Hep concentrations were prepared by sol-gel technique for these homogeneous solutions were neutralised with sodium bicarbonate (NaHCO3) at 4 °C. Solutions (CS/HA/Hep) constituted hydrogels setting at 37 °C which was initiated from surface in 5-10 minutes. Hydrogels were characterised by performing injectability, gelation, rheology, morphology, chemical and biological analyses. Hydrogel solutions facilitated manual dropwise injection from 21 Gauge which is highly used for orthopaedic and dental administrations, and the maximum injection force measured through 19 G needle (17.191 ± 2.296N) was convenient for manual injections. Angiogenesis tests were performed by an ex-ovo chick chorioallantoic membrane (CAM) assay by applying injectable solutions on CAM, which produced in situ hydrogels. Hydrogels induced microvascularity in CAM assay this was confirmed by histology analyses. Hydrogels with lower concentration of Hep showed more efficiency in pro-angiogenic response. Thereof, novel injectable hydrogels inducing angiogenesis (CS/HA/Hep) are potential candidates for bone regeneration and drug delivery applications.

A Simple Injectable Moldable Hydrogel Assembled from Natural Glycyrrhizic Acid with Inherent Antibacterial Activity

Injectable low-molecular-weight hydrogels (LMWHs) from biocompatible materials have attracted much attention in biomedical applications because they can adapt any desired sizes and cavity shapes. Searching for simple, biocompatible injectable LMWHs owning inherent antibacterial activity without complicated chemical modification remains an open question to avoid the tedious synthesis/purification process and the easy bacterial infection of hydrogels in a moist environment. In this work, glycyrrhizic acid (GL), a naturally occurring compound, was found to form a stable transparent LMWH at 37 °C in physiological phosphate buffered saline (PBS) with nanoclusters as the microstructures. Moreover, this hydrogel exhibited great injectable and moldable properties. The antibacterial study showed that the growth of Gram-positive Staphylococcus aureus (S. aureus) could be completely inhibited by GL, whereas noneffect on Gram-negative Escherichia coli (E. coli) was observed. In addition, cell viability and hemolysis assay revealed that GL had good biocompatibility and hemocompatibility to mammalian cells because of its natural origin. Our simple biocompatible injectable moldable LMWH with inherent antibacterial ability has potential in the area of biomaterials and 3D bioprinting.

Polyethylene Oxide (PEO) Molecular Weight Effects on Abuse-Deterrent Properties of Matrix Tablets

While polyethylene oxide (PEO)-based matrix tablets are frequently used as abuse-deterrent dosage forms, there is limited information available regarding how the selection of formulation components and manufacturing processes affect the resulting abuse-deterrent properties. The objective of the current study was to evaluate the effects of formulation and process variables on the abuse-deterrent features of PEO-containing tablets. Directly compressed tablets were prepared using three different PEO molecular weights (100,000; 900,000; and 5,000,000). As anticipated, sintering/thermal treatment above the melting point of PEO was crucial to impart crush-resistant features (tablet hardness > 500 N). In addition to the sintering temperature, the weight fraction of PEO in the tablets affected their mechanical strength, and at least 50% w/w PEO was required to impart the desired crush-resistant features. In addition, the formulation and process variables also impacted syringeability and injectability of the PEO gels formed when the tablets were hydrated to simulate attempted drug extraction. High molecular weight PEO (900,000 and 5,000,000) produced gels more resistant to syringeability and injectability compared to low molecular weight PEO (100,000). Sintering above the polymer melting point decreased PEO crystallinity after cooling, and longer sintering times resulted in PEO degradation producing lower viscosity gels with reduced resistance to syringeability and injectability. Although sintering above the melting point of PEO imparts optimal mechanical strength to the tablets, prolonged sintering durations negatively impact polymer stability and alter the resulting abuse-deterrent features of the PEO-based tablet formulations.

Setting Mechanism of a CDHA Forming α-TCP Cement Modified with Sodium Phytate for Improved Injectability

A calcium deficient hydroxyapatite (CDHA) forming cement with a bimodal grain size distribution, composed of α-TCP and fine grained CDHA at a weight ratio of 9:1, was modified by the addition of sodium phytate (IP6) in variable amounts ranging from 0.25 to 2 wt.%, related to the powder content. The injectability of the cement paste was drastically increased by the IP6 addition, independent of the amount of added IP6. Additionally, the cement paste viscosity during the first minutes decreased. These effects could be clearly related to a slightly more negative zeta potential. Furthermore, IP6 was shown to strongly retard the setting reaction, as can be seen both in the calorimetry and X-ray diffraction measurements. In addition, octacalcium phosphate (OCP) was identified as a further setting product. All measurements were performed at 23 °C and 37 °C to assess the effect of temperature on the setting reaction for both clinical handling by the surgeon and the final hardening in the bone defect.

Enhanced Osteogenesis of Injectable Calcium Phosphate Bone Cement Mediated by Loading Chondroitin Sulfate

Toward repairing critical-sized bone defects, calcium phosphate cement (CPC) has been well recognized as a fairly promising bone graft because of its properties of injectability, self-setting, biocompatibility, and osteoconductivity. However, poor osteogenic capacity of CPC still limits its applications for meeting the demands of bone healing. In this work, chondroitin sulfate (CS), as an important component of the extracellular matrix network, was introduced into CPC to enhance its osteogenesis ability. Incorporation of CS had no evident effect on the phase, morphology, apparent porosity, and compressive strength of hydrated cement products, but it notably enhanced the injectability and improved the antiwashout property of the cement pastes. CS was able to be sustainably released from CS-CPCs in a CS-dose-dependent manner and supposed to have a long-term release potential for constant biological stimulation. CS-CPCs markedly accelerated the preferential adsorption of fibronectin. Furthermore, CS-CPCs significantly improved the adhesion, proliferation, and osteogenic differentiation of bone mesenchymal stem cells, which was synergistically mediated by the adhesion events of cells on the hydrated cements and the stimulation effects of CS molecules. Herein, utilization of CS is supposed to endow injectable calcium phosphate bone cements with enhanced osteogenic capacity and suitable physicochemical properties for numerous promising orthopedic applications.

Incorporating Germanium Oxide into the Glass Phase of Novel Zinc/Magnesium-Based GPCs Designed for Bone Void Filling: Evaluating Their Physical and Mechanical Properties

The structural role of Germanium (Ge), when substituting for Zinc (Zn) up to 8 mol % in the 0.48SiO₂⁻0.12CaO⁻0.36ZnO⁻0.04MgO glass series, was investigated with respect to both the glass chemistry and also the properties of glass polyalkenoate cements (GPCs) manufactured from them. The Network connectivity (NC) of the glass was calculated to increase from 1.83 to 2.42 with the addition of GeO₂ (0⁻8 mol %). Differential thermal analysis (DTA) results confirmed an increase in the glass transition temperature (T_g) of the glass series with GeO₂ content. X-ray photoelectron spectroscopy (XPS) showed an increase in the ratio of bridging oxygens (BO) to non-bridging oxygens (NBO) with the addition of GeO₂, supporting the NC and DTA results. ²⁹Si magic angle spinning nuclear magnetic resonance spectroscopy (²⁹Si MAS-NMR) determined a chemical shift from -80.3 to -83.7 ppm as the GeO₂ concentration increased. These ionomeric glasses were subsequently used as the basic components in a series of GPCs by mixing them with aqueous polyacrylic acid (PAA). The handling properties of the GPCs resulting were evaluated with respect to the increasing concentration of GeO₂ in the glass phase. It was found that the working times of these GPCs increased from 3 to 15 min, while their setting times increased from 4 to 18 min, facilitating the injectability of the Zn/Mg-GPCs through a 16-gauge needle. These Ge-Zn/Mg-GPCs were found to be injectable up to 96% within 12 min. Zn/Mg-GPCs containing GeO₂ show promise as injectable cements for use in bone void filling.

Delivery Considerations of Highly Viscous Polymeric Fluids Mimicking Concentrated Biopharmaceuticals: Assessment of Injectability via Measurement of Total Work Done "WT"

An account is given of the recent development of the highly viscous complex biopharmaceuticals in relation to syringeability and injectability. The specific objective of this study is to establish a convenient method to examine problem of the injectability for the needle-syringe-formulation system when complex formulations with diverse viscosities are used. This work presents the inter-relationship between needle size, syringe volume, viscosity, and injectability of polymeric solutions having typical viscosities encountered in concentrated biologics, by applying a constant probe crosshead speed on the plunger-syringe needle assembly and continuously recording the force-distance profiles. A computerized texture analyzer was used to accurately capture, display, and store force, displacement, and time data. The force-distance curve and area under the curve are determined, and total work done for complete extrusion of the syringe content was calculated automatically by applying an established Matlab program. Various concentrations (i.e., 0.5-4% w/v of polymeric fluids/dispersions) of polyethylene oxide (PEO) and hydroxypropyl methylcellulose (HPMC) with viscosity ranges of 5-100 cP mimicking concentrated monoclonal antibody solutions and complex biopharmaceutical formulations are investigated. Results indicate that calculated values of total work done to completely extrude the syringe content are the most appropriate parameter that describes viscosity-injection force of dispersed formulations. Additionally, the rheological properties of HPMC and PEO fluids in the context of syringeability and injectability are discussed.

Rheological and Mechanical Properties of Thermoresponsive Methylcellulose/Calcium Phosphate-Based Injectable Bone Substitutes

In this study, a novel injectable bone substitute (IBS) was prepared by incorporating a bioceramic powder in a polymeric solution comprising of methylcellulose (MC), gelatin and citric acid. Methylcellulose was utilized as the polymeric matrix due to its thermoresponsive properties and biocompatibility. 2.5 wt % gelatin and 3 wt % citric acid were added to the MC to adjust the rheological properties of the prepared IBS. Then, 0, 20, 30 and 50 wt % of the bioceramic component comprising tetracalcium phosphate/hydroxyapatite (TTCP/HA), dicalcium phosphate dehydrate (DCPD) and calcium sulfate dehydrate (CSD) were added into the prepared polymeric component. The prepared IBS samples had a chewing gum-like consistency. IBS samples were investigated in terms of their chemical structure, rheological characteristics, and mechanical properties. After that, in vitro degradation studies were carried out by measurement of pH and % remaining weight. Viscoelastic characteristics of the samples indicated that all of the prepared IBS were injectable and they hardened at approximately 37 °C. Moreover, with increasing wt % of the bioceramic component, the degradation rate of the samples significantly reduced and the mechanical properties were improved. Therefore, the experimental results indicated that the P50 mix may be a promising candidates to fill bone defects and assist bone recovery for non-load bearing applications.

Nanoscale Silk-Hydroxyapatite Hydrogels for Injectable Bone Biomaterials

Injectable hydrogel systems are important bone substitutes for regeneration because of their handling properties and the ability to fill irregular defects. Silk-hydroxyapatite composite materials with silk nanofibers in hydrogels were prepared and used as biomaterials for osteogenesis. These thixotropic silk nanofiber hydrogels and water-dispersible silk-HA nanoparticles were blended to form injectable nanoscale systems with a homogeneous distribution of a high HA content [60% (w/w)] to imitate bone niche. A modulus of ∼21 kPa was also achieved following the addition of HA in the systems, providing physical cues to induce osteodifferentiation. The composite hydrogels supported improved osteogenesis compared to that with silk nanofiber hydrogels. The newly formed bone tissue and bone defect healing were detected after implantation of the silk-HA composite hydrogels, suggesting utility for the regeneration of irregular bone defects.

Injectable uncrosslinked biomimetic hydrogels as candidate scaffolds for neural stem cell delivery

Mammalian central nervous system has a limited ability for self-repair under diseased or injury conditions. Repair strategies focused on exogenously delivering autologous neural stem cells (NSCs) to replace lost neuronal populations and axonal pathways in situ, and promote endogenous repair mechanisms are gaining traction. Successful outcomes are contingent on selecting an appropriate delivery vehicle for injecting cells that promotes cell retention and survival, elicits differentiation to desired lineages, and enhances axonal outgrowth upon integration into the host tissue. Hydrogels made of varying compositions of collagen, laminin, hyaluronic acid (HA), and chondroitin sulfate proteoglycan (CSPG) were developed, with no external crosslinking agents, to mimic the native extracellular matrix composition. The physical (porosity, pore-size, gel integrity, swelling ratio, and enzymatic degradation), mechanical (viscosity, storage and loss moduli, Young's modulus, creep, and stress-relaxation), and biological (cell survival, differentiation, neurite outgrowth, and integrin expression) characteristics of these hydrogels were assessed. These hydrogels exhibited excellent injectability, retained gel integrity, and matched the mechanical moduli of native brain tissue, possibly due to natural collagen fibril polymerization and physical-crosslinking between HA molecules and collagen fibrils. Depending on the composition, these hydrogels promoted cell survival, neural differentiation, and neurite outgrowth, as evident from immunostaining and western blots. These cellular outcomes were facilitated by cellular binding via α₆ , β₁ , and CD44 surface integrins to these hydrogels. Results attest to the utility of uncrosslinked, ECM-mimicking hydrogels to deliver NSCs for tissue engineering and regenerative medicine applications. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 790-805, 2017.

Injectable, degradable, electroactive nanocomposite hydrogels containing conductive polymer nanoparticles for biomedical applications

Injectable electroactive hydrogels (eGels) are promising in regenerative medicine and drug delivery, however, it is still a challenge to obtain such hydrogels simultaneously possessing other properties including uniform structure, degradability, robustness, and biocompatibility. An emerging strategy to endow hydrogels with desirable properties is to incorporate functional nanoparticles in their network. Herein, we report the synthesis and characterization of an injectable hydrogel based on oxidized alginate (OA) crosslinking gelatin reinforced by electroactive tetraaniline-graft-OA nanoparticles (nEOAs), where nEOAs are expected to impart electroactivity besides reinforcement without significantly degrading the other properties of hydrogels. Assays of transmission electron microscopy, (1)H nuclear magnetic resonance, and dynamic light scattering reveal that EOA can spontaneously and quickly self-assemble into robust nanoparticles in water, and this nanoparticle structure can be kept at pH 3~9. Measurement of the gel time by rheometer and the stir bar method confirms the formation of the eGels, and their gel time is dependent on the weight content of nEOAs. As expected, adding nEOAs to hydrogels does not cause the phase separation (scanning electron microscopy observation), but it improves mechanical strength up to ~8 kPa and conductivity up to ~10(-6) S/cm in our studied range. Incubating eGels in phosphate-buffered saline leads to their further swelling with an increase of water content <6% and gradual degradation. When growing mesenchymal stem cells on eGels with nEOA content ≤14%, the growth curves and morphology of cells were found to be similar to that on tissue culture plastic; when implanting these eGels on a chick chorioallantoic membrane for 1 week, mild inflammation response appeared without any other structural changes, indicating their good in vitro and in vivo biocompatibility. With injectability, uniformity, degradability, electroactivity, relative robustness, and biocompatibility, these eGels may have a huge potential as scaffolds for tissue regeneration and matrix for stimuli responsive drug release.

Bioinspired Nanoparticulate Medical Glues for Minimally Invasive Tissue Repair

Delivery of tissue glues through small-bore needles or trocars is critical for sealing holes, affixing medical devices, or attaching tissues together during minimally invasive surgeries. Inspired by the granule-packaged glue delivery system of sandcastle worms, a nanoparticulate formulation of a viscous hydrophobic light-activated adhesive based on poly(glycerol sebacate)-acrylate is developed. Negatively charged alginate is used to stabilize the nanoparticulate surface to significantly reduce its viscosity and to maximize injectability through small-bore needles. The nanoparticulate glues can be concentrated to ≈30 w/v% dispersions in water that remain localized following injection. With the trigger of a positively charged polymer (e.g., protamine), the nanoparticulate glues can quickly assemble into a viscous glue that exhibits rheological, mechanical, and adhesive properties resembling the native poly(glycerol sebacate)-acrylate based glues. This platform should be useful to enable the delivery of viscous glues to augment or replace sutures and staples during minimally invasive procedures.

Premixed calcium silicate cement for endodontic applications: injectability, setting time and radiopacity

Calcium silicate-based materials (also called MTA) are increasingly being used in endodontic applications. However, the handling properties of MTA are not optimal when it comes to injectability and cohesion. Premixing the cements using glycerol avoids these issues. However, there is a lack of data on the effect of common cement variables on important properties of premixed cements for endodontic applications. In this study, the effects of liquid-to-powder ratio, amount of radiopacifier and amount of calcium sulfate (added to control the setting time) were screened using a statistical model. In the second part of the study, the liquid-to-powder ratio was optimized for cements containing three different amounts of radiopacifier. Finally, the effect of using glycerol rather than water was evaluated in terms of radiopacity. The setting time was found to increase with the amount of radiopacifier when the liquid-to-powder ratio was fixed. This was likely due to the higher density of the radiopacifier in comparison to the calcium silicate, which gave a higher liquid-to-powder ratio in terms of volume. Using glycerol rather than water to mix the cements led to a decrease in radiopacity of the cement. In conclusion, we were able to produce premixed calcium silicate cements with acceptable properties for use in endodontic applications.

Development and characterization of an injectable cement of nano calcium-deficient hydroxyapatite/multi(amino acid) copolymer/calcium sulfate hemihydrate for bone repair

A novel injectable bone cement was developed by integration of nano calcium-deficient hydroxyapatite/multi(amino acid) copolymer (n-CDHA/MAC) and calcium sulfate hemihydrate (CSH; CaSO4 · 1/2H2O). The structure, setting time, and compressive strength of the cement were investigated. The results showed that the cement with a liquid to powder ratio of 0.8 mL/g exhibited good injectability and appropriate setting time and mechanical properties. In vitro cell studies indicated that MC3T3-E1 cells cultured on the n-CDHA/MAC/CSH composite spread well and showed a good proliferation state. The alkaline phosphatase activity of the MC3T3-E1 cells cultured on the n-CDHA/MAC/CSH composite was significantly higher than that of the cells on pure CSH at 4 and 7 days of culture. The n-CDHA/MAC/CSH cement was implanted into critical size defects of the femoral condyle in rabbits to evaluate its biocompatibility and osteogenesis in vivo. Radiological and histological results indicated that introduction of the n-CDHA/MAC into CSH enhanced new bone formation, and the n-CDHA/MAC/CSH cement exhibited good biocompatibility and degradability. In conclusion, the injectable n-CDHA/MAC/CSH composite cement has a significant clinical advantage over pure CSH cement, and may be a promising bone graft substitute for the treatment of bone defects.

Calcium Phosphate Bone Cements Including Sugar Surfactants: Part Two-Injectability, Adhesive Properties and Biocompatibility

Addition of sugar surfactants, sucrose fatty acid esters and alkylpolyglucosides to a calcium phosphate cement, designed for bone reconstruction, is described. Thanks to their adsorption at the surface of the calcium phosphate particles, the sugar surfactants allowed a full injectability and brought a very good workability. Injectability was measured by monitoring force-distance curves. With some of the selected sugar surfactants adhesive properties of the cement pastes were also observed, which were measured by tack tests. Finally, some properties related to biological applications are described, including gentamicine release and osteoblast viability experiments. The whole study demonstrates that addition of these mild surfactants improved several properties of the calcium phosphate cement, without impairing function.