Injectable thermosensitive PEG–PCL–PEG hydrogel/acellular bone matrix composite for bone regeneration in cranial defects

Melt-extruded biocompatible surgical sutures loaded with microspheres designed for wound healing

Sutures are commonly used in surgical procedures and have immense potential for direct drug delivery into the wound site. However, incorporating active pharmaceutical ingredients into the sutures has always been challenging as their mechanical strength deteriorates. This study proposes a new method to produce microspheres-embedded surgical sutures that offer adequate mechanical properties for effective wound healing applications. The study used curcumin, a bioactive compound found in turmeric, as a model drug due to its anti-inflammatory, antioxidant, and anti-bacterial properties, which make it an ideal candidate for a surgical suture drug delivery system. Curcumin-loaded microspheres were produced using the emulsion solvent evaporation method with polyvinyl alcohol (PVA) as the aqueous phase. The microspheres' particle sizes, drug loading (DL) capacity, and encapsulation efficiency (EE) were investigated. Microspheres were melt-extruded with polycaprolactone and polyethylene glycol via a 3D bioplotter, followed by a drawing process to optimise the mechanical strength. The sutures' thermal, physiochemical, and mechanical properties were investigated, and the drug delivery and biocompatibility were evaluated. The results showed that increasing the aqueous phase concentration resulted in smaller particle sizes and improved DL capacity and EE. However, if PVA was used at 3% w/v or below, it prevented aggregate formation after lyophilisation, and the average particle size was found to be 34.32 ± 12.82 μm. The sutures produced with the addition of microspheres had a diameter of 0.38 ± 0.02 mm, a smooth surface, minimal tissue drag, and proper tensile strength. Furthermore, due to the encapsulated drug-polymer structure, the sutures exhibited a prolonged and sustained drug release of up to 14 d. Microsphere-loaded sutures demonstrated non-toxicity and accelerated wound healing in thein vitrostudies. We anticipate that the microsphere-loaded sutures will serve as an excellent biomedical device for facilitating wound healing.

Dynamic Transcriptome Analysis of SFRP Family in Guided Bone Regeneration With Occlusive Periosteum in Swine Model

BACKGROUND

A variety of congenital or acquired conditions can cause craniomaxillofacial bone defects, resulting in a heavy financial burden and psychological stress. Guided bone self-generation with periosteum-preserved has great potential for reconstructing large bone defects.

METHODS

A swine model of guided bone regeneration with occlusive periosteum was established, the rib segment was removed, and the periosteum was sutured to form a closed regeneration chamber. Hematoxylin and eosin staining, Masson's staining, and Safranine O-Fast Green staining were done. Nine-time points were chosen for collecting the periosteum and regenerated bone tissue for gene sequencing. The expression level of each secreted frizzled-related protein (SFRP) member and the correlations among them were analyzed.

RESULTS

The process of bone regeneration is almost complete 1 month after surgery, and up to 1 week after surgery is an important interval for initiating the process. The expression of each SFRP family member fluctuated greatly. The highest expression level of all members ranged from 3 days to 3 months after surgery. The expression level of SFRP2 was the highest, and the difference between 2 groups was the largest. Secreted frizzled-related protein 2 and SFRP4 showed a notable positive correlation between the control and model groups. Secreted frizzled-related protein 1, SFRP2, and SFRP4 had a significant spike in fold change at 1 month postoperatively. Secreted frizzled-related protein 1 and SFRP2 had the strongest correlation.

CONCLUSIONS

This study revealed the dynamic expression of the SFRP family in guided bone regeneration with occlusive periosteum in a swine model, providing a possibility to advance the clinical application of bone defect repair.

Crosslinking strategies for biomimetic hydrogels in bone tissue engineering

Bone tissue engineering has become a popular area of study for making biomimetic hydrogels to treat bone diseases. In this work, we looked at biocompatible hydrogels that can be injected into bone defects that require the smallest possible surgery. Mineral ions can be attached to polymer chains to make useful hydrogels that help bones heal faster. These ions are very important for the balance of the body. In the chemically-triggered sector, advanced hydrogels cross-linked by different molecular agents have many advantages, such as being selective, able to form gels, and having mechanical properties that can be modified. In addition, different photo-initiators can be used to make photo cross linkable hydrogels react quickly and moderately under certain light bands. Enzyme-triggered hydrogels are another type of hydrogel that can be used to repair bone tissue because they are biocompatible and gel quickly. We also look at some of the important factors mentioned above that could change how well bone tissue engineering works as a therapy. Finally, this review summarizes the problems that still need to be solved to make clinically relevant hydrogels.

Cyclical endometrial repair and regeneration: Molecular mechanisms, diseases, and therapeutic interventions

The endometrium is a unique human tissue with an extraordinary ability to undergo a hormone-regulated cycle encompassing shedding, bleeding, scarless repair, and regeneration throughout the female reproductive cycle. The cyclical repair and regeneration of the endometrium manifest as changes in endometrial epithelialization, glandular regeneration, and vascularization. The mechanisms encompass inflammation, coagulation, and fibrinolytic system balance. However, specific conditions such as endometriosis or TCRA treatment can disrupt the process of cyclical endometrial repair and regeneration. There is uncertainty about traditional clinical treatments' efficacy and side effects, and finding new therapeutic interventions is essential. Researchers have made substantial progress in the perspective of regenerative medicine toward maintaining cyclical endometrial repair and regeneration in recent years. Such progress encompasses the integration of biomaterials, tissue-engineered scaffolds, stem cell therapies, and 3D printing. This review analyzes the mechanisms, diseases, and interventions associated with cyclical endometrial repair and regeneration. The review discusses the advantages and disadvantages of the regenerative interventions currently employed in clinical practice. Additionally, it highlights the significant advantages of regenerative medicine in this domain. Finally, we review stem cells and biologics among the available interventions in regenerative medicine, providing insights into future therapeutic strategies.

Hydrogels as Scaffolds in Bone-Related Tissue Engineering and Regeneration

Several years have passed since the medical and scientific communities leaned toward tissue engineering as the most promising field to aid bone diseases and defects resulting from degenerative conditions or trauma. Owing to their histocompatibility and non-immunogenicity, bone grafts, precisely autografts, have long been the gold standard in bone tissue therapies. However, due to issues associated with grafting, especially the surgical risks and soaring prices of the procedures, alternatives are being extensively sought and researched. Fibrous and non-fibrous materials, synthetic substitutes, or cell-based products are just a few examples of research directions explored as potential solutions. A very promising subgroup of these replacements involves hydrogels. Biomaterials resembling the bone extracellular matrix and therefore acting as 3D scaffolds, providing the appropriate mechanical support and basis for cell growth and tissue regeneration. Additional possibility of using various stimuli in the form of growth factors, cells, etc., within the hydrogel structure, extends their use as bioactive agent delivery platforms and acts in favor of their further directed development. The aim of this review is to bring the reader closer to the fascinating subject of hydrogel scaffolds and present the potential of these materials, applied in bone and cartilage tissue engineering and regeneration.

Monotropein Protects Mesenchymal Stem Cells from Lipopolysaccharide-Induced Impairments and Promotes Fracture Healing in an Ovariectomized Mouse Model

Monotropein is one of the active ingredients in Morinda Officinalis, which has been used for the treatment in multiple bone and joint diseases. This study aimed to observe the in vitro effects of Monotropein on osteogenic differentiation of lipopolysaccharide treated bone marrow mesenchymal stem cells (bMSCs), and the in vivo effects of local application of Monotropein on bone fracture healing in ovariectomized mice. Lipopolysaccharide was used to set up the inflammatory model in bMSCs, which were treated by Monotropein. Molecular docking analysis was performed to evaluate the potential interaction between Monotropein and p65. Transverse fractures of middle tibias were established in ovariectomized mice, and Monotropein was locally applied to the fracture site using injectable hydrogel. Monotropein enhanced the ability of primary bMSCs in chondro-osteogenic differentiation. Furthermore, Monotropein rescued lipopolysaccharide-induced osteogenic differentiation impairment and inhibited lipopolysaccharide-induced p65 phosphorylation in primary bMSCs. Docking analysis showed that the binding activity of Monotropein and p65/14-3-3 complex is stronger than the selective inhibitor of NF-κB (p65), DP-005. Local application of Monotropein partially rescued the decreased bone mass and biomechanical properties of callus or healed tibias in ovariectomized mice. The expressions of Runx2, Osterix and Collagen I in the 2-week callus were partially restored in Monotropein-treated ovariectomized mice. Taking together, local application of Monotropein promoted fracture healing in ovariectomized mice. Inhibition of p65 phosphorylation and enhancement in osteogenesis of mesenchymal stem cells could be partial of the effective mechanisms.

Stimuli-responsive dynamic hydrogels: design, properties and tissue engineering applications

The field of tissue engineering and regenerative medicine has been evolving at a rapid pace with numerous novel and interesting biomaterials being reported. Hydrogels have come a long way in this regard and have been proven to be an excellent choice for tissue regeneration. This could be due to their innate properties such as water retention, and ability to carry and deliver a multitude of therapeutic and regenerative elements to aid in better outcomes. Over the past few decades, hydrogels have been developed into an active and attractive system that can respond to various stimuli, thereby presenting a wider control over the delivery of the therapeutic agents to the intended site in a spatiotemporal manner. Researchers have developed hydrogels that respond dynamically to a multitude of external as well as internal stimuli such as mechanics, thermal energy, light, electric field, ultrasonics, tissue pH, and enzyme levels, to name a few. This review gives a brief overview of the recent developments in such hydrogel systems which respond dynamically to various stimuli, some of the interesting fabrication strategies, and their application in cardiac, bone, and neural tissue engineering.

Injectable hydrogels for cartilage and bone tissue regeneration: A review

Annually, millions of patients suffer from irreversible injury owing to the loss or failure of an organ or tissue caused by accident, aging, or disease. The combination of injectable hydrogels and the science of stem cells have emerged to address this persistent issue in society by generating minimally invasive treatments to augment tissue function. Hydrogels are composed of a cross-linked network of polymers that exhibit a high-water retention capacity, thereby mimicking the wet environment of native cells. Due to their inherent mechanical softness, hydrogels can be used as needle-injectable stem cell carrier materials to mend tissue defects. Hydrogels are made of different natural or synthetic polymers, displaying a broad portfolio of eligible properties, which include biocompatibility, low cytotoxicity, shear-thinning properties as well as tunable biological and physicochemical properties. Presently, novel ongoing developments and native-like hydrogels are increasingly being used broadly to improve the quality of life of those with disabling tissue-related diseases. The present review outlines various future and in-vitro applications of injectable hydrogel-based biomaterials, focusing on the newest ongoing developments of in-situ forming injectable hydrogels for bone and cartilage tissue engineering purposes.

Band-Aid-Like Self-Fixed Barrier Membranes Enable Superior Bone Augmentation

In guided bone regeneration surgery, a barrier membrane is usually used to inhibit soft tissue from interfering with osteogenesis. However, current barrier membranes usually fail to resist the impact of external forces on bone-augmented region, thus causing severe displacement of membranes and their underlying bone graft materials, eventually leading to unsatisfied bone augmentation. Herein, a new class of local double-layered adhesive barrier membranes (ABMs) is developed to successfully immobilize bone graft materials. The air-dried adhesive hydrogel layers with suction-adhesion properties enable ABMs to firmly adhere to the wet bone surface through a "stick-and-use" band-aid-like strategy and effectively prevent the displacement of membranes and the leakage of bone grafts in uncontained bone defect treatment. Furthermore, the strategy is versatile for preparing diverse adhesive barrier membranes and immobilizing different bone graft materials for various surgical regions. By establishing such a continuous barrier for the bone graft material, this strategy may open a novel avenue for designing the next-generation barrier membranes.

Recent Advances in Nanoparticle Development for Drug Delivery: A Comprehensive Review of Polycaprolactone-Based Multi-Arm Architectures

Controlled drug delivery is a crucial area of study for improving the targeted availability of drugs; several polymer systems have been applied for the formulation of drug delivery vehicles, including linear amphiphilic block copolymers, but with some limitations manifested in their ability to form only nanoaggregates such as polymersomes or vesicles within a narrow range of hydrophobic/hydrophilic balance, which can be problematic. For this, multi-arm architecture has emerged as an efficient alternative that overcame these challenges, with many interesting advantages such as reducing critical micellar concentrations, producing smaller particles, allowing for various functional compositions, and ensuring prolonged and continuous drug release. This review focuses on examining the key variables that influence the customization of multi-arm architecture assemblies based on polycaprolactone and their impact on drug loading and delivery. Specifically, this study focuses on the investigation of the structure-property relationships in these formulations, including the thermal properties presented by this architecture. Furthermore, this work will emphasize the importance of the type of architecture, chain topology, self-assembly parameters, and comparison between multi-arm structures and linear counterparts in relation to their impact on their performance as nanocarriers. By understanding these relationships, more effective multi-arm polymers can be designed with appropriate characteristics for their intended applications.

A novel injectable hydrogel containing polyetheretherketone for bone regeneration in the craniofacial region

Polyetheretherketone (PEEK) is an organic material introduced as an alternative for titanium implants. Injectable hydrogels are the most promising approach for bone regeneration in the oral cavity to fill the defects with irregular shapes and contours conservatively. In the current study, injectable Aldehyde-cellulose nanocrystalline/silk fibroin (ADCNCs/SF) hydrogels containing PEEK were synthesized, and their bone regeneration capacity was evaluated. Structure, intermolecular interaction, and the reaction between the components were assessed in hydrogel structure. The cytocompatibility of the fabricated scaffolds was evaluated on human dental pulp stem cells (hDPSCs). Moreover, the osteoinduction capacity of ADCNCs/SF/PEEK hydrogels on hDPSCs was evaluated using Real-time PCR, Western blot, Alizarin red staining and ALP activity. Bone formation in critical-size defects in rats' cranial was assessed histologically and radiographically. The results confirmed the successful fabrication of the hydrogel and its osteogenic induction ability on hDPSCs. Furthermore, in in vivo phase, bone formation was significantly higher in ADCNCs/SF/PEEK group. Hence, the enhanced bone regeneration in response to PEEK-loaded hydrogels suggested its potential for regenerating bone loss in the craniofacial region, explicitly surrounding the dental implants.

Engineering exosomes for bone defect repair

Currently, bone defect repair is still an intractable clinical problem. Numerous treatments have been performed, but their clinical results are unsatisfactory. As a key element of cell-free therapy, exosome is becoming a promising tool of bone regeneration in recent decades, because of its promoting osteogenesis and osteogenic differentiation function in vivo and in vitro. However, low yield, weak activity, inefficient targeting ability, and unpredictable side effects of natural exosomes have limited the clinical application. To overcome the weakness, various approaches have been applied to produce engineering exosomes by regulating their production and function at present. In this review, we will focus on the engineering exosomes for bone defect repair. By summarizing the exosomal cargos affecting osteogenesis, the strategies of engineering exosomes and properties of exosome-integrated biomaterials, this work will provide novel insights into exploring advanced engineering exosome-based cell-free therapy for bone defect repair.

Recent advances in hydrogels-based osteosarcoma therapy

Osteosarcoma (OS), as a typical kind of bone tumors, has a high incidence among adolescents. Traditional tumor eradication avenues for OS such as chemotherapy, surgical therapy and radiation therapy usually have their own drawbacks including recurrence and metastasis. In addition, another serious issue in the treatment of OS is bone repair because the bone after tumor invasion usually has difficulty in repairing itself. Hydrogels, as a synthetic or natural platform with a porous three-dimensional structure, can be applied as desirable platforms for OS treatment. They can not only be used as carriers for tumor therapeutic drugs but mimic the extracellular matrix for the growth and differentiation of mesenchymal stem cells (MSCs), thus providing tumor treatment and enhancing bone regeneration at the same time. This review focuses the application of hydrogels in OS suppression and bone regeneration, and give some suggests on future development.

Long-acting formulation strategies for protein and peptide delivery in the treatment of PSED

The invigoration of protein and peptides in serious eye disease includes age-related macular degeneration, choroidal neovascularization, retinal neovascularization, and diabetic retinopathy. The transportation of macromolecules like aptamers, recombinant proteins, and monoclonal antibodies to the posterior segment of the eye is challenging due to their high molecular weight, rapid degradation, and low solubility. Moreover, it requires frequent administration for prolonged therapy. The long-acting novel formulation strategies are helpful to overcome these issues and provide superior therapy. It avoids frequent administration, improves stability, high retention time, and avoids burst release. This review briefly enlightens posterior segments of eye diseases with their diagnosis techniques and treatments. This article mainly focuses on recent advanced approaches like intravitreal implants and injectables, electrospun injectables, 3D printed drug-loaded implants, nanostructure thin-film polymer devices encapsulated cell technology-based intravitreal implants, injectable and depots, microneedles, PDS with ranibizumab, polymer nanoparticles, inorganic nanoparticles, hydrogels and microparticles for delivering macromolecules in the eye for intended therapy. Furthermore, novel techniques like aptamer, small Interference RNA, and stem cell therapy were also discussed. It is predicted that these systems will make revolutionary changes in treating posterior segment eye diseases in future.

Advances of Stimulus-Responsive Hydrogels for Bone Defects Repair in Tissue Engineering

Bone defects, as one of the most urgent problems in the orthopedic clinic, have attracted much attention from the biomedical community and society. Hydrogels have been widely used in the biomedical field for tissue engineering research because of their excellent hydrophilicity, biocompatibility, and degradability. Stimulus-responsive hydrogels, as a new type of smart biomaterial, have more advantages in sensing external physical (light, temperature, pressure, electric field, magnetic field, etc.), chemical (pH, redox reaction, ions, etc.), biochemical (glucose, enzymes, etc.) and other different stimuli. They can respond to stimuli such as the characteristics of the 3D shape and solid-liquid phase state, and exhibit special properties (injection ability, self-repair, shape memory, etc.), thus becoming an ideal material to provide cell adhesion, proliferation, and differentiation, and achieve precise bone defect repair. This review is focused on the classification, design concepts, and research progress of stimulus-responsive hydrogels based on different types of external environmental stimuli, aiming at introducing new ideas and methods for repairing complex bone defects.

Injectable hydrogels for bone and cartilage tissue engineering: a review

Tissue engineering, using a combination of living cells, bioactive molecules, and three-dimensional porous scaffolds, is a promising alternative to traditional treatments such as the use of autografts and allografts for bone and cartilage tissue regeneration. Scaffolds, in this combination, can be applied either through surgery by implantation of cell-seeded pre-fabricated scaffolds, or through injection of a solidifying precursor and cell mixture, or as an injectable cell-seeded pre-fabricated scaffold. In situ forming and pre-fabricated injectable scaffolds can be injected directly into the defect site with complex shape and critical size in a minimally invasive manner. Proper and homogeneous distribution of cells, biological factors, and molecular signals in these injectable scaffolds is another advantage over pre-fabricated scaffolds. Due to the importance of injectable scaffolds in tissue engineering, here different types of injectable scaffolds, their design challenges, and applications in bone and cartilage tissue regeneration are reviewed.

Fabrication of physical and chemical crosslinked hydrogels for bone tissue engineering

Bone tissue engineering has emerged as a significant research area that provides promising novel tools for the preparation of biomimetic hydrogels applied in bone-related diseases (e.g., bone defects, cartilage damage, osteoarthritis, etc.). Herein, thermal sensitive polymers (e.g., PNIPAAm, Soluplus, etc.) were introduced into main chains to fabricate biomimetic hydrogels with injectability and compatibility for those bone defect need minimally invasive surgery. Mineral ions (e.g., calcium, copper, zinc, and magnesium), as an indispensable role in maintaining the balance of the organism, were linked with polymer chains to form functional hydrogels for accelerating bone regeneration. In the chemically triggered hydrogel section, advanced hydrogels crosslinked by different molecular agents (e.g., genipin, dopamine, caffeic acid, and tannic acid) possess many advantages, including extensive selectivity, rapid gel-forming capacity and tunable mechanical property. Additionally, photo crosslinking hydrogel with rapid response and mild condition can be triggered by different photoinitiators (e.g., I2959, LAP, eosin Y, riboflavin, etc.) under specific wavelength of light. Moreover, enzyme triggered hydrogels were also utilized in the tissue regeneration due to its rapid gel-forming capacity and excellent biocompatibility. Particularly, some key factors that can determine the therapy effect for bone tissue engineering were also mentioned. Finally, brief summaries and remaining issues on how to properly design clinical-oriented hydrogels were provided in this review.

An Injectable Platform of Engineered Cartilage Gel and Gelatin Methacrylate to Promote Cartilage Regeneration

Cell–hydrogel constructs are frequently used as injectable platforms for irregular cartilage regeneration. However, cell–hydrogel constructs have obvious disadvantages, such as long culture times, high probability of infection, and poor cartilage formation capacity, significantly limiting their clinical translation. In this study, we aimed to develop a novel injectable platform comprising engineered cartilage gel (ECG) and gelatin methacrylate (GelMA) to improve cartilage regeneration. We first prepared an ECG by cutting the in vitro engineered cartilage sheet into pieces. The chondrocytes and ECG were evenly encapsulated into GelMA to form Cell-GelMA and ECG-GelMA constructs. The ECG-GelMA construct exhibited preferred gel characteristics and superior biocompatibility compared with the Cell-GelMA construct counterpart. After subcutaneous implantation in nude mice and goat, both gross views and histological evaluations showed that the ECG-GelMA construct achieved more homogenous, stable, and mature cartilage regeneration than the Cell-GelMA construct. Immunological evaluations showed that ECG-GelMA had a mitigatory immunologic reaction than the Cell-GelMA construct. Overall, the results suggest that the ECG-GelMA is a promising injectable platform for cartilage regeneration that may advance clinical translation.

Future Challenges and Opportunities of Extracellular Matrix Hydrogels in Female Reproductive Medicine

Bioengineering and reproductive medicine have progressed shoulder to shoulder for several decades. A key point of overlap is the development and clinical translation of technologies to support reproductive health, e.g., scaffold-free constructs, polymeric scaffolds, bioprinting or microfluidics, and hydrogels. Hydrogels are the focus of intense study, and those that are derived from the extracellular matrix (ECM) of reproductive tissues and organs are emerging as promising new players given their results in pre-clinical models. This literature review addresses the recent advances in the use of organ-specific ECM hydrogels in reproductive medicine, considering the entire female reproductive tract. We discuss in-depth papers describing the development of ECM hydrogels, their use in in vitro models, and their in vivo application in preclinical studies. We also summarize the functions of hydrogels, including as grafts, carriers for cell transplantation, or drug depots, and present the potential and possible scope for use of ECM hydrogels in the near future based on recent scientific advances.

Polymeric Hydrogels as Mesenchymal Stem Cell Secretome Delivery System in Biomedical Applications

Secretomes of mesenchymal stem cells (MSCs) have been successfully studied in preclinical models for several biomedical applications, including tissue engineering, drug delivery, and cancer therapy. Hydrogels are known to imitate a three-dimensional extracellular matrix to offer a friendly environment for stem cells; therefore, hydrogels can be used as scaffolds for tissue construction, to control the distribution of bioactive compounds in tissues, and as a secretome-producing MSC culture media. The administration of a polymeric hydrogel-based MSC secretome has been shown to overcome the fast clearance of the target tissue. In vitro studies confirm the bioactivity of the secretome encapsulated in the gel, allowing for a controlled and sustained release process. The findings reveal that the feasibility of polymeric hydrogels as MSC -secretome delivery systems had a positive influence on the pace of tissue and organ regeneration, as well as an enhanced secretome production. In this review, we discuss the widely used polymeric hydrogels and their advantages as MSC secretome delivery systems in biomedical applications.

Injectable nanocomposite hydrogels as an emerging platform for biomedical applications: A review

Hydrogels have attracted much attention for biomedical and pharmaceutical applications due to the similarity of their biomimetic structure to the extracellular matrix of natural living tissues, tunable soft porous microarchitecture, superb biomechanical properties, proper biocompatibility, etc. Injectable hydrogels are an exciting type of hydrogels that can be easily injected into the target sites using needles or catheters in a minimally invasive manner. The more comfortable use, less pain, faster recovery period, lower costs, and fewer side effects make injectable hydrogels more attractive to both patients and clinicians in comparison to non-injectable hydrogels. However, it is difficult to achieve an ideal injectable hydrogel using just a single material (i.e., polymer). This challenge can be overcome by incorporating nanofillers into the polymeric matrix to engineer injectable nanocomposite hydrogels with combined or synergistic properties gained from the constituents. This work aims to critically review injectable nanocomposite hydrogels, their preparation methods, properties, functionalities, and versatile biomedical and pharmaceutical applications such as tissue engineering, drug delivery, and cancer labeling and therapy. The most common natural and synthetic polymers as matrices together with the most popular nanomaterials as reinforcements, including nanoceramics, carbon-based nanostructures, metallic nanomaterials, and various nanosized polymeric materials, are highlighted in this review.

Thermosensitive hydrogel for in situ-controlled methotrexate delivery

Methotrexate (MTX) is widely used for the treatment of various types of cancer; however, it has drawbacks such as low solubility, lack of selectivity, premature degradation, and side effects. To solve these weaknesses, a hydrogel with the ability to contain and release MTX under physiological conditions without burst release was synthesized. The hydrogel was fabricated with a poly(ɛ-caprolactone)-b-poly(ethylene glycol)-b-poly(ɛ-caprolactone) (PCL–PEG–PCL) triblock copolymer, synthesized by ring-opening polymerization. The characterizations by proton nuclear magnetic resonance spectroscopy and Fourier-transform infrared spectrometry confirmed the copolymer assembly, whereas the molecular weight analysis validated the PCL2000–PEG1000–PCL2000 structure. The copolymer aqueous solution exhibited sol–gel phase transition at 37°C and injection capacity. The hydrogel supported a load of 1,000 μg MTX·mL−1, showing a gradual and sustained release profile of the drug for 14 days, with a delivery up to 92% at pH 6.7. The cytotoxicity of the MTX-loaded hydrogel was performed by the methyl thiazole tetrazolium assay, showing a mean inhibitory concentration of 50% of MCF-7 cells (IC50) at 43 µg MTX·mL−1.

An oxygen-enriched thermosensitive hydrogel for the relief of a hypoxic tumor microenvironment and enhancement of radiotherapy

The rapid proliferation of tumor cells and tortuous vasculature in solid tumors often bring about a hypoxic tumor microenvironment, which renders tumor cells more resistant to many cancer treatments, including radiotherapy. In this study, an injectable and thermosensitive composite hydrogel composed of perfluorooctanoic acid (PFOA) modified monomethoxy poly(ethylene glycol)-poly(D,L-lactide-co-glycolide) (mPEG-PLGA-PFOA) and perfluorooctyl bromide (PFOB) that presented a thermoreversible sol-gel transition upon heating was developed to deliver exogenous oxygen for the relief of tumor hypoxia and enhancement of radiotherapy. The fluorinated modification of copolymers significantly increased the stability of PFOB in the mPEG-PLGA-PFOA aqueous solution owing to the fluorophilic interaction between PFOB and PFOA-modified copolymers. The introduction of PFOB not only efficiently heightened the oxygen loading capacity of the composite hydrogel, but also endowed it with excellent X-ray opacity, allowing the visual observation of the hydrogel via micro-CT imaging. After peritumoral injection of the oxygen-enriched composite hydrogel, the continuous supply of oxygen effectively relieved tumor hypoxia and down-regulated the expression of hypoxia-inducible factor-1α. Profiting from this, the hyposensitivity of tumor cells to radiation was successfully reversed, and the tumor growth in mice was significantly suppressed and the survival of mice was prolonged when combined with multiple X-ray exposure. As a result, the oxygen-enriched composite hydrogel shows a great potential for radiosensitization to improve the radiotherapeutic efficacy.

A Multidisciplinary Journey towards Bone Tissue Engineering

Millions of patients suffer yearly from bone fractures and disorders such as osteoporosis or cancer, which constitute the most common causes of severe long-term pain and physical disabilities. The intrinsic capacity of bone to repair the damaged bone allows normal healing of most small bone injuries. However, larger bone defects or more complex diseases require additional stimulation to fully heal. In this context, the traditional routes to address bone disorders present several associated drawbacks concerning their efficacy and cost-effectiveness. Thus, alternative therapies become necessary to overcome these limitations. In recent decades, bone tissue engineering has emerged as a promising interdisciplinary strategy to mimic environments specifically designed to facilitate bone tissue regeneration. Approaches developed to date aim at three essential factors: osteoconductive scaffolds, osteoinduction through growth factors, and cells with osteogenic capability. This review addresses the biological basis of bone and its remodeling process, providing an overview of the bone tissue engineering strategies developed to date and describing the mechanisms that underlie cell-biomaterial interactions.

Hydrogel Composites with Different Dimensional Nanoparticles for Bone Regeneration

The treatment of large segmental bone defects and complex types of fractures caused by trauma, inflammation, or tumor resection is still a challenge in the field of orthopedics. Various natural or synthetic biological materials used in clinical applications cannot fully replicate the structure and performance of raw bone. This highlights how to endow materials with multiple functions and biological properties, which is a problem that needs to be solved in practical applications. Hydrogels with outstanding biocompatibility, for their casting into any shape, size, or form, are suitable for different forms of bone defects. Therefore, they have been used in regenerative medicine more widely. In this review, versatile hydrogels are compounded with nanoparticles of different dimensions, and many desirable features of these materials in bone regeneration are introduced, including drug delivery, cell factor vehicle, cell scaffolds, which have potential in bone regeneration applications. The combination of hydrogels and nanoparticles of different dimensions encourages better filling of bone defect areas and has higher adaptability. This is due to the minimally invasive properties of the material and ability to match irregular defects. These biological characteristics make composite hydrogels with different dimensional nanoparticles become one of the most attractive options for bone regeneration materials.

Transformation of acellular dermis matrix with dicalcium phosphate into 3D porous scaffold for bone regeneration

Animal derived biomaterials have attracted much attentions in treating large size bone defect due to their excellent biocompatibility and potent bioactivities offered by the biomacromolecules and growth factors contained in these materials. Dermis-derived matrix (ADM) has been used as skin grafts and wound dressings for decades, however its application in bone tissue engineering has been largely limited as ADM possesses a dense structure which does not support bone tissue ingrowth. Recently, we have successfully fabricated porous scaffold structure using an ADM with the aid of micronization technique. When integrated with inorganic components such as calcium phosphate, ADM could be transformed to bone graft substitutes with desirable osteogenic properties. While purified and chemically cross-linked collagen has lost its natural structure, our ADM successfully preserved natural tropocollagen structure, as well as other bioactive components. A composite scaffold was fabricated by incorporating dicalcium phosphate (DCP) microparticles into ADM microfibers and freeze-dried to form a highly porous structure. Unlike conventional ADM materials, this scaffold possesses high porosity with interconnected pores. More importantly, our evaluation data demonstrated that it performed much more effective in treating critical bone defects in comparison with best commercial product on the market. In a head-to-head comparison with a commercial bone graft material Bongold^®, the ADM/DCP scaffold showed superior osteogenic capacity by filling the defect with well-organized new bone tissue in a rabbit radius segmental defect model. Put together, our results exhibited a novel bone graft substitute was developed by circumventing processing barriers associated with natural ADM, which offers another novel bone graft substitute for bone regeneration.

PEG-based thermosensitive and biodegradable hydrogels

Injectable thermosensitive hydrogels are free-flowing polymer solutions at low or room temperature, making them easy to encapsulate the therapeutic payload or cells via simply mixing. Upon injection into the body, in situ forming hydrogels triggered by body temperature can act as drug-releasing reservoirs or cell-growing scaffolds. Finally, the hydrogels are eliminated from the administration sites after they accomplish their missions as depots or scaffolds. This review outlines the recent progress of poly(ethylene glycol) (PEG)-based biodegradable thermosensitive hydrogels, especially those composed of PEG-polyester copolymers, PEG-polypeptide copolymers and poly(organophosphazene)s. The material design, performance regulation, thermogelation and degradation mechanisms, and corresponding applications in the biomedical field are summarized and discussed. A perspective on the future thermosensitive hydrogels is also highlighted. STATEMENT OF SIGNIFICANCE: Thermosensitive hydrogels undergoing reversible sol-to-gel phase transitions in response to temperature variations are a class of promising biomaterials that can serve as minimally invasive injectable systems for various biomedical applications. Hydrophilic PEG is a main component in the design and fabrication of thermoresponsive hydrogels due to its excellent biocompatibility. By incorporating hydrophobic segments, such as polyesters and polypeptides, into PEG-based systems, biodegradable and thermosensitive hydrogels with adjustable properties in vitro and in vivo have been developed and have recently become a research hotspot of biomaterials. The summary and discussion on molecular design, performance regulation, thermogelation and degradation mechanisms, and biomedical applications of PEG-based thermosensitive hydrogels may offer a demonstration of blueprint for designing new thermogelling systems and expanding their application scope.

A Dual-sensitive Hydrogel Based on Poly(Lactide-co-Glycolide)-Polyethylene Glycol-Poly(Lactide-co-Glycolide) Block Copolymers for 3D Printing

The thermo-sensitive hydrogel formed by triblock copolymers of polyethylene glycols and aliphatic polyesters serves as a promising candidate for bioink due to its excellent biodegradability and biocompatibility. However, the thermo-crosslinking alone cannot achieve a robust hydrogel to support the 3D printed constructs without collapse. Herein, a photo-crosslinkable group was introduced into the triblock copolymers to achieve a dual-sensitive hydrogel. A triblock copolymer poly(lactide-co-glycolide)-polyethylene glycol-poly(lactide-co-glycolide) decorated with acrylate group in the chain end was prepared. The obtained aqueous solutions of the copolymers could transform into hydrogels with excellent shear thinning properties and rapid elastic recovery properties spontaneously on the increase of temperature. The resulted thermogels also allowed for photo-crosslinking by exposure to ultraviolet radiation, with storage modulus dramatically increased to stable the printed constructs. Through a two-step crosslinking strategy, complicated tissue-like constructs with high shape fidelity can be printed using the dual-sensitive inks. Moreover, the mechanical strength, swelling ratio, and printability of the hydrogels can be tuned by varying the substitution rate of the acrylate group without compromising the inks' extrudability. We expect that the dual-sensitive hydrogels may be used as bioinks to print large constructs for applications in tissue engineering.

Injectable and thermosensitive hydrogels mediating a universal macromolecular contrast agent with radiopacity for noninvasive imaging of deep tissues

It is very challenging to visualize implantable medical devices made of biodegradable polymers in deep tissues. Herein, we designed a novel macromolecular contrast agent with ultrahigh radiopacity (iodinate content > 50%) via polymerizing an iodinated trimethylene carbonate monomer into the two ends of poly(ethylene glycol) (PEG). A set of thermosensitive and biodegradable polyester-PEG-polyester triblock copolymers with varied polyester compositions synthesized by us, which were soluble in water at room temperature and could spontaneously form hydrogels at body temperature, were selected as the demonstration materials. The addition of macromolecular contrast agent did not obviously compromise the injectability and thermogelation properties of polymeric hydrogels, but conferred them with excellent X-ray opacity, enabling visualization of the hydrogels at clinically relevant depths through X-ray fluoroscopy or Micro-CT. In a mouse model, the 3D morphology of the radiopaque hydrogels after injection into different target sites was visible using Micro-CT imaging, and their injection volume could be accurately obtained. Furthermore, the subcutaneous degradation process of a radiopaque hydrogel could be non-invasively monitored in a real-time and quantitative manner. In particular, the corrected degradation curve based on Micro-CT imaging well matched with the degradation profile of virgin polymer hydrogel determined by the gravimetric method. These findings indicate that the macromolecular contrast agent has good universality for the construction of various radiopaque polymer hydrogels, and can nondestructively trace and quantify their degradation in vivo. Meanwhile, the present methodology developed by us affords a platform technology for deep tissue imaging of polymeric materials.

Review of a new bone tumor therapy strategy based on bifunctional biomaterials

Bone tumors, especially those in osteosarcoma, usually occur in adolescents. The standard clinical treatment includes chemotherapy, surgical therapy, and radiation therapy. Unfortunately, surgical resection often fails to completely remove the tumor, which is the main cause of postoperative recurrence and metastasis, resulting in a high mortality rate. Moreover, bone tumors often invade large areas of bone, which cannot repair itself, and causes a serious effect on the quality of life of patients. Thus, bone tumor therapy and bone regeneration are challenging in the clinic. Herein, this review presents the recent developments in bifunctional biomaterials to achieve a new strategy for bone tumor therapy. The selected bifunctional materials include 3D-printed scaffolds, nano/microparticle-containing scaffolds, hydrogels, and bone-targeting nanomaterials. Numerous related studies on bifunctional biomaterials combining tumor photothermal therapy with enhanced bone regeneration were reviewed. Finally, a perspective on the future development of biomaterials for tumor therapy and bone tissue engineering is discussed. This review will provide a useful reference for bone tumor-related disease and the field of complex diseases to combine tumor therapy and tissue engineering.

Fabrication of nanocomposite/nanofibrous functionally graded biomimetic scaffolds for osteochondral tissue regeneration

One of the main challenges in treating osteochondral lesions via tissue engineering approach is providing scaffolds with unique characteristics to mimic the complexity. It has led to application of heterogeneous scaffolds as a potential candidate for engineering of osteochondral tissues, in which graded multilayered-structure should promote bone and cartilage growth. By designing three-dimensional (3D)-nanofibrous scaffolds mimicking the native extracellular matrix's nanoscale structure, cells can grow in controlled conditions and regenerate the damaged tissue. In this study, novel 3D-functionality graded nanofibrous scaffolds composed of five layers based on different compositions containing polycaprolactone(PCL)/gelatin(Gel)/nanohydroxyapatite (nHA) for osteoregeneration and chitosan(Cs)/polyvinylalcohol(PVA) for chondral regeneration are introduced. This scaffold is fabricated by electrospinning technique using spring as collector to create 3D-nanofibrous scaffolds. Fourier-transform infrared spectroscopy, X-ray diffraction, energy dispersive X-ray spectroscopy, scanning electron microscopy, mechanical compression test, porosimetry, and water uptake studies were applied to study each layer's physicochemical properties and whole functionally graded scaffold. Besides, biodegradation and biological studies were done to investigate biological performance of scaffold. Results showed that each layer has a fibrous structure with continuous nanofibers with improved pore size and porosity of novel 3D scaffold (6-13 μm and 90%) compared with two-dimensional (2D) mat (2.2 μm and 19.3%) with higher water uptake capacity (about 100 times of 2D mat). Compression modulus of electrospun scaffold was increased to 78 MPa by adding nHA. The biological studies revealed that the layer designed for osteoregeneration could improve cell proliferation rate in comparison to the layer designed for chondral regeneration. These results showed such structure possesses a promising potential for the treatment of osteochondral defects.

Sterilization and disinfection methods for decellularized matrix materials: Review, consideration and proposal

Sterilization is the process of killing all microorganisms, while disinfection is the process of killing or removing all kinds of pathogenic microorganisms except bacterial spores. Biomaterials involved in cell experiments, animal experiments, and clinical applications need to be in the aseptic state, but their physical and chemical properties as well as biological activities can be affected by sterilization or disinfection. Decellularized matrix (dECM) is the low immunogenicity material obtained by removing cells from tissues, which retains many inherent components in tissues such as proteins and proteoglycans. But there are few studies concerning the effects of sterilization or disinfection on dECM, and the systematic introduction of sterilization or disinfection for dECM is even less. Therefore, this review systematically introduces and analyzes the mechanism, advantages, disadvantages, and applications of various sterilization and disinfection methods, discusses the factors influencing the selection of sterilization and disinfection methods, summarizes the sterilization and disinfection methods for various common dECM, and finally proposes a graphical route for selecting an appropriate sterilization or disinfection method for dECM and a technical route for validating the selected method, so as to provide the reference and basis for choosing more appropriate sterilization or disinfection methods of various dECM.

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Asepsis is the prerequisite for the experiment and application of biomaterials.

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Sterilization or disinfection affects physic-chemical properties of biomaterials.

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Mechanism, advantages and disadvantages of sterilization or disinfection methods.

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Factors influencing the selection of sterilization or disinfection methods.

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Selection of sterilization or disinfection methods for decellularized matrix.

A robust regenerated cellulose-based dual stimuli-responsive hydrogel as an intelligent switch for controlled drug delivery

Constructing robust hydrogels with biodegradability and dual stimuli-responsive by utilizing natural polymer as raw materials remains a sustaining challenge. Herein, we proposed an interpenetrating strategy in which N-isopropyl acrylamide (NIPAM) and acrylamide (AM) block copolymers were introduced as the second network into the carboxymethyl cellulose single network gel (CMC gel) to construct a dual-network robust hydrogel (CMC/PNIPAM-co-PAM). The dual-network design strategy effectively improves the mechanical strength of CMC gel. The hydrogel suggests intelligent dual stimuli-responsive behavior to pH and temperature. Furthermore, the copolymerization of NIPAM and AM regulated the low critical solution temperature (LCST) of the hybrid hydrogel, making it close to the physiological temperature of the human body. With the aim of evaluating its application in drug delivery, we loaded tetracycline into the dual-network hydrogel and simulated its release process under the pH microenvironment of the small intestine and the physiological temperature to infer its potential application in intestinal inflammation treatments. Moreover, it is proved that the strong hydrogel possesses good cytocompatibility in vitro biocompatibility testing. In addition, the embedding of tetracycline makes the hydrogel excellent antioxidant performance. This dual-stimulus response integrated hydrogel is expected to play a critical role in drug delivery and targeted therapy.

"Dual-Key-and-Lock" dual drug carrier for dual mode imaging guided chemo-photothermal therapy

Drug resistance and side effects are the two main problems of chemotherapy. In order to address these big challenges, p-PB@d-SiO₂, which has the ability to co-deliver both the hydrophobic drug doxorubicin hydrochloride (DOX) and the hydrophilic drug ibuprofen (IBU), is constructed to achieve synergistic treatment. The drug-loaded nanoparticle consists of porous Prussian blue (p-PB) as the core and dendrimer-like SiO₂ (d-SiO₂) as the shell, which is further thiolated and coated with polyethylene glycol thiol (HS-PEG) to form the "Dual-Key-and-Lock" drug carrier p-PB@d-SiO₂-SS-PEG. The locked drugs can only be released in the presence of cooperative triggers, i.e., a high glutathione concentration (the first key) and an acidic environment (the second key). The "dual key"-triggered release is much more significant in cancer lesions than in normal tissues, reducing side effects. Furthermore, cell viability experiments highlight the superior therapeutic efficacy of the dual-drug-loaded nanoparticles compared with the single-drug systems (60%, 73% and 86% vs. 56%, 68%, and 76% at 100, 200 and 500 μg mL^-1, respectively). In vitro and in vivo experiments demonstrate the potential application of p-PB@d-SiO₂-SS-PEG for dual-mode fluorescence and magnetic-resonance-imaging-guided chemo-photothermal therapy. The "Dual-Key-and-Lock" drug carrier system exhibits the "1 + 1 > 2" effect, demonstrating its excellent performance in synergy therapy for improved therapeutic efficiency and thereby reducing conventional drug resistance and side effects.

Gold nanorods enable noninvasive longitudinal monitoring of hydrogels in vivo with photoacoustic tomography

Longitudinal in vivo monitoring is essential for the design and evaluation of biomaterials. An ideal method would provide three-dimensional quantitative information, high spatial resolution, deep tissue penetration, and contrast between tissue and material structures. Photoacoustic (PA) or optoacoustic imaging is a hybrid technique that allows three-dimensional imaging with high spatial resolution. In addition, photoacoustic imaging allows for imaging of vascularization based on the intrinsic contrast of hemoglobin. In this study, we investigated photoacoustic computed tomography (PACT) as a tool for longitudinal monitoring of an implanted hydrogel in a small animal model. Hydrogels were loaded with gold nanorods to enhance contrast and imaged weekly for 8 weeks. PACT allowed non-invasive three-dimensional, quantitative imaging of the hydrogels over the entire 8 weeks. Quantitative volume analysis was used to evaluate the in vivo degradation kinetics of the implants which deviated slightly from in vitro predictions. Multispectral imaging allowed for the simultaneous analysis of hydrogel degradation and local vascularization. These results provide support for the substantial potential of PACT as a tool for insight into biomaterial performance in vivo.

Porous shape memory scaffold of dextran and hydroxyapatite for minimum invasive implantation for bone tissue engineering applications

Minimally invasive implantation of a porous scaffold of large volume into bone defect site remains a challenge. Scaffolds based on shape memory polymer (SMP) show potential to be delivered in the compact form via minimally invasive surgery. The present study chooses poly (ε-caprolactone)-diols (PCL-diols) as the SMP to cross-link carboxyl dextran via ester bonds together with particle leaching method to yield a porous SMP scaffold. The inner surfaces of porous SMP scaffold are then mineralized via in situ precipitation to yield mineralized porous SMP-hydroxyapatite (SMP-HA) scaffold. The porous SMP-HA scaffold possesses pore size of 400-500 μm, with HA particles uniformly distributed and orientationally aligned on the inner surfaces of scaffold. X-ray diffraction (XRD) and differential scanning calorimetry (DSC) are carried out to identify the HA deposition. The phase transition temperature of the scaffold is adjusted to 38°C via changing the dosage of PCL (molecule weight: 2800) to endow the scaffold with shape deformation and fixed properties, as well as well-performed shape recovery property under body temperature. Bone marrow mesenchymal stem cells (BMSCs) adhere on the inner surfaces of SMP-HA scaffold, exhibiting larger spreading area when compared to cells adhered on SMP scaffold without HA, promoting its osteogenesis. In vivo degradation showed that the scaffold degrades completely after 6 months post-implantation. At the same time, significant tissue and capillary invasion indicated that the present porous SMP-HA scaffold hold great promise towards bone tissue engineering applications.

Tissue Engineering for Musculoskeletal Regeneration and Disease Modeling

Musculoskeletal injuries and associated conditions are the leading cause of physical disability worldwide. The concept of tissue engineering has opened up novel approaches to repair musculoskeletal defects in a fast and/or efficient manner. Biomaterials, cells, and signaling molecules constitute the tissue engineering triad. In the past 40 years, significant progress has been made in developing and optimizing all three components, but only a very limited number of technologies have been successfully translated into clinical applications. A major limiting factor of this barrier to translation is the insufficiency of two-dimensional cell cultures and traditional animal models in informing the safety and efficacy of in-human applications. In recent years, microphysiological systems, often referred to as organ or tissue chips, generated according to tissue engineering principles, have been proposed as the next-generation drug testing models. This chapter aims to first review the current tissue engineering-based approaches that are being applied to fabricate and develop the individual critical elements involved in musculoskeletal organ/tissue chips. We next highlight the general strategy of generating musculoskeletal tissue chips and their potential in future regenerative medicine research. Exemplary microphysiological systems mimicking musculoskeletal tissues are described. With sufficient physiological accuracy and relevance, the human cell-derived, three-dimensional, multi-tissue systems have been used to model a number of orthopedic disorders and to test new treatments. We anticipate that the novel emerging tissue chip technology will continually reshape and improve our understanding of human musculoskeletal pathophysiology, ultimately accelerating the development of advanced pharmaceutics and regenerative therapies.

Thermosensitive Hydrogel Delivery of Human Periodontal Stem Cells Overexpressing Platelet-Derived Growth Factor-BB Enhances Alveolar Bone Defect Repair

Alveolar bone defects can arise as a consequence of trauma, infection, periodontal disease, or congenital alveolar fenestration. Many approaches have been employed in an effort to treat or overcome such defects, but the ability to effectively achieve alveolar regeneration remains elusive. Platelet-derived growth factor-BB (PDGF-BB) has been shown to serve as a key factor capable of orchestrating cell proliferation, angiogenesis, and chemoattraction in the context of osteogenic processes. Exactly how PDGF-BB affects human periodontal ligament stem cells (hPDLSCs), however, requires further exploration. In this report, we utilized a lentiviral construct to achieve PDGF-BB overexpression in hPDLSCs, allowing us to establish that this gene was able to enhance the proliferation of these cells and to mediate osteogenic gene upregulation therein. In addition, we established a rat model of alveolar defects that were implanted using different complexes, and then monitored through histological and micro-CT analyses 4 and 8 weeks postsurgery to assess bone repair outcomes. These analyses revealed that a thermosensitive hydrogel was an effective 3D cell culture scaffold, while PDLSCs overexpressing PDGF-BB enhanced bone growth in the context of alveolar bone defects. Together, these results thus indicate that PDGF-BB represents a potent means of promoting stem cell-based alveolar bone tissue regeneration.

Thermo-sensitive hydrogels for delivering biotherapeutic molecules: A review

To date, a variety of delivery systems based on organic or inorganic materials have been investigated. Among them, hydrogels have become one of the most promising field in drug delivery system due to their unique properties. Temperature-sensitive hydrogels, which gelation at physiological temperature, gift the delivery system with excellent spatial and temporal control, and have a widely application in drug delivery, tissue engineering, imaging, and wound dressing. This review provides a brief overview on the concept and classification of temperature-sensitive hydrogels, and covers the application of temperature-sensitive gel systems in delivery of biotherapeutic molecules.

[A rapid histological preparation method for observation of morphology and composition distribution of tendon collagen fascicle and endotendinium]

Objective

To explore a rapid histological preparation method to observe morphology and composition distribution of tendon collagen fascicle and endotendinum.

Methods

Taking porcine superflexor tendon of foot as an example, tendons were sliced into sections with 6 μm by frozen section technology, after which general observation of the section integrity was carried out. After fixed with 10% neutral buffered formalin and performed with HE staining, the tissue integrity and ice crystal formation were observed under microscope. Sections were then divided into 5 groups by different methods of dyeing. Group A: Priodic acid-Shiff (PAS) staining; group B: Masson staining; group C: reticular fibers staining; group D: immunohistochemical and immunofluorescent staining of type Ⅲ collagen; group E: the sections were baked at 65℃ for 10 minutes and stained with Masson. The composition distribution of tendon collagen fascicle and endotendinum in different groups were observed.

Results

From general observation, the frozen section of tendon tissue was complete and continuous. Although the tissue integrity in the tendon sections could be seen and no ice crystal was formed, the composition distribution could not be identified by HE staining. The entire tendons in groups A, B, and C were dyed, and the composition distribution of collagen fascicle and endotendinum could not be identified. The endotendinum in group D was stained weakly positive for type Ⅲ collagen alone, and the two components were differentiated dyed but the contrast was not obvious. In group E, the collagen fascicle and endotendinium were differentiated dyed and the two components in tendon tissue were clearly visible.

Conclusion

The morphology and the composition distribution of tendon collagen fascicle and endotendinum can be characterized rapidly and accurately, using a combination of baking at 65℃ for 10 minutes and Masson staining after porcine superflexor tendons were sliced by frozen section technology.