Cellulose nanocrystals-reinforced dual crosslinked double network GelMA/hyaluronic acid injectable nanocomposite cryogels with improved mechanical properties for cartilage tissue regeneration.

Improvement of mechanical properties of injectable tissue engineering scaffolds is a current challenge. The objective of the current study is to produce a highly porous injectable scaffold with improved mechanical properties. For this aim, cellulose nanocrystals-reinforced dual crosslinked porous nanocomposite cryogels were prepared using chemically crosslinked methacrylated gelatin (GelMA) and ionically crosslinked hyaluronic acid (HA) through the cryogelation process. The resulting nanocomposites showed highly porous structures with interconnected porosity (>90%) and mean pore size in the range of 130-296 µm. The prepared nanocomposite containing 3%w/v of GelMA, 20 w/w% of HA, and 1%w/v of CNC showed the highest Young's modulus (10 kPa) and excellent reversibility after 90% compression and could regain its initial shape after injection by a 16-gauge needle in the aqueous media. The in vitro results demonstrated acceptable viability (>90%) and migration of the human chondrocyte cell line (C28/I2), and chondrogenic differentiation of human adipose stem cells. A two-month in vivo assay on a rabbit's ear model confirmed that the regeneration potential of the prepared cryogel is comparable to the natural autologous cartilage graft, suggesting it is a promising alternative for autografts in the treatment of cartilage defects.

Preliminary evaluation of fish cartilage as a promising biomaterial in cartilage tissue engineering.

Fish cartilage is known as a valuable source of natural biomaterials due to its unique composition and properties. It contains a variety of bioactive components that contribute to its potential applications in different domains such as tissue engineering. The present work aimed to consider the properties of backbone cartilage from fish with a cartilaginous skeleton, including elasmobranch (reticulate whipray: Himantura uarnak and milk shark: Rhizoprionodon acutus) and sturgeon (beluga: Huso huso). The histomorphometric findings showed that the number of chondrocytes was significantly higher in reticulate whipray and milk shark compared to beluga (p < 0.05). The highest GAGs content was recorded in reticulate whipray cartilage compared to the other two species (p < 0.05). The cartilage from reticulate whipray and beluga showed higher collagen content than milk shark cartilage (p < 0.05), and the immunohistochemical assay for type II collagen (Col II) showed higher amounts of this component in reticulate whipray compared to the other two species. Young's modulus of the cartilage from reticulate whipray was significantly higher than that of milk shark and beluga (p < 0.05), while no significant difference was recorded between Young's modulus of the cartilage from milk shark and beluga. The gene expression of ACAN, Col II, and Sox9 showed that the cartilage-ECM from three species was able to induce chondrocyte differentiation from human adipose tissue-derived stem cells (hASCs). From these results, it can be concluded that the cartilage from three species, especially reticulate whipray, enjoys the appropriate biological properties and provides a basis for promoting its applications in the field of cartilage tissue engineering.

Targeted Delivery of Pennyroyal via Methotrexate Functionalized PEGylated Nanostructured Lipid Carriers into Breast Cancer Cells; A Multiple Pathways Apoptosis Activator.

Purpose: Pennyroyal is a species of the Lamiaceae family with potent anti-cancer and antioxidant properties. Combining this antioxidant with chemotherapeutic agents enhances the effectiveness of these agents by inducing more apoptosis in cancerous cells. Methods: Here, methotrexate (MTX) combined with pennyroyal oil based on PEGylated nanostructured lipid carriers (NLCs) was assessed. These nanoparticles were physiochemically characterized, and their anti-cancer effects and targeting efficiency were investigated on the folate receptor-positive human breast cancer cell line (MCF-7) and negative human alveolar basal epithelial cells (A549). Results: Results showed a mean size of 97.4 ± 12.1 nm for non-targeted PEGylated NLCs and 220.4 ± 11.4 nm for targeted PEGylated NLCs, with an almost small size distribution assessed by TEM imaging. Furthermore, in vitro molecular anti-cancer activity investigations showed that pennyroyal-NLCs and pennyroyal-NLCs/MTX activate the apoptosis and autophagy pathway by changing their related mRNA expression levels. Furthermore, in vitro cellular studies showed that these changes in the level of gene expression could lead to a rise in apoptosis rate from 15.6 ± 8.1 to 25.0 ± 3.2 (P<0.05) for the MCF-7 cells treated with pennyroyal-NLCs and pennyroyal-NLCs/MTX, respectively. Autophagy and reactive oxygen species (ROS) cellular evaluation indicated that treating the cells with pennyroyal-NLCs and pennyroyal-NLCs/MTX could significantly increase their intensity in these cells. Conclusion: Our results present a new NLCs-based approach to enhance the delivery of pennyroyal and MTX to cancerous breast tissues.

Antibacterial aligned nanofibrous chitosan/PVA patch for repairing chronic tympanic membrane perforations.

Chronic tympanic membrane (TM) perforation is a consequence of trauma or chronic otitis media, and these chronic TM perforations often lead to conduction hearing loss. This study focuses on the development of a patch using a combination of chitosan (CS) and polyvinyl alcohol (PVA) as graft material for repairing chronic tympanic membrane (TM) perforations. Aligned nanofibers were created using a specially designed collector (SDC) through the electrospinning method. The scanning electron microscopy (SEM) analysis revealed that the CS/PVA ratio of (15:85) resulted in uniform and bead-free nanofibers. The aligned nanofibers had a diameter of 131.11 ± 28 nm, indicating that the influence of the electrostatic field introduced by the SDC affected not only the nanofiber alignment but also the nanofiber diameter. The nanofiber angles demonstrated effective alignment. This patch is infused with thyme essential oil (TEO) for antibacterial properties. The results showed that its antibacterial property for Pseudomonas aeruginosa bacteria was enhanced in such a way that the diameter of the antibacterial halo increased from zero to 25 mm. Cell viability assays showed >80 % viability. A preclinical case study on six patients demonstrated the biocompatibility and promising potential of the fabricated patch for eardrum repair.

Bioinspired scaffolds based on aligned polyurethane nanofibers mimic tendon and ligament fascicles.

Topographical factors of scaffolds play an important role in regulating cell functions. Although the effects of alignment topography and three-dimensional (3D) configuration of nanofibers as well as surface stiffness on cell behavior have been investigated, there are relatively few reports that attempt to understand the relationship between synergistic effects of these parameters and cell responses. Herein, the influence of biophysical and biomechanical cues of electrospun polyurethane (PU) scaffolds on mesenchymal stem cells (MSCs) activities was evaluated. To this aim, multiscale bundles were developed by rolling up the aligned electrospun mats mimicking the fascicles of tendons/ligaments and other similar tissues. Compared to mats, the 3D bundles not only maintained the desirable topographical features (i.e., fiber diameter, fiber orientation, and pore size), but also boosted tensile strength (∼40 MPa), tensile strain (∼260%), and surface stiffness (∼1.75 MPa). Alignment topography of nanofibers noticeably dictated cell elongation and a uniaxial orientation, resulting in tenogenic commitment of MSCs. MSCs seeded on the bundles expressed higher levels of tenogenic markers compared to mats. Moreover, the biomimetic bundle scaffolds improved synthesis of extracellular matrix components compared to mats. These results suggest that biophysical and biomechanical cues modulate cell-scaffold interactions, providing new insights into hierarchical scaffold design for further studies.

Physicochemical and Biochemical Properties of Trypsin-like Enzyme from Two Sturgeon Species.

This work aimed to determine the physicochemical and biochemical properties of trypsin from beluga Huso huso and sevruga Acipenser stellatus, two highly valuable sturgeon species. According to the results obtained from the methods of casein-zymogram and inhibitory activity staining, the molecular weight of trypsin for sevruga and beluga was 27.5 and 29.5 kDa, respectively. Optimum pH and temperature values for both trypsins were recorded at 8.5 and 55 °C by BAPNA (a specific substrate), respectively. The stability of both trypsins was well-preserved at pH values from 6.0 to 11.0 and temperatures up to 50 °C. TLCK and SBTI, two specific trypsin inhibitors, showed a significant inhibitory effect on the enzymatic activity of both trypsins (p < 0.05). The enzyme activity was significantly increased in the presence of Ca+2 and surfactants and decreased by oxidizing agents, Cu+2, Zn+2, and Co+2 (p < 0.05). However, univalent ions Na+ and K+ did not show any significant effect on the activity of both trypsins (p > 0.05). The results of our study show that the properties of trypsin from beluga and sevruga are in agreement with data reported in bony fish and can contribute to the clear understanding of trypsin activity in these primitive species.

Capsaicin-loaded alginate nanoparticles embedded polycaprolactone-chitosan nanofibers as a controlled drug delivery nanoplatform for anticancer activity.

Nanocarrier-based drug delivery systems have been designed into various structures that can effectively prevent cancer progression and improve the therapeutic cancer index. However, most of these delivery systems are designed to be simple nanostructures with several limitations, including low stability and burst drug release features. A nano-in-nano delivery technique is explored to address the aforementioned concerns. Accordingly, this study investigated the release behavior of a novel nanoparticles-in-nanofibers delivery system composed of capsaicin-loaded alginate nanoparticles embedded in polycaprolactone-chitosan nanofiber mats. First, alginate nanoparticles were prepared with different concentrations of cationic gemini surfactant and using nanoemulsion templates. The optimized formulation of alginate nanoparticles was utilized for loading capsaicin and exhibited a diameter of 19.42 ± 1.8 nm and encapsulation efficiency of 98.7 % ± 0.6 %. Likewise, blend polycaprolactone-chitosan nanofibers were prepared with different blend ratios of their solutions (i.e., 100:0, 80:20, 60:40) by electrospinning method. After the characterization of electrospun mats, the optimal nanofibers were employed for embedding capsaicin-loaded alginate nanoparticles. Our findings revealed that embedding capsaicin-loaded alginate nanoparticles in polycaprolactone-chitosan nanofibers, prolonged capsaicin release from 120 h to more than 500 h. Furthermore, the results of in vitro analysis demonstrated that the designed nanoplatform could effectively inhibit the proliferation of MCF-7 human breast cells while being nontoxic to human dermal fibroblasts (HDF). Collectively, the prepared nanocomposite drug delivery platform might be promising for the long-term and controlled release of capsaicin for the prevention and treatment of cancer.

A hydrogel-fiber-hydrogel composite scaffold based on silk fibroin with the dual-delivery of oxygen and quercetin.

Supplying sufficient oxygen within the scaffolds is one of the essential hindrances in tissue engineering that can be resolved by oxygen-generating biomaterials (OGBs). Two main issues related to OGBs are controlling oxygenation and reactive oxygen species (ROS). To address these concerns, we developed a composite scaffold entailing three layers (hydrogel-electrospun fibers-hydrogel) with antioxidant and antibacterial properties. The fibers, the middle layer, reinforced the composite structure, enhancing the mechanical strength from 4.27 ± 0.15 to 8.27 ± 0.25 kPa; also, this layer is made of calcium peroxide and silk fibroin (SF) through electrospinning, which enables oxygen delivery. The first and third layers are physical SF hydrogels to control oxygen release, containing quercetin (Q), a nonenzymatic antioxidant. This composite scaffold resulted in almost more than 40 mmHg of oxygen release for at least 13 days, and compared with similar studies is in a high range. Here, Q was used for the first time for an OGB to scavenge the possible ROS. Q delivery not only led to antioxidant activity but also stabilized oxygen release and enhanced cell viability. Based on the given results, this composite scaffold can be introduced as a safe and controllable oxygen supplier, which is promising for tissue engineering applications, particularly for bone.

Surface Heparinization of a Magnesium-Based Alloy: A Comparison Study of Aminopropyltriethoxysilane (APTES) and Polyamidoamine (PAMAM) Dendrimers.

Magnesium (Mg)-based alloys are biodegradable metallic biomaterials that show promise in minimizing the risks of permanent metallic implants. However, their clinical applications are restricted due to their rapid in vivo degradation and low surface hemocompatibilities. Surface modifications are critically important for controlling the corrosion rates of Mg-based alloys and improving their hemocompatibilities. In the present study, two heparinization methods were developed to simultaneously increase the corrosion resistance and hemocompatibility of the AZ31 Mg alloy. In the first method, the surface of the AZ31 alloy was modified by alkali-heat treatment and then aminolyzed by 3-amino propyltriethoxy silane (APTES), a self-assembly molecule, and heparin was grafted onto the aminolyzed surface. In the second method, before heparinization, polyamidoamine dendrimers (PAMAM4-4) were grafted onto the aminolyzed surface with APTES to increase the number of surface functional groups, and heparinization was subsequently performed. The presence of a peak with a wavelength of about 1560 cm-1 in the FTIR spectrum for the sample modified with APTES and dendrimers indicated aminolysis of the surface. The results indicated that the corrosion resistance of the Mg alloy was significantly improved as a result of the formation of a passive layer following the alkali-heat treatment. The results obtained from a potentiodynamic polarization (PDP) test showed that the corrosion current in the uncoated sample decreased from 25 µA to 3.7 µA in the alkali-heat-treated sample. The corrosion current density was reduced by 14 and 50 times in samples treated with the self-assembly molecules, APTES and dendrimers, respectively. After heparinization, the clotting time for pristine Mg was greatly improved. Clotting time increased from 480 s for the pristine Mg sample to 630 s for the APTES- and heparin-modified samples and to 715 s for the PAMAM- and heparin-modified samples. Cell culture data showed a slight improvement in the cell-supporting behavior of the modified samples.

A dual functional chondro-inductive chitosan thermogel with high shear modulus and sustained drug release for cartilage tissue engineering.

We report a chitosan-based nanocomposite thermogel with superior shear modulus resembling that of cartilage and dual pro-chondrogenic and anti-inflammatory functions. Two therapeutic agents, kartogenin (KGN) and diclofenac sodium (DS), are employed to promote chondrogenesis of stem cells and suppress inflammation, respectively. To extend the release time in a controlled manner, KGN is encapsulated in the uniform-sized starch microspheres and DS is loaded into the halloysite nanotubes. Both drug carriers are doped into the maleimide-modified chitosan hydrogel to produce a shear modulus of 167 ± 5 kPa that is comparable to that of articular cartilage (50-250 kPa). Owing to the hydrogel injectability and relatively suitable gelation time (5 ± 0.5 min) at 37 °C, this system potentially constitutes a manageable platform for clinical practice. Moreover, sustained linear drug release for over a month boosts chondro-differentiation of stem cells to eliminate the necessity for multiple administrations. Considering virtues such as thermogel strength and ability to co-deliver anti-inflammatory and chondro-inductive biomolecules continuously, the materials and strategy have promising potential in functional cartilage tissue engineering.

Hemostatic Electrospun Nanocomposite Containing Poly(lactic acid)/Halloysite Nanotube Functionalized by Poly(amidoamine) Dendrimer for Wound Healing Application: In Vitro and In Vivo Assays.

The main challenge in treating injuries is excessive bleeding whereas intervention is required if the body's hemostatic systems fail to control the bleeding. Herein, a novel nanocomposite consisting of poly(lactic acid) (PLA) and poly(amidoamine) (PAMAM) dendrimer functionalized halloysite nanotube (HNT) with a highly porous structure via electrospinning is developed. HNT is functionalized by PAMAM via divergent synthetic routes from zero to third-generation numbers. The effect of different percentages and generation numbers of PAMAM dendrimer (G1, G2, and G3) functionalized HNT on PLA is studied using physicochemical nanocomposite characteristics. These resultant nanocomposites provide a nanofibrous structure with appropriate physicochemical characteristics such as mechanical properties, surface wettability, and water permeability. The hemostatic assays indicate that nanocomposite with PAMAM G3 functionalized HNT have the quickest blood clotting time due to the abundant amino functional group. Furthermore, the nanocomposites with 10 wt% of nanoparticles significantly promote cellular behavior in vitro. The in vivo study demonstrates that PLA/PAMAM G3 functionalized HNT promotes angiogenesis, collagen deposition, and re-epithelialization in the wound sites of the rat model, as well as inhibiting inflammatory response. The findings indicate that nanofibrous structure and the presence of dendrimer functionalized HNT have a synergetic effect on the enhanced nanocomposite wound healing performance.

A novel substrate based on electrospun polyurethane nanofibers and electrosprayed polyvinyl alcohol microparticles for recombinant human erythropoietin delivery.

After myocardial infarction caused by a heart attack, endothelial cells need to be preserved in order to regenerate new capillaries. Moreover, sufficient mechanical support is necessary for the infarcted myocardium to pump the blood. Herein, we designed a novel substrate containing polyurethane (PU) nanofibrous layers and recombinant human erythropoietin (rhEPO)-loaded microparticles for both controlled releases of rhEPO and mechanical support of myocardium. In this system, the single-layer (SL) and double-layer (DL) PU nanofibers were electrospun, and then microparticles with different rhEPO:polyvinyl alcohol (PVA) ratios were electrosprayed on the layers. The in vitro release behavior of rhEPO from SL substrates was not satisfactory, and then the study focused on DL patches in which the release profile was in accordance with Korsmeyer-Peppas model. The release exponent of 0.89 for the DL PU/120PVA:1rhEPO represented zero-order release. The results inferred that these substrates possessed highly tailored mechanical properties; Young's modulus and ultimate tensile strength of the substrates were 74-172 kPa and 7.4-9.9 MPa, respectively. The rhEPO release from the substrates was leading to the proper adhesion of endothelial cells and more than 95% cell viability. The results indicated that the patch of elastic nanofibers and microparticles offered a potential substrate for simultaneous rhEPO delivery to endothelial cells and also mechanically supporting the infarcted myocardium.

Cationic gemini surfactant properties, its potential as a promising bioapplication candidate, and strategies for improving its biocompatibility: A review.

Gemini surfactants consist of two cationic monomers of a surfactant linked together with a spacer. The specific structure of a cationic gemini surfactant is the reason for both its high surface activity and its ability to decrease the surface tension of water. The high surface activity and unique structure of gemini surfactants result in outstanding properties, including antibacterial and antifungal activity, anticorrosion properties, unique aggregation behaviour, the ability to form various structures reversibly in response to environmental conditions, and interactions with biomacromolecules such as DNA and proteins. These properties can be tailored by selecting the optimal structure of a gemini surfactant in terms of the nature and length of its alkyl substituents, spacer, and head group. Additionally, regarding their properties, comparison with their monomeric counterparts demonstrates that gemini surfactants have higher performance efficacy at lower concentrations. Hence, less material is needed, and the toxicity is lower. However, there are some limitations regarding their biocompatibility that have led researchers to develop amino acid-based and sugar-based gemini surfactants. Owing to their remarkable properties, cationic gemini surfactants are promising candidates for bioapplications such as drug delivery systems, gene carriers, and biomaterial surface modification.

Ionic conductive nanocomposite based on poly(l-lactic acid)/poly(amidoamine) dendrimerelectrospun nanofibrous for biomedical application.

The modification of poly (l-lactic acid) (PLLA) electrospun nanofibrous scaffolds was carried out by blending with second-generation poly amidoamine (PAMAM) for enhancement of their ionic conductivity. The samples containing PLLA and various amounts of PAMAM (1%, 3%, 5%, and 7% by wt.) were fabricated by electrospinning techniques. The electrospun fibers were characterized using scanning electron microscopy (SEM), porosity, Fourier-transform infrared (FTIR) spectroscopy, differential scanning calorimetry, contact angle measurement, water uptake measurement, mechanical properties, and electrical properties. Furthermore,in vitrodegradation study and cell viability assay were investigated in biomaterial applications. Creating amide groups through aminolysis reaction was confirmed by FTIR analysis successfully. The results reveal that adding PAMAM caused an increase in fiber diameter, crystallinity percentage, hydrophilicity, water absorption, elongation-at-break, and OE-mesenchymal stem cell viability. It is worth mentioning that this is the first report investigating the conductivity of PLLA/PAMAM nanofiber. The results revealed that by increasing the amount of PAMAM, the ionic conductivity of scaffolds was enhanced by about nine times. Moreover, the outcomes indicated that the presence of PAMAM could improve the limitations of PLLA like hydrophobicity, lack of active group, and poor cell adhesion.

Amine-terminated dendritic polymers as promising nanoplatform for diagnostic and therapeutic agents' modification: A review.

It is often challenging to design diagnostic and therapeutic agents that fulfill all functional requirements. So, bulk and surface modifications as a common approach for biomedical applications have been suggested. There have been considerable research interests in using nanomaterials to the prementioned methods. Among all nanomaterials, dendritic materials with three-dimensional structures, host-guest properties, and nano-polymeric dimensions have received considerable attention. Amine-terminated dendritic structures including, polyamidoamine (PAMAM), polypropyleneimine (PPI), and polyethyleneimine (PEI), have been enormously utilized in bio-modification. This review briefly described the structure of these three common dendritic polymers and their use to modify diagnostic and therapeutic agents in six major applications, including drug delivery, gene delivery, biosensor, bioimaging, tissue engineering, and antimicrobial activity. The current review covers amine-terminated dendritic polymers toxicity challenging and improvement strategies as well.

Silk fibroin hydrogel/dexamethasone sodium phosphate loaded chitosan nanoparticles as a potential drug delivery system.

The application of nanoparticles-loaded hydrogel as a novel formulation has gotten much attention for a potential drug delivery method for desire drug controlling and targeting. This study prepared a sustained release formulation using dexamethasone sodium phosphate-loaded chitosan nanoparticles embedded in silk fibroin hydrogel. Dexamethasone sodium phosphate-loaded chitosan nanoparticles (DEX-CSNPs) was developed using the ionotropic-gelation technique and inserted in the silk fibroin hydrogel (SFH). Mean particle size, polydispersity index (PDI), and zeta potential of DEX-CSNPs were 488.05±38.69 nm, 0.15±0.07, 32.12±2.42 mV, respectively. The encapsulation efficiency (EE), drug loading capacity (LC), and the cumulative amount of released drug of DEX-loaded CSNPs, which detected in phosphate buffer saline (PBS) solution, were 67.6±6.7%, 15.7±5.7%, and 75.84%, respectively. The DEX-CSNPs were then mixed with silk fibroin (SF) solution and induced gelation by sonication to prepare a drug-releasing system. As a result, the scanning electron microscopy (SEM) image shows that the prepared drug delivery system had a properly interconnected porous structure. Smaller pore size, greater porosity, higher water uptake, and swelling ratio were achieved by incorporating CSNPs and DEX-loaded CSNPs. The cytotoxicity study was performed for the L929 fibroblast cell line. The drug release kinetics study was performed on a prepared drug delivery system. Finally, the release test results showed a suitable extended-release of DEX from the carrier over 16 days. Overall, the developed drug-releasing system can be a promising candidate for drug delivery applications.

Novel decorated nanostructured lipid carrier for simultaneous active targeting of three anti-cancer agents.

Cancer-targeted co-delivery of therapeutic agents has been recognized as an effective strategy for increasing efficacy and reducing side effects of therapeutic agents. In this study, we used methotrexate (MTX) alone as a targeting moiety and chemotherapeutic agent and in combination with docetaxel (DTX) and doxorubicin (DOX) as chemotherapeutic agents to stop cancer cell proliferation with the aid of newly designed nanostructured lipid carriers (NLCs). The physicochemical properties of our designed nanocomplexes were evaluated by DLS, FT-IR spectroscopy, SEM, and TEM. Moreover, the targeting efficiency of the designed and synthesized nanoplatforms was evaluated on the folate receptor (FR) positive human breast cancer cell line (MCF-7) and FR negative human alveolar basal epithelial cells (A549). The NLCs/DTX/DOX/CS and NLCs/DTX/DOX/CS-MTX complexes significantly increased the cell cytotoxicity and the cell apoptosis rate. However, the complexes significantly reduced the capability of colony formation and cell migration. Our results revealed that NLCs/DTX/DOX/CS-MTX had synergistic cytotoxicity, reactive oxygen spaces, autophagy, and the apoptosis induction ability with an enhanced cellular internalization rate in FR-positive cancer cells, thorough MTX recognition capability. We conclude that the NLCs/DTX/DOX/CS-MTX complex is a new promising paradigm for breast cancer-targeted co-delivery.

Injectable and reversible preformed cryogels based on chemically crosslinked gelatin methacrylate (GelMA) and physically crosslinked hyaluronic acid (HA) for soft tissue engineering.

Hydrogels are a promising choice for soft tissue (cartilage, skin and adipose) engineering and repair. However, lack of interconnected porosity and poor mechanical performance have hindered their application, especially in natural polymer-based hydrogels. Cryogels with the potential to overcome the shortcomings of hydrogels have drawn attention in the last few years. Thus, in this study, highly porous and mechanically robust cryogels based on interpenetrating polymer network (IPN) of gelatin methacrylate (GelMA) and hyaluronic acid (HA) were fabricated for soft tissue engineering application. Cryogels have a constant amount of GelMA (3% wt) with different concentrations of HA (from 5% to 20 % w/w). In fact, crosslinking through cryogelation in subzero temperature facilitates the formation of interconnected pores with 90 % porosity percentage without external progen. On the other hand, high mechanical stability (no failure up to 90 % compression) was achieved due to the cryogelation and chemical crosslinking of GelMA as well as physical crosslinking of HA. Furthermore, the porous and hydrophile nature of the cryogels resulted in shape memory properties under compression, which can reverse to initial shape after retaining the water. Although increasing the HA concentration followed by the density of physical crosslinking boosted the mechanical performance of cryogels under compression, it limited the reversibility properties. Nevertheless, all cryogels with different HA concentrations showed acceptable gel strength and Young's modulus (G-H-20, E = 6kPa) and had appropriate pore size for cell infiltration and nutrient transportation with good cell adhesion and high cell viability (more than 90 %). The unique property of fabricated cryogels that facilitate less invasive delivery makes them a promising alternative for the soft tissue application.

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.

Crosslinking strategies for silk fibroin hydrogels: promising biomedical materials.

Due to their strong biomimetic potential, silk fibroin (SF) hydrogels are impressive candidates for tissue engineering, due to their tunable mechanical properties, biocompatibility, low immunotoxicity, controllable biodegradability, and a remarkable capacity for biomaterial modification and the realization of a specific molecular structure. The fundamental chemical and physical structure of SF allows its structure to be altered using various crosslinking strategies. The established crosslinking methods enable the formation of three-dimensional (3D) networks under physiological conditions. There are different chemical and physical crosslinking mechanisms available for the generation of SF hydrogels (SFHs). These methods, either chemical or physical, change the structure of SF and improve its mechanical stability, although each method has its advantages and disadvantages. While chemical crosslinking agents guarantee the mechanical strength of SFH through the generation of covalent bonds, they could cause some toxicity, and their usage is not compatible with a cell-friendly technology. On the other hand, physical crosslinking approaches have been implemented in the absence of chemical solvents by the induction of ß-sheet conformation in the SF structure. Unfortunately, it is not easy to control the shape and properties of SFHs when using this method. The current review discusses the different crosslinking mechanisms of SFH in detail, in order to support the development of engineered SFHs for biomedical applications.