Influence of macroporous protein scaffolds on bone tissue engineering from bone marrow stem cells

Novel collagen gradient membranes with multiphasic structures: Preparation, characterization, and biocompatibility

Scaffolds with multiphasic structures are considered to be superior for guided tissue regeneration. Two types of tilapia skin collagen gradient membranes (stepped gradient and linear gradient) with multiphasic structures were prepared by controlling the collagen concentrations and the freezing rates. The results revealed that collagen gradient membranes were more capable of guiding tissue regeneration compared to homogeneous membranes. These two gradient membranes featured a dense outer layer and a loose inner layer, with good mechanical properties as indicated by tensile strengths of more than 250 Kpa and porosities exceeding 85 %. Additionally, these membranes also showed good hydrophilicity and water absorption, with an inner layer contact angle of less than 91° and a water absorption ratio greater than 40 times. Furthermore, the multiphasic scaffolds were proved to be biocompatible by the acute toxicity assay, the intradermal irritation test and so on. Gradient membranes could effectively promote the adhesion and proliferation of fibroblasts and osteoblasts, through elevating the TGF-β/Smad signaling pathway by TGF-β and Smads, and activating the Wnt/β-catenin signaling pathway by LRP5 and β-catenin, similar to homogenous membranes. Therefore, collagen gradient membranes from tilapia skin show important application value in guiding tissue regeneration.

Decoding the "Fingerprint" of Implant Materials: Insights into the Foreign Body Reaction

Foreign body reaction (FBR) is a prevalent yet often overlooked pathological phenomenon, particularly within the field of biomedical implantation. The presence of FBR poses a heavy burden on both the medical and socioeconomic systems. This review seeks to elucidate the protein "fingerprint" of implant materials, which is generated by the physiochemical properties of the implant materials themselves. In this review, the activity of macrophages, the formation of foreign body giant cells (FBGCs), and the development of fibrosis capsules in the context of FBR are introduced. Additionally, the relationship between various implant materials and FBR is elucidated in detail, as is an overview of the existing approaches and technologies employed to alleviate FBR. Finally, the significance of implant components (metallic materials and non-metallic materials), surface CHEMISTRY (charge and wettability), and physical characteristics (topography, roughness, and stiffness) in establishing the protein "fingerprint" of implant materials is also well documented. In conclusion, this review aims to emphasize the importance of FBR on implant materials and provides the current perspectives and approaches in developing implant materials with anti-FBR properties.

Multi-Niche Human Bone Marrow On-A-Chip for Studying the Interactions of Adoptive CAR-T Cell Therapies with Multiple Myeloma

Multiple myeloma (MM), a cancer of bone marrow plasma cells, is the second-most common hematological malignancy. However, despite immunotherapies like chimeric antigen receptor (CAR)-T cells, relapse is nearly universal. The bone marrow (BM) microenvironment influences how MM cells survive, proliferate, and resist treatment. Yet, it is unclear which BM niches give rise to MM pathophysiology. Here, we present a 3D microvascularized culture system, which models the endosteal and perivascular bone marrow niches, allowing us to study MM-stroma interactions in the BM niche and model responses to therapeutic CAR-T cells. We demonstrated the prolonged survival of cell line-based and patient-derived multiple myeloma cells within our in vitro system and successfully flowed in donor-matched CAR-T cells. We then measured T cell survival, differentiation, and cytotoxicity against MM cells using a variety of analysis techniques. Our MM-on-a-chip system could elucidate the role of the BM microenvironment in MM survival and therapeutic evasion and inform the rational design of next-generation therapeutics.

TEASER

A multiple myeloma model can study why the disease is still challenging to treat despite options that work well in other cancers.

Physical stimuli-emitting scaffolds: The role of piezoelectricity in tissue regeneration

The imbalance between life expectancy and quality of life is increasing due to the raising prevalence of chronic diseases. Musculoskeletal disorders and chronic wounds affect a growing percentage of people and demand more efficient tools for regenerative medicine. Scaffolds that can better mimic the natural physical stimuli that tissues receive under healthy conditions and during healing may significantly aid the regeneration process. Shape, mechanical properties, pore size and interconnectivity have already been demonstrated to be relevant scaffold features that can determine cell adhesion and differentiation. Much less attention has been paid to scaffolds that can deliver more dynamic physical stimuli, such as electrical signals. Recent developments in the precise measurement of electrical fields in vivo have revealed their key role in cell movement (galvanotaxis), growth, activation of secondary cascades, and differentiation to different lineages in a variety of tissues, not just neural. Piezoelectric scaffolds can mimic the natural bioelectric potentials and gradients in an autonomous way by generating the electric stimuli themselves when subjected to mechanical loads or, if the patient or the tissue lacks mobility, ultrasound irradiation. This review provides an analysis on endogenous bioelectrical signals, recent developments on piezoelectric scaffolds for bone, cartilage, tendon and nerve regeneration, and their main outcomes in vivo. Wound healing with piezoelectric dressings is addressed in the last section with relevant examples of performance in animal models. Results evidence that a fine adjustment of material composition and processing (electrospinning, corona poling, 3D printing, annealing) provides scaffolds that act as true emitters of electrical stimuli that activate endogenous signaling pathways for more efficient and long-term tissue repair.

Concentric-mineralized hybrid silk-based scaffolds for bone tissue engineering in vitro models

There are many challenges in the development of 3D-tissue models for studying bone physiology and disease. Silk fibroin (SF), a natural fibrous protein used in biomedical applications has been studied for bone tissue engineering (TE) due to its mechanical properties, biocompatibility and biodegradability. However, low osteogenic capacity as well as the necessity to reinforce the protein mechanically for some orthopedic applications prompts the need for further designs for SF-based materials for TE bone. Concentric mineralized porous SF-based scaffolds were developed to improve mechanics and mineralization towards osteoregeneration. Hybrid SF silica microparticles (MP) or calcium carbonate nano-structured microparticles (NMP) were seeded with hMSCs co-cultured under osteogenic and osteoclastic conditions with THP-1 human monocytes up to 10 weeks to simulate and recapitulate bone regeneration. Scaffolds with appropriate pore size for cell infiltration, resulted in improved compressive strength, increased cell attachment and higher levels of expression of osteogenic markers and mineralization after adding the NMPs, compared to controls systems without these particles. These hybrid SF-based 3D-structures can provide improved scaffold designs for in vitro bone TE.

Magnetic nanocomposites for magneto-promoted osteogenesis: from simulation auxiliary design to experimental validation

Magnetically actuated mechanical stimulation, as a novel form of intelligent responsive force stimulation, has a great potential for remote spatiotemporal regulation of a variety of life processes. Hence, the optimal design of magnetic nanomaterials for generating magneto-mechanical stimuli becomes an important driving force in the development of magneto-controlled biotherapy. This study aims to clarify the general rule that the surface modification amount of magnetic nanoparticles (NPs) affects the biological behavior (e.g., cell adhesion, proliferation and differentiation) of pre-osteoblast cells. First of all, course-grained molecular dynamics simulations predict that 23.3% graft modification of the NPs can maximize the heterogeneity of the dynamics of the polymer matrix, which may generate enhanced mechanical stimuli. Then, experimentally, iron oxide (IO) NPs grafted with different amounts of poly(γ-benzyl-L-glutamate) (PBLG) were prepared to obtain homogeneous magnetic nanocomposites with improved mechanical properties. Further in vitro cell experiments demonstrate that the grafting amounts of 21.46% and 32.34% of PBLG on IO NPs are the most beneficial for the adhesion and osteogenic differentiation of cells. Simultaneously, the maximized upregulation of the Piezo1 gene indicates that the cells receive the strongest magneto-mechanical stimuli. The consistent conclusion of the experiments and simulations indicates that 20-30% PBLG grafted on the IO surface could maximize the ability of magnetic stimuli to regulate the biological behavior of the cells, which validates the feasibility of simulation auxiliary material design and is of great importance for promoting the application of magneto-controlled biotherapy in bioengineering and biomedicine.

Additive Manufacturing of Polyhydroxyalkanoate-Based Blends Using Fused Deposition Modelling for the Development of Biomedical Devices

In the last few decades Additive Manufacturing has advanced and is becoming important for biomedical applications. In this study we look at a variety of biomedical devices including, bone implants, tooth implants, osteochondral tissue repair patches, general tissue repair patches, nerve guidance conduits (NGCs) and coronary artery stents to which fused deposition modelling (FDM) can be applied. We have proposed CAD designs for these devices and employed a cost-effective 3D printer to fabricate proof-of-concept prototypes. We highlight issues with current CAD design and slicing and suggest optimisations of more complex designs targeted towards biomedical applications. We demonstrate the ability to print patient specific implants from real CT scans and reconstruct missing structures by means of mirroring and mesh mixing. A blend of Polyhydroxyalkanoates (PHAs), a family of biocompatible and bioresorbable natural polymers and Poly(L-lactic acid) (PLLA), a known bioresorbable medical polymer is used. Our characterisation of the PLA/PHA filament suggest that its tensile properties might be useful to applications such as stents, NGCs, and bone scaffolds. In addition to this, the proof-of-concept work for other applications shows that FDM is very useful for a large variety of other soft tissue applications, however other more elastomeric MCL-PHAs need to be used.

Multiple Cell Cultures for MRI Analysis

Magnetic resonance imaging (MRI) is an imaging method that enables diagnostics. In recent years, this technique has been widely used for research using cell cultures used in pharmaceutical science to understand the distribution of various drugs in a variety of biological samples, from cellular models to tissues. MRI's dynamic development in recent years, in addition to diagnostics, has allowed the method to be implemented to assess response to applied therapies. Conventional MRI imaging provides anatomical and pathological information. Due to advanced technology, MRI provides physiological information. The use of cell cultures is very important in the process of testing new synthesized drugs, cancer research, and stem cell research, among others. Two-dimensional (2D) cell cultures conducted under laboratory conditions, although they provide a lot of information, do not reflect the basic characteristics of the tumor. To replicate the tumor microenvironment in science, a three-dimensional (3D) culture of tumor cells was developed. This makes it possible to reproduce in vivo conditions where, in addition, there is a complex and dynamic process of cell-to-cell communication and cell-matrix interaction. In this work, we reviewed current research in 2D and 3D cultures and their use in MRI studies. Articles for each section were collected from PubMed, ScienceDirect, Web of Science, and Google Scholar.

A Beginner’s Guide to the Characterization of Hydrogel Microarchitecture for Cellular Applications

The extracellular matrix (ECM) is a three-dimensional, acellular scaffold of living tissues. Incorporating the ECM into cell culture models is a goal of cell biology studies and requires biocompatible materials that can mimic the ECM. Among such materials are hydrogels: polymeric networks that derive most of their mass from water. With the tuning of their properties, these polymer networks can resemble living tissues. The microarchitectural properties of hydrogels, such as porosity, pore size, fiber length, and surface topology can determine cell plasticity. The adequate characterization of these parameters requires reliable and reproducible methods. However, most methods were historically standardized using other biological specimens, such as 2D cell cultures, biopsies, or even animal models. Therefore, their translation comes with technical limitations when applied to hydrogel-based cell culture systems. In our current work, we have reviewed the most common techniques employed in the characterization of hydrogel microarchitectures. Our review provides a concise description of the underlying principles of each method and summarizes the collective data obtained from cell-free and cell-loaded hydrogels. The advantages and limitations of each technique are discussed, and comparisons are made. The information presented in our current work will be of interest to researchers who employ hydrogels as platforms for cell culture, 3D bioprinting, and other fields within hydrogel-based research.

Development of silk fibroin‑sodium alginate scaffold loaded silk fibroin nanoparticles for hemostasis and cell adhesion

During wound healing process, it is essential to promote hemostasis and cell adhesion. Herein, we incorporated a scaffold with nanoparticles to improve the hemostatic properties and stimulate cell adhesion. The nanoparticles were prepared by self-assembling of silk fibroin, and the scaffold loaded nanoparticles were synthesized by crosslinking and freeze-drying. Macroscopical images showed that the nanoparticles distributed uniformly and increased the surface roughness of scaffold pore wall. The addition of nanoparticles decreased the pore size, enhanced the compression strength, lowered the degradation rate, and maintained the resilience and water uptake capacity. Compared with pure scaffold, the scaffold loaded nanoparticles revealed higher blood clotting index and promoted platelets adhesion. Furthermore, in vitro tests showed that scaffold loaded nanoparticles exhibited excellent biocompatibility, and stimulation effects on cell proliferation, migration, and adhesion for both L929 cells and HUVECs. Therefore, the scaffold loaded nanoparticles possessed great potential as a wound dressing for efficient hemostasis and subsequent wound healing.

Medical Applications of Porous Biomaterials: Features of Porosity and Tissue-Specific Implications for Biocompatibility

Porosity is an important material feature commonly employed in implants and tissue scaffolds. The presence of material voids permits the infiltration of cells, mechanical compliance, and outward diffusion of pharmaceutical agents. Various studies have confirmed that porosity indeed promotes favorable tissue responses, including minimal fibrous encapsulation during the foreign body reaction (FBR). However, increased biofilm formation and calcification is also described to arise due to biomaterial porosity. Additionally, the relevance of host responses like the FBR, infection, calcification, and thrombosis are dependent on tissue location and specific tissue microenvironment. In this review, the features of porous materials and the implications of porosity in the context of medical devices is discussed. Common methods to create porous materials are also discussed, as well as the parameters that are used to tune pore features. Responses toward porous biomaterials are also reviewed, including the various stages of the FBR, hemocompatibility, biofilm formation, and calcification. Finally, these host responses are considered in tissue specific locations including the subcutis, bone, cardiovascular system, brain, eye, and female reproductive tract. The effects of porosity across the various tissues of the body is highlighted and the need to consider the tissue context when engineering biomaterials is emphasized.

Elastomer-Hydrogel Systems: From Bio-Inspired Interfaces to Medical Applications

Novel advanced biomaterials have recently gained great attention, especially in minimally invasive surgical techniques. By applying sophisticated design and engineering methods, various elastomer-hydrogel systems (EHS) with outstanding performance have been developed in the last decades. These systems composed of elastomers and hydrogels are very attractive due to their high biocompatibility, injectability, controlled porosity and often antimicrobial properties. Moreover, their elastomeric properties and bioadhesiveness are making them suitable for soft tissue engineering. Herein, we present the advances in the current state-of-the-art design principles and strategies for strong interface formation inspired by nature (bio-inspiration), the diverse properties and applications of elastomer-hydrogel systems in different medical fields, in particular, in tissue engineering. The functionalities of these systems, including adhesive properties, injectability, antimicrobial properties and degradability, applicable to tissue engineering will be discussed in a context of future efforts towards the development of advanced biomaterials.

Enhanced Bone Regeneration via PHA Scaffolds Coated with Polydopamine-Captured BMP2

The hierarchical three-dimensional (3D)-printing scaffolds based on microbial polyester poly(3-hydrxoybutyrate-co-4-hydroxybutyrate) (P34HB) were designed and used for bone tissue engineering via surface functionalization on the 3D-printed (P34HB) scaffolds using polydopamine (PDA)-mediated...

Biocompatible Micron-Scale Silk Fibers Fabricated by Microfluidic Wet Spinning

For successful material deployment in tissue engineering, the material itself, its mechanical properties, and the microscopic geometry of the product are of particular interest. While silk is a widely applied protein-based tissue engineering material with strong mechanical properties, the size and shape of artificially spun silk fibers are limited by existing processes. This study adjusts a microfluidic spinneret to manufacture micron-sized wet-spun fibers with three different materials enabling diverse geometries for tissue engineering applications. The spinneret is direct laser written (DLW) inside a microfluidic polydimethylsiloxane (PDMS) chip using two-photon lithography, applying a novel surface treatment that enables a tight print-channel sealing. Alginate, polyacrylonitrile, and silk fibers with diameters down to 1 µm are spun, while the spinneret geometry controls the shape of the silk fiber, and the spinning process tailors the mechanical property. Cell-cultivation experiments affirm bio-compatibility and showcase an interplay between the cell-sized fibers and cells. The presented spinning process pushes the boundaries of fiber fabrication toward smaller diameters and more complex shapes with increased surface-to-volume ratio and will substantially contribute to future tailored tissue engineering materials for healthcare applications.

Silk Fibroin as a Green Material

Silk fibroin has been explored as a suitable biomaterial due to its biocompatibility, tunable degradability, low toxicity, and mechanical properties. To harness silk fibroin's innate properties, it is purified from native silkworm cocoons by removing proteins and debris that have the potential to cause inflammatory responses. Typically, within the purification and fabrication steps, chemical solvents, energy-intensive equipment, and large quantities of water are used to reverse engineer silk fibroin into an aqueous solution and then process into the final material format. Gentler, green methods for extraction and fabrication have been developed that reduce or remove the need for harmful chemical additives and energy-inefficient equipment while still producing mechanically robust biomaterials. This review will focus on the alternative green processing and fabrication methods that have proven useful in creating silk fibroin materials for a range of applications including consumer and medical materials.

Naringin-inlaid silk fibroin/hydroxyapatite scaffold enhances human umbilical cord-derived mesenchymal stem cell-based bone regeneration

OBJECTIVES

Large bone defects are a common, debilitating clinical condition that have substantial global health and economic burden. Bone tissue engineering technology has become one of the most promising approaches for regenerating defective bones. In this study, we fabricated a naringin-inlaid composite silk fibroin/hydroxyapatite (NG/SF/HAp) scaffold to repair bone defects.

MATERIALS AND METHODS

The salt-leaching technology was used to fabricate the NG/SF/HAp scaffold. The cytocompatibility of the NG/SF/HAp scaffold was assessed using scanning electron microscopy, live/dead cell staining and phalloidin staining. The osteogenic and angiogenic properties were assessed in vitro and in vivo.

RESULTS

The porous NG/SF/HAp scaffold had a well-designed biomimetic porous structure with osteoinductive and angiogenic activities. A gene microarray identified 854 differentially expressed genes between human umbilical cord-derived mesenchymal stem cells (hUCMSCs) cultured on SF-nHAp scaffolds and cells cultured on NG/SF/HAp scaffolds. The underlying osteoblastic mechanism was investigated using hUCMSCs in vitro. Naringin facilitated hUCMSC ingrowth into the SF/HAp scaffold and promoted osteogenic differentiation. The osteogenic and angiogenic capabilities of cells cultured in the NG/SF/HAp scaffold were superior to those of cells cultured in the SF/HAp scaffold.

CONCLUSIONS

The data indicate the potential of the SF/HAp composite scaffold incorporating naringin for bone regeneration.

Investigations into the role of non-bond interaction on gelation mechanism of silk fibroin hydrogel

Silk fibroin hydrogel not only has biocompatibility, but also has environmental response ability. It plays an important role in the development of material. The gelation mechanism of silk fibroin hydrogel is very important to textile and medicine fields. The molecular dynamics simulation was used to discuss the structure and non-bond interaction of silk fibroin hydrogel. The results show that the non-bond interactions between silk fibroin molecules and water molecules have certain influence on the formation of silk fibroin hydrogel. According to the hydrogen bond analysis, the hydrogen bonds are mainly formed between random coil peptide fragments at the two ends of silk fibroin molecules and residues 252-254 are the key residues. The electrostatic and polar solvation interactions between silk fibroin molecules plays a major role in cross-linking of the coil segments of two silk fibroin molecules.

The utility of biomedical scaffolds laden with spheroids in various tissue engineering applications

A spheroid is a complex, spherical cellular aggregate supporting cell-cell and cell-matrix interactions in an environment that mimics the real-world situation. In terms of tissue engineering, spheroids are important building blocks that replace two-dimensional cell cultures. Spheroids replicate tissue physiological activities. The use of spheroids with/without scaffolds yields structures that engage in desired activities and replicate the complicated geometry of three-dimensional tissues. In this mini-review, we describe conventional and novel methods by which scaffold-free and scaffolded spheroids may be fabricated and discuss their applications in tissue regeneration and future perspectives.

Systematic Review of Silk Scaffolds in Musculoskeletal Tissue Engineering Applications in the Recent Decade

During the past decade, various novel tissue engineering (TE) strategies have been developed to maintain, repair, and restore the biomechanical functions of the musculoskeletal system. Silk fibroins are natural polymers with numerous advantageous properties such as good biocompatibility, high mechanical strength, and low degradation rate and are increasingly being recognized as a scaffolding material of choice in musculoskeletal TE applications. This current systematic review examines and summarizes the latest research on silk scaffolds in musculoskeletal TE applications within the past decade. Scientific databases searched include PubMed, Web of Science, Medline, Cochrane library, and Embase. The following keywords and search terms were used: musculoskeletal, tendon, ligament, intervertebral disc, muscle, cartilage, bone, silk, and tissue engineering. Our Review was limited to articles on musculoskeletal TE, which were published in English from 2010 to September 2019. The eligibility of the articles was assessed by two reviewers according to prespecified inclusion and exclusion criteria, after which an independent reviewer performed data extraction and a second independent reviewer validated the data obtained. A total of 1120 articles were reviewed from the databases. According to inclusion and exclusion criteria, 480 articles were considered as relevant for the purpose of this systematic review. Tissue engineering is an effective modality for repairing or replacing injured or damaged tissues and organs with artificial materials. This Review is intended to reveal the research status of silk-based scaffolds in the musculoskeletal system within the recent decade. In addition, a comprehensive translational research route for silk biomaterial from bench to bedside is described in this Review.

Polymeric nanofibrous scaffolds laden with cell-derived extracellular matrix for bone regeneration

Bone tissue engineering aims to alleviate the shortage of available autograft material and the biological/mechanical incompatibility of allografts through fabrication of bioactive synthetic bone graft substitutes. However, these substitute grafting materials have insufficient biological potency that limits their clinical efficacy in regenerating large defects. Extracellular matrix, a natural tissue scaffold laden with biochemical and structural cues regulating cell adhesion and tissue morphogenesis, may be a versatile supplement that can extend its biological functionality to synthetic grafts. Embedding decellularized extracellular matrix (dECM) into synthetic polymers offers a promising strategy to enhance cellular response to synthetic materials, mitigate physical and mechanical limitations of dECMs, and improve clinical utility of synthetic bone grafts. Enriched with dECM biochemical cues, synthetic polymers can be readily fabricated into complex biocomposite grafts that mimic bone structure and stimulate endogenous cells to regenerate bone. In this study, cell-derived dECMs from osteoblast and endothelial cells were incorporated into polycaprolactone (PCL) solutions for electrospinning dual-layer nanofibrous scaffolds with osteogenic and vascular cues. The study examined the bioactivity of dECM scaffolds in osteoblast cultures for cell number, mineral deposits, and osteogenic markers, as well as regeneration of cortical bone defect in a rat femur. Scaffolds with osteoblast dECM had a significantly robust osteoblast proliferation, Alizarin Red staining/concentration, and osteopontin-positive extracellular deposits. Implanted scaffolds increased bone growth in femoral defects, and constructs with both osteogenic and vascular cues significantly improved cortical width. These findings demonstrate the potential to fabricate tailored biomimetic grafts with dECM cues and fibrous architecture for bone applications.

Gelatin-Based Microribbon Hydrogels Support Robust MSC Osteogenesis across a Broad Range of Stiffness

Scaffold macroporosity has been shown to be critical for promoting bone regeneration. Although injectable materials are preferred for minimally invasive delivery, conventional macroporous scaffolds were not injectable and do not support homogeneous cell encapsulation. We recently reported a gelatin-based microribbon (μRB) scaffold that offers macroporosity while also supporting homogeneous cell encapsulation. Compared to conventional gelatin hydrogels, macroporous gelatin μRB scaffolds demonstrated great advantage in enhancing mesenchymal stem cell (MSC)-based cartilage formation. However, whether gelatin-based μRBs support MSC osteogenesis and bone formation remains unknown. The goal of this study is to assess the potential of gelatin-based μRBs for supporting MSC-based osteogenesis and bone formation in vitro. Given recent evidence from the literature that osteogenesis is sensitive to substrate stiffness, we further investigate how varying μRB stiffness modulates MSC osteogenesis. We first determine the maximal stiffness range of gelatin μRBs that can be fabricated (13-57 kPa), which supports both retention of μRB shape and macroporosity within scaffolds after inter-cross-linking. Interestingly, varying μRB stiffness across a broad range of stiffness did not significantly impact osteogenesis, with all groups supporting upregulation of bone markers and extensive collagen deposition. All gelatin μRBs also supported a comparable level of cell spreading and upregulation of mechanosensing markers. However, soft μRB (13 kPa) scaffolds did not maintain structural integrity and condensed into a pellet over time. Both intermediate and stiff gelatin μRB-based scaffolds maintained their integrity and supported robust bone formation, leading to a more than 10-fold increase in the compressive moduli of engineered bone after 5 weeks of culture in osteogenic media. Incorporating hydroxyapatite (HA) nanoparticle coating onto the gelatin μRB surface further accelerated the maturation of MSCs into osteoblasts and mineralization. Together, these results validate that gelatin μRBs can support MSC osteogenesis across a broad range of stiffness and offers an injectable macroporous scaffold for enhancing stem-cell-based bone regeneration.

Bioprocess Technologies that Preserve the Quality of iPSCs

Large-scale production of induced pluripotent stem cells (iPSCs) is essential for the treatment of a variety of clinical indications. However, culturing enough iPSCs for clinical applications is problematic due to their sensitive pluripotent state and dependence on a supporting matrix. Developing stem cell bioprocessing strategies that are scalable and meet clinical needs requires incorporating methods that measure and monitor intrinsic markers of cell differentiation state, developmental status, and viability in real time. In addition, proper cell culture modalities that nurture the growth of high-quality stem cells in suspension are critical for industrial scale-up. In this review, we present an overview of cell culture media, suspension modalities, and monitoring techniques that preserve the quality and pluripotency of iPSCs during initiation, expansion, and manufacturing.

Collagen-I/silk-fibroin biocomposite exhibits microscalar confinement of cells and induces anisotropic morphology and migration of embedded fibroblasts

Microstructural anisotropy of tumor-associated matrix correlates with invasion of cancer cells into the surrounding matrix during metastasis. Here, we report the fabrication and characterization of a three-dimensional (3D) silk-fibroin/collagen-I bio-composite based cell-culture model that exhibits microstructural and biochemical anisotropy. Using RGD-deficient silk-fibroin fibers to confine collagen-I gelation, we develop a silk-fibroin/collagen-I (SFC) bio-composite in a one-step process allowing control over the microstructural and biochemical anisotropy and the pore-size. Two forms of the SFC bio-composite are reported: a sandwich (S_fc ) configuration amenable to live-cell microscopy and an unsupported membrane (M_fc ) for use as a scaffold. Both microscalar and macroscalar mechanical properties of the SFC bio-composite are characterized using atomic force microscope (AFM)-based indentation and tensile-testing. We find that the modulus of stiffness of both S_fc and M_fc can be controlled and falls in the physiological range of 5-20 kPa. Furthermore, the modulus of stiffness of M_fc exhibits a ~200% increase in axial direction of microstructure, as compared to lateral direction. This implies a highly anisotropic mechanical stiffness of the microenvironment. Live-cell morphology and migration studies show that both the morphology and the migration of NIH-3 T3 fibroblasts is anisotropic and correlates with microstructural anisotropy. Our results show that SFC bio-composite permits proliferation of cells in both S_fc and M_fc configuration, promotes cell-migration along the major axis of anisotropy and together with morphological and migration data, suggest a potential application of both the composite configurations as a biomimetic scaffold for tissue engineering applications.

Lossless immunocytochemistry using photo-polymerized hydrogel thin-films

Encapsulating cell samples in porous hydrogel thin-films eliminates cell loss and reduces processing time in standard immunocytochemistry workflows.

Halloysite Nanoclay/Biopolymers Composite Materials in Tissue Engineering

Biocompatible materials for the fabrication of tissue substitutes are crucially important in the advancement of modern medicinal biotechnology. These materials, to serve their function, should be similar in physical, chemical, biological, and structural properties to native tissues which they are aimed to mimic. The porosity of artificial scaffolds is essential for normal nutrient transmission to cells, gas diffusion, and cell attachment and proliferation. Nanoscale inorganic additives and dopants are widely used to improve the functional properties of the polymer materials for tissue engineering. Among these inorganic dopants, halloysite nanotubes are arguably the most perspective candidates because of their biocompatibility and functional properties allowing to enhance significantly the mechanical and chemical stability of tissue engineering scaffolds. Here, this vibrant field of biotechnology for regenerative medicine is overviewed.

Nanomaterials for bone tissue regeneration: updates and future perspectives

Joint replacement and bone reconstructive surgeries are on the rise globally. Current strategies for implants and bone regeneration are associated with poor integration and healing resulting in repeated surgeries. A multidisciplinary approach involving basic biological sciences, tissue engineering, regenerative medicine and clinical research is required to overcome this problem. Considering the nanostructured nature of bone, expertise and resources available through recent advancements in nanobiotechnology enable researchers to design and fabricate devices and drug delivery systems at the nanoscale to be more compatible with the bone tissue environment. The focus of this review is to present the recent progress made in the rationale and design of nanomaterials for tissue engineering and drug delivery relevant to bone regeneration.

Acellular polycaprolactone scaffolds laden with fibroblast/endothelial cell-derived extracellular matrix for bone regeneration

Inconsistencies in graft osteoconduction and osteoinduction present a clinical challenge in regeneration of large bone defects. Deposition of decellularized extracellular matrix (dECM) on tissue engineered scaffolds offers an alternative approach that can enhance these properties by mimicking bone's molecular complexity and direct infiltrating cells to repair damaged bone. However, dECMs derived from homogenous cell populations do not adequately simulate the heterogeneous and vascularized microenvironment of the bone. In this study, successive culture and decellularization of fibroblasts and endothelial cells (ECs) grown on polycaprolactone microfibers was used to develop a bioactive scaffold with heterogeneous dECM mimicking endothelial basement membrane. These scaffolds had greater amount of protein and minimally increased nucleic acid content than scaffolds with homogenous culture dECM. Coomassie Blue and antibody staining revealed extensive tube formation by ECs on fibroblast dECM. Fibroblast/endothelial dECM significantly enhanced osteoblast attachment, alkaline phosphatase activity, and osteocalcin- and osteopontin-positive extracellular mineral deposits. We demonstrated that the osteoconduction of dECMs can be tailored with the appropriate combination of cells to accelerate osteoblast mineral secretion. The overall concept can be expanded to generate increasingly more complex tissue constructs for regeneration of bone defects and other vascularized tissues.

Specific concentration of hyaluronan amide derivative induces osteogenic mineralization of human mesenchymal stromal cells: Evidence of RUNX2 and COL1A1 genes modulation

Hyaluronic acid (HA) is an ideal material for tissue regeneration. The aim of this study was to investigate whether a hyaluronan amide derivative (HAD) can enhance the mineralization of human mesenchymal stem cells (hMSCs). Osteogenically induced hMSCs cultured with or without HAD at different concentrations (0.5 mg/ml or 1 mg/ml) were analyzed for mineral matrix deposition, metabolic activity, cellular proliferation, and the expression of 14 osteogenic genes. Unmodified HA (HYAL) was used as control. We demonstrated that only cells treated daily until day 28 with 0.5 mg/ml HAD, but not with 1 mg/ml of HAD and HYAL, showed a significant induction of mineralization at day 14 compared to the osteogenic control group. HAD at both concentrations tested, significantly decreased the expression of the proliferating marker MKI67 at day 2. By contrast, increased metabolic activity was induced only by HYAL from day 14. HAD at both concentrations significantly down modulated SNAI2, DLX5, RUNX2, COL1A1, and IBSP genes, while significantly up regulated COL15A1. The induction of mineralization of 0.5 mg/ml of HAD at day 14 was significantly dependent on a specific modulation of RUNX2 and COL1A1. Our data demonstrate that only 0.5 mg/ml of HAD, but not HYAL, modulated hMSCs osteogenic differentiation, suggesting that the physicochemical features and concentration of HA products could differently affect osteogenic maturation.

Osteostimulatory effect of biocomposite scaffold containing phytomolecule diosmin by Integrin/FAK/ERK signaling pathway in mouse mesenchymal stem cells

Non-availability of an ideal alternative for autografts in treating critical-size bone defects is a major challenge in orthopedics. Phytocompounds have been proven to enhance osteogenesis via various osteogenic signaling pathways, but its decreased bioavailability and increased renal clearance limit its application. In this study, we designed a biocomposite scaffold comprising gelatin (Gel) and nanohydroxyapatite (nHAp) incorporated with diosmin (DM) and we investigated its bone forming potential in vitro and in vivo. Physiochemical characterization of the scaffold showed that DM had no effect on altering the material characteristics of the scaffold. The addition of DM enhanced the osteoblast differentiation potential of the scaffold in mouse mesenchymal stem cells at both cellular and molecular levels, possibly via the integrin-mediated activation of FAK and ERK signaling components. Using the rat tibial bone defective model, we identified the effect of DM in Gel/nHAp scaffold on enhancing bone formation in vivo. Based on our results, we suggest that Gel/nHAp/DM can be a potential therapeutic agent in scaffold-mediated bone regeneration.

Combining Stem Cells and Biomaterial Scaffolds for Constructing Tissues and Cell Delivery

Combining stem cells with biomaterial scaffolds serves as a promising strategy for engineering tissues for both in vitro and in vivo applications. This updated review details commonly used biomaterial scaffolds for engineering tissues from stem cells. We first define the different types of stem cells and their relevant properties and commonly used scaffold formulations. Next, we discuss natural and synthetic scaffold materials typically used when engineering tissues, along with their associated advantages and drawbacks and gives examples of target applications. New approaches to engineering tissues, such as 3D bioprinting, are described as they provide exciting opportunities for future work along with current challenges that must be addressed. Thus, this review provides an overview of the available biomaterials for directing stem cell differentiation as a means of producing replacements for diseased or damaged tissues.

Biomaterials: Foreign Bodies or Tuners for the Immune Response?

The perspectives of regenerative medicine are still severely hampered by the host response to biomaterial implantation, despite the robustness of technologies that hold the promise to recover the functionality of damaged organs and tissues. In this scenario, the cellular and molecular events that decide on implant success and tissue regeneration are played at the interface between the foreign body and the host inflammation, determined by innate and adaptive immune responses. To avoid adverse events, rather than the use of inert scaffolds, current state of the art points to the use of immunomodulatory biomaterials and their knowledge-based use to reduce neutrophil activation, and optimize M1 to M2 macrophage polarization, Th1 to Th2 lymphocyte switch, and Treg induction. Despite the fact that the field is still evolving and much remains to be accomplished, recent research breakthroughs have provided a broader insight on the correct choice of biomaterial physicochemical modifications to tune the reaction of the host immune system to implanted biomaterial and to favor integration and healing.

Native-mimicking in vitro microenvironment: an elusive and seductive future for tumor modeling and tissue engineering

Human connective tissues are complex physiological microenvironments favorable for optimal survival, function, growth, proliferation, differentiation, migration, and death of tissue cells. Mimicking native tissue microenvironment using various three-dimensional (3D) tissue culture systems in vitro has been explored for decades, with great advances being achieved recently at material, design and application levels. These achievements are based on improved understandings about the functionalities of various tissue cells, the biocompatibility and biodegradability of scaffolding materials, the biologically functional factors within native tissues, and the pathophysiological conditions of native tissue microenvironments. Here we discuss these continuously evolving physical aspects of tissue microenvironment important for human disease modeling, with a focus on tumors, as well as for tissue repair and regeneration. The combined information about human tissue spaces reflects the necessities of considerations when configuring spatial microenvironments in vitro with native fidelity to culture cells and regenerate tissues that are beyond the formats of 2D and 3D cultures. It is important to associate tissue-specific cells with specific tissues and microenvironments therein for a better understanding of human biology and disease conditions and for the development of novel approaches to treat human diseases.

Differentiated adipose-derived stem cell cocultures for bone regeneration in RADA16-I in vitro

Craniofacial defects can cause morbidness. Adipose-derived stem cells (ADSCs) have shown great promise for osteogeneration and vascularization; therefore cocultures of differentiated ADSCs are explored to increase bone and vessel formation. In this study, ADSCs were induced into osteogenic ADSCs (os-ADSCs) and endothelial ADSCs (endo-ADSCs) cells, which were then cocultured in variable proportions (os-ADSCs/endo-ADSCs = 2:1, 1:1, 1:2). The os-ADSCs in a ratio of 1:1 expressed more ALP, RUNX2 and COL-I, whereas VEGF, vWF and CD31 were upregulated in the endo-ADSCs of this group. Next generation RNA sequencing (RNA-seq) was performed to evaluate the molecular mechanisms of cocultured ADSCs. The os-ADSCs and endo-ADSCs interacted with each other during osteogenic and angiogenic differentiation, especially at the ratio of 1:1, and were regulated by vascular-related genes, cell-mediated genes, bone-related genes and the transforming growth factor β signaling pathway (TGF-β), mitogen-activated protein kinase signaling pathway (MAPK) and wnt signaling pathway (Wnt). Angptl4, apoe, mmp3, bmp6, mmp13 and fgf18 were detected to be up-regulated, and cxcl12 and wnt5a were down-regulated. The results showed that the gene expression levels were consistent with that in RNA-seq. The cells were then seeded into self-assembling peptide RADA16-I scaffolds as cocultures (1:1) and monocultures (ADSCs, os-ADSCs, endo-ADSCs). The results showed that the cells of all groups grew and proliferated well on the scaffolds, and the cocultured group exhibited better osteogeneration and vascularization. In conclusion, cocultured os-ADSCs and endo-ADSCs at the ratio of 1:1 showed strong osteogenic and angiogenic differentiation. There is a great potential for osteogenesis and vascularization by 3D culturing cells in a 1:1 ratio in self-assembling peptide RADA16-I scaffolds, which requires evaluation for bone regeneration in vivo.

Numerical optimization of cell colonization modelling inside scaffold for perfusion bioreactor: A multiscale model

Part of clinically applicable bone graft substitutes are developed by using mechanical stimulation of flow-perfusion into cell-seeded scaffolds. The role of fluid flow is crucial in driving the nutrient to seeded cells and in stimulating cell colonization. A common numerical approach is to use a multiscale model to link some physical quantities (wall shear stress and inlet flow rate) that act at different scales. In this study, a multiscale model is developed in order to determine the optimal inlet flow rate to cultivate osteoblast-like cells seeded in a controlled macroporous biomaterial inside a perfusion bioreactor system. We focus particularly on the influence of Wall Shear Stress on cell colonization to predict cell colonization at the macroscale. Results obtained at the microscale are interpolated at the macroscale to determine the optimal flow rate. For a macroporous scaffold made of interconnected pores with pore diameters of above 350 μm and interconnection diameters of 150 μm, the model predicts a cell colonization of 325% after a 7-day-cell culture with a constant inlet flow rate of 0.69 mL·min^-1. Furthermore, the strength of this protocol is the possibility to adapt it to most porous biomaterials and dynamic cell culture systems.

Adipogenic differentiation of human adipose derived mesenchymal stem cells in 3D architectured gelatin based hydrogels (ArcGel)

Polymeric matrices mimicking multiple functions of the ECM are expected to enable a material induced regeneration of tissues. Here, we investigated the adipogenic differentiation of human adipose derived mesenchymal stem cells (hADSCs) in a 3D architectured gelatin based hydrogel (ArcGel) prepared from gelatin and L-lysine diisocyanate ethyl ester (LDI) in an one-step process, in which the formation of an open porous morphology and the chemical network formation were integrated. The ArcGel was designed to support adipose tissue regeneration with its 3D porous structure, high cell biocompatibility, and mechanical properties compatible with human subcutaneous adipose tissue. The ArcGel could support initial cell adhesion and survival of hADSCs. Under static culture condition, the cells could migrate into the inner part of the scaffold with a depth of 840±120 μm after 4 days, and distributed in the whole scaffold (2 mm in thickness) within 14 days. The cells proliferated in the scaffold and the fold increase of cell number after 7 days of culture was 2.55±0.08. The apoptotic rate of hADSCs in the scaffold was similar to that of cells maintained on tissue culture plates. When cultured in adipogenic induction medium, the hADSCs in the scaffold differentiated into adipocytes with a high efficiency (93±1%). Conclusively, this gelatin based 3D scaffold presented high cell compatibility for hADSC cultivation and differentiation, which could serve as a potential implant material in clinical applications for adipose tissue reparation and regeneration.

Novel cellulose/hydroxyapatite scaffolds for bone tissue regeneration: In vitro and in vivo study

Cellulose scaffolds containing nano- or micro-hydroxyapatite (nHA or μHA) were prepared by the regeneration of cellulose from its acetylated derivative and the mechanical immobilization of inorganic particles, followed by freeze-drying. Microtomographic (micro-computed tomography) evaluation revealed that both scaffolds presented a highly interconnected porous structure, with a mean pore diameter of 490 ± 94 and 540 ± 132 μm for cellulose/nHA and cellulose/μHA, respectively. In vitro and in vivo characterizations of the developed scaffolds were investigated. Commercially available bone allograft was used as a control material. For the in vitro characterization, osteoblastic cell cultures were used and characterized over time to evaluate cell adhesion, metabolic activity, and functional output (alkaline phosphatase activity and osteoblastic gene expression). The results revealed greater spreading cell distribution alongside an increased number of filopodia, higher MTT values, and significantly increased expression of osteoblastic genes (Runx-2, alkaline phosphatase, and BMP-2) for cellulose/nHA, compared with cellulose/μHA and the control. The in vivo biocompatibility was evaluated in a rabbit calvarial defect model. The investigated scaffolds were implanted in circular rabbit calvaria defects. Four- and 12-week bone biopsies were investigated using micro-computed tomography and histological analysis. Although both cellulose/HA scaffolds outperformed the assayed control, a significantly higher amount of newly formed mineralized tissue was found within the defects loaded with cellulose/nHA. Within the limitations of this study, the developed cellulose/HA scaffolds showed promising results for bone regeneration applications. The biological response to the scaffold seems to be greatly dependent on the HA particles' characteristics, with cellulose scaffolds loaded with nHA eliciting an enhanced bone response.

NF-κB signaling is key in the wound healing processes of silk fibroin

Silk fibroin (SF) is a well-studied biomaterial for tissue engineering applications including wound healing. However, the signaling mechanisms underlying the impact of SF on this phenomenon have not been determined. In this study, through microarray analysis, regulatory genes of NF-ĸB signaling were activated in SF-treated NIH3T3 cells along with other genes. Immunoblot analysis confirmed the activation of the NF-ĸB signaling pathway as SF induced protein expression levels of IKKα, IKKβ, p65, and the degradation of IκBα. The treatment of NIH3T3 cells with SF also increased the expression of cyclin D1, vimentin, fibronectin, and vascular endothelial growth factor (VEGF). The expression of these factors by SF treatment was abrogated when NF-ĸB was inhibited by a pharmacological inhibitor Bay 11-7082. Knockdown of NF-ĸB using siRNA of IKKα and IKKβ also inhibited the SF-induced wound healing response of the NIH3T3 cells in a wound scratch assay. Collectively, these results indicated that SF-induced wound healing through the canonical NF-κB signaling pathway via regulation of the expression of cyclin D1, vimentin, fibronectin, and VEGF by NIH3T3 cells. Using an in vivo study with a partial-thickness excision wound in rats we demonstrated that SF-induced wound healing via NF-κB regulated proteins including cyclin D1, fibronectin, and VEGF. The in vitro and in vivo data suggested that SF induced wound healing via modulation of NF-ĸB signaling regulated proteins.

STATEMENT OF SIGNIFICANCE

Silk fibroin has been effectively used as a dressing for wound treatment for more than a century. However, mechanistic insight into the basis for wound healing via silk fibroin has not been elucidated. Here we report a key mechanism involved in silk fibroin induced wound healing both in vitro and in vivo. Using genetic- and protein-level analyses, NF-κB signaling was found to regulate silk fibroin-induced wound healing by modulating target proteins. Thus, the NF-κB signaling pathway may be utilized as a therapeutic target during the formulation of silk fibroin-based biomaterials for wound healing and tissue engineering.

Silk scaffolds in bone tissue engineering: An overview

Bone tissue plays multiple roles in our day-to-day functionality. The frequency of accidental bone damage and disorder is increasing worldwide. Moreover, as the world population continues to grow, the percentage of the elderly population continues to grow, which results in an increased number of bone degenerative diseases. This increased elderly population pushes the need for artificial bone implants that specifically employ biocompatible materials. A vast body of literature is available on the use of silk in bone tissue engineering. The current work presents an overview of this literature from materials and fabrication perspective. As silk is an easy-to-process biopolymer; this allows silk-based biomaterials to be molded into diverse forms and architectures, which further affects the degradability. This makes silk-based scaffolds suitable for treating a variety of bone reconstruction and regeneration objectives. Silk surfaces offer active sites that aid the mineralization and/or bonding of bioactive molecules that facilitate bone regeneration. Silk has also been blended with a variety of polymers and minerals to enhance its advantageous properties or introduce new ones. Several successful works, both in vitro and in vivo, have been reported using silk-based scaffolds to regenerate bone tissues or other parts of the skeletal system such as cartilage and ligament. A growing trend is observed toward the use of mineralized and nanofibrous scaffolds along with the development of technology that allows to control scaffold architecture, its biodegradability and the sustained releasing property of scaffolds. Further development of silk-based scaffolds for bone tissue engineering, taking them up to and beyond the stage of human trials, is hoped to be achieved in the near future through a cross-disciplinary coalition of tissue engineers, material scientists and manufacturing engineers.

STATEMENT OF SIGNIFICANCE

The state-of-art of silk biomaterials in bone tissue engineering, covering their wide applications as cell scaffolding matrices to micro-nano carriers for delivering bone growth factors and therapeutic molecules to diseased or damaged sites to facilitate bone regeneration, is emphasized here. The review rationalizes that the choice of silk protein as a biomaterial is not only because of its natural polymeric nature, mechanical robustness, flexibility and wide range of cell compatibility but also because of its ability to template the growth of hydroxyapatite, the chief inorganic component of bone mineral matrix, resulting in improved osteointegration. The discussion extends to the role of inorganic ions such as Si and Ca as matrix components in combination with silk to influence bone regrowth. The effect of ions or growth factor-loaded vehicle incorporation into regenerative matrix, nanotopography is also considered.

Gradient nanocomposite hydrogels for interface tissue engineering

Two-dimensional (2D) nanomaterials are an emerging class of materials with unique physical and chemical properties due to their high surface area and disc-like shape. Recently, these 2D nanomaterials have been investigated for a range of biomedical applications including tissue engineering, therapeutic delivery and bioimaging, due to their ability to physically reinforce polymeric networks. Here, we present a facile fabrication of a gradient scaffold with two natural polymers (gelatin methacryloyl (GelMA) and methacrylated kappa carrageenan (MκCA)) reinforced with 2D nanosilicates to mimic the native tissue interface. The addition of nanosilicates results in shear-thinning characteristics of prepolymer solution and increases the mechanical stiffness of crosslinked gradient structure. A gradient in mechanical properties, microstructures and cell adhesion characteristics was obtained using a microengineered flow channel. The gradient structure can be used to understand cell-matrix interactions and to design gradient scaffolds for mimicking tissue interfaces.

Nonmulberry Silk Braids Direct Terminal Osteocytic Differentiation through Activation of Wnt-Signaling

Silk polymers can regulate osteogenesis by mimicking some features of the extracellular matrix of bone and facilitate mineralized deposition on their surface by cultured osteoprogenitors. However, terminal differentiation of these mineralizing osteoblasts into osteocytic phenotypes has not yet been demonstrated on silk. Therefore, in this study we test the hypothesis that flat braids of natively (nonregenerated) spun nonmulberry silk A. mylitta, possessing mechanical stiffness in the range of trabecular bone, can regulate osteocyte differentiation within their 3D microenvironment. We seeded human preosteoblasts onto these braids and cultured them under varied temperatures (33.5 and 39 °C), soluble factors (dexamethasone, ascorbic acid, and β-glycerophosphate), and cytokine (TGF-β1). After 1 week, cell dendrites were conspicuously evident, confirming osteocyte differentiation, especially, in the presence of osteogenic factors and TGF-β1 expressing all characteristic osteocyte markers (podoplanin, DMP-1, and sclerostin). A. mylitta silk braids alone were sufficient to induce this differentiation, albeit only transiently. Therefore, we believe that the combinatorial effect of A. mylitta silk (surface chemistry, braid rigidity, and topography), osteogenic differentiation factors, and TGF-β1 were critical in stabilizing the mature osteocytic phenotype. Interestingly, Wnt signaling promoted osteocytic differentiation as evidenced by the upregulated expression of β-catenin in the presence of osteogenic factors and growth factor. This study highlights the role of nonmulberry silk braids in regulating stable osteocytic differentiation. Future studies could benefit from this understanding of the signaling mechanisms associated with silk-based matrices in order to develop 3D in vitro bone model systems.

Effects of silk fibroin in murine dry eye

The study aimed to investigate the effects of silk fibroin in a mouse model of dry eye. The experimental dry eye mouse model was developed using more than twelve-weeks-old NOD.B10.H2^b mice exposing them to 30–40% ambient humidity and injecting them with scopolamine hydrobromide for 10 days. Tear production and corneal irregularity score were measured by the instillation of phosphate buffered saline or silk fibroin. Corneal detachment and conjunctival goblet cell density were observed by hematoxylin and eosin or periodic acid Schiff staining in the cornea or conjunctiva. The expression of inflammatory markers was detected by immunohistochemistry in the lacrimal gland. The silk group tear production was increased, and corneal smoothness was improved. The corneal epithelial cells and conjunctival goblet cells were recovered in the silk groups. The expression of inflammatory factors was inhibited in the lacrimal gland of the silk group. These results show that silk fibroin improved the cornea, conjunctiva, and lacrimal gland in the mouse model of dry eye. These findings suggest that silk fibroin has anti-inflammatory effects in the experimental models of dry eye.

13C NMR characterization of hydrated 13C labeled Bombyx mori silk fibroin sponges prepared using glycerin, poly(ethylene glycol diglycidyl ether) and poly(ethylene glycol) as porogens

There is a need to prepare softer and highly flexible Bombyx mori silk fibroin (SF) sponges for the development of biomaterials that are biodegradable and with stiffness that matches sponges and soft tissues. In this paper, we prepared SF sponges using glycerin (Glyc), poly(ethylene)glycol diglycidyl ether (PGDE) and poly(ethylene)glycol (PEG) as porogens. The detailed characterization of the hydrated SF sponges was done using three ¹³C solid state NMR techniques, viz.,¹³C refocused insensitive nuclei enhanced by polarization transfer (r-INEPT) NMR, ¹³C cross polarization/magic angle spinning (CP/MAS) NMR, and ¹³C dipolar decoupled-magic angle spinning (DD/MAS) NMR. These three NMR methods gave respective information on fast motion, slow motion, and both fast and slow motions for the local structure and dynamics of the hydrated SF sponges. There was no significant difference in the r-INEPT spectra of the three hydrated SF sponges. On the other hand, there were significant differences among the ¹³C CP/MAS NMR spectra of the three sponges. The fractions of two kinds of β-sheet structure, two kinds of random coil conformations with mobile and immobile motions, and the Silk I* (type II β-turn) conformation were determined for the Ser residues in the ¹³C DD/MAS NMR spectra. Similarly, the fractions of several conformations were also determined for Tyr, Ala and Gly residues in SF, which showed significant differences among the three hydrated sponges. The relationship between the local structure of these hydrated SF sponges and their mechanical properties was also briefly discussed.