Enhanced osteogenic potential of human mesenchymal stem cells on electrospun nanofibrous scaffolds prepared from eri-tasar silk fibroin

Recent advancement in vascularized tissue-engineered bone based on materials design and modification

Bone is one of the most vascular network-rich tissues in the body and the vascular system is essential for the development, homeostasis, and regeneration of bone. When segmental irreversible damage occurs to the bone, restoring its vascular system by means other than autogenous bone grafts with vascular pedicles is a therapeutic challenge. By pre-generating the vascular network of the scaffold in vivo or in vitro, the pre-vascularization technique enables an abundant blood supply in the scaffold after implantation. However, pre-vascularization techniques are time-consuming, and in vivo pre-vascularization techniques can be damaging to the body. Critical bone deficiencies may be filled quickly with immediate implantation of a supporting bone tissue engineered scaffold. However, bone tissue engineered scaffolds generally lack vascularization, which requires modification of the scaffold to aid in enhancing internal vascularization. In this review, we summarize the relationship between the vascular system and osteogenesis and use it as a basis to further discuss surgical and cytotechnology-based pre-vascularization strategies and to describe the preparation of vascularized bone tissue engineered scaffolds that can be implanted immediately. We anticipate that this study will serve as inspiration for future vascularized bone tissue engineered scaffold construction and will aid in the achievement of clinical vascularized bone.

Development of a bioactive dentin adhesive resin modified with magnesium-doped synthetic hydroxyapatite crystals

The aim is to evaluate the development of an experimental multi-mode/Universal resin-based dentin adhesive modified with synthetic Mg²⁺ doped hydroxyapatite crystals (HAp) having self-remineralization and antibiofilm properties. HAp doped with Mg²⁺ was prepared by the precipitation method. Experimental adhesives were subjected to degree of conversion and X-ray diffraction test for size and crystal structure. Bond strength was tested, and electron microscopy (SEM/TEM) imaging of resin-dentin interface was done along with nanoleakage, nanoindentation, confocal and Raman analyses. S. mutans was analysed using CLSM images against modified adhesive specimens. Nucleating abilities within the resin-dentin specimens are determined by measuring Ca²⁺. Alkaline phosphatase, Runx2, and Ocn transcripts are amplified using quantitative polymerase chain reaction (q-PCR). A calcium assay is performed to quantify level of mineralisation. When compared to control adhesives, the 0.5% Hap/Mg²⁺ containing experimental dentin adhesive demonstrated improved interaction with dentin. The preservation of uniform intact hybrid layer with the absence of nanoleakage indicated dentin bond integrity with 0.5% HAP/Mg²⁺ modified adhesive. Self-remineralization and antibiofilm potentials are supported.

Silk fibroin scaffolds: A promising candidate for bone regeneration

It remains a big challenge in clinical practice to repair large-sized bone defects and many factors limit the application of autografts and allografts, The application of exogenous scaffolds is an alternate strategy for bone regeneration, among which the silk fibroin (SF) scaffold is a promising candidate. Due to the advantages of excellent biocompatibility, satisfying mechanical property, controllable biodegradability and structural adjustability, SF scaffolds exhibit great potential in bone regeneration with the help of well-designed structures, bioactive components and functional surface modification. This review will summarize the cell and tissue interaction with SF scaffolds, techniques to fabricate SF-based scaffolds and modifications of SF scaffolds to enhance osteogenesis, which will provide a deep and comprehensive insight into SF scaffolds and inspire the design and fabrication of novel SF scaffolds for superior osteogenic performance. However, there still needs more comprehensive efforts to promote better clinical translation of SF scaffolds, including more experiments in big animal models and clinical trials. Furthermore, deeper investigations are also in demand to reveal the degradation and clearing mechanisms of SF scaffolds and evaluate the influence of degradation products.

Nonmulberry silk proteins: multipurpose ingredient in bio-functional assembly

The emerging field of tissue engineering and regenerative medicines utilising artificial polymers is facing many problems. Despite having mechanical stability, non-toxicity and biodegradability, most of them lack cytocompatibility and biocompatibility. Natural polymers (such as collagen, hyaluronic acid, fibrin, fibroin, and others), including blends, are introduced to the field to solve some of the relevant issues. Another natural biopolymer: silkworm silk gained special attention primarily due to its specific biophysical, biochemical, and material properties, worldwide availability, and cost-effectiveness. Silk proteins, namely fibroin and sericin extracted from domesticated mulberry silkwormBombyx mori, are studied extensively in the last few decades for tissue engineering. Wild nonmulberry silkworm species, originated from India and other parts of the world, also produce silk proteins with variations in their nature and properties. Among the nonmulberry silkworm species,Antheraea mylitta(Indian Tropical Tasar),A. assamensis/A. assama(Indian Muga), andSamia ricini/Philosamia ricini(Indian Eri), along withA. pernyi(Chinese temperate Oak Tasar/Tussah) andA. yamamai(Japanese Oak Tasar) exhibit inherent tripeptide motifs of arginyl glycyl aspartic acid in their fibroin amino acid sequences, which support their candidacy as the potential biomaterials. Similarly, sericin isolated from such wild species delivers unique properties and is used as anti-apoptotic and growth-inducing factors in regenerative medicines. Other characteristics such as biodegradability, biocompatibility, and non-inflammatory nature make it suitable for tissue engineering and regenerative medicine based applications. A diverse range of matrices, including but not limited to nano-micro scale structures, nanofibres, thin films, hydrogels, and porous scaffolds, are prepared from the silk proteins (fibroins and sericins) for biomedical and tissue engineering research. This review aims to represent the progress made in medical and non-medical applications in the last couple of years and depict the present status of the investigations on Indian nonmulberry silk-based matrices as a particular reference due to its remarkable potentiality of regeneration of different types of tissues. It also discusses the future perspective in tissue engineering and regenerative medicines in the context of developing cutting-edge techniques such as 3D printing/bioprinting, microfluidics, organ-on-a-chip, and other electronics, optical and thermal property-based applications.

Three-Dimensional Modeling of the Structural Microenvironment in Post-Traumatic War Wounds

BACKGROUND:

The development of post-traumatic heterotopic ossification (HO) is a common, undesirable sequela in patients with high-energy (war-related) extremity injuries. While inflammatory and osteoinductive signaling pathways are known to be involved in the development and progression of post-traumatic HO, features of the structural microenvironment within which the ectopic bone begins to form remain poorly understood. Thus, increasing our knowledge of molecular and structural changes within the healing wound may help elucidate the pathogenesis of post-traumatic HO and aid in the development of specific treatment and/or prevention strategies.

METHODS:

In this study, we performed high-resolution microscopy and biochemical analysis of tissues obtained from traumatic war wounds to characterize changes in the structural microenvironment. In addition, using an electrospinning approach, we modeled this microenvironment to reconstitute a three-dimensional type I collagen scaffold with non-woven, randomly oriented nanofibers where we evaluated the performance of primary mesenchymal progenitor cells.

RESULTS:

We found that traumatic war wounds are characterized by a disorganized, densely fibrotic collagen I matrix that influences progenitor cells adhesion, proliferation and osteogenic differentiation potential.

CONCLUSION:

Altogether, these results suggest that the structural microenvironment present in traumatic war wounds has the potential to contribute to the development of post-traumatic HO. Our findings may support novel treatment strategies directed towards modifying the structural microenvironment after traumatic injury.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13770-021-00355-y.

Bioinspired mineralization of a functionalized injectable dense collagen hydrogel through silk sericin incorporation

The incorporation of silk sericin into injectable dense collagen hydrogels represents a powerful approach to mimic the biomineralization process, together with the osteogenic stimulation of seeded mesenchymal stem cells, in vitro.

Electrospun silk fibroin/poly(lactide-co-ε-caprolactone) nanofibrous scaffolds for bone regeneration

Background

Tissue engineering has become a promising therapeutic approach for bone regeneration. Nanofibrous scaffolds have attracted great interest mainly due to their structural similarity to natural extracellular matrix (ECM). Poly(lactide-co-ε-caprolactone) (PLCL) has been successfully used in bone regeneration, but PLCL polymers are inert and lack natural cell recognition sites, and the surface of PLCL scaffold is hydrophobic. Silk fibroin (SF) is a kind of natural polymer with inherent bioactivity, and supports mesenchymal stem cell attachment, osteogenesis, and ECM deposition. Therefore, we fabricated hybrid nanofibrous scaffolds by adding different weight ratios of SF to PLCL in order to find a scaffold with improved properties for bone regeneration.

Methods

Hybrid nanofibrous scaffolds were fabricated by blending different weight ratios of SF with PLCL. Human adipose-derived stem cells (hADSCs) were seeded on SF/PLCL nanofibrous scaffolds of various ratios for a systematic evaluation of cell adhesion, proliferation, cytotoxicity, and osteogenic differentiation; the efficacy of the composite of hADSCs and scaffolds in repairing critical-sized calvarial defects in rats was investigated.

Results

The SF/PLCL (50/50) scaffold exhibited favorable tensile strength, surface roughness, and hydrophilicity, which facilitated cell adhesion and proliferation. Moreover, the SF/PLCL (50/50) scaffold promoted the osteogenic differentiation of hADSCs by elevating the expression levels of osteogenic marker genes such as BSP, Ocn, Col1A1, and OPN and enhanced ECM mineralization. In vivo assays showed that SF/PLCL (50/50) scaffold improved the repair of the critical-sized calvarial defect in rats, resulting in increased bone volume, higher trabecular number, enhanced bone mineral density, and increased new bone areas, compared with the pure PLCL scaffold.

Conclusion

The SF/PLCL (50/50) nanofibrous scaffold facilitated hADSC proliferation and osteogenic differentiation in vitro and further promoted new bone formation in vivo, suggesting that the SF/PLCL (50/50) nanofibrous scaffold holds great potential in bone tissue regeneration.

Changing Paradigms in Cranio-Facial Regeneration: Current and New Strategies for the Activation of Endogenous Stem Cells

Craniofacial area represent a unique district of human body characterized by a very high complexity of tissues, innervation and vascularization, and being deputed to many fundamental function such as eating, speech, expression of emotions, delivery of sensations such as taste, sight, and earing. For this reasons, tissue loss in this area following trauma or for example oncologic resection, have a tremendous impact on patients' quality of life. In the last 20 years regenerative medicine has emerged as one of the most promising approach to solve problem related to trauma, tissue loss, organ failure etc. One of the most powerful tools to be used for tissue regeneration is represented by stem cells, which have been successfully implanted in different tissue/organs with exciting results. Nevertheless, both autologous and allogeneic stem cell transplantation raise many practical and ethical concerns that make this approach very difficult to apply in clinical practice. For this reason different cell free approaches have been developed aiming to the mobilization, recruitment, and activation of endogenous stem cells into the injury site avoiding exogenous cells implant but instead stimulating patients' own stem cells to repair the lesion. To this aim many strategies have been used including functionalized bioscaffold, controlled release of stem cell chemoattractants, growth factors, BMPs, Platelet-Rich-Plasma, and other new strategies such as ultrasound wave and laser are just being proposed. Here we review all the current and new strategies used for activation and mobilization of endogenous stem cells in the regeneration of craniofacial tissue.

Biomimetic approaches to complex craniofacial defects

The primary goals of craniofacial reconstruction include the restoration of the form, function, and facial esthetics, and in the case of pediatric patients, respect for craniofacial growth. The surgeon, however, faces several challenges when attempting a reconstructive cranioplasty. For that reason, craniofacial defect repair often requires sophisticated treatment strategies and multidisciplinary input. In the ideal situation, autologous tissue similar in structure and function to that which is missing can be utilized for repair. In the context of the craniofacial skeleton, autologous cranial bone, or secondarily rib, iliac crest, or scapular bone, is most favorable. Often, this option is limited by the finite supply of available bone. Therefore, alternative strategies to repair craniofacial defects are necessary. In the field of regenerative medicine, tissue engineering has emerged as a promising concept, and several methods of bone engineering are currently under investigation. A growth factor-based approach utilizing bone morphogenetic proteins (BMPs) has demonstrated stimulatory effects on cranial bone and defect repair. When combined with cell-based and matrix-based models, regenerative goals can be optimized. This manuscript intends to review recent investigations of tissue engineering models used for the repair of craniofacial defects with a focus on the role of BMPs, scaffold materials, and novel cell lines. When sufficient autologous bone is not available, safe and effective strategies to engineer bone would allow the surgeon to meet the reconstructive goals of the craniofacial skeleton.