Silk fibroin-bioactive glass based advanced biomaterials: towards patient-specific bone grafts

Silk-gelatin hybrid hydrogel: a potential carrier for RNA therapeutics

RNA-based therapeutics have exhibited remarkable potential in targeting genetic factors for disease intervention, exemplified by recent mRNA vaccines for COVID-19. Nevertheless, the intrinsic instability of RNA and challenges related to its translational efficiency remain significant obstacles to the development of RNA as therapeutics. This study introduces an innovative RNA delivery approach using a silk fibroin (SF) and positively charged gelatin (Gel) hydrogel matrix to enhance RNA stability for controlled release. As a proof of concept, whole-cell RNA was incorporated into the hydrogel to enhance interactions with RNA molecules. Additionally, molecular modeling studies were conducted to explore the interactions between SF, collagen, chitosan (Chi), and the various RNA species including ribosomal RNAs (28S, 18S, 8.5S, and 5S rRNAs), transfer RNAs (tRNA-ALA, tRNA-GLN, and tRNA-Leu), as well as messenger RNAs (mRNA-GAPDH, mRNA-β actin, and mRNA-Nanog), shedding light on the RNA-polymer interaction and RNA stability; SF exhibits a more robust interaction with RNA compared to collagen/gel and chitosan. We confirmed the molecular interactions of SF and RNA by FTIR and Raman spectroscopy, which were further supported by AFM and contact angle measurement. This research introduces a novel RNA delivery platform and insights into biopolymer-RNA interactions, paving the way for tailored RNA delivery systems in therapeutics and biomedical applications.

Could an Anterior Cruciate Ligament Be Tissue-Engineered from Silk?

Silk has a long history as an exclusive textile, but also as a suture thread in medicine; nowadays, diverse cell carriers are manufactured from silk. Its advantages are manifold, including high biocompatibility, biomechanical strength and processability (approved for nearly all manufacturing techniques). Silk's limitations, such as scarcity and batch to batch variations, are overcome by gene technology, which allows for the upscaled production of recombinant "designed" silk proteins. For processing thin fibroin filaments, the sericin component is generally removed (degumming). In contrast to many synthetic biomaterials, fibroin allows for superior cell adherence and growth. In addition, silk grafts demonstrate superior mechanical performance and long-term stability, making them attractive for anterior cruciate ligament (ACL) tissue engineering. Looking at these promising properties, this review focusses on the responses of cell types to silk variants, as well as their biomechanical properties, which are relevant for ACL tissue engineering. Meanwhile, sericin has also attracted increasing interest and has been proposed as a bioactive biomaterial with antimicrobial properties. But so far, fibroin was exclusively used for experimental ACL tissue engineering approaches, and fibroin from spider silk also seems not to have been applied. To improve the bone integration of ACL grafts, silk scaffolds with osteogenic functionalization, silk-based tunnel fillers and interference screws have been developed. Nevertheless, signaling pathways stimulated by silk components remain barely elucidated, but need to be considered during the development of optimized silk cell carriers for ACL tissue engineering.

Recent Advance of Strontium Functionalized in Biomaterials for Bone Regeneration

Bone defect disease causes damage to people’s lives and property, and how to effectively promote bone regeneration is still a big clinical challenge. Most of the current repair methods focus on filling the defects, which has a poor effect on bone regeneration. Therefore, how to effectively promote bone regeneration while repairing the defects at the same time has become a challenge for clinicians and researchers. Strontium (Sr) is a trace element required by the human body, which mainly exists in human bones. Due to its unique dual properties of promoting the proliferation and differentiation of osteoblasts and inhibiting osteoclast activity, it has attracted extensive research on bone defect repair in recent years. With the deep development of research, the mechanisms of Sr in the process of bone regeneration in the human body have been clarified, and the effects of Sr on osteoblasts, osteoclasts, mesenchymal stem cells (MSCs), and the inflammatory microenvironment in the process of bone regeneration have been widely recognized. Based on the development of technology such as bioengineering, it is possible that Sr can be better loaded onto biomaterials. Even though the clinical application of Sr is currently limited and relevant clinical research still needs to be developed, Sr-composited bone tissue engineering biomaterials have achieved satisfactory results in vitro and in vivo studies. The Sr compound together with biomaterials to promote bone regeneration will be a development direction in the future. This review will present a brief overview of the relevant mechanisms of Sr in the process of bone regeneration and the related latest studies of Sr combined with biomaterials. The aim of this paper is to highlight the potential prospects of Sr functionalized in biomaterials.

Biomimetic AgNPs@antimicrobial peptide/silk fibroin coating for infection-trigger antibacterial capability and enhanced osseointegration

Endowing implant surfaces with combined antibacterial and osteogenic properties by drug-loaded coatings has made great strides, but how to achieve the combined excellence of infection-triggered bactericidal and in vivo-proven osteogenic activities without causing bacterial resistance still remains a formidable challenge. Herein, antimicrobial peptides (AMPs) with osteogenic fragments were designed and complexed on the surface of silver nanoparticle (AgNP) through hydrogen bonding, and the collagen structure-bionic silk fibroin (SF) was applied to carry AgNPs@ AMPs to achieve infection-triggered antibacterial and osteointegration. As verified by TEM, AMPs contributed to the dispersion and size-regulation of AgNPs, with a particle size of about 20 nm, and a clear protein corona structure was observed on the particle surface. The release curve of silver ion displayed that the SF-based coating owned sensitive pH-responsive properties. In the antibacterial test against S.aureus for up to 21 days, the antibacterial rate had always remained above 99%. Meanwhile, the underlying mechanism was revealed, originating from the destruction of the bacterial cell membranes and ROS generation. The SF-based coating was conducive to the adhesion, diffusion, and proliferation of bone marrow stem cells (BMSCs) on the surface, and promoted the expression of osteogenic genes and collagen secretion. The in vivo implantation results showed that compared with the untreated Ti implants, SF-based coating enhanced osseointegration at week 4 and 8. Overall, the AgNPs@AMPs-loaded SF-based coating presented the ability to synergistically inhibit bacteria and promote osseointegration, possessing tremendous potential application prospects in bone defects and related-infection treatments.

•

AMPs and AgNPs were complexed through hydrogen bonds to form a protein crowns structure.

•

Silk fibroin matrix was able to maintain the activity of AMPs over 21 d and endow with the infection-trigger release.

•

The functional coating achieved synergistic antibacterial properties by damaging membrane structure and generating ROS.

•

The coating displayed acceptable osteogenic properties in vitro and observably promoted osteointegration in vivo.

3D printed tissue models: From hydrogels to biomedical applications

The development of new advanced constructs resembling structural and functional properties of human organs and tissues requires a deep knowledge of the morphological and biochemical properties of the extracellular matrices (ECM), and the capacity to reproduce them. Manufacturing technologies like 3D printing and bioprinting represent valuable tools for this purpose. This review will describe how morphological and biochemical properties of ECM change in different tissues, organs, healthy and pathological states, and how ECM mimics with the required properties can be generated by 3D printing and bioprinting. The review describes and classifies the polymeric materials of natural and synthetic origin exploited to generate the hydrogels acting as "inks" in the 3D printing process, with particular emphasis on their functionalization allowing crosslinking and conjugation with signaling molecules to develop bio-responsive and bio-instructive ECM mimics.

Three-Dimensional Impression of Biomaterials for Alveolar Graft: Scoping Review

Craniofacial bone defects are one of the biggest clinical challenges in regenerative medicine, with secondary autologous bone grafting being the gold-standard technique. The development of new three-dimensional matrices intends to overcome the disadvantages of the gold-standard method. The aim of this paper is to put forth an in-depth review regarding the clinical efficiency of available 3D printed biomaterials for the correction of alveolar bone defects. A survey was carried out using the following databases: PubMed via Medline, Cochrane Library, Scopus, Web of Science, EMBASE, and gray literature. The inclusion criteria applied were the following: in vitro, in vivo, ex vivo, and clinical studies; and studies that assessed bone regeneration resorting to 3D printed biomaterials. The risk of bias of the in vitro and in vivo studies was performed using the guidelines for the reporting of pre-clinical studies on dental materials by Faggion Jr and the SYRCLE risk of bias tool, respectively. In total, 92 publications were included in the final sample. The most reported three-dimensional biomaterials were the PCL matrix, β-TCP matrix, and hydroxyapatite matrix. These biomaterials can be combined with different polymers and bioactive molecules such as rBMP-2. Most of the included studies had a high risk of bias. Despite the advances in the research on new three-dimensionally printed biomaterials in bone regeneration, the existing results are not sufficient to justify the application of these biomaterials in routine clinical practice.

Recent advances in bioprinting using silk protein-based bioinks

3D printing has experienced swift growth for biological applications in the field of regenerative medicine and tissue engineering. Essential features of bioprinting include determining the appropriate bioink, printing speed mechanics, and print resolution while also maintaining cytocompatibility. However, the scarcity of bioinks that provide printing and print properties and cell support remains a limitation. Silk Fibroin (SF) displays exceptional features and versatility for inks and shows the potential to print complex structures with tunable mechanical properties, degradation rates, and cytocompatibility. Here we summarize recent advances and needs with the use of SF protein from Bombyx mori silkworm as a bioink, including crosslinking methods for extrusion bioprinting using SF and the maintenance of cell viability during and post bioprinting. Additionally, we discuss how encapsulated cells within these SF-based 3D bioprinted constructs are differentiated into various lineages such as skin, cartilage, and bone to expedite tissue regeneration. We then shift the focus towards SF-based 3D printing applications, including magnetically decorated hydrogels, in situ bioprinting, and a next-generation 4D bioprinting approach. Future perspectives on improvements in printing strategies and the use of multicomponent bioinks to improve print fidelity are also discussed.

3D Printed Hydroxyapatite Promotes Congruent Bone Ingrowth in Rat Load Bearing Defects

3D porous hydroxyapatite scaffolds produced by conventional foaming processes have limited control over the scaffold's pore size, geometry, and pore interconnectivity. In addition, random internal pore architecture often results in limited clinical success. Imitating the intricate 3D architecture and the functional dynamics of skeletal deformations is a difficult task, highlighting the necessity for a custom-made, on-demand tissue replacement, for which 3D printing is a potential solution. To combat these problems, here we report the ability of 3D printed hydroxyapatite scaffolds for in vivo bone regeneration in a rat tibial defect model. Rapid prototyping using the direct-write technique to fabricate 25 mm2 hydroxyapatite scaffolds were employed for precise control over geometry (both external and internal) and scaffold chemistry. Bone ingrowth was determined using histomorphometry and a novel micro-CT image analysis. Substantial bone ingrowth was observed in implants that filled the defect site. Further validating this quantitatively by micro-CT, the Bone mineral density of the implant at the defect site was 1024 mgHA/ccm, which was approximately 61.5% more than the bone mineral density found with the sham control at the defect site. In addition, no evident immunoinflammatory response was observed in the H&E micrographs. Interestingly, the present study showed a positive correlation with the outcomes obtained in our previous in vitro study. Overall, the results suggest that 3D printed hydroxyapatite scaffolds developed in this study offer a suitable matrix for rendering patient-specific and defect-specific bone formation and warrant further testing for clinical application.

Strontium Functionalization of Biomaterials for Bone Tissue Engineering Purposes: A Biological Point of View

Strontium (Sr) is a trace element taken with nutrition and found in bone in close connection to native hydroxyapatite. Sr is involved in a dual mechanism of coupling the stimulation of bone formation with the inhibition of bone resorption, as reported in the literature. Interest in studying Sr has increased in the last decades due to the development of strontium ranelate (SrRan), an orally active agent acting as an anti-osteoporosis drug. However, the use of SrRan was subjected to some limitations starting from 2014 due to its negative side effects on the cardiac safety of patients. In this scenario, an interesting perspective for the administration of Sr is the introduction of Sr ions in biomaterials for bone tissue engineering (BTE) applications. This strategy has attracted attention thanks to its positive effects on bone formation, alongside the reduction of osteoclast activity, proven by in vitro and in vivo studies. The purpose of this review is to go through the classes of biomaterials most commonly used in BTE and functionalized with Sr, i.e., calcium phosphate ceramics, bioactive glasses, metal-based materials, and polymers. The works discussed in this review were selected as representative for each type of the above-mentioned categories, and the biological evaluation in vitro and/or in vivo was the main criterion for selection. The encouraging results collected from the in vitro and in vivo biological evaluations are outlined to highlight the potential applications of materials’ functionalization with Sr as an osteopromoting dopant in BTE.

Cutaneous Regeneration Mechanism of β-Sheet Silk Fibroin in a Rat Burn Wound Healing Model

Therapeutic dressings to enhance burn wound repair and regeneration are required. Silk fibroin (SF), a natural protein, induces cell migration and serves as a biomaterial in various dressings. SF dressings usually contain α-helices and β-sheets. The former has been confirmed to improve cell proliferation and migration, but the wound healing effect and related mechanisms of β-sheet SF remain unclear. We investigated the effects of β-sheet SF in vivo and in vitro. Alcohol-treated α-helix SF transformed into the β-sheet form, which promoted granulation formation and re-epithelialization when applied as lyophilized SF dressing (LSFD) in a rat burn model. Our in vitro results showed that β-sheet SF increased human dermal fibroblast (HDF) migration and promoted the expression of extracellular matrix (ECM) proteins (fibronectin and type III collagen), matrix metalloproteinase-12, and the cell adhesion molecule, integrin β1, in rat granulation tissue and HDFs. This confirms the role of crosstalk between integrin β1 and ECM proteins in cell migration. In summary, we demonstrated that β-sheet SF facilitates tissue regeneration by modulating cell adhesion molecules in dermal fibroblasts. LSFD could find clinical application for burn wound regeneration. Moreover, β-sheet SF could be combined with anti-inflammatory materials, growth factors, or antibiotics to develop novel dressings.

Open Curettage With Bone Augmentation for Symptomatic Tumors and Tumor-like Lesions of Calcaneus: A Comparison of Bioactive Glass Versus Allogeneic Bone

Few studies have characterized the clinical outcomes of 45S5 Bioglass® applied as a bone graft to that of allogeneic bone applied in calcaneal open curettage. Therefore, the purpose of the present investigation was to compare the outcomes of patients with calcaneal tumors and tumor-like lesions treated by open curettage with 45S5 Bioglass® or allogeneic bone. Of the 31 patients who underwent open curettage (18 cases of unicameral bone cysts, 7 cases of aneurysmal bone cysts, and 6 cases of intraosseous lipoma), 16 (52%) received grafts with 45S5 Bioglass® and 15 (48%) with allogeneic bone. All the feet achieved bone fusion according to the modified Neer radiographic classification system at the last follow-up examination. The mean bone ingrowth time for the grafts with 45S5 Bioglass® versus allogeneic bone was 3.71 ± 0.86 versus 4.46 ± 1.04 months (p = .038), the mean bone healing time was 4.86 ± 0.93 versus 5.73 ± 1.07 months (p = .021), and the mean incision drying time was 7.2 ± 1.8 versus 8.2 ± 1.5 days (p = .047), respectively. No differences were found in the postoperative American Orthopaedic Foot and Ankle Society ankle-hindfoot scale scores between the 2 groups (p = .213). These results show that 45S5 Bioglass® can better facilitate the formation of new bone with a faster drying time of the incision than allogeneic bone. Although both materials can benefit the clinical outcomes of calcaneal tumors and tumor-like lesions, further studies are needed to observe the long-term complications and lesion recurrence rates.

Injectable chitosan/collagen hydrogels nano-engineered with functionalized single wall carbon nanotubes for minimally invasive applications in bone

Mechanical robustness is an essential consideration in the development of hydrogel platforms for bone regeneration, and despite significant advances in the field of injectable hydrogels, many fail in this regard. Inspired by the mechanical properties of carboxylated single wall carbon nanotubes (COOH-SWCNTs) and the biological advantages of natural polymers, COOH-SWCNTs were integrated into chitosan and collagen to formulate mechanically robust, injectable and thermoresponsive hydrogels with interconnected molecular structure for load-bearing applications. This study presents a complete characterisation of the structural and biological properties, and mechanism of gelation of these novel formulated hydrogels. Results demonstrate that β-glycerophosphate (β-GP) and temperature play important roles in attaining gelation at physiological conditions, and the integration with COOH-SWCNTs significantly changed the structural morphology of the hydrogels to a more porous and aligned network. This led to a crystalline structure and significantly increased the mechanical strength of the hydrogels from kPa to MPa, which is closer to the mechanical strength of the bone. Moreover, increased osteoblast proliferation and rapid adsorption of hydroxyapatite on the surface of the hydrogels indicates increased bioactivity with addition of COOH-SWCNTs. Therefore, these nano-engineered hydrogels are expected to have wide utility in the area of bone tissue engineering and regenerative medicine.

Upgrading Hepatic Differentiation and Functions on 3D Printed Silk-Decellularized Liver Hybrid Scaffolds

We developed hybrid liver-specific three-dimensional (3D) printed scaffolds using a solubilized native decellularized liver (DCL) matrix and silk fibroin (SF) and investigated their ability to support functional cultures of hepatic cells. Rat livers were decellularized by perfusing detergents via the portal vein, solubilized using pepsin to form DCL, and characterized. SF blended with gelatin (8% w/v) was optimized with varying percentages of DCL to obtain silk gelatin-DCL bioink (SG-DCL). Different compositions of SG-DCL were studied by rheology for optimum versatility and print fidelity. 3D printed six-layered scaffolds were fabricated using a sophisticated direct-write 3D bioprinter. Huh7 cells were cultured on the 3D printed scaffolds for 3 weeks. 3D printed SG scaffolds without DCL along with 2D films (SG and SG-DCL) and 2D culture on tissue culture Petri dish control were used for comparative studies. The DCL matrix showed the absence of cells in histology and SEM. The combined SG-DCL ink at all of the studied DCL percentages (1-10%) revealed shear-thinning behavior in the printable range. The storage modulus value for the SG-DCL ink at all DCL percentages was higher than the loss modulus. In comparison to 2D controls, hepatic cells cultured on 3D SG-DCL revealed increased proliferation until 2 weeks and an upregulated expression of hepatocyte markers, including asialoglycoprotein receptor 1 (ASGR1). The Wnt pathway gene β-catenin was upregulated by more than 4-fold in 3D SG-DCL on day 3, while it showed a decline on day 7 as compared to 3D SG and also 2D controls. The expression of the epithelial cell adhesion molecule (EpCAM) was however lower in both 2D SG-DCL (2-fold) and 3D SG-DCL (2.5-fold) as compared to that in 2D controls. Immunofluorescence studies validated the protein expression of ASGR1 in 3D SG-DCL. Albumin (ALB) was not identified on SG scaffolds but prominently expressed in 3D SG-DCL constructs. In comparison to 2D SG, both ALB (1.8-fold) and urea (5-fold) were enhanced in cells cultured on 3D SG-DCL on day 7 of culture. Hence, the SG-DCL 3D printed scaffolds provide a conducive microenvironment for elevating differentiation and functions of hepatic cells possibly through an involvement of the Wnt/β-catenin signaling pathway.

Nanomaterials for bioprinting: functionalization of tissue-specific bioinks

Three-dimensional (3D) bioprinting is rapidly evolving, offering great potential for manufacturing functional tissue analogs for use in diverse biomedical applications, including regenerative medicine, drug delivery, and disease modeling. Biomaterials used as bioinks in printing processes must meet strict physiochemical and biomechanical requirements to ensure adequate printing fidelity, while closely mimicking the characteristics of the native tissue. To achieve this goal, nanomaterials are increasingly being investigated as a robust tool to functionalize bioink materials. In this review, we discuss the growing role of different nano-biomaterials in engineering functional bioinks for a variety of tissue engineering applications. The development and commercialization of these nanomaterial solutions for 3D bioprinting would be a significant step towards clinical translation of biofabrication.

Angiogenic property of silk fibroin scaffolds with adipose-derived stem cells on chick chorioallantoic membrane

Angiogenesis is a crucial step in tissue regeneration and repair. Biomaterials that allow or promote angiogenesis are thus beneficial. In this study, angiogenic properties of salt-leached silk fibroin (SF) scaffolds seeded with human adipose stem cells (hADSCs) were studied using chick chorioallantoic membrane (CAM) as a model. The hADSC-seeded SF scaffolds (SF-hADSC) with the porosity of 77.34 ± 6.96% and the pore diameter of 513.95 ± 4.99 µm were implanted on the CAM of chick embryos that were on an embryonic day 8 (E8) of development. The SF-hADSC scaffolds induced a spoke-wheel pattern of capillary network indicative of angiogenesis, which was evident since E11. Moreover, the ingrowth of blood vessels into the scaffolds was seen in histological sections. The unseeded scaffolds induced the same extent of angiogenesis later on E14. By contrast, the control group could not induce the same extent of angiogenesis. In vitro cytotoxicity tests and in vivo angioirritative study reaffirmed the biocompatibility of the scaffolds. This work highlighted that the biocompatible SF-hADSC scaffolds accelerate angiogenesis, and hence they can be a promising biomaterial for the regeneration of tissues that require angiogenesis.

How to Improve Physico-Chemical Properties of Silk Fibroin Materials for Biomedical Applications?-Blending and Cross-Linking of Silk Fibroin-A Review

This review supplies a report on fresh advances in the field of silk fibroin (SF) biopolymer and its blends with biopolymers as new biomaterials. The review also includes a subsection about silk fibroin mixtures with synthetic polymers. Silk fibroin is commonly used to receive biomaterials. However, the materials based on pure polymer present low mechanical parameters, and high enzymatic degradation rate. These properties can be problematic for tissue engineering applications. An increased interest in two- and three-component mixtures and chemically cross-linked materials has been observed due to their improved physico-chemical properties. These materials can be attractive and desirable for both academic, and, industrial attention because they expose improvements in properties required in the biomedical field. The structure, forms, methods of preparation, and some physico-chemical properties of silk fibroin are discussed in this review. Detailed examples are also given from scientific reports and practical experiments. The most common biopolymers: collagen (Coll), chitosan (CTS), alginate (AL), and hyaluronic acid (HA) are discussed as components of silk fibroin-based mixtures. Examples of binary and ternary mixtures, composites with the addition of magnetic particles, hydroxyapatite or titanium dioxide are also included and given. Additionally, the advantages and disadvantages of chemical, physical, and enzymatic cross-linking were demonstrated.

Silk-Based Materials for Hard Tissue Engineering

Hard tissues, e.g., bone, are mechanically stiff and, most typically, mineralized. To design scaffolds for hard tissue regeneration, mechanical, physico-chemical and biological cues must align with those found in the natural tissue. Combining these aspects poses challenges for material and construct design. Silk-based materials are promising for bone tissue regeneration as they fulfill several of such necessary requirements, and they are non-toxic and biodegradable. They can be processed into a variety of morphologies such as hydrogels, particles and fibers and can be mineralized. Therefore, silk-based materials are versatile candidates for biomedical applications in the field of hard tissue engineering. This review summarizes silk-based approaches for mineralized tissue replacements, and how to find the balance between sufficient material stiffness upon mineralization and cell survival upon attachment as well as nutrient supply.

[Possible applications of free microsurgical fibula transplantation in the reconstruction of complex bone defects in the extremities: review of the literature and case series]

BACKGROUND

 Extensive osseous defects of the extremities following trauma and tumour resection represent a major challenge for plasticreconstructive surgical teams. Defect reconstruction by free microsurgical fibula transplantation has become a standard method but is associated with a considerable rate of complications. The aim of the present work is to provide an up-to-date overview of the various reconstruction methods and to report our personal experiences with free fibula transplantation in a case series.

PATIENTS AND METHODS

 The literature search on the subject was performed on Pubmed and Web of Science, and a retrospective collection of data was conducted based on our own cases, including clinical and radiological data.

RESULTS

 From 2007 to 2018, free fibula transplantation was performed in 11 patients under the guidance of the senior author (MS). The defects were a result of pseudarthrosis in four cases, osteitis in three, and a tumour in two cases. Two patientssustained a primary defect due to a high-energy trauma. In nine cases the upper limb was affected; only two had the defect in the lower limb. No graft failure was observed. In eight cases, an osteoseptocutaneous graft was taken; in two cases there was a post-operative loss of the skin island. Fibula length ranged between 5 and 22 cm. In all cases, bony integration of the graft was complete. The range of motion in the affected limb after physiotherapy was very good to satisfactory.

CONCLUSION

 Extensive bone defect reconstruction using free fibula flaps is undoubtedly the gold standard method, but the high rate of complications described in the literature necessitates a strict indication in due consideration of possible alternatives. Close cooperation between the disciplines of plastic reconstructive surgery and trauma orthopaedics is indispensable.

Silk Polymers and Nanoparticles: A Powerful Combination for the Design of Versatile Biomaterials

Silk fibroin (SF) is a natural protein largely used in the textile industry but also in biomedicine, catalysis, and other materials applications. SF is biocompatible, biodegradable, and possesses high tensile strength. Moreover, it is a versatile compound that can be formed into different materials at the macro, micro- and nano-scales, such as nanofibers, nanoparticles, hydrogels, microspheres, and other formats. Silk can be further integrated into emerging and promising additive manufacturing techniques like bioprinting, stereolithography or digital light processing 3D printing. As such, the development of methodologies for the functionalization of silk materials provide added value. Inorganic nanoparticles (INPs) have interesting and unexpected properties differing from bulk materials. These properties include better catalysis efficiency (better surface/volume ratio and consequently decreased quantify of catalyst), antibacterial activity, fluorescence properties, and UV-radiation protection or superparamagnetic behavior depending on the metal used. Given the promising results and performance of INPs, their use in many different procedures has been growing. Therefore, combining the useful properties of silk fibroin materials with those from INPs is increasingly relevant in many applications. Two main methodologies have been used in the literature to form silk-based bionanocomposites: in situ synthesis of INPs in silk materials, or the addition of preformed INPs to silk materials. This work presents an overview of current silk nanocomposites developed by these two main methodologies. An evaluation of overall INP characteristics and their distribution within the material is presented for each approach. Finally, an outlook is provided about the potential applications of these resultant nanocomposite materials.

From Silk Spinning to 3D Printing: Polymer Manufacturing using Directed Hierarchical Molecular Assembly

Silk spinning offers an evolution-based manufacturing strategy for industrial polymer manufacturing, yet remains largely inaccessible as the manufacturing mechanisms in biological and synthetic systems, especially at the molecular level, are fundamentally different. The appealing characteristics of silk spinning include the sustainable sourcing of the protein material, the all-aqueous processing into fibers, and the unique material properties of silks in various formats. Substantial progress has been made to mimic silk spinning in artificial manufacturing processes, despite the gap between natural and artificial systems. This report emphasizes the universal spinning conditions utilized by both spiders and silkworms to generate silk fibers in nature, as a scientific and technical framework for directing molecular assembly into high-performance structures. The preparation of regenerated silk feedstocks and mimicking native spinning conditions in artificial manufacturing are discussed, as is progress and challenges in fiber spinning and 3D printing of silk-composites. Silk spinning is a biomimetic model for advanced and sustainable artificial polymer manufacturing, offering benefits in biomedical applications for tissue scaffolds and implantable devices.

Delivery of Salvianolic Acid B for Efficient Osteogenesis and Angiogenesis from Silk Fibroin Combined with Graphene Oxide

The efficiency of drugs often hinges on drug carriers. To effectively transport therapeutic plant molecules, drug delivery carriers should be able to carry large doses of therapeutic drugs, enable their sustained release, and maintain their biological activity. Here, graphene oxide (GO) is demonstrated to be a valid carrier for delivering therapeutic plant molecules. Salvianolic acid B (SB), which contains a large number of hydroxyl groups, bound to the carboxyl groups of GO by self-assembly. Silk fibroin (SF) substrates were combined with functionalized GO through the freeze-drying method. SF/GO scaffolds could be loaded with large doses of SB, maintain the biological activity of SB while continuously releasing SB, and significantly promote the osteogenic differentiation of rat bone marrow mesenchymal stem cells (rBMSCs). SF/GO/SB also dramatically enhanced endothelial cell (EA-hy9.26) migration and tubulogenesis in vitro. Eight weeks after implantation of SF/GO/SB scaffolds in a rat cranial defect model, the defect area showed more new bone and angiogenesis than that following SF and SF/GO scaffold implantation. Therefore, GO is an effective sustained-release carrier for therapeutic plant molecules, such as SB, which can repair bone defects by promoting osteogenic differentiation and angiogenesis.

Bioinspired 3D porous human placental derived extracellular matrix/silk fibroin sponges for accelerated bone regeneration

Critical bone defects arising from traumatic injury and diseases are of major health concern since they are unable to heal spontaneously without clinical intervention. In this context, bone tissue engineering provides an attractive approach to treat bone defects by providing a bioactive template which has the potential to guide osseous tissue regeneration. In this study, porous hybrid placental extracellular matrix sponge (PIMS) was fabricated by a combinatorial method using silk fibroin (SF)/placental derived extracellular matrix and subsequently evaluated its efficacy towards bone tissue regeneration. The presence of intrinsic growth factors was evidenced by immunoblotting of the extracted proteins derived from the placental derived extracellular matrix. This growth factor rich PIMS lends a unique bioactive scaffolding to human amniotic mesenchymal stem cells (HAMSCs) which supported enhanced proliferation as well as superior osteogenic differentiation. Gene expression studies demonstrated significant up-regulation of osteogenic related genes in the PIMS group. PIMS when implanted in the chick chorioallantoic membrane, significantly attracted allantoic vessels revealing its potential to stimulate angiogenesis ex vivo. Furthermore, no severe immune response to the host was observed on subcutaneous implantation of PIMS in vivo. Instead, it supported the formation of blood vessels, revealing its outstanding biocompatibility. Additionally, critical tibial defects treated with PIMS demonstrated higher bone volume after six weeks when analyzed by micro-CT, which was accompanied by high mineral density. Histological and immunofluorescence studies validated the results and revealed enhanced osseous tissue regeneration after six weeks of surgery. All these findings recapitulated that the growth factors incorporated bioactive PIMS could perform as an appropriate matrix for osteogenic differentiation and efficient bone regeneration.

In Vitro Evaluation of a Novel Osteo-Inductive Scaffold for Osteogenic Differentiation of Bone-Marrow Mesenchymal Stem Cells

BACKGROUND

Demineralized bone matrices (DBMs) were demonstrated to be a promising candidate for bone regeneration by previous studies. However, the limited osteoinductivity of DBMs was insufficient for a better repairing of bone defect. Osteoblasts (OBs), the major cellular component of bone tissues, play an important role in the formation of new bone. The extracellular matrix (ECM) of OB is one of the main components of bone formation niche.

OBJECTIVE

To combine the DBMs with the ECM of OBs to construct a novel scaffold that could be used for bone reconstruction.

METHODS

In this study, OBs were cultured on the surface of DBMs for 10 days and removed by Triton X-100 and ammonium hydroxide to prepare the OBs-ECM-DBMs (OEDBMs). A series of material features such as residues of OBs and ECM, cytotoxity, and osteoinductive capability of OEDBMs were evaluated.

RESULTS

Low cell residues and low content of DNA were observed in OEDBMs. Compared with DBMs, OEDBMs possessed more bone tissues organic matrix proteins, such as osteocalcin, osteopontin, and collagen I. Rat bone marrow mesenchymal stem cells (rBMSCs) presented a good viability when cultured on both 2 materials. The significant upregulations of osteogenic genes and proteins of rBMSCs were observed in OEDBMs group compared with DBMs group.

CONCLUSION

Taken together, these findings suggested that the OB-secreted ECM may be qualified as an ideal modification method for enhancing the performance of engineered bone scaffold.

In vitro evaluation of novel low-pressure spark plasma sintered HA–BG composite scaffolds for bone tissue engineering

The low-pressure spark plasma sintering (SPS) technique is adopted to fabricate hydroxyapatite–bioglass (HA–BG) scaffolds while maintaining the physical properties of both components, including their bulk and relative density and hardness. However, prior to their orthopaedic and dental applications, these scaffolds must be validated via pre-clinical assessments. In the present study, scaffolds with different ratios of HA : BG, namely, 100 : 0 (HB 0 S), 90 : 10 (HB 10 S), 80 : 20 (HB 20 S) and 70 : 30 (HB 30 S) were fabricated. These scaffolds were characterized by investigating their physicochemical properties (X-ray diffraction (XRD) and surface wettability), bioactivity in a simulated body fluid (SBF) (field emission scanning electron microscopy (FESEM), Fourier-transform infrared spectroscopy (FTIR) and calcium dissolution), antimicrobial properties, biocompatibility and osteoinduction of human bone marrow-derived mesenchymal stromal cells (hBMSCs) and human monocyte immune cell response. The XRD and surface wettability results confirmed no formation of undesirable phases and the enhanced surface hydrophilicity of the scaffolds, respectively. The bioactivity in SBF indicated the formation of bone-like apatite on the surface of the scaffolds, corresponding to an increase in BG%, which was confirmed through FTIR spectra and the increasing trend of calcium release in SBF. The scaffolds showed inhibition properties against Staphylococcus aureus and Staphylococcus epidermidis. The scanning electron microscopy (SEM) micrographs and Alamar Blue proliferation assay indicated the good attachment and significant proliferation, respectively, of hBMSCs on the scaffolds. Alizarin Red S staining confirmed that the scaffolds supported the mineralisation of hBMSCs. The osteogenic protein secretion (bone morphogenetic protein-2 (BMP2), type-I collagen (COL1) and osterix (OSX)) was significant on the HB 30 S-seeded hBMSCs when compared with that of HB 0 S. The monocyte migration was significantly halted in response to HA–BG-conditioned media when compared with the positive control (monocyte chemoattractant protein-1: MCP-1). In conclusion, the HB 30 S composite scaffold has a greater potential to substitute bone grafts in orthopaedic and dental applications.

HB 30 S composite scaffold inhibits Staphylococcus spp., supports the biocompatibility and osteogenic differentiation of hBMSCs and resists monocyte migration.

The assembly of silk fibroin and graphene-based nanomaterials with enhanced mechanical/conductive properties and their biomedical applications

The assembly of silk fibroin and graphene-based nanomaterials would present fantastic properties and functions via optimizing the interaction between each other, and can be processed into various formats to tailor specific biomedical applications.

Bioinks and bioprinting technologies to make heterogeneous and biomimetic tissue constructs

The native tissues are complex structures consisting of different cell types, extracellular matrix materials, and biomolecules. Traditional tissue engineering strategies have not been able to fully reproduce biomimetic and heterogeneous tissue constructs because of the lack of appropriate biomaterials and technologies. However, recently developed three-dimensional bioprinting techniques can be leveraged to produce biomimetic and complex tissue structures. To achieve this, multicomponent bioinks composed of multiple biomaterials (natural, synthetic, or hybrid natural-synthetic biomaterials), different types of cells, and soluble factors have been developed. In addition, advanced bioprinting technologies have enabled us to print multimaterial bioinks with spatial and microscale resolution in a rapid and continuous manner, aiming to reproduce the complex architecture of the native tissues. This review highlights important advances in heterogeneous bioinks and bioprinting technologies to fabricate biomimetic tissue constructs. Opportunities and challenges to further accelerate this research area are also described.

Cell laden alginate-keratin based composite microcapsules containing bioactive glass for tissue engineering applications

Microcapsules based on alginate-keratin, alginate dialdehyde (ADA)-keratin and ADA-keratin-45S5 bioactive glass (BG) were successfully prepared. The samples were characterized by light microscopy, scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). The results showed that ADA-based materials possess higher degradation rate compared to alginate-based materials. The incorporation of BG particles (mean particle size: 2.0 µm) improved the bioactivity of the materials. Moreover, the biological properties of the samples were evaluated by encapsulating MG-63 osteosarcoma cells into the microcapsules. The cell viability in all samples increased during 21 days of cultivation. However, the presence of 0.5% BG particle seemed to have initial negative effect on cell growth compared to other samples without BG. On the other hand, the positive effect of CaP formation was visible after 3 weeks in the BG containing samples. The results are relevant to consider the development of cell laden bioinks incorporating inorganic bioactive particles for biofabrication approaches.