Three-Dimensional Scaffolds of Carbonized Polyacrylonitrile for Bone Tissue Regeneration

Carbon fiber: Characterization and evaluation of the inflammatory response and toxicity in rats

This study aimed to evaluate the Carbon Fiber obtained from PAN textile and cotton fiber in their different forms of presentation: non-activated carbon fiber felt (NACFF), activated carbon fiber felt (ACFF), silver activated carbon fiber felt (Ag-ACFF), and activated carbon fiber tissue (ACFT), to obtain scaffolds as a potential material with properties related to the synthetic bone graft. Characterization tests performed: surface wettability, traction, swelling, and in vivo tests: evaluation of the inflammatory response by implanting the materials in the subcutaneous tissue of 14 Wistar rats, evaluation of collagen fibers by picrosirius red staining and assessment of toxicity in the following organs: heart, spleen, liver, and kidney. In the wettability test, NACFF and ACFT were hydrophobic (θ124° and 114°), ACFF and Ag-ACFF were hydrophilic. For maximum stress, ACFF was more resistant (2.983 ± 1.059) p < .05. In the swelling test, the Ag-ACFF and ACFF groups showed the highest absorption percentage for the PBS solution and distilled water (p < .001). The organs showed no signs of acute systemic toxicity. The implant regions showed mild to moderate inflammatory infiltrate at 7 and 21 days. Only the ACFT group did not show the maturation of type I collagen fibers in 21 days. Through the conducted analyses, the ACFT shows little potential to be indicated as a possible scaffold. Therefore NACFF, ACFF, and Ag-ACFF have the potential to be considered scaffolds due to the following characteristics presented: good absorption rate, hydrophilicity, and non-toxic.

Electroactive Hydroxyapatite/Carbon Nanofiber Scaffolds for Osteogenic Differentiation of Human Adipose-Derived Stem Cells

Traditional bone defect treatments are limited by an insufficient supply of autologous bone, the immune rejection of allogeneic bone grafts, and high medical costs. To address this medical need, bone tissue engineering has emerged as a promising option. Among the existing tissue engineering materials, the use of electroactive scaffolds has become a common strategy in bone repair. However, single-function electroactive scaffolds are not sufficient for scientific research or clinical application. On the other hand, multifunctional electroactive scaffolds are often complicated and expensive to prepare. Therefore, we propose a new tissue engineering strategy that optimizes the electrical properties and biocompatibility of carbon-based materials. Here, a hydroxyapatite/carbon nanofiber (HAp/CNF) scaffold with optimal electrical activity was prepared by electrospinning HAp nanoparticle-incorporated polyvinylidene fluoride (PVDF) and then carbonizing the fibers. Biochemical assessments of the markers of osteogenesis in human adipose-derived stem cells (h-ADSCs) cultured on HAp/CNF scaffolds demonstrate that the material promoted the osteogenic differentiation of h-ADSCs in the absence of an osteogenic factor. The results of this study show that electroactive carbon materials with a fibrous structure can promote the osteogenic differentiation of h-ADSCs, providing a new strategy for the preparation and application of carbon-based materials in bone tissue engineering.

Fabrication strategies and biomedical applications of three-dimensional bacterial cellulose-based scaffolds: A review

Bacterial cellulose (BC), an extracellular polysaccharide, is a versatile biopolymer due to its intrinsic physicochemical properties, broad-spectrum applications, and remarkable achievements in different fields, especially in the biomedical field. Presently, the focus of BC-related research is on the development of scaffolds containing other materials for in-vitro and in-vivo biomedical applications. To this end, prime research objectives concern the biocompatibility of BC and the development of three-dimensional (3D) BC-based scaffolds. This review summarizes the techniques used to develop 3D BC scaffolds and discusses their potential merits and limitations. In addition, we discuss the various biomedical applications of BC-based scaffolds for which the 3D BC matrix confers desired structural and conformational features. Overall, this review provides comprehensive coverage of the idea, requirements, synthetic strategies, and current and prospective applications of 3D BC scaffolds, and thus, should be useful for researchers working with polysaccharides, biopolymers, or composite materials.

Fabrication of Highly Oriented Cylindrical Polyacrylonitrile, Poly(lactide-co-glycolide), Polycaprolactone and Poly(vinyl acetate) Nanofibers for Vascular Graft Applications

Small-diameter vascular grafts fabricated from synthetic polymers have found limited applications so far in vascular surgeries, owing to their poor mechanical properties. In this study, cylindrical nanofibrous structures of highly oriented nanofibers made from polyacrylonitrile, poly (lactide-co-glycolide) (PLGA), polycaprolactone (PCL) and poly(vinyl acetate) (PVAc) were investigated. Cylindrical collectors with alternate conductive and non-conductive segments were used to obtain highly oriented nanofibrous structures at the same time with better mechanical properties. The surface morphology (orientation), mechanical properties and suture retention of the nanofibrous structures were characterized using SEM, mechanical tester and universal testing machine, respectively. The PLGA nanofibrous cylindrical structure exhibited excellent properties (tensile strength of 9.1 ± 0.6 MPa, suture retention strength of 27N and burst pressure of 350 ± 50 mmHg) when compared to other polymers. Moreover, the PLGA grafts showed good porosity and elongation values, that could be potentially used for vascular graft applications. The combination of PLGA nanofibers with extracellular vesicles (EVs) will be explored as a potential vascular graft in future.

Evaluation of Polyacrylonitrile Nonwoven Mats and Silver-Gold Bimetallic Nanoparticle-Decorated Nonwoven Mats for Potential Promotion of Wound Healing In Vitro and In Vivo and Bone Growth In Vitro

We prepared polyacrylonitrile (PAN) and urchin-like Ag-Au bimetallic or Ag nanoparticle-decorated PAN nonwoven mats using electrospinning and evaluated them in vitro and in vivo for wound healing, antibacterial effects on skin tissue, and promotion of bone ingrowth in vitro. A facile, green, low-temperature protocol was developed to obtain these nonwoven mats. The sterilization rate of urchin-like Ag-Au bimetallic and Ag nanoparticle-decorated PAN nonwoven mats against Staphylococcus aureus was 96.81 ± 2.81% and 51.90 ± 9.07%, respectively, after 5 h treatment. In an in vitro cell model, these two mats did not show significant toxicity; cell viability of >80% was obtained within 5 h of treatment. In vivo animal model preclinical assessment showed that the urchin-like Ag-Au bimetallic nonwoven mat group showed significant wound recovery because of sebaceous gland, hair follicle, and fat formation during skin tissue regeneration; increased neovascularization and compact collagen fibers were observed in the dermal layer, comparable to the findings for the control group. The mother substrate of the urchin-like Ag-Au bimetallic nanoparticle-decorated PAN nonwoven mats, that is, pure PAN nonwoven mats, was found to be a potential scaffold for bone tissue engineering as osteoblast ingrowth from the top to the bottom of the membrane and proliferation inside the membrane were observed. The key genetic factor Cbfa1 was identified as a key osteoblast differentiation regulator in vitro. Thus, electrospun membrane materials show potential for use as dual-functional biomaterials for bone regeneration and infection control and composite grafts for infectious bone and soft tissue defects.

Enhanced Electrochemical Properties of Catalyst by Phosphorous Addition for Direct Urea Fuel Cell

An anode bimetallic catalyst comprising Ni-Pd alloy nanoparticles was loaded on acid-treated multi-walled carbon nanotubes (MWCNTs) for application in a direct urea fuel cell. The bimetallic catalyst and MWCNTs were synthesized by a hydrothermal method at 160°C for 5 h. To reduce the catalyst particle size, alkaline resistance, and facilitate their uniform distribution on the surface of the MWCNTs, phosphorus (P) was added to the Ni-Pd/MWCNT catalyst. The effects of P on the distribution and reduction in size of catalyst particles were investigated by Brunauer-Emmett-Teller analysis, transmission electron microscopy, and X-ray diffraction analysis. The enhanced catalytic activity and durability of the P-containing catalyst was confirmed by the high current density [1897.76 mA/cm2 (vs. Ag/AgCl)] obtained at 0.45 V in a 3 M KOH/1.0 M urea alkaline aqueous solution compared with that of the catalyst without P [604.87 mA/cm2 (vs. Ag/AgCl)], as determined by cyclic voltammetry and chronoamperometry. A Urea-O2 fuel cell assembled with a membrane electrode assembly comprising the Ni-Pd(P)/MWCNT catalyst delivered peak power densities of 0.756 and 3.825 mW/cm2 at 25 and 60°C, respectively, in a 3 M KOH/1 M urea solution.

Bone Tissue Engineering via Carbon-Based Nanomaterials

Bone tissue engineering (BTE) has received significant attention due to its enormous potential in treating critical-sized bone defects and related diseases. Traditional materials such as metals, ceramics, and polymers have been widely applied as BTE scaffolds; however, their clinical applications have been rather limited due to various considerations. Recently, carbon-based nanomaterials attract significant interests for their applications as BTE scaffolds due to their superior properties, including excellent mechanical strength, large surface area, tunable surface functionalities, high biocompatibility as well as abundant and inexpensive nature. In this article, recent studies and advancements on the use of carbon-based nanomaterials with different dimensions such as graphene and its derivatives, carbon nanotubes, and carbon dots, for BTE are reviewed. Current challenges of carbon-based nanomaterials for BTE and future trends in BTE scaffolds development are also highlighted and discussed.

Carbon based nanomaterials for tissue engineering of bone: Building new bone on small black scaffolds: A review

Tissue engineering is a rapidly-growing approach to replace and repair damaged and defective tissues in the human body. Every year, a large number of people require bone replacements for skeletal defects caused by accident or disease that cannot heal on their own. In the last decades, tissue engineering of bone has attracted much attention from biomedical scientists in academic and commercial laboratories. A vast range of biocompatible advanced materials has been used to form scaffolds upon which new bone can form. Carbon nanomaterial-based scaffolds are a key example, with the advantages of being biologically compatible, mechanically stable, and commercially available. They show remarkable ability to affect bone tissue regeneration, efficient cell proliferation and osteogenic differentiation. Basically, scaffolds are templates for growth, proliferation, regeneration, adhesion, and differentiation processes of bone stem cells that play a truly critical role in bone tissue engineering. The appropriate scaffold should supply a microenvironment for bone cells that is most similar to natural bone in the human body. A variety of carbon nanomaterials, such as graphene oxide (GO), carbon nanotubes (CNTs), fullerenes, carbon dots (CDs), nanodiamonds and their derivatives that are able to act as scaffolds for bone tissue engineering, are covered in this review. Broadly, the ability of the family of carbon nanomaterial-based scaffolds and their critical role in bone tissue engineering research are discussed. The significant stimulating effects on cell growth, low cytotoxicity, efficient nutrient delivery in the scaffold microenvironment, suitable functionalized chemical structures to facilitate cell-cell communication, and improvement in cell spreading are the main advantages of carbon nanomaterial-based scaffolds for bone tissue engineering.

In situ bone regeneration enabled by a biodegradable hybrid double-network hydrogel

The biodegradable hybrid double-network hydrogel for stem cell-enhanced bone regeneration.

Biomaterial aided differentiation and maturation of induced pluripotent stem cells

Engineering/reprogramming differentiated adult somatic cells to gain the ability to differentiate into any type of cell lineage are called as induced pluripotent stem cells (iPSCs). Offering unlimited self-renewal and differentiation potential, these iPSC are aspired to meet the growing demands in the field of regenerative medicine, tissue engineering, disease modeling, nanotechnology, and drug discovery. Biomaterial fabrication with the rapid evolution of technology increased their versatility and utility in regenerative medicine and tissue engineering, revolutionizing the stem cell biology research with the property to guide the process of proliferation, differentiation, and morphogenesis. Combining traditional culture platforms of iPSC with biomaterials aids to overcome the limitations associated with derivation, proliferation, and maturation, thereby could improve the clinical translation of iPSC. The present review discusses in brief about the reprogramming techniques for the derivation iPSC and details on several biomaterial guided differentiation of iPSC to different cell types with specific relevance to tissue engineering/regenerative medicine.

Porous Heat-Treated Polyacrylonitrile Scaffolds for Bone Tissue Engineering

Heat-treated polyacrylonitrile (HT-PAN), also referred to as black orlon (BO), is a promising carbon-based material used for applications in tissue engineering and regenerative medicine. To the best of our knowledge, no such complex bone morphology-mimicking three-dimensional (3D) BO structure has been reported to date. We report that BO can be easily made into 3D cryogel scaffolds with porous structures, using succinonitrile as a porogen. The cryogels possess a porous morphology, similar to bone tissue. The prepared scaffolds showed strong osteoconductive activity, providing excellent support for the adhesion, proliferation, and mitochondrial activity of human bone-derived cells. This effect was more apparent in scaffolds prepared from a matrix with a higher content of PAN (i.e., 10% rather than 5%). The scaffolds with 10% of PAN also showed enhanced mechanical properties, as revealed by higher compressive modulus and higher compressive strength. Therefore, these scaffolds have a robust potential for use in bone tissue engineering.

Neural differentiation on aligned fullerene C60 nanowhiskers

Highly-aligned fullerene nanowhiskers (C₆₀ NWs) are prepared by a modified liquid–liquid interfacial precipitation method. Neural stem cells on the aligned C₆₀ NWs are oriented and have a high capacity to differentiate into mature neurons.

Fabrication of Aligned Nanofiber Polymer Yarn Networks for Anisotropic Soft Tissue Scaffolds

Nanofibrous scaffolds with defined architectures and anisotropic mechanical properties are attractive for many tissue engineering and regenerative medicine applications. Here, a novel electrospinning system is developed and implemented to fabricate continuous processable uniaxially aligned nanofiber yarns (UANY). UANY were processed into fibrous tissue scaffolds with defined anisotropic material properties using various textile-forming technologies, i.e., braiding, weaving, and knitting techniques. UANY braiding dramatically increased overall stiffness and strength compared to the same number of UANY unbraided. Human adipose derived stem cells (HADSC) cultured on UANY or woven and knitted 3D scaffolds aligned along local fiber direction and were >90% viable throughout 21 days. Importantly, UANY supported biochemical induction of HADSC differentiation toward smooth muscle and osteogenic lineages. Moreover, we integrated an anisotropic woven fiber mesh within a bioactive hydrogel to mimic the complex microstructure and mechanical behavior of valve tissues. Human aortic valve interstitial cells (HAVIC) and human aortic root smooth muscle cells (HASMC) were separately encapsulated within hydrogel/woven fabric composite scaffolds for generating scaffolds with anisotropic biomechanics and valve ECM like microenvironment for heart valve tissue engineering. UANY have great potential as building blocks for generating fiber-shaped tissues or tissue microstructures with complex architectures.

Bioinspired trimodal macro/micro/nano-porous scaffolds loading rhBMP-2 for complete regeneration of critical size bone defect

Critical size bone defects raise great demands for efficient bone substitutes. Mimicking the hierarchical porous architecture and specific biological cues of natural bone has been considered as an effective strategy to facilitate bone regeneration. Herein, a trimodal macro/micro/nano-porous scaffold loaded with recombinant human bone morphogenetic protein-2 (rhBMP-2) was developed. With mesoporous bioactive glass (MBG) as matrix, a trimodal MBG scaffold (TMS) with enhanced compressive strength (4.28 MPa, porosity of 80%) was prepared by a "viscosity controlling" and "homogeneous particle reinforcing" multi-template process. A 7.5 nm, 3D cubic (Im3m) mesoporous structure was tailored for a "size-matched entrapment" of rhBMP-2 to achieve sustained release and preserved bioactivity. RhBMP-2-loaded TMS (TMS/rhBMP-2) induced excellent cell attachment, ingrowth and osteogenesis in vitro. Further in vivo ectopic bone formation and orthotopic rabbit radius critical size defect results indicated that compared to the rhBMP-2-loaded bimodal macro/micro- and macro/nano-porous scaffolds, TMS/rhBMP-2 exhibited appealing bone regeneration capacity. Particularly, in critical size defect, complete bone reconstruction with rapid medullary cavity reunion and sclerotin maturity was observed on TMS/rhBMP-2. On the basis of these results, TMS/rhBMP-2 developed here represents a promising bone substitute for clinical application and the concepts proposed in this study might provide new thoughts on development of future orthopedic biomaterials.

STATEMENT OF SIGNIFICANCE

Limited self-regenerating capacity of human body makes the reconstruction of critical size bone defect a significant challenge. Current bone substitutes often exhibit undesirable therapeutic efficacy due to poor osteoconductivity or low osteoinductivity. Herein, TMS/rhBMP-2, an advanced mesoporous bioactive glass (MBG) scaffold with osteoconductive trimodal macro/micro/nano-porosity and osteoinductive rhBMP-2 delivery was developed. The preparative and mechanical problems of hierarchical MBG scaffold were solved without affecting its excellent biocompatibilities, and rhBMP-2 immobilization in sizematched mesopores was first explored. Combining structural and biological cues, TMS/rhBMP-2 achieved a complete regeneration with rapid medullary cavity reunion and sclerotin maturity in rabbit radius critical size defects. The design conceptions proposed in this study might provide new thoughts on development of future orthopedic biomaterials.

Nanothin Coculture Membranes with Tunable Pore Architecture and Thermoresponsive Functionality for Transfer-Printable Stem Cell-Derived Cardiac Sheets

Coculturing stem cells with the desired cell type is an effective method to promote the differentiation of stem cells. The features of the membrane used for coculturing are crucial to achieving the best outcome. Not only should the membrane act as a physical barrier that prevents the mixing of the cocultured cell populations, but it should also allow effective interactions between the cells. Unfortunately, conventional membranes used for coculture do not sufficiently meet these requirements. In addition, cell harvesting using proteolytic enzymes following coculture impairs cell viability and the extracellular matrix (ECM) produced by the cultured cells. To overcome these limitations, we developed nanothin and highly porous (NTHP) membranes, which are ∼20-fold thinner and ∼25-fold more porous than the conventional coculture membranes. The tunable pore size of NTHP membranes at the nanoscale level was found crucial for the formation of direct gap junctions-mediated contacts between the cocultured cells. Differentiation of the cocultured stem cells was dramatically enhanced with the pore size-customized NTHP membrane system compared to conventional coculture methods. This was likely due to effective physical contacts between the cocultured cells and the fast diffusion of bioactive molecules across the membrane. Also, the thermoresponsive functionality of the NTHP membranes enabled the efficient generation of homogeneous, ECM-preserved, highly viable, and transfer-printable sheets of cardiomyogenically differentiated cells. The coculture platform developed in this study would be effective for producing various types of therapeutic multilayered cell sheets that can be differentiated from stem cells.

"Cleaning" the Surface of Hydroxyapatite Nanorods by a Reaction-Dissolution Approach

Synthetic nanoparticles are always terminated with coating molecules, which are often cytotoxic and not desired in biomedicine. Here we propose a novel reaction-dissolution approach to remove the cytotoxic coating molecules. A two-component solution is added to the nanoparticle solution; one component reacts with the coating molecules to form a salt whereas another is a solvent for dissolving and thus removing the salt. As a proof of concept, this work uses a NaOH-ethanol solution to remove the cytotoxic linoleic acid molecules coated on the hydroxyapatite nanorods (HAP-NRs). The removal of the coating molecules not only significantly improves the biocompatibility of HAP-NRs but also enables their oriented attachment into tightly-bound superstructures, which mimic the organized HAP crystals in bone and enamel and can promote the osteogenic differentiation of mesenchymal stem cells. Our reaction-dissolution approach can be extended to the surface "cleaning" of other nanomaterials.

Highly Ordered 1D Fullerene Crystals for Concurrent Control of Macroscopic Cellular Orientation and Differentiation toward Large-Scale Tissue Engineering

A highly aligned 1D fullerene whisker (FW) scaffold in a centimeter area is fabricated by interfacial alignment. The resulting aligned FW scaffold enables concurrent control over cellular orientation and differentiation to muscle cells. This aligned FW scaffold is made by a facile method, and hence the substrate is a promising alternative to other cell scaffolds for tissue engineering.

Highly biocompatible nanofibrous microspheres self-assembled from chitin in NaOH/urea aqueous solution as cell carriers

In this work, chitin microspheres (NCM) having a nanofibrous architecture were constructed using a "bottom-up" fabrication pathway. The chitin chains rapidly self-assembled into nanofibers in NaOH/urea aqueous solution by a thermally induced method and subsequently formed weaved microspheres. The diameter of the chitin nanofibers and the size of the NCM were tunable by controlling the temperature and the processing parameters to be in the range from 26 to 55 nm and 3 to 130 μm, respectively. As a result of the nanofibrous surface and the inherent biocompatibility of chitin, cells could adhere to the chitin microspheres and showed a high attachment efficiency, indicating the great potential of the NCM for 3D cell microcarriers.