Laser-treated electrospun fibers loaded with nano-hydroxyapatite for bone tissue engineering

Cell-Tissue Interaction: The Biomimetic Approach to Design Tissue Engineered Biomaterials

The advancement achieved in Tissue Engineering is based on a careful and in-depth study of cell-tissue interactions. The choice of a specific biomaterial in Tissue Engineering is fundamental, as it represents an interface for adherent cells in the creation of a microenvironment suitable for cell growth and differentiation. The knowledge of the biochemical and biophysical properties of the extracellular matrix is a useful tool for the optimization of polymeric scaffolds. This review aims to analyse the chemical, physical, and biological parameters on which are possible to act in Tissue Engineering for the optimization of polymeric scaffolds and the most recent progress presented in this field, including the novelty in the modification of the scaffolds' bulk and surface from a chemical and physical point of view to improve cell-biomaterial interaction. Moreover, we underline how understanding the impact of scaffolds on cell fate is of paramount importance for the successful advancement of Tissue Engineering. Finally, we conclude by reporting the future perspectives in this field in continuous development.

Investigations into the effects of scaffold microstructure on slow-release system with bioactive factors for bone repair

In recent years, bone tissue engineering (BTE) has played an essential role in the repair of bone tissue defects. Although bioactive factors as one component of BTE have great potential to effectively promote cell differentiation and bone regeneration, they are usually not used alone due to their short effective half-lives, high concentrations, etc. The release rate of bioactive factors could be controlled by loading them into scaffolds, and the scaffold microstructure has been shown to significantly influence release rates of bioactive factors. Therefore, this review attempted to investigate how the scaffold microstructure affected the release rate of bioactive factors, in which the variables included pore size, pore shape and porosity. The loading nature and the releasing mechanism of bioactive factors were also summarized. The main conclusions were achieved as follows: i) The pore shapes in the scaffold may have had no apparent effect on the release of bioactive factors but significantly affected mechanical properties of the scaffolds; ii) The pore size of about 400 μm in the scaffold may be more conducive to controlling the release of bioactive factors to promote bone formation; iii) The porosity of scaffolds may be positively correlated with the release rate, and the porosity of 70%-80% may be better to control the release rate. This review indicates that a slow-release system with proper scaffold microstructure control could be a tremendous inspiration for developing new treatment strategies for bone disease. It is anticipated to eventually be developed into clinical applications to tackle treatment-related issues effectively.

Intervertebral disc degeneration-Current therapeutic options and challenges

Degeneration of the intervertebral disc (IVD) is a normal part of aging. Due to the spine's declining function and the development of pain, it may affect one's physical health, mental health, and socioeconomic status. Most of the intervertebral disc degeneration (IVDD) therapies today focus on the symptoms of low back pain rather than the underlying etiology or mechanical function of the disc. The deteriorated disc is typically not restored by conservative or surgical therapies that largely focus on correcting symptoms and structural abnormalities. To enhance the clinical outcome and the quality of life of a patient, several therapeutic modalities have been created. In this review, we discuss genetic and environmental causes of IVDD and describe promising modern endogenous and exogenous therapeutic approaches including their applicability and relevance to the degeneration process.

Fibers by Electrospinning and Their Emerging Applications in Bone Tissue Engineering

Bone tissue engineering (BTE) is an optimized approach for bone regeneration to overcome the disadvantages of lacking donors. Biocompatibility, biodegradability, simulation of extracellular matrix (ECM), and excellent mechanical properties are essential characteristics of BTE scaffold, sometimes including drug loading capacity. Electrospinning is a simple technique to prepare fibrous scaffolds because of its efficiency, adaptability, and flexible preparation of electrospinning solution. Recent studies about electrospinning in BTE are summarized in this review. First, we summarized various types of polymers used in electrospinning and methods of electrospinning in recent work. Then, we divided them into three parts according to their main role in BTE, (1) ECM simulation, (2) mechanical support, and (3) drug delivery system.

Functionalized Porous Hydroxyapatite Scaffolds for Tissue Engineering Applications: A Focused Review

Biomaterials have been widely used in tissue engineering applications at an increasing rate in recent years. The increased clinical demand for safe scaffolds, as well as the diversity and availability of biomaterials, has sparked rapid interest in fabricating diverse scaffolds to make significant progress in tissue engineering. Hydroxyapatite (HAP) has drawn substantial attention in recent years owing to its excellent physical, chemical, and biological properties and facile adaptable surface functionalization with other innumerable essential materials. This focused review spotlights a brief introduction on HAP, scope, a historical outline, basic structural features/properties, various synthetic strategies, and their scientific applications concentrating on functionalized HAP in the diverse area of tissue engineering fields such as bone, skin, periodontal, bone tissue fixation, cartilage, blood vessel, liver, tendon/ligament, and corneal are emphasized. Besides clinical translation aspects, the future challenges and prospects of HAP based biomaterials involved in tissue engineering are also discussed. Furthermore, it is expected that researchers may find this review expedient in gaining an overall understanding of the latest advancement of HAP based biomaterials.

Enhanced bone tissue regeneration via bioactive electrospun fibrous composite coated titanium orthopedic implant

One of the very reliable, attractive, and cheapest techniques for synthesizing nanofibers for biomedical applications is electrospinning. Here, we have created a novel nanofibrous composite coated Ti plate to mimic an Extra Cellular Matrix (ECM) of native bone in order to enhance the bone tissue regeneration. An electrospun fibrous composite was obtained by the combination of minerals (Zn, Mg, Si) substituted hydroxyapatite (MHAP)/Polyethylene Glycol (PEG)/Cissus quadrangularis (CQ) extract. Fibrous composite's functionality, phase characteristics, and morphology were evaluated by FT-IR, XRD, and SEM techniques, respectively. The average fiber diameter of MHAP/PVA had decreased from ~274 to ~255 nm after incorporating PEG polymer. That further increased from ~255 to ~275 nm after adding CQ extract. Besides the bioactivity in SBF solution, the degradable nature was confirmed by immersing the fibrous composite in Tris-HCL solution. The degradable studies evaluate that the composite was degraded depending on time, and it degrades about 9.42% after 7 days of immersion. Osteoblasts like MG-63 cells differentiation, proliferation, and calcium deposition were also determined. These results show that this new fibrous composite exhibits advanced osteoblasts properties. Thus, we concluded that this new fibrous scaffold coated Ti implant could act as a better implant to mimic ECM of bone structure and to improve osteogenesis during bone regeneration.

Antibacterial Poly(ε-CL)/Hydroxyapatite Electrospun Fibers Reinforced by Poly(ε-CL)-b-poly(ethylene phosphoric acid)

In bone surgery and orthopedics, bioresorbable materials can be helpful in bone repair and countering post-op infections. Explicit antibacterial activity, osteoinductive and osteoconductive effects are essential to achieving this objective. Nonwoven electrospun (ES) fibers are receiving the close attention of physicians as promising materials for wound dressing and tissue engineering; potentially, in high contrast with dense materials, ES mats hamper regeneration of the bone extracellular matrix to a lesser extent. The use of the compositions of inherently biodegradable polyesters (poly(ε-caprolactone) PCL, poly(lactoglycolide), etc.), calcium phosphates and antibiotics is highly prospective, but the task of forming ES fibers from such compositions is complicated by the incompatibility of the main organic and inorganic ingredients, polyesters and calcium phosphates. In the present research we report the synthesis of hydroxyapatite (HAp) nanoparticles with uniform morphology, and demonstrate high efficiency of the block copolymer of PCL and poly(ethylene phosphoric acid) (PEPA) as an efficient compatibilizer for PCL/HAp mixtures that are able to form ES fibers with improved mechanical characteristics. The materials obtained in the presence of vancomycin exhibited incremental drug release against Staphylococcus aureus (St. aureus).

Bilayer Membrane Composed of Mineralized Collagen and Chitosan Cast Film Coated With Berberine-Loaded PCL/PVP Electrospun Nanofiber Promotes Bone Regeneration

Bone defects are difficult to repair and reconstruct as bone regeneration remains technically challenging, with exogenous factors required to accelerate this process. Biodegradable synthetic scaffolds are promising materials for stimulating bone tissue repair. In this study, we investigated whether a bilayer membrane that includes mineralized collagen (MC) and chitosan (CS) delivering berberine (BER)—a typical Chinese herbal monomer—could promote bone healing in a rat model. An MC/CS cast film was coated with polycaprolactone (PCL)/polyvinylpyrrolidone (PVP) electrospun nanofibers loaded with BER, yielding the BER@PCL/PVP-MC/CS bilayer membrane. The 3-dimensional structure had nanofibers of uniform diameter and showed good hydrophilicity; the bilayer membrane showed favorable mechanical properties. BER@PCL/PVP-MC/CS enhanced the proliferation and attachment of MC3T3-E1 cells in vitro and induced bone regeneration when implanted into a rat femoral bone defect. These findings provide evidence that BER@PCL/PVP-MC/CS has clinical potential for effective bone repair.

The efficiency of PCL/HAp electrospun nanofibers in bone regeneration: a review

Electrospinning is a method which produces various nanofiber scaffolds for different tissues was attractive for researchers. Nanofiber scaffolds could be made from several biomaterials and polymers. Quality and virtues of final scaffolds depend on used biomaterials (even about single substance, the origin is effective), additives (such as some molecules, ions, drugs, and inorganic materials), electrospinning parameter (voltage, injection speed, temperature, …), etc. In addition to its benefits, which makes it more attractive is the possibility of modifications. Common biomaterials in bone tissue engineering such as poly-caprolactone (PCL), hydroxyapatite (HAp), and their important features, electrospinning nanofibers were widely studied. Related investigations indicate the critical role of even small parameters (like the concentration of PCL or HAp) in final product properties. These changes also, cause deference in cell proliferation, adhesion, differentiation, and in vivo repair process. In this review was focussed on PCL/HAp based nanofibers and additives that researchers used for scaffold improvement. Then, reviewing properties of gained nanofibers, their effect on cell behaviour, and finally, their valency in bone tissue engineering studies (in vitro and in vivo).

Mesoporous silica pellets as bifunctional bone drug delivery system for cefazolin

For decades, bone drug delivery systems dedicated for osteomyelitis treatment have been investigated as bifunctional materials that exhibit prolonged drug release and mineralization potential. Herein, composite-type pellets based on cefazolin-loaded amino-modified mesoporous silica SBA-15 and microwave-assisted hydroxyapatite were investigated as potential bone drug delivery system in vitro. Pellets were obtained by granulation, extrusion and spheronization methods in laboratory scale and studied in terms of physical properties, drug release, mineralization potential, antimicrobial activity and cytotoxicity towards human osteoblasts. The obtained pellets were characterized for hardness and friability which indicated the pellets durability during further investigations. Prolonged (5-day) release of cefazolin from pellets was observed. The pellets exhibited mineralization potential in simulated body fluid, i.e., a continuous layer of bone-like apatite was formed on the surface of pellets after 28 days of incubation. An antimicrobial assay of pellets revealed an antibacterial effect against Staphylococcus aureus strain during 6 days. No cytotoxic effects of pellets towards human osteoblasts were observed. The obtained results proved that proposed pellets appear to have potential applications as bone drug delivery systems.

Potential Implantable Nanofibrous Biomaterials Combined with Stem Cells for Subchondral Bone Regeneration

The treatment of osteochondral defects remains a challenge. Four scaffolds were produced using Food and Drug Administration (FDA)-approved polymers to investigate their therapeutic potential for the regeneration of the osteochondral unit. Polycaprolactone (PCL) and poly(vinyl-pyrrolidone) (PVP) scaffolds were made by electrohydrodynamic techniques. Hydroxyapatite (HAp) and/or sodium hyaluronate (HA) can be then loaded to PCL nanofibers and/or PVP particles. The purpose of adding hydroxyapatite and sodium hyaluronate into PCL/PVP scaffolds is to increase the regenerative ability for subchondral bone and joint cartilage, respectively. Human bone marrow-derived mesenchymal stem cells (hBM-MSCs) were seeded on these biomaterials. The biocompatibility of these biomaterials in vitro and in vivo, as well as their potential to support MSC differentiation under specific chondrogenic or osteogenic conditions, were evaluated. We show here that hBM-MSCs could proliferate and differentiate both in vitro and in vivo on these biomaterials. In addition, the PCL-HAp could effectively increase the mineralization and induce the differentiation of MSCs into osteoblasts in an osteogenic condition. These results indicate that PCL-HAp biomaterials combined with MSCs could be a beneficial candidate for subchondral bone regeneration.

Recent Developments in Nanofiber Fabrication and Modification for Bone Tissue Engineering

Bone tissue engineering is an alternative therapeutic intervention to repair or regenerate lost bone. This technique requires three essential components: stem cells that can differentiate into bone cells, growth factors that stimulate cell behavior for bone formation, and scaffolds that mimic the extracellular matrix. Among the various kinds of scaffolds, highly porous nanofibrous scaffolds are a potential candidate for supporting cell functions, such as adhesion, delivering growth factors, and forming new tissue. Various fabricating techniques for nanofibrous scaffolds have been investigated, including electrospinning, multi-axial electrospinning, and melt writing electrospinning. Although electrospun fiber fabrication has been possible for a decade, these fibers have gained attention in tissue regeneration owing to the possibility of further modifications of their chemical, biological, and mechanical properties. Recent reports suggest that post-modification after spinning make it possible to modify a nanofiber's chemical and physical characteristics for regenerating specific target tissues. The objectives of this review are to describe the details of recently developed fabrication and post-modification techniques and discuss the advanced applications and impact of the integrated system of nanofiber-based scaffolds in the field of bone tissue engineering. This review highlights the importance of nanofibrous scaffolds for bone tissue engineering.

Core-Shell Fibers: Design, Roles, and Controllable Release Strategies in Tissue Engineering and Drug Delivery

The key attributes of core-shell fibers are their ability to preserve bioactivity of incorporated-sensitive biomolecules (such as drug, protein, and growth factor) and subsequently control biomolecule release to the targeted microenvironments to achieve therapeutic effects. Such qualities are highly favorable for tissue engineering and drug delivery, and these features are not able to be offered by monolithic fibers. In this review, we begin with an overview on design requirement of core-shell fibers, followed by the summary of recent preparation methods of core-shell fibers, with focus on electrospinning-based techniques and other newly discovered fabrication approaches. We then highlight the importance and roles of core-shell fibers in tissue engineering and drug delivery, accompanied by thorough discussion on controllable release strategies of the incorporated bioactive molecules from the fibers. Ultimately, we touch on core-shell fibers-related challenges and offer perspectives on their future direction towards clinical applications.

Hydroxyapatite/silk fibroin composite biomimetic scaffold for dental pulp repair

Dental pulp repair is a difficult clinical problem. In the present study, the authors aimed to mimic the extracellular matrix of dental pulp tissue structurally and compositionally. Nanofibrous silk fibroin (SF) scaffolds containing hydroxyapatite (HAp) nanoparticles were fabricated by using the freeze-drying approach. Rod-shaped HAp was successfully embedded in the composite scaffold, the diameter of which was about 100–200 nm as shown by transmission electron microscopy analysis. The three-dimensional microstructure of the composite scaffold prepared in various ratios of HAp to SF was observed by scanning electron microscopy and the pore size of the optimal scaffold was about 30–120 μm. Meanwhile, the hemocompatibility of the composite scaffolds was evaluated based on their impact on the clotting function by way of activated partial thromboplastin time, prothrombin time and thromboelastographic assays. The scaffolds possessed a low hemolysis rate of red blood cells. Furthermore, cell culture tests using dental pulp stem cells found that the scaffolds had good biocompatibility. There biomimetic HAp/SF composite scaffolds may serve as a promising biomaterial for dental pulp repair.

PCL-Based Composite Scaffold Matrices for Tissue Engineering Applications

Biomaterial-based scaffolds are important cues in tissue engineering (TE) applications. Recent advances in TE have led to the development of suitable scaffold architecture for various tissue defects. In this narrative review on polycaprolactone (PCL), we have discussed in detail about the synthesis of PCL, various properties and most recent advances of using PCL and PCL blended with either natural or synthetic polymers and ceramic materials for TE applications. Further, various forms of PCL scaffolds such as porous, films and fibrous have been discussed along with the stem cells and their sources employed in various tissue repair strategies. Overall, the present review affords an insight into the properties and applications of PCL in various tissue engineering applications.

Biological monitoring of workers exposed to engineered nanomaterials

As the number of nanomaterial workers increase there is need to consider whether biomonitoring of exposure should be used as a routine risk management tool. Currently, no biomonitoring of nanomaterials is mandated by authoritative or regulatory agencies. However, there is a growing knowledge base to support such biomonitoring, but further research is needed as are investigations of priorities for biomonitoring. That research should be focused on validation of biomarkers of exposure and effect. Some biomarkers of effect are generally nonspecific. These biomarkers need further interpretation before they should be used. Overall biomonitoring of nanomaterial workers may be important to supplement risk assessment and risk management efforts.

Improved connective integration of a degradable 3D-nano-apatite/agarose scaffold subcutaneously implanted in a rat model

In this work, we evaluate the tissue response and tolerance to a designed 3D porous scaffold composed of nanocrystalline carbonate-hydroxyapatite and agarose as a preliminary step in bone repair and regeneration. These scaffolds were subcutaneously implanted into rats, which were sacrificed at different times. CD4+, CD8+ and ED1+ cells were evaluated as measurements of inflammatory reaction and tolerance. We observed some inflammatory response early after subcutaneous implantation. The 3D interconnected porosity increased scaffold integration via the formation of granulation tissue and the generation of a fibrous capsule around the scaffold. The capsule is initially formed by collagen which progressively invades the scaffold, creating a network that supports the settlement of connective tissue and generating a compact structure. The timing of the appearance of CD4+ and CD8+ cell populations is in agreement with the resolved inflammatory response. The appearance of macrophage activity evidences a slow and gradual degradation activity. Degradation started with the agarose component of the scaffold, but the nano-apatite was kept intact for up to 30 days. Therefore, this apatite/agarose scaffold showed a high capacity for integration by a connective network that stabilizes the scaffold and results in slow nano-apatite degradation. The fundamental properties of the scaffold would provide mechanical support and facilitate bone mobilization, which is of great importance in the masticatory system or large bones.

Polymeric electrospun scaffolds for bone morphogenetic protein 2 delivery in bone tissue engineering

HYPOTHESIS

The development of novel scaffolds based on biocompatible polymers is of great interest in the field of bone repair for fabrication of biodegradable scaffolds that mimic the extracellular matrix and have osteoconductive and osteoinductive properties for enhanced bone regeneration.

EXPERIMENTS

Polycaprolactone (PCL) and polycaprolactone/polyvinyl acetate (PCL/PVAc) core-shell fibers were synthesised and decorated with poly(lactic-co-glycolic acid) [PLGA] particles loaded with bone morphogenetic protein 2 (BMP2) by simultaneous electrospinning and electrospraying. Hydroxyapatite nanorods (HAn) were loaded into the core of fibers. The obtained scaffolds were characterised by scanning and transmission electron microscopy, Fourier-transform infrared spectroscopy, and thermogravimetric analysis. The in vitro potential of these materials for bone regeneration was assessed in biodegradation assays, osteoblast viability assays, and analyses of expression of specific bone markers, such as alkaline phosphatase (ALP), osteocalcin (OCN), and osteopontin (OPN).

FINDINGS

PLGA particles were homogeneously distributed in the entire fibre mat. The growth factor load was 1.2-1.7 μg/g of the scaffold whereas the HAn load was in the 8.8-12.6 wt% range. These scaffolds were able to support and enhance cell growth and proliferation facilitating the expression of osteogenic and osteoconductive markers (OCN and OPN). These observations underline the great importance of the presence of BMP2 in scaffolds for bone remodelling as well as the good potential of the newly developed scaffolds for clinical use in tissue engineering.

Covalent immobilization of acetylcholinesterase on a novel polyacrylic acid-based nanofiber membrane

In this study, polyacrylic acid-based nanofiber (NF) membrane was prepared via electrospinning method. Acetylcholinesterase (AChE) from Electrophorus electricus was covalently immobilized onto polyacrylic acid-based NF membrane by demonstrating efficient enzyme immobilization, and immobilization capacity of polymer membranes was found to be 0.4 mg/g. The novel NF membrane was synthesized via thermally activated surface reconstruction, and activation with carbonyldiimidazole upon electrospinning. The morphology of the polyacrylic acid-based membrane was investigated by scanning electron microscopy, Fourier Transform Infrared Spectroscopy, and thermogravimetric analysis. The effect of temperature and pH on enzyme activity was investigated and maxima activities for free and immobilized enzyme were observed at 30 and 35°C, and pH 7.4 and 8.0, respectively. The effect of 1 mM Mn²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Mg²⁺, Ca²⁺ ions on the stability of the immobilized AChE was also investigated. According to the Michaelis-Menten plot, AChE possessed a lower affinity to acetylthiocholine iodide after immobilization, and the Michaelis-Menten constant of immobilized and free AChE were found to be 0.5008 and 0.4733 mM, respectively. The immobilized AChE demonstrated satisfactory reusability, and even after 10 consecutive activity assay runs, AChE maintained ca. 87% of its initial activity. Free enzyme lost its activity completely within 60 days, while the immobilized enzyme retained approximately 70% of the initial activity under the same storage time. The favorable reusability of immobilized AChE enables the support to be employable to develop the AChE-based biosensors.