Physicochemical, in vitro and in vivo evaluation of VEGF loaded PCL-mPEG and PDGF loaded PCL-Chitosan dual layered vascular grafts

The present study has attempted to evaluate the endothelialization and smooth muscle regeneration efficiency of a novel dual-layer small-diameter vascular graft. Two types of layers (PCL-mPEG-VEGF and PCL-Chitosan-PDGF) were fabricated to find out the best layer giving endothelialization support for the lumen and unique contractile function for outer layer of blood vessels. Platelet-derived growth factor (PDGF) and chitosan were immobilized onto PCL surface by aminolysis-based surface modification technique. Besides, Poly (ethylene glycol) methyl ether (mPEG) and vascular endothelial growth factor (VEGF) were directly blended with PCL. Morphological analysis of membranes ensured consistency of average fibers diameter with native extracellular matrix. A favorable interaction of PCL-mPEG-VEGF with cow pulmonary endothelial cells (CPAEs) and PCL-Chitosan-PDGF with rat bone marrow mesenchymal stem cells (RBMSCs) was obtained during in vitro study. Controlled growth factor release patterns were found from both layers. Further, PCL-mPEG-VEGF exhibited endothelial markers expression properties from RBMSCs. Up-regulation of SMCs markers expression was significantly ensured by the PCL-Chitosan-PDGF membrane. Thus, PCL-mPEG-VEGF and PCL-Chitosan-PDGF were preferred as inner and outer layers respectively of a finally prepared tubular hybrid tissue engineered small diameter vascular graft. Finally, the dual-layer vascular graft was implanted onto a rat abdominal aorta model for 2 months. The extracted samples exhibited the presence of endothelial marker (ICAM 1) in the inner layer and smooth muscle cell marker (αSMA) in the outer layer as well as substantial amount of collagen deposition was observed in the both layers.

Oxidized Hyaluronic Acid-Gelatin-Based Hydrogels for Tissue Engineering and Soft Tissue Mimicking

Hydrogels are ideal materials for mimicking and engineering soft tissue. Hyaluronic acid is a linear polysaccharide native to the human extracellular matrix. In this study, we first develop and characterize two hydrogel compositions built from oxidized HA and gelatin with and without alginate-di-aldehyde (ADA) crosslinked by ionic and enzymatic agents with potential applications in soft tissue engineering and tissue mimicking structures. The stability under incubation conditions was improved by adjusting crosslinking times. Through large-strain mechanical measurements, the hydrogels' properties were compared to human brain tissue and the samples containing ADA revealed similar mechanical properties to the native tissue specimens in cyclic compression-tension. In vitro characterization demonstrated a high viability of encapsulated mouse embryonic fibroblasts and a spreading of the cells in case of ADA-free samples.

[Advantages and challenges of carbon nanotubes as bone repair materials]

With the in-depth research on bone repair process, and the progress in bone repair materials preparation and characterization, a variety of artificial bone substitutes have been fully developed in the treatment of bone related diseases such as bone defects. However, the current various natural or synthetic biomaterials are still unable to achieve the structure and properties of natural bone. Carbon nanotubes (CNTs) have provided a new direction for the development of new materials in the field of bone repair due to their excellent structural stability, mechanical properties, and functional group modifiability. Moreover, CNTs and their composites have broad prospects in the design of bone repair materials and as drug delivery carriers. This paper describes the advantages of CNTs related to bone tissue regeneration from the aspects of morphology, chemistry, mechanics, electromagnetism, and biosafety, as well as the application of CNTs in drug delivery carriers and reinforcement components of scaffold materials. In addition, the potential problems and prospects of CNTs in bone regenerative medicine are discussed.

Applications of Carbon Nanotubes in Bone Tissue Regeneration and Engineering: Superiority, Concerns, Current Advancements, and Prospects

With advances in bone tissue regeneration and engineering technology, various biomaterials as artificial bone substitutes have been widely developed and innovated for the treatment of bone defects or diseases. However, there are no available natural and synthetic biomaterials replicating the natural bone structure and properties under physiological conditions. The characteristic properties of carbon nanotubes (CNTs) make them an ideal candidate for developing innovative biomimetic materials in the bone biomedical field. Indeed, CNT-based materials and their composites possess the promising potential to revolutionize the design and integration of bone scaffolds or implants, as well as drug therapeutic systems. This review summarizes the unique physicochemical and biomedical properties of CNTs as structural biomaterials and reinforcing agents for bone repair as well as provides coverage of recent concerns and advancements in CNT-based materials and composites for bone tissue regeneration and engineering. Moreover, this review discusses the research progress in the design and development of novel CNT-based delivery systems in the field of bone tissue engineering.

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.

Biomimetic Properties of Force-Spun PHBV Membranes Functionalised with Collagen as Substrates for Biomedical Application

The force-spinning process parameters (i.e., spin speed, spinneret-collector distance, and polymer concentration), optimised and characterised in previous work by this group, allowed the rapid fabrication of large quantities of high surface area poly(3-hydroxybutyric acid-co-3-hydroxyvaleric acid) (PHBV) polymeric fibre membranes. This paper examined the potential application for force-spun PHBV fibres functionalised with type I collagen for tissue regeneration applications. PHBV fibre scaffolds provide a biologically suitable substrate to guide the regeneration of dermal tissues, however, have poor cellular adhesion properties. The grafting of collagen type-I to PHBV fibres demonstrated improved cell adhesion and growth in Neo-NHDF (neonatal human dermal fibroblasts) fibroblasts. The examination of fibre morphology, thermal properties, collagen content, and degradability was used to contrast the physicochemical properties of the PHBV and PHBV-Collagen fibres. Biodegradation models using phosphate buffered saline determined there was no appreciable change in mass over the course of 6 weeks; a Sirius Red assay was performed on degraded samples, showing no change in the quantity of collagen. Cell metabolism studies showed an increase in cell metabolism on conjugated samples after three and 7 days. In addition, in vitro cytocompatibility studies demonstrated superior cell activity and adhesion on conjugated samples over 7 days.

Plasma-Coated Polycaprolactone Nanofibers with Covalently Bonded Platelet-Rich Plasma Enhance Adhesion and Growth of Human Fibroblasts

Biodegradable nanofibers are extensively employed in different areas of biology and medicine, particularly in tissue engineering. The electrospun polycaprolactone (PCL) nanofibers are attracting growing interest due to their good mechanical properties and a low-cost structure similar to the extracellular matrix. However, the unmodified PCL nanofibers exhibit an inert surface, hindering cell adhesion and negatively affecting their further fate. The employment of PCL nanofibrous scaffolds for wound healing requires a certain modification of the PCL surface. In this work, the morphology of PCL nanofibers is optimized by the careful tuning of electrospinning parameters. It is shown that the modification of the PCL nanofibers with the COOH plasma polymers and the subsequent binding of NH2 groups of protein molecules is a rather simple and technologically accessible procedure allowing the adhesion, early spreading, and growth of human fibroblasts to be boosted. The behavior of fibroblasts on the modified PCL surface was found to be very different when compared to the previously studied cultivation of mesenchymal stem cells on the PCL nanofibrous meshes. It is demonstrated by X-ray photoelectron spectroscopy (XPS) that the freeze-thawed platelet-rich plasma (PRP) immobilization can be performed via covalent and non-covalent bonding and that it does not affect biological activity. The covalently bound components of PRP considerably reduce the fibroblast apoptosis and increase the cell proliferation in comparison to the unmodified PCL nanofibers or the PCL nanofibers with non-covalent bonding of PRP. The reported research findings reveal the potential of PCL matrices for application in tissue engineering, while the plasma modification with COOH groups and their subsequent covalent binding with proteins expand this potential even further. The use of such matrices with covalently immobilized PRP for wound healing leads to prolonged biological activity of the immobilized molecules and protects these biomolecules from the aggressive media of the wound.

3D printed poly(ε-caprolactone) scaffolds function with simvastatin-loaded poly(lactic-co-glycolic acid) microspheres to repair load-bearing segmental bone defects

Repairing critical-sized bone defects has been a major challenge for orthopedic surgeons in the clinic. The generation of functioning bone tissue scaffolds using osteogenic induction factors is a promising method to facilitate bone healing. In the present study, three-dimensional (3D) printing of a poly(lactic-co-glycolic acid) (PLGA) scaffold with simvastatin (SIM) release functioning was generated by rapid prototyping, which was incorporated with collagen for surface activation, and was finally mixed with SIM-loaded PLGA microspheres. In vitro assays with bone marrow-derived mesenchymal stem cells were conducted. For the in vivo study, scaffolds were implanted into segmental defects created on the femurs of Sprague-Dawley rats. At 4 and 12 weeks following surgery, X-ray, micro-computed tomography and histological analysis were performed in order to evaluate bone regeneration. The results demonstrated that collagen functionalization of PLGA produced better cell adhesion, while the sustained release of SIM promoted greater cell proliferation with no significant cytotoxicity, compared with the blank PCL scaffold. Furthermore, in vivo experiments also confirmed that SIM-loaded scaffolds played a significant role in promoting bone regeneration. In conclusion, the present study successfully manufactured a 3D printing PLGA scaffold with sustained SIM release, which may meet the requirements for bone healing, including good mechanical strength and efficient osteoinduction ability. Thus, the results are indicative of a promising bone substitute to be used in the clinic.

* Engineering Membranes for Bone Regeneration

This review is focused on the use of membranes for the specific application of bone regeneration. The first section focuses on the relevance of membranes in this context and what are the specifications that they should possess to improve the regeneration of bone. Afterward, several techniques to engineer bone membranes by using "bulk"-like methods are discussed, where different parameters to induce bone formation are disclosed in a way to have desirable structural and functional properties. Subsequently, the production of nanostructured membranes using a bottom-up approach is discussed by highlighting the main advances in the field of bone regeneration. Primordial importance is given to the promotion of osteoconductive and osteoinductive capability during the membrane design. Whenever possible, the films prepared using different techniques are compared in terms of handability, bone guiding ability, osteoinductivity, adequate mechanical properties, or biodegradability. A last chapter contemplates membranes only composed by cells, disclosing their potential to regenerate bone.

Preparation and characterization of polycaprolactone–polyethylene glycol methyl ether and polycaprolactone–chitosan electrospun mats potential for vascular tissue engineering

Recently, natural polymers are frequently comingled with synthetic polymers either by physical or chemical modification to prepare numerous tissue-engineered graft with promising biological function, strength, and stability. The aim of this study was to determine the efficiency for vascular tissue engineering of two distinctly different mats, one that comprised polycaprolactone–polyethylene glycol methyl ether and other that comprised polycaprolactone–chitosan. Nano/microfibrous mats prepared from electro-spinning were characterized for fiber diameter, porosity, wettability, and mechanical strength. Biological efficacy on both biodegradable mats was assessed by rat bone marrow mesenchymal stem cells, and polycaprolactone–polyethylene glycol methyl ether showed feasibility for use as an inner layer by inducing endothelial-specific gene expression and polycaprolactone–chitosan as an outer layer on dual layered without sacrificing tensile strength, small-diameter blood vessels. Therefore, scaffolds fabricated from this research could be potential sources for tissue-engineered vascular graft and could also overcome the well-known drawbacks, such as thrombogenicity and stenosis, in managing vascular disease.

Physicochemical properties of polycaprolactone/collagen/elastin nanofibers fabricated by electrospinning

Collagen and elastin are the two most abundant proteins in the human body, and as biomaterials offer fascinating properties to composite materials. More detailed investigations including these biomaterials within reinforced composites are still needed. This report describes physicochemical properties of fibers composed of collagen type I, collagen III, elastin and polycaprolactone (PCL). Prior to the electrospinning process, PCL was functionalized through covalent attachment of -NH₂ groups by aminolysis reaction with hexamentilendiamine. The fibers were fabricated by electrospinning technique set up with a non-conventional collector. A morphological comparative study was developed at different rations of collagen type I, observing in some cases two populations of fibers. The diameters and morphology were analyzed by SEM, observing a wide array of nanostructures with diameters of ~310 to 693nm. Chemical characterization was assessed by FT-IR spectroscopy and the functionalized PCL was characterized through ninhydrin assay resulting in 0.36mM NH₂/mg fiber. Swelling tests were performed for 24h, obtaining 320% for the majority of the fibers indicating morphological stability and good water uptake. In addition, contact angle analysis demonstrated adequate permeability and differences for each system depending mainly upon the type of biopolymer incorporated and the functionalization of PCL, ranging the values from 108° to 17°. Moreover, differential scanning calorimetry results showed a melting temperature (T_m) of ~60°C. The onset degradation temperatures (T_d,onset) ranged between 115 and 148°C, and were obtained by thermogravimetric analysis. The local mechanical properties of individual fibers were quantified by atomic force acoustic microscopy. These results propose that the physicochemical and mechanical properties of these scaffolds offer the possibility for enhanced biological activity Thus, they have a great potential as candidate scaffolds in tissue engineering applications.

In vitro cytotoxicity and antibacterial activity of silver-coated electrospun polycaprolactone/gelatine nanofibrous scaffolds

The development of nano-sized scaffolds with antibacterial properties that mimic the architecture of tissue is one of the challenges in tissue engineering. In this study, polycaprolactone (PCL) and PCL/gelatine (Ge) (70:30) nanofibrous scaffolds were fabricated using a less toxic and common solvent, formic acid and an electrospinning technique. Nanofibrous scaffolds were coated with silver (Ag) in different concentrations of silver nitrate (AgNO₃) aqueous solution (1.25, 2.5, 5, and 10 %) by using dipping method, drying and followed by ultraviolet (UV) photoreduction. The PCL/Ge (70:30) nanofibrous scaffold had an average fibre diameter of 155.60 ± 41.13 nm. Characterization showed that Ag was physically entrapped in both the PCL and PCL/Ge (70:30) nanofibrous scaffolds. Ag⁺ ions release study was performed and showed much lesser release amount than the maximum toxic concentration of Ag⁺ ions in human cells. Both scaffolds were non-toxic to cells and demonstrated antibacterial effects towards Gram-positive Bacillus cereus (B. cereus) and Gram-negative Escherichia coli (E. coli). The Ag/PCL/Ge (70:30) nanofibrous scaffold has potential for tissue engineering as it can protect wounds from bacterial infection and promote tissue regeneration.

Nanofibrous polycaprolactone scaffolds with adhered platelets stimulate proliferation of skin cells

OBJECTIVES

Faulty wound healing is a global healthcare problem. Chronic wounds are generally characterized by a reduction in availability of growth factors. New strategies are being developed to deliver growth factors more effectively.

METHODS

In this study, we introduced electrospun scaffolds composed of polycaprolactone (PCL) nanofibers functionalized with adhered platelets, as a source of numerous growth factors. Three concentrations of platelets were immobilized to nanofibrous scaffolds by simple adhesion, and their influence on adhesion, proliferation and metabolic activity of seeded cells (murine fibroblasts, keratinocytes and melanocytes) was investigated.

RESULTS

The data obtained indicated that presence of platelets significantly promoted cell spreading, proliferation and metabolic activity in all the skin-associated cell types. There were no significant differences among tested concentrations of platelets, thus even the lowest concentration sufficiently promoted proliferation of the seeded cells.

CONCLUSIONS

Such complex stimulation is needed for improved healing of chronic wounds. However, the nanofibrous system can be used not only as a skin cover, but also in broader applications in regenerative medicine.

The preosteoblast response of electrospinning PLGA/PCL nanofibers: effects of biomimetic architecture and collagen I

Constructing biomimetic structure and incorporating bioactive molecules is an effective strategy to achieve a more favorable cell response. To explore the effect of electrospinning (ES) nanofibrous architecture and collagen I (COL I)-incorporated modification on tuning osteoblast response, a resorbable membrane composed of poly(lactic-co-glycolic acid)/poly(caprolactone) (PLGA/PCL; 7:3 w/w) was developed via ES. COL I was blended into PLGA/PCL solution to prepare composite ES membrane. Notably, relatively better cell response was delivered by the bioactive ES-based membrane which was fabricated by modification of 3,4-dihydroxyphenylalanine and COL I. After investigation by field emission scanning electron microscopy, Fourier transform infrared spectroscopy, contact angle measurement, and mechanical test, polyporous three-dimensional nanofibrous structure with low tensile force and the successful integration of COL I was obtained by the ES method. Compared with traditional PLGA/PCL membrane, the surface hydrophilicity of collagen-incorporated membranes was largely enhanced. The behavior of mouse preosteoblast MC3T3-E1 cell infiltration and proliferation on membranes was studied at 24 and 48 hours. The negative control was fabricated by solvent casting. Evaluation of cell adhesion and morphology demonstrated that all the ES membranes were more favorable for promoting the cell adhesion and spreading than the casting membrane. Cell Counting Kit-8 assays revealed that biomimetic architecture, surface topography, and bioactive properties of membranes were favorable for cell growth. Analysis of β1 integrin expression level by immunofluorescence indicated that such biomimetic architecture, especially COL I-grafted surface, plays a key role in cell adhesion and proliferation. The real-time polymerase chain reaction suggested that both surface topography and bioactive properties could facilitate the cell adhesion. The combined effect of biomimetic architecture with enhanced surface activity by 3,4-dihydroxyphenylalanine-assisted modification and COL I incorporation of PLGA/PCL electrospun membranes could successfully fill osteogenic defects and allow for better cell proliferation and differentiation.

A novel 3D bone-mimetic scaffold composed of collagen/MTA/MWCNT modulates cell migration and osteogenesis

AIMS

This study characterized a three-dimensional (3D) biocomposite scaffolds produced using type I collagen, mineral trioxide aggregate (MTA) and multi-walled carbon nanotubes (MWCNT) to be used in bone tissue regeneration.

MAIN METHODS

The scaffolds were analyzed via scanning (SEM) and transmission (TEM) electron microscopy, as well as the viability and migration of osteoblasts and mineralization of the scaffolds.

KEY FINDINGS

SEM and TEM analyses showed that MTA and MWCNT were distributed as both large agglomerates entrapped within the collagen network and as smaller accumulations or individual molecules dispersed throughout the scaffold. Ultrastructural analysis revealed that osteoblastic MC3T3-E1 cells grown in the biocomposite endocytosed MWCNT, which were localized in the cytoplasm and in vesicles. Analysis of cells grown in the 3D scaffolds demonstrated that >95% of the cells remained viable in all tested combinations and concentrations of the biocomposite. MC3T3-E1 osteoblasts migrated into scaffolds formed with concentrations of type I collagen between 1.75 and 3.0mg/mL. Cells displayed increased migration into scaffolds formed with collagen and a range of low to high concentrations of MTA. In contrast, the presence of MWCNT in the biocomposite had a slight negative effect on migration. Collagen gels containing specific concentrations of MTA, or MWCNT, or combinations of MTA/MWCNT, caused an increase in mineralization of scaffolds.

SIGNIFICANCE

Scaffolds composed of defined concentrations of type I collagen, MTA and MWCNT are biocompatible, promote migration and mineralization of osteoblasts, and hence may be useful as bone tissue mimetics.