From design of bio-based biocomposite electrospun scaffolds to osteogenic differentiation of human mesenchymal stromal cells

Design of Collagen and Gelatin-based Electrospun Fibers for Biomedical Purposes: An Overview

Collagen and gelatin are essential natural biopolymers commonly utilized in biomaterials and tissue engineering because of their excellent physicochemical and biocompatibility properties. They can be used either in combination with other biomacromolecules or particles or even exclusively for the enhancement of bone regeneration or for the development of biomimetic scaffolds. Collagen or gelatin derivatives can be transformed into nanofibrous materials with porous micro- or nanostructures and superior mechanical properties and biocompatibility using electrospinning technology. Specific attention was recently paid to electrospun mats of such biopolymers, due to their high ratio of surface area to volume, as well as their biocompatibility, biodegradability, and low immunogenicity. The fiber mats with submicro- and nanometer scale can replicate the extracellular matrix structure of human tissues and organs, making them highly suitable for use in tissue engineering due to their exceptional bioaffinity. The drawbacks may include rapid degradation and complete dissolution in aqueous media. The use of gelatin/collagen electrospun nanofibers in this form is thus greatly restricted for biomedicine. Therefore, the cross-linking of these fibers is necessary for controlling their aqueous solubility. This led to enhanced biological characteristics of the fibers, rendering them excellent options for various biomedical uses. The objective of this review is to highlight the key research related to the electrospinning of collagen and gelatin, as well as their applications in the biomedical field. The review features a detailed examination of the electrospinning fiber mats, showcasing their varying structures and performances resulting from diverse solvents, electrospinning processes, and cross-linking methods. Judiciously selected examples from literature will be presented to demonstrate major advantages of such biofibers. The current developments and difficulties in this area of research are also being addressed.

Physico-Chemical, Mechanical, and Biological Properties of Polylactide/Portulaca oleracea Extract Electrospun Fibers

Electrospinning was used to create fibrous polylactide (PLA) materials loaded with Portulaca oleracea (P. oleracea) plant extract obtained by supercritical carbon dioxide. Morphological, physico-chemical, mechanical, and biological characteristics of the fibers were studied. According to the SEM results, the diameters of smooth and defect-free fibers fabricated by a one-pot electrospinning method were at micron scale. All the obtained materials possess good mechanical properties. Additionally, it was found that the composite fibers exhibited considerable antioxidant activity. The antimicrobial activity of the fibrous materials against Gram-positive and Gram-negative bacteria was determined as well. In vitro studies showed that the electrospun biomaterials had no cytotoxic effects and that the combination of PLA and the P. oleracea extract in the fiber structure promoted cell survival and proliferation of normal mouse fibroblasts. The obtained results reveal that microfibrous mats containing the polyester-PLA and the plant extract-P. oleracea can be suitable for applications in wound healing.

Multifunctional Scaffolds Based on Emulsion and Coaxial Electrospinning Incorporation of Hydroxyapatite for Bone Tissue Regeneration

Tissue engineering is nowadays a powerful tool to restore damaged tissues and recover their normal functionality. Advantages over other current methods are well established, although a continuous evolution is still necessary to improve the final performance and the range of applications. Trends are nowadays focused on the development of multifunctional scaffolds with hierarchical structures and the capability to render a sustained delivery of bioactive molecules under an appropriate stimulus. Nanocomposites incorporating hydroxyapatite nanoparticles (HAp NPs) have a predominant role in bone tissue regeneration due to their high capacity to enhance osteoinduction, osteoconduction, and osteointegration, as well as their encapsulation efficiency and protection capability of bioactive agents. Selection of appropriated polymeric matrices is fundamental and consequently great efforts have been invested to increase the range of properties of available materials through copolymerization, blending, or combining structures constituted by different materials. Scaffolds can be obtained from different processes that differ in characteristics, such as texture or porosity. Probably, electrospinning has the greater relevance, since the obtained nanofiber membranes have a great similarity with the extracellular matrix and, in addition, they can easily incorporate functional and bioactive compounds. Coaxial and emulsion electrospinning processes appear ideal to generate complex systems able to incorporate highly different agents. The present review is mainly focused on the recent works performed with Hap-loaded scaffolds having at least one structural layer composed of core/shell nanofibers.

Methods to Characterize Electrospun Scaffold Morphology: A Critical Review

Electrospun scaffolds can imitate the hierarchical structures present in the extracellular matrix, representing one of the main concerns of modern tissue engineering. They are characterized in order to evaluate their capability to support cells or to provide guidelines for reproducibility. The issues with widely used methods for morphological characterization are discussed in order to provide insight into a desirable methodology for electrospun scaffold characterization. Reported methods include imaging and physical measurements. Characterization methods harbor inherent limitations and benefits, and these are discussed and presented in a comprehensive selection matrix to provide researchers with the adequate tools and insights required to characterize their electrospun scaffolds. It is shown that imaging methods present the most benefits, with drawbacks being limited to required costs and expertise. By making use of more appropriate characterization, researchers will avoid measurements that do not represent their scaffolds and perhaps might discover that they can extract more characteristics from their scaffold at no further cost.

Metronidazole Topically Immobilized Electrospun Nanofibrous Scaffold: Novel Secondary Intention Wound Healing Accelerator

The process of secondary intention wound healing includes long repair and healing time. Electrospun nanofibrous scaffolds have shown potential for wound dressing. Biopolymers have gained much attention due to their remarkable characteristics such as biodegradability, biocompatibility, non-immunogenicity and nontoxicity. This study anticipated to develop a new composite metronidazole (MTZ) immobilized nanofibrous scaffold based on poly (3-hydroxy butyrate) (PHB) and Gelatin (Gel) to be utilized as a novel secondary intention wound healing accelerator. Herein, PHB and Gel were mixed together at different weight ratios to prepare polymer solutions with final concentration of (7%), loaded with two different concentrations 5% (Z₁) and 10% (Z₂) of MTZ. Nanofibrous scaffolds were obtained by manipulating electrospinning technique. The properties of MTZ immobilized PHB/Gel nanofibrous scaffold were evaluated (SEM, FTIR, TGA, water uptake, contact angle, porosity, mechanical properties and antibacterial activity). Additionally, in vitro cytocompatibility of the obtained nanofibrous scaffolds were assessed by using the cell counting kit-8 (CCK-8 assay). Moreover, in vivo wound healing experiments revealed that the prepared nanofibrous scaffold highly augmented the transforming growth factor (TGF-β) signaling pathway, moderately suppressed the pro-inflammatory cytokine (IL-6). These results indicate that MTZ immobilized PHB/Gel nanofibrous scaffold significantly boost accelerating secondary intention wound healing.

Microbial-Derived Polyhydroxyalkanoate-Based Scaffolds for Bone Tissue Engineering: Biosynthesis, Properties, and Perspectives

Polyhydroxyalkanoates (PHAs) are a class of structurally diverse natural biopolyesters, synthesized by various microbes under unbalanced culture conditions. PHAs as biomedical materials have been fabricated in various forms to apply to tissue engineering for the past years due to their excellent biodegradability, inherent biocompatibility, modifiable mechanical properties, and thermo-processability. However, there remain some bottlenecks in terms of PHA production on a large scale, the purification process, mechanical properties, and biodegradability of PHA, which need to be further resolved. Therefore, scientists are making great efforts via synthetic biology and metabolic engineering tools to improve the properties and the product yields of PHA at a lower cost for the development of various PHA-based scaffold fabrication technologies to widen biomedical applications, especially in bone tissue engineering. This review aims to outline the biosynthesis, structures, properties, and the bone tissue engineering applications of PHA scaffolds with different manufacturing technologies. The latest advances will provide an insight into future outlooks in PHA-based scaffolds for bone tissue engineering.

Review of Hybrid Materials Based on Polyhydroxyalkanoates for Tissue Engineering Applications

This review is focused on hybrid polyhydroxyalkanoate-based (PHA) biomaterials with improved physico-mechanical, chemical, and piezoelectric properties and controlled biodegradation rate for applications in bone, cartilage, nerve and skin tissue engineering. PHAs are polyesters produced by a wide range of bacteria under unbalanced growth conditions. They are biodegradable, biocompatible, and piezoelectric polymers, which make them very attractive biomaterials for various biomedical applications. As naturally derived materials, PHAs have been used for multiple cell and tissue engineering applications; however, their widespread biomedical applications are limited due to their lack of toughness, elasticity, hydrophilicity and bioactivity. The chemical structure of PHAs allows them to combine with other polymers or inorganic materials to form hybrid composites with improved structural and functional properties. Their type (films, fibers, and 3D printed scaffolds) and properties can be tailored with fabrication methods and materials used as fillers. Here, we are aiming to fill in a gap in literature, revealing an up-to-date overview of ongoing research strategies that make use of PHAs as versatile and prospective biomaterials. In this work, a systematic and detailed review of works investigating PHA-based hybrid materials with tailored properties and performance for use in tissue engineering applications is carried out. A literature survey revealed that PHA-based composites have better performance for use in tissue regeneration applications than pure PHA.

Scaffolds from Self-Assembling Tetrapeptides Support 3D Spreading, Osteogenic Differentiation, and Angiogenesis of Mesenchymal Stem Cells

The apparent rise of bone disorders demands advanced treatment protocols involving tissue engineering. Here, we describe self-assembling tetrapeptide scaffolds for the growth and osteogenic differentiation of human mesenchymal stem cells (hMSCs). The rationally designed peptides are synthetic amphiphilic self-assembling peptides composed of four amino acids that are nontoxic. These tetrapeptides can quickly solidify to nanofibrous hydrogels that resemble the extracellular matrix and provide a three-dimensional (3D) environment for cells with suitable mechanical properties. Furthermore, we can easily tune the stiffness of these peptide hydrogels by just increasing the peptide concentration, thus providing a wide range of peptide hydrogels with different stiffnesses for 3D cell culture applications. Since successful bone regeneration requires both osteogenesis and vascularization, our scaffold was found to be able to promote angiogenesis of human umbilical vein endothelial cells (HUVECs) in vitro. The results presented suggest that ultrashort peptide hydrogels are promising candidates for applications in bone tissue engineering.

Biomedical applications of environmental friendly poly-hydroxyalkanoates

Biological polyesters of hydroxyacids are known as polyhydroxyalkanoates (PHA). They have proved to be an alternative, environmentally friendly and attractive candidate for the replacement of petroleum-based plastics in many applications. Many bacteria synthesize these compounds as an intracellular carbon and energy compound usually under unbalanced growth conditions. Biodegradability and biocompatibility of different PHA has been studied in cell culture systems or in an animal host during the last few decades. Such investigations have proposed that PHA can be used as biomaterials for applications in conventional medical devices such as sutures, patches, meshes, implants, and tissue engineering scaffolds as well. Moreover, findings related to encapsulation capability and degradation kinetics of some PHA polymers has paved their way for development of controlled drug delivery systems. The present review discusses about bio-plastics, their characteristics, examines the key findings and recent advances highlighting the usage of bio-plastics in different medical devices. The patents concerning to PHA application in biomedical field have been also enlisted that will provide a brief overview of the status of research in bio-plastic. This would help medical researchers and practitioners to replace the synthetic plastics aids that are currently being used. Simultaneously, it could also prove to be a strong step in reducing the plastic pollution that surged abruptly due to the COVID-19 medical waste.

Poly(3-hydroxybutyrate): Promising biomaterial for bone tissue engineering

Poly(3-hydroxybutyrate) is a natural polymer, produced by different bacteria, with good biocompatibility and biodegradability. Cardiovascular patches, scaffolds in tissue engineering and drug carriers are some of the possible biomedical applications of poly(3-hydroxybutyrate). In the past decade, many researchers examined the different physico-chemical modifications of poly(3-hydroxybutyrate) in order to improve its properties for use in the field of bone tissue engineering. Poly(3-hydroxybutyrate) composites with hydroxyapatite and bioglass are intensively tested with animal and human osteoblasts in vitro to provide information about their biocompatibility, biodegradability and osteoinductivity. Good bone regeneration was proven when poly(3-hydroxy-butyrate) patches were implanted in vivo in bone tissue of cats, minipigs and rats. This review summarizes the recent reports of in vitro and in vivo studies of pure poly(3-hydroxy-butyrate) and poly(3-hydroxybutyrate) composites with the emphasis on their bioactivity and biocompatibility with bone cells.

Biomedical Processing of Polyhydroxyalkanoates

The rapidly growing interest on polyhydroxyalkanoates (PHA) processing for biomedical purposes is justified by the unique combinations of characteristics of this class of polymers in terms of biocompatibility, biodegradability, processing properties, and mechanical behavior, as well as by their great potential for sustainable production. This article aims at overviewing the most exploited processing approaches employed in the biomedical area to fabricate devices and other medical products based on PHA for experimental and commercial applications. For this purpose, physical and processing properties of PHA are discussed in relationship to the requirements of conventionally-employed processing techniques (e.g., solvent casting and melt-spinning), as well as more advanced fabrication approaches (i.e., electrospinning and additive manufacturing). Key scientific investigations published in literature regarding different aspects involved in the processing of PHA homo- and copolymers, such as poly(3-hydroxybutyrate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate), and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), are critically reviewed.

Comparison of 2D and 3D cell culture models for cell growth, gene expression and drug resistance

In vitro drug screening is widely used in the development of new drugs, because they constitute a cost-effective approach to select compounds with more potential for therapy. They are also an attractive alternative to in vivo testing. However, most of these assays are done in two-dimensional culture models, where cells are grown on a polystyrene or glass flat surface. In order to develop in vitro models that would more closely resemble physiological conditions, three-dimensional models have been developed. Here, we introduce two novel fully synthetic scaffolds produced using the polymer polyhydroxybutyrate (PHB): a Solvent-Casting Particle-Leaching (SCPL) membrane; and an electrospun membrane, to be used for 3D cultures of B16 F10 murine melanoma cells and 4T1 murine breast cancer cells. A 2D cell culture system in regular tissue culture plates and a classical 3D model where cells are grown on a commercially available gel derived from Engelbreth-Holm Swarm (EHS) tumor were used for comparison with the synthetic scaffolds. Cells were also collected from in vivo tumors grown as grafts in syngeneic mice. Morphology, cell viability, response to chemotherapy and gene expression analysis were used to compare all systems. In the electrospun membrane model, cells were grown on nanometer-scale fibers and in the SCPL membrane, which provides a foam-like structure for cell growth, pore sizes varied. Cells grown on all 3D models were able to form aggregates and spheroids, allowing for increased cell-cell contact when compared with the 2D system. Cell morphology was also more similar between 3D systems and cells collected from the in vivo tumors. Cells grown in 3D models showed an increase in resistance to dacarbazine, and cisplatin. Gene expression analysis also revealed similarities among all 3D platforms. The similarities between the two synthetic systems to the classic EHS gel model highlight their potential application as cost effective substitutes in drug screening, in which fully synthetic models could represent a step towards higher reproducibility. We conclude PHB synthetic membranes offer a valuable alternative for 3D cultures.

Advanced Therapy Medicinal Products: A Guide for Bone Marrow-derived MSC Application in Bone and Cartilage Tissue Engineering

Millions of people worldwide suffer from trauma- or age-related orthopedic diseases such as osteoarthritis, osteoporosis, or cancer. Tissue Engineering (TE) and Regenerative Medicine are multidisciplinary fields focusing on the development of artificial organs, biomimetic engineered tissues, and cells to restore or maintain tissue and organ function. While allogenic and future autologous transplantations are nowadays the gold standards for both cartilage and bone defect repair, they are both subject to important limitations such as availability of healthy tissue, donor site morbidity, and graft rejection. Tissue engineered bone and cartilage products represent a promising and alternative approach with the potential to overcome these limitations. Since the development of Advanced Therapy Medicinal Products (ATMPs) such as TE products requires the knowledge of diverse regulation and an extensive communication with the national/international authorities, the aim of this review is therefore to summarize the state of the art on the clinical applications of human bone marrow-derived stromal cells for cartilage and bone TE. In addition, this review provides an overview of the European legislation to facilitate the development and commercialization of new ATMPs.

Enhanced Differentiation of Human Preosteoblasts on Electrospun Blend Fiber Mats of Polydioxanone and Anionic Sulfated Polysaccharides

The viability and differentiation of SaOS-2 preosteoblasts on fiber mats of blends comprising of the biodegradable poly(ester-ether) polydioxanone (PDX) and the sulfate-containing anionic polysaccharides kappa-carrageenan (KCG) and fucoidan (FUC) were investigated for a range of different blend compositions. The detailed analysis of the blend nanofiber properties revealed a different degree of miscibility of PDX and the polysaccharide leading to a different enrichment at the surface of the blend nanofibers, which were observed to be stable in phosphate buffer solution (PBS) for up to 5 weeks. The fibrous mats of PDX/FUC led to the highest osteogenic differentiation with very good cell viability. The electrospun blend fibers also supported human-induced pluripotent stem (iPS) cells and iPS cell-derived embryoid bodies with high cell viability, which underlines the potential of these novel blend fiber systems for optimized performance in bone tissue engineering applications.

κ-Carrageenan Enhances the Biomineralization and Osteogenic Differentiation of Electrospun Polyhydroxybutyrate and Polyhydroxybutyrate Valerate Fibers

Novel electrospun materials for bone tissue engineering were obtained by blending biodegradable polyhydroxybutyrate (PHB) or polyhydroxybutyrate valerate (PHBV) with the anionic sulfated polysaccharide κ-carrageenan (κ-CG) in varying ratios. In both systems, the two components phase separated as shown by FTIR, DSC and TGA. According to the contact angle data, κ-CG was localized preferentially at the fiber surface in PHBV/κ-CG blends in contrast to PHB/κ-CG, where the biopolymer was mostly found within the fiber. In contrast to the neat polyester fibers, the blends led to the formation of much smaller apatite crystals (800 nm vs 7 μm). According to the MTT assay, NIH3T3 cells grew in higher density on the blend mats in comparison to neat polyester mats. The osteogenic differentiation potential of the fibers was determined by SaOS-2 cell culture for 2 weeks. Alizarin red-S staining suggested an improved mineralization on the blend fibers. Thus, PHBV/κ-CG fibers resulted in more pronounced bioactive and osteogenic properties, including fast apatite-forming ability and deposition of nanosized apatite crystals.

Third generation poly(hydroxyacid) composite scaffolds for tissue engineering

Bone tissue engineering based on scaffolds is quite a complex process as a whole gamut of criteria needs to be satisfied to promote cellular attachment, proliferation and differentiation: biocompatibility, right surface properties, adequate mechanical performance, controlled bioresorbability, osteoconductivity, angiogenic cues, and vascularization. Third generation scaffolds are more of composite types to maximize biological-mechanical-chemical properties. In the present review, our focus is on the performance of micro-organism-derived polyhydroxyalkanoates (PHAs)-polyhydroxybutyrate (PHB) and polyhydroxybutyrate-co-valerate (PHBV)-composite scaffolds with ceramics and natural polymers for tissue engineering applications with emphasis on bone tissue. We particularly emphasize on how material properties of the composites affect scaffold performance. PHA-based composites have demonstrated their biocompatibility with a range of tissues and their capacity to induce osteogenesis due to their piezoelectric properties. Electrospun PHB/PHBV fiber mesh in combination with human adipose tissue-derived stem cells (hASCs) were shown to improve vascularization in engineered bone tissues. For nerve and skin tissue engineering applications, natural polymers such as collagen and chitosan remain the gold standard but there is scope for development of scaffolds combining PHAs with other natural polymers which can address some of the limitations such as brittleness, lack of bioactivity and slow degradation rate presented by the latter. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 1667-1684, 2017.

Safety of bioabsorbable implants in vitro

Background

The aim of the present study was to investigate the safety of bioabsorbable plates and screws in humans.

Methods

For this purpose, an implant system based on [poly(lactic-co-glycolic acids)(85:15)] was designed. The system was tested for pH, temperature, and swelling and then its surface morphology was analyzed for surface porosity using environmental electron microscopy. Then, the effects of this bioabsorbable system on the viability and profileration of osteocytes were examined on a molecular level via in vitro experiments. A [poly(lactic-co-glycolic acids)(90:10)] bioabsorbable implant, which is commercially available and used in orthopedic surgery, was used as control group. For the statistical evaluation of the data obtained in the present study, the groups were compared by Tukey HSD test following ANOVA. The significance level was set as p < 0.05.

Results

It was observed that the osteocytes cultivated on the PLGA system designed in the present study included more live cells and allowed more proliferation compared to the control.

Conclusion

One of the criteria in the selection of implants for orthopedic surgery is that a good implant should not need removal and thus a second surgery. In the present study, a bioabsorbable implant was designed considering this criterion. The present study is the first step to prove the safety of this new design by in vitro toxicity and viability experiments.

Controlled release of drugs in electrosprayed nanoparticles for bone tissue engineering

Generating porous topographic substrates, by mimicking the native extracellular matrix (ECM) to promote the regeneration of damaged bone tissues, is a challenging process. Generally, scaffolds developed for bone tissue regeneration support bone cell growth and induce bone-forming cells by natural proteins and growth factors. Limitations are often associated with these approaches such as improper scaffold stability, and insufficient cell adhesion, proliferation, differentiation, and mineralization with less growth factor expression. Therefore, the use of engineered nanoparticles has been rapidly increasing in bone tissue engineering (BTE) applications. The electrospray technique is advantageous over other conventional methods as it generates nanomaterials of particle sizes in the micro/nanoscale range. The size and charge of the particles are controlled by regulating the polymer solution flow rate and electric voltage. The unique properties of nanoparticles such as large surface area-to-volume ratio, small size, and higher reactivity make them promising candidates in the field of biomedical engineering. These nanomaterials are extensively used as therapeutic agents and for drug delivery, mimicking ECM, and restoring and improving the functions of damaged organs. The controlled and sustained release of encapsulated drugs, proteins, vaccines, growth factors, cells, and nucleotides from nanoparticles has been well developed in nanomedicine. This review provides an insight into the preparation of nanoparticles by electrospraying technique and illustrates the use of nanoparticles in drug delivery for promoting bone tissue regeneration.

Recent Advances in Hydroxyapatite Scaffolds Containing Mesenchymal Stem Cells

Modern day tissue engineering and cellular therapies have gravitated toward using stem cells with scaffolds as a dynamic modality to aid in differentiation and tissue regeneration. Mesenchymal stem cells (MSCs) are one of the most studied stem cells used in combination with scaffolds. These cells differentiate along the osteogenic lineage when seeded on hydroxyapatite containing scaffolds and can be used as a therapeutic option to regenerate various tissues. In recent years, the combination of hydroxyapatite and natural or synthetic polymers has been studied extensively. Due to the interest in these scaffolds, this review will cover the wide range of hydroxyapatite containing scaffolds used with MSCs for in vitro and in vivo experiments. Further, in order to maintain a progressive scope of the field this review article will only focus on literature utilizing adult human derived MSCs (hMSCs) published in the last three years.

Graphene oxide nanoflakes incorporated gelatin-hydroxyapatite scaffolds enhance osteogenic differentiation of human mesenchymal stem cells

In this study, graphene oxide (GO) nanoflakes (0.5 and 1 wt%) were incorporated into a gelatin-hydroxyapatite (GHA) matrix through a freeze drying technique and its effect to enhance mechanical strength and osteogenic differentiation was studied. The GHA matrix with GO demonstrated less brittleness in comparison to GHA scaffolds. There was no significant difference in mechanical strength between GOGHA0.5 and GOGHA1.0 scaffolds. When the scaffolds were immersed in phosphate buffered saline (to mimic physiologic condition) for 60 days, around 50-60% of GO was released in sustained and linear manner and the concentration was within the toxicity limit as reported earlier. Further, GOGHA0.5 scaffolds were continued for cell culture experiments, wherein the scaffold induced osteogenic differentiation of human adipose derived mesenchymal stem cells without providing supplements like dexamethasone, L-ascorbic acid and β glycerophosphate in the medium. The level of osteogenic differentiation of stem cells was comparable to those cultured on GHA scaffolds with osteogenic supplements. Thus biocompatible, biodegradable and porous GO reinforced gelatin-HA 3D scaffolds may serve as a suitable candidate in promoting bone regeneration in orthopaedics.