Electrospun P34HB fibres: a scaffold for tissue engineering

Metabolically activated energetic materials mediate cellular anabolism for bone regeneration

The understanding of cellular energy metabolism activation by engineered scaffolds remains limited, posing challenges for therapeutic applications in tissue regeneration. This study presents biosynthesized poly(3-hydroxybutyrate-co-4-hydroxybutyrate) [P(3HB-co-4HB)] and its major degradation product, 3-hydroxybutyrate (3HB), as endogenous bioenergetic fuels that augment cellular anabolism, thereby facilitating the progression of human bone marrow-derived mesenchymal stem cells (hBMSCs) towards osteoblastogenesis. Our research demonstrated that 3HB markedly boosts in vitro ATP production, elevating mitochondrial membrane potential and capillary-like tube formation. Additionally, it raises citrate levels in the tricarboxylic acid (TCA) cycle, facilitating the synthesis of citrate-containing apatite during hBMSCs osteogenesis. Furthermore, 3HB administration significantly increased bone mass in rats with osteoporosis induced by ovariectomy. The findings also showed that P(3HB-co-4HB) scaffold substantially enhances long-term vascularized bone regeneration in rat cranial defect models. These findings reveal a previously unknown role of 3HB in promoting osteogenesis of hBMSCs and highlight the metabolic activation of P(3HB-co-4HB) scaffold for bone regeneration.

Engineering an oleic acid-induced system for Halomonas, E. coli and Pseudomonas

Ligand-induced system plays an important role for microbial engineering due to its tunable gene expression control over timings and levels. An oleic acid (OA)-induced system was recently constructed based on protein FadR, a transcriptional regulator involved in fatty acids metabolism, for metabolic control in Escherichia coli. In this study, we constructed a synthetic FadR-based OA-induced systems in Halomonas bluephagenesis by hybridizing the porin promoter core region and FadR-binding operator (fadO). The dynamic control range was optimized over 150-fold, and expression leakage was significantly reduced by tuning FadR expression and positioning fadO, forming a series of OA-induced systems with various expression strengths, respectively. Additionally, ligand orthogonality and cross-species portability were also studied and showed highly linear correlation among Halomonas spp., Escherichia coli and Pseudomonas spp. Finally, OA-induced systems with medium- and small-dynamic control ranges were employed to dynamically control the expression levels of morphology associated gene minCD, and monomer precursor 4-hydroxybutyrate-CoA (4HB-CoA) synthesis pathway for polyhydroxyalkanoates (PHA), respectively, in the presence of oleic acid as an inducer. As a result, over 10 g/L of poly-3-hydroxybutyrate (PHB) accumulated by elongated cell sizes, and 6 g/L of P(3HB-co-9.57 mol% 4HB) were obtained by controlling the dose and induction time of oleic acid only. This study provides a systematic approach for ligand-induced system engineering, and demonstrates an alternative genetic tool for dynamic control of industrial biotechnology.

Electrospun porous poly(3-hydroxybutyrate-co-4-hydroxybutyrate)/lecithin scaffold for bone tissue engineering

Bone tissue engineering has emerged as a promising restorative strategy for bone reconstruction and bone defect repair. It is challenging to establish an appropriate scaffold with an excellent porous microstructure for bone defects and thereby promote bone repair. In this study, electrospinning as a simple and efficient technology was employed to fabricate a porous poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P34HB) scaffold coated with lecithin. The morphology, phase composition, and physical properties of the electrospun P34HB/lec scaffold were characterized. Meanwhile, cellular behaviors of bone marrow mesenchymal stem cells (BMSCs), including proliferation, adhesion, migration, osteogenic differentiation, and related gene expression, were also investigated. Finally, a rat subcutaneous implant model and a calvarial defect model were used to evaluated the biocompatibility and effect of these scaffolds on bone repair, respectively. The in vitro results demonstrated that these electrospun fibers were interwoven with each other to form the porous P34HB/lec scaffold and the addition of lecithin improved the hydrophilicity of the pure P34HB scaffold, enhanced the efficiency of cell migration, and decreased inflammatory response. Furthermore, the in vivo results showed that P34HB/lec scaffold had excellent biocompatibility, improved the vascularization, and promoted the bone regeneration. All these results indicated that nanofibers of P34HB scaffolds in combination with the lecithin could exert a synergistic effect on promoting osteogenesis and regeneration of bone defects; thus, the P34HB scaffold with lecithin showed great application potential for bone tissue engineering.

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.

Fabrication and Characterization of the Core-Shell Structure of Poly(3-Hydroxybutyrate-4-Hydroxybutyrate) Nanofiber Scaffolds

Tissue engineering scaffolds with nanofibrous structures provide positive support for cell proliferation and differentiation in biomedical fields. These scaffolds are widely used for defective tissue repair and drug delivery. However, the degradation performance and mechanical properties of scaffolds are often unsatisfactory. Here, we successfully prepared a novel poly(3-hydroxybutyrate-4-hydroxybutyrate)/polypyrrole (P34HB-PPy) core-shell nanofiber structure scaffold with electrospinning and in situ surface polymerization technology. The obtained composite scaffold showed good mechanical properties, hydrophilicity, and thermal stability based on the universal material testing machine, contact angle measuring system, thermogravimetric analyzer, and other methods. The results of the in vitro bone marrow-derived mesenchymal stem cells (BMSCs) culture showed that the P34HB-PPy composite scaffold effectively mimicked the extracellular matrix (ECM) and exhibited good cell retention and proliferative capacity. More importantly, P34HB is a controllable degradable polyester material, and its degradation product 3-hydroxybutyric acid (3-HB) is an energy metabolite that can promote cell growth and proliferation. These results strongly support the application potential of P34HB-PPy composite scaffolds in biomedical fields, such as tissue engineering and soft tissue repair.

An easy long-acting BMP7 release system based on biopolymer nanoparticles for inducing osteogenic differentiation of adipose mesenchymal stem cells

In contrast to the early acting bone morphogenetic protein 2, bone morphogenetic protein 7 (BMP7) plays a decisive role mainly in the late stages of bone formation. To overcome deactivation and degradation of expensive BMP7, we designed a novel long-acting BMP7 release system based on poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P34HB) nanoparticles to enable the induction of osteogenic differentiation in human adipose mesenchymal stem cells (ADSCs). In order to improve the encapsulation efficiency of BMP7 and avoid damage by organic solvents, BMP7 was modified and protected using the biosurfactant soybean lecithin. In an in vitro test, BMP7-soybean lecithin-P34HB nanoparticles (BMP7-SPNPs) showed a short initial burst of BMP7 release during the first 24h, followed by a steady increase to a cumulative 80% release in 20days. Compared with the rapid release of control P34HB nanoparticles without soybean phospholipids loaded with BMP7 without soybean lecithin, BMP7-SPNPs significantly reduced the initial burst of BMP7 release and stabilized the content of BMP7 to allow long-term osteogenic differentiation during the late phase of bone development. Human ADSCs treated with BMP7-SPNPs showed higher alkaline phosphatase activity and higher expression levels of genetic markers of osteogenic differentiation compared with the control group. Thus, the results indicate that BMP7-SPNPs can be used as a rapid and long-acting BMP7 delivery system for osteogenic differentiation.

Polyhydroxyalkanoate (PHA): applications in drug delivery and tissue engineering

INTRODUCTION

The applications of naturally obtained polymers are tremendously increased due to them being biocompatible, biodegradable, environmentally friendly and renewable in nature. Among them, polyhydroxyalkanoates are widely studied and they can be utilized in many areas of human life research such as drug delivery, tissue engineering, and other medical applications.

AREAS COVERED

This review provides an overview of the polyhydroxyalkanoates biosynthesis and their possible applications in drug delivery in the range of micro- and nano-size. Moreover, the possible applications in tissue engineering are covered considering macro- and microporous scaffolds and extracellular matrix analogs.

EXPERT COMMENTARY

The majority of synthetic plastics are non-biodegradable so, in the last years, a renewed interest is growing to develop alternative processes to produce biologically derived polymers. Among them, PHAs present good properties such as high immunotolerance, low toxicity, biodegradability, so, they are promisingly using as biomaterials in biomedical applications.

P34HB electrospun fibres promote bone regeneration in vivo

OBJECTIVE

Bone tissue engineering was introduced in 1995 and provides a new way to reconstruct bone and repair bone defects. However, the design and fabrication of suitable bionic bone scaffolds are still challenging, and the ideal scaffolds in bone tissue engineering should have a three-dimensional porous network, good biocompatibility, excellent biodegradability and so on. The purpose of our research was to investigate whether a bioplasticpoly3-hydroxybutyrate4-hydroxybutyrate (P34HB) electrospun fibre scaffold is conducive to the repair of bone defects, and whether it is a potential scaffold for bone tissue engineering.

MATERIALS AND METHODS

The P34HB electrospun fibre scaffolds were prepared by electrospinning technology, and the surface morphology, hydrophilicity, mechanical properties and cytological behaviour of the scaffolds were tested. Furthermore, a calvarial defect model was created in rats, and through layer-by-layer paper-stacking technology, the P34HB electrospun fibre scaffolds were implanted into the calvarial defect area and their effect on bone repair was evaluated.

RESULTS

The results showed that the P34HB electrospun fibre scaffolds are interwoven with several fibres and have good porosity, physical properties and chemical properties and can promote cell adhesion and proliferation with no cytotoxicity in vitro. In addition, the P34HB electrospun fibre scaffolds can promote the repair of calvarial defects in vivo.

CONCLUSIONS

These results demonstrated that the P34HB electrospun fibre scaffold has a three-dimensional porous network with good biocompatibility, excellent biosafety and ability for bone regeneration and repair; thus, the P34HB electrospun fibre scaffold is a potential scaffold for bone tissue engineering.

Engineering of Halomonas bluephagenesis for low cost production of poly(3-hydroxybutyrate-co-4-hydroxybutyrate) from glucose

Poly(3-hydroxybutyrate-co-4-hydroxybutyrate) [P(3HB-co-4HB)] is one of the most promising biomaterials expected to be used in a wide range of scenarios. However, its large-scale production is still hindered by the high cost. Here we report the engineering of Halomonas bluephagenesis as a low-cost platform for non-sterile and continuous fermentative production of P(3HB-co-4HB) from glucose. Two interrelated 4-hydroxybutyrate (4HB) biosynthesis pathways were constructed to guarantee 4HB monomer supply for P(3HB-co-4HB) synthesis by working in concert with 3-hydroxybutyrate (3HB) pathway. Interestingly, only 0.17 mol% 4HB in the copolymer was obtained during shake flask studies. Pathway debugging using structurally related carbon source located the failure as insufficient 4HB accumulation. Further whole genome sequencing and comparative genomic analysis identified multiple orthologs of succinate semialdehyde dehydrogenase (gabD) that may compete with 4HB synthesis flux in H. bluephagenesis. Accordingly, combinatory gene-knockout strains were constructed and characterized, through which the molar fraction of 4HB was increased by 24-fold in shake flask studies. The best-performing strain was grown on glucose as the single carbon source for 60 h under non-sterile conditions in a 7-L bioreactor, reaching 26.3 g/L of dry cell mass containing 60.5% P(3HB-co-17.04 mol%4HB). Besides, 4HB molar fraction in the copolymer can be tuned from 13 mol% to 25 mol% by controlling the residual glucose concentration in the cultures. This is the first study to achieve the production of P(3HB-co-4HB) from only glucose using Halomonas.

PCL-PEG-PCL film promotes cartilage regeneration in vivo

OBJECTIVE

Management of chondral defects has long been a challenge due to poor self-healing capacity of articular cartilage. Many approaches, ranging from symptomatic treatment to structural cartilage regeneration, have obtained very limited satisfactory results. Cartilage tissue engineering, which involves optimized combination of novel scaffolds, cell sources and growth factors, has emerged as a promising strategy for cartilage regeneration and repair. In this study, the aim was to investigate the role of poly(ε-caprolactone)-poly(ethylene glycol)-poly(ε-caprolactone) (PCL-PEG-PCL, PCEC) PCEC scaffold in cartilage repair.

MATERIALS AND METHODS

First, PCEC film was fabricated, and its characteristics were tested using SEM and AFM. Cell (rASC - rat adipose-derived stem cells, and mASCs - green fluorescent mouse adipose-derived stem cells) morphologies on PCEC film were observed using SEM and fluorescence microscopy, after cell seeding. Tests of cell viability on PCEC film were conducted using the CCK-8 assay. Furthermore, full cartilage defects in rats were created, and PCEC films were implanted, to evaluate their healing effects, over 8 weeks.

RESULTS

It was found that PCEC film, as a biomaterial implant, possessed good in vitro properties for cell adhesion, migration and proliferation. Importantly, in the in vivo experiment, PCEC film exhibited desirable healing outcomes.

CONCLUSIONS

These results demonstrated that PCEC film was a good scaffold for cartilage tissue engineering for improving cell proliferation and adhesion and could lead to excellent repair of cartilage defects.

Novel Poly(3-hydroxybutyrate-g-vinyl alcohol) Polyurethane Scaffold for Tissue Engineering

The design of new synthetic grafted poly(3-hydroxybutyrate) as composite 3D-scaffolds is a convenient alternative for tissue engineering applications. The chemically modified poly(3-hydroxybutyrate) is receiving increasing attention for use as biomimetic copolymers for cell growth. As of yet, these copolymers cannot be used efficiently because of the lack of good mechanical properties. Here, we address this challenge, preparing a composite-scaffold of grafted poly(3-hydroxybutyrate) polyurethane for the first time. However, it is unclear if the composite structure and morphology can also offer a biological application. We obtained the polyurethane by mixing a polyester hydroxylated resin with polyisocyanate and the modified polyhydroxyalkanoates. The results show that the poly(3-hydroxybutyrate) grafted with poly(vinyl alcohol) can be successfully used as a chain extender to form a chemically-crosslinked thermosetting polymer. Furthermore, we show a proposal for the mechanism of the polyurethane synthesis, the analysis of its morphology and the ability of the scaffolds for growing mammalian cells. We demonstrated that astrocytes isolated from mouse cerebellum, and HEK293 can be cultured in the prepared material, and express efficiently fluorescent proteins by adenoviral transduction. We also tested the metabolism of Ca(2+) to obtain evidence of the biological activity.

Repair of liver mediated by adult mouse liver neuro-glia antigen 2-positive progenitor cell transplantation in a mouse model of cirrhosis

NG2-expressing cells are a population of periportal vascular stem/progenitors (MLpvNG2(+) cells) that were isolated from healthy adult mouse liver by using a "Percoll-Plate-Wait" procedure. We demonstrated that isolated cells are able to restore liver function after transplantation into a cirrhotic liver, and co-localized with the pericyte marker (immunohistochemistry: PDGFR-β) and CK19. Cells were positive for: stem cell (Sca-1, CD133, Dlk) and liver stem cell markers (EpCAM, CD14, CD24, CD49f); and negative for: hematopoietic (CD34, CD45) and endothelial markers (CD31, vWf, von Willebrand factor). Cells were transplanted (1 × 10(6) cells) in mice with diethylnitrosamine-induced cirrhosis at week 6. Cells showed increased hepatic associated gene expression of alpha-fetoprotein (AFP), Albumin (Alb), Glucose-6-phosphatase (G6Pc), SRY (sex determining region Y)-box 9 (Sox9), hepatic nuclear factors (HNF1a, HNF1β, HNF3β, HNF4α, HNF6, Epithelial cell adhesion molecule (EpCAM), Leucine-rich repeated-containing G-protein coupled receptor 5-positive (Lgr5) and Tyrosine aminotransferase (TAT). Cells showed decreased fibrogenesis, hepatic stellate cell infiltration, Kupffer cells and inflammatory cytokines. Liver function markers improved. In a cirrhotic liver environment, cells could differentiate into hepatic lineages. In addition, grafted MLpvNG2(+) cells could mobilize endogenous stem/progenitors to participate in liver repair. These results suggest that MLpvNG2(+) cells may be novel adult liver progenitors that participate in liver regeneration.

Crosstalk between adipose-derived stem cells and chondrocytes: when growth factors matter

Adipose-derived stem cells (ASCs) and mesenchymal stem cells are promising for tissue repair because of their multilineage differentiation capacity. Our previous data confirmed that the implantation of mixed ASCs and chondrocytes into cartilage defects induced desirable in vivo healing outcomes. However, the paracrine action of ASCs on chondrocytes needs to be further elucidated. In this study, we established a co-culture system to achieve cell-to-cell and cell-to-tissue crosstalk and explored the soluble growth factors in both ASCs and chondrocytes supplemented with 1% fetal bovine serum to mimic the physiological microenvironment. In ASCs, we screened for growth factors by semi-quantitative PCR and quantitative real-time PCR and found that the expression of bone morphogenetic protein 2 (BMP-2), vascular endothelial growth factor B (VEGFB), hypoxia inducible factor-1α (HIF-1α), fibroblast growth factor-2 (FGF-2), and transforming growth factor-β1 significantly increased after co-culture in comparison with mono-culture. In chondrocytes, VEGFA was significantly enhanced after co-culture. Unexpectedly, the expression of collagen II and aggrecan was significantly down-regulated in the co-culture group compared with the mono-culture group. Meanwhile, among all the growth factors screened, we found that the BMP family members BMP-2, BMP-4, and BMP-5 were down-regulated and that VEGFB, HIF-1α, FGF-2, and PDGF were significantly decreased after co-culture. These results suggest that crosstalk between ASCs and chondrocytes is a pathway through the regulated growth factors that might have potential in cartilage repair and regeneration and could be useful for tissue engineering.

P34HB film promotes cell adhesion, in vitro proliferation, and in vivo cartilage repair

The management of chondral defects is a challenging topic of current interest for scientists and surgeons, which has a crucial impact on human cost.