The expression of cross-linked elastin by rabbit blood vessel smooth muscle cells cultured in polyhydroxyalkanoate scaffolds

Extracellular matrix-derived materials for tissue engineering and regenerative medicine: A journey from isolation to characterization and application

Biomaterial choice is an essential step during the development tissue engineering and regenerative medicine (TERM) applications. The selected biomaterial must present properties allowing the physiological-like recapitulation of several processes that lead to the reestablishment of homeostatic tissue or organ function. Biomaterials derived from the extracellular matrix (ECM) present many such properties and their use in the field has been steadily increasing. Considering this growing importance, it becomes imperative to provide a comprehensive overview of ECM biomaterials, encompassing their sourcing, processing, and integration into TERM applications. This review compiles the main strategies used to isolate and process ECM-derived biomaterials as well as different techniques used for its characterization, namely biochemical and chemical, physical, morphological, and biological. Lastly, some of their applications in the TERM field are explored and discussed.

Polyhydroxyalkanoates: the natural biopolyester for future medical innovations

Polyhydroxyalkanoates (PHAs) are a family of natural microbial biopolyesters with the same basic chemical structure and diverse side chain groups. Based on their excellent biodegradability, biocompatibility, thermoplastic properties and diversity, PHAs are highly promising medical biomaterials and elements of medical devices for applications in tissue engineering and drug delivery. However, due to the high cost of biotechnological production, most PHAs have yet to be applied in the clinic and have only been studied at laboratory scale. This review focuses on the biosynthesis, diversity, physical properties, biodegradability and biosafety of PHAs. We also discuss optimization strategies for improved microbial production of commercial PHAs via novel synthetic biology tools. Moreover, we also systematically summarize various medical devices based on PHAs and related design approaches for medical applications, including tissue repair and drug delivery. The main degradation product of PHAs, 3-hydroxybutyrate (3HB), is recognized as a new functional molecule for cancer therapy and immune regulation. Although PHAs still account for only a small percentage of medical polymers, up-and-coming novel medical PHA devices will enter the clinical translation stage in the next few years.

Biomedical Applications of Polyhydroxyalkanoate in Tissue Engineering

Tissue engineering technology aids in the regeneration of new tissue to replace damaged or wounded tissue. Three-dimensional biodegradable and porous scaffolds are often utilized in this area to mimic the structure and function of the extracellular matrix. Scaffold material and design are significant areas of biomaterial research and the most favorable material for seeding of in vitro and in vivo cells. Polyhydroxyalkanoates (PHAs) are biopolyesters (thermoplastic) that are appropriate for this application due to their biodegradability, thermo-processability, enhanced biocompatibility, mechanical properties, non-toxicity, and environmental origin. Additionally, they offer enormous potential for modification through biological, chemical and physical alteration, including blending with various other materials. PHAs are produced by bacterial fermentation under nutrient-limiting circumstances and have been reported to offer new perspectives for devices in biological applications. The present review discusses PHAs in the applications of conventional medical devices, especially for soft tissue (sutures, wound dressings, cardiac patches and blood vessels) and hard tissue (bone and cartilage scaffolds) regeneration applications. The paper also addresses a recent advance highlighting the usage of PHAs in implantable devices, such as heart valves, stents, nerve guidance conduits and nanoparticles, including drug delivery. This review summarizes the in vivo and in vitro biodegradability of PHAs and conducts an overview of current scientific research and achievements in the development of PHAs in the biomedical sector. In the future, PHAs may replace synthetic plastics as the material of choice for medical researchers and practitioners.

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.

A Polyhydroxyalkanoates-Based Carrier Platform of Bioactive Substances for Therapeutic Applications

Bioactive substances (BAS), such as small molecule drugs, proteins, RNA, cells, etc., play a vital role in many therapeutic applications, especially in tissue repair and regeneration. However, the therapeutic effect is still a challenge due to the uncontrollable release and instable physico-chemical properties of bioactive components. To address this, many biodegradable carrier systems of micro-nano structures have been rapidly developed based on different biocompatible polymers including polyhydroxyalkanoates (PHA), the microbial synthesized polyesters, to provide load protection and controlled-release of BAS. We herein highlight the developments of PHA-based carrier systems in recent therapeutic studies, and give an overview of its prospective applications in various disease treatments. Specifically, the biosynthesis and material properties of diverse PHA polymers, designs and fabrication of micro- and nano-structure PHA particles, as well as therapeutic studies based on PHA particles, are summarized to give a comprehensive landscape of PHA-based BAS carriers and applications thereof. Moreover, recent efforts focusing on novel-type BAS nano-carriers, the functionalized self-assembled PHA granules in vivo, was discussed in this review, proposing the underlying innovations of designs and fabrications of PHA-based BAS carriers powered by synthetic biology. This review outlines a promising and applicable BAS carrier platform of novelty based on PHA particles for different medical uses.

Bioglass promotes wound healing by inhibiting endothelial cell pyroptosis through regulation of the connexin 43/reactive oxygen species (ROS) signaling pathway

Bioactive glass (BG) has recently shown great promise in soft tissue repair, especially in wound healing; however, the underlying mechanism remains unclear. Pyroptosis is a novel type of programmed cell death that is involved in various traumatic injury diseases. Here, we hypothesized that BG may promote wound healing through suppression of pyroptosis. To test this scenario, we investigated the possible effect of BG on pyroptosis in wound healing both in vivo and in vitro. This study showed that BG can accelerate wound closure, granulation formation, collagen deposition, and angiogenesis. Moreover, western blot analysis and immunofluorescence staining revealed that BG inhibited the expression of pyroptosis-related proteins in vivo and in vitro. In addition, while BG regulated the expression of connexin43 (Cx43), it inhibited reactive oxygen species (ROS) production. Cx43 activation and inhibition experiments further indicate that BG inhibited pyroptosis in endothelial cells by decreasing Cx43 expression and ROS levels. Taken together, these studies suggest that BG promotes wound healing by inhibiting pyroptosis via Cx43/ROS signaling pathway.

Development and Advantages of Biodegradable PHA Polymers Based on Electrospun PHBV Fibers for Tissue Engineering and Other Biomedical Applications

Biodegradable polymeric biomaterials offer a significant advantage in disposable or fast-consuming products in medical applications. Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) is an example of a polyhydroxyalkanoate (PHA), i.e., one group of natural polyesters that are byproducts of reactions taking place in microorganisms in conditions with an excess carbon source. PHA polymers are a promising material for the production of everyday materials and biomedical applications. Due to the high number of monomers in the group, PHAs permit modifications enabling the production of copolymers of different compositions and with different proportions of individual monomers. In order to change and improve the properties of polymer fibers, PHAs are combined with either other natural and synthetic polymers or additives of inorganic phases. Importantly, electrospun PHBV fibers and mats showed an enormous potential in both the medical field (tissue engineering scaffolds, plasters, wound healing, drug delivery systems) and industrial applications (filter systems, food packaging). This Review summarizes the current state of the art in processing PHBV, especially by electrospinning, its degradation processes, and biocompatibility studies, starting from a general introduction to the PHA group of polymers.

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.

3D bioactive cell-free-scaffolds for in-vitro/in-vivo capture and directed osteoinduction of stem cells for bone tissue regeneration

Hydrophilic bone morphogenetic protein 2 (BMP2) is easily degraded and difficult to load onto hydrophobic carrier materials, which limits the application of polyester materials in bone tissue engineering. Based on soybean-lecithin as an adjuvant biosurfactant, we designed a novel cell-free-scaffold of polymer of poly(ε-caprolactone) and poly(lactide-co-glycolide)-co-polyetherimide with abundant entrapped and continuously released BMP2 for in vivo stem cell-capture and in situ osteogenic induction, avoiding the use of exogenous cells. The optimized bioactive osteo-polyester scaffold (BOPSC), i.e. SBMP-10SC, had a high BMP2 entrapment efficiency of 95.35%. Due to its higher porosity of 83.42%, higher water uptake ratio of 850%, and sustained BMP2 release with polymer degradation, BOPSCs were demonstrated to support excellent in vitro capture, proliferation, migration and osteogenic differentiation of mouse adipose derived mesenchymal stem cells (mADSCs), and performed much better than traditional BMP-10SCs with unmodified BMP2 and single polyester scaffolds (10SCs). Furthermore, in vivo capture and migration of stem cells and differentiation into osteoblasts was observed in mice implanted with BOPSCs without exogenous cells, which enabled allogeneic bone formation with a high bone mineral density and ratios of new bone volume to existing tissue volume after 6 months. The BOPSC is an advanced 3D cell-free platform with sustained BMP2 supply for in situ stem cell capture and osteoinduction in bone tissue engineering with potential for clinical translation.

Biomedical Applications of Bacteria-Derived Polymers

Plastics have found widespread use in the fields of cosmetic, engineering, and medical sciences due to their wide-ranging mechanical and physical properties, as well as suitability in biomedical applications. However, in the light of the environmental cost of further upscaling current methods of synthesizing many plastics, work has recently focused on the manufacture of these polymers using biological methods (often bacterial fermentation), which brings with them the advantages of both low temperature synthesis and a reduced reliance on potentially toxic and non-eco-friendly compounds. This can be seen as a boon in the biomaterials industry, where there is a need for highly bespoke, biocompatible, processable polymers with unique biological properties, for the regeneration and replacement of a large number of tissue types, following disease. However, barriers still remain to the mass-production of some of these polymers, necessitating new research. This review attempts a critical analysis of the contemporary literature concerning the use of a number of bacteria-derived polymers in the context of biomedical applications, including the biosynthetic pathways and organisms involved, as well as the challenges surrounding their mass production. This review will also consider the unique properties of these bacteria-derived polymers, contributing to bioactivity, including antibacterial properties, oxygen permittivity, and properties pertaining to cell adhesion, proliferation, and differentiation. Finally, the review will select notable examples in literature to indicate future directions, should the aforementioned barriers be addressed, as well as improvements to current bacterial fermentation methods that could help to address these barriers.

Poly(hydroxybutyrate-co-hydroxyvalerate) Porous Matrices from Thermally Induced Phase Separation

Thermally induced phase separation followed by freeze drying has been used to prepare biodegradable and biocompatible scaffolds with interconnected 3D microporous structures from poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) copolymers containing 5 and 12 wt % of 3-hydroxyvalerate (HV). Solutions of PHBV in 1,4-dioxane, underwent phase separation by cooling under two different thermal gradients (at -25 °C and -5 °C). The cloud point and crystallization temperature of the polymer solutions were determined by turbidimetry and differential scanning calorimetry, respectively. Parameters affecting the phase separation mechanism such as variation of both the cooling process and the composition of the PHBV copolymer were investigated. Afterwards, the influence of these variables on the morphology of the porous structure and the final mechanical properties (i.e., rigidity and damping) was evaluated via scanning electron microscopy and dynamic mechanical thermal analysis, respectively. While the morphology of the scaffolds was considerably affected by polymer crystallization upon a slow cooling rate, the effect of solvent crystallization was more evident at either high hydroxyvalerate content (i.e., 12 wt % of HV) or high cooling rate. The decrease in the HV content gave rise to scaffolds with greater stiffness because of their higher degree of crystallinity, being also noticeable the greater consistency of the structure attained when the cooling rate was higher. Scaffolds were fully biocompatible supports for cell adhesion and proliferation in 3D cultures and show potential application as a tool for tissue regeneration.

NIR-controlled HSP90 inhibitor release from hollow mesoporous nanocarbon for synergistic tumor photothermal therapy guided by photoacoustic imaging

Photothermal therapy (PTT) has been widely studied for tumor therapy. However, the clinical transformation of PTT has encountered significant challenges in tumor recurrence, because the uneven hyperthermia in tumor tissues can result in the survival of cancer cells in the lower temperature regions close to blood vessels (as the blood flow can dissipate the localized heat). It is therefore important for clinical treatments to retain the excellent therapeutic efficiency of PTT at relatively low temperatures. In this article, innocuous hollow mesoporous carbon spheres (HMCS) with a high photothermal conversion efficiency were obtained by a one-pot synthesis method. After modification with DSPE-PEG, the HMCS-PEG exhibited a superior stability in biomedia, which is beneficial for further biological applications. Interestingly, combined with hydrophobic gambogic acid (GA) which can downregulate heat shock protein 90 (HSP90), the HMCS-PEG-GA system showed a significant NIR-enhanced tumor therapeutic effect in vitro and in vivo under mild temperature conditions (∼43 °C), and the combination index (CI) value of HMCS-PEG-GA was found to be 0.72. Meanwhile, this nano-system possessed good photothermal imaging and photoacoustic imaging abilities. Guided by the photoacoustic imaging signal, HMCS-PEG-GA showed enormous potential for use in accurate tumor diagnosis and mild-temperature PPT treatment applications, which is very important for clinical transformation of this nano-system.

Properties of scaffolds prepared by fused deposition modeling of poly(hydroxyalkanoates)

Poly(hydroxyalkanoates) are biodegradable and biocompatible polymers suitable for tissue engineering. Fused deposition modeling (FDM) belongs to modern rapid prototyping techniques for the fabrication of scaffolds. In this work, poly(3-hydroxybutyrate (PHB), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH) were tested for FDM. Thermal and rheological properties of industrial PHAs were compared with poly(lactic acid) (PLA), which is a biodegradable polymer commonly used for FDM. The massive decrease in viscosity and loss of molecular weight of PHB and PHBV precluded their use for FDM. On the other hand, the thermal stability of PHBH was comparable to that of PLA. PHBH scaffolds prepared by FDM exhibited excellent mechanical properties, no cytotoxicity and large proliferation of mouse embryonic fibroblast cells within 96 h. The hydrolytic degradation of PHBH and PLA scaffolds tested in synthetic gastric juice for 52 days confirmed a faster degradation of PHBH than PLA. The decrease in molecular weight confirmed the first-order kinetics with a slightly higher (0.0169 day^-1) degradation rate constant for PHBH as compared to the value (0.0107 day^-1) obtained for PLA. These results indicate that PHBH could be used to produce scaffolds by FDM with application in tissue engineering.

A Pulsatile Flow System to Engineer Aneurysm and Atherosclerosis Mimetic Extracellular Matrix

Alterations of blood flow patterns strongly correlate with arterial wall diseases such as atherosclerosis and aneurysm. Here, a simple, pumpless, close-loop, easy-to-replicate, and miniaturized flow device is introduced to concurrently expose 3D engineered vascular smooth muscle tissues to high-velocity pulsatile flow versus low-velocity disturbed flow conditions. Two flow regimes are distinguished, one that promotes elastin and impairs collagen I assembly, while the other impairs elastin and promotes collagen assembly. This latter extracellular matrix (ECM) composition shares characteristics with aneurysmal or atherosclerotic tissue phenotypes, thus recapitulating crucial hallmarks of flow-induced tissue morphogenesis in vessel walls. It is shown that the mRNA levels of ECM of collagens and elastin are not affected by the differential flow conditions. Instead, the differential gene expression of matrix metalloproteinase (MMP) and their inhibitors (TIMPs) is flow-dependent, and thus drives the alterations in ECM composition. In further support, treatment with doxycycline, an MMP inhibitor and a clinically used drug to treat vascular diseases, halts the effect of low-velocity flow on the ECM remodeling. This illustrates how the platform can be exploited for drug efficacy studies by providing crucial mechanistic insights into how different therapeutic interventions may affect tissue growth and ECM assembly.

Designing Novel Interfaces via Surface Functionalization of Short-Chain-Length Polyhydroxyalkanoates

Polyhydroxyalkanoates (PHA), a microbial plastic has emerged as promising biomaterial owing to the broad range of mechanical properties. However, some studies revealed that PHA is hydrophobic and has no recognition site for cell attachment and this is often a limitation in tissue engineering aspects. Owing to this, the polymer is tailored accordingly in order to enhance the biocompatibilityin vivoas well as to suit the intended application. Thus far, these surface modifications have led to PHA being widely used in various biomedical and pharmaceutical applications such as cardiac patches, wound management, nerve, bone, and cartilage repair. This review addresses the surface modification on biomedical applications focusing on short-chain-length PHA such as poly(3-hydroxybutyrate) [P(3HB)], poly(3-hydroxybutyrate-co-4-hydroxybutyrate) [P(3HB-co-4HB)] and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) [P(3HB-co-3HV)].

Recent Progress in Vascular Tissue-Engineered Blood Vessels

Cardiovascular disease is the number one cause of death in the U.S and results in the loss of approximately one million lives and more than 400 billion U.S. dollars for treatments every year. Recently, tissue engineered blood vessels have been studied and developed as promising replacements for treatment with autologous veins. Here, we summarize the cell sources and methods to make tissue-engineered blood vessels (TEBVs), the recent progress in TEBV related research, and also the recent progress in TEBV related clinical studies.

Developing a Clinically Relevant Tissue Engineered Heart Valve-A Review of Current Approaches

Tissue engineered heart valves (TEHVs) have the potential to address the shortcomings of current implants through the combination of cells and bioactive biomaterials that promote growth and proper mechanical function in physiological conditions. The ideal TEHV should be anti-thrombogenic, biocompatible, durable, and resistant to calcification, and should exhibit a physiological hemodynamic profile. In addition, TEHVs may possess the capability to integrate and grow with somatic growth, eliminating the need for multiple surgeries children must undergo. Thus, this review assesses clinically available heart valve prostheses, outlines the design criteria for developing a heart valve, and evaluates three types of biomaterials (decellularized, natural, and synthetic) for tissue engineering heart valves. While significant progress has been made in biomaterials and fabrication techniques, a viable tissue engineered heart valve has yet to be translated into a clinical product. Thus, current strategies and future perspectives are also discussed to facilitate the development of new approaches and considerations for heart valve tissue engineering.

Polycation-mediated integrated cell death processes

One of the major challenges in the field of nucleic acid delivery is the design of delivery vehicles with attributes that render them safe as well as efficient in transfection. To this end, polycationic vectors have been intensely investigated with native polyethylenimines (PEIs) being the gold standard. PEIs are highly efficient transfectants, but depending on their architecture and size they induce cytotoxicity through different modes of cell death pathways. Here, we briefly review dynamic and integrated cell death processes and pathways, and discuss considerations in cell death assay design and their interpretation in relation to PEIs and PEI-based engineered vectors, which are also translatable for the design and studying the safety of other transfectants.

Nano/Micro Hybrid Scaffold of PCL or P3HB Nanofibers Combined with Silk Fibroin for Tendon and Ligament Tissue Engineering

A novel biodegradable nano/micro hybrid structure was obtained by electrospinning P3HB or PCL nanofibers onto a twisted silk fibroin (SF) structure, with the aim of fabricating a suitable scaffold for tendon and ligament tissue engineering. The electrospinning (ES) processing parameters for P3HB and PCL were optimized on 2D samples, and applied to produce two different nano/micro hybrid constructs (SF/ES-PCL and SF/ES-P3HB).

Morphological, chemico-physical and mechanical properties of the novel hybrid scaffolds were evaluated by SEM, ATR FT-IR, DSC, tensile and thermodynamic mechanical tests. The results demonstrated that the nanofibers were tightly wrapped around the silk filaments, and the crystallinity of the SF twisted yarns was not influenced by the presence of the electrospun polymers. The slightly higher mechanical properties of the hybrid constructs confirmed an increase of internal forces due to the interaction between nano and micro components. Cell culture tests with L929 fibroblasts, in the presence of the sample eluates or in direct contact with the hybrid structures, showed no cytotoxic effects and a good level of cytocompatibility of the nano/micro hybrid structures in term of cell viability, particularly at day 1. Cell viability onto the nano/micro hybrid structures decreased from the first to the third day of culture when compared with the control culture plastic, but appeared to be higher when compared with the uncoated SF yarns. Although additional in vitro and in vivo tests are needed, the original fabrication method here described appears promising for scaffolds suitable for tendon and ligament tissue engineering.

Biodegradability, cellular compatibility and cell infiltration of poly(3-hydroxybutyrate-co-4-hydroxybutyrate) in comparison with poly(ε-caprolactone) and poly(lactide-co-glycolide)

Poly(3-hydroxybutyrate-co-4-hydroxybutyrate), poly(ε-caprolactone), and poly(1actide-co-glycolide) films were prepared by solution casting and electrospinning. The degradability of cast films was evaluated in vitro and in vivo by recording the weight remaining, observing the morphology, and measuring change in molecular weight and Mw/ Mn polydispersity. In addition, cell proliferation on electrospun films was tested by MTT assay, and cell infiltration into electrospun films was assessed through subcutaneous implantation in rats. By analyzing data obtained from these tests, we discovered that the degradation rates of poly(3-hydroxybutyrate-co-4-hydroxybutyrate) copolymers were between those of poly(ε-caprolactone) and poly(1actide-co-glycolide) and could be controlled by adjusting 4-hydroxybutyrate content. Moreover, tissue responses to materials made from poly(3-hydroxybutyrate-co-4-hydroxybutyrate) were milder compared with those elicited by poly(ε-caprolactone) and poly(1actide-co-glycolide), and poly(3-hydroxybutyrate-co-4-hydroxybutyrate) films exhibited a good and moderate cell infiltration. Therefore, our data demonstrate that poly(3-hydroxybutyrate-co-4-hydroxybutyrate) copolymers are promising candidates for the construction of scaffolds designed for various types of tissue regeneration with special biodegradability requirements.

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.

Thymopentin nanoparticles engineered with high loading efficiency, improved pharmacokinetic properties, and enhanced immunostimulating effect using soybean phospholipid and PHBHHx polymer

Formulation of protein and peptide drugs with sustained release properties is crucial to enhance their therapeutic effect and minimize administration frequency. In this study, immunomodulating polymeric systems were designed by manufacturing PHBHHx nanoparticles (NPs) containing thymopentin (TP5). The release profile of the drug was studied over a period of 7 days. The PHBHHx NPs containing TP5-phospholipid (PLC) complex (TP5-PLC) displayed a spherical shape with a mean size, zeta potential, and encapsulation efficiency of 238.9 nm, -32.0 mV, and 72.81%, respectively. The cytotoxicity results showed the PHBHHx NPs had a relatively low toxicity in vitro. TP5 entrapped in the NPs could hardly release in vitro, while the NPs had longer than 7 days release duration after a single subcutaneous injection in Wistar rats. The immunodepression rat model was built to evaluate the immunomodulating effects of TP5-PLC-NPs in vivo. The results of T-lymphocyte subsets (CD3(+), CD4(+), CD8(+), and CD4(+)/CD8(+) ratio) analysis and superoxide dismutase (SOD) values suggested that TP5-PLC-NPs had stronger immunoregulation effects than TP5 solution. In conclusion, an applicable approach to markedly enhancing the loading of a water-soluble peptide into a hydrophobic polymer matrix has been introduced. Thus, TP5-PLC-NPs are promising nanomedicine systems for sustained release effects of TP5.

3D artificial bones for bone repair prepared by computed tomography-guided fused deposition modeling for bone repair

The medical community has expressed significant interest in the development of new types of artificial bones that mimic natural bones. In this study, computed tomography (CT)-guided fused deposition modeling (FDM) was employed to fabricate polycaprolactone (PCL)/hydroxyapatite (HA) and PCL 3D artificial bones to mimic natural goat femurs. The in vitro mechanical properties, in vitro cell biocompatibility, and in vivo performance of the artificial bones in a long load-bearing goat femur bone segmental defect model were studied. All of the results indicate that CT-guided FDM is a simple, convenient, relatively low-cost method that is suitable for fabricating natural bonelike artificial bones. Moreover, PCL/HA 3D artificial bones prepared by CT-guided FDM have more close mechanics to natural bone, good in vitro cell biocompatibility, biodegradation ability, and appropriate in vivo new bone formation ability. Therefore, PCL/HA 3D artificial bones could be potentially be of use in the treatment of patients with clinical bone defects.

Electrospun P34HB fibres: a scaffold for tissue engineering

OBJECTIVES

Amongst the fourth generation of PHAs is bio-plasticpoly3-hydroxybutyrate4-hydroxybutyrate (P34HB); it is thus appropriate to perform novel research on its uses and applications. The main objective of this study was to determine whether electrospun P34HB fibres would accommodate viability, growth and differentiation of mouse adipose-derived stem cells (mASCs).

MATERIALS AND METHODS

In the present study, we looked at P34HB in two forms, electrospun P34HB fibres and P34HB film. Morphology of electrospun P34HB fibres and P34HB film were characterized using scanning electron microscopy, fluorescence microscopy and confocal laser scanning microscopy, after cell seeding. Cell adhesion, proliferation and cytotoxicity tests were conducted on both by MTT and CCK-8 assays, respectively. After being cultured with osteogenic induction, expression of adipogenic genes Runx2, OPN and OCN, were examined by real-time PCR.

RESULTS

By scanning electron microscopy, light microscopy and confocal laser scanning microscopy, we observed that the mASCs grew well associated with the P34HB materials. After MTT and CCK-8 assay, we concluded that P34HB would, indeed, be a material suitable for further cell adhesion and proliferation studies. More importantly, we found that the P34HB matrices promoted expression of Runx2, OPN and OCN with osteogenic induction.

CONCLUSIONS

In this investigation, we can confirm that the electrospun P34HB fibres accommodated survival, proliferation and differentiation of mASCs, and we have been able to draw the conclusion that fibre scaffolds produced by the electrospinning process are promising for application of bone tissue engineering.

Scaffolds for tissue engineering of cardiac valves

Tissue engineered heart valves offer a promising alternative for the replacement of diseased heart valves avoiding the limitations faced with currently available bioprosthetic and mechanical heart valves. In the paradigm of tissue engineering, a three-dimensional platform - the so-called scaffold - is essential for cell proliferation, growth and differentiation, as well as the ultimate generation of a functional tissue. A foundation for success in heart valve tissue engineering is a recapitulation of the complex design and diverse mechanical properties of a native valve. This article reviews technological details of the scaffolds that have been applied to date in heart valve tissue engineering research.

Dopamine-Mediated Sclerotization of Regenerated Chitin in Ionic Liquid

Chitin is a promising structural material for biomedical applications, due to its many advantageous properties and abundance in nature. However, its usage and development in the biomedical field have been stagnant, because of chitin’s poor mechanical properties in wet conditions and the difficulties in transforming it into an applicable form. To overcome these challenges, we created a novel biomimetic chitin composite. This regenerated chitin, prepared with ionic liquid, showed improved mechanical properties in wet conditions by mimicking insect cuticle and squid beak sclerotization, i.e., catechol-meditated cross-linking. By ionic liquid-based heat treatment, dopamine oxidation produced melanin-like compounds and dopamine-meditated cross-links without any solvent evaporation and oxidant utilization. The dopamine-meditated sclerotization increased the ultimate tensile strength (UTS) of the regenerated chitin by 2.52-fold, measured after six weeks of phosphate-buffered saline (PBS) submersion. In addition, the linear swelling ratio (LSR) of the chitin film was reduced by about 22%. This strategy raises a possibility of using regenerated chitin as an artificial hard tissue in wet conditions.

Induction of osteogenic differentiation of stem cells via a lyophilized microRNA reverse transfection formulation on a tissue culture plate

MicroRNA (miRNA) regulation is a novel approach to manipulating the fate of mesenchymal stem cells, but an easy, safe, and highly efficient method of transfection is required. In this study, we developed an miRNA reverse transfection formulation by lyophilizing Lipofectamine 2000-miRNA lipoplexes on a tissue culture plate. The lipoplexes can be immobilized on a tissue culture plate with an intact pseudospherical structure and lyophilization without any lyoprotectant. In this study, reverse transfection resulted in highly efficient cellular uptake of miRNA and enabled significant manipulation of the intracellular target miRNA level. Reverse transfection formulations containing Lipofectamine 2000 1 μL per well generated much higher transfection efficiency without obvious cytotoxicity compared with conventional and other transfection methods. Further, the transfection efficiency of the reverse transfection formulations did not deteriorate during 90 days of storage at 4°C and -20°C. We then assessed the efficiency of the miRNA reverse transfection formulation in promoting osteogenic differentiation of mesenchymal stem cells. We found that transfection with anti-miR-138 and miR-148b was efficient for enhancing osteogenic differentiation, as indicated by enhanced osteogenesis-related gene expression, amount of alkaline phosphatase present, production of collagen, and matrix mineralization. Overall, the miRNA reverse transfection formulation developed in this study is a promising approach for miRNA transfection which can control stem cell fate and is suitable for loading miRNAs onto various biomaterials.

MicroRNA functionalized microporous titanium oxide surface by lyophilization with enhanced osteogenic activity

Developing biomedical titanium (Ti) implants with high osteogenic ability and consequent rigid osseointegration is a constant requirement from the clinic. In this study, we fabricate novel miRNA functionalized microporous Ti implants by lyophilizing miRNA lipoplexes onto a microporous titanium oxide surface formed by microarc oxidation (MAO). The microporous titanium oxide surface provides a larger surface area for miRNA loading and enables spatial retention of the miRNAs within the pores until cellular delivery. The loading of lipoplexes into the micropores on the MAO Ti surface is facilitated by the superhydrophilicity and Ti-OH groups gathering of the MAO surface after UV irradiation followed by lyophilization. A high miRNA transfection efficiency was observed in mesenchymal stem cells (MSCs) seeded onto the miRNA functionalized surface with no apparent cytotoxicity. When functionalizing the Ti surface with miR-29b that enhances osteogenic activity and antimiR-138 that inhibits miR-138 inhibition of endogenous osteogenesis, clear stimulation of MSC osteogenic differentiation was observed, in terms of up-regulating osteogenic expression and enhancing alkaline phosphatase production, collagen secretion and ECM mineralization. The novel miRNA functionalized Ti implants with enhanced osteogenic activity promisingly lead to more rapid and robust osseointegration of a clinical bone implant interface. Our study implies that lyophilization may constitute a versatile method for miRNA loading to other biomaterials with the aim of controlling cellular function.

Induced apoptosis of osteoblasts proliferating on polyhydroxyalkanoates

The mechanism study on behaviors of cells influenced by biomaterial surface properties can provide profound guidances for functional tissue engineering scaffolds design. In this study, regulation of integrin-mediated cell-substrate interactions using rat osteoblasts incubated on PHA films was investigated. Compared with tissue culture plate (TCP), poly-3-hydroxybutyrate (PHB), copolymer of 3-hydroxybutyrate and 3-hydroxyvalerate (PHBV) and copolymer of 3-hydroxybutyrate and 3-hydroxyhexanoate (PHBHHx), osteoblasts inoculated on a terpolymer of 3-hydroxybutyrate, 3-hydroxyvalerate and 3-hydroxyhexanoate (PHBVHHx) were found to have higher apoptosis rates. Several integrin subunits in osteoblasts grown on PHBVHHx showed altered expressions. Simultaneously, extracellular matrics (ECM) were also remodeled on the material surface. Osteoblasts showed a higher expression of integrin subunit β3 and αv on PHBVHHx films compared with that on TCP. On the other hand, less vitronectin, osteopontin and fibronectin, the main ligands for integrin β3 were expressed and deposited in ECM. The unligated integrin β3 could recruit caspase-8 to the membrane and activate its downstream signaling which was proven by the caspase-8 activation assay. It was therefore concluded that the induced apoptosis of osteoblasts on PHBVHHx was regulated by recruitment of caspase-8 to the unligated integrin β3.

Fabrication of three-dimensional nano, micro and micro/nano scaffolds of porous poly(lactic acid) by electrospinning and comparison of cell infiltration by Z-stacking/three-dimensional projection technique

The use of electrospun extracellular matrix (ECM)-mimicking nanofibrous scaffolds for tissue engineering is limited by poor cellular infiltration. The authors hypothesised that cell penetration could be enhanced in scaffolds by using a hierarchical structure where nano fibres are combined with micron-scale fibres while preserving the overall scaffold architecture. To assess this, we fabricated electrospun porous poly(lactic acid) (PLA) scaffolds having nanoscale, microscale and combined micro/nano architecture and evaluated the structural characteristics and biological response in detail. Although the bioactivity was intermediate to that for nanofibre and microfibre scaffold, a unique result of this study was that the micro/nano combined fibrous scaffold showed improved cell infiltration and distribution than the nanofibrous scaffold. Although the cells were found to be lining the scaffold periphery in the case of nanofibrous scaffold, micro/nano scaffolds had cells dispersed throughout the scaffold. Further, as expected, the addition of nanoparticles of hydroxyapatite (nHAp) improved the bioactivity, although it did not play a significant role in cell penetration. Thus, this strategy of creating a three-dimensional (3D) micro/nano architecture that would increase the porosity of the fibrous scaffold and thereby improving the cell penetration, can be utilised for the generation of functional tissue engineered constructs in vitro.

Examination of PHB Depolymerases in Ralstonia eutropha: Further Elucidation of the Roles of Enzymes in PHB Homeostasis

Polyhydroxyalkanoates (PHA) are biodegradable polymers that are attractive materials for use in tissue engineering and medical device manufacturing. Ralstonia eutropha is regarded as the model organism for PHA biosynthesis. We examined the effects of PHA depolymerase (PhaZ) expression on PHA homeostasis in R. eutropha strains. In order to analyze the impact of PhaZs on R. eutropha granule architecture, we performed electron microscopy on several phaZ knockout strains and the wild type strain grown under PHA production conditions. Analysis of the acquired micrographs was based on stereology: the ratio of granule area and cell area was determined, along with total granule count per full-size cell image. Cells bearing a phaZ2 knockout mutation alone or in conjunction with a phaZ1 mutation were found to have a high granule volume per cell volume and a higher granule count compared to wild type. A phaZ quadruple knockout strain appeared to have a low granule volume per cell volume and a low granule count per cell. Cells bearing a phaZ3 knockout were found to have a higher granule count than the wild type, whereas granule volume per cell volume was similar. Accordingly, we hypothesize that PhaZs have not only an impact on PHA degradation but also on the 3-dimensional granule architecture. Based on our data, PhaZ2 is postulated to affect granule density. This work increased our knowledge about PHA depolymerases in R. eutropha, including enzymes that had previously been uncharacterized.

Tissue engineering and regenerative strategies to replicate biocomplexity of vascular elastic matrix assembly

Cardiovascular tissues exhibit architecturally complex extracellular matrices, of which the elastic matrix forms a major component. The elastic matrix critically maintains native structural configurations of vascular tissues, determines their ability to recoil after stretch, and regulates cell signaling pathways involved in morphogenesis, injury response, and inflammation via biomechanical transduction. The ability to tissue engineer vascular replacements that incorporate elastic matrix superstructures unique to cardiac and vascular tissues is thus important to maintaining vascular homeostasis. However, the vascular elastic matrix is particularly difficult to tissue engineer due to the inherently poor ability of adult vascular cells to synthesize elastin precursors and organize them into mature structures in a manner that replicates the biocomplexity of elastic matrix assembly during development. This review discusses current tissue engineering materials (e.g., growth factors and scaffolds) and methods (e.g., dynamic stretch and contact guidance) used to promote cellular synthesis and assembly of elastic matrix superstructures, and the limitations of these approaches when applied to smooth muscle cells, the primary elastin-generating cell type in vascular tissues. The potential application of these methods for in situ regeneration of disrupted elastic matrix at sites of proteolytic vascular disease (e.g., abdominal aortic aneurysms) is also discussed. Finally, the review describes the potential utility of alternative cell types to elastic tissue engineering and regenerative matrix repair. Future progress in the field is contingent on developing a thorough understanding of developmental elastogenesis and then mimicking the spatiotemporal changes in the cellular microenvironment that occur during that phase. This will enable us to tissue engineer clinically applicable elastic vascular tissue replacements and to develop elastogenic therapies to restore homeostasis in de-elasticized vessels.

Oral intake of hydrogen-rich water inhibits intimal hyperplasia in arterialized vein grafts in rats

AIMS

Arterialized vein grafts often fail due to intimal hyperplasia. Hydrogen potently protects organs and cells from many insults via its anti-inflammatory and antioxidant properties. We investigated the efficacy of oral administration of hydrogen-rich water (HW) for prevention of intimal hyperplasia.

METHODS AND RESULTS

The inferior vena cava was excised, stored in cold Ringer solution for 2 h, and placed as an interposition graft in the abdominal aorta of syngeneic Lewis rats. HW was generated by immersing a magnesium stick in tap water (Mg + 2H(2)O → Mg (OH)(2) + H(2)). Beginning on the day of graft implantation, recipients were given tap water [regular water (RW)], HW or HW that had been subsequently degassed water (DW). Six weeks after grafting, the grafts in the rats given RW or DW had developed intimal hyperplasia, accompanied by increased oxidative injury. HW significantly suppressed intimal hyperplasia. One week after grafting, the grafts in HW-treated rats exhibited improved endothelial integrity with less platelet and white blood cell aggregation. Up-regulation of the mRNAs for intracellular adhesion molecules was attenuated in the vein grafts of the rats receiving HW. Activation of p38 mitogen-activated protein kinase, matrix metalloproteinase (MMP)-2, and MMP-9 was also significantly inhibited in grafts receiving HW. In rat smooth muscle cell (A7r5) cultures, hydrogen treatment for 24 h reduced smooth muscle cell migration.

CONCLUSION

Drinking HW significantly reduced neointima formation after vein grafting in rats. Drinking HW may have therapeutic value as a novel therapy for intimal hyperplasia and could easily be incorporated into daily life.

A rapid-acting, long-acting insulin formulation based on a phospholipid complex loaded PHBHHx nanoparticles

The application of poly(hydroxybutyrate-co-hydroxyhexanoate) (PHBHHx) for sustained and controlled delivery of hydrophilic insulin was made possible by preparing insulin phospholipid complex loaded biodegradable PHBHHx nanoparticles (INS-PLC-NPs). The INS-PLC-NPs produced by a solvent evaporation method showed a spherical shape with a mean particle size, zeta potential and entrapment efficiency of 186.2 nm, -38.4 mv and 89.73%, respectively. In vitro studies demonstrated that only 20% of insulin was released within 31 days with a burst release of 5.42% in the first 8 h. The hypoglycaemic effect in STZ induced diabetic rats lasted for more than 3 days after the subcutaneous injection of INS-PLC-NPs, which significantly prolonged the therapeutic effect compared with the administration of insulin solution. The pharmacological bioavailability (PA) of INS-PLC-NPs relative to insulin solution was over 350%, indicating that the bioavailability of insulin was significantly enhanced by INS-PLC-NPs. Therefore, the INS-PLC-NPs system is promising to serve as a long lasting insulin release formulation, by which the patient compliance can be enhanced significantly. This study also showed that phospholipid complex loaded biodegradable nanoparticles (PLC-NPs) have a great potential to be used as a sustained delivery system for hydrophilic proteins to be encapsulated in hydrophobic polymers.

Synthesis, characterizations and biocompatibility of alternating block polyurethanes based on P3/4HB and PPG-PEG-PPG

Block copolymers with exactly controlled structures, that is, alternating block polyurethanes based on poly(3-hydroxybutyrate-co-4-hydroxybutrate) (P3/4HB-diol) and poly (propylene glycol)-poly(ethylene glycol)-poly(propylene glycol) (PPG-PEG-PPG) were synthesized by solution polymerization via specifically selective coupling reaction between terminal hydroxyl P3/4HB segment and isocyanate group end-capped PPG-PEG-PPG segment, using 1,6-hexamethylene diisocyanate (HDI) as end-capped agent. The chemical structure, molecular weight and distribution were systematically characterized by nuclear magnetic resonance spectrum (¹H NMR), Fourier transform infrared spectroscopy (FTIR) and gel permeation chromatography (GPC). The thermal property was investigated by differential scanning calorimetry (DSC) and thermogravimetric analysis. The hydrophilicity was studied by static contact angle of H₂O and CH₂I₂. DSC revealed that the PU3/4HB-alt-PPG-PEG-PPG exhibited a distinct change from amorphous to 30% crystallinity degree, T(g) from -25 to -50 °C, T(m) from 110 to 145 °C. The polyurethanes were more hydrophilic (water contact angle centers around 80 °) than the raw PHA materials. The platelet adhesion assay showed that the obtained polyurethanes had a lower platelet adhesion than the raw materials and the amount of platelet adhesion could be controlled by varying the segmental length of P3/4HB-diol. This could be explained by the inclusion of PPG-PEG-PPG between the P3/4HB segments, improving the hemocompatibility of P3/4HB. The cell culture assay revealed that the obtained polyurethanes were cell inert and unfavorable for the attachment of mouse fibroblast cell line L929 and rabbit blood vessel smooth muscle cells (RaSMCs). This suggests that these polyurethanes would be promising candidates as hemocompatibility and tissue-inert materials.

Biodegradable block poly(ester-urethane)s based on poly(3-hydroxybutyrate-co-4-hydroxybutyrate) copolymers

A series of block poly(ester-urethane)s (abbreviated as PU3/4HB) based on biodegradable poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P3/4HB) segments were synthesized by a facile way of melting polymerization using 1,6-hexamethylene diisocyanate (HDI) as the coupling agent and stannous octanoate (Sn(Oct)(2)) as catalyst, with different 4HB contents and segment lengths. The chemical structure, molecular weight and distribution were systematically characterized by (1)H nuclear magnetic resonance spectrum (NMR), Fourier transform infrared spectroscopy (FTIR) and gel permeation chromatography (GPC). The thermal property was studied by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The hydrophilicity was investigated by static contact angle of deionized water and CH(2)I(2). DSC curves revealed that the PU3/4HB polyurethanes have their T(g) from -25.6 °C to -4.3 °C, and crystallinity from 2.5% to 25.3%, being almost amorphous to semi-crystalline. The obtained PU3/4HBs are hydrophobic (water contact angle 77.4°-95.9°), and their surface free energy (SFE) were studied. The morphology of platelets adhered on the polyurethane film observed by scanning electron microscope (SEM) showed that platelets were activated on the PU3/4HB films which would lead to blood coagulation. The lactate dehydrogenase (LDH) assay revealed that the PU3/4HBs displayed higher platelet adhesion property than raw materials and biodegradable polymer polylactic acid (PLA) and would be potential hemostatic materials. Crystallinity degree, hydrophobicity, surface free energy and urethane linkage content play important roles in affecting the LDH activity and hence the platelet adhesion. CCK-8 assay showed that the PU3/4HB is non-toxic and well for cell growth and proliferation of mouse fibroblast L929. It showed that the hydrophobicity is an important factor for cell growth while 3HB content of the PU3/4HB is important for the cell proliferation. Through changing the composition and the chain-length of P3/4HB-diol prepolymers, the biocompatibility of the poly(ester-urethane)s can be tailored.

Scaffolds in tissue engineering of blood vessels

Tissue engineering of small diameter (<5 mm) blood vessels is a promising approach for developing viable alternatives to autologous vascular grafts. It involves in vitro seeding of cells onto a scaffold on which the cells attach, proliferate, and differentiate while secreting the components of extracellular matrix that are required for creating the tissue. The scaffold should provide the initial requisite mechanical strength to withstand in vivo hemodynamic forces until vascular smooth muscle cells and fibroblasts reinforce the extracellular matrix of the vessel wall. Hence, the choice of scaffold is crucial for providing guidance cues to the cells to behave in the required manner to produce tissues and organs of the desired shape and size. Several types of scaffolds have been used for the reconstruction of blood vessels. They can be broadly classified as biological scaffolds, decellularized matrices, and polymeric biodegradable scaffolds. This review focuses on the different types of scaffolds that have been designed, developed, and tested for tissue engineering of blood vessels, including use of stem cells in vascular tissue engineering.