Tissue engineered cartilage on collagen and PHBV matrices

Ultrasound-activated piezoelectric biomaterials for cartilage regeneration

Due to the low density of chondrocytes and limited ability to repair damaged extracellular matrix (ECM) in cartilage, many patients with congenital or acquired craniofacial trauma require filler graft materials to support facial structure, restore function, improve self-confidence, and regain socialization. Ultrasound has the capacity to stimulate piezoelectric materials, converting mechanical energy into electrical signals that can regulate the metabolism, proliferation, and differentiation of chondrocytes. This unique property has sparked growing interest in using piezoelectric biomaterials in regenerative medicine. In this review, we first explain the principle behind ultrasound-activated piezoelectric materials and how they generate piezopotential. We then review studies demonstrating how this bioelectricity promotes chondrocyte regeneration, stimulates the secretion of key extracellular components and supports cartilage regeneration by activating relevant signaling pathways. Next, we discuss the properties, synthesis, and modification strategies of various piezoelectric biomaterials. We further discuss recent progresses in the development of ultrasound-activated piezoelectric biomaterials specifically designed for cartilage regeneration. Lastly, we discuss future research challenges facing this technology, ultrasound-activated piezoelectric materials for cartilage regeneration engineering. While the technology holds great promise, certain obstacles remain, including issues related to material stability, precise control over ultrasound parameters, and the integration of these systems into clinical settings. The combination of ultrasound-activated piezoelectric technology with other emerging fields, such as Artificial Intelligence (AI) and cartilage organoid chips, may open new frontiers in regenerative medicine. We hope this review encourages further exploration of ultrasound-activated strategies for piezoelectric materials and their future applications in regenerative medicines.

Implanted Magnetoelectric Bionic Cartilage Hydrogel

Enhancing defective cartilage repair by creating a bionic cartilage hydrogel supplemented with in situ electromagnetic stimulation, replicating endogenous electromagnetic effects, remains challenging. To achieve this, a unique three-phase solvent system is designed to prepare a magnetoelectric bionic cartilage hydrogel incorporating piezoelectric poly(3-hydroxybutyric acid-3-hydroxyvaleric acid) (PHBV) and magnetostrictive triiron tetraoxide nanoparticles (Fe3O4 NPs) into sodium alginate (SA) hydrogel to form a dual-network, semi-crosslinked chain entanglement structure. The synthesized hydrogel features similar composition, structure, and mechanical properties to natural cartilage. In addition, after the implantation of cartilage, the motion-driven magnetoelectric-coupled cyclic transformation model is triggered by gentle joint forces, initiating a piezoelectric response that leads to magnetoelectric-coupled cyclic transformation. The freely excitable and cyclically enhanced electromagnetic stimulation it can provide, by simulating and amplifying endogenous electromagnetic effects, obtains induced defective cartilage repair efficacy superior to piezoelectric or magnetic stimulation alone.

Electrically Active Biomaterials for Stimulation and Regeneration in Tissue Engineering

In the human body, bioelectric cues are crucial for tissue stimulation and regeneration. Electrical stimulation (ES) significantly enhances the regeneration of nerves, bones, cardiovascular tissues, and wounds. However, the use of conventional devices with stimulating metal electrodes is invasive and requires external batteries. Consequently, electrically active materials with excellent biocompatibility have attracted attention for their applications in stimulation and regeneration in tissue engineering. To fully exploit the potential of these materials, biocompatibility, operating mechanisms, electrical properties, and even biodegradability should be carefully considered. In this review, we categorize various electrically active biomaterials based on their mechanisms for generating electrical cues, such as piezoelectric effect, triboelectric effect, and others. We also summarize the key material properties, including electrical characteristics and biodegradability, and describe their applications in tissue stimulation and regeneration for nerves, musculoskeletal tissues, and cardiovascular tissues. The electrically active biomaterials hold great potential for advancing the field of tissue engineering and their demonstrated success underscores the importance of continued research in this field.

Piezoelectric Scaffolds as Smart Materials for Bone Tissue Engineering

Bone repair and regeneration require physiological cues, including mechanical, electrical, and biochemical activity. Many biomaterials have been investigated as bioactive scaffolds with excellent electrical properties. Amongst biomaterials, piezoelectric materials (PMs) are gaining attention in biomedicine, power harvesting, biomedical devices, and structural health monitoring. PMs have unique properties, such as the ability to affect physiological movements and deliver electrical stimuli to damaged bone or cells without an external power source. The crucial bone property is its piezoelectricity. Bones can generate electrical charges and potential in response to mechanical stimuli, as they influence bone growth and regeneration. Piezoelectric materials respond to human microenvironment stimuli and are an important factor in bone regeneration and repair. This manuscript is an overview of the fundamentals of the materials generating the piezoelectric effect and their influence on bone repair and regeneration. This paper focuses on the state of the art of piezoelectric materials, such as polymers, ceramics, and composites, and their application in bone tissue engineering. We present important information from the point of view of bone tissue engineering. We highlight promising upcoming approaches and new generations of piezoelectric materials.

Piezoelectric dressings for advanced wound healing

The treatment of chronic refractory wounds poses significant challenges and threats to both human society and the economy. Existing research studies demonstrate that electrical stimulation fosters cell proliferation and migration and promotes the production of cytokines that expedites the wound healing process. Presently, clinical settings utilize electrical stimulation devices for wound treatment, but these devices often present issues such as limited portability and the necessity for frequent recharging. A cutting-edge wound dressing employing the piezoelectric effect could transform mechanical energy into electrical energy, thereby providing continuous electrical stimulation and accelerating wound healing, effectively addressing these concerns. This review primarily reviews the selection of piezoelectric materials and their application in wound dressing design, offering a succinct overview of these materials and their underlying mechanisms. This study also provides a perspective on the current limitations of piezoelectric wound dressings and the future development of multifunctional dressings harnessing the piezoelectric effect.

The Preparation and Characterization of Chitosan/Calcium Phosphate Composite Microspheres for Biomedical Applications

In this study, we successfully prepared porous composite microspheres composed of hydroxyapatite (HAp), di-calcium phosphate di-hydrated (DCPD), and chitosan through the hydrothermal method. The chitosan played a crucial role as a chelating agent to facilitate the growth of related calcium phosphates. The synthesized porous composite microspheres exhibit a specific surface area of 38.16 m2/g and a pore volume of 0.24 cm3/g, with the pore size ranging from 4 to 100 nm. Given the unique properties of chitosan and the exceptional porosity of these composite microspheres, they may serve as carriers for pharmaceuticals. After being annealed, the chitosan transforms into a condensed form and the DCPD transforms into Ca2P2O7 at 300 °C. Then, the Ca2P2O7 initially combines with HAp to transform into β tricalcium phosphate (β-TCP) at 500 °C where the chitosan is also completely combusted. Finally, the microspheres are composed of Ca2P2O7, β-TCP, and HAp, also making them suitable for applications such as injectable bone graft materials.

Injectable and biodegradable piezoelectric hydrogel for osteoarthritis treatment

Osteoarthritis affects millions of people worldwide but current treatments using analgesics or anti-inflammatory drugs only alleviate symptoms of this disease. Here, we present an injectable, biodegradable piezoelectric hydrogel, made of short electrospun poly-L-lactic acid nanofibers embedded inside a collagen matrix, which can be injected into the joints and self-produce localized electrical cues under ultrasound activation to drive cartilage healing. In vitro, data shows that the piezoelectric hydrogel with ultrasound can enhance cell migration and induce stem cells to secrete TGF-β1, which promotes chondrogenesis. In vivo, the rabbits with osteochondral critical-size defects receiving the ultrasound-activated piezoelectric hydrogel show increased subchondral bone formation, improved hyaline-cartilage structure, and good mechanical properties, close to healthy native cartilage. This piezoelectric hydrogel is not only useful for cartilage healing but also potentially applicable to other tissue regeneration, offering a significant impact on the field of regenerative tissue engineering.

Microbial Poly(hydroxybutyrate-co-hydroxyvalerate) Scaffold for Periodontal Tissue Engineering

In this study, we fabricated three dimensional (3D) porous scaffolds of poly(hydroxybutyrate-co-hydroxyvalerate) with 50% HV content. P(HB-50HV) was biosynthesized from bacteria Cupriavidus necator H16 and the in vitro proliferation of dental cells for tissue engineering application was evaluated. Comparisons were made with scaffolds prepared by poly(hydroxybutyrate) (PHB), poly(hydroxybutyrate-co-12%hydroxyvalerate) (P(HB-12HV)), and polycaprolactone (PCL). The water contact angle results indicated a hydrophobic character for all polymeric films. All fabricated scaffolds exhibited a high porosity of 90% with a sponge-like appearance. The P(HB-50HV) scaffolds were distinctively different in compressive modulus and was the material with the lowest stiffness among all scaffolds tested between the dry and wet conditions. The human gingival fibroblasts (HGFs) and periodontal ligament stem cells (PDLSCs) cultured onto the P(HB-50HV) scaffold adhered to the scaffold and exhibited the highest proliferation with a healthy morphology, demonstrating excellent cell compatibility with P(HB-50HV) scaffolds. These results indicate that the P(HB-50HV) scaffold could be applied as a biomaterial for periodontal tissue engineering and stem cell applications.

Effects of Electrical Stimulation on Articular Cartilage Regeneration with a Focus on Piezoelectric Biomaterials for Articular Cartilage Tissue Repair and Engineering

There is increasing evidence that chondrocytes within articular cartilage are affected by endogenous force-related electrical potentials. Furthermore, electrical stimulation (ES) promotes the proliferation of chondrocytes and the synthesis of extracellular matrix (ECM) molecules, which accelerate the healing of cartilage defects. These findings suggest the potential application of ES in cartilage repair. In this review, we summarize the pathogenesis of articular cartilage injuries and the current clinical strategies for the treatment of articular cartilage injuries. We then focus on the application of ES in the repair of articular cartilage in vivo. The ES-induced chondrogenic differentiation of mesenchymal stem cells (MSCs) and its potential regulatory mechanism are discussed in detail. In addition, we discuss the potential of applying piezoelectric materials in the process of constructing engineering articular cartilage, highlighting the important advances in the unique field of tissue engineering.

Engineering Dental Tissues Using Biomaterials with Piezoelectric Effect: Current Progress and Future Perspectives

Dental caries and traumatic injuries to teeth may cause irreversible inflammation and eventual death of the dental pulp. Nevertheless, predictably, repair and regeneration of the dentin-pulp complex remain a formidable challenge. In recent years, smart multifunctional materials with antimicrobial, anti-inflammatory, and pro-regenerative properties have emerged as promising approaches to meet this critical clinical need. As a unique class of smart materials, piezoelectric materials have an unprecedented advantage over other stimuli-responsive materials due to their inherent capability to generate electric charges, which have been shown to facilitate both antimicrobial action and tissue regeneration. Nonetheless, studies on piezoelectric biomaterials in the repair and regeneration of the dentin-pulp complex remain limited. In this review, we summarize the biomedical applications of piezoelectric biomaterials in dental applications and elucidate the underlying molecular mechanisms contributing to the biological effect of piezoelectricity. Moreover, we highlight how this state-of-the-art can be further exploited in the future for dental tissue engineering.

Smart piezoelectric biomaterials for tissue engineering and regenerative medicine: a review

Due to the presence of electric fields and piezoelectricity in various living tissues, piezoelectric materials have been incorporated into biomedical applications especially for tissue regeneration. The piezoelectric scaffolds can perfectly mimic the environment of natural tissues. The ability of scaffolds which have been made from piezoelectric materials in promoting cell proliferation and regeneration of damaged tissues has encouraged researchers in biomedical areas to work on various piezoelectric materials for fabricating tissue engineering scaffolds. In this review article, the way that cells of different tissues like cardio, bone, cartilage, bladder, nerve, skin, tendon, and ligament respond to electric fields and the mechanism of tissue regeneration with the help of piezoelectric effect will be discussed. Furthermore, all of the piezoelectric materials are not suitable for biomedical applications even if they have high piezoelectricity since other properties such as biocompatibility are vital. Seen in this light, the proper piezoelectric materials which are approved for biomedical applications are mentioned. Totally, the present review introduces the recent materials and technologies that have been used for tissue engineering besides the role of electric fields in living tissues.

Fabrication, microstructure characterization, and degradation performance of electrospun mats based on poly(3-hydroxybutyrate-co-3 hydroxyvalerate)/polyethylene glycol blend for potential tissue engineering

There have been strong demands for nanofibrous scaffolds fabricated by electrospinning for various fields due to their various advantages. Electrospun poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) fibre mats were prepared. The effects of processing variables as well as the inclusion of poly(ethylene glycol) (PEG) on the morphologies of generated fibres were investigated using Fourier-transform infrared spectroscopy and scanning electron microscopy. The average fibrous diameter was monitored in the range 400-3000 nm relying on the total content of PEG. The fluorescence cell imaging of electrospun mats was also explored. The results of cell viability demonstrated that skin fibroblast BJ-1 cells showed different adhesions and growth rates for the three kinds of PHBV fibres. Electrospun PHBV mats with low amount of PEG offer a high-quality medium for cell growth. Therefore, those mats exhibited high potential for soft tissue engineering, in particular wound healing.

Development and Utilization of Multifunctional Polymeric Scaffolds for the Regulation of Physical Cellular Microenvironments

Polymeric biomaterials exhibit excellent physicochemical characteristics as a scaffold for cell and tissue engineering applications. Chemical modification of the polymers has been the primary mode of functionalization to enhance biocompatibility and regulate cellular behaviors such as cell adhesion, proliferation, differentiation, and maturation. Due to the complexity of the in vivo cellular microenvironments, however, chemical functionalization alone is usually insufficient to develop functionally mature cells/tissues. Therefore, the multifunctional polymeric scaffolds that enable electrical, mechanical, and/or magnetic stimulation to the cells, have gained research interest in the past decade. Such multifunctional scaffolds are often combined with exogenous stimuli to further enhance the tissue and cell behaviors by dynamically controlling the microenvironments of the cells. Significantly improved cell proliferation and differentiation, as well as tissue functionalities, are frequently observed by applying extrinsic physical stimuli on functional polymeric scaffold systems. In this regard, the present paper discusses the current state-of-the-art functionalized polymeric scaffolds, with an emphasis on electrospun fibers, that modulate the physical cell niche to direct cellular behaviors and subsequent functional tissue development. We will also highlight the incorporation of the extrinsic stimuli to augment or activate the functionalized polymeric scaffold system to dynamically stimulate the cells.

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.

Preliminary Study on Fish Scale Collagen Lamellar Matrix as Artificial Cornea

To construct a novel artificial cornea biomaterial, a method to prepare collagen lamellar matrix was developed in this study using grass carp scales as raw materials. The relationship between the structure of fish scale collagen lamellar matrix and the optical and mechanical properties was analyzed, and co-culture of it and rat bone marrow mesenchymal stem cells (BMSCs) was performed to preliminarily analyze the cellular compatibility of fish scale collagen lamellar matrix. The results show that the grass carp scales could be divided into base region, lateral region and parietal region according to the surface morphology. The inorganic calcium in the surface layer could be effectively removed by decalcification, and the decalcification rate could reach 99%. After etching treatment, homogeneous collagen lamellar matrix could be obtained. With the decalcification and etching treatment, the water content of the sample increased gradually, but the cross-linking treatment had no obvious effect on the water content of fish scale collagen lamellar matrix. Fish scale collagen lamellar matrix has good transparency, refractive index, mechanical properties and cellular compatibility, which may represent a prospect for the construction of cornea tissue engineering products.

Poly‐3‐hydroxybutyrate‐based constructs with novel characteristics for drug delivery and tissue engineering applications—A review

Herein, we reviewed polymeric constructs of polyhydroxyalkanoates (PHAs) at large and poly‐3‐hydroxybutyrate (P3HB), in particular, for drug delivery and tissue engineering applications. Polymeric constructs that can efficiently respond to numerous variations in their surroundings have gained notable attention from different industrial sectors such as biomedical, clinical, pharmaceutical, and cosmeceutical. Among them, considerable importance is given to their drug delivery and tissue engineering applications. PHAs with peculiar reference to P3HB are gaining prominence attention as candidate materials with such requisite potentialities. The unique structural and functional characteristics of PHAs and P3HB are of supreme interest and being used to engineer novel constructs for efficient drug delivery and tissue regeneration purposes. So far, an array of methodological approaches, such as in vitro, in vivo, and ex vivo techniques have been exploited though using different materials with different geometries for a said purpose. However, a low‐level production majorly limits their proper exploitation. Various physiochemical characteristics and production strategies have been introduced in this review. The data have been summarized on PHAs production by several microorganisms aiming to cover the scope of the last 10 years. The present review highlights the recent applications of PHAs and P3HB‐based constructs, such as micro/nanoparticles, biocomposite, nanofibers, and hydrogels as novel drug carries for regenerative medicine and tissue engineering. In summary, drug delivery and tissue engineering potentialities of PHAs and P3HB‐based constructs are discussed with suitable examples and envisioned directions of future developments.

A novel long-acting azathioprine polyhydroxyalkanoate nanoparticle enhances treatment efficacy for systemic lupus erythematosus with reduced side effects

Chemical immunosuppressants have been widely used for the treatment of systemic lupus erythematosus (SLE). However, these small chemical drugs suffer from poor solubility, short circulating half-life and adverse side effects. One of the most effective strategies to extend the circulating time is loading drugs into nanocarriers to form nanomedicines, which is of particular interest for the treatment of cancer and viral diseases but has seldom been applied to autoimmune disorders. Herein, we successfully developed an easy but general drug delivery platform based on the new biocompatible polyhydroxyalkanoate (PHA) terpolymer poly(3-hydroxybutyrate-co-3-hydroxyvalerate-co-3-hydroxyhexanoate) (PHBVHHx). In this proof of concept study, we loaded the PHBVHHx nanocarrier with the immunosuppressant azathioprine (AZA) for SLE therapy for the first time. The AZA-PHA nanoparticles possessed ∼30% cytotoxicity and slow clearance from the kidneys. In a murine SLE model, AZA-PHA nanoparticles exhibited superior therapeutic efficacy to AZA and AZA-polylactic acid (PLA) nanoparticles without appreciable toxicity. This delivery system may provide a new and general platform for the development of nanomedicines with enhanced therapeutic efficacy and reduced side effects in SLE therapy.

Cartilage progenitor cells combined with PHBV in cartilage tissue engineering

Background

Bone marrow-derived stem cells (BMSCs) and chondrocytes have been reported to present “dedifferentiation” and “phenotypic loss” during the chondrogenic differentiation process in cartilage tissue engineering, and cartilage progenitor cells (CPCs) are novel seeding cells for cartilage tissue engineering. In our previous study, cartilage progenitor cells from different subtypes of cartilage tissue were isolated and identified in vitro, but the study on in vivo chondrogenic characteristics of cartilage progenitor cells remained rarely. In the current study, we explored the feasibility of combining cartilage progenitor cells with poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) to produce tissue-engineered cartilage and compared the proliferation ability and chondrogenic characteristics of cartilage progenitor cells with those of bone marrow-derived stem cells and chondrocytes.

Methods

These three cells combined with PHBV were cultured in vitro for 1 week without chondrogenic induction and then transplanted subcutaneously into nude mice for 6 weeks. The cell-PHBV constructs were evaluated by gross observation, histological staining, glycosaminoglycan content measurement, biomechanical analysis and RT-PCR.

Results

The chondrocyte-PHBV constructs and CPC-PHBV constructs became an ivory-whitish cartilage-like tissue, while the BMSC-PHBV constructs became vascularized 6 weeks after the subcutaneous implantation. Histological examination showed that many typical cartilage structures were present in the chondrocyte group, some typical cartilage structures were observed in the CPC group, while no typical cartilage structures were observed in the BMSC group.

Conclusions

Cartilage progenitor cells may undergo chondrogenesis without chondrogenic induction and are better at chondrogenesis than BMSCs but worse than chondrocytes in the application of cartilage tissue engineering.

One-Step Labeling of Collagen Hydrogels with Polydopamine and Manganese Porphyrin for Non-Invasive Scaffold Tracking on Magnetic Resonance Imaging

Biomaterial scaffolds are the cornerstone to supporting 3D tissue growth. Optimized scaffold design is critical to successful regeneration, and this optimization requires accurate knowledge of the scaffold's interaction with living tissue in the dynamic in vivo milieu. Unfortunately, non-invasive methods that can probe scaffolds in the intact living subject are largely underexplored, with imaging-based assessment relying on either imaging cells seeded on the scaffold or imaging scaffolds that have been chemically altered. In this work, the authors develop a broadly applicable magnetic resonance imaging (MRI) method to image scaffolds directly. A positive-contrast "bright" manganese porphyrin (MnP) agent for labeling scaffolds is used to achieve high sensitivity and specificity, and polydopamine, a biologically derived universal adhesive, is employed for adhering the MnP. The technique was optimized in vitro on a prototypic collagen gel, and in vivo assessment was performed in rats. The results demonstrate superior in vivo scaffold visualization and the potential for quantitative tracking of degradation over time. Designed with ease of synthesis in mind and general applicability for the continuing expansion of available biomaterials, the proposed method will allow tissue engineers to assess and fine-tune the in vivo behavior of their scaffolds for optimal regeneration.

Developing improved tissue-engineered buccal mucosa grafts for urethral reconstruction

INTRODUCTION

We aimed to compare alternative synthetic scaffolds suitable for future implantation and to examine the use of an inhibitor of lysyl oxidase (beta-amino-propionitrile [β-APN]) to reduce contraction in these implants.

METHODS

Three synthetic scaffolds were compared to natural dermis as substrates for the production of tissue-engineered skin. For natural dermis, Euroskin was used to provide a cell-free cadaveric dermis. Synthetic scaffolds consisted of microfibrous poly-L-lactic acid (PLA), nanofibrous poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), and a micro-/nanofibrous trilayer of PLA-PHBV-PLA. The latter were all electrospun and then all four scaffolds (three synthetic, one natural) were placed in six well plates. A culture well was formed on the scaffold using a 1 cm diameter stainless steel ring and 1.5×105 oral fibroblasts were seeded one side; after two days of culture, the ring was placed on the other side of the scaffolds and 3×105 oral keratinocytes were seeded on to the scaffolds and cultured with keratinocytes uppermost. After a further two days of culture, scaffolds were cut to 1 cm2 and raised to an air-liquid interface on stainless steel grids; some were treated with 200 μg/mL β-APN throughout the culture period (28 days). Contraction in vitro was assessed by serial digital photography of cell-seeded scaffolds and cell-free scaffolds three times a week for 28 days. All cell-seeded scaffolds were assessed for cell metabolic activity, mechanical properties, histology, and morphology by scanning electron microscopy (SEM).

RESULTS

The mean fibre diameters and pore sizes of PLA and PHBV scaffolds were 2.4±0.77, 0.85±0.21 μm (p<0.001), and 10.8±2.3, 4.3±1.1 μm (p<0.001), respectively. Oral fibroblasts and keratinocytes were tightly adhered and grew well on both surfaces of trilayer. The ultimate tensile strength (UTS) and Young's modulus (YM) of PLA samples were significantly lower than Euroskin (p<0.001 and p<0.05, respectively); only the UTS of the trilayer samples was slightly significantly lower (p<0.05). Metabolic activity was significantly increased for cells on all scaffolds, without significant differences between them from Day 0 to Day 28. There were no adverse effects of β-APN on cell viability. With respect to contraction, cells on trilayer and PHBV monolayers did not undergo any significant contraction; however, cells on PLA monolayer and Euroskin contracted 25.3% and 56.4%, respectively, over 28 days. The addition of 200 μg/ml β-APN significantly reduced contraction of Euroskin compared with the control (p<0.01); however, β-APN did not affect PLA contraction during this culture period (p>0.05).

CONCLUSIONS

This study shows that a trilayer micro-nano-3D porous synthetic scaffold is suitable for oral keratinocyte and fibroblast growth with good cell viability and minimal contraction. This material also has good mechanical properties and histological analyses showed its ability to mimic normal human oral mucosal morphology. Furthermore, synthetic trilayer scaffolds have advantages over biological scaffolds - there is no risk of disease transmission or immunological rejection and they appear resistant to contraction. We suggest they present a good alternative to allodermis for future use in urethral reconstruction.

Piezoelectric smart biomaterials for bone and cartilage tissue engineering

Tissues like bone and cartilage are remodeled dynamically for their functional requirements by signaling pathways. The signals are controlled by the cells and extracellular matrix and transmitted through an electrical and chemical synapse. Scaffold-based tissue engineering therapies largely disturb the natural signaling pathways, due to their rigidity towards signal conduction, despite their therapeutic advantages. Thus, there is a high need of smart biomaterials, which can conveniently generate and transfer the bioelectric signals analogous to native tissues for appropriate physiological functions. Piezoelectric materials can generate electrical signals in response to the applied stress. Furthermore, they can stimulate the signaling pathways and thereby enhance the tissue regeneration at the impaired site. The piezoelectric scaffolds can act as sensitive mechanoelectrical transduction systems. Hence, it is applicable to the regions, where mechanical loads are predominant. The present review is mainly concentrated on the mechanism related to the electrical stimulation in a biological system and the different piezoelectric materials suitable for bone and cartilage tissue engineering.

Surface modification of PHBV nanofiber mats for rapid cell cultivation and harvesting

To maintain the original function of a specific tissue for therapeutic tissue engineering, an advanced cell culture surface for repeat cell proliferation is necessary. We designed a novel cell proliferation and rapid harvesting surface by combining nonwoven nanofiber mat and a thermo-responsive polymer. Nanofibrous poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) mats were fabricated by the electrospinning technique. A poly(N-isopropylacrylamide) (PNIPAM) thermo-responsive layer was grafted on the PHBV nanofiber mat by electron beam irradiation. The average diameter of the PNIPAM-grafted PHBV nanofibers was determined by SEM. ATR-FTIR and ESCA were used to confirm the grafting of PNIPAM onto the PHBV nanofiber surface. Water contact angles on the mats were measured in response to temperature changes. Human adipose-derived stem cells (ADSCs) were cultured on the PNIPAM-grafted PHBV nanofiber mat to investigate cell proliferation, harvesting, and functionality during repeat subculture. Detached ADSCs from each surface by low temperature treatment and trypsin-EDTA were compared by a fluorescence-activated cell sorter (FACS) using expression of stem cell membrane-specific markers such as CD-13 PE, CD-29 PE, and CD-90 FITC. The mass cultivation and intact harvesting of stem cells by low temperature treatment using a thermo-responsive PHBV nanofiber mat is a promising technique for use in regenerative medicine and stem cell therapy.

Assessment of Scaffolding Properties for Chondrogenic Differentiation of Adipose-Derived Mesenchymal Stem Cells in Nasal Reconstruction

Importance

Nasal reconstruction in patients who are missing a significant amount of structural nasal support remains a difficult challenge. One challenge is the deficiency of cartilage left within the nose as a consequence of rhinectomy or a midline destructive disease. Historically, the standard donor source for large quantities of native cartilage has been costal cartilage.

Objective

To enable the development of protocols for new mesenchymal stem cell technologies as alternative procedures with reduced donor site morbidity, risk of infection and extrusion.

Design, Setting, and Materials

We examined 6 popular scaffold materials in current practice in terms of their biodegradability in tissue culture, effect on adipose-derived mesenchymal stem cell growth, and chondrogenic fate commitment. Various biomaterials of matching size, porosity, and fiber alignment were synthesized by electrospinning and overlaid with rabbit adipose-derived mesenchymal cells in media supplemented or not with chondrogenic factors. Experiments were performed in vitro using as end points biomarkers for cell growth and chondrogenic differentiation. Polydioxanone (PDO), poly-3-hydroxybutyrate-co-3-hydroxyvalerate (PHBV), PHBV-polycaprolactone, poly(L-lactide-co-caprolactone), poly(lactic-co-glycolic acid), and polystyrene scaffolds of 60% to 70% porosity and random fiber alignment were coated with poly(L)-lysine/laminin to promote cell adhesion and incubated for 28 days with 2.5 to 3.5 × 105 rabbit adipose mesenchymal cells.

Main Outcomes and Measures

Cell growth was measured by fluorometric DNA quantitation and chondrogenic differentiation of stem cells by spectrophotometric sulfated glycosaminoglycan (sGAG) assay. Microscopic visualization of cell growth and matrix deposition on formalin-fixed, paraffin-embedded tissue sections was performed, respectively, with nuclear fast red and Alcian blue.

Results

Of 6 scaffold materials tested using rabbit apidose mesenchymal cells, uncoated scaffolds promoted limited cell adhesion but coating with poly(L)-lysine/laminin enabled efficient cell saturation of scaffold surfaces, albeit with limited involvement of scaffold interiors. Similar growth rates were observed under these conditions, based on DNA content analysis. However, PDO and PHBV/PCL scaffolds supported chondrogenic fate commitment better than other materials, based on soluble sGAG analysis and microscopic observation of chondrogenic matrix deposition. The mean (SD) sGAG scaffold values expressed as fold increase over control were PDO, 2.26 (0.88), PHBV/PCL, 2.09 (0.83), PLCL, 1.36 (0.39), PLGA, 1.34 (0.77), PHBV, 1.07 (0.31), and PS, 0.38 (0.14).

Conclusions and Relevance

These results establish materials, reagents, and protocols for tissue engineering for nasal reconstruction using single-layer, chondrogenically differentiated, adipose-derived mesenchymal stem cells. Stackable, scaffold-supported, multisheet bioengineered tissue may be generated using these protocols.

Level of Evidence

NA.

Experimental wound dressings of degradable PHA for skin defect repair

The present study reports construction of wound dressing materials from degradable natural polymers such as hydroxy derivatives of carboxylic acids (PHAs) and 3-hydroxybutyrate/4-hydroxybutyrate [P(3HB/4HB)] as copolymer. The developed polymer films and electrospun membranes were evaluated for its wound healing properties with Grafts-elastic nonwoven membranes carrying fibroblast cells derived from adipose tissue multipotent mesenchymal stem cells. The efficacy of nonwoven membranes of P(3HB/4HB) carrying the culture of allogenic fibroblasts was assessed against model skin defects in Wistar rats. The morphological, histological and molecular studies revealed the presence of fibroblasts on dressing materials which facilitated wound healing, vascularization and regeneration. Further it was also observed that cells secreted extracellular matrix proteins which formed a layer on the surface of membranes and promoted the migration of epidermal cells from the neighboring tissues surrounding the wound. The wounds under the P(3HB/4HB) membrane carrying cells healed 1.4 times faster than the wounds under the cell-free membrane and 3.5 times faster than the wounds healing under the eschar (control).The complete wound healing process was achieved at Day 14. Thus the study highlights the importance of nonwoven membranes developed from degradable P(3HB/4HB) polymers in reducing inflammation, enhancing angiogenic properties of skin and facilitating better wound healing process.

Composite hydrogel of chitosan-poly(hydroxybutyrate-co-valerate) with chondroitin sulfate nanoparticles for nucleus pulposus tissue engineering

Intervertebral disc degeneration, occurring mainly in nucleus pulposus (NP), is a leading cause of low back pain. In seeking to mitigate this condition, investigators in the field of NP tissue engineering have increasingly studied the use of hydrogels. However, these hydrogels should possess appropriate mechanical strength and swelling pressure, and concurrently support the proliferation of chondrocyte-like cells. The objective of this study was to develop and validate a composite hydrogel for NP tissue engineering, made of chitosan-poly(hydroxybutyrate-co-valerate) (CP) with chondroitin sulfate (CS) nanoparticles, without using a cross linker. The water uptake ability, as well as the viscoelastic properties of this composite hydrogel, was similar to native tissue, as reflected in the complex shear modulus and stress relaxation values. The hydrogel could withstand varying stress corresponding to daily activities like lying down (0.01 MPa), sitting (0.5 MPa) and standing (1.0 MPa) under dynamic conditions. The hydrogels were stable in PBS for 2 weeks and its stiffness, elastic and viscous modulus did not alter significantly during this period. Both CP and CP-CS hydrogels could assist the viability and adhesion of adipose derived rat mesenchymal stem cells (ADMSCs). The viability and chondrogenic differentiation of MSCs was significantly enhanced in presence of CS nanoparticles. Thus, CS nanoparticles-incorporated chitosan-PHBV hydrogels offer great potential for NP tissue engineering.

FMN-coated fluorescent USPIO for cell labeling and non-invasive MR imaging in tissue engineering

Non-invasive magnetic resonance imaging (MRI) is gaining significant attention in the field of tissue engineering, since it can provide valuable information on in vitro production parameters and in vivo performance. It can e.g. be used to monitor the morphology, location and function of the regenerated tissue, the integrity, remodeling and resorption of the scaffold, and the fate of the implanted cells. Since cells are not visible using conventional MR techniques, ultrasmall superparamagnetic iron oxide (USPIO) nanoparticles are routinely employed to label and monitor the cells embedded in tissue-engineered implants. We here set out to optimize cell labeling procedures with regard to labeling efficiency, biocompatibility and in vitro validation during bioreactor cultivation, using flavin mononucleotide (FMN)-coated fluorescent USPIO (FLUSPIO). Efficient FLUSPIO uptake is demonstrated in three different cell lines, applying relatively short incubation times and low labeling concentrations. FLUSPIO-labeled cells were successfully employed to visualize collagen scaffolds and tissue-engineered vascular grafts. Besides promoting safe and efficient cell uptake, an exquisite property of the non-polymeric FMN-coating is that it renders the USPIO fluorescent, providing a means for in vitro, in vivo and ex vivo validation via fluorescence microscopy and fluorescence reflectance imaging (FRI). FLUSPIO cell labeling is consequently considered to be a suitable tool for theranostic tissue engineering purposes.

Iron Oxide-labeled Collagen Scaffolds for Non-invasive MR Imaging in Tissue Engineering

Non-invasive imaging holds significant potential for implementation in tissue engineering. It can e.g. be used to monitor the localization and function of tissue-engineered implants, as well as their resorption and remodelling. Thus far, however, the vast majority of efforts in this area of research have focused on the use of ultrasmall super-paramagnetic iron oxide (USPIO) nanoparticle-labeled cells, colonizing the scaffolds, to indirectly image the implant material. Reasoning that directly labeling scaffold materials might be more beneficial (enabling imaging also in case of non-cellularized implants), more informative (enabling the non-invasive visualization and quantification of scaffold degradation) and more easy to translate into the clinic (since cell-free materials are less complex from a regulatory point-of-view), we here prepared three different types of USPIO nanoparticles, and incorporated them both passively and actively (via chemical conjugation; during collagen crosslinking) into collagen-based scaffold materials. We furthermore optimized the amount of USPIO incorporated into the scaffolds, correlated the amount of entrapped USPIO with MR signal intensity, showed that the labeled scaffolds are highly biocompatible, demonstrated that scaffold degradation can be visualized using MRI and provided initial proof-of-principle for the in vivo visualization of the scaffolds. Consequently, USPIO-labeled scaffold materials seem to be highly suitable for image-guided tissue engineering applications.

Cell-free cartilage engineering approach using hyaluronic acid–polycaprolactone scaffolds: A study in vivo

Polycaprolactone scaffolds modified with cross-linked hyaluronic acid were prepared in order to establish whether a more hydrophilic and biomimetic microenvironment benefits the progenitor cells arriving from bone marrow in a cell-free tissue-engineering approach. The polycaprolactone and polycaprolactone/hyaluronic acid scaffolds were characterized in terms of morphology and water absorption capacity. The polycaprolactone and polycaprolactone/hyaluronic acid samples were implanted in a chondral defect in rabbits; bleeding of the subchondral bone was provoked to generate a spontaneous healing response. Repair at 1, 4, 12, and 24 weeks was assessed macroscopically using the International Cartilage Repair Society score and the Oswestry Arthroscopy Score and microscopically using immunohistological staining for collagen type I and type II, and for Ki-67. The presence of hyaluronic acid improves scaffold performance, which supports a good repair response without biomaterial pre-seeding.

Improvement of PHBV scaffolds with bioglass for cartilage tissue engineering

Polymer scaffold systems consisting of poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) have proven to be possible matrices for the three-dimensional growth of chondrocyte cultures. However, the engineered cartilage grown on these PHBV scaffolds is currently unsatisfactory for clinical applications due to PHBV’s poor hydrophilicity, resulting in inadequate thickness and poor biomechanical properties of the engineered cartilage. It has been reported that the incorporation of Bioglass (BG) into PHBV can improve the hydrophilicity of the composites. In this study, we compared the effects of PHBV scaffolds and PHBV/BG composite scaffolds on the properties of engineered cartilage in vivo. Rabbit articular chondrocytes were seeded into PHBV scaffolds and PHBV/BG scaffolds. Short-term in vitro culture followed by long-term in vivo transplantation was performed to evaluate the difference in cartilage regeneration between the cartilage layers grown on PHBV and PHBV/BG scaffolds. The results show that the incorporation of BG into PHBV efficiently improved both the hydrophilicity of the composites and the percentage of adhered cells and promoted cell migration into the inner part the constructs. With prolonged incubation time in vivo, the chondrocyte-scaffold constructs in the PHBV/BG group formed thicker cartilage-like tissue with better biomechanical properties and a higher cartilage matrix content than the constructs in the PHBV/BG group. These results indicate that PHBV/BG scaffolds can be used to prepare better engineered cartilage than pure PHBV.

Hydrogen sulfide prevents H₂O₂-induced senescence in human umbilical vein endothelial cells through SIRT1 activation

The aim of the present study was to investigate the attenuation of endothelial cell senescence by H2S and to explore the mechanisms underlying the anti-aging effects of H2S. Senescence was induced in human umbilical vein endothelial cells (HUVECs) by incubation in 25 µmol/l H2O2 for 1 h. Senescence-associated β-galactosidase (SA-β-gal) activity was examined to determine the effects of H2S on senescent HUVECs. The results indicated that SA-β-gal activity in the H2O2-treated HUVECs was 11.2 ± 1.06%, which was attenuated in the NaHS group. Pretreatment with nicotinamide (NAM), a sirtuin 1 (SIRT1) inhibitor, inhibited the reduction in senescence associated with H2S. Immunoblot analyses revealed that SIRT1 levels in senescent HUVECs treated with NaHS (60 µM) were indistinguishable from controls; however, analyses of SIRT1 activity indicated that SIRT1 enzyme activity was enhanced. In addition, we found that H2S improves the function of senescent HUVECs. The present study demonstrated that H2S protects against HUVEC senescence, potentially through modulation of SIRT1 activity. Furthermore, this study establishes a novel endothelial protective effect of H2S.