In vivo biocompatibility and vascularization of biodegradable porous polyurethane scaffolds for tissue engineering

Fabrication of chitosan-based fluorescent hydrogel membranes cross-linked with bisbenzaldehyde for efficient selective detection and adsorption of Fe2

Chitosan, as a natural biomass material, is green, recyclable, sustainable and well biocompatible. The molecular chain is rich in active groups such as amino and hydroxyl groups, and its preparation of fluorescent probes has the advantages of biocompatibility and efficient detection performance. In this study, a bis(benzaldehyde) (BHD) fluorescent functional molecule was designed. Then a series of fluorescent chitosan-based hydrogel films (CSBHD) were prepared using chitosan as raw material and BHD as cross-linking agent. As a fluorescent probe for metal ions, CSBHD was able to efficiently detect Fe2+ with a linear correlation of fluorescence intensity in the range of 0-160 μM, and the limit of detection (LOD) was 0.55 μM. Moreover, it has excellent adsorption performance for Fe2+ ions, with a maximum adsorption capacity of 223.5 g/mg at 500 mg/L Fe2+ concentration. Finally, we characterised the structure and microscopic morphology of CSBHD films and found that CSBHD as a hydrogel film has a high cross-linking density, good water resistance, excellent thermal stability, strong resistance to swelling, and excellent stability in cycling tests. Hence, it has great potential for application in adsorption and detection of Fe2+ ions. It also provides a good strategy for the application of chitosan based fluorescent probe materials in environmental monitoring and heavy metal ion adsorption.

In-Bath 3D Printing of Anisotropic Shape-Memory Cryogels Functionalized with Bone-Bioactive Nanoparticles

Cryogels exhibit unique shape memory with full recovery and structural stability features after multiple injections. These constructs also possess enhanced cell permeability and nutrient diffusion when compared to typical bulk hydrogels. Volumetric processing of cryogels functionalized with nanosized units has potential to widen their biomedical applications, however this has remained challenging and relatively underexplored. In this study, we report a novel methodology that combines suspension 3D printing with directional freezing for the fabrication of nanocomposite cryogels with configurable anisotropy. When compared to conventional bulk or freeze-dried hydrogels, nanocomposite cryogel formulations exhibit excellent shape recovery (>95%) and higher pore connectivity. Suspension printing, assisted with a prechilled metal grid, was optimized to induce anisotropy. The addition of calcium- and phosphate-doped mesoporous silica nanoparticles into the cryogel matrix enhanced bioactivity toward orthopedic applications without hindering the printing process. Notably, the nanocomposite 3D printed cryogels exhibit injectable shape memory while also featuring a lamellar topography. The fabrication of these constructs was highly reproducible and exhibited potential for a cell-delivery injectable cryogel with no cytotoxicity to human-derived adipose stem cells. Hence, in this work, it was possible to combine a gravity defying 3D printed methodology with injectable and controlled anisotropic macroporous structures containing bioactive nanoparticles. This methodology ameliorates highly tunable injectable 3D printed anisotropic nanocomposite cryogels with a user-programmable degree of structural complexity.

Hydroxyapatite/Polyurethane Scaffolds for Bone Tissue Engineering

Polyurethane (PU) and PU ceramic scaffolds are the principal materials investigated for developing synthetic bone materials due to their excellent biocompatibility and biodegradability. PU has been combined with calcium phosphate (such as hydroxyapatite [HA] and tricalcium phosphate) to prepare scaffolds with enhanced mechanical properties and biocompatibility. This article reviews the latest progress in the design, synthesis, modification, and biological attributes of HA/PU scaffolds for bone tissue engineering. Diverse HA/PU scaffolds have been proposed and discussed in terms of their osteogenic, antimicrobial, biocompatibility, and bioactivities. The application progress of HA/PU scaffolds in bone tissue engineering is predominantly introduced, including bone repair, bone defect filling, drug delivery, and long-term implants.

A biomimetic multi-layer scaffold with collagen and zinc doped bioglass as a skin-regeneration agent in full-thickness injuries and its effects in vitro and in vivo

Due to the multilayer structure of skin tissue, the fabrication of a 3-layer scaffold could result in planned dermal regeneration. Herein, polyurethane (PU) and polycaprolactone (PCL), as a function of their mechanical stability and collagen due to its arginine-glycine-aspartic acid sequences, zinc ions because of overcoming the common problems of biological factors were employed. The scaffolds' physical, mechanical, and biological properties were examined by SEM, FTIR, contact angle, mechanical tensile, bacteriocidal efficacy, and hemolysis. Also, after L-929 fibroblast seeding, their biological activity was determined by SEM, DAPI, and MTT assays. Then, the cell-seeded scaffolds were implanted in full-thickness wounds of rats and evaluated by wound closure, histological, and molecular techniques. The in vivo studies showed better wound closure with the composite scaffold containing zinc ions. While its dermal re-organization was retarded in the presence of zinc ions compared to the composite scaffold containing non-doped bioglass. Despite this, the doped composite scaffold indicated better observations with the histological evaluations than the nontreated and bare scaffold groups. Real-time PCR confirmed the higher expression of FGF2 and FGFR genes in rats treated with the zinc-doped composite scaffold. In conclusion, PU/PCL-collagen/PCL-collagen containing the doped or non-doped nanoparticles showed better potential to heal dermal injuries.

Recyclable photoresins for light-mediated additive manufacturing towards Loop 3D printing

Additive manufacturing (AM) of polymeric materials enables the manufacturing of complex structures for a wide range of applications. Among AM methods vat photopolymerization (VP) is desired owing to improved efficiency, excellent surface finish, and printing resolution at the micron-scale. Nevertheless, the major portion of resins available for VP are based on systems with limited or negligible recyclability. Here, we describe an approach that enables the printing of a resin that is amenable to re-printing with retained properties and appearance. To that end, we take advantage of the potential of polythiourethane chemistry, which not only permits the click reaction between polythiols and polyisocyanates in the presence of organic bases, allowing a fast-printing process but also chemical recycling, reshaping, and reparation of the printed structures, paving the way toward the development of truly sustainable recyclable photoprintable resins. We demonstrate that this closed-loop 3D printing process is feasible both at the macroscale and microscale via DLP or DLW, respectively.

Zein nanospheres assisting inorganic and organic drug combination to overcome stent implantation-induced thrombosis and infection

The complication of stent implantation is the biggest obstacle to the success of its clinical application. In this study, we developed a combination way of 3D printing and the coating technique for preparation of functional polyurethane stents against stent implantation-induced thrombosis and postoperative infection. SEM, XPS, static water contact angle, and XRD demonstrated that the functional polyurethane stent had a 37 μm-thickness membrane composed of zein nanospheres (250-350 nm). Meanwhile, ZnO nanoparticles were encapsulated in zein nanospheres while heparin was adsorbed on the surface, causing 97.1 ± 6.4 % release of heparin in 120 min (first-order kinetic model) and 62.7 ± 5.6 % release of Zn²⁺ in 9 days (Korsmeyer-Peppas model). The mechanical analysis revealed that the functional polyurethane stents had about 8.61 MPa and 2.5 MPa tensile strength and bending strength, respectively. The in vitro biological analysis showed that the functional polyurethane stents had good EA.hy926 cells compatibility (97.9 ± 3.8 %), anti-coagulation response (comparable plasma protein, platelet adhesion and suppressed clotting) and sustained antibacterial activities by comparison with the bare polyurethane stent. The preliminary evaluation by rabbit ex vivo carotid artery intervention experiment demonstrated that the functional polyurethane stents could maintain blood circulation under the continuous stresses of blood flow. Meanwhile, the detailed data from the simulated implant infection experiment in vivo showed the functional polyurethane stents could effectively reduce microbial infection by 3-6 times lower and improve fibrosis and macrophage infiltration.

Composition, host responses and clinical applications of bioadhesives

Bioadhesives are medical devices used to join or seal tissues that have been injured or incised. They have been classified into tissue adhesives, sealants, and hemostatic agents. Bioadhesives such as FloSeal®, CoSeal®, BioGlue®, Evicel®, Tisseel®, Progel™ PALS, and TissuGlu® have been commercialized and used in clinical setting. They can be formulated with natural or synthetic components or a combination of both including albumin, glutaraldehyde, chitosan, cyanoacrylate, fibrin and thrombin, gelatin, polyethylene glycol (PEG), along with urethanes. Each formulation has intrinsic properties and has been developed and validated for a specific application. This review article briefs the mechanisms by which bioadhesives forms adhesion to tissues and highlights the correlation between bioadhesives composition and their potential host responses. Furthermore, clinical applications of bioadhesives and their application-driven requirements are outlined.

Polyurethane and polyurethane/hydroxyapatite scaffold in a three-dimensional culture system

Designing a new scaffold with an optimal ability of osteogenesis differentiation is a significant step bone tissue engineering along with the growing demands for bone craft in recent decades. Herein, we used Polyurethane (PU), a novel biocompatible and flexible polymer, and Hydroxyapatite (HA), the major component of human hard tissues matrix for developing new scaffolds and analyzing the in vitro osteogenic differentiation potential of human adipose-derived mesenchymal stem cells (Ad-MSCs) in basal and induction media. Gene expression analysis was performed to evaluate the expression level of four osteogenic differentiation genes. MTT assays were also done to assess the attachment and proliferation of the cells after 7 and 21 days of seeding to scaffolds. The expression level of RUNX2 was increased in seeded cells on PU/HA scaffolds compared with the PU. Cellular adhesion and proliferation of the Ad-MSCs were higher in PU/HA than PU scaffolds according to the histology analysis. The PU and PU/HA scaffolds supported the attachment, proliferation, and differentiation of Ad-MSCs, and they are suitable candidates for producing constructs in bone regeneration. However, further in-vitro and in-vivo studies on these scaffolds are needed to introduce an appropriate candidate for clinical bone regeneration.

Tissue engineering application combining epoxidized natural rubber blend and mesenchymal stem cells in in vivo response

This study aimed to investigate biocompatibility, integration, and tissue host response of the Poly (Lactic-co-Glycolic acid) (PLGA)/Poly (isoprene) (PI) epoxidized (PLGA/PIepox) innovative scaffold combined with adipose derived mesenchymal stem cells (ADSC). We implanted the scaffold subcutaneously on the back of 18 female rats and monitored them for up to 14 days. When compared to controls, PLGA/PIepox + ADSC demonstrated an earlier vascularization, a tendency of inflammation reduction, an adequate tissue integration, higher cell proliferation, and a tendency of expression of collagen decreasing. However, 14 days post-implantation we found similar levels of CD31, Ki67 and AE1/AE3 in PLGA/PIepox when compared to control groups. The interesting results, lead us to the assumption that PLGA/PIepox is able to provide an effective delivery system for ADSC on tissue host. This animal study assesses PLGA/PIepox + ADSC in in vivo tissue functionality and validation of use, serving as a proof of concept for future clinical translation as it presents an innovative and promising tissue engineering opportunity for the use in tissue reconstruction.

Cell-Seeded Biomaterial Scaffolds: The Urgent Need for Unanswered Accelerated Angiogenesis

One of the most arduous challenges in tissue engineering is neovascularization, without which there is a lack of nutrients delivered to a target tissue. Angiogenesis should be completed at an optimal density and within an appropriate period of time to prevent cell necrosis. Failure to meet this challenge brings about poor functionality for the tissue in comparison with the native tissue, extensively reducing cell viability. Prior studies devoted to angiogenesis have provided researchers with some biomaterial scaffolds and cell choices for angiogenesis. For example, while most current angiogenesis approaches require a variety of stimulatory factors ranging from biomechanical to biomolecular to cellular, some other promising stimulatory factors have been underdeveloped (such as electrical, topographical, and magnetic). When it comes to choosing biomaterial scaffolds in tissue engineering for angiogenesis, key traits rush to mind including biocompatibility, appropriate physical and mechanical properties (adhesion strength, shear stress, and malleability), as well as identifying the appropriate biomaterial in terms of stability and degradation profile, all of which may leave essential trace materials behind adversely influencing angiogenesis. Nevertheless, the selection of the best biomaterial and cells still remains an area of hot dispute as such previous studies have not sufficiently classified, integrated, or compared approaches. To address the aforementioned need, this review article summarizes a variety of natural and synthetic scaffolds including hydrogels that support angiogenesis. Furthermore, we review a variety of cell sources utilized for cell seeding and influential factors used for angiogenesis with a concentrated focus on biomechanical factors, with unique stimulatory factors. Lastly, we provide a bottom-to-up overview of angiogenic biomaterials and cell selection, highlighting parameters that need to be addressed in future studies.

Fluorescent dialdehyde-BODIPY chitosan hydrogel and its highly sensing ability to Cu2+ ion

Fluorescent hydrogel with proper hydrophilicity and thermal stability, excellent sensitivity and high selectivity has important practical and scientific significance, especially in heavy metal ion detection. In this work, by adjusting the content of [2, 6-Bis-[4-formylthiophene]]-1,3,5,7-tetramethyl-8-phenyl-4, 4-difluoroborazaindoloene (B3), as a cross-linking agent, a series of chitosan- fluoroboron dipyrrole-chitosan-based fluorescent hydrogels (CBC) with large stokes shift were designed and prepared. The hydrogels can be used as fluorescent probes for identifying Cu²⁺ in aqueous solution. The linear quenching range of Cu²⁺ is 0-50 μM, and the detection limit and quenching constant are 4.75 μM and 3.52 × 10⁴ M^-1, respectively. Under the interaction of Cu²⁺, the imine bond CN was converted to C- N bond, which causes the phenomenon of fluorescence quenching. In addition, relatively high crosslink density improves hydrophilicity and thermal stability of initial chitosan, and made the swelling ability better.

Biostable Shape Memory Polymer Foams for Smart Biomaterial Applications

Polyurethane foams provide a wide range of applications as a biomaterial system due to the ability to tune their physical, chemical, and biological properties to meet the requirements of the intended applications. Another key parameter that determines the usability of this biomaterial is its degradability under body conditions. Several current approaches focus on slowing the degradation rate for applications that require the implant to be present for a longer time frame (over 100 days). Here, biostable shape memory polymer (SMP) foams were synthesized with added ether-containing monomers to tune the degradation rates. The physical, thermal and shape memory properties of these foams were characterized along with their cytocompatibility and blood interactions. Degradation profiles were assessed in vitro in oxidative (3% H₂O₂; real-time) and hydrolytic media (0.1 M NaOH; accelerated) at 37 °C. The resulting foams had tunable degradation rates, with up 15% mass remaining after 108 days, and controlled erosion profiles. These easy-to-use, shape-filling SMP foams have the potential for various biomaterial applications where longer-term stability without the need for implant removal is desired.

Shape Memory Polymer Foams with Tunable Degradation Profiles

Uncontrolled hemorrhage is the leading cause of preventable death on the battlefield and results in ∼1.5 million deaths each year. The primary current treatment options are gauze and/or tourniquets, which are ineffective for up to 80% of wounds. Additionally, most hemostatic materials must be removed from the patient within <12 h, which limits their applicability in remote scenarios and can cause additional bleeding upon removal. Here, degradable shape memory polymer (SMP) foams were synthesized to overcome these limitations. SMP foams were modified with oxidatively labile ether groups and hydrolytically labile ester groups to degrade after implantation. Foam physical, thermal, and shape memory properties were assessed along with cytocompatibility and blood interactions. Degradation profiles were obtained in vitro in oxidative and hydrolytic media (3% H2O2 (oxidation) and 0.1 M NaOH (hydrolysis) at 37 °C). The resulting foams had tunable, clinically relevant degradation rates, with complete mass loss within 30-60 days. These SMP foams have potential to provide an easy-to-use, shape-filling hemostatic dressing that can be left in place during traumatic wound healing with future potential use in regenerative medicine applications.

Recent Developments in Polyurethane-Based Materials for Bone Tissue Engineering

To meet the needs of clinical medicine, bone tissue engineering is developing dynamically. Scaffolds for bone healing might be used as solid, preformed scaffolding materials, or through the injection of a solidifiable precursor into the defective tissue. There are miscellaneous biomaterials used to stimulate bone repair including ceramics, metals, naturally derived polymers, synthetic polymers, and other biocompatible substances. Combining ceramics and metals or polymers holds promise for future cures as the materials complement each other. Further research must explain the limitations of the size of the defects of each scaffold, and additionally, check the possibility of regeneration after implantation and resistance to disease. Before tissue engineering, a lot of bone defects were treated with autogenous bone grafts. Biodegradable polymers are widely applied as porous scaffolds in bone tissue engineering. The most valuable features of biodegradable polyurethanes are good biocompatibility, bioactivity, bioconductivity, and injectability. They may also be used as temporary extracellular matrix (ECM) in bone tissue healing and regeneration. Herein, the current state concerning polyurethanes in bone tissue engineering are discussed and introduced, as well as future trends.

Graphene-based hybrid materials as promising scaffolds for peripheral nerve regeneration

Peripheral nerve injury (PNI) is a serious clinical health problem caused by the damage of peripheral nerves which results in neurological deficits and permanent disability. There are several factors that may cause PNI such as localized damage (car accident, trauma, electrical injury) and outbreak of the systemic diseases (autoimmune or diabetes). While various diagnostic procedures including X-ray, magnetic resonance imaging (MRI), as well as other type of examinations such as electromyography or nerve conduction studies have been efficiently developed, a full recovery in patients with PNI is in many cases deficient or incomplete. This is the reason why additional therapeutic strategies should be explored to favor a complete rehabilitation in order to get appropriate nerve injury regeneration. The use of biomaterials acting as scaffolds opens an interesting approach in regenerative medicine and tissue engineering applications due to their ability to guide the growth of new tissues, adhesion and proliferation of cells including the expression of bioactive signals. This review discusses the preparation and therapeutic strategies describing in vitro and in vivo experiments using graphene-based materials in the context of PNI and their ability to promote nerve tissue regeneration.

Actually Seeing What Is Going on - Intravital Microscopy in Tissue Engineering

Intravital microscopy (IVM) study approach offers several advantages over in vitro, ex vivo, and 3D models. IVM provides real-time imaging of cellular events, which provides us a comprehensive picture of dynamic processes. Rapid improvement in microscopy techniques has permitted deep tissue imaging at a higher resolution. Advances in fluorescence tagging methods enable tracking of specific cell types. Moreover, IVM can serve as an important tool to study different stages of tissue regeneration processes. Furthermore, the compatibility of different tissue engineered constructs can be analyzed. IVM is also a promising approach to investigate host reactions on implanted biomaterials. IVM can provide instant feedback for improvising tissue engineering strategies. In this review, we aim to provide an overview of the requirements and applications of different IVM approaches. First, we will discuss the history of IVM development, and then we will provide an overview of available optical modalities including the pros and cons. Later, we will summarize different fluorescence labeling methods. In the final section, we will discuss well-established chronic and acute IVM models for different organs.

Tendon-like tether formation for tongue-base advancement in an ovine model using a novel implant device intended for the surgical management of obstructive sleep apnoea

Obstructive sleep apnoea (OSA) is a serious debilitating condition with significant morbidity and mortality affecting almost one billion adults globally. The current gold standard in the non-surgical management of airway collapse is continuous positive airway pressure (CPAP). However, non-compliance leads to a high abandon rate (27-46%). While there are multiple sites of airway obstruction during sleep, the tongue base is recognized as the key player in the pathogenesis of OSA. Poor outcomes of current tongue suspension devices are due to fracture, slippage or migration of devices. Three tongue tethering device groups, namely a polydioxanone/polyurethane combination (PDO + PU) treatment group, a PDO analytical control group, and a polypropylene (PP) descriptive control group, were implanted into 22 sheep (75-85 kg) in a two-phased study. After implant times of 8, 16, and 32 weeks, sheep were serially euthanized to allow for explantation of their tongues and chins. The PDO + PU devices remodeled during the 32-week implant period into a hybrid biological tendon-like tether through the process of gradual degradation of the PDO and collagen deposition as shown by electrophoresis, histology and mechanical testing. The control PDO device degraded completely after 32 weeks and the PP devices remained intact. The hybrid biological tendon-like tether exhibited a break-strength of 60 N, thus exceeding the maximum force to overcome upper airway collapse.

In Vitro and in Vivo Analysis of Adhesive, Anti-Inflammatory, and Proangiogenic Properties of Novel 3D Printed Hyaluronic Acid Glycidyl Methacrylate Hydrogel Scaffolds for Tissue Engineering

In this study, we prepared hydrogel scaffolds for tissue engineering by computer-assisted extrusion three-dimensional (3D) printing with photocured (λ = 445 nm) hyaluronic acid glycidyl methacrylate (HAGM). The developed product was compared with the polylactic-co-glycolic acid (PLGA) scaffolds generated by means of the original antisolvent 3D printing methodology. The cytotoxicity and cytocompatibility of the scaffolds were analyzed in vitro by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide tests, flow cytometry, and scanning electron microscopy. Anti-inflammatory and proangiogenic properties of the scaffolds were evaluated in the dorsal skinfold chamber mouse model by means of intravital fluorescence microscopy, histology, and immunohistochemistry throughout an observation period of 14 days. In vitro, none of the scaffolds revealed cytotoxicity on days 1, 2, and 5 after seeding with umbilical cord-derived multipotent stromal cells, and the primary cell adhesion to the surface of HAGM scaffolds was low. In vivo, implanted HAGM scaffolds showed enhanced vascularization and host tissue ingrowth, and the inflammatory response to them was less pronounced compared with PLGA scaffolds. The results indicate excellent biocompatibility and vascularization capacity of the developed 3D printed HAGM scaffolds and position them as strong candidates for advanced tissue engineering applications.

Designing Polymeric Mixed Conductors and Their Application to Electrochemical-Transistor-Based Biosensors

Organic electrochemical transistors that employ polymeric mixed conductors as their active channels are one of the most prominent biosensor platforms because of their signal amplification capability, low fabrication cost, mechanical flexibility, and various properties tunable through molecular design. For application to biomedical devices, polymeric mixed conductors should fulfill several requirements, such as excellent conductivities of both holes/electrons and ions, long-term operation stability, and decent biocompatibility. However, trade-offs may exist, for instance, one between ionic conduction and overall device stability. In this report, the fundamental understanding of polymeric mixed conductors, the recent advance in enhancing their ionic and electrical conductivity, and their practical applications as biosensors based on organic electrochemical transistors are reviewed. Finally, key strategies are suggested for developing novel polymeric mixed conductors that may exceed the trade-off between device performance and stability.

Farnesol-Containing Macromolecular Systems for Antibiofilm Strategies

Farnesol is a natural sesquiterpenoid and an interesting quorum-sensing molecule. Its insolubility in water is the biggest obstacle to its application for bacterial biofilm treatments since it compromises the bioavailability. Recently, an increasing interest in farnesol encapsulation or loading in polymeric materials may be noted due to the prolonged action of the active macromolecular systems. In this short review, we present an overview of methods leading to improved interactions between farnesol and microbial biofilms.

Poly-phosphate increases SMC differentiation of mesenchymal stem cells on PLGA-polyurethane nanofibrous scaffold

The use of bioactive scaffolds in tissue engineering has a significant effect on the damaged tissue healing by an increase in speed and quality of the process. Herein, electrospinning was applied to fabricate composite nanofibrous scaffolds by Poly lactic-co-glycolic acid (PLGA) and Polyurethane (PU) with and without poly-phosphate (poly-P). Scaffolds were characterized morphologically by scanning electron microscope (SEM), and their biocompatibility was also investigated by SEM, protein adsorption, cell attachment and survival assays. The applicability of the scaffolds for bladder tissue engineering was also evaluated by culturing mesenchymal stem cells (MSCs) on the scaffolds and their differentiation into smooth muscle cell (SMC) was studied at the gene and protein levels. The results demonstrated that scaffold biocompatibility was increased significantly by loading poly-P. SMC related gene and protein expression level in MSCs cultured on poly-P-loaded scaffold was also increased significantly compared to those cells cultured on empty scaffold. It can be concluded that poly-P hasn’t also increased scaffold biocompatibility, but also SMC differentiation potential of MSCs was also increased while cultured on the poly-P containing scaffold compared to the empty scaffold. Taken together, our study showed that PLGA–PU–poly-P alone and in combination with MSCs has a promising potential for support urinary bladder smooth muscle tissue engineering.

Biological coating with platelet-rich plasma and adipose tissue-derived microvascular fragments improves the vascularization, biocompatibility and tissue incorporation of porous polyethylene

Porous polyethylene (pPE) is a commonly used biomaterial in craniofacial reconstructive surgery. However, implant failure due to insufficient vascularization represents a major issue. To overcome this problem, we herein introduce an effective strategy to improve the vascularization and incorporation of pPE. Adipose tissue-derived microvascular fragments (MVF) from transgenic green fluorescent protein (GFP)⁺ mice were suspended in platelet-rich plasma (PRP) for the coating of pPE. PRP/MVF-coated pPE as well as PRP-coated and uncoated controls were subsequently implanted into the dorsal skinfold chamber and the flanks of GFP^- wild-type mice to analyze their in vivo performance throughout 2, 4 and 8 weeks by means of intravital fluorescence microscopy, histology and immunohistochemistry. The GFP⁺/GFP^- cross-over design allowed the identification of GFP⁺ MVF within the implants. Shortly after implantation, they rapidly reassembled into new blood-perfused microvascular networks, resulting in a significantly accelerated vascularization of PRP/MVF-coated pPE when compared to both controls. The overall numbers of rolling and adherent leukocytes within the microcirculation as well as macrophages, multi-nucleated giant cells and mast cells around the implants did not differ between the three groups. However, in contrast to uncoated controls, PRP/MVF-coated and PRP-coated pPE promoted pro-angiogenic M2 macrophage polarization at the implantation site. These findings demonstrate that PRP/MVF-coating represents a highly effective strategy to enhance the vascularization, biocompatibility and tissue incorporation of pPE. STATEMENT OF SIGNIFICANCE: The clinical in vivo performance of implanted biomaterials is crucially dependent on their adequate incorporation into the body. To achieve this, we herein introduce an effective biological coating strategy. Our results demonstrate that coating with PRP and MVF accelerates and enhances the vascularization, biocompatibility and tissue incorporation of porous polyethylene. Because this type of biological coating is easily applicable on any type of biomaterial, our approach may rapidly be translated into clinical practice to improve the outcome of various regenerative approaches.

Bone Substitutes in Orthopaedic Surgery: Current Status and Future Perspectives

Bone replacement materials have been successfully supplied for a long time. But there are cases, especially in critical sized bone defects, in which the therapy is not sufficient. Nowadays, there are multiple bone substitutes available. Autologous bone grafts remain the "gold standard" in bone regeneration. Yet, donor-site morbidity and the available amount of sufficient material are limitations for autologous bone grafting. This study aimed to provide information about the current status in research regarding bone substitutes. We report on the advantages and drawbacks of several bone substitutes. At the end, we discuss the current developments of combining ceramic substitutes with osteoinductive substances.

Bone Tissue Regeneration in the Oral and Maxillofacial Region: A Review on the Application of Stem Cells and New Strategies to Improve Vascularization

Bone tissue engineering techniques are a promising alternative for the use of autologous bone grafts to reconstruct bone defects in the oral and maxillofacial region. However, for successful bone regeneration, adequate vascularization is a prerequisite. This review presents and discusses the application of stem cells and new strategies to improve vascularization, which may lead to feasible clinical applications. Multiple sources of stem cells have been investigated for bone tissue engineering. The stromal vascular fraction (SVF) of human adipose tissue is considered a promising single source for a heterogeneous population of essential cells with, amongst others, osteogenic and angiogenic potential. Enhanced vascularization of tissue-engineered grafts can be achieved by different mechanisms: vascular ingrowth directed from the surrounding host tissue to the implanted graft, vice versa, or concomitantly. Vascular ingrowth into the implanted graft can be enhanced by (i) optimizing the material properties of scaffolds and (ii) their bioactivation by incorporation of growth factors or cell seeding. Vascular ingrowth directed from the implanted graft towards the host tissue can be achieved by incorporating the graft with either (i) preformed microvascular networks or (ii) microvascular fragments (MF). The latter may have stimulating actions on both vascular ingrowth and outgrowth, since they contain angiogenic stem cells like SVF, as well as vascularized matrix fragments. Both adipose tissue-derived SVF and MF are cell sources with clinical feasibility due to their large quantities that can be harvested and applied in a one-step surgical procedure. During the past years, important advancements of stem cell application and vascularization in bone tissue regeneration have been made. The development of engineered in vitro 3D models mimicking the bone defect environment would facilitate new strategies in bone tissue engineering. Successful clinical application requires innovative future investigations enhancing vascularization.

Nanocellulose/bioactive glass cryogels as scaffolds for bone regeneration

A major challenge exists in the preparation of scaffolds for bone regeneration, namely, achieving simultaneously bioactivity, biocompatibility, mechanical performance and simple manufacturing. Here, cellulose nanofibrils (CNF) are introduced for the preparation of scaffolds taking advantage of their biocompatibility and ability to form strong 3D porous networks from aqueous suspensions. CNF are made bioactive for bone formation through a simple and scalable strategy that achieves highly interconnected 3D networks. The resultant materials optimally combine morphological and mechanical features and facilitate hydroxyapatite formation while releasing essential ions for in vivo bone repair. The porosity and roughness of the scaffolds favor several cell functions while the ions act in the expression of genes associated with cell differentiation. Ion release is found critical to enhance the production of the bone morphogenetic protein 2 (BMP-2) from cells within the fractured area, thus accelerating the in vivo bone repair. Systemic biocompatibility indicates no negative effects on vital organs such as the liver and kidneys. The results pave the way towards a facile preparation of advanced, high performance CNF-based scaffolds for bone tissue engineering.

Modulation of Cellular Colonization of Porous Polyurethane Scaffolds via the Control of Pore Interconnection Size and Nanoscale Surface Modifications

Full-scale cell penetration within porous scaffolds is required to obtain functional connective tissue components in tissue engineering applications. For this aim, we produced porous polyurethane structures with well-controlled pore and interconnection sizes. Although the influence of the pore size on cellular behavior is widely studied, we focused on the impact of the size of the interconnections on the colonization by NIH 3T3 fibroblasts and Wharton's jelly-derived mesenchymal stem cells (WJMSCs). To render the material hydrophilic and allow good material wettability, we treated the material either by plasma or by polydopamine (PDA) coating. We show that cells weakly adhere on these surfaces. Keeping the average pore diameter constant at 133 μm, we compare two structures, one with LARGE (52 μm) and one with SMALL (27 μm) interconnection diameters. DNA quantification and extracellular matrix (ECM) production reveal that larger interconnections is more suitable for cells to move across the scaffold and form a three-dimensional cellular network. We argue that LARGE interconnections favor cell communication between different pores, which then favors the production of the ECM. Moreover, PDA treatment shows a truly beneficial effect on fibroblast viability and on matrix production, whereas plasma treatment shows the same effect for WJMSCs. We, therefore, claim that both pore interconnection size and surface treatment play a significant role to improve the quality of integration of tissue engineering scaffolds.

In situ preparation and osteogenic properties of bionanocomposite scaffolds based on aliphatic polyurethane and bioactive glass nanoparticles

Bionanocomposite scaffolds based on aliphatic polyurethane (PU) and bioactive glass nanoparticles were produced by using a one-step in situ polymerization method. Bioactive glass nanoparticles (nBG) or mesoporous BG nanospheres (nMBG) were incorporated during the polymerization reaction to produce simultaneous formation and foaming of porous nanocomposite scaffolds. The in vitro bioactivity of the scaffolds was assessed in simulated body fluid (SBF), and through cytocompatibility and osteogenic differentiation assays with stem cells. Bone regeneration properties of the scaffold materials were in vivo assessed by using a critical-sized femoral defect model in rat. The scaffold nanocomposites showed excellent cytocompatibility and ability to accelerate the crystallization of bone-like apatite in vitro. nBG/PU bionanocomposite scaffold exhibited the higher capacity to stimulate osteogenic cell differentiation as judged by an increased ALP activity and the presence of mineralized nodules associated with the stem cells. nBG (5%)/PU scaffold significantly also produces in vivo a denser and more significant amount of new bone after 8 weeks of implantation, which is attributed to the more rapid dissolution rate of nBG into osteogenic ionic products compared to nMBG. The results of this work show that the in situ polymerization method combined with the use of nanodimensional BG particles enable the production of PU - based scaffolds with enhanced bioactive properties to stimulate the bone tissue regeneration.

In Vivo Biocompatibility of a Novel Expanded Polytetrafluoroethylene Suture for Annuloplasty

BACKGROUND

Expanded polytetrafluoroethylene (ePTFE) is a suture material for annuloplasty in aortic valve repair. For this particular application, it should induce minimal local stress and promote rapid tissue incorporation. To achieve this, a novel ePTFE suture with a larger diameter and high porosity in its midsection has been developed. Herein, we analyzed the acute and chronic tissue reaction to this suture material compared with a commercially available control ePTFE suture.

METHODS

Novel and control suture samples were implanted into dorsal skinfold chambers of BALB/c mice to analyze the early inflammatory response using intravital fluorescence microscopy over 14 days. Additional suture samples were implanted for 4 and 12 weeks in the flank musculature of mice and analyzed by histology and immunohistochemistry.

RESULTS

The implantation of novel and control ePTFE suture into the dorsal skinfold chamber did not induce an acute inflammation, as indicated by physiological numbers of rolling and adherent leukocytes in all analyzed venules. Chronic implantation into the flank musculature showed a better tissue incorporation of the novel ePTFE suture with more infiltrating cells and a higher content of Sirius red+ collagen fibers when compared with controls. Cell proliferation and viability as well as numbers of recruited CD68+ macrophages, myeloperoxidase+ neutrophilic granulocytes and CD3+ lymphocytes did not significantly differ between the groups.

CONCLUSION

The novel ePTFE suture exhibits a good in vivo biocompatibility which is comparable to that of the control suture. Due to its improved tissue incorporation, it may provide a better long-term stability during annuloplasty.

Strategies for Annulus Fibrosus Regeneration: From Biological Therapies to Tissue Engineering

Intervertebral disc (IVD) is an avascular tissue which contributes to the weight bearing, motion, and flexibility of spine. However, IVD is susceptible to damage and even failure due to injury, pathology, and aging. Annulus fibrosus (AF), the structural and functional integrity of which is critically essential to confine nucleus pulpous (NP) and maintain physiological intradiscal pressure under mechanical loading, plays a critical role in the biomechanical properties of IVD. AF degeneration commonly results in substantial deterioration of IVD. During this process, the biomechanical properties of AF and the balance between anabolism and catabolism in IVD are progressively disrupted, leading to chronic back pain, and even disability of individuals. Therefore, repairing and regenerating AF are effective treatments to degeneration-associated pains. However, they remain highly challenging due to the complexity of natural AF tissue in the aspects of cell phenotype, biochemical composition, microstructure, and mechanical properties. Tissue engineering (TE), by combining biological science and materials engineering, shed lights on AF regeneration. In this article, we review recent advances in the pro-anabolic approaches in the form of cell delivery, bioactive factors delivery, gene therapy, and TE strategies for achieving AF regeneration.

Accelerated Angiogenic Induction and Vascular Integration in a Novel Synthetic Scaffolding Matrix for Tissue Replacement

Purpose

Reduced or delayed neovascularization is a major obstacle with regard to tissue-engineered constructs. The aim of this study was to evaluate the early microvascular response to a novel degradable ε-caprolactone terpolymer matrix.

Methods

ε-caprolactone terpolymer matrices (Suprathel Plus®; Institute of Textile and Process Engineering, Denkendorf, Germany) were implanted into dorsal skinfold chambers of balb/c mice (n=10). Microcirculatory changes were observed by intravital fluorescence microscopy. Scaffolding matrices from PEGT/PBT copolymer were used as controls (n=10).

Results

The formation of de novo vascular networks within both scaffolding matrices was noted throughout the experiment. A vascular ingrowth of perfused microvessels into the matrices up to 600 μm apart from the edge was noted within 10 days of implantation. The earliest signs of neoangiogenesis were visible in ε-caprolactone terpolymer matrices on day 1. In both scaffolds the new developed vessels extended centripetally from the border of the matrices towards the center and anastomosed to form a perfused microvascular network. There was significantly earlier onset of vascularization, increased vascularized area and higher vessel density in ε-caprolactone terpolymer matrices compared to PEGT/PBT copolymer matrices were observed.

Conclusions

The scaffolding matrix from ε-caprolactone terpolymer allowed for an earlier and more intense induction of angiogenesis and displayed the tendency to vascularize more rapidly within a shorter period of time after transplantation compared to PEGT/PBT copolymer scaffolds, thus indicating its potential application for tissue engineering purposes.

Nondegradable magnetic poly (carbonate urethane) microspheres with good shape memory as a proposed material for vascular embolization

In this study, nondegradable poly (carbonate urethane) (PCU) and poly (carbonate urethane) incorporated variable Fe₃O₄ content microspheres (PCU/Fe₃O₄) were synthesized using pre-polymerization and suspension polymerization. Synthesis was confirmed through Fourier transform infrared spectroscopy (FTIR). The effect of Fe₃O₄ incorporation was investigated on crystalline, thermal, shape memory and degradation properties by X-Ray diffraction (XRD), Differential scanning calorimetery (DSC), compression test and degradation in vitro, respectively. Otherwise, the assessment of magnetic characteristics by vibrational sample magnetometry (VSM) disclosed superparamagnetic behavior. The tunable superparamagnetic behavior depends on the amount of magnetic particles incorporated within the networks. The biological study results of as-synthesized polymers from the platelet adhesion test and the cell proliferation inhibition test indicated they were biocompatible in vitro. Fe₃O₄ incorporation was conductive to reducing platelet adhesion in blood contacting test and promotion of rat vascular smooth muscle cell proliferation and growth. These nondegradable, superparamagnetic, biocompatible polymers, combined with their good shape memory properties may allow for their future exploitation in the biomedical field, such as, in cardiovascular implants, targeted tumor treatment, tissue engineering and artificial organ's engineering.

Self-fitting shape memory polymer foam inducing bone regeneration: A rabbit femoral defect study

Although tissue engineering has been attracted greatly for healing of critical-sized bone defects, great efforts for improvement are still being made in scaffold design. In particular, bone regeneration would be enhanced if a scaffold precisely matches the contour of bone defects, especially if it could be implanted into the human body conveniently and safely. In this study, polyurethane/hydroxyapatite-based shape memory polymer (SMP) foam was fabricated as a scaffold substrate to facilitate bone regeneration. The minimally invasive delivery and the self-fitting behavior of the SMP foam were systematically evaluated to demonstrate its feasibility in the treatment of bone defects in vivo. Results showed that the SMP foam could be conveniently implanted into bone defects with a compact shape. Subsequently, it self-matched the boundary of bone defects upon shape-recovery activation in vivo. Micro-computed tomography determined that bone ingrowth initiated at the periphery of the SMP foam with a constant decrease towards the inside. Successful vascularization and bone remodeling were also demonstrated by histological analysis. Thus, our results indicate that the SMP foam demonstrated great potential for bone regeneration.

Bone regeneration in minipigs by intrafibrillarly-mineralized collagen loaded with autologous periodontal ligament stem cells

Biomimetic intrafibrillarly-mineralized collagen (IMC) is a promising scaffold for bone regeneration because of its structural and functional similarity to natural bone. The objective of this study was to evaluate the bone regeneration potential of IMC loaded with autologous periodontal ligament stem cells (PDLSCs) in large bone defects in minipigs. A macroporous IMC with a bone-like subfibrillar nanostructure was fabricated using a biomimetic bottom-up approach. Non-healing full thickness defects were established on the cranial bone in minipigs, and IMC and hydroxyapatite (HA) scaffolds seeded with autologous PDLSCs were implanted into these defects. Computed tomographic imaging, histology staining, and atomic force microscopy were applied to evaluate to the quantity, micro/nano structures, and mechanical performance of the neo-bone after 12 weeks of implantation. Compared with HA, IMC showed superior regeneration properties characterized by the profuse deposition of new bony structures with a normal architecture and vascularization. Immunohistochemistry showed that the runt-related transcription factor 2 and transcription factor Osterix were highly expressed in the neo-bone formed by IMC. Furthermore, the nanostructure and nanomechanics of the neo-bone formed by IMC were similar to that of natural bone. This study provides strong evidence for the future clinical applications of the IMC-based bone grafts.

Development of polyurethanes for bone repair

The purpose of this paper is to review recent developments on polyurethanes aimed at the design, synthesis, modifications, and biological properties in the field of bone tissue engineering. Different polyurethane systems are presented and discussed in terms of biodegradation, biocompatibility and bioactivity. A comprehensive discussion is provided of the influence of hard to soft segments ratio, catalysts, stiffness and hydrophilicity of polyurethanes. Interaction with various cells, behavior in vivo and current strategies in enhancing bioactivity of polyurethanes are described. The discussion on the incorporation of biomolecules and growth factors, surface modifications, and obtaining polyurethane-ceramics composites strategies is held. The main emphasis is placed on the progress of polyurethane applications in bone regeneration, including bone void fillers, shape memory scaffolds, and drug carrier.

Design of Xylose-Based Semisynthetic Polyurethane Tissue Adhesives with Enhanced Bioactivity Properties

Developing biocompatible tissue adhesives with high adhesion properties is a highly desired goal of the tissue engineering due to adverse effects of the sutures. Therefore, our work involves synthesis, characterization, adhesion properties, protein adsorption, in vitro biodegradation, in vitro and in vivo biocompatibility properties of xylose-based semisynthetic polyurethane (NPU-PEG-X) bioadhesives. Xylose-based semisynthetic polyurethanes were developed by the reaction among 4,4'-methylenebis(cyclohexyl isocyanate) (MCI), xylose and polyethylene glycol 200 (PEG). Synthesized polyurethanes (PUs) showed good thermal stability and high adhesion strength. The highest values in adhesion strength were measured as 415.0 ± 48.8 and 94.0 ± 2.8 kPa for aluminum substrate and muscle tissue in 15% xylose containing PUs (NPU-PEG-X-15%), respectively. The biodegradation of NPU-PEG-X-15% was also determined as 19.96 ± 1.04% after 8 weeks of incubation. Relative cell viability of xylose containing PU was above 86%. Moreover, 10% xylose containing NPU-PEG-X (NPU-PEG-X-10%) sample has favorable tissue response, and inflammatory reaction between 1 and 6 weeks implantation period. With high adhesiveness and biocompatibility properties, NPU-PEG-X can be used in the medical field as supporting materials for preventing the fluid leakage after abdominal surgery or wound closure.

Biomimetic collagenous scaffold to tune inflammation by targeting macrophages

The inflammatory response following implantation of a biomaterial is one of the major regulatory aspects of the overall regenerative process. The progress of inflammation determines whether functional tissue is restored or if nonfunctional fibrotic tissue is formed. This delicate balance is directed by the activity of different cells. Among these, macrophages and their different phenotypes, the inflammatory M1 to anti-inflammatory M2, are considered key players in the process. Recent approaches exploit macrophage’s regenerative potential in tissue engineering. Here, we propose a collagen scaffold functionalized with chondroitin sulfate (CSCL), a glycosaminoglycan known to be able to tune inflammation. We studied CSCL effects on bone-marrow-derived macrophages in physiological, and lipopolysaccharides-inflamed, conditions in vitro. Our data demonstrate that CSCL is able to modulate macrophage phenotype by inhibiting the LPS/CD44/NF-kB cascade. As a consequence, an upregulation of anti-inflammatory markers (TGF-β, Arg, MRC1, and IL-10) was found concomitantly with a decrease in the expression of pro-inflammatory markers (iNOS, TNF-α, IL-1β, IL-12β). We then implanted CSCL subcutaneously in a rat model to test whether the same molecular mechanism could be maintained in an in vivo environment. In vivo data confirmed the in vitro studies. A significant reduction in the number of infiltrating cells around and within the implants was observed at 72 h, with a significant downregulation of pro-inflammatory genes expression. The present work provides indications regarding the immunomodulatory potential of molecules used for the development of biomimetic materials and suggests their use to direct macrophage immune modulation for tissue repair.

Toxicity and inflammatory response in Swiss albino mice after intraperitoneal and oral administration of polyurethane nanoparticles

In this work in vivo experiments were conducted in order to characterize the biocompatibility of polyurethane nanoparticles (PU-NPs) after intraperitoneal (i.p.) and oral administration. Additionally, ex vivo assays were performed to assess human blood compatibility as well as in vitro assays to assess protein binding. Our results indicated that administration of three different concentrations of PU-NPs induced a significant increase in visceral fat accumulation after oral dosing. In addition, fat tissue of mice intraperitoneally treated with the highest concentration of nanoparticles showed diffuse mononuclear inflammatory infiltrate in the fat tissue. Histopathological assessment showed inflammatory infiltrate and hepatocyte vacuolization in the liver, inflammatory infiltration and vascular congestion in the lung and glomerular necrosis in the kidney. Hepatic enzymes related with liver function were significantly increased in both groups of mice treated with PU-NPs. The PU-NPs did not affect the human blood cells number as well as coagulation time but showed a susceptibility to bind in proteins commonly found in the blood stream. In addition, increased amounts of pro inflammatory cytokines in vivo, as well as ex vivo in human cells were observed. Further studies to establish the consequences of long-term exposure to PU-NPs are warranted.

Cardiomyocyte behavior on biodegradable polyurethane/gold nanocomposite scaffolds under electrical stimulation

Following a myocardial infarction (MI), cardiomyocytes are replaced by scar tissue, which decreases ventricular contractile function. Tissue engineering is a promising approach to regenerate such damaged cardiomyocyte tissue. Engineered cardiac patches can be fabricated by seeding a high density of cardiac cells onto a synthetic or natural porous polymer. In this study, nanocomposite scaffolds made of gold nanotubes/nanowires incorporated into biodegradable castor oil-based polyurethane were employed to make micro-porous scaffolds. H9C2 cardiomyocyte cells were cultured on the scaffolds for one day, and electrical stimulation was applied to improve cell communication and interaction in neighboring pores. Cells on scaffolds were examined by fluorescence microscopy and scanning electron microscopy, revealing that the combination of scaffold design and electrical stimulation significantly increased cell confluency of H9C2 cells on the scaffolds. Furthermore, we showed that the gene expression levels of Nkx2.5, atrial natriuretic peptide (ANF) and natriuretic peptide precursor B (NPPB), which are functional genes of the myocardium, were up-regulated by the incorporation of gold nanotubes/nanowires into the polyurethane scaffolds, in particular after electrical stimulation.

In vitro investigations of a novel wound dressing concept based on biodegradable polyurethane

Non-healing and partially healing wounds are an important problem not only for the patient but also for the public health care system. Current treatment solutions are far from optimal regarding the chosen material properties as well as price and source. Biodegradable polyurethane (PUR) scaffolds have shown great promise for in vivo tissue engineering approaches, but accomplishment of the goal of scaffold degradation and new tissue formation developing in parallel has not been observed so far in skin wound repair. In this study, the mechanical properties and degradation behavior as well as the biocompatibility of a low-cost synthetic, pathogen-free, biocompatible and biodegradable extracellular matrix mimicking a PUR scaffold was evaluated in vitro. The novel PUR scaffolds were found to meet all the requirements for optimal scaffolds and wound dressings. These three-dimensional scaffolds are soft, highly porous, and form-stable and can be easily cut into any shape desired. All the material formulations investigated were found to be nontoxic. One formulation was able to be defined that supported both good fibroblast cell attachment and cell proliferation to colonize the scaffold. Tunable biodegradation velocity of the materials could be observed, and the results additionally indicated that calcium plays a crucial role in PUR degradation. Our results suggest that the PUR materials evaluated in this study are promising candidates for next-generation wound treatment systems and support the concept of using foam scaffolds for improved in vivo tissue engineering and regeneration.