Endothelium regeneration on luminal surface of polyurethane vascular scaffold modified with diamine and covalently grafted with gelatin

Surface functionalization of polyurethanes: A critical review

Synthetic polymers, particularly polyurethanes (PUs), have revolutionized bioengineering and biomedical devices due to their customizable mechanical properties and long-term stability. However, the inherent hydrophobic nature of PU surfaces arises common issues such as high friction, strong protein adsorption, and thrombosis, especially in the physiological environment of blood contact. To overcome these issues, researchers have explored various modification techniques to improve the surface biofunctionality of PUs. In this review, we have systematically summarized several typical surface modification methods including surface plasma modification, surface oxidation-induced grafting polymerization, isocyanate-based chemistry coupling, UV-induced surface grafting polymerization, adhesives-assisted attachment strategy, small molecules-bridge grafting, solvent evaporation technique, and hydrogen bonding interaction. Correspondingly, the advantages, limitations, and future prospects of these surface modification methods were discussed. This review provides an important guidance or tool for developing surface functionalized PUs in the fields of bioengineering and medical devices.

Effect of Curcumin-containing Nanofibrous Gelatin-hydroxyapatite Scaffold on Proliferation and Early Osteogenic Differentiation of Dental Pulp Stem Cells

BACKGROUND

In recent years, the electrospinning method has received attention because of its usage in producing a mimetic nanocomposite scaffold for tissue regeneration. Hydroxyapatite and gelatin are suitable materials for producing scaffolds, and curcumin has the osteogenesis induction effect.

AIMS

This study aimed to evaluate the toxicity and early osteogenic differentiation stimulation of nanofibrous gelatin-hydroxyapatite scaffold containing curcumin on dental pulp stem cells (DPSCs).

OBJECTIVE

The objective of the present investigation was the evaluation of the proliferative effect and primary osteogenic stimulation of DPSCs with a nanofibrous gelatin-hydroxyapatite scaffold containing curcumin. Hydroxyapatite and gelatin were used as suitable and biocompatible materials to make a scaffold suitable for stimulating osteogenesis. Curcumin was added to the scaffold as an osteogenic differentiation- enhancing agent.

METHODS

The effect of nano-scaffold on the proliferation of DPSCs was evaluated. The activity of alkaline phosphatase (ALP) as the early osteogenic marker was considered to assess primary osteogenesis stimulation in DPSCs.

RESULTS

The nanofibrous gelatin-hydroxyapatite scaffold containing curcumin significantly increased the proliferation and the ALP activity of DPSCs (P<0.05). The proliferative effect was insignificant in the first 2 days, but the scaffold increased cell proliferation by more than 40% in the fourth and sixth days. The prepared scaffold increased the activity of the ALP of DPSCs by 60% compared with the control after 14 days (p<0.05).

CONCLUSION

The produced nanofibrous gelatin-hydroxyapatite scaffold containing curcumin can be utilized as a potential candidate in tissue engineering and regeneration of bone and tooth.

FUTURE PROSPECTS

The prepared scaffold in the present study could be a beneficial biomaterial for tissue engineering and the regeneration of bone and tooth soon.

Effects of Chemical Composition on the Shape Memory Property of Poly(dl-lactide-co-trimethylene carbonate) as Self-Morphing Small-Diameter Vascular Scaffolds

Smart materials have great potential in many biomedical applications, in which biodegradable shape memory polymers (SMPs) can be used as surgical sutures, implants, and stents. Poly(dl-lactide-co-trimethylene carbonate) (PDLLTC) represents one of the promising SMPs and is widely used in biomedical applications. However, the relationship between its shape memory property and chemical structure has not been fully studied and needs further elaboration. In this work, PDLLTC copolymers in different compositions have been synthesized, and their shape memory properties have been investigated. It has been found that the shape memory property is related to the chemical composition and polymeric chain segments. The copolymer with a DLLA/TMC ratio of 75:25 (PDLLTC7525) has been demonstrated with great shape fixation and recovery ratio at human body temperature. Furthermore, PDLLTC7525-based self-morphing small-diameter vascular scaffolds adhered with inner electrospun aligned gelatin/hyaluronic acid (Gel/HA) nanofibers have been constructed, as a merit of its shape memory property. The scaffolds have been demonstrated to facilitate the proliferation and adhesion of endothelial cells on the inner layer. Therefore, PDLLTC with tailorable shape memory properties represents a promising candidate for the development of SMPs, as well as for small-diameter vascular scaffolds construction.

Gelatin-grafted tubular asymmetric scaffolds promote ureteral regeneration via activation of the integrin/Erk signaling pathway

Introduction: The repair of a diseased ureter is an urgent clinical issue that needs to be solved. A tissue-engineered scaffold for ureteral replacement is currently insufficient due to its incompetent bioactivity, especially in long-segment abnormalities. The primary reason is the failure of urothelialization on scaffolds. Methods: In this work, we investigated the ability of gelatin-grafted tubular scaffold in ureteral repairment and its related biological mechanism. We designed various porous asymmetric poly (L-lactic acid) (PLLA)/poly (L-lactide-co-e-caprolactone) (PLCL) tubes with a thermally induced phase separation (TIPS) method via a change in the ratio of solvents (named PP). To regulate the phenotype of urothelial cells and ureteral reconstruction, gelatin was grafted onto the tubular scaffold using ammonolysis and glutaraldehyde crosslinking (named PP-gel). The in vitro and in vivo experiments were performed to test the biological function and the mechanism of the scaffolds. Results and Discussion: The hydrophilicity of the scaffold significantly increased after gelatin grafting, which promoted the adhesion and proliferation of urothelial cells. Through subcutaneous implantation in rats, PP-gel scaffolds demonstrated good biocompatibility. The in vivo replacement showed that PP-gel could improve urothelium regeneration and maintain renal function after the ureter was replaced with an ∼4 cm-long PP-gel tube using New Zealand rabbits as the experimental animals. The related biologic mechanism of ureteral reconstruction was detected in detail. The gelatin-grafted scaffold upgraded the integrin α6/β4 on the urothelial cell membrane, which phosphorylates the focal adhesion kinase (FAK) and enhances urothelialization via the MAPK/Erk signaling pathway. Conclusion: All these results confirmed that the PP46-gel scaffold is a promising candidate for the constitution of an engineered ureter and to repair long-segment ureteral defects.

Crystallographic characterization and application of copper doped hydroxyapatite as a biomaterial

Cu-doped hydroxyapatite is synthesized from eggshell and its suitability as a potential biomaterial is examined via cytotoxicity, haemolysis and antibacterial activity.

Immobilization of Gelatin on Fibers for Tissue Engineering Applications: A Comparative Study of Three Aliphatic Polyesters

Immobilization of cell adhesive proteins on the scaffold surface has become a widely reported method that can improve the interaction between scaffold and cells. In this study, three nanofibrous scaffolds obtained by electrospinning of poly(caprolactone) (PCL), poly(L-lactide-co-caprolactone) (PLCL) 70:30, or poly(L-lactide) (PLLA) were subjected to chemical immobilization of gelatin based on aminolysis and glutaraldehyde cross-linking, as well as physisorption of gelatin. Two sets of aminolysis conditions were applied to evaluate the impact of amine group content. Based on the results of the colorimetric bicinchoninic acid (BCA) assay, it was shown that the concentration of gelatin on the surface is higher for the chemical modification and increases with the concentration of free NH2 groups. XPS (X-ray photoelectron spectroscopy) analysis confirmed this outcome. On the basis of XPS results, the thickness of the gelatin layer was estimated to be less than 10 nm. Initially, hydrophobic scaffolds are completely wettable after coating with gelatin, and the time of waterdrop absorption was correlated with the surface concentration of gelatin. In the case of all physically and mildly chemically modified samples, the decrease in stress and strain at break was relatively low, contrary to strongly aminolyzed PLCL and PLLA samples. Incubation testing performed on the PCL samples showed that a chemically immobilized gelatin layer is more stable than a physisorbed one; however, even after 90 days, more than 60% of the initial gelatin concentration was still present on the surface of physically modified samples. Mouse fibroblast L929 cell culture on modified samples indicates a positive effect of both physical and chemical modification on cell morphology. In the case of PCL and PLCL, the best morphology, characterized by stretched filopodia, was observed after stronger chemical modification, while for PLLA, there was no significant difference between modified samples. Results of metabolic activity indicate the better effect of chemical immobilization than of physisorption of gelatin.

Negative In Vivo Results Despite Promising In Vitro Data With a Coated Compliant Electrospun Polyurethane Vascular Graft

INTRODUCTION

There is a growing need for small-diameter (<6 mm) off-the-shelf synthetic vascular conduits for different surgical bypass procedures, with actual synthetic conduits showing unacceptable thrombosis rates. The goal of this study was to build vascular grafts with better compliance than standard synthetic conduits and with an inner layer stimulating endothelialization while remaining antithrombogenic.

METHODS

Tubular vascular conduits made of a scaffold of polyurethane/polycaprolactone combined with a bioactive coating based on chondroitin sulfate (CS) were created using electrospinning and plasma polymerization. In vitro testing followed by a comparative in vivo trial in a sheep model as bilateral carotid bypasses was performed to assess the conduits' performance compared to the actual standard.

RESULTS

In vitro, the novel small-diameter (5 mm) electrospun vascular grafts coated with chondroitin sulfate (CS) showed 10 times more compliance compared to commercial expanded polytetrafluoroethylene (ePTFE) conduits while maintaining adequate suturability, burst pressure profiles, and structural stability over time. The subsequent in vivo trial was terminated after electrospun vascular grafts coated with CS showed to be inferior compared to their expanded polytetrafluoroethylene counterparts.

CONCLUSIONS

The inability of the experimental conduits to perform well in vivo despite promising in vitro results may be related to the low porosity of the grafts and the lack of rapid endothelialization despite the presence of the CS coating. Further research is warranted to explore ways to improve electrospun polyurethane/polycaprolactone scaffold in order to make it prone to transmural endothelialization while being resistant to strenuous conditions.

Effect of cellulose nanocrystals on chitosan/PVA/nano β-TCP composite scaffold for bone tissue engineering application

The need for an ideal tissue construct has lead to the search of a myriad of polymer composites with desirable properties. The nature, location and type of tissue to be regenerated determines the type of material to be used. A bone construct has its own requirements such as osteoconductivity, mineralization tendency, synchronized degradation rate, osteogenic differentiation potential etc, which results in search of new possible combination of materials aimed to improve tissue response. The present study involves fabrication of Chitosan/Polyvinyl alcohol (PVA)/β-Tricalcium Phosphate (β-TCP)/Cellulose nanocrystals (CNC) porous composite by freeze drying process to be used as bone tissue engineering matrix. CNCs were isolated by acid hydrolysis of cellulose derived from pistachio shells. The prepared scaffold samples were characterized by Fourier-transform infrared spectroscopy (FTIR), Thermogravimetric analysis (TGA), Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM) and X-RAY Diffraction analysis (XRD). The scaffolds exhibited refinement in pore morphology and increased mineralization tendency on increasing CNC concentration. Samples with 1% and 5% CNC concentration have deposited apatite crystals with Ca/P ratio of 1.61 and 1.66 which is very close to the stoichiometric ratio of natural bone apatite. Compressive modulus of CS/PVA/β-TCP/CNC composite increased on increasing the CNC concentration to 5%. The highest cell viability was recorded in scaffolds with 5% CNC content. Though cell attachment tendency was observed in all samples but the samples with 5 and 10% CNC content demonstrated higher cell densities with significant calcium depositions when cultured for 72 h. Samples with 5% CNC concentration also possessed highest cell differentiation capabilities.

Effect of Polymeric Matrix Stiffness on Osteogenic Differentiation of Mesenchymal Stem/Progenitor Cells: Concise Review

Mesenchymal stem/progenitor cells (MSCs) have a multi-differentiation potential into specialized cell types, with remarkable regenerative and therapeutic results. Several factors could trigger the differentiation of MSCs into specific lineages, among them the biophysical and chemical characteristics of the extracellular matrix (ECM), including its stiffness, composition, topography, and mechanical properties. MSCs can sense and assess the stiffness of extracellular substrates through the process of mechanotransduction. Through this process, the extracellular matrix can govern and direct MSCs' lineage commitment through complex intracellular pathways. Hence, various biomimetic natural and synthetic polymeric matrices of tunable stiffness were developed and further investigated to mimic the MSCs' native tissues. Customizing scaffold materials to mimic cells' natural environment is of utmost importance during the process of tissue engineering. This review aims to highlight the regulatory role of matrix stiffness in directing the osteogenic differentiation of MSCs, addressing how MSCs sense and respond to their ECM, in addition to listing different polymeric biomaterials and methods used to alter their stiffness to dictate MSCs' differentiation towards the osteogenic lineage.

Immunomodulatory and antimicrobial non-mulberry Antheraea mylitta silk fibroin accelerates in vitro fibroblast repair and regeneration by protecting oxidative stress

The antimicrobial nature of Antharaea mylitta silk-fibroin (SF) is reported but antioxidant potential and the immunomodulatory role towards the fibroblast cell repair process is not explored. Polyurethane is reported to have inflammatory potential by mononuclear cells directed cytokine release, which can guide fibroblast repair. Present study demonstrates the conjunctive effect of inflammatory PU/SF to regulate the favorable shift from pro-inflammatory to anti-inflammatory cytokine stimulation for accelerated fibroblast repair. Minimal inhibitory concentration of SF was determined against pathogenic strains and the effect of SF was investigated for fibroblast NIH3T3 cell adhesion. SF doses (8, 8.5, 9 mg mL⁻¹) were found to be greater than both the IC₅₀ of DPPH scavenging and the ED₅₀ for NIH3T3 proliferation. Anti-lipid peroxidase (ALP) activity of SF doses and citric acid-treated NIH3T3 cells were compared under hydrogen peroxide (H₂O₂) induced oxidative stress. 9 mg mL⁻¹ SF showed greater ALP activity than the citric acid standard. SF-driven protection to oxidative damage was measured by viable cell fraction in trypan blue dye exclusion assay where 9 mg mL⁻¹ SF showed the highest viability (p ≤ 0.05). 9 mg mL⁻¹ SF was blended with PU for scaffold (w/v = 2 : 5, 2 : 7, 2 : 9) fabrication. The protective effect of PU/SF (2 : 5, 2 : 7, 2 : 9) against oxidative stress was verified by damaged cell survival in MTT assay and DNA quantification. The highest number of cells survived on PU/SF (2 : 9) at all intervals (p ≤ 0.01) upon oxidative damage; PU/SF (2 : 9) was also fabricated by employing the immobilization technique. Immobilized PU/SF (2 : 9) exhibited a greater zone of microbial inhibition, a higher extent of inhibition to microbial adherence, and caused more LDH release from bacterial cell membrane due to membrane rupture, resulting in bacterial cell death (E. coli, K. pneumoniae, P. aeruginosa, S. aureus) compared to the experimental results shown by blended PU/SF (2 : 9). The protective nature of PU/SF (2 : 9) against oxidative stress was ensured through the LDH activity of damaged NIH3T3 cells. Initial raised IL-6, TNF-alpha (pro-inflammatory cytokines) and lowered IL-8, IL-10 (anti-inflammatory cytokine) profiles coupled with fallen IL-6, TNF-alpha, and elevated IL-8, IL-10 at later hours synergistically progress the inflammatory phase of in vitro scratch wound repair in mononuclear culture treated by PU/SF (2 : 9).

Initially SF accelerated pro-inflammatory cytokines, restricted anti-inflammatory cytokines; later it regulated in reverse order. SF potentially eradicated ROS and promoted Ki-67 cellular regeneration whereas pristine PU could not.

Hydrogels and Dentin-Pulp Complex Regeneration: From the Benchtop to Clinical Translation

Dentin-pulp complex is a term which refers to the dental pulp (DP) surrounded by dentin along its peripheries. Dentin and dental pulp are highly specialized tissues, which can be affected by various insults, primarily by dental caries. Regeneration of the dentin-pulp complex is of paramount importance to regain tooth vitality. The regenerative endodontic procedure (REP) is a relatively current approach, which aims to regenerate the dentin-pulp complex through stimulating the differentiation of resident or transplanted stem/progenitor cells. Hydrogel-based scaffolds are a unique category of three dimensional polymeric networks with high water content. They are hydrophilic, biocompatible, with tunable degradation patterns and mechanical properties, in addition to the ability to be loaded with various bioactive molecules. Furthermore, hydrogels have a considerable degree of flexibility and elasticity, mimicking the cell extracellular matrix (ECM), particularly that of the DP. The current review presents how for dentin-pulp complex regeneration, the application of injectable hydrogels combined with stem/progenitor cells could represent a promising approach. According to the source of the polymeric chain forming the hydrogel, they can be classified into natural, synthetic or hybrid hydrogels, combining natural and synthetic ones. Natural polymers are bioactive, highly biocompatible, and biodegradable by naturally occurring enzymes or via hydrolysis. On the other hand, synthetic polymers offer tunable mechanical properties, thermostability and durability as compared to natural hydrogels. Hybrid hydrogels combine the benefits of synthetic and natural polymers. Hydrogels can be biofunctionalized with cell-binding sequences as arginine-glycine-aspartic acid (RGD), can be used for local delivery of bioactive molecules and cellularized with stem cells for dentin-pulp regeneration. Formulating a hydrogel scaffold material fulfilling the required criteria in regenerative endodontics is still an area of active research, which shows promising potential for replacing conventional endodontic treatments in the near future.

Biomedical Implants for Regenerative Therapies

Regenerative therapies aim to develop novel treatments to restore tissue function. Several strategies have been investigated including the use of biomedical implants as three-dimensional artificial matrices to fill the defect side, to replace damaged tissues or for drug delivery. Bioactive implants are used to provide growth environments for tissue formation for a variety of applications including nerve, lung, skin and orthopaedic tissues. Implants can either be biodegradable or non-degradable, should be nontoxic and biocompatible, and should not trigger an immunological response. Implants can be designed to provide suitable surface area-to-volume ratios, ranges of porosities, pore interconnectivities and adequate mechanical strengths. Due to their broad range of properties, numerous biomaterials have been used for implant manufacture. To enhance an implant’s bioactivity, materials can be functionalised in several ways, including surface modification using proteins, incorporation of bioactive drugs, growth factors and/or cells. These strategies have been employed to create local bioactive microenvironments to direct cellular responses and to promote tissue regeneration and controlled drug release. This chapter provides an overview of current bioactive biomedical implants, their fabrication and applications, as well as implant materials used in drug delivery and tissue regeneration. Additionally, cell- and drug-based bioactivity, manufacturing considerations and future trends will be discussed.

Riboflavin-mediated photooxidation to improve the characteristics of decellularized human arterial small diameter vascular grafts

Vascular grafts with a diameter of less than 6 mm are made from a variety of materials and techniques to provide alternatives to autologous vascular grafts. Decellularized materials have been proposed as a possible approach to create extracellular matrix (ECM) vascular prostheses as they are naturally derived and inherently support various cell functions. However, these desirable graft characteristics may be limited by alterations of the ECM during the decellularization process leading to decreased biomechanical properties and hemocompatibility. In this study, arteries from the human placenta chorion were decellularized using two distinct detergents (Triton X-100 or SDS), which differently affect ECM ultrastructure. To overcome biomechanical strength loss and collagen fiber exposure after decellularization, riboflavin-mediated UV (RUV) crosslinking was used to uniformly crosslink the collagenous ECM of the grafts. Graft characteristics and biocompatibility with and without RUV crosslinking were studied in vitro and in vivo. RUV-crosslinked ECM grafts showed significantly improved mechanical strength and smoothening of the luminal graft surfaces. Cell seeding using human endothelial cells revealed no cytotoxic effects of the RUV treatment. Short-term aortic implants in rats showed cell migration and differentiation of host cells. Functional graft remodeling was evident in all grafts. Thus, RUV crosslinking is a preferable tool to improve graft characteristics of decellularized matrix conduits.

Wavy small-diameter vascular graft made of eggshell membrane and thermoplastic polyurethane

In this study, a small-diameter, double-layered eggshell membrane/thermoplastic polyurethane (ESM/TPU) vascular graft with a wavy structure was developed. The avian eggshell membrane, a fibrous structure similar to the extracellular matrix (ECM), has the potential to yield rapid endothelialization in vitro. The dopamine and heparin modification of the ESM surface not only promoted human umbilical vein endothelial cell (HUVEC) proliferation via cytocompatibility assessment, but also improved its anticoagulation properties as verified in platelet adhesion tests. The biomimetic mechanical properties of the vascular graft were provided by the elastic TPU fibers via electrospinning using a wavy cross-section rotating collector. The advantage of combining these two materials is to make use of the bioactivity of ESM as the internal membrane and the tunable mechanical properties of TPU as the external layer. The circumferentially wavy structure of the vascular graft produced a toe region in the non-linear section of the stress-strain curve similar to that of natural blood vessels. The ESM/TPU graft's circumferential ultimate strength was 2.57 MPa, its strain was 339% mm/mm, and its toe region was found to be around 20% mm/mm. Cyclical tension tests showed that the vascular graft could maintain good mechanical properties and showed no structural damage under repeated extension tests.

Osteochondral Tissue Regeneration Using a Tyramine-Modified Bilayered PLGA Scaffold Combined with Articular Chondrocytes in a Porcine Model

Repairing damaged articular cartilage is challenging due to the limited regenerative capacity of hyaline cartilage. In this study, we fabricated a bilayered poly (lactic-co-glycolic acid) (PLGA) scaffold with small (200–300 μm) and large (200–500 μm) pores by salt leaching to stimulate chondrocyte differentiation, cartilage formation, and endochondral ossification. The scaffold surface was treated with tyramine to promote scaffold integration into native tissue. Porcine chondrocytes retained a round shape during differentiation when grown on the small pore size scaffold, and had a fibroblast-like morphology during transdifferentiation in the large pore size scaffold after five days of culture. Tyramine-treated scaffolds with mixed pore sizes seeded with chondrocytes were pressed into three-mm porcine osteochondral defects; tyramine treatment enhanced the adhesion of the small pore size scaffold to osteochondral tissue and increased glycosaminoglycan and collagen type II (Col II) contents, while reducing collagen type X (Col X) production in the cartilage layer. Col X content was higher for scaffolds with a large pore size, which was accompanied by the enhanced generation of subchondral bone. Thus, chondrocytes seeded in tyramine-treated bilayered scaffolds with small and large pores in the upper and lower parts, respectively, can promote osteochondral regeneration and integration for articular cartilage repair.

Antimicrobial coatings prepared from Dhvar-5-click-grafted chitosan powders

Antimicrobial peptides (AMP) are powerful components of the innate immune system, as they display wide activity spectrum and low tendency to induce pathogen resistance. Hence, the development of AMP-based coatings is a very promising strategy to prevent biomaterials-associated infections. This work aims to investigate if Dhvar-5-chitosan conjugates, previously synthesized by us via azide-alkyne "click" reaction, can be applied as antimicrobial coatings. Ultrathin coatings were prepared by spin coater after dissolving Dhvar-5-chitosan conjugate powder in aqueous acetic acid. Peptide orientation and exposure from the surface was confirmed by ellipsometry and contact angle measurements. Bactericidal activity was evaluated against Staphylococcus epidermidis, Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosa, the most prevalent pathogens in implant-associated infections. Results showed that Dhvar-5-chitosan coatings displayed bactericidal effect. Moreover, since Dhvar-5 has head-to-tail amphipathicity, it was clear that the bactericidal potency was dependent on which domain of the peptide (cationic or hydrophobic) was exposed. In this context, Dhvar-5 immobilized through its C-terminus (exposing its hydrophobic end) presented higher antimicrobial activity against Gram-positive bacteria and reduced adhesion of Gram-negative bacteria. This orientation-dependent antimicrobial activity was further corroborated by the anti-biofilm assay, as covalent immobilization of Dhvar-5 through its C-terminus provided anti-biofilm properties to the chitosan thin film. Immobilization of Dhvar-5 showed no cytotoxic effect against HFF-1 cells, as both metabolic activity and cell morphology were similar to control. In conclusion, Dhvar-5-chitosan coatings are promising antimicrobial surfaces without cytotoxic effects against human cells. STATEMENT OF SIGNIFICANCE: AMP-tethering onto ground biomaterial is still a poorly explored strategy in research. In this work, AMP-tethered ground chitosan is used to produce highly antibacterial ultrathin films. Powdered AMP-tethered chitosan appears as an alternative solution for antimicrobial devices production, as it is suitable for large scale production, being easier to handle for fabrication of different coatings and materials with antimicrobial properties and without inducing toxicity.

Biodegradable waterborne polyurethane grafted with gelatin hydrolysate via solvent-free copolymerization for potential porous scaffold material

One potential porous scaffold material based on polyester waterborne polyurethane (PEUR) grafted with modified gelatin hydrolysate (GH) has been investigated in this research. First, the GH was modified with a silane coupling agent (KH550), and then the modified GH was mixed with pre-polymer emulsion of PEUR to obtain the PEUR grafted GH emulsion (PEUR-g-GH). The synthesized PEUR-g-GH emulsions were characterized by stability analysis and viscosity test. Moreover, the film-forming property of PEUR-g-GH has also been studied, and the PEUR-g-GH films were characterized regarding the water resistance, solvent resistance, mechanical properties, FTIR, AFM, SEM, DMA, TGA and contact angle testing. Finally, the bioactivity and biodegradation were investigated by soaking PEUR-g-GH scaffolds in simulated body fluid (SBF). The results indicated that the PEUR-g-GH emulsion has good stability, water resisting (the contact angle was over 90^o), the PEUR-g-GH showed excellent film-forming, high storage modulus, good structural homogeneity and thermal stability (the temperature of maximum weight loss was over 350 °C). The freeze-dried sample showed porous structure, and the mutual crosslinking of layers can contribute to a good bearing capacity for scaffold. The SBF biodegradability revealed that the biodegradation rate and degree of films gradually increased with the content of GH increased. In addition, the cells on the material were markedly enhanced, and most of cells have proliferated and formed vesicles, which shown a good biocompatibility.

Oxygen-plasma treatment-induced surface engineering of biomimetic polyurethane nanofibrous scaffolds for gelatin-heparin immobilization

Polyurethane (PU) has been extensively used in vascular tissue engineering due to its outstanding mechanical performance and blood compatibility behavior. Here, biomimetic PU-based scaffolds were prepared using an electrospinning technique and gelatin-heparin was introduced as a surface modifier after oxygen plasma treatment to improve cell attachment and release an anticoagulation agent. Morphology, Fourier transform infrared (FTIR) spectroscopy, compression strength, swelling and biodegradation ratio, drug release level and cellular interactions were evaluated. According to the scanning electron microscopy (SEM) micrographs, gelatin-heparin immobilized PU nanofibers exhibited a smooth surface and a bead free structure that nanofibers distributed in the range of 300–1000 nm. The mechanical strength of constructs, swelling and biodegradation ratio, and drug release level illustrated higher values for oxygen plasma-treated samples compared with bilayered scaffolds. Cellular adhesion and biocompatibility ameliorated after plasma treatment. All the mentioned findings indicated the initial physicomechanical and biological potential of biomimetic PU-based fibers in the improvements of vascular scaffolds.

Preparation, Physicochemical Properties and Hemocompatibility of Biodegradable Chitooligosaccharide-Based Polyurethane

The purpose of this study was to develop a process to achieve biodegradable chitooligosaccharide-based polyurethane (CPU) with improved hemocompatibility and mechanical properties. A series of CPUs with varying chitooligosaccharide (COS) content were prepared according to the conventional two-step method. First, the prepolymer was synthesized from poly(ε-caprolactone) (PCL) and uniform-size diurethane diisocyanates (HBH). Then, the prepolymer was chain-extended by COS in N,N-dimethylformamide (DMF) to obtain the weak-crosslinked CPU, and the corresponding films were obtained from the DMF solution by the solvent evaporation method. The uniform-size hard segments and slight crosslinking of CPU were beneficial for enhancing the mechanical properties, which were one of the essential requirements for long-term implant biomaterials. The chemical structure was characterized by FT-IR, and the influence of COS content in CPU on the physicochemical properties and hemocompatibility was extensively researched. The thermal stability studies indicated that the CPU films had lower initial decomposition temperature and higher maximum decomposition temperature than pure polyurethane (CPU-1.0) film. The ultimate stress, initial modulus, and surface hydrophilicity increased with the increment of COS content, while the strain at break and water absorption decreased, which was due to the increment of crosslinking density. The results of in vitro degradation signified that the degradation rate increased with the increasing content of COS in CPU, demonstrating that the degradation rate could be controlled by adjusting COS content. The surface hemocompatibility was examined by protein adsorption and platelet adhesion tests. It was found that the CPU films had improved resistance to protein adsorption and possessed good resistance to platelet adhesion. The slow degradation rate and good hemocompatibility of the CPUs showed great potential in blood-contacting devices. In addition, many active amino and hydroxyl groups contained in the structure of CPU could carry out further modification, which made it an excellent candidate for wide application in biomedical field.

Maskless Surface Modification of Polyurethane Films by an Atmospheric Pressure He/O₂ Plasma Microjet for Gelatin Immobilization

A localized maskless modification method of polyurethane (PU) films through an atmospheric pressure He/O₂ plasma microjet (APPμJ) was proposed. The APPμJ system combines an atmospheric pressure plasma jet (APPJ) with a microfabricated silicon micronozzle with dimension of 30 μm, which has advantages of simple structure and low cost. The possibility of APPμJ in functionalizing PU films with hydroxyl (–OH) groups and covalent grafting of gelatin for improving its biocompatibility was demonstrated. The morphologies and chemical compositions of the modified surface were analyzed by scanning electronic microscopy (SEM), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). The fluorescent images show the modified surface can be divided into four areas with different fluorescence intensity from the center to the outside domain. The distribution of the rings could be controlled by plasma process parameters, such as the treatment time and the flow rate of O₂. When the treatment time is 4 to 5 min with the oxygen percentage of 0.6%, the PU film can be effectively local functionalized with the diameter of 170 μm. In addition, the modification mechanism of PU films by the APPμJ is investigated. The localized polymer modified by APPμJ has potential applications in the field of tissue engineering.

Synthesis of a novel biomedical poly(ester urethane) based on aliphatic uniform-size diisocyanate and the blood compatibility of PEG-grafted surfaces

The purpose of this study is to offer a novel kind of polyurethane with improved surface blood compatibility for long-term implant biomaterials. In this work, the aliphatic poly(ester-urethane) (PEU) with uniform-size hard segments was prepared and the PEU surface was grafted with hydrophilic poly(ethylene glycol) (PEG). The PEU was obtained by chain-extension of poly(ɛ-caprolactone) (PCL) with isocyanate-terminated urethane triblock. Free amino groups were introduced onto the surface of PEU film via aminolysis with hexamethylenediamine, and then the NH₂-grafted PEU surfaces (PEU-NH₂) were reacted with isocyanate-terminated monomethoxyl PEG (MPEG-NCO) to obtain the PEG-grafted PEU surfaces (PEU-PEG). Analysis by nuclear magnetic resonance spectroscopy, Fourier transform infrared spectroscopy, and gel permeation chromatography were performed to confirm the chemical structures of the chain extender, PCL, PEU, and PEU-PEG. Additionally, the influence of aminolysis on the physical-mechanical properties of PEU films was investigated. Two glass transition temperatures and a broad endothermic peak were observed in the differential scanning calorimetry curves of PEU, which demonstrated a microphase-separated and semicrystalline structure, respectively. The PEU-PEG film exhibited excellent mechanical properties with an ultimate stress of ∼39 MPa and an elongation at break of ∼1190%, which was slightly lower than that of PEU, indicating that the aminolysis has little influence on the tensile properties. Evaluation of the blood compatibility of the films by bovine serum albumin adsorption and the platelet adhesion test revealed that the PEG-grafted surface had improved resistance to protein adsorption and excellent resistance to platelet adhesion. In vitro degradation tests showed that the PEU-PEG film could maintain its mechanical properties for more than six months and only lost ∼25% weight after 18 months. Due to the excellent mechanical properties, good blood compatibility and slow degradability, this novel kind of polyurethane hold significant promise for long-term implant biomaterials, especially soft tissue augmentation and regeneration.

Assembling of hydrophilic and cytocompatible three-dimensional scaffolds based on aminolyzed poly(l-lactide) single crystals

3D scaffolds based on aminolyzed poly(l-lactide) single crystals have suitable hydrophilicity and cytocompatibility toward fibroblast cell growth and adhesion.

Engineered tubular structures based on chitosan for tissue engineering applications

The development of versatile tubular structures is a subject of broad interest in tissue engineering applications. Herein, we demonstrate the production of tubular structures based on chitosan through a combination of dipping, freeze-drying and supercritical technology approaches. The combination of these techniques yields versatile tubes with a perfectly defined hollow imprint, which upon chemical cross-linking with genipin acquire enhanced mechanical properties (Young Modulus ( E) and ultimate tensile stress (σ_max)), as well as improved stability in wet conditions. The biological performance reveals that cells remain attached, well-spread and viable on the surface of cross-linked tubes. As so, is envisioned that our methodology opens up new avenues on tissue engineering approaches, where the design of tubular structures with tuned length, diameter and elasticity is required.

Preparation and characterization of polycaprolactone–polyethylene glycol methyl ether and polycaprolactone–chitosan electrospun mats potential for vascular tissue engineering

Recently, natural polymers are frequently comingled with synthetic polymers either by physical or chemical modification to prepare numerous tissue-engineered graft with promising biological function, strength, and stability. The aim of this study was to determine the efficiency for vascular tissue engineering of two distinctly different mats, one that comprised polycaprolactone–polyethylene glycol methyl ether and other that comprised polycaprolactone–chitosan. Nano/microfibrous mats prepared from electro-spinning were characterized for fiber diameter, porosity, wettability, and mechanical strength. Biological efficacy on both biodegradable mats was assessed by rat bone marrow mesenchymal stem cells, and polycaprolactone–polyethylene glycol methyl ether showed feasibility for use as an inner layer by inducing endothelial-specific gene expression and polycaprolactone–chitosan as an outer layer on dual layered without sacrificing tensile strength, small-diameter blood vessels. Therefore, scaffolds fabricated from this research could be potential sources for tissue-engineered vascular graft and could also overcome the well-known drawbacks, such as thrombogenicity and stenosis, in managing vascular disease.

Oppositely Charged Polyurethane Microspheres with Tunable Zeta Potentials as an Injectable Dual-Loaded System for Bone Repair

To effectively repair irregular shaped bone defects by a minimally invasive procedure, the exploration of an injectable gel to fill the defect is desirable. Herein, positively and negatively charged polyurethane microspheres (PU-A and PU-B) with adjustable zeta potentials as well as the hydroxyapatite-loaded PU microsphere (PU-A/HA) and the dexamethasone-loaded PU microsphere (PU-B/Dex) were successfully prepared, and the oppositely charged microspheres could self-assemble into injectable gels with 3D structures by a mutually electrostatic attraction. The self-assembly PU-A/HA+PU-B/Dex gel exhibited a much higher elastic modulus (about 0.20 MPa) and excellent shear-thinning and self-recovery behaviors, which would allow the gel to be injected through a fine syringe to fill the irregular defect. The in vitro and in vivo experiments demonstrated that the coexistence of HA and Dex in PU-A/HA+PU-B/Dex gel had a synergistic effect on cell differentiation and accelerating new bone formation, displaying a good prospect as an injectable gel for bone repair in minimally invasive surgery.

End-point immobilization of heparin on plasma-treated surface of electrospun polycarbonate-urethane vascular graft

Small-diameter synthetic vascular grafts have high failure rate due to primarily surface thrombogenicity, and effective surface chemical modification is critical to maintain the patency of the grafts. In this study, we engineered a small-diameter, elastic synthetic vascular graft with off-the-shelf availability and anti-thrombogenic activity. Polycarbonate-urethane (PCU), was electrospun to produce nanofibrous grafts that closely mimicked a native blood vessel in terms of structural and mechanical strength. To overcome the difficulty of adding functional groups to PCU, we explored various surface modification methods, and determined that plasma treatment was the most effective method to modify the graft surface with functional amine groups, which were subsequently employed to conjugate heparin via end-point immobilization. In addition, we confirmed in vitro that the combination of plasma treatment and end-point immobilization of heparin exhibited the highest surface density and correspondingly the highest anti-thrombogenic activity of heparin molecules. Furthermore, from an in vivo study using a rat common carotid artery anastomosis model, we showed that plasma-heparin grafts had higher patency rate at 2weeks and 4weeks compared to plasma-control (untreated) grafts. More importantly, we observed a more complete endothelialization of the luminal surface with an aligned, well-organized monolayer of endothelial cells, as well as more extensive graft integration in terms of vascularization and cell infiltration from the surrounding tissue. This work demonstrates the feasibility of electrospinning PCU as synthetic elastic material to fabricate nanofibrous vascular grafts, as well as the potential to endow desired functionalization to the graft surface via plasma treatment for the conjugation of heparin or other bioactive molecules.

STATEMENT OF SIGNIFICANCE

Vascular occlusion remains the leading cause of death all over the world, despite advances made in balloon angioplasty and conventional surgical intervention. Currently, autografts are the gold-standard grafts used to treat vascular occlusive disease. However, many patients with vascular occlusive disease do not have autologous vascular graft available. Therefore, there is a widely recognized need for a readily available, functional, small-diameter vascular graft (inner diameter of <6mm). This work addresses this critical need by developing a method of antithrombogenic modification of synthetic grafts.

Co-self-assembly of cationic microparticles to deliver pEGFP-ZNF580 for promoting the transfection and migration of endothelial cells

The gene transfection efficiency of polyethylenimine (PEI) varies with its molecular weight. Usually, high molecular weight of PEI means high gene transfection, as well as high cytotoxicity in gene delivery in vivo. In order to enhance the transfection efficiency and reduce the cytotoxicity of PEI-based gene carriers, a novel cationic gene carrier was developed by co-self-assembly of cationic copolymers. First, a star-shaped copolymer poly(3(S)-methyl-morpholine-2,5-dione-co-lactide) (P(MMD-co-LA)) was synthesized using D-sorbitol as an initiator, and the cationic copolymer (P(MMD-co-LA)-g-PEI) was obtained after grafting low-molecular weight PEI. Then, by co-self-assembly of this cationic copolymer and a diblock copolymer methoxy-poly(ethylene glycol) (mPEG)-b-P(MMD-co-LA), microparticles (MPs) were formed. The core of MPs consisted of a biodegradable block of P(MMD-co-LA), and the shell was formed by mPEG and PEI blocks. Finally, after condensation of pEGFP-ZNF580 by these MPs, the plasmids were protected from enzymatic hydrolysis effectively. The result indicated that pEGFP-ZNF580-loaded MP complexes were suitable for cellular uptake and gene transfection. When the mass ratio of mPEG-b-P(MMD-co-LA) to P(MMD-co-LA)-g-PEI reached 3/1, the cytotoxicity of the complexes was very low at low concentration (20 μg mL-1). Additionally, pEGFP-ZNF580 could be transported into endothelial cells (ECs) effectively via the complexes of MPs/pEGFP-ZNF580. Wound-healing assay showed that the transfected ECs recovered in 24 h. Cationic MPs designed in the present study could be used as an applicable gene carrier for the endothelialization of artificial blood vessels.

Biomaterial-Based Approaches to Address Vein Graft and Hemodialysis Access Failures

Veins used as grafts in heart bypass or as access points in hemodialysis exhibit high failure rates, thereby causing significant morbidity and mortality for patients. Interventional or revisional surgeries required to correct these failures have been met with limited success and exorbitant costs, particularly for the US Centers for Medicare & Medicaid Services. Vein stenosis or occlusion leading to failure is primarily the result of neointimal hyperplasia. Systemic therapies have achieved little long-term success, indicating the need for more localized, sustained, biomaterial-based solutions. Numerous studies have demonstrated the ability of external stents to reduce neointimal hyperplasia. However, successful results from animal models have failed to translate to the clinic thus far, and no external stent is currently approved for use in the US to prevent vein graft or hemodialysis access failures. This review discusses current progress in the field, design considerations, and future perspectives for biomaterial-based external stents. More comparative studies iteratively modulating biomaterial and biomaterial-drug approaches are critical in addressing mechanistic knowledge gaps associated with external stent application to the arteriovenous environment. Addressing these gaps will ultimately lead to more viable solutions that prevent vein graft and hemodialysis access failures.

Biomacromolecule immobilization: grafting of fish-scale collagen peptides onto aminolyzed P(3HB-co-4HB) scaffolds as a potential wound dressing

Polyhydroxyalkanoate (PHA) is a microbial polymer that has been at the forefront of many attempts at tissue engineering. However, the surface of poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P(3HB-co-4HB)) is hydrophobic with few recognition sites for cell attachment. Various concentrations of fish-scale collagen peptides (FSCPs) were incorporated into P(3HB-co-4HB) copolymer by aminolysis. Later, FSCPs were introduced onto the aminolyzed P(3HB-co-4HB) scaffolds. Introduction of the FSCP groups was verified using Fourier transform infrared spectroscopy and the ninhydrin method. The effect of the incorporation of FSCPs on hydrophilicity was investigated using the water contact angle. As the concentration of FSCPs increased, the water contact angle decreased. In vitro study demonstrated that P(3HB-co-4HB)/FSCP scaffolds provided better cell attachment and growth of L929 mouse fibroblast cells and better cell proliferation. In vivo study showed that P(3HB-co-4HB)/1.5 wt% FSCPs had a significant effect on wound contractions, with the highest percentage of wound closure (61%) in 7 d.

Self-driven perfusion culture system using a paper-based double-layered scaffold

Shear stress caused by fluid flow is known to promote tissue development from cells in vivo. Therefore, perfusion cultures have been studied to investigate the mechanisms involved and to fabricate engineered tissues in vitro, particularly those that include blood vessels. Microfluidic devices, which function with fine machinery of chambers and microsyringes for fluid flow and have small culture areas, are conventionally used for perfusion culture. In contrast, we have developed a self-driven perfusion culture system by using a paper-based double-layered scaffold as the fundamental component. Gelatin microfibers were electrospun onto a paper material to prepare the scaffold system, in which the constant perfusion of the medium and the scaffold for cell adhesion/proliferation were functionally divided into a paper and a gelatin microfiber layer, respectively. By applying both the capillary action and siphon phenomenon of the paper-based scaffold, which bridged two medium chambers at different height levels, a self-driven medium flow was achieved and the flow rate was also stable, constant, and quantitatively controllable. Moreover, the culture area was enlargeable to the cm(2) scale. The endothelial cells cultivated on this system oriented along the medium-flow direction, suggesting that the shear stress caused by medium flow was effectively applied. This perfusion culture system is expected to be useful for fabricating three-dimensional and large engineered tissues in the future.