Comparative Evaluation on Impacts of Fibronectin, Heparin-Chitosan, and Albumin Coating of Bacterial Nanocellulose Small-Diameter Vascular Grafts on Endothelialization In Vitro

In this study, we contrast the impacts of surface coating bacterial nanocellulose small-diameter vascular grafts (BNC-SDVGs) with human albumin, fibronectin, or heparin–chitosan upon endothelialization with human saphenous vein endothelial cells (VEC) or endothelial progenitor cells (EPC) in vitro. In one scenario, coated grafts were cut into 2D circular patches for static colonization of a defined inner surface area; in another scenario, they were mounted on a customized bioreactor and subsequently perfused for cell seeding. We evaluated the colonization by emerging metabolic activity and the preservation of endothelial functionality by water soluble tetrazolium salts (WST-1), acetylated low-density lipoprotein (AcLDL) uptake assays, and immune fluorescence staining. Uncoated BNC scaffolds served as controls. The fibronectin coating significantly promoted adhesion and growth of VECs and EPCs, while albumin only promoted adhesion of VECs, but here, the cells were functionally impaired as indicated by missing AcLDL uptake. The heparin–chitosan coating led to significantly improved adhesion of EPCs, but not VECs. In summary, both fibronectin and heparin–chitosan coatings could beneficially impact the endothelialization of BNC-SDVGs and might therefore represent promising approaches to help improve the longevity and reduce the thrombogenicity of BNC-SDVGs in the future.

Tissue-Inspired Interfacial Coatings for Regenerative Medicine

Biomedical devices have come a long way since they were first introduced as a medically interventional methodology in treating various types of diseases. Different techniques were employed to make the devices more biocompatible and promote tissue repair; such as chemical surface modifications, using novel materials as the bulk of a device, physical topological manipulations and so forth. One of the strategies that recently gained a lot of attention is the use of tissue-inspired biomaterials that are coated on the surface of biomedical devices via different coating techniques, such as the use of extracellular matrix (ECM) coatings, extracted cell membrane coatings, and so on. In this chapter, we will give a general overview of the different types of tissue-inspired coatings along with a summary of recent studies reported in this scientific arena.

Tissue and organ decellularization in regenerative medicine

The advancement and improvement in decellularization methods can be attributed to the increasing demand for tissues and organs for transplantation. Decellularized tissues and organs, which are free of cells and genetic materials while retaining the complex ultrastructure of the extracellular matrix (ECM), can serve as scaffolds to subsequently embed cells for transplantation. They have the potential to mimic the native physiology of the targeted anatomic site. ECM from different tissues and organs harvested from various sources have been applied. Many techniques are currently involved in the decellularization process, which come along with their own advantages and disadvantages. This review focuses on recent developments in decellularization methods, the importance and nature of detergents used for decellularization, as well as on the role of the ECM either as merely a physical support or as a scaffold in retaining and providing cues for cell survival, differentiation and homeostasis. In addition, application, status, and perspectives on commercialization of bioproducts derived from decellularized tissues and organs are addressed. © 2018 American Institute of Chemical Engineers Biotechnol. Prog., 34:1494-1505, 2018.

A density gradient of VAPG peptides on a cell-resisting surface achieves selective adhesion and directional migration of smooth muscle cells over fibroblasts

Selective adhesion and migration of smooth muscle cells (SMCs) over fibroblasts (FIBs) is required to prevent adventitia fibrosis in vascular regeneration. In this study, a uniform cell-resisting layer of poly(ethylene glycol) (PEG) with a density gradient of azide groups was generated on a substrate by immobilizing two kinds of PEG molecules in a gradient manner. A density gradient of alkynyl-functionalized Val-Ala-Pro-Gly (VAPG) peptides was then prepared on the PEG layer via click chemistry. The VAPG density gradient was characterized by fluorescence imaging, revealing the gradual enhancement of the fluorescent intensity along the substrate direction. The adhesion and mobility of SMCs were selectively enhanced on the VAPG density gradient, leading to directional migration toward the higher peptide density (up to 84%). In contrast, the adhesion and mobility of FIBs were significantly weakened. The net displacement of SMCs also significantly increased compared with that on tissue culture polystyrene (TCPS) and that of FIBs on the gradient. The mitogen-activated protein kinase (MAPK) signaling pathways related to cell migration were studied, showing higher expressions of functional proteins from SMCs on the VAPG-modified surface in a density-dependent manner. For the first time the selective adhesion and directional migration of SMCs over FIBs was achieved by an elaborative design of a gradient surface, leading to a new insight in design of novel vascular regenerative materials.

STATEMENT OF SIGNIFICANCE

Selective cell adhesion and migration guided by regenerative biomaterials are extremely important for the regeneration of targeted tissues, which can avoid the drawbacks of incorrect and uncontrolled responses of tissue cells to implants. For example, selectivity of smooth muscle cells (SMCs) over fibroblasts (FIBs) is required to prevent adventitia fibrosis in vascular regeneration. Herein we prepare a uniform cell-repelling layer, on which SMCs-selective Val-Ala-Pro-Gly (VAPG) peptides are immobilized in a continuous manner. Selective adhesion and enhanced and directional migration of SMCs over FIBs are achieved by the interplay of cell-repelling layer and gradient SMCs-selective VAPG peptides, paving a new way for the design of novel vascular grafts with enhanced biological performance.

Guggulsterone-releasing microspheres direct the differentiation of human induced pluripotent stem cells into neural phenotypes

Parkinson's disease (PD), a common neurodegenerative disorder, results from the loss of motor function when dopaminergic neurons (DNs) in the brain selectively degenerate. While pluripotent stem cells (PSCs) show promise for generating replacement neurons, current protocols for generating terminally differentiated DNs require a complicated cocktail of factors. Recent work demonstrated that a naturally occurring steroid called guggulsterone effectively differentiated PSCs into DNs, simplifying this process. In this study, we encapsulated guggulsterone into novel poly-ε-caprolactone-based microspheres and characterized its release profile over 44 d in vitro, demonstrating we can control its release over time. These guggulsterone-releasing microspheres were also successfully incorporated in human induced pluripotent stem cell-derived cellular aggregates under feeder-free and xeno-free conditions and cultured for 20 d to determine their effect on differentiation. All cultures stained positive for the early neuronal marker TUJ1 and guggulsterone microsphere-incorporated aggregates did not adversely affect neurite length and branching. Guggulsterone microsphere incorporated aggregates exhibited the highest levels of TUJ1 expression as well as high Olig 2 expression, an inhibitor of the STAT3 astrogenesis pathway previously known as a target for guggulsterone in cancer treatment. Together, this study represents an important first step towards engineered neural tissues consisting of guggulsterone microspheres and PSCs for generating DNs that could eventually be evaluated in a pre-clinical model of PD.

In-vitro degradation characteristics of poly(e-caprolactone)/poly(glycolic acid) scaffolds fabricated via solid-state cryomilling

Poly(e-caprolactone) (PCL)/poly(glycolic acid) (PGA) scaffolds were fabricated via solid-state cryomilling along with compression molding and porogen leaching techniques. Four types of scaffolds were produced using four distinct cryomilling times. These scaffolds were evaluated for their in-vitro degradation behavior hydrolytically in phosphate buffer saline (PBS). The degradation profiles were investigated over a period of 60 days. The percentage of weight loss, percentage of water absorption, morphology, compressive, thermal, and material properties were studied as a function of degradation time. Weight loss and water absorption demonstrated a high correlation, which showed an increasing behavior with increase in cryomilling time and degradation time. Morphology of the scaffolds analyzed through scanning electron microscopy (SEM) revealed micro-cracks on the surface of the cylindrical struts due to hydrolytic attack and dissolution of hydrophilic PGA. Changes in compressive modulus and crystallinity over the degradation period and material properties were analyzed using X-ray powder diffraction (XRD), differential scanning calorimetry (DSC), and Fourier transform infrared (FTIR) spectroscopy. DSC and XRD results indicated that hydrolytic attack had taken place during degradation, resulting in moments of increased and decreased percent crystallinity. This study successfully brought forth the differences in resultant properties of the PCL/PGA scaffolds as a function of degradation time.

A sacrificial process for fabrication of biodegradable polymer membranes with submicron thickness

A new sacrificial molding process using a single mask has been developed to fabricate ultrathin 2-dimensional membranes from several biocompatible polymeric materials. The fabrication process is similar to a sacrificial microelectromechanical systems (MEMS) process flow, where a mold is created from a material that can be coated with a biodegradable polymer and subsequently etched away, leaving behind a very thin polymer membrane. In this work, two different sacrificial mold materials, silicon dioxide (SiO2 ) and Liftoff Resist (LOR) were used. Three different biodegradable materials; polycaprolactone (PCL), poly(lactic-co-glycolic acid) (PLGA), and polyglycidyl methacrylate (PGMA), were chosen as model polymers. We demonstrate that this process is capable of fabricating 200-500 nm thin, through-hole polymer membranes with various geometries, pore-sizes and spatial features approaching 2.5 µm using a mold fabricated via a single contact photolithography exposure. In addition, the membranes can be mounted to support rings made from either SU8 or PCL for easy handling after release. Cell culture compatibility of the fabricated membranes was evaluated with human dermal microvascular endothelial cells (HDMECs) seeded onto the ultrathin porous membranes, where the cells grew and formed confluent layers with well-established cell-cell contacts. Furthermore, human trabecular meshwork cells (HTMCs) cultured on these scaffolds showed similar proliferation as on flat PCL substrates, further validating its compatibility. All together, these results demonstrated the feasibility of our sacrificial fabrication process to produce biocompatible, ultra-thin membranes with defined microstructures (i.e., pores) with the potential to be used as substrates for tissue engineering applications. © 2015 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 104B: 1192-1201, 2016.

Hybrid Membranes of PLLA/Collagen for Bone Tissue Engineering: A Comparative Study of Scaffold Production Techniques for Optimal Mechanical Properties and Osteoinduction Ability

Synthetic and natural polymer association is a promising tool in tissue engineering. The aim of this study was to compare five methodologies for producing hybrid scaffolds for cell culture using poly-l-lactide (PLLA) and collagen: functionalization of PLLA electrospun by (1) dialkylamine and collagen immobilization with glutaraldehyde and by (2) hydrolysis and collagen immobilization with carbodiimide chemistry; (3) co-electrospinning of PLLA/chloroform and collagen/hexafluoropropanol (HFP) solutions; (4) co-electrospinning of PLLA/chloroform and collagen/acetic acid solutions and (5) electrospinning of a co-solution of PLLA and collagen using HFP. These materials were evaluated based on their morphology, mechanical properties, ability to induce cell proliferation and alkaline phosphatase activity upon submission of mesenchymal stem cells to basal or osteoblastic differentiation medium (ODM). Methods (1) and (2) resulted in a decrease in mechanical properties, whereas methods (3), (4) and (5) resulted in materials of higher tensile strength and osteogenic differentiation. Materials yielded by methods (2), (3) and (5) promoted osteoinduction even in the absence of ODM. The results indicate that the scaffold based on the PLLA/collagen blend exhibited optimal mechanical properties and the highest capacity for osteodifferentiation and was the best choice for collagen incorporation into PLLA in bone repair applications.

A fibronectin-fibrinogen-tropoelastin coating reduces smooth muscle cell growth but improves endothelial cell function

Reendothelialization of the stent surface after percutaneous coronary intervention (PCI) is known to be an important determinant of clinical outcome. We compared the effects of biological stent coatings, fibronectin, fibrinogen and tropoelastin, on human umbilical vein endothelial cell (HUVEC) and vascular smooth muscle cell (VSMC) characteristics. Umbilical cord arterial segments were cultured on coated surfaces and VSMC outgrowth (indicating proliferation and migration) was measured after 12 days. mRNA was isolated from HUVEC and VSMC cultured on these coatings and gene expression was profiled by QPCR. Procoagulant properties of HUVEC were determined by an indirect chromogenic assay which detects tissue factor activity. The varying stent coatings influence VSMC outgrowth: 31.2 ± 4.0 mm² on fibronectin, 1.6 ± 0.3 mm² on tropoelastin and 8.1 ± 1.5 mm² on a mixture of fibronectin/fibrinogen/tropoelastin, although HUVEC migration remains unaffected. Culturing HUVEC on tropoelastin induces increased expression of VCAM-1 (13.1 ± 4.4 pg/ml), ICAM-1 (5.1 ± 1.3 pg/ml) and IL-8 (11.6 ± 3.1 pg/ml) compared to fibronectin (0.7 ± 0.2, 0.8 ± 0.2, 2.3 ± 0.5 pg/ml, respectively), although expression levels on fibronectin/fibrinogen/tropoelastin remain unaltered. No significant differences in VCAM-1, ICAM-1 and IL-8 mRNA expression are found in VSMC. Finally, HUVEC cultured on tropoelastin display a fivefold increased tissue factor activity (511.6 ± 26.7%), compared to cells cultured on fibronectin (100 ± 3.9%) or fibronectin/fibrinogen/tropoelastin (76.3 ± 25.0%). These results indicate that tropoelastin inhibits VSMC migration but leads to increased inflammatory and procoagulant markers on endothelial cells. Fibronectin/fibrinogen/tropoelastin inhibits VSMCs while compensating the inflammatory and procoagulant effects. These data suggest that coating a mixture of fibronectin/fibrinogen/tropoelastin on a stent may promote reendothelialization, while keeping unfavourable processes such as restenosis and procoagulant activity limited.

Immobilization of gelatin onto poly(glycidyl methacrylate)-grafted polycaprolactone substrates for improved cell-material interactions

To enhance the cytocompatibility of polycaprolactone (PCL), cell-adhesive gelatin is covalently immobilized onto the PCL film surface via two surface-modified approaches: a conventional chemical immobilization process and a surface-initiated atom transfer radical polymerization (ATRP) process. Kinetics studies reveal that the polymer chain growth from the PCL film using the ATRP process is formed in a controlled manner, and that the amount of immobilized gelatin increases with an increasing concentration of epoxide groups on the grafted P(GMA) brushes. In vitro cell adhesion and proliferation studies demonstrate that cell affinity and growth are significantly improved by the immobilization of gelatin on PCL film surfaces, and that this improvement is positively correlated to the amount of covalently immobilized gelatin. With the versatility of the ATRP process and tunable grafting efficacy of gelatin, this study offers a suitable methodology for the functionalization of biodegradable polyesters scaffolds to improve cell-material interactions.

Quantification of protein incorporated into electrospun polycaprolactone tissue engineering scaffolds

The surface modification of synthetic tissue engineering scaffolds is essential to improving their hydrophilicity and cellular compatibility. Plasma treatment is an effective way to increase the hydrophilicity of a surface, but the incorporation of biomolecules is also important to control cellular adhesion and differentiation, among many other outcomes. In this work, oriented polycaprolactone (PCL) electrospun fibers were modified by air-plasma treatment, followed by the covalent attachment of laminin. The amount of protein incorporated onto the fiber surface was controlled by varying the reaction time and the protein solution concentration. The protein concentration and coverage were quantified using X-ray photoelectron spectroscopy (XPS), solid-state ultraviolet-visible spectroscopy (UV-vis) and two fluorescence-based assays. XPS results showed a nearly linear increase in protein coverage with increasing protein soaking solution concentration until a monolayer was formed. Results from XPS and the NanoOrange fluorescence assay revealed multilayer protein coverage at protein solution concentrations between 25 and 50 μg/mL, whereas the UV-vis assay demonstrated multilayer coverage at lower protein solution concentrations. The effect of protein concentration on the neurite outgrowth of neuron-like PC12 cells was evaluated, and outgrowth rates were found to be positively correlated to increasing protein concentration.

Surface modification of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) copolymer films for promoting interaction with bladder urothelial cells

Often bladder dysfunction and diseases lead to therapeutic interventions that require partial or complete replacement of damaged tissue. For this reason, the development of biomaterials to repair the bladder by promoting the adhesion and growth of urothelial cells is of interest. With this aim, a modified copolyester of biocompatible and biodegradable poly(3-hydroxybutyrate-co-3-hydroxyvalerate) [P(HB-co-HV)] was used as scaffold for porcine urothelial cell culture. In addition to good biocompatibility, the surface of P(HB-co-HV) substrates was modified to provide both, higher hydrophilicity and a better interaction with urothelial cells. Chemical treatments with ethylenediamine (ED) and sodium hydroxide (NaOH) led to substrate surfaces with decreasing hydrophobicity and provided functional groups that enable the grafting of bioactive molecules, such as a laminin derived YIGSR sequence. Physico-chemical properties of modified substrates were studied and compared with those of the pristine P(HB-co-HV). Urothelial cell morphology on treated substrates was studied. The results showed that focal attachment and cell-related properties were improved for peptide grafted polymer compared with both, the unmodified and functionalized copolyester.