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It is increasingly appreciated that the properties of a biomaterial used in intramyocardial injection therapy influence the outcomes of infarcted hearts that are treated. In this report the extended in vivo efficacy of a thermally responsive material that can deliver dual growth factors while providing a slow degradation time and high mechanical stiffness is examined. Copolymers consisting of N-isopropyla-crylamide, 2-hydroxyethyl methacrylate, and degradable methacrylate polylactide were synthesized. The release of bioactive basic fibroblast growth factor (bFGF) and insulin-like growth factor 1 (IGF1) from the gel and loaded poly(lactide-co-glycolide) microparticles was assessed. Hydrogel with or without loaded growth factors was injected into 2 week-old infarcts in Lewis rats and animals were followed for 16 weeks. The hydrogel released bioactive bFGF and IGF1 as shown by mitogenic effects on rat smooth muscle cells in vitro. Cardiac function and geometry were improved for 16 weeks after hydrogel injection compared to saline injection. Despite demonstrating that left ventricular levels of bFGF and IGF1 were elevated for two weeks after injection of growth factor loaded gels, both functional and histological assessment showed no added benefit to inclusion of these proteins. This result points to the complexity of designing appropriate materials for this application and suggests that the nature of the material alone, without exogenous growth factors, has a direct ability to influence cardiac remodeling.

Heart failure initiated by coronary artery disease and myocardial infarction (MI) is a widespread, debilitating condition for which there are a limited number of options to prevent disease progression. Intra-myocardial biomaterial injection following MI theoretically provides a means to reduce the stresses experienced by the infarcted ventricular wall, which may alter the pathological remodeling process in a positive manner. Furthermore, biomaterial injection provides an opportunity to concurrently introduce cellular components and depots of bioactive agents. Biologically derived, synthetic and hybrid materials have been applied, as well as materials designed expressly for this purpose, although optimal design parameters, including degradation rate and profile, injectability, elastic modulus and various possible bioactivities, largely remain to be elucidated. This review seeks to summarize the current body of growing literature where biomaterial injection, with and without concurrent pharmaceutical or cellular delivery, has been pursued to improve functional outcomes following MI. The literature to date generally demonstrates acute functional benefits associated with biomaterial injection therapy across a broad variety of animal models and material compositions. Further functional improvements have been reported when cellular or pharmaceutical agents have been incorporated into the delivery system. Despite these encouraging early results, the specific mechanisms behind the observed functional improvements remain to be fully explored and future studies employing hypothesis-driven material design and selection may increase the potential of this approach to alleviate the morbidity and mortality of heart failure.

Injectable thermoresponsive hydrogels are of interest for a variety of biomedical applications, including regional tissue mechanical support as well as drug and cell delivery. Within this class of materials there is a need to provide options for gels with stronger mechanical properties as well as variable degradation profiles. To address this need, the hydrolytically labile monomer, methacrylate-polylactide (MAPLA), with an average 2.8 lactic acid units, was synthesized and copolymerized with N-isopropylacrylamide (NIPAAm) and 2-hydroxyethyl methacrylate (HEMA) to obtain bioabsorbable thermally responsive hydrogels. Poly(NIPAAm-co-HEMA-co-MAPLA) with three monomer feed ratios (84/10/6, 82/10/8, and 80/10/10) was synthesized and characterized with NMR, FTIR, and GPC. The copolymers were soluble in saline at reduced temperature (10 degrees C), forming clear solutions that increased in viscosity with the MAPLA feed ratio. The copolymers underwent sol-gel transition at lower critical solution temperatures of 12.4, 14.0, and 16.2 degrees C, respectively, and solidified immediately upon being placed in a 37 degrees C water bath. The warmed hydrogels gradually excluded water to reach final water contents of approximately 45%. The hydrogels as formed were mechanically strong, with tensile strengths as high as 100 kPa and shear moduli of 60 kPa. All three hydrogels were completely degraded (solubilized) in PBS over a 6-7 month period at 37 degrees C, with a higher MAPLA feed ratio resulting in a faster degradation period. Culture of primary vascular smooth muscle cells with degradation solutions demonstrated a lack of cytotoxicity. The synthesized hydrogels provide new options for biomaterial injection therapy where increased mechanical strength and relatively slow resorption rates would be attractive.

Non-woven polyethersulfone (PES) membranes were prepared by electrospinning. After heat treatment and surface activation, the membranes were covalently functionalized with ligands to be used as affinity membranes. The membranes were characterized in terms of fiber diameter, porosity, specific area, pore size, ligand density and binding capacities. To evaluate the binding efficiency of the membrane, dynamic adsorption of bovine serum albumin (BSA) on the Cibacron blue F3GA (CB) functionalized PES membrane was studied. Experimental breakthrough curves were fitted with the theoretical curves based on the plate model to estimate plate height ( H p ) of the affinity membrane. The high value of H p (1.6–8 cm) of the affinity membrane implied a poor dynamic binding efficiency, which can be explained by the intrinsic microstructures of the material. Although the electrospun membrane might not be an ideal candidate for the preparative affinity membrane chromatography for large-scale production, it still can be used for fast small-scale protein purification in which a highly efficient binding is not required. Spin columns packed with protein A/G immobilized PES membranes were demonstrated to be capable of binding IgG specifically. SDS-PAGE results demonstrated that the PES affinity membrane had high specific binding selectivity for IgG molecules and low non-specific protein adsorption. Compared with other reported affinity membranes, the PES affinity membrane had a comparable IgG binding capacity of 4.5 mg/ml, and had a lower flow through pressure drop due to its larger pore size. In conclusion, the novel PES affinity membrane is an ideal spin column packing material for fast protein purification.

Injection of a bulking material into the ventricular wall has been proposed as a therapy to prevent progressive adverse remodeling due to high wall stresses that develop after myocardial infarction. Our objective was to design, synthesize and characterize a biodegradable, thermoresponsive hydrogel for this application based on copolymerization of N-isopropylacrylamide (NIPAAm), acrylic acid (AAc) and hydroxyethyl methacrylate-poly(trimethylene carbonate) (HEMAPTMC). By evaluating a range of monomer ratios, poly(NIPAAm-co-AAc-co-HEMAPTMC) at a feed ratio of 86/4/10 was shown to be ideal since it formed a hydrogel at 37 degrees C, and gradually became soluble over a 5 month period in vitro through hydrolytic cleavage of the PTMC residues. HEMAPTMC, copolymer and degradation product chemical structures were verified by NMR. No degradation product cytotoxicity was observed in vitro. In a rat chronic infarction model, the infarcted left ventricular (LV) wall was injected with the hydrogel or phosphate buffered saline (PBS). In the PBS group, LV cavity area increased and contractility decreased at 8 wk (p

Quick establishment of a confluent and stable endothelial cells (ECs) layer in the lumen of vascular grafts is critical for long-term patency of small-diameter vascular grafts. The objective of the study was to fabricate tubular nanofiber scaffolds, incorporate ECs onto the lumen of the scaffolds, and establish an animal model to prove the basic concept of using the scaffolds as vascular grafts. Poly(L-lactic acid)-co-poly(epsilon-caprolactone) P(LLA-CL 70:30) tubular nanofiber scaffolds were fabricated by electrospinning onto a rotating mandrel. Collagen was coated onto the scaffolds after air plasma treatment. Structure and mechanical property of the scaffolds were studied by scanning electron microscopy and tensile stress measurement, respectively. Human coronary artery endothelial cells (HCAECs) were rotationally seeded onto the lumen of the scaffolds at the speed of 6 rpm for 4 h through a customized seeding device, followed with static culture. Results showed evenly distributed and well-spread HCAECs throughout the lumen of the scaffold from 1 day onward to 10 days after seeding. Further, HCAECs maintained phenotypic expression of PECAM-1. To prove the basic concept of using the scaffolds as vascular grafts, acellular tubular P(LLA-CL) nanofiber scaffolds (inner diameter 1 mm) were implanted into rabbits to replace the inferior superficial epigastric veins. Results showed the scaffolds sustained the surgical process, kept the structure integrity, and showed the patency for 7 weeks.

The aim of this work is to prepare protein A/G functionalized electrospun regenerated cellulose (RC) nanofiber mesh as affinity membrane for immunoglobulin G (IgG) purification. Cellulose acetate (CA) nonwoven nanofiber membrane was prepared by electrospinning, followed by heat treatment and alkaline treatment to obtain RC nonwoven nanofiber membrane. After oxidization of the RC membrane by NaIO4, protein A/G was covalently immobilized on the membrane, giving an affinity membrane capable of specifically capturing IgG molecules. Physical and chemical properties of the affinity membrane were characterized. Surface chemistry of the membranes during the membrane modification process was monitored with XPS and ATR-FTIR. Oxidization degree of the RC membrane was optimized to get a high ligand binding capacity without too much loss of mechanical strength for handling of the material. Ligand (protein A/G) amount immobilized on the RC membrane oxidized for 9 h was measured as 30 μg/mg and the membrane's IgG binding capacity was measured as 18 μg/mg. The IgG purification ability of the affinity membrane was evaluated with BSA as a model impurity. Five layers of the cellulose affinity membrane were packed into a spin column to separate IgG from an IgG/BSA mixture solution. SDS-PAGE analysis showed that the BSA was completely removed after the purification.

Electrospun nanofibrous membranes (ENM) which have a porous structure have a huge potential for various liquid filtration applications. In this paper, we explore the viability of using plasma-induced graft copolymerization to reduce the pore sizes of ENMs. Poly(vinylidene) fluoride (PVDF) was electrospun to produce a nonwoven membrane, comprised of nanofibers with diameters in the range of 200-600 nm. The surface of the ENM was exposed to argon plasma and subsequently graft-copolymerized with methacrylic acid. The effect of plasma exposure time on grafting was studied for both the ENM and a commercial hydrophobic PVDF (HVHP) membrane. The grafting density was quantitatively measured with toluidine blue-O. The degree of grafting increased steeply with an increase in plasma exposure time for the ENM, attaining a maximum of 180 nmol/mg after 120 s of plasma treatment. However, the increase in the grafting density on the surface of the HVHP membrane was not as drastic, reaching a plateau of 65 nmol/mg after 60 s. The liquid entry permeation of water dropped extensively for both membranes, indicating a change in surface properties. Field emission scanning electron microscopy micrographs revealed an alteration in the surface pore structure for both membranes after grafting. Bubble point measurements of the ENM reduced from 3.6 to 0.9 um after grafting. The pore-size distribution obtained using the capillary flow porometer for the grafted ENM revealed that it had a similar profile to that of a commercial hydrophilic commercial PVDF (HVLP) membrane. More significantly, water filtration studies revealed that the grafted ENM had a better flux throughput than the HVLP membrane. This suggests that ENMs can be successfully engineered through surface modification to achieve smaller pores while retaining their high flux performance.

The response of host organism in macroscopic, cellular and protein levels to biomaterials is, in most cases, closely associated with the materials' surface properties. In tissue engineering, regenerative medicine and many other biomedical fields, surface engineering of the bio-inert synthetic polymers is often required to introduce bioactive species that can promote cell adhesion, proliferation, viability and enhanced ECM-secretion functions. Up to present, a large number of surface engineering techniques for improving biocompatibility have been well established, the work of which generally contains three main steps: (1) surface modification of the polymeric materials; (2) chemical and physical characterizations; and (3) biocompatibility assessment through cell culture. This review focuses on the principles and practices of surface engineering of biomedical polymers with regards to particular aspects depending on the authors' research background and opinions. The review starts with an introduction of principles in designing polymeric biomaterial surfaces, followed by introduction of surface modification techniques to improve hydrophilicity, to introduce reactive functional groups and to immobilize functional protein molecules. The chemical and physical characterizations of the modified biomaterials are then discussed with emphasis on several important issues such as surface functional group density, functional layer thickness, protein surface density and bioactivity. Three most commonly used surface composition characterization techniques, i.e. ATR-FTIR, XPS, SIMS, are compared in terms of their penetration depth. Ellipsometry, CD, EPR, SPR and QCM's principles and applications in analyzing surface proteins are introduced. Finally discussed are frequently applied methods and their principles to evaluate biocompatibility of biomaterials via cell culture. In this section, current techniques and their developments to measure cell adhesion, proliferation, morphology, viability, migration and gene expression are reviewed.

Polymer porous scaffolds and hydrogels have been separately employed as analogues of the native extra-cellular matrix (ECM). However, both of these two kinds of materials have their own advantages and shortcomings. In this work, an attempt to combine the advantages of these two kinds of materials is carried out. Poly-L-lactide (PLLA) scaffolds with good mechanical properties were prepared by thermally induced phase separation, which were then filled with hydrogel aiming at entrapment of cells within a support of predefined shape. Agar, which has a function to promote chondrogenesis, was selected to entrap chondrocytes, acting as analogues of native ECM. A straight forward merit of this construct is that both mechanical strength and macroscopic shape, and analogous ECM can be simultaneously achieved. The morphology and distribution of the chondrocytes were studied by confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM). The cell growth behaviors were determined by MTT assay and collagen and glycosaminoglycan (GAG) secretion. After culture for 7 and 14 days, the cells in the construct were round and surrounded by the hydrogel. The MTT viability and the cell secretion in the chondrocytes/agar/scaffold construct were also higher than that of the chondrocytes/scaffold construct (control). Gelatin was further introduced into the construct, yielding improved GAG secretion and cytoviability. After implantation in the subcutaneous dorsum of nude mice for 4 weeks, cartilage-like specimens maintaining their original rectangular shapes were harvested. Histological examination showed that new cartilage was regenerated and a large quantity of collagen and GAG were secreted, while the cells in the control PLLA scaffold turned to be fibroblast-like with less secretion of extracellular matrices. The method provides a useful pathway of scaffold preparation and cell transplantation, which can achieve suitable mechanical properties and good cell performance simultaneously.

Non-woven polymer membrane with nano- or micro-scaled fiber diameter prepared by electrospinning technique is a potential material for affinity membrane application. In this work, electrospun polysulphone (PSU) fiber membrane was surface modified and studied as a novel affinity membrane, using Cibacron blue F3GA (CB) and bovine serum albumin (BSA) as a ligand–ligate research model. Methacrylic acid (MAA) was graft polymerized on the PSU fiber surface initiated by Ce(IV) to introduce carboxyl groups. With carbodiimide as coupling agent, the carboxyl groups were reacted with diamino-dipropylamine (DADPA) to introduce amino groups. Finally, CB was covalently attached on the PSU fiber surface through reaction with the amino groups. The surface of the membrane was characterized by ATR-FTIR, XPS and other colorimetric methods. The novel PSU affinity membrane showed higher water permeability than commercial microporous membranes. BSA adsorption isotherm curve on the CB immobilized PSU membrane was tested. The CB functionalized PSU membrane showed a capturing capacity of 22 mg/g for BSA. Regeneration of the membrane using elution buffer with increased ionic strength and pH value made the membrane reusable. To understand the dynamic adsorption and desorption of BSA, breakthrough curve and elution curve of the affinity membrane were tested. This work demonstrated that electrospun polymer fiber membrane has potential for affinity membrane applications.

This paper explores the viability of developing a fibrous membrane via electrospun nanofibrous web for liquid separation and demonstrates its applicability in particulate removal. Polyvinylidene fluoride nanofibers were electrospun into membranes and characterized to relate its structural properties to membrane separation properties and performance. Characterization of these electrospun membranes revealed that they have similar properties to that of conventional microfiltration membranes. The electrospun membranes were used to separate 1, 5 and 10 μm polystyrene particles. The electrospun membranes were successful in rejecting more than 90% of the micro-particles from solution. This work opens up the avenue of exploring the use of nanofibers for more mainstream application in the separation technology as a potential membrane for pre-treatment of water prior to reverse osmosis or as pre-filters to minimize fouling and contamination prior to ultra- or nano-filtration.

Maintaining functions of endothelial cells in vitro is a prerequisite for effective endothelialization of biomaterials as an approach to prevent intimal hyperplasia of small-diameter vascular grafts. The aim of this study was to design suitable nanofiber meshes (NFMs) that further maintain the phenotype and functions of human coronary artery endothelial cells (HCAECs). Collagen-coated random and aligned poly(L-lactic acid)-co-poly(epsilon-caprolactone) (P(LLA-CL)) NFMs were fabricated using electrospinning. Mechanical testing showed that tensile modulus and strength were greater for the aligned P(LLA-CL) NFM than for the random NFM. Spatial distribution of the collagen in the NFMs was visualized by labeling with fluorescent dye. HCAECs grew along the direction of nanofiber alignment and showed elongated morphology that simulated endothelial cells in vivo under blood flow. Both random and aligned P(LLA-CL) NFMs preserved phenotype (expression of platelet endothelial cell adhesion molecule-1, fibronectin, and collagen type IV in protein level) and functions (complementary DNA microarray analysis of 112 genes relevant to endothelial cell functions) of HCAECs. The P(LLA-CL) NFMs are potential materials for tissue-engineered vascular grafts that may enable effective endothelialization.

Nanofibers exist widely in human tissue with different patterns. Electrospinning nanotechnology has recently gained a new impetus due to the introduction of the concept of biomimetic nanofibers for tissue regeneration. The advanced electrospinning technique is a promising method to fabricate a controllable continuous nanofiber scaffold similar to the natural extracellular matrix. Thus, the biomedical field has become a significant possible application field of electrospun fibers. Although electrospinning has developed rapidly over the past few years, electrospun nanofibers are still at a premature research stage. Further comprehensive and deep studies on electrospun nanofibers are essential for promoting their biomedical applications. Current electrospun fiber materials include natural polymers, synthetic polymers and inorganic substances. This review briefly describes several typically electrospun nanofiber materials or composites that have great potential for tissue regeneration, and describes their fabrication, advantages, drawbacks and future prospects.

Nonwoven meshes composed of polysulphone (PSU) ultrafine fibers (diameter 1–2 μm) were fabricated via electrospinning technique and then surface modified towards development of a novel affinity membrane. After the electrospinning, the PSU fiber mesh was heat treated under 188 °C to significantly improve the mechanical strength of the fiber mesh. For surface modification, carboxyl groups were introduced onto the PSU fiber surfaces through grafting co-polymerization of methacrylic acid (MAA) initiated by Ce(IV) after an air plasma treatment of the PSU fiber mesh. Toluidine Blue O (TBO), a dye, which can form stable complex with carboxyl groups, was used as a model target molecule to be captured by the PMAA grafted PSU fiber mesh. The adsorption isotherm and rate of the TBO were studied. Further more, the carboxyl groups on the PMAA grafted PSU fiber mesh can be used as coupling sites for immobilization of other protein ligands. Bovine serum albumin (BSA) was chosen as a model protein ligand to be immobilized into the PSU fiber mesh with a capacity of 17 μg/mg. The surface modification processes were verified by XPS and ATR-FRIR spectroscopy. Filtration analysis showed that the nonwoven fibrous membrane has much smaller pressure drop (ΔP = 0.7–1.5 psi) and higher flux compared with conventional micro-filtration membranes. The electrospun PSU fiber mesh developed in this work is a potential candidate material to be used as affinity membranes.

Nanofibers are able to form a highly porous mesh and their large surface-to-volume ratio improves performance for many applications. Electrospinning has the unique ability to produce nanofibers of different materials in various fibrous assemblies. The relatively high production rate and simplicity of the setup makes electrospinning highly attractive to both academia and industry. A variety of nanofibers can be made for applications in energy storage, healthcare, biotechnology, environmental engineering, and defense and security.

An attempt was made to incorporate β-Cyclodextrin (β-CD) onto the surface of the nanofiber to target potential applications in organic waste treatment. Phenylcarbomylated and azido phenylcarbomylated β-CD were successfully blended with poly(methyl methacrylate) (PMMA) and electrospun into nanofibrous membrane respectively with an approximate diameter of 900 nm. The presence of this selective agent on the surface of the nanofibers was confirmed by ATR-FTIR and XPS. To determine the functionalized membranes ability to capture small organic molecules, a solution containing phenolphthalein (PHP), a small organic molecule, was used. The results obtained showed that the functionalized nanofibrous membranes were able to effectively capture the PHP molecules. Thus the developed β-CD functionalized nanofibrous membranes may have the potential to capture similar small organic molecules in organic waste.

Poly(L-lactic acid) (PLLA) scaffolds with pore diameters from several micrometers to ∼300 μm were fabricated by a specially elaborated thermally induced phase separation technique. Two different coarsening protocols, i.e., normal coarsening and multi-step coarsening were compared in consideration of phase separation and domain growth. A normal coarsening route produced scaffolds with pore size from several micrometers to 150 μm depending on the coarsening time after phase separation, accompanying with the emergence of isolated pores at long time coarsening. Scaffolds with large pores with size up to ∼300 μm were fabricated by the two-step coarsening technique, e.g., the PLLA-solvent (dioxane/water) system was coarsened at a temperature after phase separation for a period, followed by coarsening at a lower temperature for another period. In parallel with formation of the large pores, the interconnectivity between pores was also improved, which was evidenced by scanning electron microscopy, gelatin solution pervasion, and collagen entrapment. The present technique provides the ability to produce scaffolds with high purity, controllable microstructures, and ease of modification, and hence can be widely used in tissue engineering field. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3336–3342, 2006

Ce(IV)-induced graft copolymerization of methacrylic acid (MAA) on polysulphone (PSU) surface is studied. After pretreatment either by formaldehyde solution or by air glow discharge plasma, the PSU fiber membrane was immersed in MAA solution with Ce(IV) and heated under 80°C under N2 protection. The MAA was induced by the Ce(IV) redox initiation system to polymerize on the PSU fiber membrane surface. It was found that the pretreatment of the membrane is a very necessary condition for the graft copolymerization to obtain high graft degree. For both the formaldehyde and the air glow discharge plasma pretreated membrane, the graft degree increase with the reaction time. To study the reaction mechanism, control experiments were carried out. Membrane surfaces were characterized by ATR-FTIR and XPS. The reaction mechanism of the graft copolymerization was discussed based on the experimental data. The effect of the graft copolymerization on the membrane's structure and water permeability was finally studied. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3835–3841, 2006

The objective of this work is to study the feasibility of applying cellulose nanofiber membrane prepared by electrospinning as affinity membrane. Cellulose acetate (CA) solution (0.16 g/ml) in a mixture solvent of acetone/DMF/trifluoroethylene (3:1:1) was electrospun into nonwoven fiber mesh with the fiber diameter ranging from 200 nm to 1 μm. The CA nanofiber mesh was heat treated under 208 °C for 1 h to improve structural integrity and mechanical strength, and then treated in 0.1 M NaOH solution in H 2 O/ethanol (4:1) for 24 h to obtain regenerated cellulose (RC) nanofiber mesh, which was used as a novel filtration membrane in this work. The RC nanofiber membrane was further surface functionalized with Cibacron Blue F3GA (CB), a general affinity dye ligand for separation of many biomolecules. The material's chemical and physical properties were studied by SEM, DSC and ATR-FTIR. Water filtration properties of the novel RC membrane were studied and compared with a commercial micro-filtration membrane. The CB derived RC nanofiber membrane has a CB content of 130 μmol/g, and capture capacity of 13 mg/g for bovine serum albumin (BSA) and 4 mg/g for bilirubin. The membrane showed reusability after regeneration with elution buffer. Dynamic adsorption of BSA on the nanofiber membrane was studied by breakthrough curve measurements.

Hydrophilic groups, i.e. hydroxyl (–OH), carboxyl (–COOH) or amide (–CONH 2 ) were introduced onto the poly- l -lactic acid (PLLA) membrane surfaces via the photo-induced grafting copolymerization of the corresponding monomers, i.e. hydroxyethyl methacrylate, methacrylic acid or acrylamide, respectively. Chondrocyte culture was used to study the correlation between the cell behaviors and the hydrophilic functional groups. The results showed that the cytocompatibility of the PLLA membranes with hydroxyl or amide groups on the surface was greatly improved compared to that of the original PLLA membrane. However, the PLLA membrane with carboxyl groups on the surface had even worse cytocompatibility though possessed a similar hydrophilicity.

Poly-L-lactic acid (PLLA) membranes were photo-oxidized in hydrogen peroxide solution under ultraviolet light (UV) to introduce hydroperoxide groups onto the PLLA membrane surfaces. The photo-oxidized membranes were then immersed in acrylamide (AAm) solution containing Fe2+ to graft polyacrylamide (PAAm) onto the PLLA membrane surfaces. The density of the hydroperoxide groups introduced on the PLLA membrane surfaces varied with the temperature and the photo-oxidization time. The occurrence of grafting was verified by X-ray photoelectron spectroscopy (XPS). The degree of grafting increased with the monomer concentration and the polymerization time. Water contact angle measurements showed that the wettability of the modified PLLA membranes had improved. Chondrocytes proliferated more rapidly and were more spread out on the modified membrane than on the control PLLA membrane, indicating that the PAAm-grafted PLLA membrane has better cytocompatibility for chondrocytes.

To covalently immobilize gelatin or collagen type I on poly-L-lactic acid (PLLA) film surfaces poly(hydroxyethyl methacrylate) (PHEMA) or poly(methacrylic acid) (PMAA) was grafted via photooxidization and subsequent UV-induced polymerization [Makromol. Chem. 186 (1985) 1533.1]. For films grafted with PHEMA, methyl sulfonyl chloride was used to activate the hydroxyl groups and for films grafted with PMAA 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide was used to activate the carboxyl groups. Gelatin and collagen were finally reacted with the activated hydroxyl or carboxyl groups to obtain covalently immobilized protein layers. Grafting of PHEMA, PMAA and protein on the surfaces was confirmed using ATR-IR and XPS. Surface wettability of the modified films was improved. The protein immobilized PLLA may be widely used as a biocompatible material.

Poly-L-lactide (PLLA) has been used to prepare scaffolds to guide tissue regeneration in tissue engineering research. However, one of the limitations to the use of PLLA as an ideal biomaterial is its high hydrophobicity. To improve the hydrophilicity of PLLA, hydrophilic polymers were grafted onto PLLA membrane surfaces through the combination of photooxidization in hydrogen peroxide and subsequent ultraviolet (UV)-induced grafting copolymerization in the monomer solution. Three kinds of modified PLLA membranes (i.e., PLLA-g-polyhydroxyethyl methacrylate, PLLA-g-polyacrylamide, and PLLA-g-polymethacrylic acid) were obtained, resulting in the more wettable PLLA membranes. The occurrence of the grafting polymerization was confirmed by attenuated total reflectance infrared spectroscopy (ATR-IR) and X-ray photoelectron spectroscopy (XPS) analysis. Surface morphology of the modified PLLA membranes was studied by scan electronic microscopy (SEM). © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2163–2171, 2002

Thermoresponsive hydrogels are attractive for their injectability and retention in tissue sites where they may serve as a mechanical support and as a scaffold to guide tissue remodeling. Our objective in this report was to develop a thermoresponsive, biodegradable hydrogel system that would be capable of protein release from two distinct reservoirs – one where protein was attached to the hydrogel backbone, and one where protein was loaded into biodegradable microparticles mixed into the network. Thermoresponsive hydrogels consisting of N-isopropylacrylamide (NIPAAm), 2-hydroxyethyl methacrylate (HEMA), and biodegradable methacrylate polylactide (MAPLA) were synthesized along with modified copolymers incorporating 1 mol% protein-reactive methacryloxy N,hydroxysuccinimide (MANHS), hydrophilic acrylic acid (AAc), or both. In vitro, bovine serum albumin (BSA) release was studied from hydrogels, poly(lactide-co-glycolide) microparticles, or microparticles mixed into the hydrogels. The synthesized copolymers were able to gel below 37°C and release protein in excess of 3 months. The presence of MANHS and AAc in the copolymers was associated with higher loaded protein retention during thermal transition (45% vs 22%) and faster release (2 months), respectively. Microspheres entrapped in the hydrogel released protein in a delayed fashion relative to microspheres in saline. The combination of a protein-reactive hydrogel mixed with protein-loaded microspheres demonstrated a sequential release of specific BSA populations. Overall, the described drug delivery system combines the advantages of injectability, degradability, extended release, and sequential release which may be useful in tissue engineering applications.

Biodegradable polyurethane urea (PUU) elastomers are ideal candidates for fabricating tissue engineering scaffolds with mechanical properties akin to strong and resilient soft tissues. PUU with a crystalline poly(e-caprolactone) (PCL) macrodiol soft segment (SS) showed good elasticity and resilience at small strains (

1Department of Chemistry, Chemical Biology and Biomedical Engineering, Stevens Institute of Technology, Hoboken, NJ 07030, USA 2Xylos Corporation, Langhorne, PA 19047, USA 3Department of Biomedical Engineering, School of Medicine, Tsinghua University, Beijing 100084, China 4RainDance Technologies Inc., Lexington, MA 02421, USA 5McGowan Institute for Regenerative Medicine, University of Pittsburgh, Pittsburgh, PA 15219, USA

Biodegradable elastomers, which can possess favorable mechanical properties and degradation rates for soft tissue engineering applications, are more recently being explored as depots for biomolecule delivery. The objective of this study was to synthesize and process biodegradable, elastomeric poly(ester urethane)urea (PEUU) scaffolds and to characterize their ability to incorporate and release bioactive insulin-like growth factor-1 (IGF-1) and hepatocyte growth factor (HGF).Porous PEUU scaffolds made from either 5 or 8 wt% PEUU were prepared with direct growth-factor incorporation. Long-term in vitro IGF-1 release kinetics were investigated in saline or saline with 100 units/ml lipase to simulate in vivo degradation. Cellular assays were used to confirm released IGF-1 and HGF bioactivity.IGF-1 release into saline occurred in a complex multi-phasic manner for up to 440 days. Scaffolds generated from 5 wt% PEUU delivered protein faster than 8 wt% scaffolds. Lipase-accelerated scaffold degradation led to delivery of90% protein over 9 weeks for both polymer concentrations. IGF-1 and HGF bioactivity in the first 3 weeks was confirmed.The capacity of a biodegradable elastomeric scaffold to provide long-term growth-factor delivery was demonstrated. Such a system might provide functional benefit in cardiovascular and other soft tissue engineering applications.

The injection of a mechanical bulking agent into the left ventricular (LV) wall of the heart has shown promise as a therapy for maladaptive remodeling of the myocardium after myocardial infarct (MI). The HeartLander robotic crawler presented itself as an ideal vehicle for minimally-invasive, highly accurate epicardial injection of such an agent. Use of the optimal bulking agent, a thermosetting hydrogel developed by our group, presents a number of engineering obstacles, including cooling of the miniaturized injection system while the robot is navigating in the warm environment of a living patient. We present herein a demonstration of an integrated miniature cooling and injection system in the HeartLander crawling robot, that is fully biocompatible and capable of multiple injections of a thermosetting hydrogel into dense animal tissue while the entire system is immersed in a 37°C water bath.

A family of injectable, biodegradable, and thermosensitive copolymers based on N-isopropylacrylamide, acrylic acid, N-acryloxysuccinimide, and a macromer polylactide-hydroxyethyl methacrylate were synthesized by free radical polymerization. Copolymers were injectable at or below room temperature and formed robust hydrogels at 37 degrees C. The effects of monomer ratio, polylactide length, and AAc content on the chemical and physical properties of the hydrogel were investigated. Copolymers exhibited lower critical solution temperatures (LCSTs) from 18 to 26 degrees C. After complete hydrolysis, hydrogels were soluble in phosphate buffered saline at 37 degrees C with LCSTs above 40.8 degrees C. Incorporation of type I collagen at varying mass fractions by covalent reaction with the copolymer backbone slightly increased LCSTs. Water content was 32-80% without collagen and increased to 230% with collagen at 37 degrees C. Hydrogels were highly flexible and relatively strong at 37 degrees C, with tensile strengths from 0.3 to 1.1 MPa and elongations at break from 344 to 1841% depending on NIPAAm/HEMAPLA ratio, AAc content, and polylactide length. Increasing the collagen content decreased both elongation at break and tensile strength. Hydrogel weight loss at 37 degrees C was 85-96% over 21 days and varied with polylactide content. Hydrogel weight loss at 37 degrees C was 85-96% over 21 days and varied with polylactide content. Degradation products were shown to be noncytotoxic. Cell adhesion on the hydrogels was 30% of that for tissue culture polystyrene but increased to statistically approximate this control surface after collagen incorporation. These newly described thermoresponsive copolymers demonstrated attractive properties to serve as cell or pharmaceutical delivery vehicles for a variety of tissue engineering applications.

Three-dimensional poly(L-lactic acid) (PLLA) scaffolds with high porosity and an average pore size of 280-450 microm were fabricated using gelatin particles as porogen. The particles were bonded together by incubation in saturated water vapor at 70 degrees C for 3.5 h. After casting the PLLA/1,4-dioxane solution, freeze-drying and porogen leaching with 70 degrees C water, a porous scaffold with well-interconnected pores and some nano-fibers was obtained. The biological performance of the scaffold was evaluated by in vitro chondrocyte culture and in vivo implantation. In comparison with the control scaffold fabricated with NaCl particles as porogen under the same conditions, the experimental scaffold had better biological performance because the gelatin molecules were stably entrapped onto the pore surfaces. A larger number of cells in the experimental scaffold were observed by confocal laser scanning microscopy after the viable cells had been stained with fluorescein diacetate. The chondrocytes showed more spreading morphology. Higher cytoviability and secretion of glycosaminoglycan (GAG) were also determined in the experimental scaffold. After implantation of the chondrocytes/PLLA scaffold construct to the subcutaneous dorsum of nude mice for 30-120 days, cartilage-like specimens were harvested. Histological examination showed that the regenerated cartilages had a large quantity of collagen and GAG.

Electrospun collagen-blended poly(L-lactic acid)-co-poly(epsilon-caprolactone) [P(LLA-CL), 70:30] nanofiber may have great potential application in tissue engineering because it mimicks the extracellular matrix (ECM) both morphologically and chemically. Blended nanofibers with various weight ratios of polymer to collagen were fabricated by electrospinning. The appearance of the blended nanofibers was investigated by scanning electron microscopy and transmission electron microscopy. The nanofibers exhibited a smooth surface and a narrow diameter distribution, with 60% of the nanofibers having diameters between 100 and 200 nm. Attenuated total reflectance-Fourier transform infrared spectra and X-ray photoelectron spectroscopy verified the existence of collagen molecules on the surface of nanofibers. Human coronary artery endothelial cells (HCAECs) were seeded onto the blended nanofibers for viability, morphogenesis, attachment, and phenotypic studies. Five characteristic endothelial cell (EC) markers, including four types of cell adhesion molecule and one EC-preferential gene (von Willebrand factor), were studied by reverse transcription-polymerase chain reaction. Results showed that the collagen-blended polymer nanofibers could enhance the viability, spreading, and attachment of HCAECs and, moreover, preserve the EC phenotype. The blending electrospinning technique shows potential in refining the composition of polymer nanofibers by adding various ingredients (e.g., growth factors) according to cell types to fabricate tissue-engineering scaffold, particularly blood vessel-engineering scaffold.

We modified the surface of electrospun poly(caprolactone) (PCL) nanofibers to improve their compatibility with endothelial cells (ECs) and to show the potential application of PCL nanofibers as a blood vessel tissue-engineering scaffold. Nonwoven PCL nanofibers (PCL NF) and aligned PCL nanofibers (APCL NF) were fabricated by electrospinning technology. To graft gelatin on the nanofiber surface, PCL nanofibers were first treated with air plasma to introduce -COOH groups on the surface, followed by covalent grafting of gelatin molecules, using water-soluble carbodiimide as the coupling agent. The chemical change in the material surface during surface modification was confirmed by X-ray photoelectron spectroscopy and quantified by colorimetric methods. ECs were cultured to evaluate the cytocompatibility of surface-modified PCL NF and APCL NF. Gelatin grafting can obviously enhance EC spreading and proliferation compared with the original material. Moreover, gelatin-grafted APCL NF readily orients ECs along the fibers whereas unmodified APCL NF does not. Immunostaining micrographs showed that ECs cultured on gelatin-grafted PCL NF were able to maintain the expression of three characteristic markers: platelet-endothelial cell adhesion molecule 1 (PECAM-1), intercellular adhesion molecule 1 (ICAM-1), and vascular cell adhesion molecule 1 (VCAM-1). The surface-modified PCL nanofibrous material is a potential candidate material in blood vessel tissue engineering.

An introduction to electrospinning and nanofibers , An introduction to electrospinning and nanofibers , کتابخانه دیجیتال جندی شاپور اهواز

Tissue-engineering scaffolds should be analogous to native extracellular matrix (ECM) in terms of both chemical composition and physical structure. Polymeric nanofiber matrix is similar, with its nanoscaled nonwoven fibrous ECM proteins, and thus is a candidate ECM-mimetic material. Techniques such as electrospinning to produce polymeric nanofibers have stimulated researchers to explore the application of nanofiber matrix as a tissue-engineering scaffold. This review covers the preparation and modification of polymeric nanofiber matrix in the development of future tissue-engineering scaffolds. Major emphasis is also given to the development and applications of aligned, core shell-structured, or surface-functionalized polymer nanofibers. The potential application of polymer nanofibers extends far beyond tissue engineering. Owing to their high surface area, functionalized polymer nanofibers will find broad applications as drug delivery carriers, biosensors, and molecular filtration membranes in future.

Endothelialization of biomaterials is a promising way to prevent intimal hyperplasia of small-diameter vascular grafts. The aim of this study was to design a nanofiber mesh (NFM) that facilitates viability, attachment and phenotypic maintenance of human coronary artery endothelial cells (HCAECs). Collagen-coated poly(L-lactic acid)-co-poly(epsilon-caprolactone) P(LLA-CL 70:30) NFM with a porosity of 64-67% and a fiber diameter of 470+/-130 nm was fabricated using electrospinning followed by plasma treatment and collagen coating. The structure of the NFM was observed by SEM and TEM, and mechanical property was studied by tensile test. The presence of collagen on the P(LLA-CL) NFM surface was verified by X-ray photoelectron spectroscopy (XPS) and quantified by colorimetric method. Spatial distribution of the collagen in the NFM was visualized by labelling with fluorescent probe. The collagen-coated P(LLA-CL) NFM enhanced the spreading, viability and attachment of HCAECs, and moreover, preserve HCAEC's phenotype. The P(LLA-CL) NFM is a potential material for tissue engineered vascular graft.

Non-woven polyethylene terephthalate nanofiber mats (PET NFM) were prepared by electrospinning technology and were surface modified to mimic the fibrous proteins in native extracellular matrix towards constructing a biocompatible surface for endothelial cells (ECs). The electrospun PET NFM was first treated in formaldehyde to yield hydroxyl groups on the surface, followed by the grafting polymerization of methacrylic acid (MAA) initiated by Ce(IV). Finally, the PMAA-grafted PET NFM was grafted with gelatin using water-soluble carbodiimide as coupling agent. Plane PET film was also surface modified and characterized for basic understanding of the surface modification process. The grafting of PMAA and gelatin on PET surface was confirmed by XPS spectroscopy and quantitatively analyzed by colorimetric methods. ECs were cultured on the original and gelatin-modified PET NFM and the cell morphology, proliferation and viability were studied. Three characteristic surface makers expressed by ECs were studied using immuno-florescent microscopy. The gelatin grafting method can obviously improve the spreading and proliferation of the ECs on the PET NFM, and moreover, can preserve the EC's phenotype.

A previously reported "grafting and coating" method (J. Biomed. Mater. Res. (Appl. Biomater.) 63 (2002) 838) was modified and used to introduce stable collagen layer and incorporate basic fibroblast growth factor (bFGF) on PLLA scaffold surface to prepare tissue engineering scaffold with improved biocompatibility. To make the modification of the 3-D porous PLLA scaffold possible, grafting of polymethacrylic acid (PMAA) onto the PLLA surface was initiated by the -OOH/Fe2+ system instead of the UV light used in the former method. Water soluble carbodimmide chemistry was applied to graft collagen onto the PLLA scaffold surface, followed by physical coating of the collagen solution with or without basic fibroblast growth factor (bFGF). Surface modification of 2-D PLLA membrane was also done for fundamental understanding of the modification. The -COOH density on/in the PMAA grafted PLLA membrane/scaffold was measured by colorimetric method and the collagen content on/in the collagen immobilized PLLA membrane/scaffold was measured by ninhydrin method. Chondrocyte culturing on the collagen immobilized PLLA surfaces showed significantly improved cell spreading and growth. Incorporation of fibroblast growth factors in the collagen layer further enhanced the cell growth. This convenient and effective method can be used to prepare bioactive scaffolds with extra cellular matrix (ECM)-mimic composition for tissue engineering.

Three-dimensional poly(L-lactic acid) (PLLA) scaffolds with high porosity and pore size ranging from 150 to 700 microm were conveniently prepared with paraffin spheres used as porogen. PLLA/1,4-dioxane solution containing a given amount of paraffin spheres was frozen at -25 degrees C to obtain a solidified mixture, followed with freeze drying and subsequent leaching with hexane to remove the 1,4-dioxane and paraffin spheres, respectively. The fabricated PLLA scaffolds were highly porous with evenly distributed and interconnected pores. The microstructures of the PLLA scaffolds as a function of paraffin-sphere size, paraffin-sphere dosage, and PLLA concentration were characterized by confocal laser scanning microscopy (CLSM) and scanning-electronic microscopy (SEM). To improve the cytocompatibility of the bioinert material, a hybrid PLLA scaffold containing Type I collagen was prepared by pressing the collagen solution into the scaffold under reduced pressure. The amounts of the collagen introduced in the scaffolds were detected by ninhydrin method. The distribution of the collagen in the scaffolds was studied with CLSM. Finally, in vitro cell culture was performed by injecting a chondrocyte suspension into the scaffolds. The results showed that the chondrocytes were more evenly distributed and more spread out in the collagen-modified PLLA scaffolds than in the unmodified ones.

With the use of a grafting-coating method, three kinds of natural macromolecules, that is, gelatin, collagen, or chitosan, were immobilized on poly-L-lactic acid (PLLA) membrane surfaces with the goal of improving of cellular interactions. Attenuated total reflectance infrared spectroscopy (ATR-IR), x-ray photoelectron spectroscopy (XPS) and surface morphology analysis using scanning electronic microscopy (SEM) confirmed that the natural macromolecule layers adhered tightly to the hydrophobic PLLA membrane surfaces. Chondrocyte culture showed that the modified PLLA membranes had higher cell attachment, higher cell proliferation rate, and higher cell activity than the control PLLA membrane. Moreover, the chondrocytes were more spread out on the modified PLLA membranes than on the control PLLA membranes.