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Platelet adhesion and activation are important early markers of biomaterial blood compatibility, while surfaces that promote enhanced endothelial cell adhesion and eNOS expression are strategic targets for long term vascular graft applications. Materials surface modified with fluorinated surface modifiers, containing peptides inspired from elastin cross-linking domains, have been used for the cross-linking of elastin-like polypeptide 4 (ELP4) macromolecules onto polyurethane surfaces. In the present study, ELP4 modified polyurethanes were evaluated in vitro to assess platelet adhesion, microparticle formation and bulk platelet activation following blood-material interactions. Reduced platelet adhesion and bulk platelet activation were observed following contact between reconstituted human blood and the ELP4 materials, relative to the uncoated base polyurethane controls. ELP4 modified materials also promoted endothelial cell adhesion and retention over a period of one week and showed that the endothelial cells exhibited an organized actin cytoskeleton and enhanced endothelial nitric oxide synthase (eNOS) expression relative to the control surfaces. These results indicate that polyurethane elastomers modified with ELP4 covalently bound to fluorinated surface modifiers provide a promising approach for endowing synthetic elastomers with both reduced blood platelet activation properties and enhanced endothelial cell adhesion for potential use in vascular graft applications., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

Study Design: Biomechanical, in vitro, and initial in vivo evaluation of a thiol-modified hyaluronan (TM-HA) and elastin-like polypeptide (ELP) composite hydrogel for nucleus pulposus (NP) tissue engineering., Objective: To investigate the utility of a TM-HA and ELP composite material as a potential tissue-engineering scaffold to reconstitute the NP in early degenerative disc disease (DDD) on the basis of both biomechanical and biologic parameters., Summary of Background Data: DDD is a common ailment with enormous medical, psychosocial, and economic ramifications. Only end-stage surgical therapies are currently widely available. A less invasive, early stage therapy may provide a clinically relevant treatment option., Methods: TM-HA and ELP were combined in various concentrations and cross-linked using poly (ethylene glycol) diacrylate. Resulting materials were evaluated biomechanically using confined compression to determine biphasic material properties. In vitro cell culture with human intervertebral disc (IVD) cells seeded within TM-HA/ELP scaffolds was analyzed for cell viability and phenotype. The hydrogels' materials were evaluated in an established New Zealand White (NZW) rabbit model of DDD., Results: The addition of ELP to TM-HA-based hydrogels resulted in a stiffer construct, which is less stiff than native NP but has time-dependant loading characteristics that may be desirable when injected into the IVD. In vitro experiments demonstrated 70% cell viability at 3 weeks with apparent maintenance of phenotype on the basis of morphologic and immunohistochemical data. The addition of ELP had a positive desirable biomechanical effect but did not have a significant positive or negative biologic effect on cell activity. The in vivo feasibility study demonstrated favorable material characteristics and biocompatibility for application as a minimally invasive injectable NP supplement., Conclusions: TM-HA-based hydrogels provide a hospitable environment for human IVD cells and have material characteristics, particularly when supplemented with ELPs that are attractive for potential application as an injectable NP supplement.

Biomaterial scaffolds for tissue engineering require appropriate cell adhesion, proliferation, and infiltration into their three-dimensional (3D) porous structures. Surface modification techniques have the potential to enhance cell infiltration into synthetic scaffolds while retaining bulk material properties intact. The objective of this work was to assess the potential of achieving a uniform surface modification in 3D porous constructs through the blending of surface-modifying additives known as bioactive fluorinated surface modifiers (BFSMs) with a base polyurethane material. By coupling RGD peptides to the fluorinated surface modifiers to form RGD-BFSMs, the BFSMs can act as a vehicle for the delivery of RGD moieties to the surface without direct covalent attachment to the polymer substrate. Fluorescent RGD-BFSMs were shown to migrate to the polymer-air interfaces within the porous scaffolds by two-photon confocal microscopy. A-10 rat aortic smooth muscle cells were cultured for 4 weeks on nonmodified and RGD-BFSM-modified porous scaffolds, and cell adhesion, proliferation, and viability were quantified at different depths. RGD-BFSM-modified scaffolds showed significantly greater cell numbers within deeper regions of the scaffolds, and this difference became more pronounced over time. This study demonstrates an effective approach to promote cell adhesion and infiltration within thick (approximately 0.5 cm) porous synthetic scaffolds by providing a uniform distribution of adhesive peptide throughout the scaffolds without the use of covalent surface reaction chemistry., ((c) 2010 Wiley Periodicals, Inc.)

The inherent flexibility of polyurethane (PU) chemistry allows the incorporation of specific chemical moieties into the backbone structure conferring a unique biological function to these synthetic polymers. We describe here the synthesis and characterization of a PU containing a Gly-Leu linkage, the cleavage site of several matrix metalloproteinases. A Gly-Leu dipeptide was introduced into the chain extender of the polyurethane through the reaction with 1,4-cyclohexane dimethanol. PUs synthesized with the Gly-Leu-based chain extender had a high weight-average molecular weight (M(w) > 125 x 10(3)) and were phase segregated, semi-crystalline polymers with a low soft-segment glass-transition temperature (T(g) < -50 degrees C). Uniaxial tensile testing of PU films indicated that the polymer could withstand high ultimate tensile strengths (approx. 13 MPa) and were flexible with breaking strains of approx. 900%. The Gly-Leu PU had a significantly higher initial modulus, yield stress and ultimate stress compared to a PU previously developed in our laboratory containing a phenylalanine-based chain extender (Phe PU). The Gly-Leu-based chain extender allowed for better hard segment packing and hydrogen bonding leading to enhanced mechanical properties. Electrospinning was used to form scaffolds with randomly organized fibers and an average fiber diameter of approx. 3.6 mum for both the Gly-Leu and Phe PUs. Mouse embryonic fibroblasts were successfully cultured on the PU scaffolds out to 28 days. Further investigations into cell-mediated polymer degradation will help to identify the suitability of this new biomaterial as scaffolds for soft tissue applications.

A successful regenerative therapy to treat damage incurred after an ischemic event in the heart will require an integrated approach including methods for appropriate revascularization of the infarct site, mechanical recovery of damaged tissue, and electrophysiological coupling with native cells. Cardiomyocytes are the ideal cell type for heart regeneration because of their inherent electrical and physiological properties, and cardiomyocytes derived from embryonic stem cells (ESCs) represent an attractive option for tissue-engineering therapies. An important step in developing tissue engineering-based approaches to cardiac cell therapy is understanding how scaffold architecture affects cell behavior. In this work, we generated large numbers of ESC-derived cardiomyocytes in bioreactors and seeded them on porous, 3-dimensional scaffolds prepared using 2 different techniques: electrospinning and thermally induced phase separation (TIPS). The effect of material macro-architecture on the adhesion, viability, and morphology of the seeded cells was determined. On the electrospun scaffolds, cells were elongated in shape, a morphology typical of cultured ESC-derived cardiomyocytes, whereas on scaffolds fabricated using TIPS, the cells retained a rounded morphology. Despite these gross phenotypic and physiological differences, sarcomeric myosin and connexin 43 expression was evident, and contracting cells were observed on both scaffold types, suggesting that morphological changes induced by material macrostructure do not directly correlate to functional differences.

A polyurethane designed to be biodegradable via hydrolysis and enzyme-mediated chain cleavage, has been investigated for its use as a temporary scaffold in tissue-engineering applications. The phase-segregated nature of the polyurethane imparts elastomeric properties that are attractive for soft tissue engineering. This polyurethane has been electrospun in order to create scaffolds that incorporate several biomimetic features including small fiber diameter, large void volume, and an interconnected porous network. Material properties were evaluated via gel-permeation chromatography, differential scanning calorimetry and Raman spectroscopy before and after processing. Analysis by gel-permeation chromatography showed that the molecular weights were similar, indicating that the bulk of the polymer chains were not degraded during processing. Thermal analysis revealed that the glass transition temperature did not shift and Raman spectra of the bulk polyurethane film compared to the electrospun mat were identical, confirming that the conformation of the polymer was unaffected by the shear and electric field used in the electrospinning process. In addition, field emission scanning electron microscopy revealed that the morphology of the electrospun mats had a broad fiber diameter distribution, and mechanical analysis showed that the mats had an ultimate tensile stress of 1.33 MPa and ultimate tensile strain of 78.6%. The degradation profile was investigated in the presence of chymotrypsin. These results were compared to a previous study of thin films of this polyurethane, and it was found that the increase of surface area aided the surface-mediated erosion of the material. It is believed that an electrospun matrix of this biodegradable polyurethane shows promise for use in soft tissue engineering and regenerative medicine applications.

A tissue-engineered adipose substitute would be invaluable to plastic surgeons for reconstructive, corrective, and cosmetic procedures. This work involves the design of a scaffold for soft tissue augmentation incorporating the decellularized extracellular matrix (ECM) of human placenta. We have developed a protocol to decellularize an intact, large segment (8 cm by 8 cm) of the human placenta. To facilitate the complete decellularization of the dense matrix, a system was designed to perfuse the required chemicals into the placenta via the existing vasculature. Following processing, the original architecture of the placental ECM was preserved, including an intact vascular network. Histological, immunohistochemical, and scanning electron microscopic analyses confirmed the removal of the cells and cellular debris and characterized the composition and structure of the matrix. In vitro cell culture experimentation showed that the placental decellular matrix (PDM) could facilitate the adhesion of primary human adipose precursor cells at early time points. The PDM has great potential for use as a scaffold for adipose tissue engineering, as the placenta is a rich source of human ECM components that can be readily harvested without harm to the donor.

In the past 30 years, the development and use of artificial skin in the treatment of acute and chronic wounds has advanced from an experimental concept to a working reality. However, while there have been an increasing number of artificial skin substitutes licensed for clinical use, they have yet to supplant the current gold standard of an autologous tissue graft for most applications. This article reviews the advantages and disadvantages of the currently available, biologically based substitutes, with special emphasis on their relative efficacy and suitability for treatment of particular wound types. Economic considerations, desirable improvements of currently available materials and the potential impact of future advances in the field will also be discussed.

Processes involving self-assembly of monomeric units into organized polymeric arrays are currently the subject of much attention, particularly in the areas of nanotechnology and biomaterials. One biological example of a protein polymer with potential for self-organization is elastin. Elastin is the extracellular matrix protein that imparts the properties of extensibility and elastic recoil to large arteries, lung parenchyma, and other tissues. Tropoelastin, the approximately 70 kDa soluble monomeric form of elastin, is highly nonpolar in character, consisting essentially of 34 alternating hydrophobic and crosslinking domains. Crosslinking domains contain the lysine residues destined to form the covalent intermolecular crosslinks that stabilize the polymer. We and others have suggested that the hydrophobic domains are sites of interactions that contribute to juxtaposition of lysine residues in preparation for crosslink formation. Here, using recombinant polypeptides based on sequences in human elastin, we demonstrate that as few as three hydrophobic domains flanking two crosslinking domains are sufficient to support a self-assembly process that aligns lysines for zero-length crosslinking, resulting in formation of the crosslinks of native elastin. This process allows fabrication of a polymeric matrix with solubility and mechanical properties similar to those of native elastin., (Copyright 2003 Wiley Periodicals, Inc. Biopolymers 70: 445-455, 2003)

Tissue engineering constructs should match the physical and mechanical properties of the native tissue. This implies that pliable scaffolds might be better suited for soft-tissue applications than rigid polymeric materials. In this study, we examined spatially organized cardiomyocyte cultures on biodegradable, elastomeric polyurethane films patterned by microcontact printing of laminin lanes. The resulting cardiomyocyte patterns on polyurethane displayed a similar morphology to those previously achieved for up to 7-10 days on other substrates, such as polystyrene dishes. However, the integrity of the cardiomyocyte patterns on thin, spin-cast or solvent-cast polyurethane films was retained for up to 4 weeks in culture. When additional cardiomyocytes (labeled with Cell Tracker reagents) were seeded onto the patterned cultures, secondary and tertiary cell populations aligned between and on top of the primary patterned cells to form a multilayered, organized tissue construct approximately 2-3 cell layers thick. In addition, dense, highly aligned monolayers of patterned cardiomyocytes were able to contract the thin, solvent-cast polyurethane films. These results indicate that elastomeric, biodegradable polyurethane films can serve as an appropriate scaffold material to support stably the engineering of spatially organized layers of cardiomyocytes in vitro. This approach may serve as a novel method for transplantation of organized cardiac tissue constructs to the heart for myocardial repair., (Copyright 2003 Wiley Periodicals, Inc. J Biomed Mater Res 66A: 586-595, 2003)