Journal of Biomedical Materials Research - Part A

The objective of this study was to evaluate the effect of two cell culture techniques, static and flow perfusion, on the osteogenic expression of rat bone marrow cells seeded into titanium fiber mesh for a period up to 16 days. A cell suspension of rat bone marrow stromal osteoblasts (5 × 10⁵ cells/300 μL) was seeded into the mesh material. Thereafter, the constructs were cultured under static conditions or in a flow perfusion system for 4, 8, and 16 days. To evaluate cellular proliferation and differentiation, constructs were examined for DNA, calcium content, and alkaline phosphatase activity. Samples were also examined with scanning electron microscopy (SEM) and plastic‐embedded histological sections. Results showed an increase in DNA from day 4 to day 8 for the flow perfusion system. At day 8, a significant enhancement in DNA content was observed for flow perfusion culture compared with static culture conditions, but similar cell numbers were found for each culture system at 16 days. Calcium measurements showed a large increase in calcium content of the meshes subjected to flow perfusion at day 16. The SEM examination revealed that the 16‐day samples subjected to flow perfusion culture were completely covered with layers of cells and mineralized matrix. In addition, this matrix extended deep into the scaffolds. In contrast, meshes cultured under static conditions had only a thin sheet of matrix present on the upper surface of the meshes. Evaluation of the light microscopy sections confirmed the SEM observations. On the basis of our results, we conclude that a flow perfusion system can enhance the early proliferation, differentiation, and mineralized matrix production of bone marrow stromal osteoblasts seeded in titanium fiber mesh. © 2002 Wiley Periodicals, Inc. J Biomed Mater Res 64A: 235–241, 2003

We sought to develop bioactive hydrogels to facilitate arterial healing, e.g., after balloon angioplasty. Toward this end, we developed a new class of proteolytically sensitive, biologically active polyethylene glycol (PEG)‐peptide hydrogels that can be formed in situ to temporarily protect the arterial injury from blood contact. Furthermore, we incorporated endothelial cell‐specific biological signals with the goal of enhancing arterial reendothelialization. Here we demonstrate efficient endothelial cell anchorage and activation on PEG hydrogel matrices modified by conjugation with both the cell adhesive peptide motif RGD and an engineered variant of vascular endothelial growth factor (VEGF). By crosslinking peptide sequences for cleavage by MMP‐2 into the polymer backbone, the hydrogels became sensitive to proteolytic degradation by cell‐derived matrix metalloproteinases (MMPs). Analysis of molecular hallmarks associated with endothelial cell activation by VEGF‐RGD hydrogel matrices revealed a 70% increase in production of the latent MMP‐2 zymogen compared with PEG‐peptide hydrogels lacking VEGF. By additional provision of transforming growth factor β1 (TGF‐β1) within the PEG‐peptide hydrogel, conversion of the latent MMP zymogen into its active form was demonstrated. As a result of MMP‐2 activation, strongly enhanced hydrogel degradation by activated endothelial cells was observed. Our data illustrate the critical importance of growth factor activities for remodeling of synthetic biomaterials into native tissue, as it is desired in many applications of regenerative medicine. Functionalized PEG‐peptide hydrogels could help restore the native vessel wall and improve the performance of angioplasty procedures. © 2004 Wiley Periodicals, Inc. J Biomed Mater Res 68A: 704–716, 2004

A statistical‐co‐kinetic model has been developed to predict effects of hydrolytic or enzymatic degradation on the macroscopic properties of hydrogels formed through Michael‐type addition reactions. Important parameters accounted for by the theoretical calculations are bond cleavage kinetics, microstructural network characteristics such as macromer functionality and crosslinking efficiency, and detailed analysis of degradation products. Previous work indicated the validity of this modeling approach for predicting swelling behavior of hydrolytically degradable gels during early stages of degradation and the quantitative dependence of gel degradation on kinetic and structural parameters. The theoretical methodology is extended in the current work to predict release of covalently bound proteins from the network via labile bonds. Release studies of a network‐bound fluoroscopic probe allow validation of model degradation parameters and indicate that macromer functionalization and network crosslinking efficiency can be appropriately tailored to achieve desired swelling profiles and protein release rates over the lifetime of the degradable gel. The effects of these network parameters on the timing of gel dissolution and the protein release that occurs during this phase of degradation are also identified, highlighting the utility of the developed model as a comprehensive tool for optimizing degradable hydrogels as matrices for drug delivery and tissue regeneration. © 2005 Wiley Periodicals, Inc. J Biomed Mater Res, 2005

The effect of biomaterial topography on healing in vivo and monocyte/macrophage stimulation in vitro was assessed. A series of expanded polytetrafluoroethylene (ePTFE) materials were characterized by increasing average intranodal distance of 1.2 μm (1.2‐ePTFE), 3.0 μm (3.0‐ePTFE), and 4.4 μm (4.4‐ePTFE), but presented consistent surface chemistry with nonporous PTFE (np‐PTFE). Subcutaneous implantation of 4.4‐ePTFE into mice resulted in a statistically thinner capsule that appeared less organized and less dense than the np‐PTFE response. In vitro, isolated monocytes/macrophages cultured on np‐PTFE produced low levels of interleukin 1‐beta (IL‐1β), 1.2‐ePTFE and 3.0‐ePTFE stimulated intermediate levels, and 4.4‐ePTFE stimulated a 15‐fold increase over np‐PTFE. Analysis of cDNA microarrays demonstrated that additional proinflammatory cytokines and chemokines, including IL‐1β, interleukin 6, tumor necrosis factor alpha, monocyte chemotactic protein 1, and macrophage inflammatory protein 1‐beta, were expressed at higher levels by monocytes/macrophages cultured on 4.4‐ePTFE at 4 and 24 h, respectively. Expression ratios for several genes were quantified by RT‐PCR and were consistent with those from the cDNA array results. These results demonstrate the effect of biomaterial topography on early proinflammatory cytokine production and gene transcription by monocytes/macrophages in vitro and decreased fibrous capsule thickness in vivo. © 2010 Wiley Periodicals, Inc. J Biomed Mater Res Part A, 2010.

Small‐diameter blood vessel substitutes are urgently needed for patients requiring replacements of their coronary and below‐the‐knee vessels and for better arteriovenous dialysis shunts. Circulatory diseases, especially those arising from atherosclerosis, are the predominant cause of mortality and morbidity in the developed world. Current therapies include the use of autologous vessels or synthetic materials as vessel replacements. The limited availability of healthy vessels for use as bypass grafts and the failure of purely synthetic materials in small‐diameter sites necessitate the development of a biological substitute. Tissue engineering is such an approach and has achieved promising results, but reconstruction of a functional vascular tunica media, with circumferentially oriented contractile smooth muscle cells (SMCs) and extracellular matrix, appropriate mechanical properties, and vasoactivity has yet to be demonstrated. This review focuses on strategies to effect the switch of SMC phenotype from synthetic to contractile, which is regarded as crucial for the engineering of a functional vascular media. The synthetic SMC phenotype is desired initially for cell proliferation and tissue remodeling, but the contractile phenotype is then necessary for sufficient vasoactivity and inhibition of neointima formation. The factors governing the switch to a more contractile phenotype with in vitro culture are reviewed. © 2008 Wiley Periodicals, Inc. J Biomed Mater Res, 2009

To determine the effect of biomaterial surface chemistry on leukocyte interaction and activity at the material/tissue interface, human peripheral blood monocytes and lymphocytes were cultured on a series of poly(ethylene terephthalate) (PET)‐based biomaterials. Both monocytes and lymphocytes were isolated from whole human blood and separated by a nonadherent density centrifugation method before being plated on PET disks, surface modified by photograft copolymerization to yield hydrophobic, hydrophilic, anionic, and cationic surface properties. Monocytes and lymphocytes were cultured separately, to elicit baseline levels of activity, in direct coculture, to promote direct cell surface interactions, or in an indirect coculture system with both cell types separated by a 0.02‐μm Transwell apparatus, to promote indirect paracrine interactions. Monocyte adhesion, macrophage fusion, and lymphocyte proliferation were measured on days 3, 7, 10, and 14 of culture. Results demonstrated that the presence of monocytes increased the activity of cocultured lymphocytes at the biomaterial/tissue interface, while the corresponding presence of lymphocytes increased the activation and fusion of indirectly cocultured monocytes. Biomaterial surface chemistry was also found to have a significant effect on monocyte adhesion and activation, and lymphocyte activity. Hydrophilic surfaces significantly inhibited both initial and long‐term monocyte adhesion, and inhibited lymphocyte proliferation at longer time points. Anionic and cationic surfaces both exhibited mild inhibition of monocyte adhesion at prolonged time points, yet evoked different responses in lymphocyte populations. Anionic surfaces increased lymphocyte proliferation at longer time points and increased levels of macrophage fusion, while cationic surfaces decreased levels of lymphocyte proliferation and inhibited monocyte activity. These results elucidate the complex role of juxtacrine and paracrine interactions between monocytes and lymphocytes in the foreign body response, as well as promote the consideration of hydrophilic surfaces in future designs of implantable biomedical devices and prostheses. © 2005 Wiley Periodicals, Inc. J Biomed Mater Res, 2005

An in vitro system of interleukin (IL)‐4‐induced foreign body giant cell (FBGC) formation was utilized to define the adhesion protein substrate(s) that promotes this aspect of the foreign body reaction on biomedical polymers. Human monocytes were cultured on cell culture polystyrene surfaces that had been pre‐adsorbed with a synthetic arginine‐glycine‐aspartate peptide previously found to support optimal FBGC formation, or with various concentrations of potential physiological protein substrates, i.e. complement C3bi, collagen types I or IV, fibrinogen, plasma fibronectin, fibroblast fibronectin, laminin, thrombospondin, vitronectin, or von Willebrand factor. Cultures were evaluated on days 0 (1.5 h), 3, and 7 by May–Grünwald/Giemsa staining. Initial monocyte adhesion occurred on all adsorbed proteins. However, by day 7 of culture, only vitronectin was striking in its ability to support significant macrophage adhesion, development, and fusion leading to FBGC formation. Vitronectin supported high degrees of FBGC formation at an absorption concentration between 5 and 25 μg/mL. These findings suggest that adsorbed vitronectin is critical in the collective events that support and promote FBGC formation on biomedical polymers, and that the propensity for vitronectin adsorption may underlie the material surface chemistry dependency of FBGC formation. © 2007 Wiley Periodicals, Inc. J Biomed Mater Res, 2008

This study investigated the surface characterizations and corrosion resistance of as‐received commercial nickel–titanium (NiTi) dental orthodontic archwires from different manufacturers using a cyclic potentiodynamic test in artificial saliva with various acidities. An atomic force microscope was used to evaluate the surface topography of the NiTi wires. The surface chemical analysis of the passive film on the NiTi wires was characterized using X‐ray photoelectron spectroscopy and Auger electron spectroscopy. A scanning electron microscope, together with an energy‐dispersive spectrometer, was used to analyze the surface characterizations of the NiTi wires before and after the corrosion tests. Two‐way analysis of variance was used to analyze the corrosion‐resistance parameters with the factors of wire manufacturer and solution pH. The results showed that the surface structure of the passive film on the tested NiTi wires were identical, containing mainly TiO₂, with small amounts of NiO. A different surface topography was observed on the NiTi wires from various manufacturers. The corrosion tests showed that both the wire manufacturer and solution pH had a statistically significant influence on the corrosion potential, corrosion rate, passive current, breakdown potential, and crevice‐corrosion susceptibility. The difference in the corrosion resistance among these NiTi dental orthodontic archwires did not correspond with the surface roughness and pre‐existing defects. © 2005 Wiley Periodicals, Inc. J Biomed Mater Res, 2005

The conformation change of bovine serum albumin (BSA) induced by bioactive titanium surfaces, including acid‐alkali‐treated titanium (AA‐Ti) and alkali–heat‐treated titanium (AH‐Ti), was studied, and its effects on the activity of MC3T3‐E1 cell were evaluated. Pure titanium metal (P‐Ti) was used as control. The AA‐Ti could adsorb more BSA on its surface than AH‐Ti and P‐Ti. The α‐helix part of the protein adsorbed on P‐Ti has weakly decreased compared with native BSA, and it dramatically decreased on AA‐Ti and AH‐Ti. The β‐sheet segment of proteins adsorbed on P‐Ti and AH‐Ti had obviously increased. Much more tryptophan residues were exposed after the protein conformation changed when it interacted with AH‐Ti, and some tryptophan residues were enveloped after it interacted with AA‐Ti and P‐Ti. AA‐Ti has more tryptophan residues enveloped than P‐Ti. All titanium surfaces induced tyrosine residues exposed, especially for the P‐Ti. The higher ratio of COO⁻/NH₃⁺ for the proteins on P‐Ti and AA‐Ti indicated an orientation of proteins on P‐Ti and AA‐Ti, which makes more COO⁻ exposed. The lower ratio of COO⁻/NH₃⁺ on AH‐Ti indicates that more NH₃⁺ is exposed on its surface. The cell proliferation ability on different treated titanium surfaces coated with BSA followed by the order: P‐Ti > AA‐Ti > AH‐Ti, which indicated that the protein conformation change on different bioactive titanium surfaces has great effect on the cell activity. Our results showed that the different biological response of bioactive titanium metals might depend on the protein conformation change induced by the surface structure. © 2013 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 102A: 1053–1062, 2014.

Surface modifications of commercially pure titanium (Cp‐Ti), a material widely used to produce dental implants, can induce specific responses on osteoblastic cells after implantation. This work aims to investigate the influence of chemically modified surfaces of Cp‐Ti by acid etching or acid etching plus alkaline treatment on the gene expression of human osteoblastic (Hob) cells. Roughness and contact angle measurements were carried out to evaluate the surface properties of the samples. The surface morphology was investigated with scanning electron microscopy. Chemical composition was analyzed by energy dispersive X‐ray spectroscopy (EDS). The expression levels of some bone‐related genes (ALPL, COL1A1, COL3A1, SPP1, RUNX2, and SPARC) were analyzed using real time Reverse Transcription‐Polymerase Chain Reaction (real time RT‐PCR). The results showed that all the chemical modifications studied in this work influenced the surface morphology, wettability, roughness and induced an osteoconductive behavior. The samples that were acid etched and alkaline treated showed a more pronounced effect. © 2013 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 102A: 1816–1822, 2014.