Adhesion behavior of monocytes, macrophages, and foreign body giant cells on poly (N-isopropylacrylamide) temperature-responsive surfaces

Effect of Oxidative Stress on Bone Remodeling in Periprosthetic Osteolysis

The success of implant performance and arthroplasty is based on several factors, including oxidative stress-induced osteolysis. Oxidative stress is a key factor of the inflammatory response. Implant biomaterials can release wear particles which may elicit adverse reactions in patients, such as local inflammatory response leading to tissue damage, which eventually results in loosening of the implant. Wear debris undergo phagocytosis by macrophages, inducing a low-grade chronic inflammation and reactive oxygen species (ROS) production. In addition, ROS can also be directly produced by prosthetic biomaterial oxidation. Overall, ROS amplify the inflammatory response and stimulate both RANKL-induced osteoclastogenesis and osteoblast apoptosis, resulting in bone resorption, leading to periprosthetic osteolysis. Therefore, a growing understanding of the mechanism of oxidative stress-induced periprosthetic osteolysis and anti-oxidant strategies of implant design as well as the addition of anti-oxidant agents will help to improve implants’ performances and therapeutic approaches.

Infochemistry and the Future of Chemical Information Processing

Nowadays, information processing is based on semiconductor (e.g., silicon) devices. Unfortunately, the performance of such devices has natural limitations owing to the physics of semiconductors. Therefore, the problem of finding new strategies for storing and processing an ever-increasing amount of diverse data is very urgent. To solve this problem, scientists have found inspiration in nature, because living organisms have developed uniquely productive and efficient mechanisms for processing and storing information. We address several biological aspects of information and artificial models mimicking corresponding bioprocesses. For instance, we review the formation of synchronization patterns and the emergence of order out of chaos in model chemical systems. We also consider molecular logic and ion fluxes as information carriers. Finally, we consider recent progress in infochemistry, a new direction at the interface of chemistry, biology, and computer science, considering unconventional methods of information processing.

Comparison of different cell culture plates for the enrichment of non-adherent human mononuclear cells

While tissue-resident monocytes and macrophages are considered to be vital players in the in vivo interaction between biomaterials and surrounding tissue, their isolation is limited. In order to establish in vitro models elucidating implant and tissue interactions, peripheral blood mononuclear cells (PBMCs) represent a viable source for bone marrow-derived monocytes and an alternative to tissue-resident cells. The aim of present study was to analyse different adhesion-preventing tissue culture plates for their potential to facilitate the culture of monocytes without differentiation into macrophages. Freshly isolated PBMCs were seeded into four commercially available tissue culture plates with different adhesive properties and were tested for surface CD14 and CD68 expression using flow cytometry following 7 days in culture. When PBMCs were cultivated in RPMI on Cellstar^® Cell culture plates with Cell-Repellent Surface, a significant increase in CD14-positive cells was observed compared with cultivation in standard tissue culture-treated plates. This was accompanied by elevated cytokine production of interleukin-6 (IL6) and interleukin-8 (IL8); however, overall cell growth was not affected. When PBMCs were pre-cultured in cell-repellent plates, there was a higher yield of adherent cells after subsequent transfer into standard tissue culture-treated plates. Cultivation of PBMCs on cell-repellent culture plates favoured a monocytic phenotype and thus, represents an alternative to increase the fraction of monocytes yielded from PBMCs.

Thermo-responsive cell culture carrier: Effects on macrophage functionality and detachment efficiency

Harvesting cultivated macrophages for tissue engineering purposes by enzymatic digestion of cell adhesion molecules can potentially result in unintended activation, altered function, or behavior of these cells. Thermo-responsive polymer is a promising tool that allows for gentle macrophage detachment without artificial activation prior to subculture within engineered tissue constructs. We therefore characterized different species of thermo-responsive polymers for their suitability as cell substrate and to mediate gentle macrophage detachment by temperature shift. Primary human monocyte- and THP-1-derived macrophages were cultured on thermo-responsive polymers and characterized for phagocytosis and cytokine secretion in response to lipopolysaccharide stimulation. We found that both cell types differentially respond in dependence of culture and stimulation on thermo-responsive polymers. In contrast to THP-1 macrophages, primary monocyte-derived macrophages showed no signs of impaired viability, artificial activation, or altered functionality due to culture on thermo-responsive polymers compared to conventional cell culture. Our study demonstrates that along with commercially available UpCell carriers, two other thermo-responsive polymers based on poly(vinyl methyl ether) blends are attractive candidates for differentiation and gentle detachment of primary monocyte-derived macrophages. In summary, we observed similar functionality and viability of primary monocyte-derived macrophages cultured on thermo-responsive polymers compared to standard cell culture surfaces. While this first generation of custom-made thermo-responsive polymers does not yet outperform standard culture approaches, our results are very promising and provide the basis for exploiting the unique advantages offered by custom-made thermo-responsive polymers to further improve macrophage culture and recovery in the future, including the covalent binding of signaling molecules and the reduction of centrifugation and washing steps. Optimizing these and other benefits of thermo-responsive polymers could greatly improve the culture of macrophages for tissue engineering applications.

The effect of adsorbed fibronectin and osteopontin on macrophage adhesion and morphology on hydrophilic and hydrophobic model surfaces

Macrophages play a crucial role in the host response to biomaterials. Here we investigated the effect of adsorbed fibronectin (FN) and osteopontin (OPN), two important proteins for tissue repair, on macrophage adhesion and morphology. Since cell-biomaterial interactions are modulated via proteins adsorbed onto biomaterial surfaces, FN and OPN were adsorbed on model self-assembled monolayers (SAMs) of alkanethiols on gold with different functional terminal groups (CH(3), OH and tetra(ethylene-glycol)). The initial interaction of inflammatory cells with a biomaterial is crucial for the ensuing phases of an inflammatory reaction. For this reason short-term cultures of primary human macrophages were performed. To account for the competitive adsorption of other proteins serum was added to the culture medium and the effect compared with serum-free medium cultures. In the presence of serum hydrophilic surfaces increased macrophage adhesion. In particular, FN induced a higher cell density, while OPN tended to decrease it. In serum-free medium cell adhesion was greater on hydrophobic surfaces, except for OPN-coated SAMs. Importantly, FN no longer enhanced macrophage adhesion, while OPN maintained its inhibitory effect. Cell polarization studies indicated that macrophage morphology variations induced by surface chemistry are overcome by pre-adsorbed OPN. Taken together our results show that in the presence of serum macrophage adhesion is promoted by FN hydrophilic surfaces, but impaired on OPN-coated surfaces. The effects of inhibited macrophage adhesion on macrophage fusion, and its relevance to the initial stages of the inflammatory response to biomaterials are discussed.

Polypropylene mesh and the host response

The use of polypropylene (PP) mesh for pelvic floor repair has been increasing dramatically over the past decade; however, tissue response in humans has not been extensively studied. This review discusses PP mesh and postimplantation host tissue response. Emphasis is placed on studies investigating the relationship between individual mesh properties and specific responses. There is an immediate inflammatory response after PP mesh implantation that lays the framework for tissue ingrowth and subsequent mesh integration. This response varies based on physical properties of individual mesh, such as pore size, weight, coatings, bacterial colonization, and biofilm production.

Biological cell detachment from poly(N-isopropyl acrylamide) and its applications

Over the past two decades, poly(N-isopropyl acrylamide) (pNIPAM) has become widely used for bioengineering applications. In particular, pNIPAM substrates have been used for the nondestructive release of biological cells and proteins. In this feature article, we review the applications for which pNIPAM substrates have been used to release biological cells, including for the study of the extracellular matrix (ECM), for cell sheet engineering and tissue transplantation, the formation of tumorlike spheroids, the study of bioadhesion and bioadsorption, and the manipulation or deformation of individual cells. The articles reviewed include submissions from our own group as well as from those performing research in the field worldwide.

Chondrogenesis of human mesenchymal stem cells encapsulated in a hydrogel construct: neocartilage formation in animal models as both mice and rabbits

In this study, in vivo studies, both nude mouse and rabbit cartilage defect, were tested for chondrogenesis using stem cells (SCs) using growth factor. Specifically, human mesenchymal stem cells (hMSCs) were embedded in a hydrogel scaffold, which was coencapsulated with transforming growth factor-beta3 (TGF-beta3). The specific extracellular matrices (ECMs) released from hMSCs transplanted into the animal were assessed via glycosaminoglycan (GAG)/DNA content, RT-PCR, real time-QPCR, immunohistochemical (IHC), and Safranin-O staining and were observed up to 7 weeks after injection. By detection of ECMs the GAG content per cell remained constant for all formulations, indicating that the dramatic increase in cell number for samples with TGF-beta3 was accompanied by the maintenance of the cell phenotypes. The histological and IHC staining of the newly repaired tissues observed after treatment with TGF-beta3 mixed with hMSCs evidenced hyaline cartilage-like characteristics. Moreover, the results observed with the animal model (rabbit) treated with hMSCs embedded in the growth factor-containing hydrogel indicate that the implantation of mixed cells with TGF-beta3 may constitute a clinically efficient method for the regeneration of hyaline articular cartilage.

Characterization of microglial attachment and cytokine release on biomaterials of differing surface chemistry

The clinical usefulness of central nervous system recording electrodes is currently limited by inconsistent long-term performance that is believed to be governed by the brain tissue response to the implant. In this study, we observed persistent macrophage biomarker expression at the biotic-abiotic interface surrounding implanted electrodes over a 12-week indwelling period. Using the cell type-specific marker CD11b to examine the cells attached to electrodes retrieved over the indwelling period, we found that most of the cells were activated microglia, the resident macrophage of brain tissue, indicating that the implanted electrodes behave as a persistent inflammatory stimulus. To determine the potential usefulness of different materials as coatings for implanted electrodes, we examined brain-derived microglial cell attachment and cytokine release on a number of medically relevant materials. Our results suggest that activated microglia attach to many of the materials used as external coatings for electrode manufacture, and likely serve as a source of pro-inflammatory and neurotoxic cytokines that may be responsible for reducing the biocompatibility of such implants. Our results also indicate that low protein-binding coatings may be useful in reducing microglial attachment upon implantation in brain tissue and may provide a means of improving electrode biocompatibility.

Corneal epithelial stem cell delivery using cell sheet engineering: not lost in transplantation

Cell-based therapies have now generated significant interest as novel drug delivery systems, with various adult cell types used in treating a wide range of diseases. To overcome the limits that restrict treatments for corneal surface dysfunction, corneal epithelial stem cells expanded ex vivo have been applied as an alternative approach. While previous studies used various carrier substrates, we present a novel method using cell sheet engineering with temperature-responsive culture dishes to create carrier-free corneal epithelial stem cell sheets that can be transplanted without sutures. Results from clinical trials reveal successful transplantation with the recovery of lost visual acuity in all cases. Cell sheet engineering, therefore, presents a novel method for the delivery of corneal epithelial stem cells, and can also be applied for other approaches of cellular therapeutics.

Effects of nonproductive binding on the kinetics of enzymatic reactions with patterned substrates

Existing models of ligand-receptor binding kinetics suggest that clustering surface-associated molecules tends to decrease the rates with which solution phase molecules associate and dissociate. Here, the authors use kinetic Monte Carlo simulations to study the case of an enzyme catalyzing the turnover of substrate molecules immobilized on a surface. The simulations reveal a crossover in the overall reaction rates for randomly distributed and clustered substrate molecules as the enzyme unbinding rate is varied. Approximate expressions for the effective kinetic parameters are introduced, and they show that the observed behavior derives from sequestration of the enzyme in the strong-sticking limit.

Electroactive self-assembled monolayers that permit orthogonal control over the adhesion of cells to patterned substrates

This article describes an electroactive substrate that displays two independent dynamic functions for controlling the adhesion of cells. The approach is based on self-assembled monolayers on gold that are patterned into regions presenting the Arg-Gly-Asp peptide cell adhesion ligand. The patterned regions differ in the electrochemical properties of the linkers that tether the peptides to the monolayer. In this work, three distinct chemistries are employed that provide for release of the ligand on application of a negative potential, release of the ligand on application of a positive potential, and no change in response to a potential. Cells were allowed to attach to a monolayer patterned into circular regions comprising the three chemistries. Treatment with electric potentials of 650 or -650 mV resulted in the selective release of adherent cells only from regions that display the relevant electroactive groups. This example establishes the preparation of dynamic substrates with multiple functions and will be important to preparing model cultures derived from multiple cell types, with control over the temporal interactions of each cell population.

RGD-grafted thermoreversible polymers to facilitate attachment of BMP-2 responsive C2C12 cells

The purpose of this study was to design thermoreversible biomaterials for enhanced adhesion of bone morphogenetic protein-2 (BMP-2)-responsive cells. Peptides containing the arginine-glycine-aspartic acid (RGD) sequence were conjugated to N-isopropylacrylamide (NiPAM) polymers via amine-reactive N-acryloxysuccinimide (NASI) groups. In monolayer cultures, the adhesion of BMP-2-responsive C2C12 cells to RGD-grafted NiPAM/NASI surfaces was significantly higher than adhesion on ungrafted NiPAM/NASI surfaces. Although the morphology of cells adhered to RGD-grafted NiPAM/NASI surfaces was comparable to cells adhered on tissue culture polystyrene (TCPS), long-term cell growth was limited on the NiPAM/NASI surfaces, even for RGD-grafted surfaces. Treatment of C2C12 cells with recombinant BMP-2 induced dose-dependent osteoblastic differentiation as assessed by alkaline phosphatase (ALP) activity. In the absence of BMP-2, cells cultured on NiPAM/NASI polymers (either grafted with RGD peptide or not) expressed significantly higher levels of ALP activity than the cells cultured on TCPS, indicating that the polymer surfaces induced some osteoblastic activity in C2C12 cells without the need for BMP-2. We conclude that NiPAM-based thermoreversible biomaterials, despite their limited ability to support cell growth, allowed an enhanced expression of the chosen osteogenic marker (ALP) by C2C12 cells in vitro.

Enhancement of diffusion-controlled reaction rates by surface-induced orientational restriction

We explore the means by which immobilization of a substrate on a surface can increase the rate of a diffusion-controlled enzymatic reaction. A quasichemical approach is developed and compared with Brownian dynamics simulations. We use these methods to show that restricting only the orientation of the enzyme by long-range interactions with the surface is sufficient for enhancing catalysis.

Local drug delivery in restenosis injury: thermoresponsive co-polymers as potential drug delivery systems

The success of percutaneous transluminal coronary angioplasty in treatment of acute coronary syndromes has been compromised by the incidence of restenosis. The physical insult of balloon insertion can damage or remove the endothelial monolayer, thereby generating a prothrombotic surface. The resulting inappropriate response to injury can also lead to penetration of inflammatory cells, conversion of the underlying media to a synthetic phenotype, deposition of extracellular matrix, constrictive remodeling, and neointimal hyperplasia. While stent implantation at the time of balloon insertion has offset some of these events, inflammatory responses to the implanted biomaterial (stent) and intimal hyperplasia are still prominent features of the procedure, leading in 20-30% of cases to in-stent restenosis within a year. Systemic delivery of drugs designed to offset in-stent restenosis injury has been largely unsuccessful, which has led to the development of strategies for coating stents with drugs for local delivery. Drug-eluting stents constitute an innovative means of further reducing the incidence of restenosis injury and clinical trials have shown encouraging results. This review focuses on properties of a class of environment-sensitive hydrogels, the N-isopropylacrylamide-based thermoresponsive co-polymers, on their potential roles as stent coatings, on their demonstrated ability to incorporate and release drugs that modify vascular endothelial and smooth muscle cell functions, and on issues that still await clarification, prior to their adoption in a clinical setting.

Dynamic interfaces between cells and surfaces: electroactive substrates that sequentially release and attach cells

An electroactive substrate that combines dual dynamic properties is demonstrated. A monolayer is patterned to first release an immobilized ligand, and therefore adherent cells, on application of an electrical potential. Subsequently, electrical oxidation of the substrate results in immobilization of ligands, and migration of adherent cells.

Adhesion of human U937 macrophages to phosphorylcholine-coated surfaces

A new type of amphiphilic phosphorylcholine (PC) polymer was used in this work to develop a cell culture surface that allows the attachment of U937 macrophages. The PC polymer was a random copolymer of N-isopropylacrylamide (45%), N-(phosphorylcholine)-N'-(ethylenedioxy-bis(ethyl)) acrylamide (41%), and the hydrophobic monomer N-(n-octadecyl) acrylamide (14%). Polypropylene (PP) films (1 cm2) were coated with the polymer solution by immersion. U937 macrophage suspensions were applied on PC polymer-coated surfaces and incubated for up to 72 h at 37 degrees C. While U937 cells did not adhere to PP, ammonia, nitrogen, or oxygen plasma-treated surfaces, they attached rapidly on PC-coated surfaces (< 1 h), proliferated, and stayed attached to the modified surface for at least 72 h, suggesting that unique features of the PC polymer, and the U937 macrophages, are responsible for the attachment of these cells. We compared the effect of Co2+ and Cr3+ ions on the expression of bone-resorbing cytokines (TNF-alpha, IL-6, IL-1beta) in U937 macrophages cultured on PC-coated surfaces to the response of U937 macrophages in suspension. Cytokine gene expression was analyzed by reverse transcription polymerase chain reaction (RT-PCR). Addition of Co2+ and Cr3+ ions led to a significant increased expression of TNF-alpha in both cultured and suspension cells. On the other hand, Co2+ and Cr3+ ions had a weak stimulatory effect or no effect on IL-1beta and IL-6, respectively, in both cultured and suspension cells. In conclusion, the use of PC polymer-modified surfaces might offer promising new opportunities for the culture of human U937 cells and may also point to the mechanism by which macrophages interact with lipid bilayers of biological membranes.

Protein and surface effects on monocyte and macrophage adhesion, maturation, and survival

Cell adhesion and maturation can be affected by the protein adsorption profile on the surface of an implanted biomaterial. In this study we have investigated how surface chemistry and adsorbed proteins can modulate monocyte and macrophage adhesion, IL-13-induced foreign-body giant cell formation, and apoptosis in vitro. Compared to a dimethylsilane-modified surface (DM), a surface modified with RGD peptides had no effect on adhesion density, foreign-body giant cell (FBGC) formation, or apoptosis in nondepleted serum conditions. The depletion of specific adhesive proteins affected adhesion, FBGC formation, and apo- ptosis. While the depletion of fibronectin and vitronectin had no overall effect compared to nondepleted serum conditions, the depletion of IgG from serum caused a significant decrease in initial adherent cell density [1000 +/- 200 compared to 2460 +/- 590 (p = 0.02)], a significant decrease in FBGC formation [2% compared to 17% (p = 0.02)], and a significant increase in the level of apoptosis [57% compared to 32% (p = 0.01)] on DM. The lowered initial adherent cell density on DM was not observed on the RGD surface, indicating that the RGD surface promotes increased initial adhesion. However, the RGD surface does not affect FBGC formation (i.e., macrophage fusion) or levels of apoptosis, which remained comparable to those on the DM surfaces at days 7 and 10.