Gene expression study of monocytes/macrophages during early foreign body reaction and identification of potential precursors of myofibroblasts

Foreign body reaction (FBR), initiated by adherence of macrophages to biomaterials, is associated with several complications. Searching for mechanisms potentially useful to overcome these complications, we have established the signaling role of monocytes/macrophages in the development of FBR and the presence of CD34(+) cells that potentially differentiate into myofibroblasts. Therefore, CD68(+) cells were in vitro activated with fibrinogen and also purified from the FBR after 3 days of implantation in rats. Gene expression profiles showed a switch from monocytes and macrophages attracted by fibrinogen to activated macrophages and eventually wound-healing macrophages. The immature FBR also contained a subpopulation of CD34(+) cells, which could be differentiated into myofibroblasts. This study showed that macrophages are the clear driving force of FBR, dependent on milieu, and myofibroblast deposition and differentiation.     

The importance of fungal pathogens and antifungal coatings in medical device infections

In recent years, increasing evidence has been collated on the contributions of fungal species, particularly Candida, to medical device infections. Fungal species can form biofilms by themselves or by participating in polymicrobial biofilms with bacteria. Thus, there is a clear need for effective preventative measures, such as thin coatings that can be applied onto medical devices to stop the attachment, proliferation, and formation of device-associated biofilms.However, fungi being eukaryotes, the challenge is greater than for bacterial infections because antifungal agents are often toxic towards eukaryotic host cells. Whilst there is extensive literature on antibacterial coatings, a far lesser body of literature exists on surfaces or coatings that prevent attachment and biofilm formation on medical devices by fungal pathogens. Here we review strategies for the design and fabrication of medical devices with antifungal surfaces. We also survey the microbiology literature on fundamental mechanisms by which fungi attach and spread on natural and synthetic surfaces. Research in this field requires close collaboration between biomaterials scientists, microbiologists and clinicians; we consider progress in the molecular understanding of fungal recognition of, and attachment to, suitable surfaces, and of ensuing metabolic changes, to be essential for designing rational approaches towards effective antifungal coatings, rather than empirical trial of coatings.     

Impact of lactic acid on cell proliferation and free radical‐induced cell death in monolayer cultures of neural precursor cells

Biomaterials prepared from polyesters of lactic acid and glycolic acid, or a mixture of the two, degrade in the presence of water into the naturally occurring metabolites, lactic acid and glycolic acid. While the lactic acid degradation product that is released from biomaterials is well tolerated by the body, lactic acid can influence the metabolic function of cells; it can serve as an energy substrate for cells, and has been shown to have antioxidant properties. Neural precursor cells, a cell population of considerable interest as a source of cells for neural tissue regeneration strategies, generate a high amount of reactive oxygen species, and when associated with a degradable biomaterial, may be impacted by released lactic acid. In this work, the effect of lactic acid on a neural cell population containing proliferative neural precursor cells was examined in monolayer culture. Lactic acid was found to scavenge exogenously added free radicals produced in the presence of either hydrogen peroxide or a photoinitiator (I2959) commonly utilized in the preparation of photopolymerizable biomaterials. In addition to its effect on exogenously added free radicals, lactic acid reduced intracellular redox state, increased the proliferation of the cell population, and modified the cell composition. The findings of this study provide insight into the role that lactic acid plays naturally on developing neural cells and are also of interest to biomaterials scientists that are focused on the development of degradable lactic‐acid‐based polymers for cell culture devices. The effect of lactic acid on other cell populations may differ and should be characterized to best understand how cells function in degradable cell culture devices. Biotechnol. Bioeng. 2009;103: 1214–1223. © 2009 Wiley Periodicals, Inc.     

Foreign Body Reaction Associated with PET and PET/Chitosan Electrospun Nanofibrous Abdominal Meshes

Electrospun materials have been widely explored for biomedical applications because of their advantageous characteristics, i.e., tridimensional nanofibrous structure with high surface-to-volume ratio, high porosity, and pore interconnectivity. Furthermore, considering the similarities between the nanofiber networks and the extracellular matrix (ECM), as well as the accepted role of changes in ECM for hernia repair, electrospun polymer fiber assemblies have emerged as potential materials for incisional hernia repair. In this work, we describe the application of electrospun non-absorbable mats based on poly(ethylene terephthalate) (PET) in the repair of abdominal defects, comparing the performance of these meshes with that of a commercial polypropylene mesh and a multifilament PET mesh. PET and PET/chitosan electrospun meshes revealed good performance during incisional hernia surgery, post-operative period, and no evidence of intestinal adhesion was found. The electrospun meshes were flexible with high suture retention, showing tensile strengths of 3 MPa and breaking strains of 8–33%. Nevertheless, a significant foreign body reaction (FBR) was observed in animals treated with the nanofibrous materials. Animals implanted with PET and PET/chitosan electrospun meshes (fiber diameter of 0.71±0.28 µm and 3.01±0.72 µm, respectively) showed, respectively, foreign body granuloma formation, averaging 4.2-fold and 7.4-fold greater than the control commercial mesh group (Marlex). Many foreign body giant cells (FBGC) involving nanofiber pieces were also found in the PET and PET/chitosan groups (11.9 and 19.3 times more FBGC than control, respectively). In contrast, no important FBR was observed for PET microfibers (fiber diameter = 18.9±0.21 µm). Therefore, we suggest that the reduced dimension and the high surface-to-volume ratio of the electrospun fibers caused the FBR reaction, pointing out the need for further studies to elucidate the mechanisms underlying interactions between cells/tissues and nanofibrous materials in order to gain a better understanding of the implantation risks associated with nanostructured biomaterials.     

Role of nanotopography in the development of tissue engineered 3D organs and tissues using mesenchymal stem cells

Recent regenerative medicine and tissue engineering strategies(using cells, scaffolds, medical devices and gene therapy) have led to fascinating progress of translation of basic research towards clinical applications. In the past decade, great deal of research has focused on developing various three dimensional(3D) organs, such as bone, skin, liver, kidney and ear,using such strategies in order to replace or regenerate damaged organs for the purpose of maintaining or restoring organs’ functions that may have been lost due to aging, accident or disease. The surface properties of a material or a device are key aspects in determining the success of the implant in biomedicine, as the majority of biological reactions in human body occur on surfaces or interfaces. Furthermore, it has been established in the literature that cell adhesion and proliferation are, to a great extent, influenced by the micro- and nanosurface characteristics of biomaterials and devices. In addition, it has been shown that the functions of stem cells, mesenchymal stem cells in particular, could be regulated through physical interaction with specific nanotopographical cues. Therefore, guided stem cell proliferation, differentiation and function are of great importance in the regeneration of 3D tissues and organs using tissue engineering strategies. This review will provide an update on the impact of nanotopography on mesenchymal stem cells for the purpose of developing laboratory-based 3D organs and tissues, as well as the most recent research and case studies on this topic.     

Fabrication of nitric oxide-releasing polyurethane glucose sensor membranes

Despite clear evidence that polymeric nitric oxide (NO) release coatings reduce the foreign body response (FBR) and may thus improve the analytical performance of in vivo continuous glucose monitoring devices when used as sensor membranes, the compatibility of the NO release chemistry with that required for enzymatic glucose sensing remains unclear. Herein, we describe the fabrication and characterization of NO-releasing polyurethane sensor membranes using NO donor-modified silica vehicles embedded within the polymer. In addition to demonstrating tunable NO release as a function of the NO donor silica scaffold and polymer compositions and concentrations, we describe the impact of the NO release vehicle and its release kinetics on glucose sensor performance.     

Surface modification and chemical surface analysis of biomaterials

The chemical composition of the surface layers of synthetic biomaterials used for human medical devices and in biotechnology plays a key role in determining interfacial interactions between biological media (such as protein solutions, cells, tissue) and the synthetic material. Accordingly, considerable research efforts focus on improving the 'biocompatibility' of biomaterials by applying various surface modification and thin film coating approaches. Here we focus on the patterning of surface chemistries, often designed to exercise spatial control over events such as cell attachment and spreading. Secondly, we review recent developments in chemical characterisation of biomaterials surfaces, which is essential both for verifying the success of intended surface modification strategies and for reliable interpretation of observed biological responses. Biomaterials surface analysis by imaging ToF-SIMS and XPS and compositional depth profiling are discussed, as is the emerging complementary technique of Metastable Induced Electron Spectroscopy.     

Biomimetic approaches to protein and gene delivery for tissue regeneration

Novel therapeutic strategies that promote wound healing seek to mimic the response of the body to wounding, to regenerate rather than repair injured tissues. Many synthetic or natural biomaterials have been developed for this purpose and are used to deliver wound therapeutics in a controlled manner that prevents unwanted and potentially harmful side-effects. Here, we review the natural and synthetic biomaterials that have been developed for protein and gene delivery to enhance tissue regeneration. Particular emphasis is placed on novel biomimetic materials that respond to environmental stimuli or release their cargo according to cellular demand. Engineering biomaterials to release therapeutic agents in response to physiologic signals mimics the natural healing process and can promote faster tissue regeneration and reduce scarring in severe acute or chronic wounds.     

The impact of physical,biochemical, and electrical signaling on Schwann cell plasticity

Peripheral nervous system (PNS) injuries are an ongoing health care concern. While autografts and allografts are regarded as the current clinical standard for traumatic injury, there are inherent limitations that suggest alternative remedies should be considered for therapeutic purposes. In recent years, nerve guidance conduits (NGCs) have become increasingly popular as surgical repair devices, with a multitude of various natural and synthetic biomaterials offering potential to enhance the design of conduits or supplant existing technologies entirely. From a cellular perspective, it has become increasingly evident that Schwann cells (SCs), the primary glia of the PNS, are a predominant factor mediating nerve regeneration. Thus, the development of severe nerve trauma therapies requires a deep understanding of how SCs interact with their environment, and how SC microenvironmental cues may be engineered to enhance regeneration. Here we review the most recent advancements in biomaterials development and cell stimulation strategies, with a specific focus on how the microenvironment influences the behavior of SCs and can potentially lead to functional repair. We focus on microenvironmental cues that modulate SC morphology, proliferation, migration, and differentiation to alternative phenotypes. Promotion of regenerative phenotypic responses in SCs and other non-neuronal cells that can augment the regenerative capacity of multiple biomaterials is considered along with innovations and technologies for traumatic injury.     

Designing biomaterials for in situ periodontal tissue regeneration

The regeneration of periodontal tissue poses a significant challenge to biomaterial scientists, tissue engineers and periodontal clinicians. Recent advances in this field have shifted the focus from the attempt to recreate tissue replacements/constructs ex vivo to the development of biofunctionalized biomaterials that incorporate and release regulatory signals in a precise and near-physiological fashion to achieve in situ regeneration. The molecular and physical information coded within the biomaterials define a local biochemical and mechanical niche with complex and dynamic regulation that establishes key interactions with host endogenous cells and, hence, may help to unlock latent regenerative pathways in the body by instructing cell homing and regulating cell proliferation/differentiation. In the future, these innovative principles and biomaterial devices promise to have a profound impact on periodontal reconstructive therapy and are also likely to reconcile the clinical and commercial pressures on other tissue engineering endeavors.     

Biologically Fe<Superscript>2+</Superscript> oxidizing fluidized bed reactor performance and controlling of Fe<Superscript>3+</Superscript> recycle during heap bioleaching: an artificial neural network-based model

The performance of a biological Fe²⁺ oxidizing fluidized bed reactor (FBR) was modeled by a popular neural network-back-propagation algorithm over a period of 220 days at 37 °C under different operational conditions. A method is proposed for modeling Fe³⁺ production in FBR and thereby managing the regeneration of Fe³⁺ for heap leaching application, based on an artificial neural network-back-propagation algorithm. Depending on output value, relevant control strategies and actions are activated, and Fe³⁺ production in FBR was considered as a critical output parameter. The modeling of effluent Fe³⁺ concentration was very successful, and an excellent match was obtained between the measured and the predicted concentrations.     

How can we bring together empiricists and modellers in functional biodiversity research?

Improving our understanding of biodiversity and ecosystem functioning and our capacity to inform ecosystem management requires an integrated framework for functional biodiversity research (FBR). However, adequate integration among empirical approaches (monitoring and experimental) and modelling has rarely been achieved in FBR. We offer an appraisal of the issues involved and chart a course towards enhanced integration. A major element of this path is the joint orientation towards the continuous refinement of a theoretical framework for FBR that links theory testing and generalization with applied research oriented towards the conservation of biodiversity and ecosystem functioning. We further emphasize existing decision-making frameworks as suitable instruments to practically merge these different aims of FBR and bring them into application. This integrated framework requires joint research planning, and should improve communication and stimulate collaboration between modellers and empiricists, thereby overcoming existing reservations and prejudices. The implementation of this integrative research agenda for FBR requires an adaptation in most national and international funding schemes in order to accommodate such joint teams and their more complex structures and data needs.     

Inhibitory effect of myristylation on transrepression by FBR (Gag-Fos) protein.

The myristylated v-fos product, FBR murine sarcoma virus (Gag-Fos) protein, exhibits a lower level of transrepression of the serum response element (SRE) than does c-fos protein (Fos). Mutation of the N-terminal myristylation site in FBR protein restored SRE transrepression. Replacement of N-terminal viral Gag sequences with the Fos N terminus also restored this activity, providing additional evidence that myristylation inhibits transrepression by FBR protein. However, the myristylated Gag domain did not inhibit SRE transrepression when fused to Fos, indicating that myristylation of a fos protein is not by itself sufficient to prevent SRE transrepression and that C-terminal mutation is necessary to inhibit transrepression by N myristylation. Comparison of transfection results with Fos C-terminal deletion mutants and the Fos/FBR chimeric mutant revealed that the FBR C terminus retained the potential for transrepression despite deletion of the normal Fos C terminus, whereas similar Fos deletion mutants did not. These results indicate that both N- and C-terminal mutations are required to inhibit transrepression by FBR protein and that multiple structural mutations accompanied by posttranslational protein modification alter gene regulation by FBR protein.     

The relationship between instability of H2 production and compositions of bacterial communities within a dark fermentation fluidized-bed bioreactor

Microbial community composition dynamics was studied during H(2) fermentation from glucose in a fluidized-bed bioreactor (FBR) aiming at obtaining insight into the H(2) fermentation microbiology and factors resulting in the instability of biofilm processes. FBR H(2) production performance was characterised by an instable pattern of prompt onset of H(2) production followed by rapid decrease. Gradual enrichment of organisms increased the diversity of FBR attached and suspended-growth phase bacterial communities during the operation. FBR bacteria included potential H(2) producers, H(2) consumers and neither H(2) producers nor consumers, and those distantly related to any known organisms. The prompt onset of H(2) production was due to rapid growth of Clostridium butyricum (99-100%) affiliated strains after starting continuous feed. The proportion trend of C. butyricum in FBR attached and suspended-growth phase communities coincided with H(2) and butyrate production. High glucose loading rate favoured the H(2) production by Escherichia coli (100%) affiliated strain. Decrease in H(2) production, associated with a shift from acetate-butyrate to acetate-propionate production, was due to changes in FBR attached and suspended-growth phase bacterial community compositions. During the shift, organisms, including potential propionate producers, were enriched in the communities while the proportion trend of C. butyricum decreased. We suggest that the instability of H(2) fermentation in biofilm reactors is due to enrichment and efficient adhesion of H(2) consumers on the carrier and, therefore, biofilm reactors may not favour mesophilic H(2) fermentation.     

Bioactive glasses as delivery systems for antimicrobial agents

Most biomaterial‐associated infections are caused by opportunistic pathogens and bacteria that are regularly found within the microflora of the implant site. In addition, a biomaterial implant or device remains at risk of infection by hematogenous spread of bacteria disseminated from infections elsewhere in the body or from infected peri‐implant tissue in revision surgery. The resulting infections are frequently accompanied by patient morbidity and discomfort and can lead to surgical replacement of the implant after lengthy, unsuccessful attempts to mitigate infections with antibiotic treatments. Therefore, extensive study is aiming to find new infection‐resistant antimicrobial biomaterials and coatings for implants and devices to effectively reduce the incidence of biomaterial‐associated infections. An overview of the in vitro and in vivo antimicrobial efficacies of the numerous biomaterials currently available is beyond the scope of this review. Herein, we provide a comprehensive review of bioactive glasses as biomaterial delivery systems for antimicrobial agents.     

Human chondrocytes and mesenchymal stem cells grown onto engineered scaffold

The development of improved methods for treatment of chondral defects using autologous cells in combination with biomaterials leads to a new generation of implantable devices. Their association gives rise to a hybrid construct combining biological and material components that can be specifically committed. The comprehension of cellular and molecular mechanisms of cartilage repair and the use of biomaterials in combination with chondrocytes or mesenchymal stem cells in the treatment of cartilage defects has opened a new era of therapeutical strategies. Recently, their applicability in the treatment of early lesions in osteoarthritis is under investigation. To obtain new information on the behaviour of chondrocytes and mesenchymal stem cells grown on a hyaluronan derivative scaffold (Hyaff-11) already used in cartilage repair, we analysed a series of molecules expressed by these cells by Real-Time RT-PCR and immunohistochemical analyses. The data obtained with this work showed that this biomaterial is able to reduce the expression of some catabolic molecules by human chondrocytes and provide a good environment to support the differentiation of mesenchymal stem cells in chondrogenic sense. These observations confirm Hyaff-11 as a suitable scaffold both for chondrocytes and mesenchymal stem cells for the treatment of articular cartilage defects.     

Investigation of parameters affecting a fixed bed bioreactor process for recombinant cell lines

A BHK 21 cell line expressing a recombinant antibody was grown in a fixed bed reactor (FBR) system using a porous support made of Siran glass beads. The contribution of five process variables (bead and inoculum sizes; circulation and dilution rates; glutamine concentration of the feed) to the productivity of the process (defined as production rate, effluent product concentration or yield of product on medium supplied) was investigated using a partial factorial experimental design. Individually, none of the variables tested had a significant affect upon productivity. The combination of smaller bead and inoculum sizes, higher circulation and dilution rates, plus higher feed glutamine concentration gave a markedly higher productivity than any other combination of variable levels tested. This combination of variable levels suggested that better results shold be obtained using a fluidised bed reactor system. However, comparison of the productivities of the two systems showed that the FBR gave the better results. This result can be explained in terms of the relationship of Qs_rAb to .Abbreviations C concentration - D dilution rate - FBR fixed bed bioreactor - FIBR fluidised bed bioreactor - Gln glutamine - Qs cell specific rate - Qv volumetric rate - rAb recombinant antibody - X_v viable cell density - specific growth rate     

Comparison of two continuous fungal bioreactors for posttreatment of anaerobically pretreated weak black liquor from kraft pulp mills

The purpose of this work was to evaluate and compare two continuous systems of posttreatment of anaerobically pretreated weak black liquor (WBL). The first system consisted of a packed bed reactor (PBR) with Trametes versicolor (Tv) immobilized on wood cubes of holm oak (biocubes). The second system was a fluidized bed reactor (FBR) with Lentinus edodes (Le) immobilized on wood cubes of holm oak. The reactors operated for 65 days at a hydraulic retention time (HRT) of 5 days, at 28 degrees C, with continuous aeration. Response variables monitored were conventional and specific, unit, net removal efficiency (eta and eta(sun), respectively) of chemical oxygen demand (COD), color, and ligninoids, and enzymatic activities of manganese peroxidase (MnP), lignin peroxidase (LiP), laccase (Lac) and proteases. The PBR showed an average color eta superior to that of the FBR (52.42 +/- 21.78% and 25.34 +/- 14.38% for PBR and FBR, respectively); removals of COD and ligninoids presented a similar pattern to that of color. Lac activity was significantly larger in PBR than in FBR. Activity of MnP in PBR was higher than that of the FBR (0.004 and 0.002 U MnP/mL, respectively). This difference could be ascribed to the different fungi present in each bioreactor. LiP activity was very low in both reactors. Average value of proteases was almost double in the FBR as compared with PBR (0.472 and 0.209 U Proteases/mL, respectively). During the last 2 weeks of operation, biocubes in the FBR experienced a significant loss of the attached Le biomass, probably by attrition. This and higher protease activity in the FBR could explain the lower pollutant removals achieved in the FBR. Overall, PBR with immobilized Tv showed a better performance than the FBR with Le for the posttreatment of the recalcitrant anaerobic effluent. Extended and sustained pollutant removal (65 days) was achieved in the PBR, although more research is needed to evaluate bioreactor performance at shorter hydraulic retention times.     

The oxidation,fate and effects of iron during on-site bioremediation of groundwater contaminated by a mixture of polychlorophenols

Kinetics of simultaneous iron and polychlorophenol (CP) oxidation by groundwater enriched cultures were studied in laboratory and during actual remediation in orderto reveal the fate and effects of iron on aerobic on-site bioremediation of boreal groundwater. 2,4,6-tri- (TCP), 2,3,4,6-tetra- (TeCP) and pentachlorophenol (PCP)were degraded in fluidized-bed bioreactor (FBR) by over 99%, over 99%, and over96%, respectively. The oxygen consumption rate for CP-biodegradation was 1.31mol DO L^-1 min^-1 and 0.29 mol DO L^-1 min^-1 for iron oxidation, i.e. approximately 12% of the oxygen was consumed by iron oxidation during normal FBR operation. Mineralization of CPs was confirmed by DOC removal and chloride release of 158% and 78%, respectively. Excess DOC removal was due to partial degradation of the natural organic matter (NOM) (1.1 mg L^-1 or 24% DOC removal) in the groundwater. Removal of NOM consumed 0.91 mol DO L^-1min^-1. Iron oxidation in the FBR was over 94% of which chemical Fe(II) oxidation accounted for up to 10%. Fe(III) partially accumulated (58 to 69%) in the system. The TCP- and CP-biodegradation consumed DO at two times higher rates than the Fe(II)-oxidation in both, laboratory and full-scale, respectively. The batch assays atvarious TCP and Fe(II) ratios and DO concentrations showed simultaneous oxygenconsumption by TCP and Fe-oxidizers and that increased Fe concentrations do notoutcompete the bioremediation of CP's for available oxygen. Abbreviations: DAPI: 4',6'-Diamidino-phenylindole; DO:Dissolved oxygen; DOC: Dissolved organic carbon; FBR: Fluidized-bed bioreactor;HRT: Hydraulic retention time; NOM: Natural organic matter; PCP: Pentachlorophenol; SEM: Scanning-electron microscopy, TeCP: 2,3,4,6-Tetrachlorophenol; TCP: 2,4,6-Trichlorophenol