Use of poly vinyl alcohol (PVA) cryogelation for tissue engineering: composites, scaffold formation and cell encapsulation

PVA cryogelation is a physical hydrogel formation method, which yields cryogels with comparable mechanical properties to vascular tissue. However PVA cryogels are not suitable for cell attachment and proliferation alone. This can be overcome by the development of composite cryogels. Moreover, cryogelation provides a unique opportunity for encapsulation and storage of cells in one-step; if the correct composite structure and gelation conditions can be attained. In this study, PVA/Biomacromolecule composite cryogels were produced with a two step physical crosslinking (cryogelation and coagulation bath treatment) in the presence of different additives and a novel procedure to produce cell encapsulated PVA cryogels was developed for vascular tissue engineering. Also it was postulated that the disturbed shear stress could be used to facilitate endothelialisation of the PVA cryogel surface. The results demonstrated that, the two step gel formation method was beneficial for degradation resistance and mechanical properties. All composites used supported cell attachment and proliferation, however PVA/Gelatin composites were superior compared to the others. Endothelialisation of PVA/Gelatin cryogels was achieved both under static and shear stress conditions with low levels of apoptosis and steady secretion of Nitric Oxide. It was shown that application of disturbed shear stress dramatically facilitated endothelialisation of the cryogel surface. A general method of encapsulation via cryogelation was developed and robust cellladen cryogels which promoted cell proliferation were obtained. Storage in frozen conditions did not affect the viability of the encapsulated cells, which suggests the prospect of safe long-term storage. Smooth muscle cell-laden cryogels were also able to support co-culture with endothelial cells. The results suggest that the novel encapsulation system developed is suitable for vascular and possibly other tissue engineering applicatio

Editorial: Adverse reactions to biomaterials: State of the art in biomaterial risk assessment, immunomodulation and in vitro models for biomaterial testing

Editorial on the Research Topi

Cell Microenvironment Engineering and Monitoring for Tissue Engineering and Regenerative Medicine: The Recent Advances

In tissue engineering and regenerative medicine, the conditions in the immediate vicinity of the cells have a direct effect on cells' behaviour and subsequently on clinical outcomes. Physical, chemical, and biological control of cell microenvironment are of crucial importance for the ability to direct and control cell behaviour in 3-dimensional tissue engineering scaffolds spatially and temporally. In this review, we will focus on the different aspects of cell microenvironment such as surface micro-, nanotopography, extracellular matrix composition and distribution, controlled release of soluble factors, and mechanical stress/strain conditions and how these aspects and their interactions can be used to achieve a higher degree of control over cellular activities. The effect of these parameters on the cellular behaviour within tissue engineering context is discussed and how these parameters are used to develop engineered tissues is elaborated. Also, recent techniques developed for the monitoring of the cell microenvironment in vitro and in vivo are reviewed, together with recent tissue engineering applications where the control of cell microenvironment has been exploited. Cell microenvironment engineering and monitoring are crucial parts of tissue engineering efforts and systems which utilize different components of the cell microenvironment simultaneously can provide more functional engineered tissues in the near future

Incorporation of resident macrophages in engineered tissues: multiple cell type response to microenvironment controlled macrophage-laden gelatin hydrogels

The success of tissue engineering strategy is strongly related to the inflammatory response, mainly through the activity of macrophages that are key cells in initial immune response to implants. For engineered tissues, the presence of resident macrophages can be beneficial for maintenance of homeostasis and healing. Thus, incorporation of macrophages in engineered tissues can facilitate the integration upon implantation. In this study, we developed an in-vitro model of interaction between encapsulated naive monocytes, macrophages induced with M1/M2 stimulation and incoming cells for immune assisted tissue engineering applications. To mimic the wound healing cascade, Naive THP-1 monocytes, endothelial cells, and fibroblasts were seeded on the gels as incoming cells. The interaction was first monitored in the absence of the gels. In order to mimic resident macrophages, THP-1 cells were encapsulated in the presence or absence of IL-4 to control their phenotype and then these hydrogels were seeded with incoming cells. Without encapsulation, activated macrophages induce apoptosis in endothelial cells. Once encapsulated no adverse effects were seen. Macrophage-laden hydrogels attracted more endothelial cells and fibroblasts compared to monocytes-laden hydrogels. The induction (M2 stimulation) of encapsulated macrophages did not change the overall number of attracted cells; but significantly affected their morphology. M1 stimulation by a defined media resulted in secretion of both pro and anti-inflammatory cytokines compared to M2 stimulation. We demonstrated that there is a distinct effect of encapsulated macrophages on the behavior of the incoming cells; this effect can be harnessed to establish a microenvironment more prone to regeneration upon implantation

Antibody response to oral biofilm is a biomarker for acute coronary syndrome in periodontal disease

This study finds that antibodies against antigens present in oral biofilm are potential biomarkers of acute coronary syndrome (ACS), the most severe form of coronary artery disease. By testing antibody response to periodontal pathogens, the authors find that patients with ACS have little or no immune response to a particular antigen epitope.Cumulative evidence over the last decades have supported the role of gum infections as a risk for future major cardiovascular events. The precise mechanism connecting coronary artery disease (CAD) with periodontal findings has remained elusive. Here, we employ next generation phage display mimotope-variation analysis (MVA) to identify the features of dysfunctional immune system that associate CAD with periodontitis. We identify a fine molecular description of the antigenic epitope repertoires of CAD and its most severe form - acute coronary syndrome (ACS) by profiling the antibody reactivity in a patient cohort with invasive heart examination and complete clinical oral assessment. Specifically, we identify a strong immune response to an EBV VP26 epitope mimicking multiple antigens of oral biofilm as a biomarker for the no-CAD group. With a 2-step biomarker test, we stratify subjects with periodontitis from healthy controls (balanced accuracy 84%), and then assess the risk for ACS with sensitivity 71-89% and specificity 67-100%, depending on the oral health status. Our findings highlight the importance of resolving the immune mechanisms related to severe heart conditions such as ACS in the background of oral health. Prospective validation of these findings will support incorporation of these non-invasive biomarkers into clinical practice.Peer reviewe

Use of Nanoparticles in Tissue Engineering and Regenerative Medicine

Advances in nanoparticle (NP) production and demand for control over nanoscale systems have had significant impact on tissue engineering and regenerative medicine (TERM). NPs with low toxicity, contrasting agent properties, tailorable characteristics, targeted/stimuli-response delivery potential, and precise control over behavior (via external stimuli such as magnetic fields) have made it possible their use for improving engineered tissues and overcoming obstacles in TERM. Functional tissue and organ replacements require a high degree of spatial and temporal control over the biological events and also their real-time monitoring. Presentation and local delivery of bioactive (growth factors, chemokines, inhibitors, cytokines, genes etc.) and contrast agents in a controlled manner are important implements to exert control over and monitor the engineered tissues. This need resulted in utilization of NP based systems in tissue engineering scaffolds for delivery of multiple growth factors, for providing contrast for imaging and also for controlling properties of the scaffolds. Depending on the application, materials, as polymers, metals, ceramics and their different composites can be utilized for production of NPs. In this review, we will cover the use of NP systems in TERM and also provide an outlook for future potential use of such systems

Polyanionic Hydrogels as Reservoirs for Polycationic Antibiotic Substitutes Providing Prolonged Antibacterial Activity

Implantation of biomedical devices is often followed by bacterial infections that may seriously affect implant functionalities and lead to their failure. In the context of bacterial resistance to antibiotics, which is a growing problem worldwide, new strategies that are able to overcome these problems are needed. In this work, we introduce a new formulation of hyaluronic acid (HA)-based antimicrobial material: HA hydrogels loaded with polyarginine (PAR), a polycationic antibiotic substitute. The loading is possible through electrostatic interactions between negatively charged HA and positively charged PAR. Such hydrogels absorb high quantities of PAR, which are then gradually released from the hydrogel. This original system provides a long-lasting antibacterial effect on an in vitro model of repetitive infection, thus demonstrating a strong potential to fight multiple rounds of infections that are resistant to antibiotic treatment. In addition, HA-PAR hydrogels could be deposited onto/into medical devices such as wound dressings and mesh prostheses used in clinical applications. Finally, we performed first in vivo tests of hydrogel-coated mesh materials to verify their biocompatibility in a rat model, which show no difference between control HA hydrogel and PAR-loaded hydrogel in terms of inflammation

Electrohydrodynamic printing as a method to micropattern large titanium implant surfaces with photocrosslinkable structures

Metallic implants are widely used in orthopaedic and orthodontic applications. However, generally surface treatment of the metallic surfaces is necessary to render them more biologically active. Herein, we describe a direct write printing method to modify metallic implant surfaces with biocompatible polymers with microscale precision. Application of polymeric micropatterns on metallic implant surfaces can (i) improve their interaction with the host tissue, (ii) enable the delivery of growth factors, antibiotics, anti-inflammatory cytokines etc from the implant surface and (iii) can control the immune responses to the implant via controlling the attachment of immune cells, such as macrophages. Surface patterns with a resolution of less than 50 μm can be created using an electro hydrodynamic (EHD) printing, a template-free and single-step process. We present a revised EHD printing method for the deposition of parallel strips of photocrosslinkable, cell adhesive polymeric composites with spacing of around 20 μm onto medical grade titanium substrates. Optimization of voltage, feeding rate and collection speed resulted in regular structures via very rapid movement of the grounded rotating collector driven to equivalent of the linear surface speed of above 100 cm s−1. In the experimental part a mixture of chemically modified PEG /gelatin was deposited onto a conductive titanium substrate with different surface pretreatments with an area of 400 mm2. Acid etched or UV treated titanium surfaces improved the stability of the printed structures. Polymeric lines induced temporary orientation of human monocytes (THP-1) and induced a thicker cell multilayer formation by 3T3 fibroblasts (p < 0.05). Staining of the monocytes for M1(CD80) and M2 (CD206) macrophage markers on the patterned surface showed mixed populations with higher anti-inflammatory cytokine secretion compared to tissue culture plastic control. The results demonstrate the suitability of this method for the preparation of biomaterials with structured surfaces on large areas and with desired chemical composition