Non-invasive Characterization of Immune Responses to Biomedical Implants

In Vivo Comparison of Synthetic Macroporous Filamentous and Sponge-like Skin Substitute Matrices Reveals Morphometric Features of the Foreign Body Reaction According to 3D Biomaterial Designs

Synthetic macroporous biomaterials are widely used in the field of skin tissue engineering to mimic membrane functions of the native dermis. Biomaterial designs can be subclassified with respect to their shape in fibrous designs, namely fibers, meshes or fleeces, respectively, and porous designs, such as sponges and foams. However, synthetic matrices often have limitations regarding unfavorable foreign body responses (FBRs). Severe FBRs can result in unfavorable disintegration and rejection of an implant, whereas mild FBRs can lead to an acceptable integration of a biomaterial. In this context, comparative in vivo studies of different three-dimensional (3D) matrix designs are rare. Especially, the differences regarding FBRs between synthetically derived filamentous fleeces and sponge-like constructs are unknown. In the present study, the FBRs on two 3D matrix designs were explored after 25 days of subcutaneous implantation in a porcine model. Cellular reactions were quantified histopathologically to investigate in which way the FBR is influenced by the biomaterial architecture. Our results show that FBR metrics (polymorph-nucleated cells and fibrotic reactions) were significantly affected according to the matrix designs. Our findings contribute to a better understanding of the 3D matrix tissue interactions and can be useful for future developments of synthetically derived skin substitute biomaterials.

Long-Term Arterial Remodeling After Bioresorbable Scaffold Implantation 4-Year Follow-up of Quantitative Coronary Angiography, Histology and Optical Coherence Tomography

PURPOSE

Our previous studies have confirmed the safety and efficacy of the novel fully bioresorbable PLLA scaffold (PowerScaffold®) at 12 months implantation. In the present study, the scaffold absorption and coronary vessel remodeling at 4 years were evaluated.

METHODS

After PowerScaffold® were implanted into 13 coronary arteries of 6 miniature pigs, quantitative coronary angiography (QCA) was performed at 15 days and 4 years follow-up to measure the mean lumen diameter (MLD), late lumen loss (LLL), and % stenosis of the coronary arteries. Optical coherence tomography (OCT) was performed to obtain the strut footprints at 4 years before euthanization for histological analysis. In addition, 2 PowerScaffold® were implanted into 2 miniature pigs for 2 years as supplementary data. All stented arteries were dissected and stained with HE, Masson, EVG, and Alcian blue to observe struts, cells, fibrinoid, elastin, and proteoglycans, respectively.

RESULTS

There were no significant differences in MLD, LLL and % stenosis in stented coronary arteries between 15 days and 4 years by QCA. At 4 years, most strut sites were indiscernible and replaced by extracellular matrix and connective tissue by histology. Both strut/vessel wall interaction and strut coverage were shown 100% by OCT.

CONCLUSION

At 4 years, the scaffold struts were completely embedded into vessel wall and mostly replaced by regenerated tissue. There was no sign of in-stent stenosis in all stented arteries.

Autologous cell membrane coatings on tissue engineering xenografts for suppression and alleviation of acute host immune responses

Xenogeneic extracellular matrix (ECM) based tissue engineering graft is one of the most promising products for transplantation therapies, which could alleviate the pain of patients and reduce surgery cost. However, in order to put ECM based xenografts into clinical use, the induced inflammatory and immune responses have yet to be resolved. Cell membrane is embedded with membrane proteins for regulation of cell interactions including self-recognition and potent in reducing foreign body rejections. In this study, a novel and facile method for evasion from immune system was developed by coating autologous red blood cell membrane as a disguise on xenogeneic ECM based tissue engineering graft surface. Porcine source Living Hyaline Cartilage Graft (LhCG) and decellularized LhCG (dLhCG) established by our group for cartilage tissue engineering were chosen as model grafts. The cell membrane coating was quite stable on xenografts with no obvious decrease in amount for 4 weeks. The autologous cell membrane coated xenograft has been proved to be recognized as "self" by immune system on cell, protein and gene levels according to the 14-day lasting in vivo study on rats with less inflammatory cells infiltrated and low inflammation-related cytokines gene expression, showing alleviated acute immune and inflammatory responses.

An implanted pH sensor read using radiography

A biomedical sensor was developed to measure local pH near orthopedic implants to detect and study implant-associated infection. The sensor is read using plain radiography, a technique which is noninvasive, inexpensive, ubiquitously available in medical facilities, and routinely used in diagnosis and follow-up. The sensor comprises a radiopaque tungsten indicator pin embedded within a chemically responsive hydrogel that exhibits a pH-dependent swelling. A stainless steel well holds this hydrogel and attaches to an orthopedic plate. The local pH may be determined from the extent of hydrogel swelling by radiographically measuring the indicator position relative to the well. We calibrated the sensor in a series of standard pH buffers and tested it during bacterial growth in culture. The sensor was robust: its response was negligibly affected by changes in temperature, ionic strength within the normal physiological range, or long-term incubation with reactive oxygen species generated from hydrogen peroxide and copper. Pooled data from several sensors fabricated at different times and tested in different conditions had a root-mean-square deviation from a pH electrode reading of 0.24 pH units. Radiographic measurements were also performed in cadaveric tissue with the sensor attached to an orthopedic plate fixed to a tibia. Pin position readings varied by 100 μm between observers surveying the same radiographs, corresponding to 0.065 pH units precision in the range pH 4-8. The sensor was designed to augment standard radiographs of tissue, bony anatomy, and hardware by also indicating local chemical concentrations.

The zebrafish embryo as a model to quantify early inflammatory cell responses to biomaterials

To rapidly assess early inflammatory cell responses provoked by biomaterials in the full complexity of the living organism, we developed a zebrafish embryo model which allows real time analysis of these responses to biomaterial microspheres. Fluorescently labeled microspheres with different properties were injected into embryos of selected transgenic zebrafish lines expressing distinct fluorescent proteins in their neutrophils and macrophages. Recruitment of leukocytes and their interactions with microspheres were monitored using fluorescence microscopy. We developed a novel method using ImageJ and the plugin ObjectJ project file "Zebrafish-Immunotest" for rapid and semi-automated fluorescence quantification of the cellular responses. In the embryo model we observed an ordered inflammatory cell response to polystyrene and poly (ε-caprolactone) microspheres, similar to that described for mammalian animal models. The responses were characterized by an early infiltration of neutrophils followed by macrophages, and subsequent differentially timed migration of these cells away from the microspheres. The size of microspheres (10 and 15 µm) did not influence the cellular responses. Poly (ε-caprolactone) microspheres provoked a stronger infiltration of neutrophils and macrophages than polystyrene microspheres did. Our study shows the potential usefulness of zebrafish embryos for in vivo evaluation of biomaterial-associated inflammatory cell responses. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 2522-2532, 2017.