New Models for Patient-specific Evaluation of the Effect of Biomaterials on Macrophages

Abstract

Biomaterials are often used in many fields of medicine to restore or replace tissue. These biomaterials always elicit a reaction of the immune system, called the foreign body reaction, which can lead to complications in patients and failure of the device. Macrophages are key players in this reaction. Because the foreign body reaction depends on the type and consistency of biomaterials but also on the patient itself, a tailor-made model will be of great help to assess the best treatment. Therefore the ultimate aim of our research was to develop a tailor-made model. Much research has already been performed on macrophages and biomaterials, therefore we started with a literature research of what is already known. First a systematic review of in vitro models describing the macrophage polarisation (pro- (M1) or anti-inflammatory (M2)) in response to different biomaterials was performed (Chapter 2). It was found that many factors are influencing this polarisation such as chemistry, pore size and surface topography. Also sterilisation and chemically crosslinking will alter the macrophage polarisation. However, since many different culture conditions were used, it was difficult to compare the biomaterials. Since we eventually aimed for a tailor-made model, the development of an in vitro model with human isolated macrophages from blood was initiated (Chapter 3). First, distinguishing genes and cytokines for polarisation were determined. These read-out parameters were used for investigating the influence of four different biomaterials on macrophage polarisation; the model showed biomaterial-dependent differences. Macrophages on polypropylene had a phenotype comparable to M2, while macrophages on polyethylene terephthalate and on a combined biomaterial Parietex™ Composite (polyethylene terephthalate and collagen) had a phenotype similar to M1. Macrophages on a collagen biomaterial (Permacol™) produced a low amount of proteins and therefore did not have a clear phenotype. This model can be useful in the future to predict the in vivo outcome of biomaterials. Most research is performed in a sterile environment. However some anatomical locations in the human body are not sterile, like in bowel surgery or rhinoplasty as described in the case report in the introduction. The use of biomaterials in these fields has an increased risk of complications, such as infection [5]. In Chapter 4a an in vivo animal model was used in which a contaminated environment was created by puncture of the bowel, creating a peritonitis to compare the performance of different biomaterials. Six different synthetic and one biological biomaterial were implanted in the abdominal wall. Significant differences in infection rate and incorporation between materials were found. Most infections occurred in C-QurTM and Dualmesh®. The incorporation of the biological mesh (Strattice®) was less than the other synthetic biomaterials, however this mesh was never infected. Dualmesh® showed the most shrinkage. In Chapter 4b samples of the previous study were used to analyse the subtype of macrophages. Parietene CompositeTM and SeprameshTM induced more iNOS-positive cells (M1 polarisation) and C-QurTM and Dualmesh® were surrounded by more CD206-positive cells (M2 polarisation), finding biomaterial-dependent differences in this in vivo rat model. The biomaterial-dependent polarisation of macrophages in a contaminated environment in the rat study inspired to modify the culture model developed in Chapter 3. Inflammatory cytokines (LPS and IFNγ) were added to our in vitro model in Chapter 5, to mimic an inflammatory environment. Polypropylene again stimulated M2 polarisation and Parietex™ Composite and polyethylene terephthalate stimulated an M1 reaction. Despite inflammation, macrophages still behaved bThe foreign body reaction differs per biomaterial and per patient. Some patients have complications after implantation of a biomaterial and some have none with the same biomaterial. For clinical practice, it would be a great benefit to have a tailor-made model with patients own cells to test pre-operatively which biomaterial is best thereby reducing complication rates. Since most of the knowledge and use of biomaterials is in general surgery, we will focus our research in this field. The ultimate goal of our research is to develop a tailor-made _in vitro_ model with human macrophages. Towards developing this model, the following aims are formulated: 1) to develop an _in vitro_ model to study the effect of biomaterials on human macrophage polarisation 2) to investigate the influence of biomaterials on macrophage phenotype in an inflammatory environment and whether this is biomaterial-dependent 3) to investigate the influence of biomaterials on stem cells and macrophages together in an adjusted _in vitro_ mode