Sven Halstenberg

The rapid anastomosis between prevascularized networks on silk fibroin scaffolds generated in vitro with cocultures of human microvascular endothelial and osteoblast cells and the host vasculature

The survival and functioning of a bone biomaterial upon implantation requires a rapidly forming and stably functioning vascularization that connects the implant to the recipient. We have previously shown that human microcapillary endothelial cells (HDMEC) and primary human osteoblast cells (HOS) in coculture on various 3-D bone biomaterial scaffolds rapidly distribute and self-assemble into a morphological structure resembling bone tissue. Endothelial cells form microcapillary-like structures containing a lumen and these were intertwined between the osteoblast cells and the biomaterial. This tissue-like self-assembly occurred in the absence of exogenously added angiogenic stimuli or artificial matrices. The purpose of this study was to determine whether this in vitro pre-formed microvasculature persists and functions in vivo and to determine how the host responds to the cell-containing scaffolds. The scaffolds with cocultures were implanted into immune-deficient mice and compared to scaffolds without cells or with HDMEC alone. Histological evaluation and immunohistochemical staining with human-specific antibodies of materials removed 14 days after implantation demonstrated that the in vitro pre-formed microcapillary structures were present on the silk fibroin scaffolds and showed a perfused lumen that contained red blood cells. This proved anastomosis with the host vasculature. Chimeric vessels in which HDMEC were integrated with the hosts ingrowing (murine) capillaries were also observed. No HDMEC-derived microvessel structures or chimeric vessels were observed on implanted silk fibroin when precultured with HDMEC alone. In addition, there was migration of the host (murine) vasculature into the silk fibroin scaffolds implanted with cocultures, whereas silk fibroin alone or silk fibroin precultured only with HDMEC were nearly devoid of ingrowing host microcapillaries. Therefore, not only do the in vitro pre-formed microcapillaries in a coculture survive and anastomose with the host vasculature to become functioning microcapillaries after implantation, the coculture also stimulates the host capillaries to rapidly grow into the scaffold to vascularize the implanted material. Thus, this coculture-based pre-vascularization of a biomaterial implant may have great potential in the clinical setting to treat large bone defects.

Analysis of the Biological Response of Endothelial and Fibroblast Cells Cultured on Synthetic Scaffolds with Various Hydrophilic/Hydrophobic Ratios: Influence of Fibronectin Adsorption and Conformation

In this study we developed polymer scaffolds intended as anchorage rings for cornea prostheses among other applications, and examined their cell compatibility. In particular, a series of interconnected porous polymer scaffolds with pore sizes from 80 to 110 microns were manufactured varying the ratio of hydrophobic to hydrophilic monomeric units along the polymer chains. Further, the effects of fibronectin precoating, a physiological adhesion molecule, were tested. The interactions between the normal human fibroblast cell line MRC-5 and primary human umbilical vein endothelial cells (HUVECs) with the scaffold surfaces were evaluated. Adhesion and growth of the cells was examined by confocal laser scanning microscopy. Whereas MRC-5 fibroblasts showed adhesion and spreading to the scaffolds without any precoating, HUVECs required a fibronectin precoating for adhesion and spreading. Although both cell types attached and spread on scaffold surfaces with a content of up to a 20% hydrophilic monomers, cell adhesion, spreading, and proliferation increased with increasing hydrophobicity of the substrate. This effect is likely due to better adsorption of serum proteins to hydrophobic substrates, which then facilitate cell adhesion. In fact, atomic force microscopy measurements of fibronectin on surfaces representative of our scaffolds revealed that the amount of fibronectin adsorption correlated directly with the hydrophobicity of the surface. Besides cell adhesion we also examined the inflammatory state of HUVECs in contact with the scaffolds. Typical patterns of platelet/endothelial cell adhesion molecule-1 expression were observed at intercellular boarders. HUVECs adhering on the scaffolds retained their proinflammatory response potential as shown by E-selectin mRNA expression after stimulation with lipopolyssacharide (LPS). The proinflammatory activation occurred in most of the cells, thus confirming the presence of a functionally intact endothelium. Little or no expression of the proinflammatory activation markers in the absence of LPS stimulation was observed for HUVECs growing on scaffolds with up to a 20% of hydrophilic component, whereas activation of these markers was observed after stimulation. In conclusion, scaffolds containing up to 20% hydrophilic monomers exhibited excellent cell compatibility toward human fibroblast cell line MRC-5 and human endothelial cells. Atomic force microscopy confirmed that adsorbed serum proteins such as fibronectin probably accounted for the positive correlation of HUVEC adhesion and surface hydrophobicity.

Signalling molecules and growth factors for tissue engineering of cartilage—what can we learn from the growth plate?†

Modern tissue engineering concepts integrate cells, scaffolds, signalling molecules and growth factors. For the purposes of regenerative medicine, fetal development is of great interest because it is widely accepted that regeneration recapitulates in part developmental processes. In tissue engineering of cartilage the growth plate of the long bone represents an interesting, well‐organized developmental structure with a spatial distribution of chondrocytes in different proliferation and differentiation stages, embedded in a scaffold of extracellular matrix components. The proliferation and differentiation of these chondrocytes is regulated by various hormonal and paracrine factors. Thus, members of the TGFβ superfamily, the parathyroid hormone‐related peptide–Indian hedgehog loop and a number of transcription factors, such as Sox and Runx, are involved in the regulation of chondrocyte proliferation and differentiation. Furthermore, adhesion molecules, homeobox genes, metalloproteinases and prostaglandins play a role in the complex regulation mechanisms. The present paper summarizes the morphological organization of the growth plate and provides a short but not exhaustive overview of the regulation of growth plate development, giving interesting insights for tissue engineering of cartilage. Copyright

Immobilization and controlled release of prostaglandin E2 from poly-L-lactide-co-glycolide microspheres

Prostaglandin E(2) (PGE(2)) is an arachidonic acid metabolite involved in physiological homeostasis and numerous pathophysiological conditions. Furthermore, it has been demonstrated that prostaglandins have a stimulating effect not only on angiogenesis in situ and in vitro but also on chondrocyte proliferation in vitro. Thus, PGE(2) represents an interesting signaling molecule for various tissue engineering strategies. However, under physiological conditions, PGE(2) has a half-life time of only 10 min, which limits its use in biomedical applications. In the present study, we investigated if the incorporation of PGE(2) into biodegradable poly-L-lactide-co-glycolide microspheres results in a prolonged release of this molecule in its active form. PGE(2)-modified microspheres were produced by a cosolvent emulsification method using CHCl(3) and HFIP as organic solvents and PVA as emulsifier. Thirteen identical batches were produced; and to each batch 1.0 mL of serum-free medium was added. The medium was removed at defined time points and then analyzed by gas chromatography tandem mass spectrometry (GC/MS/MS) to measure the residual PGE(2) content. In this study we demonstrated the prolonged release of PGE(2), showing a linear increase over the first 12 h, followed by a plateau and a slow decrease. The microspheres were further characterized by scanning electron microscopy.

Phenotypic redifferentiation and cell cluster formation of cultured human articular chondrocytes in a three-dimensional oriented gelatin scaffold in the presence of PGE2 - first results of a pilot study†

Modern tissue engineering strategies comprise three elemental parameters: cells, scaffolds and growth factors. Articular cartilage represents a highly specialized tissue which allows frictionless gliding of corresponding articulating surfaces. As the regenerative potential of cartilage is low, tissue engineering-based strategies for cartilage regeneration represent a huge challenge. Prostaglandins function as regulators in cartilage development and metabolism, especially in growth plate chondrocytes. In this study, it was analyzed if prostaglandin E2 (PGE2 ) has an effect on the phenotypic differentiation of human chondrocytes cultured in a three-dimensional (3D) gelatin-based scaffold made by directional freezing and subsequent freeze-drying. As a result, it was clearly demonstrated that low doses of PGE2 revealed beneficial effects on the phenotypic differentiation and collagen II expression of human articular chondrocytes in this 3D cell culture system. In conclusion, PGE2 is an interesting candidate for tissue engineering applications since it represents an already well-studied molecule which is available in pharmaceutical quality.

Human Endothelial and Osteoblast Co-cultures on 3D Biomaterials

Increasingly, in vitro experiments are being used to evaluate the cell compatibility of novel biomaterials. Single cell cultures have been used to determine how well cells attach, grow, and exhibit characteristic functions on these materials and the outcome of such tests is generally accepted as an indicator of biocompatibility. However, organs and tissues are not made up of one cell type and the interaction of cells is known to be an essential factor for physiological cell function. To more accurately examine biomaterials for bone regeneration, we have developed methods to coculture osteoblasts, which are the primary cell type making up bone, and endothelial cells, which form the vasculature supplying cells in the bone with oxygen and nutrients to survive on 2- and 3-D biomaterials.

Bewertung von neuartigen Biomaterialien zum Zweck der Knochenrekonstruktion und -regeneration

ZusammenfassungViele verschiedene Knochenersatzstoffe werden für klinische Anwendungen entwickelt. Laut geläufigem Dogma gelten diese Stoffe für die Rekonstruktion und Regeneration von Knochengewebe als geeignet, wenn Osteoblasten und Endothelzellen als Monokulturen oder Kokulturen auf ihnen wachsen und normale Zellfunktionen aufweisen. Jedoch werden auch Tierexperimente vorausgesetzt, um die klinische Eignung der Materialien zu bestätigen. Gute standardisierte In-vitro-Tests dienen also dazu, nur ausgewählte und vielversprechende Stoffe für Tierversuche zuzulassen. Vor allem Kokulturmodelle mit Beteiligung aller relevanter Zelltypen haben ein vielversprechendes Zukunftspotential.AbstractMany different types of bone substitute biomaterials are being developed for different applications in the body. The current dogma is that if osteoblasts and endothelial cells grow and exhibit normal cell functions on these materials in vitro as single cultures or in co-cultures, then the biomaterials are suitable for implantation for bone reconstruction and regeneration. Generally, only in vivo animal studies will prove whether this is the case. However, in vitro studies offer a good pre-screening and selection basis to evaluate the biocompatibility of novel biomaterials prior to animal studies. Multicell type co-culture systems hold a great promise for the future.Many different types of bone substitute biomaterials are being developed for different applications in the body. The current dogma is that if osteoblasts and endothelial cells grow and exhibit normal cell functions on these materials in vitro as single cultures or in co-cultures, then the biomaterials are suitable for implantation for bone reconstruction and regeneration. Generally, only in vivo animal studies will prove whether this is the case. However, in vitro studies offer a good pre-screening and selection basis to evaluate the biocompatibility of novel biomaterials prior to animal studies. Multicell type co-culture systems hold a great promise for the future.

Tomographic and Topographic Investigation of Poly-D,L-Lactide-Co-Glycolide Microspheres Loaded with Prostaglandine E2 for Extended Drug Release Applications

Polymeric, biodegradable microspheres represent a good reliable system to investigate the release of bioactive substances in both in vitro and in vivo applications. Common biomaterials for the synthesis of these microspheres are aliphatic polyesters of the poly(α-hydroxy)acids, especially poly-L-lactides (PLA) and polyglycolides (PGA) or their copolymers poly-D,L-lactide-co-glycolides (PLGA). In our own previous studies we have developed PLGA microspheres with integrated PGE2 as model substance for a wide range of biomedical applications, especially in angiogenesis, fracture healing and cartilage repair. The synthesis is based on a binary solvent in water emulsion approach, where two different solvents are used to dissolve the active agent and the polymer, while being miscible in each other (CHCl3, ethyl acetate). Both, the degradation of the material and the release profiles were investigated using SEM and mass spectrometry coupled with gas- or high performance liquid chromatography. SEM and AFM measurements indicated a porous structure of the microspheres but could not resolve the true three dimensional structure of the microspheres. Therefore, synchrotron radiation-based µCT (SR-µCT) investigations were performed to link the release profile to the structural design of the microspheres. As a result, we were able to cross validate the experimental data from SEM and AFM with SR-µCT, demonstrating both micro-porosity and nano-porosity. The polymer itself appears to consist of 200 nm – 300 nm sized particles.

[In vitro trials with single and co-cultures of osteoblasts and endothelial cells : evaluation of new biomaterials for bone reconstruction and regeneration].

ZusammenfassungViele verschiedene Knochenersatzstoffe werden für klinische Anwendungen entwickelt. Laut geläufigem Dogma gelten diese Stoffe für die Rekonstruktion und Regeneration von Knochengewebe als geeignet, wenn Osteoblasten und Endothelzellen als Monokulturen oder Kokulturen auf ihnen wachsen und normale Zellfunktionen aufweisen. Jedoch werden auch Tierexperimente vorausgesetzt, um die klinische Eignung der Materialien zu bestätigen. Gute standardisierte In-vitro-Tests dienen also dazu, nur ausgewählte und vielversprechende Stoffe für Tierversuche zuzulassen. Vor allem Kokulturmodelle mit Beteiligung aller relevanter Zelltypen haben ein vielversprechendes Zukunftspotential.AbstractMany different types of bone substitute biomaterials are being developed for different applications in the body. The current dogma is that if osteoblasts and endothelial cells grow and exhibit normal cell functions on these materials in vitro as single cultures or in co-cultures, then the biomaterials are suitable for implantation for bone reconstruction and regeneration. Generally, only in vivo animal studies will prove whether this is the case. However, in vitro studies offer a good pre-screening and selection basis to evaluate the biocompatibility of novel biomaterials prior to animal studies. Multicell type co-culture systems hold a great promise for the future.Many different types of bone substitute biomaterials are being developed for different applications in the body. The current dogma is that if osteoblasts and endothelial cells grow and exhibit normal cell functions on these materials in vitro as single cultures or in co-cultures, then the biomaterials are suitable for implantation for bone reconstruction and regeneration. Generally, only in vivo animal studies will prove whether this is the case. However, in vitro studies offer a good pre-screening and selection basis to evaluate the biocompatibility of novel biomaterials prior to animal studies. Multicell type co-culture systems hold a great promise for the future.

Growth Factors and Signalling Molecules for Cartilage Tissue Engineering – from Embryology to Innovative Release Strategies for Guided Tissue Engineering

Modern Tissue Engineering represents a highly complex interdisciplinary branch of science which brings the life sciences and engineering together to design innovative solutions for the treatment of critical tissue defects after traumatic or degenerative damage. In this area an interesting evolution can be observed in the approach to achieve this goal: Originally understood as a principally biomaterial-based strategy using natural and synthetic materials as implants to be integrated into the neighbouring tissue, during the last two decades a change of paradigm has taken place which involves a movement away from the structural replacement of damaged tissue towards strategies to regenerate functional tissue (Kirkpatrick et al., 2006). In this approach cells play an important role, for example in seeding scaffold materials, which give a preformed structure for the regenerating tissue. A major aim is the synthesis of so-called tissue-like structures in vitro which can be implanted in the damaged tissue site and should be integrated into the body’s own tissue. Relevant obstacles to this strategy are the proper morphological integration of the cell-material construct in the structural context of the damaged tissue site as well as the maintenance of its function. The use of cells in combination with different biomaterials gives an important