Vitronectin promotes the vascularization of porous polyethylene biomaterials

Advances and Prospects in Materials for Craniofacial Bone Reconstruction

The craniofacial region is composed of 23 bones, which provide crucial function in keeping the normal position of brain and eyeballs, aesthetics of the craniofacial complex, facial movements, and visual function. Given the complex geometry and architecture, craniofacial bone defects not only affect the normal craniofacial structure but also may result in severe craniofacial dysfunction. Therefore, the exploration of rapid, precise, and effective reconstruction of craniofacial bone defects is urgent. Recently, developments in advanced bone tissue engineering bring new hope for the ideal reconstruction of the craniofacial bone defects. This report, presenting a first-time comprehensive review of recent advances of biomaterials in craniofacial bone tissue engineering, overviews the modification of traditional biomaterials and development of advanced biomaterials applying to craniofacial reconstruction. Challenges and perspectives of biomaterial development in craniofacial fields are discussed in the end.

Electrospun Fibrous Silica for Bone Tissue Engineering Applications

The production of highly porous and three-dimensional (3D) scaffolds with biomimicking abilities has gained extensive attention in recent years for tissue engineering (TE) applications. Considering the attractive and versatile biomedical functionality of silica (SiO₂) nanomaterials, we propose herein the development and validation of SiO₂-based 3D scaffolds for TE. This is the first report on the development of fibrous silica architectures, using tetraethyl orthosilicate (TEOS) and polyvinyl alcohol (PVA) during the self-assembly electrospinning (ES) processing (a layer of flat fibers must first be created in self-assembly electrospinning before fiber stacks can develop on the fiber mat). The compositional and microstructural characteristics of obtained fibrous materials were evaluated by complementary techniques, in both the pre-ES aging period and post-ES calcination. Then, in vivo evaluation confirmed their possible use as bioactive scaffolds in bone TE.

A Novel Window into Angiogenesis-Intravital Microscopy in the AV-Loop-Model

Due to the limitations of current in vivo experimental designs, our comprehensive knowledge of vascular development and its implications for the development of large-scale engineered tissue constructs is very limited. Therefore, the purpose of this study was to develop unique in vivo imaging chambers that allow the live visualization of cellular processes in the arteriovenous (AV) loop model in rats. We have developed two different types of chambers. Chamber A is installed in the skin using the purse sting fixing method, while chamber B is installed subcutaneously under the skin. Both chambers are filled with modified gelatin hydrogel as a matrix. Intravital microscopy (IVM) was performed after the injection of fluorescein isothiocyanate (FITC)-labeled dextran and rhodamine 6G dye. The AV loop was functional for two weeks in chamber A and allowed visualization of the leukocyte trafficking. In chamber B, microvascular development in the AV loop could be examined for 21 days. Quantification of the microvascular outgrowth was performed using Fiji-ImageJ. Overall, by combining these two IVM chambers, we can comprehensively understand vascular development in the AV loop tissue engineering model¯.

Developing a pro-angiogenic placenta derived amniochorionic scaffold with two exposed basement membranes as substrates for cultivating endothelial cells

Decellularized and de-epithelialized placenta membranes have widely been used as scaffolds and grafts in tissue engineering and regenerative medicine. Exceptional pro-angiogenic and biomechanical properties and low immunogenicity have made the amniochorionic membrane a unique substrate which provides an enriched niche for cellular growth. Herein, an optimized combination of enzymatic solutions (based on streptokinase) with mechanical scrapping is used to remove the amniotic epithelium and chorion trophoblastic layer, which resulted in exposing the basement membranes of both sides without their separation and subsequent damages to the in-between spongy layer. Biomechanical and biodegradability properties, endothelial proliferation capacity, and in vivo pro-angiogenic capabilities of the substrate were also evaluated. Histological staining, immunohistochemistry (IHC) staining for collagen IV, and scanning electron microscope demonstrated that the underlying amniotic and chorionic basement membranes remained intact while the epithelial and trophoblastic layers were entirely removed without considerable damage to basement membranes. The biomechanical evaluation showed that the scaffold is suturable. Proliferation assay, real-time polymerase chain reaction for endothelial adhesion molecules, and IHC demonstrated that both side basement membranes could support the growth of endothelial cells without altering endothelial characteristics. The dorsal skinfold chamber animal model indicated that both side basement membranes could promote angiogenesis. This bi-sided substrate with two exposed surfaces for cultivating various cells would have potential applications in the skin, cardiac, vascularized composite allografts, and microvascular tissue engineering.

Watching the Vessels Grow: Establishment of Intravital Microscopy in the Arteriovenous Loop Rat Model

Tissue engineering in reconstructive surgery seeks to generate bioartificial tissue substitutes. The arteriovenous (AV) loop allows the generation of axially vascularized tissue constructs. Cellular mechanisms of this vascularization process are largely unclear. In this study, we developed two different chamber models for intravital microscopy and imaging of the AV loop in the rat. Multiple design variations were implanted and the stability of the chamber and AV loop patency was tested in vivo. Our novel chamber facilitates repetitive observation of the AV loop using fluorescence-enhanced intravital microscopy. This technique can be used for daily evaluation of leukocyte-endothelial cell interactions, vascularization, and tissue formation in the AV loop model on 14 consecutive days. Therefore, our newly developed model for intravital microscopy will provide better understanding of cellular and molecular processes in tissue engineering in the AV loop. Moreover, it supports initiation of the novel approaches for therapeutic applications. Impact statement In the Arteriovenous (AV) loop, axially vascularized tissue can be generated and modified using different tissue engineering approaches. Cellular mechanisms of this vascularization process are largely unclear. We managed to develop an intravital microscopy model for long-term observation of intravascular and perivascular events in the AV loop. Leukocyte-endothelial cell interactions, vascularization, and tissue formation in the AV loop can now be evaluated on a day-to-day basis. This will provide better understanding of cellular and molecular processes happening during tissue engineering within the AV loop.

Actually Seeing What Is Going on - Intravital Microscopy in Tissue Engineering

Intravital microscopy (IVM) study approach offers several advantages over in vitro, ex vivo, and 3D models. IVM provides real-time imaging of cellular events, which provides us a comprehensive picture of dynamic processes. Rapid improvement in microscopy techniques has permitted deep tissue imaging at a higher resolution. Advances in fluorescence tagging methods enable tracking of specific cell types. Moreover, IVM can serve as an important tool to study different stages of tissue regeneration processes. Furthermore, the compatibility of different tissue engineered constructs can be analyzed. IVM is also a promising approach to investigate host reactions on implanted biomaterials. IVM can provide instant feedback for improvising tissue engineering strategies. In this review, we aim to provide an overview of the requirements and applications of different IVM approaches. First, we will discuss the history of IVM development, and then we will provide an overview of available optical modalities including the pros and cons. Later, we will summarize different fluorescence labeling methods. In the final section, we will discuss well-established chronic and acute IVM models for different organs.

TNF-α-Inhibition Improves the Biocompatibility of Porous Polyethylene Implants In Vivo

Background:

To improve the biocompatibility of porous polyethylene (PPE) implants and expand their application range for reconstructive surgery in poorly vascularized environments, implants were coated with tumor necrosis factor α (TNFα) inhibitor Etanercept. While approved for systemic application, local application of the drug is a novel experimental approach. Microvascular and mechanical integration as well as parameters of inflammation were analyzed in vivo.

Methods:

PPE implants were coated with Etanercept and extracellular matrix (ECM) components prior to implantation into dorsal skinfold chambers of C57BL/6 mice. Fluorescence microscopy analyses of angiogenesis and local inflammatory response were thrice performed in vivo over a period of 14 days to assess tissue integration and biocompatibility. Uncoated implants and ECM-coated implants served as controls.

Results:

TNFα inhibition with Etanercept led to a reduced local inflammatory response: leukocyte-endothelial cell adherence was significantly lowered compared to both control groups (n = 6/group) on days 3 and 14, where the lowest values were reached: 3573.88 leukocytes/mm-2 ± 880.16 (uncoated implants) vs. 3939.09 mm-2 ± 623.34 (Matrigel only) vs. 637.98 mm-2 + 176.85 (Matrigel and Etanercept). Implant-coating with Matrigel alone and Matrigel and Etanercept led to significantly higher vessel densities 7 and 14 days vs. 3 days after implantation and compared to uncoated implants. Mechanical implant integration as measured by dynamic breaking strength did not differ after 14 days.

Conclusion:

Our data show a reduced local inflammatory response to PPE implants after immunomodulatory coating with Etanercept in vivo, suggesting improved biocompatibility. Application of this tissue engineering approach is therefore warranted in models of a compromised host environment.

Electronic supplementary material

The online version of this article (10.1007/s13770-020-00325-w) contains supplementary material, which is available to authorized users.

Bioactive zinc-doped sol-gel coating modulates protein adsorption patterns and in vitro cell responses

Zinc is an essential element with an important role in stimulating the osteogenesis and mineralization and suppressing osteoclast differentiation. In this study, new bioactive ZnCl₂-doped sol-gel materials were designed to be applied as coatings onto titanium. The biomaterials were physicochemically characterized and the cellular responses evaluated in vitro using MC3T3-E1 osteoblasts and RAW264.7 macrophages. The effect of Zn on the adsorption of human serum proteins onto the material surface was evaluated through nLC-MS/MS. The incorporation of Zn did not affect the crosslinking of the sol-gel network. A controlled Zn²⁺ release was obtained, reaching values below 10 ppm after 21 days. The materials were no cytotoxic and lead to increased gene expression of ALP, TGF-β, and RUNX2 in the osteoblasts. In macrophages, an increase of IL-1β, TGF-β, and IL-4 gene expression was accompanied by a reduced TNF-α liberation. Proteomic results showed changes in the adsorption patterns of proteins associated with immunological, coagulative, and regenerative functions, in a Zn dose-dependent manner. The variations in protein adsorption might lead to the downregulation of the NF-κB pathway, thus explain the observed biological effects of Zn incorporation into biomaterials. Overall, these coatings demonstrated their potential to promote bone tissue regeneration.

Vascularization Strategies for Porous Polyethylene Implants

Porous polyethylene (pPE) is a frequently implanted biomaterial in craniofacial reconstructive surgery. Its rapid vascularization and tissue incorporation are major prerequisites to prevent complications, such as material infection, migration, and extrusion. To achieve this, several sophisticated strategies have been introduced and evaluated during the last 20 years. These include (i) the angiogenic stimulation of the host tissue with epidermal growth factor, basic fibroblast growth factor or macrophage-activating lipopeptide-2, (ii) material modifications, such as increase of surface roughness and incorporation of bioactive glass particles, (iii) surface coatings with growth factors, glycoproteins, acrylic acid, arginine/glycine/aspartic acid peptide as well as components of the plasminogen activation system and autologous clotted blood or serum, and (iv) the seeding with fibroblasts, chondrocytes, stem cells, or adipose-tissue-derived microvascular fragments. The majority of these approaches showed promising results in experimental studies and, thus, may be capable of improving the success rates after pPE implantation in future clinical practice.

Biological coating with platelet-rich plasma and adipose tissue-derived microvascular fragments improves the vascularization, biocompatibility and tissue incorporation of porous polyethylene

Porous polyethylene (pPE) is a commonly used biomaterial in craniofacial reconstructive surgery. However, implant failure due to insufficient vascularization represents a major issue. To overcome this problem, we herein introduce an effective strategy to improve the vascularization and incorporation of pPE. Adipose tissue-derived microvascular fragments (MVF) from transgenic green fluorescent protein (GFP)⁺ mice were suspended in platelet-rich plasma (PRP) for the coating of pPE. PRP/MVF-coated pPE as well as PRP-coated and uncoated controls were subsequently implanted into the dorsal skinfold chamber and the flanks of GFP^- wild-type mice to analyze their in vivo performance throughout 2, 4 and 8 weeks by means of intravital fluorescence microscopy, histology and immunohistochemistry. The GFP⁺/GFP^- cross-over design allowed the identification of GFP⁺ MVF within the implants. Shortly after implantation, they rapidly reassembled into new blood-perfused microvascular networks, resulting in a significantly accelerated vascularization of PRP/MVF-coated pPE when compared to both controls. The overall numbers of rolling and adherent leukocytes within the microcirculation as well as macrophages, multi-nucleated giant cells and mast cells around the implants did not differ between the three groups. However, in contrast to uncoated controls, PRP/MVF-coated and PRP-coated pPE promoted pro-angiogenic M2 macrophage polarization at the implantation site. These findings demonstrate that PRP/MVF-coating represents a highly effective strategy to enhance the vascularization, biocompatibility and tissue incorporation of pPE. STATEMENT OF SIGNIFICANCE: The clinical in vivo performance of implanted biomaterials is crucially dependent on their adequate incorporation into the body. To achieve this, we herein introduce an effective biological coating strategy. Our results demonstrate that coating with PRP and MVF accelerates and enhances the vascularization, biocompatibility and tissue incorporation of porous polyethylene. Because this type of biological coating is easily applicable on any type of biomaterial, our approach may rapidly be translated into clinical practice to improve the outcome of various regenerative approaches.

Extent of Inflammation and Foreign Body Reaction to Porous Polyethylene In Vitro and In Vivo

BACKGROUND/AIM

High-density porous polyethylene (PP) offers possibilities for reconstruction in craniofacial surgery. The purpose of this study was to evaluate the extent of inflammation and foreign body reactions to PP in vitro and in vivo.

MATERIALS AND METHODS

Cell attachment, proliferation and expression of inflammatory cytokines were assessed using murine macrophages (RAW 264.7) on two different PP materials in vitro. In vivo, Balb/c mice received PP implants at their dorsum. After sacrifice, samples were analyzed histologically and real-time PCR was used to assess expression of inflammatory cytokines.

RESULTS

Cells showed a significantly decreased proliferation (p<0.001) after 48 h and a significantly increased expression of TNF-α (p<0.05) at 24, 48 and 72 h. All animals showed foreign body cell reactions and signs of chronic inflammation. Expression of all but one of the investigated cytokines dropped to non-significant levels after an initial increase.

CONCLUSION

Application of porous polyethylene can cause local chronic inflammatory reactions. Although clinical application seems to be immunologically safe, indication and risks should be evaluated carefully when using PP implants.