Tissue engineering solutions for traumatic bone loss

Soft tissue grafts for dural reconstruction after meningioma surgery

The meninges are involved in various pathologies and are often directly or indirectly severed during surgical procedures, especially the dura mater. This can pose a real challenge for the surgeon, as a proper reconstruction of the meninges is important to prevent complications such as cerebrospinal fluid leak (CSF). A variety of techniques for dural reconstruction have been described, employing natural and artificial materials. A novel technique for dural reconstruction involves soft tissue grafts in the form of fibrous or fibromuscular flaps, which are placed on the dural defects to seal the gaps. These soft tissue grafts represent an appropriate scaffold for cell ingrowth and fibrosis, thus preventing CSF. In this pilot study, we described the application of soft tissue grafts for dural reconstruction in 10 patients who underwent convexity meningioma surgery.

Tissue Augmentation in Wound Healing: the Role of Endothelial and Epithelial Cells

Introduction

Wounds and their complications present a frequent cause of morbidity and mortality in everyday clinical practice. In order to reduce the wound burden, much effort has been directed into the physiology of healing and new therapeutic approaches.

Aim

This paper provides an overview from the literature about the role of endothelial and epithelial cells in tissue filler employment for wound healing.

Material and Methods

The scientific literature was reviewed through PubMed, Medline and Science Direct. The articles were chosen in correlation with the study objective and their scientific relevance.

Results

Successful wound healing depends on many diverse processes, cell types and molecular mediators. The definitive aim of wound healing is a properly healed wound. Tissue fillers are becoming an important alternative in wound management, although augmentation of soft tissue can present a demanding problem due to the difficulties in tissue survival. In order to prevent its failure, an optimal vascular network needs to form from wound edges into the filler.

Conclusions

Because of the importance of chemotaxis and angiogenesis in various physiological and pathological processes, both events present an extensive area of intense research. Additionally, epithelial cells are needed to cover the wound defect and sealing the wound environment from outer world.

[Evaluation of interest in research among surgically active medical officers in the German Armed Forces]

BACKGROUND

Research in military medicine and in particular combat surgery is a broad field that has gained international importance during the last decade. In the context of increased NATO missions, this also holds true for the Bundeswehr (German Armed Forces); however, medical officers in surgery must balance research between their clinical work load, missions, civilian and family obligation.

MATERIAL AND METHODS

To evaluate engagement with and interest in research, a questionnaire was distributed among the doctors of the surgical departments of the Bundeswehr hospitals by the newly founded working group Chirurgische Forschung der Bundeswehr (surgical research of the Bundeswehr). Returned data were recorded from October 2013 to January 2014 and descriptive statistics were performed.

RESULTS

Answers were received from 87 out of 193 military surgeons (45 %). Of these 81 % announced a general interest in research with a predominance on clinical research in preference to experimental settings. At the time of the evaluation 32 % of the participants were actively involved in research and 53 % regarded it as difficult to invest time in research activities parallel to clinical work. Potential keys to increase the interest and engagement in research were seen in the implementation of research coordinators and also in a higher amount of free time, for example by research rotation.

CONCLUSION

Research can be regarded as having a firm place in the daily work of medical officers in the surgical departments of the Bundeswehr; however, the engagement is limited by time and structural factors. At the departmental level and in the command structures of the military medical service, more efforts are recommended in the future in order to enhance the engagement with surgical research. This evaluation should be repeated in the coming years as a measuring instrument and data should be compared in an international context.

Effect of VEGF-A165 addition on the integration of a cortical allograft in a tibial segmental defect in rabbits

PURPOSE

Long-bone segmental defects caused by infection, fracture, or tumour are a challenge for orthopaedic surgeons. Structural allografts are sometimes used in their treatment but their poor biological characteristics are a liability. The objective of this study was to determine whether the addition of recombinant vascular endothelial growth factor-A (VEGF) to a structural allograft improved its integration into a rabbit tibial segmental defect in a non-union model.

METHODS

Tibial segmental defects were filled with heat sterilized allogenic tubular tibiae sections and then stabilized with a screw plate. In the VEGF treatment group (n = 6 tibiae), 2 μg of VEGF added to a 50 μl matrigel solution was inserted into the allograft cavity. In the control group (n = 6 tibiae), only matrigel was added. After 12 weeks, macroscopic and microscopic analysis, radiographs, and computerized micro-tomography (micro-CT) were performed. If allograft consolidation was present, a torsional resistance analysis was performed.

RESULTS

Addition of VEGF to the allograft decreased the rate of osteosynthesis failure compared with the control group (1/6 vs. 5/6, p = 0.08), increased trabecular continuity evaluated by micro-CT in the bone-allograft interphases (8/12 vs. 2/12, p = 0.036) and histological trabecular continuity (7/12 vs. 0/12, p = 0.0046). Full consolidation was observed in three tibiae of the VEGF group and one in the control group (differences not significant); however, torsional resistance showed no significant differences (n.s.).

CONCLUSION

Addition of VEGF to a structural allograph inserted into a rabbit tibial segmental defect increased allograft integration rate. Further research in this direction might help clinicians in dealing with large bone defects.

Is tissue augmentation a reality in biosurgery? An experimental study of endothelial cell invasion into tissue filler

New therapeutic approaches for wound treatment are evolving. Non healing wounds in oncology and after trauma may be cured by a novel technique of tissue augmentation with soft tissue fillers. The principle resides in filling the wound with collagen filler in order to seal the defect and promote healing. Successful angiogenesis forms the basis of tissue filler survival and determines the outcome of the healing process. During this study, basic data about endothelial cell invasion into collagen-made substratum was collected that could be used for neoangiogenesis studies in tissue augmentation techniques for large wound defect treatment. In the in vitro assay, the human umbilical vein endothelial cells (HUVEC) grow into a three-dimensional framework of collagenous tissue fillers, forming the basic step for angiogenesis. After heparins were used as chemotactic agents, a typical bell-shaped relationship between chemotaxis and agent concentrations was found. Significant cell infiltration was present in the assays with chemotactic agents. These observations support the potential for tissue augmentation with soft tissue fillers that could be used in acute and chronic non healing traumatic and oncology wounds after extensive surgical resections and radiotherapy.

The effect of intramedullary reaming on a diaphyseal bone defect of the tibia

BACKGROUND

The effect of intramedullary reaming on diaphyseal tibial defects has not been examined in the literature. The present aim was to relate the extent of reaming to angiogenesis and bone formation occurring around a critical-sized defect in the tibia for two scenarios, namely, when the bone defect is left empty and when the bone defect is treated with autograft.

METHODS

Eleven canines were allocated into two groups, namely, empty (n=5) or iliac crest autograft (n=6). All tibiae were reamed to 7.0 mm and fixed with a 6.5-mm statically locked intramedullary nail after creation of an 8.0-mm diaphyseal defect. The extent of reaming of the canal was dependent on the cross-sectional area of the tibia, because all tibiae were reamed to 7.0 mm. Fluorescent markers were administered at different times: calcein green (6 weeks), xylenol orange (9 weeks), and tetracycline (11 weeks and 14 weeks). Animals were sacrificed at 15 weeks and perfused with a barium compound. Analysis consisted of radiography, micro-computed tomography scan, and histology.

RESULTS

Linear regression analysis of percent bone volume and canal area provided a Pearson correlation coefficient of r=0.925 (p=0.025) for empty samples and r=0.244 (p=0.641) for autograft samples. Linear regression analysis of percent vasculature volume and canal area provided a Pearson correlation coefficient of r=0.784 (p=0.117) for empty samples and r=-0.146 (p=0.783) for autograft samples. Bone formation rates were reported as the distance between the fluorescent labels and were less within the endosteum, cortex, and periosteum, with extensive reaming in empty samples.

CONCLUSIONS

The results suggest that limited reaming may be beneficial to the acute management of tibial shaft fractures with a bone defect.

Mesenchymal stem cell function on hybrid organic/inorganic microparticles in vitro

The aim of this study was to investigate mesenchymal stem cell (MSC) function on novel type hybrid organic/inorganic microparticles (MPs) for application to bone regeneration. The MPs were based on chitosan (CS) and consisted of inorganic components, such as dibasic calcium phosphate (CaHPO(4)) or calcium carbonate (CaCO(3)). The MPs were crosslinked using tripolyphosphate. Four types of hybrid MPs were fabricated: CS; CS-10% CaHPO(4); CS-20% CaHPO(4); and CS-10% CaCO(3). The MSCs were attached to all the types of MPs at day 1 and started to spread and proliferate further by days 2 and 7, as analysed by fluorescence microcopy. Cell proliferation was measured at days 7, 14, 21 and 28 by counting the cells attached on the MPs. The number of proliferated cells increased significantly for all types of MPs as time increased. MSC differentiation was analysed using osteoblast (OB) phenotype markers, including alkaline phosphatase activity (ALP), collagen I (COLLI) and osteocalcin (OCN) at days 7, 14, 21 and 28, using quantitative real-time PCR. The normalized mRNA expression of ALP for all MPs was observed only at day 7. The normalized mRNA expression of COLLI and OCN was significantly increased for all types of hybrid MPs at each time point compared to the control samples. Collectively, our results proved that hybrid organic/inorganic MPs were non-cytotoxic and supported MSC attachment, spreading, proliferation and differentiation into the OB phenotype. These hybrid MPs have great potential for application as bone-void fillers or bone tissue engineering scaffolds in bone regeneration.

The epigenetic mechanism of mechanically induced osteogenic differentiation

Epigenetic regulation of gene expression occurs due to alterations in chromatin proteins that do not change DNA sequence, but alter the chromatin architecture and the accessibility of genes, resulting in changes to gene expression that are preserved during cell division. Through this process genes are switched on or off in a more durable fashion than other transient mechanisms of gene regulation, such as transcription factors. Thus, epigenetics is central to cellular differentiation and stem cell linage commitment. One such mechanism is DNA methylation, which is associated with gene silencing and is involved in a cell's progression towards a specific fate. Mechanical signals are a crucial regulator of stem cell behavior and important in tissue differentiation; however, there has been no demonstration of a mechanism whereby mechanics can affect gene regulation at the epigenetic level. In this study, we identified candidate DNA methylation sites in the promoter regions of three osteogenic genes from bone marrow derived mesenchymal stem cells (MSCs). We demonstrate that mechanical stimulation alters their epigenetic state by reducing DNA methylation and show an associated increase in expression. We contrast these results with biochemically induced differentiation and distinguish expression changes associated with durable epigenetic regulation from those likely to be due to transient changes in regulation. This is an important advance in stem cell mechanobiology as it is the first demonstration of a mechanism by which the mechanical micro-environment is able to induce epigenetic changes that control osteogenic cell fate, and that can be passed to daughter cells. This is a first step to understanding that will be vital to successful bone tissue engineering and regenerative medicine, where continued expression of a desired long-term phenotype is crucial.

A biodegradable scaffold for the treatment of a diaphyseal bone defect of the tibia

The aim of this study was to compare angiogenesis and osteogenesis occurring within 8.0 mm diaphyseal defects created in canine tibiae treated using autograft or a biodegradable bone scaffold. All tibiae were reamed to 7.0 mm and fixed with a 6.5-mm statically locked intramedullary nail. Each of the 18 canines as allotted to one of three treatment groups: (1) left empty (N = 5), (2) treated with iliac crest autograft (N = 6), or (3) treated with a PLGA/calcium phosphate biodegradable scaffold (N = 7). Fluorescent markers were given at successive time periods: calcein green at 6 weeks, xylenol orange at 9 weeks, and tetracycline at 11 and 14 weeks. Animals were sacrificed at 15 weeks and their legs were perfused with a radio opaque compound. Samples were analyzed using Micro CT, bright-field microscopy and fluorescent microscopy. Scaffold samples were found to have significantly greater bone formation (p = 0.015) and blood vessel formation (p < 0.001) at their osteotomy sites than autograft samples. Bone formation rate in the periosteum was significantly greater in the autograft samples than the scaffold samples for all time periods. Bone formation at the osteotomy site was found to be significantly greater when associated with greater blood vessel formation (p = 0.026). The PLGA/calcium phosphate biodegradable scaffold we have employed supports angiogenesis within a segmental tibial defect that has adequate soft tissue coverage.