Biodegradation of a magnesium alloy implant in the intercondylar femoral notch showed an appropriate response to the synovial membrane in a rabbit model in vivo

Degradable magnesium alloys are promising biomaterials for orthopedic applications. The aim of this study was to evaluate the potential effects on both the synovial membrane (synovialis) and the synovial fluid (synovia) of the degradation products of a MgYREZr-pin implanted in the intercondylar femoral notch in a rabbit model. Thirty-six animals were randomized into two groups (MgYREZr or Ti6Al4V alloy) of 18 animals each. Each group was then divided into three subgroups with implantation periods of 1, 4, and 12 weeks, with six animals in each subgroup. The initial inflammatory reaction caused by the surgical trauma declined after 12 weeks of implantation, and elucidated a progressive recovery of the synovial membrane. Compared with control Ti6Al4V pins, there were no significant differences between the groups. However, after 12 weeks, recovery of the synovial membrane was more advanced in the titanium group, in which 92% showed no signs of synovitis, than in the magnesium group. A cytotoxicity test with L929 cells and human osteoblasts (HOB) was also conducted, according to EN ISO 10993-5/12, and no toxic leachable products were observed after 24 h of incubation. In conclusion, the MgYREZr alloy seems to be a suitable material for intra-articular degradable implants. © The Author(s) 2014 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav

In situ optical coherence tomography of percutaneous implant-tissue interfaces in a murine model

Novel surface coatings of percutaneous implants need to be tested in biocompatibility studies. The use of animal models for testing usually involves numerous lethal biopsies for the analysis of the implant-tissue interface. In this study, optical coherence tomography (OCT) was used to monitor the reaction of the skin to a percutaneous implant in an animal model of hairless but immunocompetent mice. In vivo optical biopsies with OCT were taken at days 7 and 21 after implantation and post mortem on the day of noticeable inflammation. A Fourier-domain OCT was programmed for spoke pattern scanning schemes centered at the implant midpoint to reduce motion artifacts during in vivo imaging. Image segmentation allowed the automatic detection and morphometric analysis of the skin contour and the subcutaneous implant anchor. On the basis of the segmentation, the overall refractive index of the tissue within one OCT data set was estimated as a free parameter of a fitting algorithm, which corrects for the curved distortion of the planar implant base in the OCT images. OCT in combination with the spoke scanning scheme and image processing provided time-resolved three-dimensional optical biopsies around the implants to assess tissue morphology.DFGBMBF/TExoProNSF-ERC/Revolutionizing Metallic Biomaterial

Polycaprolactone-Based 3D-Printed Scaffolds as Potential Implant Materials for Tendon-Defect Repair

Chronic tendon ruptures are common disorders in orthopedics. The conventional surgical methods used to treat them often require the support of implants. Due to the non-availability of suitable materials, 3D-printed polycaprolactone (PCL) scaffolds were designed from two different starting materials as suitable candidates for tendon-implant applications. For the characterization, mechanical testing was performed. To increase their biocompatibility, the PCL-scaffolds were plasma-treated and coated with fibronectin and collagen I. Cytocompatibility testing was performed using L929 mouse fibroblasts and human-bone-marrow-derived mesenchymal stem cells. The mechanical testing showed that the design adaptions enhanced the mechanical stability. Cell attachment was increased in the plasma-treated specimens compared to the control specimens, although not significantly, in the viability tests. Coating with fibronectin significantly increased the cellular viability compared to the untreated controls. Collagen I treatment showed an increasing trend. The desired cell alignment and spread between the pores of the construct was most prominent on the collagen-I-coated specimens. In conclusion, 3D-printed scaffolds are possible candidates for the development of tendon implants. Enhanced cytocompatibility was achieved through surface modifications. Although adaptions in mechanical strength still require alterations in order to be applied to human-tendon ruptures, we are optimistic that a suitable implant can be designed

Vascularization and biocompatibility of poly(ε-caprolactone) fiber mats for rotator cuff tear repair

Rotator cuff tear is the most frequent tendon injury in the adult population. Despite current improvements in surgical techniques and the development of grafts, failure rates following tendon reconstruction remain high. New therapies, which aim to restore the topology and functionality of the interface between muscle, tendon and bone, are essentially required. One of the key factors for a successful incorporation of tissue engineered constructs is a rapid ingrowth of cells and tissues, which is dependent on a fast vascularization. The dorsal skinfold chamber model in female BALB/cJZtm mice allows the observation of microhemodynamic parameters in repeated measurements in vivo and therefore the description of the vascularization of different implant materials. In order to promote vascularization of implant material, we compared a porous polymer patch (a commercially available porous polyurethane based scaffold from Biomerix™) with electrospun polycaprolactone (PCL) fiber mats and chitosan-graft-PCL coated electrospun PCL (CS-g-PCL) fiber mats in vivo. Using intravital fluorescence microscopy microcirculatory parameters were analyzed repetitively over 14 days. Vascularization was significantly increased in CS-g-PCL fiber mats at day 14 compared to the porous polymer patch and uncoated PCL fiber mats. Furthermore CS-g-PCL fiber mats showed also a reduced activation of immune cells. Clinically, these are important findings as they indicate that the CS-g-PCL improves the formation of vascularized tissue and the ingrowth of cells into electrospun PCL scaffolds. Especially the combination of enhanced vascularization and the reduction in immune cell activation at the later time points of our study points to an improved clinical outcome after rotator cuff tear repair. © 2020 Gniesmer et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited

In vivo analysis of vascularization and biocompatibility of electrospun polycaprolactone fibre mats in the rat femur chamber

In orthopaedic medicine, connective tissues are often affected by traumatic or degenerative injuries, and surgical intervention is required. Rotator cuff tears are a common cause of shoulder pain and disability among adults. The development of graft materials for bridging the gap between tendon and bone after chronic rotator cuff tears is essentially required. The limiting factor for the clinical success of a tissue engineering construct is a fast and complete vascularization of the construct. Otherwise, immigrating cells are not able to survive for a longer period of time, resulting in the failure of the graft material. The femur chamber allows the observation of microhaemodynamic parameters inside implants located in close vicinity to the femur in repeated measurements in vivo. We compared a porous polymer patch (a commercially available porous polyurethane-based scaffold from Biomerix™) with electrospun polycaprolactone (PCL) fibre mats and chitosan (CS)-graft-PCL modified electrospun PCL (CS-g-PCL) fibre mats in vivo. By means of intravital fluorescence microscopy, microhaemodynamic parameters were analysed repetitively over 20 days at intervals of 3 to 4 days. CS-g-PCL modified fibre mats showed a significantly increased vascularization at Day 10 compared with Day 6 and at Day 14 compared with the porous polymer patch and the unmodified PCL fibre mats at the same day. These results could be verified by histology. In conclusion, a clear improvement in terms of vascularization and biocompatibility is achieved by graft-copolymer modification compared with the unmodified material. © 2019 The Authors Journal of Tissue Engineering and Regenerative Medicine Published by John Wiley & Sons Lt

Muller glia cells and their possible roles during retina differentiation in vivo and in vitro

Muller cells are astrocyte-like radial glia cells which are formed exclusively in the retina. Here we present evidence that Muller cells are crucially involved in the development of the retina's architecture and circuitry. There is increasing evidence that Muller cells are present from the very early beginning of retinogenesis. We postulate the "gradual maturation hypothesis of Muller cells". According to this hypothesis, Miiller cells are continuously generated by a gradual transition of neuroepithelial stem cells into mature Muller cells. This process may be partly reversible. Muller cells, or their immature precursors, are able to subserve different functions. They are primary candidates for stabilizing the complex retina1 architecture and for providing an orientation scaffold. Thereby, they introduce a reference system for the migration and correct allocation of neurons. Moreover, they may provide spatial information and microenvironmental cues for differentiating neurons, and may also be important for the segregation of cell and fibre layers. Additionally, they seem to be involved in the guidance of axonal fibres both in radial and in lateral directions, as they are involved in the support and stabilization of synapses

A Hidden Retinal Regenerative Capacity from the Chick Ciliary Margin is Reactivated In Vitro, that is Accompanied by Down-regulation of Butyrylcholinesterase.

The chicken retina has a capacity to regenerate in vivo, which is restricted up to embryonic day 4 (E4). Here we test the proliferative patterns of dissociated chicken cells from the centre retina or the ciliary margin, including pigmented cells, after their transfer into rotation culture. For central cells in culture, the uptake of [3H]thymidine after a short initial rise decreases similarly to their in ovo counterparts. In contrast, marginal cells that have been shown to regenerate up to E9 into retinotypic stratospheroids re-enter a novel and long-lasting phase of in vitro cell division. We have shown previously that cell types of all nuclear layers are produced. Both observations taken together indicate a pronounced self-renewal of multipotent stem cells. Molecularly, the enzyme butyrylcholinesterase, which in other systems has been shown to mark transitory neuronal cells between proliferation and differentiation, is strongly expressed at the ciliary margin over most of the embryonic period. After these cells are transferred into rotation culture, butyrylcholinesterase is down-regulated. Concomitantly, the neuronal differentiation marker acetylcholinesterase increases. We conclude that the regenerative capacity of the chick retina is not lost at E4, but rather remains hidden in the chicken ciliary margin, since it can be reactivated in vitro at least up to E9. We suggest that butyrylcholinesterase may be linked to the regulation of stem cell activity

Lateral and radial growth uncoupled in reaggregated retinospheroids of embryonic avian retina

According to an earlier resented model (Layer and Willbold, Int. Rev. Cytol. 146: 1-47, 1993), growth of the retina can be conceived of as an areal increase of an epithelial tissue sheet ("lateralization") plus a concomitant establishment of the layered retina ("radialization"). To provide further support for this model, here we have reaggregated dissociated retinal plus pigmented cells from chick or quail embryos and observed their development into histotypic three-dimensional spheres in rotation culture. These so-called stratospheroids consist of a continuous fully laminated retinal part with a coiled-up pigmented epithelial core. Using BrdU-labeling, we show that radial growth, i.e. the sequential production of cell types in spheroids, is comparable to normal vitreal-scleral retinogenesis. The region next to the pigmented epithelial core represents a "lateral growth zone" (equivalent to an ora serrata in vivo), where mitotic cell numbers are highest, even when in the laminated part proliferation has already ceased. Gradients of lateral differentiation emanate from this growth zone into the retinal tissue, as revealed by immunostaining of the photoreceptor protein opsin and the cell recognition molecule F11. Moreover, we found that stratospheroids derived from older embryos consist only of a hollow monolayered neuroepithelium which develops in the absence of any radial growth. This indicates that cell production is sustained longer in lateral than in radial direction. These differently staged stratospheroids will be excellent models to characterize genes involved in the regulation of lateral and radial growth processes