Publications by authors named "Birgit Glasmacher"

61 Publications

Coaxial Alginate Hydrogels: From Self-Assembled 3D Cellular Constructs to Long-Term Storage.

Int J Mol Sci 2021 Mar 18;22(6). Epub 2021 Mar 18.

Institute for Multiphase Processes, Leibniz University Hannover, An der Universität 1, Building 8143, 30823 Garbsen, Germany.

Alginate as a versatile naturally occurring biomaterial has found widespread use in the biomedical field due to its unique features such as biocompatibility and biodegradability. The ability of its semipermeable hydrogels to provide a favourable microenvironment for clinically relevant cells made alginate encapsulation a leading technology for immunoisolation, 3D culture, cryopreservation as well as cell and drug delivery. The aim of this work is the evaluation of structural properties and swelling behaviour of the core-shell capsules for the encapsulation of multipotent stromal cells (MSCs), their 3D culture and cryopreservation using slow freezing. The cells were encapsulated in core-shell capsules using coaxial electrospraying, cultured for 35 days and cryopreserved. Cell viability, metabolic activity and cell-cell interactions were analysed. Cryopreservation of MSCs-laden core-shell capsules was performed according to parameters pre-selected on cell-free capsules. The results suggest that core-shell capsules produced from the low viscosity high-G alginate are superior to high-M ones in terms of stability during in vitro culture, as well as to solid beads in terms of promoting formation of viable self-assembled cellular structures and maintenance of MSCs functionality on a long-term basis. The application of 0.3 M sucrose demonstrated a beneficial effect on the integrity of capsules and viability of formed 3D cell assemblies, as compared to 10% dimethyl sulfoxide (DMSO) alone. The proposed workflow from the preparation of core-shell capsules with self-assembled cellular structures to the cryopreservation appears to be a promising strategy for their off-the-shelf availability.
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http://dx.doi.org/10.3390/ijms22063096DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8003018PMC
March 2021

Electrospun PCL/PLA Scaffolds Are More Suitable Carriers of Placental Mesenchymal Stromal Cells Than Collagen/Elastin Scaffolds and Prevent Wound Contraction in a Mouse Model of Wound Healing.

Front Bioeng Biotechnol 2020 16;8:604123. Epub 2020 Dec 16.

Division of Cell Biology, Histology and Embryology, Gottfried Schatz Research Center, Medical University of Graz, Graz, Austria.

Mesenchymal stem/stromal cells (MSCs) exert beneficial effects during wound healing, and cell-seeded scaffolds are a promising method of application. Here, we compared the suitability of a clinically used collagen/elastin scaffold (Matriderm) with an electrospun Poly(ε-caprolactone)/poly(l-lactide) (PCL/PLA) scaffold as carriers for human amnion-derived MSCs (hAMSCs). We created an epidermal-like PCL/PLA scaffold and evaluated its microstructural, mechanical, and functional properties. Sequential spinning of different PCL/PLA concentrations resulted in a wide-meshed layer designed for cell-seeding and a dense-meshed layer for apical protection. The Matriderm and PCL/PLA scaffolds then were seeded with hAMSCs, with or without Matrigel coating. The quantity and quality of the adherent cells were evaluated . The results showed that hAMSCs adhered to and infiltrated both scaffold types but on day 3, more cells were observed on PCL/PLA than on Matriderm. Apoptosis and proliferation rates were similar for all carriers except the coated Matriderm, where apoptotic cells were significantly enhanced. On day 8, the number of cells decreased on all carrier types except the coated Matriderm, which had consistently low cell numbers. Uncoated Matriderm had the highest percentage of proliferative cells and lowest apoptosis rate of all carrier types. Each carrier also was topically applied to skin wound sites in a mouse model and analyzed over 14 days via optical imaging and histological methods, which showed detectable hAMSCs on all carrier types on day 8. On day 14, all wounds exhibited newly formed epidermis, and all carriers were well-integrated into the underlying dermis and showing signs of degradation. However, only wounds treated with uncoated PCL/PLA maintained a round appearance with minimal contraction. Overall, the results support a 3-day culture of scaffolds with hAMSCs before wound application. The PCL/PLA scaffold showed higher cell adherence than Matriderm, and the effect of the Matrigel coating was negligible, as all carrier types maintained sufficient numbers of transplanted cells in the wound area. The anti-contractive effects of the PCL/PLA scaffold offer potential new therapeutic approaches to wound care.
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http://dx.doi.org/10.3389/fbioe.2020.604123DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7793771PMC
December 2020

Human Amniotic Membrane: A review on tissue engineering, application, and storage.

J Biomed Mater Res B Appl Biomater 2020 Dec 14. Epub 2020 Dec 14.

Institute for Multiphase Processes, Leibniz University Hannover, Garbsen, Germany.

Human amniotic membrane (hAM) has been employed as scaffolding material in a wide range of tissue engineering applications, especially as a skin dressing and as a graft for corneal treatment, due to the structure of the extracellular matrix and excellent biological properties that enhance both wound healing and tissue regeneration. This review highlights recent work and current knowledge on the application of native hAM, and/or production of hAM-based tissue-engineered products to create scaffolds mimicking the structure of the native membrane to enhance the hAM performance. Moreover, an overview is presented on the available (cryo) preservation techniques for storage of native hAM and tissue-engineered products that are necessary to maintain biological functions such as angiogenesis, anti-inflammation, antifibrotic and antibacterial activity.
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http://dx.doi.org/10.1002/jbm.b.34782DOI Listing
December 2020

Impact of Apparatus Orientation and Gravity in Electrospinning-A Review of Empirical Evidence.

Polymers (Basel) 2020 Oct 22;12(11). Epub 2020 Oct 22.

Institute for Multiphase Processes (IMP), Leibniz University Hannover, 30823 Garbsen, Hannover, Germany.

Electrospinning is a versatile fibre fabrication method with applications from textile to tissue engineering. Despite the appearance that the influencing parameters of electrospinning are fully understood, the effect of setup orientation has not been thoroughly investigated. With current burgeoning interest in modified and specialised electrospinning apparatus, it is timely to review the impact of this seldom-considered parameter. Apparatus configuration plays a major role in the morphology of the final product. The primary difference between spinning setups is the degree to which the electrical force and gravitational force contribute. Since gravity is much lower in magnitude when compared with the electrostatic force, it is thought to have no significant effect on the spinning process. But the shape of the Taylor cone, jet trajectory, fibre diameter, fibre diameter distribution, and overall spinning efficiency are all influenced by it. In this review paper, we discuss all these developments and more. Furthermore, because many research groups build their own electrospinning apparatus, it would be prudent to consider this aspect as particular orientations are more suitable for certain applications.
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http://dx.doi.org/10.3390/polym12112448DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7690589PMC
October 2020

Mueller Matrix Analysis of Collagen and Gelatin Containing Samples Towards More Objective Skin Tissue Diagnostics.

Polymers (Basel) 2020 Jun 22;12(6). Epub 2020 Jun 22.

Institute for Multiphase Processes (IMP), Leibniz University Hannover, 30167 Hannover, Germany.

Electrospun polycaprolactone:gelatin (PCL:GT) fibre scaffolds are widely employed in the field of tissue implants. Here, the orientation of fibres plays an important role in regard to implantation due to the impact on the mechanical properties. Likewise, the orientation of collagen fibres in skin tissue is relevant for dermatology. State-of-the-art fibre orientation measurement methods like electron microscopy are time consuming and destructive. In this work, we demonstrate polarimetry as a non-invasive approach and evaluate its potential by measuring the Mueller matrix (MM) of gelatin and collagen containing samples as simple skin tissue phantoms. We demonstrate that it is possible to determine the orientation of PCL:GT fibre scaffolds within one MM measurement. Furthermore, we determine the structural orientation in collagen film samples. Currently, the diagnosis of skin diseases is often performed by image analysis or histopathology respectively, which are either subjective or invasive. The method presented, here, provides an interesting alternative approach for such investigations. Our findings indicate that the orientation of collagen fibres within skin lesions might be detectable by MM measurements in the future, which is of interest for skin diagnostics, and will be further investigated during the next step.
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http://dx.doi.org/10.3390/polym12061400DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7361993PMC
June 2020

Repeated Freezing Procedures Preserve Structural and Functional Properties of Amniotic Membrane for Application in Ophthalmology.

Int J Mol Sci 2020 Jun 4;21(11). Epub 2020 Jun 4.

Institute of Transfusion Medicine and Transplant Engineering, Hannover Medical School, 30625 Hannover, Germany.

For decades, the unique regenerative properties of the human amniotic membrane (hAM) have been successfully utilized in ophthalmology. As a directly applied biomaterial, the hAM should be available in a ready to use manner in clinical settings. However, an extended period of time is obligatory for performing quality and safety tests. Hence, the low temperature storage of the hAM is a virtually inevitable step in the chain from donor retrieval to patient application. At the same time, the impact of subzero temperatures carries an increased risk of irreversible alterations of the structure and composition of biological objects. In the present study, we performed a comprehensive analysis of the hAM as a medicinal product; this is intended for a novel strategy of application in ophthalmology requiring a GMP production protocol including double freezing-thawing cycles. We compared clinically relevant parameters, such as levels of growth factors and extracellular matrix proteins content, morphology, ultrastructure and mechanical properties, before and after one and two freezing cycles. It was found that epidermal growth factor (EGF), transforming growth factor beta 1 (TGF-β1), hepatocyte growth factor (HGF), basic fibroblast growth factor (bFGF), hyaluronic acid, and laminin could be detected in all studied conditions without significant differences. Additionally, histological and ultrastructure analysis, as well as transparency and mechanical tests, demonstrated that properties of the hAM required to support therapeutic efficacy in ophthalmology are not impaired by dual freezing.
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http://dx.doi.org/10.3390/ijms21114029DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7312941PMC
June 2020

Effect of 'in air' freezing on post-thaw recovery of Callithrix jacchus mesenchymal stromal cells and properties of 3D collagen-hydroxyapatite scaffolds.

Cryobiology 2020 02 20;92:215-230. Epub 2020 Jan 20.

Institute for Multiphase Processes, Leibniz University Hannover, Hannover, Germany.

Through enabling an efficient supply of cells and tissues in the health sector on demand, cryopreservation is increasingly becoming one of the mainstream technologies in rapid translation and commercialization of regenerative medicine research. Cryopreservation of tissue-engineered constructs (TECs) is an emerging trend that requires the development of practically competitive biobanking technologies. In our previous studies, we demonstrated that conventional slow-freezing using dimethyl sulfoxide (MeSO) does not provide sufficient protection of mesenchymal stromal cells (MSCs) frozen in 3D collagen-hydroxyapatite scaffolds. After simple modifications to a cryopreservation protocol, we report on significantly improved cryopreservation of TECs. Porous 3D scaffolds were fabricated using freeze-drying of a mineralized collagen suspension and following chemical crosslinking. Amnion-derived MSCs from common marmoset monkey Callithrix jacchus were seeded onto scaffolds in static conditions. Cell-seeded scaffolds were subjected to 24 h pre-treatment with 100 mM sucrose and slow freezing in 10% MeSO/20% FBS alone or supplemented with 300 mM sucrose. Scaffolds were frozen 'in air' and thawed using a two-step procedure. Diverse analytical methods were used for the interpretation of cryopreservation outcome for both cell-seeded and cell-free scaffolds. In both groups, cells exhibited their typical shape and well-preserved cell-cell and cell-matrix contacts after thawing. Moreover, viability test 24 h post-thaw demonstrated that application of sucrose in the cryoprotective solution preserves a significantly greater portion of sucrose-pretreated cells (more than 80%) in comparison to MeSO alone (60%). No differences in overall protein structure and porosity of frozen scaffolds were revealed whereas their compressive stress was lower than in the control group. In conclusion, this approach holds promise for the cryopreservation of 'ready-to-use' TECs.
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http://dx.doi.org/10.1016/j.cryobiol.2020.01.015DOI Listing
February 2020

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

PLoS One 2020 13;15(1):e0227563. Epub 2020 Jan 13.

Department of Oral and Maxillofacial Surgery, Hannover Medical School, Hannover, Germany.

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.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0227563PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6957163PMC
April 2020

Mueller Matrix Measurement of Electrospun Fiber Scaffolds for Tissue Engineering.

Polymers (Basel) 2019 Dec 11;11(12). Epub 2019 Dec 11.

Hannover Centre for Optical Technologies (HOT), Leibniz University Hannover, 30167 Hannover, Germany.

Electrospun fiber scaffolds are gaining in importance in the area of tissue engineering. They can be used, for example, to fabricate graded implants to mimic the tendon bone junction. For the grading of the tensile strength of the fiber scaffolds, the orientation of the fibers plays a major role. This is currently measured by hand in scanning electron microscope (SEM) images. In this work, a correlation between polarimetric information generated by measuring the Mueller matrix (MM) and the orientation of the fibers of electrospun fiber scaffolds is reported. For this, the MM of fiber scaffolds, which were manufactured with different production parameters, was measured and analyzed. These data were correlated with fiber orientation and mechanical properties, which were evaluated in an established manner. We found that by measurement of the MM the production parameters as well as the relative orientation of the fibers in space can be determined. Thus, the MM measurement is suitable as an alternative tool for non-contact, non-destructive determination of the production parameters and, thus, the degree of alignment of electrospun fiber scaffolds.
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http://dx.doi.org/10.3390/polym11122062DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6960730PMC
December 2019

Possibilities and limitations of electrospun chitosan-coated polycaprolactone grafts for rotator cuff tear repair.

J Tissue Eng Regen Med 2020 01 10;14(1):186-197. Epub 2019 Nov 10.

Laboratory for Biomechanics and Biomaterials, Department of Orthopaedic Surgery, Hannover Medical School, Hannover, Germany.

Acute and chronic rotator cuff tears remain challenging for therapy. A wide range of therapeutic approaches were developed but re-tears and postoperative complications occur regularly. Especially in elderly people, the natural regeneration processes are decelerated, and graft materials are often necessary to stabilize the tendon-to-bone attachment and to improve the healing process. We here investigated in a small animal model a newly developed electrospun polycaprolactone fiber implant coated with a chitosan-polycaprolactone graft copolymer and compared these implants biomechanically and histologically with either a commercially available porous polyurethane implant (Biomerix 3D Scaffold) or suture-fixed tendons. Fifty-one rats were divided into three groups of 17 animals each. In the first surgery, the left infraspinatus tendons of all rats were detached, and the animals recovered for 4 weeks. In the second surgery, the tendons were fixed with suture material only (suture-fixed group; n = 17), whereas in the two experimental groups, the tendons were fixed with suture material and the polyurethane implant (Biomerix scaffold group; n = 17) or the modified electrospun polycaprolactone fiber implant (CS-g-PCL scaffold group; n=17), respectively. The unaffected right infraspinatus tendons were used as native controls. After a recovery of 8 weeks, all animals were clinically inconspicuous. In 12 animals of each group, repaired entheses were biomechanically tested for force at failure, stiffness, and modulus of elasticity, and in five animals, repaired entheses were analyzed histologically. Biomechanically, all parameters did not differ statistically significant between both implant groups, and the entheses failed typically at the surgical site. However, with respect to the force at failure, the median values of the two implant groups were smaller than the median value of the suture-fixed group. Histologically, the modified polycaprolactone fiber implant showed no acute inflammation processes, a good infiltration with cells, ingrowth of blood vessels and tendinous tissue, and a normal fibrous ensheathment. Further improvement of the implant material could be achieved by additional implementation of drug delivery systems. Therewith, the used CS-g-PCL fiber mat is a promising basic material to reach the goal of a clinically usable graft for rotator cuff tear repair.
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http://dx.doi.org/10.1002/term.2985DOI Listing
January 2020

MeSO- and serum-free cryopreservation of human umbilical cord mesenchymal stem cells using electroporation-assisted delivery of sugars.

Cryobiology 2019 12 5;91:104-114. Epub 2019 Oct 5.

Institute for Multiphase Processes, Leibniz University Hannover, Hannover, Germany.

Cryopreservation is the universal technology used to enable long-term storage and continuous availability of cell stocks and tissues for regenerative medicine demands. The main components of standard freezing media are dimethyl sulfoxide (hereinafter MeSO) and fetal bovine serum (FBS). However, for manufacturing of cells and tissue-engineered products in accordance with the principles of Good Manufacturing Practice (GMP), current considerations in regenerative medicine suggest development of MeSO- and serum-free biopreservation strategies due to safety concerns over MeSO-induced side effects and immunogenicity of animal serum. In this work, the effect of electroporation-assisted pre-freeze delivery of sucrose, trehalose and raffinose into human umbilical cord mesenchymal stem cells (hUCMSCs) on their post-thaw survival was investigated. The optimal strength of electric field at 8 pulses with 100 μs duration and 1 Hz pulse repetition frequency was determined to be 1.5 kV/cm from permeabilization (propidium iodide uptake) vs. cell recovery data (resazurin reduction assay). Using sugars as sole cryoprotectants with electroporation, concentration-dependent increase in cell survival was observed. Irrespective of sugar type, the highest cell survival (up to 80%) was achieved at 400 mM extracellular concentration and electroporation. Cell freezing without electroporation yielded significantly lower survival rates. In the optimal scenario, cells were able to attach 24 h after thawing demonstrating characteristic shape and sugar-loaded vacuoles. Application of 10% MeSO/90% FBS as a positive control provided cell survival exceeding 90%. Next, high glass transition temperatures determined for optimal concentrations of sugars by differential scanning calorimetry (DSC) suggest the possibility to store samples at -80 °C. In summary, using electroporation to incorporate cryoprotective sugars into cells is an effective strategy towards MeSO- and serum-free cryopreservation and may pave the way for further progress in establishing clinically safe biopreservation strategies for efficient long-term biobanking of cells.
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http://dx.doi.org/10.1016/j.cryobiol.2019.10.002DOI Listing
December 2019

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

J Tissue Eng Regen Med 2019 07 29;13(7):1190-1202. Epub 2019 May 29.

Department of Oral and Maxillofacial Surgery, Hannover Medical School, Hannover, Germany.

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.
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http://dx.doi.org/10.1002/term.2868DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6771623PMC
July 2019

Impact of sterilization by electron beam, gamma radiation and X-rays on electrospun poly-(ε-caprolactone) fiber mats.

J Mater Sci Mater Med 2019 Mar 27;30(4):42. Epub 2019 Mar 27.

Institute for Technical Chemistry, Braunschweig University of Technology, Braunschweig, Germany.

Biodegradable polymers such as polycaprolactone (PCL) are increasingly used for electrospinning substrates for tissue engineering. These materials offer great advantages such as biocompatibility and good mechanical properties. However, in order to be approved for human implantation they have to be sterilized. The impact of commonly used irradiation sterilization methods on electrospun PCL fiber mats was investigated systematically. Electron beam (β-irradiation), gamma and X-ray irradiation with two different doses (25 and 33 kGy) were investigated. To determine the impact on the fiber mats, mechanical, chemical, thermal properties and crystallinity were investigated. Irradiation resulted in a significant decrease in molecular weight. At the same time, crystallinity of fiber mats increased significantly. However, the mechanical properties did not change significantly upon irradiation, mostly likely because effects of a lower molecular weight were balanced with the higher degree of crystallinity. The irradiation effects were dose dependent, a higher irradiation dose led to stronger changes. Gamma irradiation seemed to be the least suited method, while electron beams (β irradiation) had a lower impact. Therefore, β irradiation is recommended as sterilization method for electrospun PCL fiber mats.
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http://dx.doi.org/10.1007/s10856-019-6245-7DOI Listing
March 2019

Histological processing of un-/cellularized thermosensitive electrospun scaffolds.

Histochem Cell Biol 2019 Apr 17;151(4):343-356. Epub 2018 Dec 17.

Department of Cell Biology, Histology and Embryology, Gottfried Schatz Research Center, Medical University of Graz, Neue Stiftingtalstraße 6, 8010, Graz, Austria.

Histological processing of thermosensitive electrospun poly(ε-caprolactone)/poly(L-lactide) (PCL/PLA) scaffolds fails, as poly(ε-caprolactone) (PCL) is characterized by its low-melting temperature (Tm = 60 °C). Here, we present an optimized low-temperature preparation method for the histological processing of un-/cellularized thermosensitive PCL/PLA scaffolds.Our study is aimed at the establishment of an optimized dehydration and low-melting-point paraffin-embedding method of electrospun PCL/PLA scaffolds (un-/cellularized). Furthermore, we compared this method with (a) automatized dehydration and standard paraffin embedding, (b) gelatin embedding followed by automatized dehydration and standard paraffin embedding, (c) cryofixation, and (d) acrylic resin embedding methods. We investigated pepsin and proteinase K antigen retrieval for their efficiency in epitope demasking at low temperatures and evaluated protocols for immunohistochemistry and immunofluorescence for cytokeratin 7 (CK7) and in situ padlock probe technology for beta actin (ACTB). Optimized dehydration and low-melting-point paraffin embedding preserved the PCL/PLA scaffold, as the diameter and structure of its fibers were unchanged. Cells attached to the PCL/PLA scaffolds showed limited alterations in size and morphology compared to control. Epitope demasking by enzymatic pepsin digestion and immunostaining of CK7 displayed an invasion of attached cells into the scaffold. Expression of ACTB and CK7 was shown by a combination of mRNA-based in situ padlock probe technology and immunofluorescence. In contrast, gelatin stabilization followed by standard paraffin embedding led to an overall shrinkage and melting of fibers, and therefore, no further analysis was possible. Acrylic resin embedding and cyrofixation caused fiber structures that were nearly unchanged in size and diameter. However, acrylic resin-embedded scaffolds are limited to 3 µm sections, whereas cyrofixation led to a reduction of the cell size by 14% compared to low-melting paraffin embedding. The combination of low-melting-point paraffin embedding and pepsin digestion as an antigen retrieval method offers a successful opportunity for histological investigations in thermosensitive specimens.
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http://dx.doi.org/10.1007/s00418-018-1757-7DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6469612PMC
April 2019

Impact of setup orientation on blend electrospinning of poly-ε-caprolactone-gelatin scaffolds for vascular tissue engineering.

Int J Artif Organs 2018 Nov;41(11):801-810

Institute for Multiphase Processes, Leibniz University Hannover, Hannover, Germany.

Introduction:: This article explores the effect of horizontal and vertical setups on blend electrospinning with two polymers having vastly different properties - poly-ε-caprolactone and gelatin, and subsequent effect of the resulting microstructure on viability of seeded cells.

Methods:: Poly-ε-caprolactone and gelatin of varying blend concentrations were electrospun in horizontal and vertical setup orientations. NIH 3T3 fibroblasts were seeded on these scaffolds to assess cell viability changes in accordance with change in microstructure.

Results:: Blend electrospinning yielded a heterogeneous microstructure in the vertical orientation beyond a critical concentration of gelatin, and a homogeneous microstructure in the horizontal orientation. Unblended poly-ε-caprolactone electrospinning showed no significant difference in fibre diameter or pore size in either orientation. Mechanical testing showed reduced elasticity when poly-ε-caprolactone is blended with gelatin but an overall increase in tensile strength in the vertically spun samples. Cells on vertically spun samples showed significantly higher viabilities by day 7.

Discussion:: The composite microstructure obtained in vertically spun poly-ε-caprolactone -gelatin blends has a positive effect on viability of seeded cells. Such scaffolds can be considered suitable candidates for cardiovascular tissue engineering where cell infiltration is crucial.
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http://dx.doi.org/10.1177/0391398818803478DOI Listing
November 2018

An acoustic method for systematic ventricular assist device thrombus evaluation with a novel artificial thrombus model.

J Thorac Dis 2018 Jun;10(Suppl 15):S1711-S1719

Department of Cardiothoracic, Transplantation and Vascular Surgery, Hannover Medical School, Hannover, Germany.

Background: Pump thrombosis (PT) is still one of the major adverse events in patients supported with left ventricular assist devices. Nowadays, thrombus detection relies on clinical parameters like reoccurring heart failure symptoms, on changes in pump power consumption, and on laboratory parameters such as increased LDH and hemolysis. Once detected PT is most often persistent and refractory to medical therapy. We therefore designed a novel, non-invasive acoustic method for early pump thrombus detection in an artificial thrombus model.

Methods: The study was performed using a mock circulation loop, artificial blood (water-glycerin) and artificial thrombus material (silicon) allowing for repeatable and defined testing. Tested ventricular assist device (VAD) type was HVAD (Medtronic). Three different thrombus locations were evaluated: on the tilted pad of the rotor, in the primary flow path, and in the secondary flow path beneath the rotor. After evaluating baseline parameters (no thrombus, n=20 for each pump), the influence of thrombi of seven different masses (no thrombus, 0.5-5.0 mg) on pump power consumption and acoustic emission of four HVAD devices was investigated via a microphone system (Sennheiser) and subsequent frequency spectrum analysis (n=12). The acoustic analysis algorithm included the number of frequency peaks recorded.

Results: Measurements with thrombi on the tilted pad showed an increased number of frequency peaks with all thrombus sizes compared to baseline measurements without any thrombus (baseline: 32.7±7.4; 0.5 mg: 45.3±10.4 up to 5 mg: 80.4±5.5). Power consumption was relevantly elevated in 5mg thrombus measurement only (6.3±1.29 W compared to 4.9±0.14 W at baseline). Measurements with thrombi in the primary and secondary showed no relevant alteration in power consumption and frequency peak count.

Conclusions: We present an acoustic method that detects pump thrombi located on the tilted pad of the HVAD rotor requiring ten times less mass compared to thrombi detected by power consumption alterations used in current detection algorithms. Assuming that pump thrombi are growing over several days, the presented method may detect PT much earlier thereby increasing efficacy of medical therapy and helping to avoid pump exchange.
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http://dx.doi.org/10.21037/jtd.2018.04.11DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6035965PMC
June 2018

Force induced piezoelectric effect of polyvinylidene fluoride and polyvinylidene fluoride-co-trifluoroethylene nanofibrous scaffolds.

Int J Artif Organs 2018 Nov 5;41(11):811-822. Epub 2018 Jul 5.

1 Institute for Multiphase Processes, Leibniz Universität Hannover, Hannover, Germany.

Polyvinylidene fluoride and its co-polymer with trifluoroethylene are promising biomaterials for supporting nerve regeneration processes because of their proven biocompatibility and piezoelectric properties that could stimulate cell ingrowth due to electrical activity upon mechanical deformation. This study reports the piezoelectric effect of electrospun polyvinylidene fluoride scaffolds in response to mechanical loading. An impact test machine was used to evaluate the generation of electrical voltage upon application of an impact load. Scaffolds were produced via electrospinning from polyvinylidene fluoride and polyvinylidene fluoride-co-trifluoroethylene with concentrations of 10-20 wt% dissolved in N,N-dimethylformamide (DMF) and acetone (6:4). The structural and thermal properties of scaffolds were analyzed using Fourier Transform Infrared Spectroscopy and Differential Scanning Calorimetry, respectively. The piezoelectric response of the scaffolds was induced using a custom-made manual impact press machine. Impact forces between 0.4 and 14 N were applied. Fourier Transform Infrared Spectroscopy and Differential Scanning Calorimetry results demonstrated the piezoelectric effect of the electrospun polyvinylidene fluoride and polyvinylidene fluoride-co-trifluoroethylene scaffolds. All the scaffolds exhibited a piezoelectric polar beta-phase formation. Their thermal enthalpies were higher than the value of the initial materials and exhibited a better tendency of crystallization. The electrospun scaffolds exhibited piezoelectric responses in form of voltage by applying impact load. Polyvinylidene fluoride-co-trifluoroethylene scaffolds showed higher values in the range of 6-30 V as compared to pure polyvinylidene fluoride. Here, the mechanically induced electrical impulses measured were between 2.5 and 8 V. Increasing the impact forces did not increase the piezoelectric effect. The results demonstrate the possibility of producing electrospun polyvinylidene fluoride and polyvinylidene fluoride-co-trifluoroethylene scaffolds as nerve guidance with piezoelectric response. Further experiments must be carried out to analyze the piezoelectricity at dynamic conditions.
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http://dx.doi.org/10.1177/0391398818785049DOI Listing
November 2018

Comparison between three in vitro methods to measure magnesium degradation and their suitability for predicting in vivo degradation.

Int J Artif Organs 2018 Nov 13;41(11):772-778. Epub 2018 May 13.

Institut für Mehrphasenprozesse, Leibniz Universität Hannover, Hannover, Germany.

A lot of research has been done in the field of magnesium-based implant material. This study is focused on finding an explanation for the large disparity in results from similar experiments in literature. The hypothesis is that many different measurement protocols are used to quantify magnesium degradation and this leads to inconsistent results. Cylindrical, pure magnesium samples were used for this study. The degradation took place in revised simulated body fluid at 37°C. Hydrogen evolution was measured to quantify the degradation. Two commonly used experimental protocols were examined: static conditions and a fluid changing method. For static testing, the samples stayed in fluid. For the fluid changing method, the fluid was changed after 2 and 5 days of immersion. In addition, a new method with continuous fluid flow was established. After an initial phase, the results confirm that for all three methods, the degradation behavior differs strongly. The static condition results in a very slow degradation rate. The fluid change method leads to a similar behavior like the static condition except that the degradation was speeded up after the fluid changes. The continuous degradation is linear for a long period after the initial phase. In comparison with in vivo degradation behavior, the degradation process in continuous flow shows the best fitting. The accumulation of degradation products, especially the increasing pH value, has a strong inhibiting effect. This cannot be observed in vivo so that a constant experimental environment realizable by continuous flow is more suitable for magnesium-based implant material testing.
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http://dx.doi.org/10.1177/0391398818772777DOI Listing
November 2018

Attachment of nanoparticulate drug-release systems on poly(ε-caprolactone) nanofibers via a graftpolymer as interlayer.

Colloids Surf B Biointerfaces 2018 Mar 29;163:309-320. Epub 2017 Dec 29.

Institute for Technical Chemistry, Braunschweig University of Technology, Hagenring 30, 38106, Braunschweig, Germany. Electronic address:

Electrospun poly(ε-caprolactone) (PCL) fiber mats are modified using a chitosan grafted with PCL (CS-g-PCL), to improve the biological performance and to enable further modifications. The graft copolymer is immobilized by the crystallization of the PCL grafts on the PCL fiber surface as binding mechanism. In this way, the surface of the fibers is covered with chitosan bearing cationic amino groups, which allow adsorption of oppositely charged nanoparticulate drug-delivery systems. The modification of the fiber mats and the attachment of the drug delivery systems are easy and scalable dip processes. The process is also versatile; it is possible to attach different polymeric and inorganic nanoparticulate drug-release systems of cationic or anionic nature. The modifications are verified using scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM). As proof of principle, the release of ciprofloxacin from silica nanoparticles attached to the modified fiber mats is shown; however, the method is also suited for other biologically active substances including growth factors. The initial cellular attachment and proliferation as well as vitality of the cells is improved by the modification with CS-g-PCL and is further influenced by the type of the drug delivery system attached. Hence, this method can be used to transfer PCL fiber mats into bioactive implants for in-situ tissue engineering applications.
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http://dx.doi.org/10.1016/j.colsurfb.2017.12.050DOI Listing
March 2018

The Osteogenic and Tenogenic Differentiation Potential of C3H10T1/2 (Mesenchymal Stem Cell Model) Cultured on PCL/PLA Electrospun Scaffolds in the Absence of Specific Differentiation Medium.

Materials (Basel) 2017 Dec 4;10(12). Epub 2017 Dec 4.

CNRS, UMR 7338 Biomechanics and Bioengineering, Sorbonne Universités, Université de Technologie de Compiègne, 60200 Compiègne, France.

The differentiation potential of mesenchymal stem cells (MSC) has been extensively tested on electrospun scaffolds. However, this potential is often assessed with lineage-specific medium, making it difficult to interpret the real contribution of the properties of the scaffold in the cell response. In this study, we analyzed the ability of different polycaprolactone/polylactic acid PCL/PLA electrospun scaffolds (pure or blended compositions, random or aligned fibers, various fiber diameters) to drive MSC towards bone or tendon lineages in the absence of specific differentiation medium. C3H10T1/2 cells (a mesenchymal stem cell model) were cultured on scaffolds for 96 h without differentiation factors. We performed a cross-analysis of the cell-scaffold interactions (spreading, organization, and specific gene expression) with mechanical (elasticity), morphological (porosity, fibers diameter and orientation) and surface (wettability) characterizations of the electrospun fibers. We concluded that (1) osteogenic differentiation can be initiated on pure PCL-based electrospun scaffolds without specific culture conditions; (2) fiber alignment modified cell organization in the short term and (3) PLA added to PCL with an increased fiber diameter encouraged the stem cells towards the tendon lineage without additional tenogenic factors. In summary, the differentiation potential of stem cells on adapted electrospun fibers could be achieved in factor-free medium, making possible future applications in clinically relevant situations.
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http://dx.doi.org/10.3390/ma10121387DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5744322PMC
December 2017

Improved in vitro models for preclinical drug and formulation screening focusing on 2D and 3D skin and cornea constructs.

Eur J Pharm Biopharm 2018 May 2;126:57-66. Epub 2017 Dec 2.

Technische Universität Braunschweig, Institut für Pharmazeutische Technologie, Mendelssohnstr. 1, 38106 Braunschweig, Germany; Technische Universität Braunschweig, Zentrum für Pharmaverfahrenstechnik, Franz-Liszt-Str. 35a, 38106 Braunschweig, Germany. Electronic address:

The present overview deals with current approaches for the improvement of in vitro models for preclinical drug and formulation screening which were elaborated in a joint project at the Center of Pharmaceutical Engineering of the TU Braunschweig. Within this project a special focus was laid on the enhancement of skin and cornea models. For this reason, first, a computation-based approach for in silico modeling of dermal cell proliferation and differentiation was developed. The simulation should for example enhance the understanding of the performed 2D in vitro tests on the antiproliferative effect of hyperforin. A second approach aimed at establishing in vivo-like dynamic conditions in in vitro drug absorption studies in contrast to the commonly used static conditions. The reported Dynamic Micro Tissue Engineering System (DynaMiTES) combines the advantages of in vitro cell culture models and microfluidic systems for the emulation of dynamic drug absorption at different physiological barriers and, later, for the investigation of dynamic culture conditions. Finally, cryopreserved shipping was investigated for a human hemicornea construct. As the implementation of a tissue-engineering laboratory is time-consuming and cost-intensive, commercial availability of advanced 3D human tissue is preferred from a variety of companies. However, for shipping purposes cryopreservation is a challenge to maintain the same quality and performance of the tissue in the laboratory of both, the provider and the customer.
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http://dx.doi.org/10.1016/j.ejpb.2017.11.014DOI Listing
May 2018

Novel strategies for the formulation and processing of poorly water-soluble drugs.

Eur J Pharm Biopharm 2018 May 19;126:40-56. Epub 2017 May 19.

Technische Universität Braunschweig, Institut für Partikeltechnik, Volkmaroder Str. 5, 38104 Braunschweig, Germany; Technische Universität Braunschweig, Zentrum für Pharmaverfahrenstechnik (PVZ), Franz-Liszt-Str. 35a, 38106 Braunschweig, Germany. Electronic address:

Low aqueous solubility of active pharmaceutical ingredients presents a serious challenge in the development process of new drug products. This article provides an overview on some of the current approaches for the formulation of poorly water-soluble drugs with a special focus on strategies pursued at the Center of Pharmaceutical Engineering of the TU Braunschweig. These comprise formulation in lipid-based colloidal drug delivery systems and experimental as well as computational approaches towards the efficient identification of the most suitable carrier systems. For less lipophilic substances the preparation of drug nanoparticles by milling and precipitation is investigated for instance by means of microsystem-based manufacturing techniques and with special regard to the preparation of individualized dosage forms. Another option to overcome issues with poor drug solubility is the incorporation into nanospun fibers.
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http://dx.doi.org/10.1016/j.ejpb.2017.05.008DOI Listing
May 2018

Novel chitin scaffolds derived from marine sponge Ianthella basta for tissue engineering approaches based on human mesenchymal stromal cells: Biocompatibility and cryopreservation.

Int J Biol Macromol 2017 Nov 30;104(Pt B):1955-1965. Epub 2017 Mar 30.

Institute of Experimental Physics, TU Bergakademie Freiberg, Leipziger Straße 23, 09599 Freiberg, Germany. Electronic address:

The extraordinary biocompatibility and mechanical properties of chitinous scaffolds from marine sponges endows these structures with unique properties that render them ideal for diverse biomedical applications. In the present work, a technological route to produce "ready-to-use" tissue-engineered products based on poriferan chitin is comprehensively investigated for the first time. Three key stages included isolation of scaffolds from the marine demosponge Ianthella basta, confirmation of their biocompatibility with human mesenchymal stromal cells, and cryopreservation of the tissue-like structures grown within these scaffolds using a slow cooling protocol. Biocompatibility of the macroporous, flat chitin scaffolds has been confirmed by cell attachment, high cell viability and the ability to differentiate into the adipogenic lineage. The viability of cells cryopreserved on chitin scaffolds was reduced by about 30% as compared to cells cryopreserved in suspension. However, the surviving cells were able to retain their differentiation potential; and this is demonstrated for the adipogenic lineage. The results suggest that chitin from the marine demosponge I. basta is a promising, highly biocompatible biomaterial for stem cell-based tissue-engineering applications.
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http://dx.doi.org/10.1016/j.ijbiomac.2017.03.161DOI Listing
November 2017

3D chitinous scaffolds derived from cultivated marine demosponge Aplysina aerophoba for tissue engineering approaches based on human mesenchymal stromal cells.

Int J Biol Macromol 2017 Nov 25;104(Pt B):1966-1974. Epub 2017 Mar 25.

Institute of Experimental Physics, TU Bergakademie Freiberg, Leipziger Straße 23, 09599 Freiberg, Germany. Electronic address:

The recently discovered chitin-based scaffolds derived from poriferans have the necessary prosperities for potential use in tissue engineering. Among the various demosponges of the Verongida order, Aplysina aerophoba is an attractive target for more in-depth investigations, as it is a renewable source of unique 3D microporous chitinous scaffolds. We found these chitinous scaffolds were cytocompatible and supported attachment, growth and proliferation of human mesenchymal stromal cells (hMSCs) in vitro. Cultivation of hMSCs on the scaffolds for 7days resulted in a two-fold increase in their metabolic activity, indicating increased cell numbers. Cells cultured onto chitin scaffolds in differentiation media were able to differentiate into the chondrogenic, adipogenic and osteogenic lineages, respectively. These results indicate A. aerophoba is a novel source of chitin scaffolds to futher hMSCs-based tissue engineering strategies.
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http://dx.doi.org/10.1016/j.ijbiomac.2017.03.116DOI Listing
November 2017

Exploring the Possibility of Cryopreservation of Feline and Canine Erythrocytes by Rapid Freezing with Penetrating and Non-Penetrating Cryoprotectants.

PLoS One 2017 10;12(1):e0169689. Epub 2017 Jan 10.

Kharkiv State Zooveterinary Academy, Mala Danylivka, Kharkiv Region, Ukraine.

Efficient application of veterinary blood transfusion approaches for small companion animals requires readily available supply of the donor material. This can be achieved by developing of effective biobanking technologies allowing long-term storage of donor blood components via cryopreservation. Transfusion of an erythrocyte concentrate allows the successful correction of various hematological pathologies, severe bleeding, and etc. While in the past there were several approaches to cryopreserve red blood cells of dogs, to our knowledge there is virtually no data on cryopreservation of feline erythrocytes. In this paper, we performed a comprehensive parameter optimization for low temperature storage of RBCs of both species. Here, the efficiency of single-component and multicomponent cryoprotective media as well as necessary time of pre-incubation with penetrating and non-penetrating cryoprotectants prior to rapid freezing is analyzed. This study showed that glycerol was not sufficient for cryopreservation of red blood cells of the studied species under the investigated conditions. Application of 10% (v/v) ME2SO allowed for a significant reduction of canine and feline erythrocytes hemolysis after thawing. 17.5% hydroxyethyl starch demonstrated the highest cryoprotective activity for both species. It was found that dog RBCs should be incubated in cryoprotective media for 30 min at 22°C prior to freezing, while for cat RBCs 20 min is sufficient. Combination of CPAs was less effective. Presented data may be considered in further studies in veterinary transfusion and blood banking optimization.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0169689PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5224986PMC
August 2017

Differential magnesium implant corrosion coat formation and contribution to bone bonding.

J Biomed Mater Res A 2017 03 7;105(3):697-709. Epub 2016 Nov 7.

Helmholtz Centre for Infection Research, Inhoffenstrasse 7, Braunschweig, 38124, Germany.

Magnesium alloys are presently under investigation as promising biodegradable implant materials with osteoconductive properties. To study the molecular mechanisms involved, the potential contribution of soluble magnesium corrosion products to the stimulation of osteoblastic cell differentiation was examined. However, no evidence for the stimulation of osteoblast differentiation could be obtained when cultured mesenchymal precursor cells were differentiated in the presence of metallic magnesium or in cell culture medium containing elevated magnesium ion levels. Similarly, in soft tissue no bone induction by metallic magnesium or by the corrosion product magnesium hydroxide could be observed in a mouse model. Motivated by the comparatively rapid accumulation solid corrosion products physicochemical processes were examined as an alternative mechanism to explain the stimulation of bone growth by magnesium-based implants. During exposure to physiological solutions a structured corrosion coat formed on magnesium whereby the elements calcium and phosphate were enriched in the outermost layer which could play a role in the established biocompatible behavior of magnesium implants. When magnesium pins were inserted into avital bones, corrosion lead to increases in the pull out force, suggesting that the expanding corrosion layer was interlocking with the surrounding bone. Since mechanical stress is a well-established inducer of bone growth, volume increases caused by the rapid accumulation of corrosion products and the resulting force development could be a key mechanism and provide an explanation for the observed stimulatory effects of magnesium-based implants in hard tissue. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 697-709, 2017.
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http://dx.doi.org/10.1002/jbm.a.35943DOI Listing
March 2017

A silicone fiber coating as approach for the reduction of fibroblast growth on implant electrodes.

J Biomed Mater Res B Appl Biomater 2017 Nov 4;105(8):2574-2580. Epub 2016 Oct 4.

Institute for Multiphase Processes, Leibniz Universität Hannover, Germany.

In cochlear implant (CI) patients, an increase in electrode impedance due to fibrotic encapsulation is frequently observed. Several attempts have been proposed to reduce fibroblast growth at the electrode contacts, but none proved to be satisfactory so far. Here, a silicone fiber coating of the electrode contacts is presented that provides a complex micro-scale surface topography and increases hydrophobicity to inhibit fibroblast growth and adhesion. A silicone fiber electrospinning process was developed to create a thin and porous fiber mesh. Fiber coatings were applied on graphite specimen holders, glass cover slips and CI electrode contacts. For characterization of the coating's pore distribution, water contact angle and electrical impedance were analyzed. Cytotoxicity and in vitro fibroblast growth were evaluated to assess biological efficacy of the coatings. It could be shown that the silicone fiber mesh itself had only minor influence on electrode impedance. A uniform, hydrophobic fiber coating could be achieved that decreased fibroblast growth without showing toxic effects. Finally, CI electrode contacts were successfully coated in order to present this promising approach for a long-term improvement of CI electrodes. We are one of the first groups that could successfully adapt the electrospinning technique on the utilization of silicone. Silicone was chosen because of its high hydrophobicity, chemical stability and excellent biocompatibility and as it is one of the biomaterials already used in CIs. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 2574-2580, 2017.
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http://dx.doi.org/10.1002/jbm.b.33798DOI Listing
November 2017

Xeno-Free Cryopreservation of Bone Marrow-Derived Multipotent Stromal Cells from Callithrix jacchus.

Biopreserv Biobank 2016 Dec 7;14(6):530-538. Epub 2016 Sep 7.

Institute for Multiphase Processes, Leibniz Universität Hannover , Hannover, Germany .

In the previous decade, numerous biobanks were established and have created large markets for the storage of bioactive compounds, cells, and tissues for medical and diagnostic applications. For in vivo clinical and therapeutic purposes, it is critical to use well-defined and xeno-free components during cultivation, preservation, and transplantation of biological material. Safe and efficacious storage of bioactive molecules, cells, and tissues, without the addition of undefined medium components, minimizes risks of zoonotic disease transmission and is thus an essential and desirable prerequisite for biobanks. This gives rise to a need for well-characterized and serum-free freezing media for application in cryopreservation. For this purpose, cryobiological additives such as methylcellulose, poloxamer-188, and α-tocopherol, which have previously been shown to exhibit a cytoprotective activity, have been investigated for cryoprotection on stem cells. With this strategy, the application of fetal bovine serum (FBS) could be avoided and the concentration of toxic cryoprotective agents such as dimethyl sulfoxide (DMSO) could be reduced. Our results suggest that the viability, as well as the adipogenic and osteogenic differentiation capacity of the thawed bone marrow-derived multipotent stromal stem cells, could be maintained using a freezing medium without FBS consisting of methylcellulose, poloxamer, and α-tocopherol with only 2.5% DMSO (% v/v).
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http://dx.doi.org/10.1089/bio.2016.0038DOI Listing
December 2016

Porous biomorphic silicon carbide ceramics coated with hydroxyapatite as prospective materials for bone implants.

Mater Sci Eng C Mater Biol Appl 2016 Nov 26;68:143-152. Epub 2016 May 26.

Institute for Multiphase Processes, Leibniz Universität Hannover, 30167 Hannover, Germany. Electronic address:

Porous and cytocompatible silicon carbide (SiC) ceramics derived from wood precursors and coated with bioactive hydroxyapatite (HA) and HA-zirconium dioxide (HA/ZrO2) composite are materials with promising application in engineering of bone implants due to their excellent mechanical and structural properties. Biomorphic SiC ceramics have been synthesized from wood (Hornbeam, Sapele, Tilia and Pear) using a forced impregnation method. The SiC ceramics have been coated with bioactive HA and HA/ZrO2 using effective gas detonation deposition approach (GDD). The surface morphology and cytotoxicity of SiC ceramics as well as phase composition and crystallinity of deposited coatings were analyzed. It has been shown that the porosity and pore size of SiC ceramics depend on initial wood source. The XRD and FTIR studies revealed the preservation of crystal structure and phase composition of in the HA coating, while addition of ZrO2 to the initial HA powder resulted in significant decomposition of the final HA/ZrO2 coating and formation of other calcium phosphate phases. In turn, NIH 3T3 cells cultured in medium exposed to coated and uncoated SiC ceramics showed high re-cultivation efficiency as well as metabolic activity. The recultivation efficiency of cells was the highest for HA-coated ceramics, whereas HA/ZrO2 coating improved the recultivation efficiency of cells as compared to uncoated SiC ceramics. The GDD method allowed generating homogeneous HA coatings with no change in calcium to phosphorus ratio. In summary, porous and cytocompatible bio-SiC ceramics with bioactive coatings show a great promise in construction of light, robust, inexpensive and patient-specific bone implants for clinical application.
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http://dx.doi.org/10.1016/j.msec.2016.05.113DOI Listing
November 2016

Phosphate conversion coating reduces the degradation rate and suppresses side effects of metallic magnesium implants in an animal model.

J Biomed Mater Res B Appl Biomater 2017 08 6;105(6):1622-1635. Epub 2016 May 6.

Helmholtz Centre for Infection Research, Inhoffenstrasse 7, 38124, Braunschweig, Germany.

Magnesium alloys have promising mechanical and biological properties for the development of degradable implants. However, rapid implant corrosion and gas accumulations in tissue impede clinical applications. With time, the implant degradation rate is reduced by a highly biocompatible, phosphate-containing corrosion layer. To circumvent initial side effects after implantation it was attempted to develop a simple in vitro procedure to generate a similarly protective phosphate corrosion layer. To this end magnesium samples were pre-incubated in phosphate solutions. The resulting coating was well adherent during routine handling procedures. It completely suppressed the initial burst of corrosion and it reduced the average in vitro magnesium degradation rate over 56 days almost two-fold. In a small animal model phosphate coatings on magnesium implants were highly biocompatible and abrogated the appearance of gas cavities in the tissue. After implantation, the phosphate coating was replaced by a layer with an elemental composition that was highly similar to the corrosion layer that had formed on plain magnesium implants. The data demonstrate that a simple pre-treatment could improve clinically relevant properties of magnesium-based implants. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 1622-1635, 2017.
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http://dx.doi.org/10.1002/jbm.b.33704DOI Listing
August 2017