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Bioinspired stem cell-based hard tissue engineering includes numerous aspects: The synthesis and fabrication of appropriate scaffold materials, their analytical characterization, and guided osteogenesis using the sustained release of osteoinducing and/or osteoconducting drugs for mesenchymal stem cell differentiation, growth, and proliferation. Here, the effect of silicon- and silicate-containing materials on osteogenesis at the molecular level has been a particular focus within the last decade. This review summarizes recently published scientific results, including material developments and analysis, with a special focus on silicon hybrid bone composites. First, the sources, bioavailability, and functions of silicon on various tissues are discussed. The second focus is on the effects of calcium-silicate biomineralization and corresponding analytical methods in investigating osteogenesis and bone formation. Finally, recent developments in the manufacturing of Si-containing scaffolds are discussed, including in vitro and in vivo studies, as well as recently filed patents that focus on the influence of silicon on hard tissue formation.
Healing of large bone defects requires implants or scaffolds that provide structural guidance for cell growth, differentiation, and vascularization. In the present work, an agarose-hydroxyapatite composite scaffold was developed that acts not only as a 3D matrix, but also as a release system. Hydroxyapatite (HA) was incorporated into the agarose gels in situ in various ratios by a simple procedure consisting of precipitation, cooling, washing, and drying. The resulting gels were characterized regarding composition, porosity, mechanical properties, and biocompatibility. A pure phase of carbonated HA was identified in the scaffolds, which had pore sizes of up to several hundred micrometers. Mechanical testing revealed elastic moduli of up to 2.8 MPa for lyophilized composites. MTT testing on Lw35human mesenchymal stem cells (hMSCs) and osteosarcoma MG-63 cells proved the biocompatibility of the scaffolds. Furthermore, scaffolds were loaded with model drug compounds for guided hMSC differentiation. Different release kinetic models were evaluated for adenosine 5′-triphosphate (ATP) and suramin, and data showed a sustained release behavior over four days.
The ability of stem cells to self-renew and differentiate into multiple lineages has made them attractive candidates for therapeutic interventions. Adult stem cells are a promising source for regenerative medicine approaches since they are easy to obtain, and bear a lower risk of immune rejection and tumor formation, compared to embryonic stem cells or iPS cells. Controlling their fate tightly is still the key challenge on their way from bench to bedside use. While conventional methods are based mainly on chemical induction of differentiation via growth factors and cytokines, concentrating on altering material properties, such as substrate stiffness and topography, to mimic the stimuli stem cells receive in their natural niche gets more into focus recently. It has been shown that (nano)structural and mechanical triggers derived from the extracellular matrix can influence stem cell fate by promoting self-renewal or differentiation if tissue repair is needed. In this chapter, the chemical structure of various nanomaterials used as scaffolds for stem cell differentiation will be discussed, including bulk and surface properties and corresponding analytical methods for surface characterization. Furthermore, recently developed methods for the design of tailor-made nanomaterial used in stem cell differentiation will be discussed in the current chapter.
Human mesenchymal stem cells (hMSCs) are considered a promising cell source for regenerative medicine, because they have the potential to differentiate into a variety of lineages among which the mesoderm-derived lineages such adipo- or osteogenesis are investigated best. Human MSCs can be harvested in reasonable to large amounts from several parts of the patient’s body and due to this possible autologous origin, allorecognition can be avoided. In addition, even in allogenic origin-derived donor cells, hMSCs generate a local immunosuppressive microenvironment, causing only a weak immune reaction. There is an increasing need for bone replacement in patients from all ages, due to a variety of reasons such as a new recreational behavior in young adults or age-related diseases. Adipogenic differentiation is another interesting lineage, because fat tissue is considered to be a major factor triggering atherosclerosis that ultimately leads to cardiovascular diseases, the main cause of death in industrialized countries. However, understanding the differentiation process in detail is obligatory to achieve a tight control of the process for future clinical applications to avoid undesired side effects. In this review, the current findings for adipo- and osteo-differentiation are summarized together with a brief statement on first clinical trials.
Background: Bile acids, end products of the pathway for cholesterol elimination, are required for dietary lipid and fatsoluble vitamin absorption and maintain the balance between cholesterol synthesis in the liver and cholesterol excretion. They are composed of a steroid structure and are primarily made in the liver by the oxidation of cholesterol. Cholesterol is also highly abundant in the human ovarian follicle, where it is used in the formation of the sex steroids.
Methodology/Principal Findings: Here we describe for the first time evidence that all aspects of the bile acid synthesis pathway are present in the human ovarian follicle, including the enzymes in both the classical and alternative pathways, the nuclear receptors known to regulate the pathway, and the end product bile acids. Furthermore, we provide functional evidence that bile acids are produced by the human follicular granulosa cells in response to cholesterol presence in the culture media.
Conclusions/Significance: These findings establish a novel pathway present in the human ovarian follicle that has the capacity to compete directly with sex steroid synthesis.
This review is divided into two interconnected parts, namely a biological and a chemical one. The focus of the first part is on the biological background for constructing tissue-engineered vascular grafts to promote vascular healing. Various cell types, such as embryonic, mesenchymal and induced pluripotent stem cells, progenitor cells and endothelial- and smooth muscle cells will be discussed with respect to their specific markers. The in vitro and in vivo models and their potential to treat vascular diseases are also introduced. The chemical part focuses on strategies using either artificial or natural polymers for scaffold fabrication, including decellularized cardiovascular tissue. An overview will be given on scaffold fabrication including conventional methods and nanotechnologies. Special attention is given to 3D network formation via different chemical and physical cross-linking methods. In particular, electron beam treatment is introduced as a method to combine 3D network formation and surface modification. The review includes recently published scientific data and patents which have been registered within the last decade.
Hox genes are an evolutionary highly conserved gene family. They determine the anterior-posterior body axis in bilateral organisms and influence the developmental fate of cells. Embryonic stem cells are usually devoid of any Hox gene expression, but these transcription factors are activated in varying spatial and temporal patterns defining the development of various body regions. In the adult body, Hox genes are among others responsible for driving the differentiation of tissue stem cells towards their respective lineages in order to repair and maintain the correct function of tissues and organs. Due to their involvement in the embryonic and adult body, they have been suggested to be useable for improving stem cell differentiations in vitro and in vivo. In many studies Hox genes have been found as driving factors in stem cell differentiation towards adipogenesis, in lineages involved in bone and joint formation, mainly chondrogenesis and osteogenesis, in cardiovascular lineages including endothelial and smooth muscle cell differentiations, and in neurogenesis. As life expectancy is rising, the demand for tissue reconstruction continues to increase. Stem cells have become an increasingly popular choice for creating therapies in regenerative medicine due to their self-renewal and differentiation potential. Especially mesenchymal stem cells are used more and more frequently due to their easy handling and accessibility, combined with a low tumorgenicity and little ethical concerns. This review therefore intends to summarize to date known correlations between natural Hox gene expression patterns in body tissues and during the differentiation of various stem cells towards their respective lineages with a major focus on mesenchymal stem cell differentiations. This overview shall help to understand the complex interactions of Hox genes and differentiation processes all over the body as well as in vitro for further improvement of stem cell treatments in future regenerative medicine approaches.
Three-dimensional scaffolds are known to directly influence proliferation and differentiation of mesenchymal stem cells into bone tissue due to their properties such as stiffness and topography. While conventional methods for chemical induction of differentiation processes are based on incorporation of growth factors and/or cytokines via blending or adhesion onto the scaffold surfaces, novel approaches use template-mediated biomineralization to mimic the stimuli stem cells receive in their natural niche. This chapter summarizes recent progresses in guided bone tissue engineering with particular focus on design and functionality of three dimensional scaffolds, chemical templates and promising approaches for the corresponding cellbased approaches for future therapies.
Recent approaches in scaffold engineering for bone defects feature hybrid hydrogels made of a polymeric network (retains water and provides light and porous structures) and inorganic ceramics (add mechanical strength and improve cell-adhesion). Innovative scaffold materials should also induce bone tissue formation and incorporation of stem cells (osteogenic differentiation) and/or growth factors (inducing/supporting differentiation). Recently, purinergic P2X and P2Y receptors have been found to significantly influence the osteogenic differentiation process of human mesenchymal stem cells (hMSC). (1) Aim of this work is to develop polysaccharide (PS) composites to be used as scaffolds containing complementary receptor ligands to enable guided stem cell differentiation towards bone formation.
Small Molecules Enhance Scaffold-Based Bone Grafts via Purinergic Receptor Signaling in Stem Cells
(2018)
The need for bone grafts is high, due to age-related diseases, such as tumor resections, but also accidents, risky sports, and military conflicts. The gold standard for bone grafting is the use of autografts from the iliac crest, but the limited amount of accessible material demands new sources of bone replacement. The use of mesenchymal stem cells or their descendant cells, namely osteoblast, the bone-building cells and endothelial cells for angiogenesis, combined with artificial scaffolds, is a new approach. Mesenchymal stem cells (MSCs) can be obtained from the patient themselves, or from donors, as they barely cause an immune response in the recipient. However, MSCs never fully differentiate in vitro which might lead to unwanted effects in vivo. Interestingly, purinergic receptors can positively influence the differentiation of both osteoblasts and endothelial cells, using specific artificial ligands. An overview is given on purinergic receptor signaling in the most-needed cell types involved in bone metabolism-namely osteoblasts, osteoclasts, and endothelial cells. Furthermore, different types of scaffolds and their production methods will be elucidated. Finally, recent patents on scaffold materials, as wells as purinergic receptor-influencing molecules which might impact bone grafting, are discussed.
Renewable resources are gaining increasing interest as a source for environmentally benign biomaterials, such as drug encapsulation/release compounds, and scaffolds for tissue engineering in regenerative medicine. Being the second largest naturally abundant polymer, the interest in lignin valorization for biomedical utilization is rapidly growing. Depending on its resource and isolation procedure, lignin shows specific antioxidant and antimicrobial activity. Today, efforts in research and industry are directed toward lignin utilization as a renewable macromolecular building block for the preparation of polymeric drug encapsulation and scaffold materials. Within the last five years, remarkable progress has been made in isolation, functionalization and modification of lignin and lignin-derived compounds. However, the literature so far mainly focuses lignin-derived fuels, lubricants and resins. The purpose of this review is to summarize the current state of the art and to highlight the most important results in the field of lignin-based materials for potential use in biomedicine (reported in 2014⁻2018). Special focus is placed on lignin-derived nanomaterials for drug encapsulation and release as well as lignin hybrid materials used as scaffolds for guided bone regeneration in stem cell-based therapies.
Bone regeneration and replacement is a major focus in regenerative medicine since degenerative diseases and tumor surgery as well as accidents or dangerous recreational behavior is leading to an increasing need for bone reconstruction strategies. Especially for critical size bone defects, tissue engineering with mesenchymal stem cells is extensively studied because these cells are functioning as precursors for osteoblast in vivo. Nevertheless to reproduce the complex interaction of various factors in vitro is not an easy approach and further investigations have to be done. The status quo is summarized. A variety of growth and transcription factors are known to be involved in osteogenesis with bone morphogenetic proteins (BMPs) and the transcription factor Runx2 being the most extensively studied ones. But also PPAR γ and Osterix are generally regarded as the master regulators of osteoblast differentiation. Recently the large family of purinergic receptors has proven to be essential molecules in osteogenesis as well. In addition, scaffolding is needed to create a three-dimensional tissue. Recent developments in scaffold design are summarized, including natural and synthetic materials with or without the use of bioactive molecules constructed to mimic the natural environment. The status quo of scaffold fabrication methods such as 3D nanoprinting and their influence on cell-scaffold interactions is discussed. In this review we summarize the most interesting results and our related work focusing on two joined approaches: 1) the complex interaction of the most promising factors improving or accelerating osteogenic differentiation and ii) the development of scaffold materials with osteoconductive and osteoinductive properties.
This study aimed to investigate the effect of conditioned media (CM) from osteo-differentiating and adipo-differentiating human mesenchymal stem cells (MSCs) isolated from lipoaspirates of healthy female donors on the viability of triple-negative breast cancer cells MDA-MB231. The CM of undifferentiated and differentiating MSCs were collected after 7, 14, 21 and 28 days of culture. The effects of MSC CM on cell proliferation were assessed using an 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay after 24 h. The effects of osteo-differentiating cell CM on apoptotic promotion, cell cycle impairment, mitochondrial transmembrane potential dissipation, production of reactive oxygen species and autophagosome accumulation were analysed by flow cytometry and Western blot. MTT assay showed that only CM collected from osteo-induced cells at day 28 (d28O-CM) reduced tumour cell viability. Treatment with d28O-CM restrained cell cycle progression through G2 phase, elicited a caspase-8-driven apoptotic effect already after 5 h of culture, and down-regulated autophagosome accumulation and beclin-1 expression. The finding that factor(s) secreted by osteo-differentiating MSCs shows properties of an apoptotic inducer and autophagy inhibitor on triple-negative breast cancer cells may have an important applicative potential that deserves further investigation.
Background and Objectives: In advanced β-cell dysfunction, proinsulin is increasingly replacing insulin as major component of the secretion product. It has been speculated that proinsulin has at least the same adipogenic potency than insulin, leading to an increased tendency of lipid tissue formation in patients with late stage β-cell dysfunction. Methods and Results: Mesenchymal stem cells obtained from liposuction material were grown in differentiation media containing insulin (0.01 μmol), proinsulin (0.01 μmol) or insulin+proinsulin (each 0.005 μmol). Cell culture supernatants were taken from these experiments and an untreated control at weeks 1, 2, and 3, and were stored at -80°C until analysis. Cell differentiation was microscopically supervised and adiponectin concentrations were measured as marker for differentiation into mature lipid cells. This experiment was repeated three times. No growth of lipid cells and no change in adiponectin values was observed in the negative control group (after 7/14/12 days: 3.2±0.5/3.3±0.1/4.4±0.5 ng/ml/12 h). A continuous differentiation into mature adipocytes (also confirmed by Red-Oil-staining) and a corresponding increase in adiponectin values was observed in the experiments with insulin (3.6±1.9/5.1±1.4/13.3±1.5 ng/ml/12 h; p<0.05 week 1 vs. week 3) and proinsulin (3.3±1.2/3.5±0.3/12.2±1.2 ng/ml/12 h; p<0.05). Comparable effects were seen with the insulin/proinsulin combination. Conclusions: Proinsulin has the same adipogenic potential than insulin in vitro. Proinsulin has only 10∼20% of the glucose-lowering effect of insulin. It can be speculated that the adipogenic potential of proinsulin may be a large contributor to the increased body weight problems in patients with type 2 diabetes and advanced β-cell dysfunction.
Human mesenchymal stem cells (HMSCs) which are isolated from bone marrow stroma, peripheral blood, dermis, muscle and adipose tissue have the advantage of potential autologous transplantation ability. They can be differentiated into chondrogenic, osteogenic, adipogenic and myogenic lineages. Problems of stem cells from bone marrow are low cell numbers, low isolated volumes, pain, and to some extent ethical concerns. The isolation of mesenchymal stem cells from human adipose tissue was recently identified as an alternative source, since these cells are easy to obtain in big cell numbers. Adipose tissue is derived from embryonic mesoderm and contains a heterogeneous stromal cell population. To achieve lineage-specific differentiation of these cells they have to be cultured in media supplemented with appropriate factors. Inductions of the cells into multiple mesenchymal lineages resulted in the expression of several lineage-specific genes, proteins and specific metabolic activity. In conclusion, the potential benefit of the multi-germline capacity of HMSCs seems to be a promising approach for allogenic cell therapy and human tissue engineering.
Despite recent advances in medical procedures, cardiovascular disease remains a clinical challenge and the leading cause of mortality in the western world. The condition causes progressive smooth muscle cell (SMC) dedifferentiation, proliferation, and migration that contribute to vascular restenosis. The incidence of disease of the internal mammary artery (IMA), however, is much lower than in nearly all other arteries. The etiology of this IMA disease resistance is not well understood. Here, using paired primary IMA and coronary artery SMCs, serum stimulation, siRNA knockdowns, and verifications in porcine vessels in vivo, we investigate the molecular mechanisms that could account for this increased disease resistance of internal mammary SMCs. We show that the residue-specific phosphorylation profile of the retinoblastoma tumor suppressor protein (Rb) appears to differ significantly between IMA and coronary artery SMCs in cultured human cells. We also report that the differential profile of Rb phosphorylation may follow as a consequence of differences in the content of cyclin-dependent kinase 2 (CDK2) and the CDK4 phosphorylation inhibitor p15. Finally, we present evidence that siRNA-mediated CDK2 knockdown alters the profile of Rb phosphorylation in coronary artery SMCs, as well as the proliferative response of these cells to mitogenic stimulation. The intrinsic functional and protein composition specificity of the SMCs population in the coronary artery may contribute to the increased prevalence of restenosis and atherosclerosis in the coronary arteries as compared with the internal mammary arteries.
Atherosclerosis is a chronic disease of the arteries and accounts for about 50 percent of all deaths in industrialized countries. For its treatment, patients primarily need to undergo lifestyle changes, concerning their diet or sportive behavior, while additional pharmaceutical approaches help to reduce major risk factors such as hypertension and hyperlipidemia. However, these two areas of treatment are only briefly mentioned here. Instead, this article focuses on literature and patents from the last decade focusing on invasive surgical procedures necessary for treatment of diseased blood vessels in severe cases of atherosclerosis. Described herein are synthetic grafts and so-called autografts, which are harvested from the patient for bypass surgery. In addition, implantable stents are discussed, which deal with different atherosclerotic aspects, such as restenosis, re-endothelialization, neointimal hyperplasia and thrombosis. And finally, publications and inventions are presented from the relatively new field of artificial tissue engineering incorporating stem cells or biomaterials to construct new vessels as substitutes for diseased veins and arteries.
Adult stem cells, including adipose tissue-derived mesenchymal stem cells (MSCs) or ectomesenchymal dental follicle cells (DFCs), attract considerable attention for their potential to differentiate into lineages, which are of major interest in the field of Regenerative Medicine. Purinergic receptors exert a wide range of biological actions in many cell and tissue types through extracellular nucleotides. Little is known about P2 receptors in adult stem cells and changes in their expression levels during differentiation. All known P2 receptors have been investigated, and a variety of P2X and P2Y receptor subtypes were detected in MSCs. Studies investigating intracellular calcium levels on receptor stimulation demonstrated that the found P2 receptors are metabolically active. Interestingly, up- or downregulation of several P2 receptor subtypes at gene and protein level was observed during adipogenic and osteogenic differentiation, and the effect on differentiation was directly influenced by both the application of agonists/antagonists and apyrase-induced nucleotide cleavage. Here, we show for the first time that the combination of several P2 receptors plays a role in the differentiation of adult stem cells. The expression pattern of the P2 receptors, as well as their fate in differentiation, varies in stem cells of mesenchymal origin if compared with stem cells of ectomesenchymal origin. The subtypes P2X6, P2Y4, and P2Y14 seem to be pivotal regulators in MSC commitment, as they are regulated in both adipogenic and osteogenic differentiation of adipose tissue-derived stem cells and DFCs. These findings provide new insights into the differentiation processes and might reveal novel options to influence stem cell fate in future applications.
Transient up-regulation of P2 receptors influence differentiation of human mesenchymal stem cells
(2012)
Purpose – To describe the development of a novel polyether(meth)acrylate-based resin material class for stereolithography with alterable material characteristics.
Design/methodology/approach – A complete overview of details to composition parameters, the optimization and bandwidth of mechanical and processing parameters is given. Initial biological characterization experiments and future application fields are depicted. Process parameters are studied in a commercial 3D systems Viper stereolithography system, and a new method to determine these parameters is described herein.
Findings – Initial biological characterizations show the non-toxic behavior in a biological environment, caused mainly by the (meth)acrylate-based core components. These photolithographic resins combine an adjustable low Young’s modulus with the advantages of a non-toxic (meth)acrylate-based process material. In contrast to the mostly rigid process materials used today in the rapid prototyping industry, these polymeric formulations are able to fulfill the extended need for a soft engineering material. A short overview of sample applications is given.
Practical implications – These polymeric formulations are able to meet the growing demand for a resin class for rapid manufacturing that covers a bandwidth from softer to stiffer materials.
Originality/value – This paper gives an overview about the novel developed material class for stereolithography and should be therefore of high interest to people with interest in novel rapid manufacturing materials and technology.
Template-mediated mineralization describes a research field of materials chemistry that deals with templates influencing product formation of foremost inorganic functional materials and composites. These templates are usually organic compounds - as far as molecules with natural origin are involved, the terminology "biomineralization" or "biomimetic mineralization" is used. The present review gives insight into recent developments in the research area of bone-tissue engineering with focus on chemical templates and cell-based approaches. The review is structured as follows: (1) a brief general overview about the principle of templating and recently used template materials, (2) important analytical methods, (3) examples of template-guided mineralization of various bone-related materials, (4) natural bone mineralization, (5) scaffolds for bone-tissue regeneration and (6) cell-based therapeutic approaches. For this purpose, a literature screening with emphasis on promising potential practical applications was performed. In particular, macromolecular structures and polymer composites with relation to naturally occurring compounds were favored. Priority was given to publications of the last five years. Although the present review does not cover the whole topic to full extent, it should provide information about current trends and the most promising approaches in the research area of bone-tissue engineering based on applications of organic templates/scaffolds as well as cell-based strategies.
Besides their extracellular activity crucial for several pathophysiological conditions, human cysteine cathepsins, in particular cathepsins K and S, represent important intracellular targets for drug development. In the present study, a prototypic dipeptide nitrile inhibitor structure was equipped with a coumarin moiety to function as a fluorescent reporter group. In a second inhibitor, a PEG linker was introduced between the dipeptide nitrile and the fluorophore. These tool compounds 6 and 7 were characterized by kinetic investigations as covalent reversible inhibitors of human cathepsins L, S, K and B. Probe 6 showed a pronounced inhibitory activity against cathepsins K and S, which was corroborated by modeling of inhibition modes. Probe 7 was highly potent (Ki = 93 nM) and selective for cathepsin S. To examine the ability of both probes to enter living cells, human embryonic kidney 293 cells were targeted. At a concentration of 10 µM, cellular uptake of probe 6 was demonstrated by fluorescence measurement after an incubation time of 30 min and 3 h, respectively. The probe’s concentration in cell lysates was ascertained on the basis of the emission at 492 nm upon excitation at 450 nm, and the results were expressed as concentrations of probe 6 relative to the protein concentration originating from the lysate. After incubation of 10 µM of probe 6 for 3 h, the cellular uptake was confirmed by fluorescence microscopy. HPLC was used to assess the probes’ lipophilicity, and the obtained log D7.4 value of 2.65 for probe 6 was in agreement with the demonstrated cellular uptake.
Embryonic stem cells (ES) have the potential of long-term viability, selfrenewal and pluripotency which makes them interesting candidates for tissue engineering and gene therapy applications. On the other hand ethical and political issues arise while using theses cells and severe problems such as their tumorgenicity have not been solved yet. In the last couple of month a new source of cells with stem cell character was developed, the induced pluripotent stem cells (iPS). These cells are derived from differentiated adult cells via transduction of three transcription factors and show features similar to embryonic stem cells. Unfortunately, this includes the tumorgenicity which is even higher in those cells since the transcription factor transduction needed until now, is performed with retrovial vectors, which have a tumor potential on their own. Thus, adult stem cells are investigated extensively as alternative source of self-renewing cells. Human mesenchymal stem cells (HMSCs), which have in addition the advantage of potential autologous transplantation, can be found in various differentiated tissues since they are needed for maintenance and repair. They can be differentiated in chondrogenic, osteogenic, adipogenic and myogenic lineages which makes them an excellent tool for future tissue replacement strategies.
Coronary artery disease represents the most common type of heart disease and accounts for about 7.4 million deaths worldwide in 2012 [1]. Prognoses indicate that annual mortality from this condition will increase because the aging population also raises the prevalence ofpatients with multimorbidity and chronic conditions.
One of the most common problems in Regenerative Medicine is the regeneration of damaged bone with the aim of repairing or replacing lost or damaged bone tissue by stimulating the natural regenerative process. Particularly in the fields of orthopedic, plastic, reconstructive, maxillofacial and craniofacial surgery there is need for successful methods to restore bone. From a regenerative point of view two different bone replacement problems can be distinguished: large bone defects and small bone defects. Currently, no perfect system exists for the treatment of large bone defects.
Renewable resources gain increasing interest as source for environmentally benign biomaterials, such as drug encapsulation/release compounds, and scaffolds for tissue engineering in regenerative medicine. Being the second largest naturally abundant polymer, the interest in lignin valorization for biomedical utilization is rapidly growing. Depending on resource and isolation procedure, lignin shows specific antioxidant and antimicrobial activity. Today, efforts in research and industry are directed toward lignin utilization as renewable macromolecular building block for the preparation of polymeric drug encapsulation and scaffold materials. Within the last five years, remarkable progress has been made in isolation, functionalization and modification of lignin and lignin-derived compounds. However, literature so far mainly focuses lignin-derived fuels, lubricants and resins. The purpose of this review is to summarize the current state of the art and to highlight the most important results in the field of lignin-based materials for potential use in biomedicine (reported in 2014–2018). Special focus is drawn on lignin-derived nanomaterials for drug encapsulation and release as well as lignin hybrid materials used as scaffolds for guided bone regeneration in stem cell-based therapies.
A major challenge modern society has to face is the increasing need for tissue regeneration due to degenerative diseases or tumors, but also accidents or warlike conflicts. There is great hope that stem cell-based therapies might improve current treatments of cardiovascular diseases, osteochondral defects or nerve injury due to the unique properties of stem cells such as their self-renewal and differentiation potential. Since embryonic stem cells raise severe ethical concerns and are prone to teratoma formation, adult stem cells are still in the focus of research. Emphasis is placed on cellular signaling within these cells and in between them for a better understanding of the complex processes regulating stem cell fate. One of the oldest signaling systems is based on nucleotides as ligands for purinergic receptors playing an important role in a huge variety of cellular processes such as proliferation, migration and differentiation. Besides their natural ligands, several artificial agonists and antagonists have been identified for P1 and P2 receptors and are already used as drugs. This review outlines purinergic receptor expression and signaling in stem cells metabolism. We will briefly describe current findings in embryonic and induced pluripotent stem cells as well as in cancer-, hematopoietic-, and neural crest-derived stem cells. The major focus will be placed on recent findings of purinergic signaling in mesenchymal stem cells addressed in in vitro and in vivo studies, since stem cell fate might be manipulated by this system guiding differentiation towards the desired lineage in the future.
Exposure to microgravity conditions causes cardiovascular deconditioning in astronauts during spaceflight. Until now, no specific drugs are available for countermeasure, since the underlying mechanism is largely unknown. Endothelial cells (ECs) and smooth muscle cells (SMCs) play key roles in various vascular functions, many of which are regulated by purinergic 2 (P2) receptors. However, their function in ECs and SMCs under microgravity conditions is still unclear. In this study, primary ECs and SMCs were isolated from bovine aorta and verified with specific markers. We show for the first time that the P2 receptor expression pattern is altered in ECs and SMCs after 24 h exposure to simulated microgravity using a clinostat. However, conditioned medium compensates this change in specific P2 receptors, for example, P2X7. Notably, P2 receptors such as P2X7 might be the important players during the paracrine interaction. Additionally, ECs and SMCs secreted different cytokines under simulated microgravity, leading into a pathogenic proliferation and migration. In conclusion, our data indicate P2 receptors might be important players responding to gravity changes in ECs and SMCs. Since some artificial P2 receptor ligands are applied as drugs, it is reasonable to assume that they might be promising candidates against cardiovascular deconditioning in the future.
Scratch assays enable the study of the migration process of an injured adherent cell layer in vitro. An apparatus for the reproducible performance of scratch assays and cell harvesting has been developed that meets the requirements for reproducibility in tests as well as easy handling. The entirely autoclavable setup is divided into a sample translation and a scratching system. The translational system is compatible with standard culture dishes and can be modified to adapt to different cell culture systems, while the scratching system can be adjusted according to angle, normal force, shape, and material to adapt to specific questions and demanding substrates. As a result, a fully functional prototype can be presented. This system enables the creation of reproducible and clear scratch edges with a low scratch border roughness within a monolayer of cells. Moreover, the apparatus allows the collection of the migrated cells after scratching for further molecular biological investigations without the need for a second processing step. For comparison, the mechanical properties of manually performed scratch assays are evaluated.
