Laccase-Treated Polystyrene Surfaces with Caffeic Acid, Dopamine, and L-3,4-Dihydroxyphenylalanine Substrates Facilitate the Proliferation of Melanocytes and Embryonal Carcinoma Cells NTERA-2.

This study presents the effects of treating polystyrene (PS) cell culture plastic with oxidoreductase enzyme laccase and the catechol substrates caffeic acid (CA), L-DOPA, and dopamine on the culturing of normal human epidermal melanocytes (NHEMs) and human embryonal carcinoma cells (NTERA-2). The laccase-substrate treatment improved PS hydrophilicity and roughness, increasing NHEM and NTERA-2 adherence, proliferation, and NHEM melanogenesis to a level comparable with conventional plasma treatment. Cell adherence dynamics and proliferation were evaluated. The NHEM endpoint function was quantified by measuring melanin content. PS surfaces treated with laccase and its substrates demonstrated the forming of polymer-like structures. The surface texture roughness gradient and the peak curvature were higher on PS treated with a combination of laccase and substrates than laccase alone. The number of adherent NHEM and NTERA-2 was significantly higher than on the untreated surface. The proliferation of NHEM and NTERA-2 correspondingly increased on treated surfaces. NHEM melanin content was enhanced 6-10-fold on treated surfaces. In summary, laccase- and laccase-substrate-modified PS possess improved PS surface chemistry/hydrophilicity and altered roughness compared to untreated and plasma-treated surfaces, facilitating cellular adherence, subsequent proliferation, and exertion of the melanotic phenotype. The presented technology is easy to apply and creates a promising custom-made, substrate-based, cell-type-specific platform for both 2D and 3D cell culture.

Online Coupling of Size Exclusion Chromatography to Capillary Enhanced Raman Spectroscopy for the Analysis of Proteins and Biopharmaceutical Drug Products.

The online coupling of size exclusion chromatography (SEC) to capillary enhanced Raman spectroscopy (CERS) based on a liquid core waveguide (LCW) flow cell was applied for the first time to assess the higher-order structure of different proteins. This setup allows recording of Raman spectra of the monomeric protein within complex mixtures, since SEC enables the separation of the monomeric protein from matrix components such as excipients of a biopharmaceutical product and higher molecular weight species (e.g., aggregates). The acquired Raman spectra were used for structural elucidation of well characterized proteins such as bovine serum albumin, hen egg white lysozyme, and ß-lactoglobulin and of the monoclonal antibody rituximab in a medicinal product. Additionally, the CERS detection of the disaccharide sucrose, which is used as a stabilizing excipient, was quantified to achieve a limit of detection (LOD) of 120 µg and a limit of quantification (LOQ) of 363 µg injected on the column.

Rapid, label-free classification of glioblastoma differentiation status combining confocal Raman spectroscopy and machine learning.

Label-free identification of tumor cells using spectroscopic assays has emerged as a technological innovation with a proven ability for rapid implementation in clinical care. Machine learning facilitates the optimization of processing and interpretation of extensive data, such as various spectroscopy data obtained from surgical samples. The here-described preclinical work investigates the potential of machine learning algorithms combining confocal Raman spectroscopy to distinguish non-differentiated glioblastoma cells and their respective isogenic differentiated phenotype by means of confocal ultra-rapid measurements. For this purpose, we measured and correlated modalities of 1146 intracellular single-point measurements and sustainingly clustered cell components to predict tumor stem cell existence. By further narrowing a few selected peaks, we found indicative evidence that using our computational imaging technology is a powerful approach to detect tumor stem cells in vitro with an accuracy of 91.7% in distinct cell compartments, mainly because of greater lipid content and putative different protein structures. We also demonstrate that the presented technology can overcome intra- and intertumoral cellular heterogeneity of our disease models, verifying the elevated physiological relevance of our applied disease modeling technology despite intracellular noise limitations for future translational evaluation.

Adjustable Thermo-Responsive, Cell-Adhesive Tissue Engineering Scaffolds for Cell Stimulation through Periodic Changes in Culture Temperature.

A three-dimensional (3D) scaffold ideally provides hierarchical complexity and imitates the chemistry and mechanical properties of the natural cell environment. Here, we report on a stimuli-responsive photo-cross-linkable resin formulation for the fabrication of scaffolds by continuous digital light processing (cDLP), which allows for the mechano-stimulation of adherent cells. The resin comprises a network-forming trifunctional acrylate ester monomer (trimethylolpropane triacrylate, or TMPTA), N-isopropyl acrylamide (NiPAAm), cationic dimethylaminoethyl acrylate (DMAEA) for enhanced cell interaction, and 4-acryloyl morpholine (AMO) to adjust the phase transition temperature (Ttrans) of the equilibrium swollen cross-polymerized scaffold. With glycofurol as a biocompatible solvent, controlled three-dimensional structures were fabricated and the transition temperatures were adjusted by resin composition. The effects of the thermally induced mechano-stimulation were investigated with mouse fibroblasts (L929) and myoblasts (C2C12) on printed constructs. Periodic changes in the culture temperature stimulated the myoblast proliferation.

Biodegradable macromers for implant bulk and surface engineering.

Macromers, polymeric molecules with at least two functional groups for cross-polymerization, are interesting materials to tailor mechanical, biochemical and degradative bulk and surface properties of implants for tissue regeneration. In this review we focus on macromers with at least one biodegradable building block. Manifold design options, such as choice of polymeric block(s), optional core molecule and reactive groups, as well as cross-co-polymerization with suitable anchor or linker molecules, allow the adaptation of macromer-based biomaterials towards specific application requirements in both hard and soft tissue regeneration. Implants can be manufactured from macromers using additive manufacturing as well as molding and templating approaches. This review summarizes and discusses the overall concept of biodegradable macromers and recent approaches for macromer processing into implants as well as techniques for surface modification directed towards bone regeneration. These aspects are reviewed including a focus on the authors' contributions to the field through research within the collaborative research project Transregio 67.

Osteogenic Potential of Mesenchymal Stem Cells from Adipose Tissue, Bone Marrow and Hair Follicle Outer Root Sheath in a 3D Crosslinked Gelatin-Based Hydrogel.

Bone transplantation is regarded as the preferred therapy to treat a variety of bone defects. Autologous bone tissue is often lacking at the source, and the mesenchymal stem cells (MSCs) responsible for bone repair mechanisms are extracted by invasive procedures. This study explores the potential of autologous mesenchymal stem cells derived from the hair follicle outer root sheath (MSCORS). We demonstrated that MSCORS have a remarkable capacity to differentiate in vitro towards the osteogenic lineage. Indeed, when combined with a novel gelatin-based hydrogel called Osteogel, they provided additional osteoinductive cues in vitro that may pave the way for future application in bone regeneration. MSCORS were also compared to MSCs from adipose tissue (ADMSC) and bone marrow (BMMSC) in a 3D Osteogel model. We analyzed gel plasticity, cell phenotype, cell viability, and differentiation capacity towards the osteogenic lineage by measuring alkaline phosphatase (ALP) activity, calcium deposition, and specific gene expression. The novel injectable hydrogel filled an irregularly shaped lesion in a porcine wound model displaying high plasticity. MSCORS in Osteogel showed a higher osteo-commitment in terms of calcium deposition and expression dynamics of OCN, BMP2, and PPARG when compared to ADMSC and BMMSC, whilst displaying comparable cell viability and ALP activity. In conclusion, autologous MSCORS combined with our novel gelatin-based hydrogel displayed a high capacity for differentiation towards the osteogenic lineage and are acquired by non-invasive procedures, therefore qualifying as a suitable and expandable novel approach in the field of bone regeneration therapy.

Artificial Extracellular Matrices Containing Bioactive Glass Nanoparticles Promote Osteogenic Differentiation in Human Mesenchymal Stem Cells.

The present study analyzes the capacity of collagen (coll)/sulfated glycosaminoglycan (sGAG)-based surface coatings containing bioactive glass nanoparticles (BGN) in promoting the osteogenic differentiation of human mesenchymal stroma cells (hMSC). Physicochemical characteristics of these coatings and their effects on proliferation and osteogenic differentiation of hMSC were investigated. BGN were stably incorporated into the artificial extracellular matrices (aECM). Oscillatory rheology showed predominantly elastic, gel-like properties of the coatings. The complex viscosity increased depending on the GAG component and was further elevated by adding BGN. BGN-containing aECM showed a release of silicon ions as well as an uptake of calcium ions. hMSC were able to proliferate on coll and coll/sGAG coatings, while cellular growth was delayed on aECM containing BGN. However, a stimulating effect of BGN on ALP activity and calcium deposition was shown. Furthermore, a synergistic effect of sGAG and BGN was found for some donors. Our findings demonstrated the promising potential of aECM and BGN combinations in promoting bone regeneration. Still, future work is required to further optimize the BGN/aECM combination for increasing its combined osteogenic effect.

A human serum-enriched medium formulation supports high viability and marker expression in primary melanocyte cultures from the outer root sheath and epidermis.

Formulating clinically relevant melanocyte cultivation media that maintain the balance between proliferation and maturation to functional melanocytes is a major experimental and regulatory challenge. Within the translation of human melanocytes from the outer root sheath of human hair follicle (HUMORS), we developed a melanocyte medium free of chemical mitogens, chemical melanogenesis enhancers and bovine products, enabling proliferation as well as melanotic differentiation. The formulation involved the replacement of bovine pituitary extract (BPE) and bovine serum (FBS) with human serum (HS) combined with ascorbic acid, CaCl2 , epinephrine, L-glutamine, insulin and fibroblast growth factor. The cultivation efficiency was characterized through proliferation and exertion of melanotic phenotype, gene and protein expression of melanotic markers and melanin content. Having established an application-directed BPE-free formulation, we then re-formulated a research-grade medium with BPE for purposes of even more effective in vitro cultivation, adjusted to specific requirements of HUMORS and normal human epidermal melanocytes (NHEM).

Dual-Functional Hydrazide-Reactive and Anhydride-Containing Oligomeric Hydrogel Building Blocks.

Biomimetic hydrogels are advanced biomaterials that have been developed following different synthetic routes. Covalent postfabrication functionalization is a promising strategy to achieve efficient matrix modification decoupled of general material properties. To this end, dual-functional macromers were synthesized by free radical polymerization of maleic anhydride with diacetone acrylamide (N-(1,1-dimethyl-3-oxobutyl)acrylamide) and pentaerythritol diacrylate monostearate. Amphiphilic oligomers (Mn < 7.5 kDa) with anhydride contents of 7-20% offered cross-linking reactivity to yield rigid hydrogels with gelatinous peptides (E = 4-13 kPa) and good cell adhesion properties. Mildly reactive methyl ketones as second functionality remained intact during hydrogel formation and potential of covalent matrix modification was shown using hydrazide and hydrazine model compounds. Successful secondary dihydrazide cross-linking was demonstrated by an increase of hydrogel stiffness (>40%). Efficient hydrazide/hydrazine immobilization depending on solution pH, hydrogel ketone content as well as ligand concentration for bioconjugation was shown and reversibility of hydrazone formation was indicated by physiologically relevant hydrazide release over 7 days. Proof-of-concept experiments with hydrazido-functionalized hyaluronan demonstrated potential for covalent aECM immobilization. The presented dual-functional macromers have perspective as reactive hydrogel building blocks for various biomedical applications.

Dual-Component Gelatinous Peptide/Reactive Oligomer Formulations as Conduit Material and Luminal Filler for Peripheral Nerve Regeneration.

Toward the next generation of nerve guidance conduits (NGCs), novel biomaterials and functionalization concepts are required to address clinical demands in peripheral nerve regeneration (PNR). As a biological polymer with bioactive motifs, gelatinous peptides are promising building blocks. In combination with an anhydride-containing oligomer, a dual-component hydrogel system (cGEL) was established. First, hollow cGEL tubes were fabricated by a continuous dosing and templating process. Conduits were characterized concerning their mechanical strength, in vitro and in vivo degradation and biocompatibility. Second, cGEL was reformulated as injectable shear thinning filler for established NGCs, here tyrosine-derived polycarbonate-based braided conduits. Thereby, the formulation contained the small molecule LM11A-31. The biofunctionalized cGEL filler was assessed regarding building block integration, mechanical properties, in vitro cytotoxicity, and growth permissive effects on human adipose tissue-derived stem cells. A positive in vitro evaluation motivated further application of the filler material in a sciatic nerve defect. Compared to the empty conduit and pristine cGEL, the functionalization performed superior, though the autologous nerve graft remains the gold standard. In conclusion, LM11A-31 functionalized cGEL filler with extracellular matrix (ECM)-like characteristics and specific biochemical cues holds great potential to support PNR.

Rat Osteosarcoma Cells as a Therapeutic Target Model for Osteoregeneration via Sclerostin Knockdown.

There are various conceptually different strategies to improve bone regeneration and to treat osteoporosis, each with distinct inherent advantages and disadvantages. The use of RNA interference strategies to suppress the biological action of catabolic factors or antagonists of osteogenic proteins is promising, and such strategies can be applied locally. They are comparably inexpensive and do not suffer from stability problems as protein-based approaches. In this study, we focus on sclerostin, encoded by the SOST gene, a key regulator of bone formation and remodeling. Sclerostin is expressed by mature osteocytes but also by late osteogenically differentiated cells. Thus, it is difficult and requires long-term cultures to investigate the effects of SOST silencing on the expression of osteogenic markers using primary cells. We, therefore, selected a rat osteosarcoma cell line, UMR-106, that has been shown to express SOST and secrete sclerostin in a comparable fashion as late osteoblasts and osteocytes. We investigated the effects of differentiating supplements on SOST expression and sclerostin secretion in UMR-106 cells and found that addition of 100 ng/ml of bone morphogenetic protein (BMP)-2 strongly induced sclerostin secretion, whereas dexamethasone inhibited secretion. Effects of silencing SOST in UMR-106 cells cultured in various differentiation media including BMP-2 and/or dexamethasone were determined next with the aim to find promising test conditions for a readout system for the evaluation of future small interfering RNA release formulations for local induction of bone formation. We found a direct correlation between attenuated SOST expression and an increase in the osteogenic potential of UMR-106 cells. The combination of SOST silencing and BMP-2 could synergistically improve osteogenic factors. A lowered proliferation rate in silenced groups may indicate a faster switch to differentiation.

Multi-Functional Macromers for Hydrogel Design in Biomedical Engineering and Regenerative Medicine.

Contemporary biomaterials are expected to provide tailored mechanical, biological and structural cues to encapsulated or invading cells in regenerative applications. In addition, the degradative properties of the material also have to be adjustable to the desired application. Oligo- or polymeric building blocks that can be further cross-linked into hydrogel networks, here addressed as macromers, appear as the prime option to assemble gels with the necessary degrees of freedom in the adjustment of the mentioned key parameters. Recent developments in the design of multi-functional macromers with two or more chemically different types of functionalities are summarized and discussed in this review illustrating recent trends in the development of advanced hydrogel building blocks for regenerative applications.

Gelatin-based biomaterial engineering with anhydride-containing oligomeric cross-linkers.

Chemically cross-linked gelatin hydrogels are versatile cell-adhesive hydrogel materials that have been established for a variety of biomedical applications. The most prominent cross-linker is glutaraldehyde, which, however, has been described to cause compatibility problems and loss of microscopic but relevant structural features. A recently developed oligomeric cross-linker that contains anhydride functionalities was evaluated as cross-linker for the fabrication of gelatin-based hydrogels and microparticles. In a fast curing reaction, hydrogels composed of gelatin and oligomeric cross-linker were fabricated with good conversion over a wide concentration range of constituents and with cross-linkers of different anhydride contents. Hydrogel properties, such as dry weight and mechanics, could be controlled by hydrogel composition and rheological properties correlated to elastic moduli from 1 to 10 kPa. The gels were shown to be cytocompatible and promoted cell adhesion. In soft formulations, cells migrated into the hydrogel bulk. Gelatin microparticles prepared by a standard water-in-oil emulsion technique were also treated with the novel oligomers, and cross-linking degrees matching those obtained with glutaraldehyde were obtained. At the same time, fewer interparticular cross-links were observed. Fluorescein-derivatized cross-linkers yielded labeled microparticles in a concentration-dependent manner. The oligomeric cross-linkers are presented as an efficient and possibly more functional and compatible alternative to glutaraldehyde. The engineered hydrogel materials hold potential for various biomedical applications.

Application of deep UV resonance Raman spectroscopy to column liquid chromatography: Development of a low-flow method for the identification of active pharmaceutical ingredients.

In this study, deep UV resonance Raman spectroscopy (DUV-RRS) was coupled with high performance liquid chromatography (HPLC) to be applied in the field of pharmaceutical analysis. Naproxen, Metformin and Epirubicin were employed as active pharmaceutical ingredients (APIs) covering different areas of the pharmacological spectrum. Raman signals were successfully generated and attributed to the test substances, even in the presence of the dominant solvent bands of the mobile phase. To increase sensitivity, a low-flow method was developed to extend the exposure time of the sample. This approach enabled the use of a deep UV pulse laser with a low average power of 0.5 mW. Compared to previous studies, where energy-intensive argon ion lasers were commonly used, we were able to achieve similar detection limits with our setup. Using affordable lasers with low operating costs may facilitate the transfer of the results of this study into practical applications.

Enhancement of lacrimal gland cell function by decellularized lacrimal gland derived hydrogel.

Sustainable treatment of aqueous deficient dry eye (ADDE) represents an unmet medical need and therefore requires new curative and regenerative approaches based on appropriatein vitromodels. Tissue specific hydrogels retain the individual biochemical composition of the extracellular matrix and thus promote the inherent cell´s physiological function. Hence, we created a decellularized lacrimal gland (LG) hydrogel (dLG-HG) meeting the requirements for a bioink as the basis of a LG model with potential forin vitroADDE studies. Varying hydrolysis durations were compared to obtain dLG-HG with best possible physical and ultrastructural properties while preserving the original biochemical composition. A particular focus was placed on dLG-HG´s impact on viability and functionality of LG associated cell types with relevance for a futurein vitromodel in comparison to the unspecific single component hydrogel collagen type-I (Col) and the common cell culture substrate Matrigel. Proliferation of LG epithelial cells (EpC), LG mesenchymal stem cells, and endothelial cells cultured on dLG-HG was enhanced compared to culture on Matrigel. Most importantly with respect to a functionalin vitromodel, the secretion capacity of EpC cultured on dLG-HG was higher than that of EpC cultured on Col or Matrigel. In addition to these promising cell related properties, a rapid matrix metalloproteinase-dependent biodegradation was observed, which on the one hand suggests a lively cell-matrix interaction, but on the other hand limits the cultivation period. Concluding, dLG-HG possesses decisive properties for the tissue engineering of a LGin vitromodel such as cytocompatibility and promotion of secretion, making it superior to unspecific cell culture substrates. However, deceleration of biodegradation should be addressed in future experiments.

Modulation of Decellularized Lacrimal Gland Hydrogel Biodegradation by Genipin Crosslinking.

Purpose: Hydrogels derived from decellularized tissues are promising biomaterials in tissue engineering, but their rapid biodegradation can hinder in vitro cultivation. This study aimed to retard biodegradation of a hydrogel derived from porcine decellularized lacrimal glands (dLG-HG) by crosslinking with genipin to increase the mechanical stability without affecting the function and viability of lacrimal gland (LG)-associated cells. Methods: The effect of different genipin concentrations on dLG-HG stiffness was measured rheologically. Cell-dependent biodegradation was quantified over 10 days, and the impact on matrix metalloproteinase (MMP) activity was quantified by gelatin and collagen zymography. The viability of LG epithelial cells (EpCs), mesenchymal stem cells (MSCs), and endothelial cells (ECs) cultured on genipin-crosslinked dLG-HG was assessed after 10 days, and EpC secretory activity was analyzed by ß-hexosaminidase assay. Results: The 0.5-mM genipin increased the stiffness of dLG-HG by about 46%, and concentrations > 0.25 mM caused delayed cell-dependent biodegradation and reduced MMP activity. The viability of EpCs, MSCs, and ECs was not affected by genipin concentrations of up to 0.5 mM after 10 days. Moreover, up to 0.5-mM genipin did not negatively affect EpC secretory activity compared to control groups. Conclusions: A concentration of 0.5-mM genipin increased dLG-HG stiffness, and 0.25-mM genipin was sufficient to prevent MMP-dependent degradation. Importantly, concentrations of up to 0.5-mM genipin did not compromise the viability of LG-associated cells or the secretory activity of EpCs. Thus, crosslinking with genipin improves the properties of dLG-HG for use as a substrate in LG tissue engineering.

The pore size of PLGA bone implants determines the de novo formation of bone tissue in tibial head defects in rats.

PURPOSE: The influence of the pore size of biodegradable poly(lactic-co-glycolic acid) scaffolds on bone regeneration was investigated. METHODS: Cylindrical poly(lactic-co-glycolic acid) scaffolds were implanted into a defect in the tibial head of rats. Pore sizes of 100-300, 300-500, and 500-710 µm were tested and compared to untreated defects as control. Two and four weeks after implantation, the specimens were explanted and defect regeneration and de novo extracellular matrix generation were investigated by MRI, quantitative solid-state NMR, and mass spectrometry. RESULTS: The pore size of the scaffolds had a pronounced influence on the quantity of the extracellular matrix synthesized in the graft; most collagen was synthesized within the first 2 weeks of implantation, while the amount of hydroxyapatite increased in the second 2 weeks. After 4 weeks, the scaffolds contained large quantities of newly formed lamellar bone while the control defects were filled by inhomogenous woven bone. Best results were obtained for scaffolds of a pore size of 300-500 µm. CONCLUSION: Our analysis showed that the structure and dynamics of the regenerated extracellular matrix was very similar to that of the native bone, suggesting that biomineralization was significantly enhanced by the choice of the most appropriate implant material.

Radiofluorination of an Anionic, Azide-Functionalized Teroligomer by Copper-Catalyzed Azide-Alkyne Cycloaddition.

This study describes the synthesis, radiofluorination and purification of an anionic amphiphilic teroligomer developed as a stabilizer for siRNA-loaded calcium phosphate nanoparticles (CaP-NPs). As the stabilizing amphiphile accumulates on nanoparticle surfaces, the fluorine-18-labeled polymer should enable to track the distribution of the CaP-NPs in brain tumors by positron emission tomography after application by convection-enhanced delivery. At first, an unmodified teroligomer was synthesized with a number average molecular weight of 4550 ± 20 Da by free radical polymerization of a defined composition of methoxy-PEG-monomethacrylate, tetradecyl acrylate and maleic anhydride. Subsequent derivatization of anhydrides with azido-TEG-amine provided an azido-functionalized polymer precursor (o14PEGMA-N3) for radiofluorination. The 18F-labeling was accomplished through the copper-catalyzed cycloaddition of o14PEGMA-N3 with diethylene glycol-alkyne-substituted heteroaromatic prosthetic group [18F]2, which was synthesized with a radiochemical yield (RCY) of about 38% within 60 min using a radiosynthesis module. The 18F-labeled polymer [18F]fluoro-o14PEGMA was obtained after a short reaction time of 2-3 min by using CuSO4/sodium ascorbate at 90 °C. Purification was performed by solid-phase extraction on an anion-exchange cartridge followed by size-exclusion chromatography to obtain [18F]fluoro-o14PEGMA with a high radiochemical purity and an RCY of about 15%.

31P and 13C solid-state NMR spectroscopy to study collagen synthesis and biomineralization in polymer-based bone implants.

A combination of solid-state NMR spectroscopy and MRI was used to evaluate the formation of extracellular matrix in poly(D,L-lactide-co-glycolide) (PLGA) bone implants. Porous PLGA scaffolds were implanted into rat tibiae and analysed after 2, 4 or 8 weeks. MRI clearly delineated the implants within the cancellous bone. Differences in the trabecular structure of the implanted material and native bone were demonstrated. In addition, implants were analyzed by solid-state NMR spectroscopy under magic angle spinning. (13)C NMR spectra showed the unambiguous signature of collagen formed in the scaffolds, but also the characteristic signals of the PLGA matrix, indicating that resorption was not complete after 8 weeks. Furthermore, (31)P NMR spectroscopy detected the inorganic component of the matrix, which is composed of bioapatite. (31)P NMR spectra were quantified and this analysis revealed that the amount of inorganic extracellular matrix formed de novo was significantly lower than in native bone. This demonstrates that solid-state NMR spectroscopy, in particular in combination with MRI, can provide useful information on the composition and structure of the extracellular matrix, and serve as a tool to evaluate the quality of tissue engineering strategies.

De novo biosynthesis of glycosaminoglycans in the extracellular matrix of skin studied by matrix-assisted laser desorption/ionization mass spectrometry.

The self-healing capacity of skin is limited, and medical intervention is often unavoidable. Skin may be generated ex vivo from cultured fibroblasts. Because the molecular composition of de novo formed skin (mostly collagen and glycosaminoglycans [GAGs]) is crucial, analytical methods are required for the quality control of tissue-engineered products. Here, we show that matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) of fibroblast cultures subsequent to digestion with chondroitinase ABC is a reliable and fast method to monitor the GAG content of native and bioengineered skin. Furthermore, the supplementation of the fibroblast medium with ¹³C-labeled glucose provides insights into the biosynthesis of GAGs.