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Cooper BG, DeMoya CD, Sikes KJ, Frisbie DD, Phillips N, Nelson BB, McIlwraith CW, Kawcak CE, Goodrich LR, Snyder BD, Grinstaff MW. A polymer network architecture provides superior cushioning and lubrication of soft tissue compared to a linear architecture. Biomater Sci 2023; 11:7339-7345. [PMID: 37847186 DOI: 10.1039/d3bm00753g] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2023]
Abstract
We report the relationships between linear vs. network polymer architecture and biomechanical outcomes including lubrication and cushioning when the polymers are applied to the surface of articulating knee cartilage. Aqueous formulations of the bioinspired polymer poly(2-methacryloyloxylethyl phosphorylcholine) (pMPC) exhibit tuneable rheological properties, with network pMPC exhibiting increased elasticity and viscosity compared to linear pMPC. Application of a polymer network, compared to a linear one, to articulating tissue surfaces reduces friction, lessens tissue strain, minimizes wear, and protects tissue - thereby improving overall tissue performance. Administration of the network pMPC to the middle carpal joint of skeletally mature horses elicits a safe response similar to saline as monitored over a 70 day period.
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Affiliation(s)
- Benjamin G Cooper
- Department of Chemistry, Boston University, Boston, MA, 02215, USA.
- Center for Advanced Orthopedic Studies (CAOS), Beth Israel Deaconess Medical Center, Boston, MA, 02215, USA
| | - Christian D DeMoya
- Center for Advanced Orthopedic Studies (CAOS), Beth Israel Deaconess Medical Center, Boston, MA, 02215, USA
- Department of Biomedical Engineering, Boston University, Boston, MA, 02215, USA
| | - Katie J Sikes
- Gail Holmes Equine Orthopaedic Research Center, Department of Clinical Sciences, College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins, CO, 80523, USA
| | - David D Frisbie
- Gail Holmes Equine Orthopaedic Research Center, Department of Clinical Sciences, College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins, CO, 80523, USA
| | - Nikki Phillips
- Gail Holmes Equine Orthopaedic Research Center, Department of Clinical Sciences, College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins, CO, 80523, USA
| | - Brad B Nelson
- Gail Holmes Equine Orthopaedic Research Center, Department of Clinical Sciences, College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins, CO, 80523, USA
| | - C Wayne McIlwraith
- Gail Holmes Equine Orthopaedic Research Center, Department of Clinical Sciences, College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins, CO, 80523, USA
| | - Chris E Kawcak
- Gail Holmes Equine Orthopaedic Research Center, Department of Clinical Sciences, College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins, CO, 80523, USA
| | - Laurie R Goodrich
- Gail Holmes Equine Orthopaedic Research Center, Department of Clinical Sciences, College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins, CO, 80523, USA
| | - Brian D Snyder
- Center for Advanced Orthopedic Studies (CAOS), Beth Israel Deaconess Medical Center, Boston, MA, 02215, USA
- Department of Orthopedic Surgery, Boston Childrens Hospital, Boston, MA, 02215, USA.
| | - Mark W Grinstaff
- Department of Chemistry, Boston University, Boston, MA, 02215, USA.
- Department of Biomedical Engineering, Boston University, Boston, MA, 02215, USA
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Vandeweerd JM, Innocenti B, Rocasalbas G, Gautier SE, Douette P, Hermitte L, Hontoir F, Chausson M. Non-clinical assessment of lubrication and free radical scavenging of an innovative non-animal carboxymethyl chitosan biomaterial for viscosupplementation: An in-vitro and ex-vivo study. PLoS One 2021; 16:e0256770. [PMID: 34634053 PMCID: PMC8504732 DOI: 10.1371/journal.pone.0256770] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2021] [Accepted: 07/21/2021] [Indexed: 11/18/2022] Open
Abstract
OBJECTIVE Lubrication and free radical scavenging are key features of biomaterials used for viscosupplementation (VS) of joints affected by osteoarthritis (OA). The objective of this study was to describe the non-clinical performance characterization of KiOmedine® CM-Chitosan, a non-animal carboxymethyl chitosan, in order to assess its intended action in VS and to compare it to existing viscosupplements based on crosslinked hyaluronan (HA) formulations. METHOD The lubrication capacity of the tested viscosupplements (VS) was evaluated in-vitro and ex-vivo. In-vitro, the coefficient of friction (COF) was measured using a novel tribological system. Meanwhile, an ex-vivo biomechanical model in ovine hindlimbs was developed to assess the recovery of join mobility after an intra-articular (IA) injection. Free radical scavenging capacity of HA and KiOmedine® CM-Chitosan formulations was evaluated using the Trolox Equivalent Antioxidant Capacity (TEAC) assay. RESULTS In the in-vitro tribological model, KiOmedine® CM-Chitosan showed high lubrication capacity with a significant COF reduction than crosslinked HA formulations. In the ex-vivo model, the lubrication effect of KiOmedine® CM-Chitosan following an IA injection in the injured knee was proven again by a COF reduction. The recovery of joint motion was optimal with an IA injection of 3 ml of KiOmedine® CM-Chitosan, which was significantly better than the crosslinked HA formulation at the same volume. In the in-vitro TEAC assay, KiOmedine® CM-Chitosan showed a significantly higher free radical scavenging capacity than HA formulations. CONCLUSION Overall, the results provide a first insight into the mechanism of action in terms of lubrication and free radical scavenging for the use of KiOmedine® CM-Chitosan as a VS treatment of OA. KiOmedine® CM-Chitosan demonstrated a higher capacity to scavenge free radicals, and it showed a higher recovery of mobility after a knee lesion than crosslinked HA formulations. This difference could be explained by the difference in chemical structure between KiOmedine® CM-Chitosan and HA and their formulations.
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Affiliation(s)
- Jean-Michel Vandeweerd
- OASIS, Integrated Veterinary Research Unit, Namur Research Institute of Life Sciences (NARILIS), Namur University, Namur, Belgium
| | | | | | | | | | | | - Fanny Hontoir
- OASIS, Integrated Veterinary Research Unit, Namur Research Institute of Life Sciences (NARILIS), Namur University, Namur, Belgium
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Vinke J, Oude Elberink M, Stokman MA, Kroese FGM, Nazmi K, Bikker FJ, van der Mei HC, Vissink A, Sharma PK. Lubricating properties of chewing stimulated whole saliva from patients suffering from xerostomia. Clin Oral Investig 2021; 25:4459-4469. [PMID: 33661446 PMCID: PMC8310523 DOI: 10.1007/s00784-020-03758-8] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2020] [Accepted: 12/21/2020] [Indexed: 12/01/2022]
Abstract
OBJECTIVES The study aimed to quantify the lubricating properties of chewing stimulated whole saliva from healthy controls (n = 22), from patients suffering from primary Sjögren's syndrome (n = 37) and from patients undergoing head-and-neck radiotherapy (n = 34). MATERIALS AND METHODS All participants had to complete the Xerostomia Inventory questionnaire to score dry mouth sensation. Lubrication was measured using an ex vivo tongue-enamel friction system in terms of Relief and Relief period. MUC5b and total protein concentrations of the saliva samples were measured by an enzyme-linked immunosorbent assay and a bicinchoninic acid assay, respectively. RESULTS Relief of Sjögren's patients' saliva and post-irradiation patients' saliva was similar compared with healthy controls, but saliva from post-irradiation patients lubricated significantly better than saliva from Sjögren's patients. The Relief period was similar between the three groups. The Relief and Relief period were higher for saliva samples post-irradiation compared to pre-irradiation. MUC5b and total protein concentrations were comparable in all groups. MUC5b and total protein output were significantly lower in patients subjected to radiotherapy compared to saliva from healthy controls and pre-irradiation patients. MUC5b concentrations positively correlated with lubricating properties of post-irradiation patient saliva. CONCLUSIONS The lubricating properties of patient saliva were not any worse than healthy controls. Lower flow rate leads to lower availability of saliva in the oral cavity and decreases the overall output of protein and MUC5b, which might result in an insufficient replenishing of the mucosal salivary film. CLINICAL RELEVANCE An insufficient replenishing might underlie the sensation of a dry mouth and loss of oral function.
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Affiliation(s)
- Jeroen Vinke
- Department of Biomedical Engineering, University of Groningen and University Medical Center Groningen, Antonius Deusinglaan 1, 9713AV, Groningen, The Netherlands
| | - Marijn Oude Elberink
- Department of Biomedical Engineering, University of Groningen and University Medical Center Groningen, Antonius Deusinglaan 1, 9713AV, Groningen, The Netherlands
| | - Monique A Stokman
- Department of Radiation Oncology, University of Groningen and University Medical Center Groningen, Groningen, The Netherlands
| | - Frans G M Kroese
- Department of Rheumatology and Clinical Immunology, University of Groningen and University Medical Center Groningen, Groningen, The Netherlands
| | - Kamran Nazmi
- Department of Oral Biochemistry, Academic Centre for Dentistry Amsterdam, Free University and University of Amsterdam, Amsterdam, The Netherlands
| | - Floris J Bikker
- Department of Oral Biochemistry, Academic Centre for Dentistry Amsterdam, Free University and University of Amsterdam, Amsterdam, The Netherlands
| | - Henny C van der Mei
- Department of Biomedical Engineering, University of Groningen and University Medical Center Groningen, Antonius Deusinglaan 1, 9713AV, Groningen, The Netherlands
| | - Arjan Vissink
- Department of Oral and Maxillofacial Surgery, University of Groningen and University Medical Center Groningen, Groningen, The Netherlands
| | - Prashant K Sharma
- Department of Biomedical Engineering, University of Groningen and University Medical Center Groningen, Antonius Deusinglaan 1, 9713AV, Groningen, The Netherlands.
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Baskaran N, Chang YC, Chang CH, Hung SK, Kao CT, Wei Y. Quantify the Protein-Protein Interaction Effects on Adsorption Related Lubricating Behaviors of α-Amylase on a Glass Surface. Polymers (Basel) 2020; 12:E1658. [PMID: 32722491 PMCID: PMC7463787 DOI: 10.3390/polym12081658] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2020] [Revised: 07/18/2020] [Accepted: 07/22/2020] [Indexed: 11/16/2022] Open
Abstract
Dental ceramic material is one of the widely preferred restorative materials to mimic the natural tooth enamel surface. However, it has continuously been degraded because of low wear resistance during mastication in the oral cavity. The friction involved was reduced by introducing the lubricant saliva protein layers to improve the wear resistance of the dental materials. However, little is understood regarding how the protein-protein interactions (PPI) influence the adsorbed-state structures and lubricating behaviors of saliva proteins on the ceramic material surface. The objective of this study is to quantify the influences of PPI effects on the structural changes and corresponding oral lubrications of adsorbed α-amylase, one of the abundant proteins in the saliva, on the dental ceramic material with glass as a model surface. α-Amylase was first adsorbed to glass surface under varying protein solution concentrations to saturate the surface to vary the PPI effects over a wide range. The areal density of the adsorbed protein was measured as an indicator of the level of PPI effects within the layer, and these values were then correlated with the measurements of the adsorbed protein's secondary structure and corresponding friction coefficient. The decreased friction coefficient value was an indicator of the lubricated surfaces with higher wear resistance. Our results indicate that PPI effects help stabilize the structure of α-amylase adsorbed on glass, and the correlation observed between the friction coefficient and the conformational state of adsorbed α-amylase was apparent. This study thus provides new molecular-level insights into how PPI influences the structure and lubricating behaviors of adsorbed protein, which is critical for the innovations of dental ceramic material designs with improved wear resistance.
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Affiliation(s)
| | | | | | | | | | - Yang Wei
- Department of Chemical Engineering and Biotechnology, National Taipei University of Technology, 1, Section 3, Zhongxiao East Road, Taipei 10608, Taiwan; (N.B.); (Y.-C.C.); (C.-H.C.); (S.-K.H.); (C.-T.K.)
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Cooper BG, Catalina Bordeianu, Nazarian A, Snyder BD, Grinstaff MW. Active agents, biomaterials, and technologies to improve biolubrication and strengthen soft tissues. Biomaterials 2018; 181:210-226. [PMID: 30092370 PMCID: PMC6766080 DOI: 10.1016/j.biomaterials.2018.07.040] [Citation(s) in RCA: 32] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2018] [Revised: 07/22/2018] [Accepted: 07/25/2018] [Indexed: 12/27/2022]
Abstract
Normal functioning of articulating tissues is required for many physiological processes occurring across length scales from the molecular to whole organism. Lubricating biopolymers are present natively on tissue surfaces at various sites of biological articulation, including eyelid, mouth, and synovial joints. The range of operating conditions at these disparate interfaces yields a variety of tribological mechanisms through which compressive and shear forces are dissipated to protect tissues from material wear and fatigue. This review focuses on recent advances in active agents and biomaterials for therapeutic augmentation of friction, lubrication, and wear in disease and injured states. Various small-molecule, biological, and gene delivery therapies are described, as are tribosupplementation with naturally-occurring and synthetic biolubricants and polymer reinforcements. While reintroduction of a diseased tissue's native lubricant received significant attention in the past, recent discoveries and pre-clinical research are capitalizing on concurrent advances in the molecular sciences and bioengineering fields, with an understanding of the underlying tissue structure and physiology, to afford a desired, and potentially patient-specific, tissue mechanical response for restoration of normal function. Small and large molecule drugs targeting recently elucidated pathways as well as synthetic and hybrid natural/synthetic biomaterials for restoring a desired tissue mechanical response are being investigated for treatment of, for example, keratoconjunctivitis sicca, xeroderma, and osteoarthritis.
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Affiliation(s)
- Benjamin G Cooper
- Department of Chemistry, Boston University, Boston, MA, United States; Center for Advanced Orthopaedic Studies, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA, United States.
| | - Catalina Bordeianu
- Department of Chemistry, Boston University, Boston, MA, United States; Department of Biomedical Engineering, Boston University, Boston, MA, United States.
| | - Ara Nazarian
- Center for Advanced Orthopaedic Studies, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA, United States.
| | - Brian D Snyder
- Center for Advanced Orthopaedic Studies, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA, United States; Department of Biomedical Engineering, Boston University, Boston, MA, United States; Department of Orthopaedic Surgery, Boston Children's Hospital, Boston, MA, United States.
| | - Mark W Grinstaff
- Department of Chemistry, Boston University, Boston, MA, United States; Department of Biomedical Engineering, Boston University, Boston, MA, United States; Department of Medicine, Boston University, Boston, MA, United States.
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Ash A, Wilde PJ, Bradshaw DJ, King SP, Pratten JR. Structural modifications of the salivary conditioning film upon exposure to sodium bicarbonate: implications for oral lubrication and mouthfeel. SOFT MATTER 2016; 12:2794-2801. [PMID: 26883483 DOI: 10.1039/c5sm01936b] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
The salivary conditioning film (SCF) that forms on all surfaces in the mouth plays a key role in lubricating the oral cavity. As this film acts as an interface between tongue, enamel and oral mucosa, it is likely that any perturbations to its structure could potentially lead to a change in mouthfeel perception. This is often experienced after exposure to oral hygiene products. For example, consumers that use dentifrice that contain a high concentration of sodium bicarbonate (SB) often report a clean mouth feel after use; an attribute that is clearly desirable for oral hygiene products. However, the mechanisms by which SB interacts with the SCF to alter lubrication in the mouth is unknown. Therefore, saliva and the SCF was exposed to high ionic strength and alkaline solutions to elucidate whether the interactions observed were a direct result of SB, its high alkalinity or its ionic strength. Characteristics including bulk viscosity of saliva and the viscoelasticity of the interfacial salivary films that form at both the air/saliva and hydroxyapatite/saliva interfaces were tested. It was hypothesised that SB interacts with the SCF in two ways. Firstly, the ionic strength of SB shields electrostatic charges of salivary proteins, thus preventing protein crosslinking within the film and secondly; the alkaline pH (≈8.3) of SB reduces the gel-like structure of mucins present in the pellicle by disrupting disulphide bridging of the mucins via the ionization of their cysteine's thiol group, which has an isoelectric point of ≈8.3.
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Affiliation(s)
- A Ash
- Institute of Food Research, Norwich Research Park, Colney, Norwich NR4 7UA, UK.
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Jongsma MA, van de Lagemaat M, Busscher HJ, Geertsema-Doornbusch GI, Atema-Smit J, van der Mei HC, Ren Y. Synergy of brushing mode and antibacterial use on in vivo biofilm formation. J Dent 2015; 43:1580-6. [DOI: 10.1016/j.jdent.2015.08.001] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2015] [Revised: 07/07/2015] [Accepted: 08/04/2015] [Indexed: 11/28/2022] Open
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Majd SE, Kuijer R, Köwitsch A, Groth T, Schmidt TA, Sharma PK. Both hyaluronan and collagen type II keep proteoglycan 4 (lubricin) at the cartilage surface in a condition that provides low friction during boundary lubrication. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2014; 30:14566-72. [PMID: 25409034 DOI: 10.1021/la504345c] [Citation(s) in RCA: 59] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
Wear resistant and ultralow friction in synovial joints is the outcome of a sophisticated synergy between the major macromolecules of the synovial fluid, e.g., hyaluronan (HA) and proteoglycan 4 (PRG4), with collagen type II fibrils and other non-collagenous macromolecules of the cartilage superficial zone (SZ). This study aimed at better understanding the mechanism of PRG4 localization at the cartilage surface. We show direct interactions between surface bound HA and freely floating PRG4 using the quartz crystal microbalance with dissipation (QCM-D). Freely floating PRG4 was also shown to bind with surface bound collagen type II fibrils. Albumin, the most abundant protein of the synovial fluid, effectively blocked the adsorption of PRG4 with HA, through interaction with C and N terminals on PRG4, but not that of PRG4 with collagen type II fibrils. The above results indicate that collagen type II fibrils strongly contribute in keeping PRG4 in the SZ during cartilage articulation in situ. Furthermore, PRG4 molecules adsorbed very well on mimicked SZ of absorbed HA molecules with entangled collagen type II fibrils and albumin was not able to block this interaction. In this last condition PRG4 adsorption resulted in a coefficient of friction (COF) of the same order of magnitude as the COF of natural cartilage, measured with an atomic force microscope in lateral mode.
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Affiliation(s)
- Sara Ehsani Majd
- Department of Biomedical Engineering, University of Groningen, University Medical Centre Groningen , Antonius Deusinglaan 1, 9713AV Groningen, The Netherlands
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Sotres J, Madsen JB, Arnebrant T, Lee S. Adsorption and nanowear properties of bovine submaxillary mucin films on solid surfaces: Influence of solution pH and substrate hydrophobicity. J Colloid Interface Sci 2014; 428:242-50. [DOI: 10.1016/j.jcis.2014.04.058] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2014] [Revised: 04/23/2014] [Accepted: 04/26/2014] [Indexed: 10/25/2022]
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Experimental Investigations of Biological Lubrication at the Nanoscale: The Cases of Synovial Joints and the Oral Cavity. LUBRICANTS 2013. [DOI: 10.3390/lubricants1040102] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
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He Y, Peterson BW, Ren Y, van der Mei HC, Busscher HJ. Antimicrobial penetration in a dual-species oral biofilm after noncontact brushing: an in vitro study. Clin Oral Investig 2013; 18:1103-1109. [PMID: 24019117 DOI: 10.1007/s00784-013-1097-x] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2013] [Accepted: 08/21/2013] [Indexed: 12/13/2022]
Abstract
OBJECTIVES Oral biofilm is inevitably left behind, even after powered brushing. As a special feature, powered brushing removes biofilm in a noncontact mode. When the brushing distance becomes too large, biofilm is left behind. We hypothesize that biofilm left behind after brushing has different viscoelastic properties than before brushing, impacting antimicrobial penetration. MATERIALS AND METHODS In vitro grown dual-species biofilms were subjected to 20 % mechanical deformation before and after powered brushing at 4-mm brushing distance. Biofilm thickness and stress relaxation were measured for unbrushed and brushed biofilms. Stress relaxation was analyzed with a three-element Maxwell model. Antimicrobial penetration from five mouthrinses was microscopically evaluated for unbrushed and brushed biofilms. RESULTS Thicknesses of unbrushed and brushed biofilms were similar. Brushing decreased the prevalence of fast and increased the prevalence of slow relaxation elements, which was accompanied by deeper penetration of chlorhexidine and cetylpyridinium chloride. Penetration of antimicrobials from other mouthrinses was relatively low in unbrushed and brushed biofilms. CONCLUSIONS This confirmation of our hypothesis points to an additional advantage of powered toothbrushing in a noncontact mode, changing the viscoelastic properties of biofilm in a direction that increases antimicrobial penetration of chlorhexidine and cetylpyridinium. CLINICAL RELEVANCE The biofilm left behind after noncontact powered toothbrushing may have less recalcitrance toward penetration of chlorhexidine and cetylpyridinium chloride than prior to brushing.
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Affiliation(s)
- Y He
- Department of Biomedical Engineering, University of Groningen and University Medical Center Groningen, Antonius Deusinglaan 1, 9713 AV, Groningen, The Netherlands
| | - B W Peterson
- Department of Biomedical Engineering, University of Groningen and University Medical Center Groningen, Antonius Deusinglaan 1, 9713 AV, Groningen, The Netherlands
| | - Y Ren
- Department of Orthodontics, University of Groningen and University Medical Center Groningen, Hanzeplein 1, 9700 RB, Groningen, The Netherlands
| | - H C van der Mei
- Department of Biomedical Engineering, University of Groningen and University Medical Center Groningen, Antonius Deusinglaan 1, 9713 AV, Groningen, The Netherlands.
| | - H J Busscher
- Department of Biomedical Engineering, University of Groningen and University Medical Center Groningen, Antonius Deusinglaan 1, 9713 AV, Groningen, The Netherlands
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