Enthesis: not the same in each localisation - a molecular, histological and biomechanical study.

The interphase between tendon and bone consists of a highly specialised tissue called enthesis. Typically, the enthesis is described as a succession of four different zones: tendon, non-mineralised fibrocartilage, mineralised fibrocartilage and bone. However, the microstructure of the entheses, cellular composition and mechanical properties vary depending on their anatomical location. The present study aimed to characterise three of the most relevant sites of enthesis injury in a rat model: the patellar tendon, the Achilles tendon and the supraspinatus enthesis, in terms of biomechanics, histology and genetic expression. The patellar enthesis presented the highest ultimate load and lowest stiffness of the three, while the supraspinatus was the weakest and stiffest. The histological characterisation revealed key differences at the insertion site for each enthesis. The patellar enthesis showed a large cartilaginous area at the tendon-to-bone interphase whilst this interphase was smaller in the supraspinatus entheses samples. Furthermore, the Achilles tendon enthesis displayed a more abrupt transition from tendon to bone. Additionally, each enthesis exhibited a particular and distinct pattern of expression of tenogenic, chondrogenic and osteogenic markers. This study provided valuable insights for a better understanding of the three entheses at relevant anatomical sites. Moreover, the larger cross-sectional area of the patellar enthesis, the strong mechanical properties and the easier surgical access to this location led to the conclusion that the patellar tendon enthesis site could be most suitable for the development of a preclinical model for general enthesis regeneration studies in rats.

Mechanical and strain behaviour of human Achilles tendon during in vitro testing to failure.

The Achilles tendon is the strongest tendon in the human body but its mechanical behaviour during failure has been little studied and the basis of its high tensile strength has not been elucidated in detail. In the present study, healthy, human, Achilles tendons were loaded to failure in an anatomically authentic fashion while the local deformation and strains were studied in real time, with very high precision, using digital image correlation (DIC). The values determined for the strength of the Achilles tendon were at the high end of those reported in the literature, consistent with the absence of a pre-existing tendinopathy in the samples, as determined by careful gross inspection and histology. Early in the loading cycle, the proximal region of the tendon accumulated high lateral strains while longitudinal strains remained low. However, immediately before rupture, the mid-substance of the Achilles tendon, its weakest part, started to show high longitudinal strains. These new insights advance the understanding of the mechanical behaviour of tendons as they are stretched to failure.

Defining the variety of cell types in developing and adult human kidneys by single-cell RNA sequencing.

The kidney is among the most complex organs in terms of the variety of cell types. The cellular complexity of human kidneys is not fully unraveled and this challenge is further complicated by the existence of multiple progenitor pools and differentiation pathways. Researchers disagree on the variety of renal cell types due to a lack of research providing a comprehensive picture and the challenge to translate findings between species. To find an answer to the number of human renal cell types, we discuss research that used single-cell RNA sequencing on developing and adult human kidney tissue and compares these findings to the literature of the pre-single-cell RNA sequencing era. We find that these publications show major steps towards the discovery of novel cell types and intermediate cell stages as well as complex molecular signatures and lineage pathways throughout development. The variety of cell types remains variable in the single-cell literature, which is due to the limitations of the technique. Nevertheless, our analysis approaches an accumulated number of 41 identified cell populations of renal lineage and 32 of non-renal lineage in the adult kidney, and there is certainly much more to discover. There is still a need for a consensus on a variety of definitions and standards in single-cell RNA sequencing research, such as the definition of what is a cell type. Nevertheless, this early-stage research already proves to be of significant impact for both clinical and regenerative medicine, and shows potential to enhance the generation of sophisticated in vitro kidney tissue.

Patient satisfaction after hook plate treatment of bony avulsion fracture of the distal phalanges.

BACKGROUND: Bony avulsion fractures of the distal phalanges can result in mallet finger deformity if not treated appropriately. Therefore, only minimally displaced fractures can be treated conservatively with a good outcome, as dislocation occurs very often. Several surgical treatment options have been developed during the past decades. Data concerning the recently developed hook plate are promising. So far, no data concerning the subjective satisfaction with this method have been published. Therefore, we have analyzed the outcome after hook plate implantation using a self-assessment score, which focuses also on subjective parameters and satisfaction. METHODS: Standardized questionnaires (self-assessment scores and SF-36 questionnaire) were sent to each patient treated with a hook plate due to fracture of the distal phalanx, type Doyle IVb and IVc. Clinical data were evaluated according to the medical record. Scores given per question range from 0 to 10, 10 is the worst and 0 the best outcome. RESULTS: From 69 patients treated, 38 (58%) were enrolled. The whole collective (n = 38) reached a score of 39.7 ± 28.7 points, while men had slightly better results. Men (n = 24) achieved 37.3 ± 27.9 points, women (n = 14) 43.9 ± 30.7 points. Women had significantly better results when analyzed later than 12 months after surgery (52.1 ± 27.9 vs. 29.1 ± 32.8), whereas no changes could be detected in the male group (37.1 ± 29.9 vs. 37.4 ± 27.6). Overall, men were slightly more satisfied than women. Most satisfaction was found regarding pain and fine motor skills (0-0.46 points). Esthetic aspect and nail deformities (3.65 points average) led to the highest dissatisfaction. No differences in the SF 36 score could be detected. CONCLUSIONS: The hook plate is not only a convenient method but it also results in high patient satisfaction. Nail deformities are challenging; however, with increasing experience of the surgeon they decrease. SF 36 score is not an appropriate testing tool for this problem.

Osteoinduction and -conduction through absorbable bone substitute materials based on calcium sulfate: in vivo biological behavior in a rabbit model.

Calcium sulfate (CS) can be used as an antibiotically impregnated bone substitute in a variety of clinical constellations. Antibiotically loaded bone substitutes find specific application in orthopedic and trauma surgery to prevent or treat bone infections especially in relation to open bone defects. However, its use as a structural bone graft reveals some concerns due to its fast biodegradation. The addition of calcium carbonate and tripalmitin makes CS formulations more resistant to resorption leaving bone time to form during a prolonged degradation process. The aim of the present study was the evaluation of biocompatibility and degradation properties of newly formulated antibiotically impregnated CS preparations. Three different types of CS bone substitute beads were implanted into the tibial metaphysis of rabbits (CS dihydrate with tripalmitin, containing gentamicin (Group A) or vancomycin (Group B); Group C: tobramycin-loaded CS hemihydrate). Examinations were performed by means of x-ray, micro-computed tomography (micro-CT) and histology after 4, 6, 8 and 12 weeks. Regarding biocompatibility of the formulations, no adverse reactions were observed. Histology showed formation of vital bone cells attached directly to the implanted materials, while no cytotoxic effect in the surrounding of the beads was detected. All CS preparations showed osteogenesis associated to implanted material. Osteoblasts attached directly to the implant surface and revealed osteoid production, osteocytes were found in newly mineralized bone. Group C implants (Osteoset®) were subject to quick degradation within 4 weeks, after 6-8 weeks there were only minor remnants with little osteogenesis demonstrated by histological investigations. Group A implants (Herafill®-G) revealed similar degradation within atleast 12 weeks. In contrast, group B implants (CaSO4-V) were still detectable after 12 weeks with the presence of implant-associated osteogenesis atlatest follow-up. In all of these preparations, giant cells were found during implant degradation on surface and inside of resorption lacunae. None of the analyzed CS preparations triggered contact activation. All implants demonstrated excellent biocompatibility, with implants of Group A and B showing excellent features as osteoconductive and -inductive scaffolds able to improve mechanical stability.

Characterization of blunt chest trauma in a long-term porcine model of severe multiple trauma.

Chest trauma has a significant relevance on outcome after severe trauma. Clinically, impaired lung function typically occurs within 72 hours after trauma. However, the underlying pathophysiological mechanisms are still not fully elucidated. Therefore, we aimed to establish an experimental long-term model to investigate physiological, morphologic and inflammatory changes, after severe trauma. Male pigs (sus scrofa) sustained severe trauma (including unilateral chest trauma, femur fracture, liver laceration and hemorrhagic shock). Additionally, non-injured animals served as sham controls. Chest trauma resulted in severe lung damage on both CT and histological analyses. Furthermore, severe inflammation with a systemic increase of IL-6 (p = 0.0305) and a local increase of IL-8 in BAL (p = 0.0009) was observed. The pO2/FiO2 ratio in trauma animals decreased over the observation period (p < 0.0001) but not in the sham group (p = 0.2967). Electrical Impedance Tomography (EIT) revealed differences between the traumatized and healthy lung (p < 0.0001). In conclusion, a clinically relevant, long-term model of blunt chest trauma with concomitant injuries has been developed. This reproducible model allows to examine local and systemic consequences of trauma and is valid for investigation of potential diagnostic or therapeutic options. In this context, EIT might represent a radiation-free method for bedside diagnostics.

[Synovial biomarkers for differential diagnosis of painful arthroplasty]. / Synoviale Biomarker für die Differenzialdiagnostik der schmerzhaften Endoprothese.

BACKGROUND: The diagnosis and treatment of periprosthetic joint infection (PJI) remain true clinical challenges. PJI diminishes therapeutic success, causes dissatisfaction for the patient and medical staff, and often requires extensive surgical revision(s). At the present time, an extensive multimodal algorithmic approach is used to avoid time- and cost-consuming diagnostic aberrations. However, especially in the case of the frequent and clinically most relevant "low-grade" PJI, the current diagnostic "gold standard" has reached its limits. EVALUATION: Synovial biomarkers are thought to close this diagnostic gap, hopefully enabling the safe differentiation among aseptic, (chronic) septic, implant allergy-related and the arthrofibrotic genesis of symptomatic arthroplasty. Therefore, joint aspiration for obtaining synovial fluid is preferred over surgical synovial tissue biopsy because of the faster results, greater practicability, greater patient safety, and lower costs. In addition to the parameters synovial IL-6, CRP, and leukocyte esterase, novel biomarkers such as antimicrobial peptides and other proinflammatory cytokines are currently highlighted because of their very high to excellent diagnostic accuracy. CONCLUSION: Independent multicenter validation studies are required to show whether a set of different innovative synovial fluid biomarkers rather than a few single parameters is favorable for a safe "one-stop shop" differential diagnosis of PJI.

HLA-DR expression on monocytes is decreased in polytraumatized patients.

BACKGROUND: Sepsis, systemic inflammatory response syndrome (SIRS) and multiple organ dysfunction syndrome (MODS) remain the most frequent causes of complications and death in severely injured patients. A main reason for the development of these syndromes is a post-traumatic dysregulation of the immune system. Several studies in intensive care unit (ICU) patients could detect a pivotal role of HLA-DR expression on monocytes. So far, its importance for development of SIRS, sepsis or MODS in the severely injured patient is not clear. METHODS: Therefore, we have analysed HLA-DR expression on monocytes from severely injured patients (ISS > 16) during the post-traumatic course, which was on the day of trauma, as well as on days 3, 7 and 14 post trauma. Clinical data were analysed and the HLA-DR expression levels of patients who developed post-traumatic sepsis, SIRS or MODS were compared to those with a more favourable outcome. Young and healthy volunteers as well as patients undergoing prosthetic hip replacement after trauma were enrolled as control groups. HLA-DR molecules on monocytes were marked with PE-conjugated antibodies and the mean fluorescence intensity (MFI) was analysed via flow cytometry. RESULTS: 24 severely injured patients (mean age 34 ± 2.7 years) mainly after high energy motor vehicle accidents as well as 8 controls (total hip replacement) and 9 healthy volunteers (mean age 26.2 ± 1.2 years) were enrolled. A total of eight patients suffered from sepsis (33.3 %) (six males, two females) and 17 patients suffered from SIRS (70.9 %) (10 males, 7 females). MODS was present in five patients (20.8 %), three male and two female patients. In four of these five patients the MODS developed subsequent to sepsis. HLA-DR expression significantly decreased after trauma and slowly returned to normal after 14 days, irrespective of the complications developed. CONCLUSION: In conclusion, post-traumatic HLA-DR expression on monocytes is significantly reduced after multiple trauma and it is back to normal on day 14. No significant changes in HLA-DR expression on monocytes from severely injured patients suffering from SIRS, MODS or sepsis compared to those who did not have complications could be detected. Nevertheless, HLA-DR expression on monocytes may be used to identify the immunological pro- or anti-inflammatory phase the patient is going through.

Association between volume of severely injured patients and mortality in German trauma hospitals.

BACKGROUND: The issue of patient volume related to trauma outcomes is still under debate. This study aimed to investigate the relationship between number of severely injured patients treated and mortality in German trauma hospitals. METHODS: This was a retrospective analysis of the TraumaRegister DGU® (2009-2013). The inclusion criteria were patients in Germany with a severe trauma injury (defined as Injury Severity Score (ISS) of at least 16), and with data available for calculation of Revised Injury Severity Classification (RISC) II score. Patients transferred early were excluded. Outcome analysis (observed versus expected mortality obtained by RISC-II score) was performed by logistic regression. RESULTS: A total of 39,289 patients were included. Mean(s.d.) age was 49.9(21.8) years, 27,824 (71.3 per cent) were male, mean(s.d.) ISS was 27.2(11.6) and 10,826 (29.2 per cent) had a Glasgow Coma Scale score below 8. Of 587 hospitals, 98 were level I, 235 level II and 254 level III trauma centres. There was no significant difference between observed and expected mortality in volume subgroups with 40-59, 60-79 or 80-99 patients treated per year. In the subgroups with 1-19 and 20-39 patients per year, the observed mortality was significantly greater than the predicted mortality (P < 0.050). High-volume hospitals had an absolute difference between observed and predicted mortality, suggesting a survival benefit of about 1 per cent compared with low-volume hospitals. Adjusted logistic regression analysis (including hospital level) identified patient volume as an independent positive predictor of survival (odds ratio 1.001 per patient per year; P = 0.038). CONCLUSION: The hospital volume of severely injured patients was identified as an independent predictor of survival. A clear cut-off value for volume could not be established, but at least 40 patients per year per hospital appeared beneficial for survival.

Human platelet lysate successfully promotes proliferation and subsequent chondrogenic differentiation of adipose-derived stem cells: a comparison with articular chondrocytes.

Fetal calf serum (FCS) bears a potential risk for carrying diseases and eliciting immune reactions. Nevertheless, it still represents the gold standard as medium supplement in cell culture. In the present study, human platelet lysate (PL) was tested as an alternative to FCS for the expansion and subsequent chondrogenic differentiation of human adipose-derived stem cells (ASCs). ASCs were expanded with 10% FCS (group F) or 5% PL (group P). Subsequently, three-dimensional (3D) micromass pellets were created and cultured for 5 weeks in chondrogenic differentiation medium. Additionally, the de- and redifferentiation potential of human articular chondrocytes (HACs) was evaluated and compared to ASCs. Both HACs and ASCs cultured with PL showed strongly enhanced proliferation rates. Redifferentiation of HACs was possible for cells expanded up to 3.3 population doublings (PD). At this stage, PL-expanded HACs demonstrated better redifferentiation potential than FCS-expanded cells. ASCs could also be differentiated following extended passaging. Glycosaminoglycan (GAG) quantification and qRT-PCR of 10 cartilage related markers demonstrated a tendency for increased chondrogenic differentiation of PL-expanded ASCs compared to cells expanded with FCS. Histologically, collagen type II but also collagen type X was mainly present in group P. The present study demonstrates that PL strongly induces proliferation of ASCs, while the chondrogenic differentiation potential is retained. HACs also showed enhanced proliferation and even better redifferentiation when previously expanded with PL. This suggests that PL is superior to FCS as a supplement for the expansion of ASCs and HACs, particularly with regard to chondrogenic (re)differentiation.

[Diagnostic biomarkers in traumatic brain injury]. / Diagnostische Biomarker des Schädel-Hirn-Traumas.

BACKGROUND: Despite advances in medicine in head trauma management, traumatic brain injury (TBI) still remains a serious health concern, affecting people regardless of age. It is a leading cause of morbidity and mortality particularly in children and young adults. Therefore, studies are being carried out to try to establish reliable biomarkers to improve the accuracy of TBI diagnosis and associated secondary pathologies. METHODS: Implementation of valid TBI biomarkers could possibly reduce the necessity to use computed cranial tomography (CCT), especially in patients suffering from mild TBI to rule out intracranial bleeding. AIM: This review provides a critical assessment of biomarkers currently under investigation and their clinical value for the diagnosis, treatment and outcome prediction of TBI.

[Cytokines as biomarkers in polytraumatized patients]. / Zytokine als Marker bei Polytrauma.

BACKGROUND: Multiple trauma can lead to posttraumatic complications such as systemic inflammatory response syndrome (SIRS), multiple organ dysfunction syndrome (MODS), and sepsis. Currently, these complications are monitored using clinical and organ-specific parameters. The immune system is activated by trauma. Cytokines, which are the messenger molecules of this system, can be determined in serum. Furthermore, they are associated with the intensity of the inflammatory and anti-inflammatory reactions. AIM: This review describes clinical studies that measured cytokines such as TNF-α, IL-1ß, IL-6, IL-8, and IL-10 to prognosticate posttraumatic complications. On the other hand, IL-6 can be helpful in deciding which primary operation to perform, i.e., external fixator or intramedullary nail. Moreover, IL-6 indicates the strength of the immune reaction. Thereby, it may help in determining the optimal time for secondary surgery.

Constitutive and inducible co-expression systems for non-viral osteoinductive gene therapy.

Tissue regenerative gene therapy requires expression strategies that deliver therapeutic effective amounts of transgenes. As physiological expression patterns are more complex than high-level expression of a singular therapeutic gene, we aimed at constitutive or inducible co-expression of 2 transgenes simultaneously. Co-expression of human bone morphogenetic protein 2 and 7 (BMP2/7) from constitutively expressing and doxycycline inducible plasmids was evaluated in vitro in C2C12 cells with osteocalcin reporter gene assays and standard assays for osteogenic differentiation. The constitutive systems were additionally tested in an in vivo pilot for ectopic bone formation after repeated naked DNA injection to murine muscle tissue. Inductor controlled differentiation was demonstrated in vitro for inducible co-expression. Both co-expression systems, inducible and constitutive, achieved significantly better osteogenic differentiation than single factor expression. The potency of the constitutive co-expression systems was dependent on relative expression cassette topology. In vivo, ectopic bone formation was demonstrated in 6/13 animals (46% bone formation efficacy) at days 14 and 28 in hind limb muscles as proven by in vivo µCT and histological evaluation. In vitro findings demonstrated that the devised single vector BMP2/7 co-expression strategy mediates superior osteoinduction, can be applied in an inductor controlled fashion and that its efficiency is dependent on expression cassette topology. In vivo results indicatethatco-expression of BMP2/7 applied by non-viral naked DNA gene transfer effectively mediates bone formation without the application of biomaterials, cells or recombinant growth factors, offering a promising alternative to current treatment strategies with potential for clinical translation in the future.

Bioreactor and scaffold design for the mechanical stimulation of anterior cruciate ligament grafts.

Various studies have shown that physical stimuli modulate cell function and this has motivated the development of a bioreactor to engineer tissues in vitro by exposing them to mechanical loads. Here, we present a bioreactor for the physical stimulation of anterior cruciate ligament (ACL) grafts, whereby complex multi-dimensional strain can be applied to the matrices. Influences from environmental conditions to the behavior of different cells on our custom-made silk scaffold can be investigated since the design of the bioreactor allows controlling these parameters precisely. With the braided design of the presented silk scaffold we achieve maximum loads and stiffness values matching those of the human ACL. Thus, the existent degummed and wet silk scaffolds absorb maximum loads of 2030±109 N with stiffness values of 336±40 N/mm.

Effects of accidental hypothermia on posttraumatic complications and outcome in multiple trauma patients.

INTRODUCTION: Accidental hypothermia seems to predispose multiple trauma patients to the development of posttraumatic complications, such as Systemic Inflammatory Response Syndrome (SIRS), sepsis, Multiple Organ Dysfunction Syndrome (MODS), and increased mortality. However, the role of accidental hypothermia as an independent prognostic factor is controversially discussed. The aim of the present study was to evaluate the incidence of accidental hypothermia in multiple trauma patients and its effects on the development of posttraumatic complications and mortality. PATIENTS AND METHODS: Inclusion criteria for patients in this retrospective study (2005-2009) were an Injury Severity Score (ISS) ≥16, age ≥16 years, admission to our Level I trauma centre within 6h after the accident. Accidental hypothermia was defined as body temperature less than 35°C measured within 2 h after admission, but always before first surgical procedure in the operation theatre. The association between accidental hypothermia and the development of posttraumatic complications as well as mortality was investigated. Statistical analysis was performed with χ(2)-test, Student's t-test, ANOVA and logistic regression. Statistical significance was considered at p<0.05. RESULTS: 310 multiple trauma patients were enrolled in the present study. Patients' mean age was 41.9 (SD 17.5) years, the mean injury severity score was 29.7 (SD 10.2). The overall incidence of accidental hypothermia was 36.8%. The overall incidence of posttraumatic complications was 77.4% (SIRS), 42.9% (sepsis) and 7.4% (MODS), respectively. No association was shown between accidental hypothermia and the development of posttraumatic complications. Overall, 8.7% died during the posttraumatic course. Despite an increased mortality rate in hypothermic patients, hypothermia failed to be an independent risk factor for mortality in multivariate analysis. CONCLUSIONS: Accidental hypothermia is very common in multiply injured patients. However, it could be assumed that the increase of mortality in hypothermic patients is primarily caused by the injury severity and does not reflect an independent adverse effect of hypothermia. Furthermore, hypothermia was not shown to be an independent risk factor for posttraumatic complications.

Systemic inflammatory effects of traumatic brain injury, femur fracture, and shock: an experimental murine polytrauma model.

OBJECTIVE: Despite broad research in neurotrauma and shock, little is known on systemic inflammatory effects of the clinically most relevant combined polytrauma. Experimental investigation in an animal model may provide relevant insight for therapeutic strategies. We describe the effects of a combined injury with respect to lymphocyte population and cytokine activation. METHODS: 45 male C57BL/6J mice (mean weight 27 g) were anesthetized with ketamine/xylazine. Animals were subjected to a weight drop closed traumatic brain injury (WD-TBI), a femoral fracture and hemorrhagic shock (FX-SH). Animals were subdivided into WD-TBI, FX-SH and combined trauma (CO-TX) groups. Subjects were sacrificed at 96 h. Blood was analysed for cytokines and by flow cytometry for lymphocyte populations. RESULTS: Mortality was 8%, 13% and 47% for FX-SH, WD-TBI and CO-TX groups (P < 0.05). TNFα (11/13/139 for FX-SH/WD-TBI/CO-TX; P < 0.05), CCL2 (78/96/227; P < 0.05) and IL-6 (16/48/281; P = 0.05) showed significant increases in the CO-TX group. Lymphocyte populations results for FX-SH, WD-TBI and CO-TX were: CD-4 (31/21/22; P = n.s.), CD-8 (7/28/34, P < 0.05), CD-4-CD-8 (11/12/18; P = n.s.), CD-56 (36/7/8; P < 0.05). CONCLUSION: This study shows that a combination of closed TBI and femur-fracture/ shock results in an increase of the humoral inflammation. More attention to combined injury models in inflammation research is indicated.

Histopathological features of the brain, liver, kidney and spleen following an innovative polytrauma model of the mouse.

OBJECT: Among the various introduced experimental traumatic brain injury models, there is a clear paucity of proper experimental polytrauma models. To overcome this experimental gap we introduced such a polytrauma model in the mouse including traumatic brain injury. Here, we report on the histopathological features of the brain, lung, kidney, spleen and liver. MATERIALS AND METHODS: 20 male C57BL mice with a mean weight of 23 g were anesthetized with ketamine and xylazine. The anaesthetized animals were subjected to a controlled cortical impact (CCI) over the left parieto-temporal cortex using rounded-tip impounder for application of a standardized brain injury. Following fracture of the right femur using a guillotine, a volume-controlled hemorrhagic shock was induced. The control groups included animals with CCI only (n=20) and animals with femur fracture plus hemorrhagic shock without CCI (n=20). Subjects were sacrified at 96 h following trauma. Brain, lung, kidney, spleen and liver of the animals underwent histopathological examinations. RESULTS: The mortality rate at 96 h was 25% in the polytrauma group versus 10% in the control groups. Within the histopathological investigations, polytraumatized animals differ from those with a single trauma (traumatic brain injury or femur fracture with hemorrhagic shock) with various severity. CONCLUSION: The findings of this study show that such a polytrauma model can be standardized resulting in a reproducible damage. This model fulfills the requirements of a standardized animal model. It allows adequate analogies and inferences to the clinical situation of a polytrauma in humans.

In vitro adipogenesis of adipose-derived stem cells in 3D fibrin matrix of low component concentration.

This study evaluated the suitability of adipose-derived stem cells (ASCs) combined with fibrin matrix of variable composition for adipose tissue-equivalent formation in vitro. Therefore, undifferentiated ASCs were embedded in fibrin clots composed of 2 IU/ml thrombin and fibrinogen of varying concentrations (6.25, 12.5 and 25 mg/ml) and kept under control or adipogenic conditions. Fibrin-cell composites were evaluated by scanning electron microscopy, live/dead staining, lactate-dehydrogenase (LDH) assay, quantitative PCR for the adipogenic markers fatty acid binding protein 4 (FABP4), peroxisome proliferative activated receptor-γ (PPARγ) and leptin, leptin ELISA and oil red O staining. Cells were found homogeneously distributed throughout the clot. Their number increased to day 7 (up to 3.62-fold median) and decreased thereafter until day 28. The proliferation was unaffected by fibrinogen concentration in the control. Adipogenic conditions generally yielded higher cell numbers, which were in addition increasing with increasing fibrinogen concentrations. FABP4, PPARγ and leptin mRNA expression was strongly upregulated by adipogenic medium, which was confirmed by the levels of leptin secretion and lipid vesicles formation demonstrated by oil red O staining. When embedded in 25 mg/ml fibrinogen clots, ASCs showed the highest expression levels of FABP4 (up to 629.0-fold), PPARγ (up to 1.6-fold) and leptin (up to 57.9-fold), corroborated by significantly elevated leptin secretion (median 33.29 ng/ml) on day 14. Constructs composed of fibrin matrix of low component concentrations-allowing homogeneous cell distribution-with ASCs should represent a suitable strategy for adipose tissue formation in vivo.