In vivo biocompatibility testing of nanoparticle-functionalized alginate-chitosan scaffolds for tissue engineering applications.

Background: There is a strong interest in designing new scaffolds for their potential application in tissue engineering and regenerative medicine. The incorporation of functionalization molecules can lead to the enhancement of scaffold properties, resulting in variations in scaffold compatibility. Therefore, the efficacy of the therapy could be compromised by the foreign body reaction triggered after implantation. Methods: In this study, the biocompatibilities of three scaffolds made from an alginate-chitosan combination and functionalized with gold nanoparticles (AuNp) and alginate-coated gold nanoparticles (AuNp + Alg) were evaluated in a subcutaneous implantation model in Wistar rats. Scaffolds and surrounding tissue were collected at 4-, 7- and 25-day postimplantation and processed for histological analysis and quantification of the expression of genes involved in angiogenesis, macrophage profile, and proinflammatory (IL-1ß and TNFα) and anti-inflammatory (IL-4 and IL-10) cytokines. Results: Histological analysis showed a characteristic foreign body response that resolved 25 days postimplantation. The intensity of the reaction assessed through capsule thickness was similar among groups. Functionalizing the device with AuNp and AuNp + Alg decreased the expression of markers associated with cell death by apoptosis and polymorphonuclear leukocyte recruitment, suggesting increased compatibility with the host tissue. Similarly, the formation of many foreign body giant cells was prevented. Finally, an increased detection of alpha smooth muscle actin was observed, showing the angiogenic properties of the elaborated scaffolds. Conclusion: Our results show that the proposed scaffolds have improved biocompatibility and exhibit promising potential as biomaterials for elaborating tissue engineering constructs.

Sodium Alginate/Chitosan Scaffolds for Cardiac Tissue Engineering: The Influence of Its Three-Dimensional Material Preparation and the Use of Gold Nanoparticles.

Natural biopolymer scaffolds and conductive nanomaterials have been widely used in cardiac tissue engineering; however, there are still challenges in the scaffold fabrication, which include enhancing nutrient delivery, biocompatibility and properties that favor the growth, maturation and functionality of the generated tissue for therapeutic application. In the present work, different scaffolds prepared with sodium alginate and chitosan (alginate/chitosan) were fabricated with and without the addition of metal nanoparticles and how their fabrication affects cardiomyocyte growth was evaluated. The scaffolds (hydrogels) were dried by freeze drying using calcium gluconate as a crosslinking agent, and two types of metal nanoparticles were incorporated, gold (AuNp) and gold plus sodium alginate (AuNp+Alg). A physicochemical characterization of the scaffolds was carried out by swelling, degradation, permeability and infrared spectroscopy studies. The results show that the scaffolds obtained were highly porous (>90%) and hydrophilic, with swelling percentages of around 3000% and permeability of the order of 1 × 10−8 m2. In addition, the scaffolds proposed favored adhesion and spheroid formation, with cardiac markers expression such as tropomyosin, troponin I and cardiac myosin. The incorporation of AuNp+Alg increased cardiac protein expression and cell proliferation, thus demonstrating their potential use in cardiac tissue engineering.

Effect of melatonin on electrical impedance and biomarkers of damage in a gastric ischemia/reperfusion model.

The damage to the gastrointestinal mucosa induced by ischemia/reperfusion (I/R) is closely related to high mortality in critically ill patients, which is attributable, in part, to the lack of an early method of diagnosis to show the degree of ischemia-induced injury in this type of patients. Electrical Impedance Spectroscopy (EIS) has been shown to be a tool to early diagnose gastric mucosal damage induced by ischemia. A therapeutic alternative to reduce this type of injury is melatonin (MT), which has gastroprotective effects in I/R models. In this work, the effect of treatment with MT on the electrical properties of gastric tissue, biomarkers of inflammatory (iNOS and COX-2), proliferation, and apoptotic process under I/R conditions in male Wistar rats was evaluated through EIS, histological and immunohistochemical analysis. Treatment with MT prevents gastric mucosa damage, causing a decrease in gastric impedance parameters related to the inflammatory process and cellular damage. This suggests that EIS could be used as a tool to diagnose and monitor the evolution of gastric mucosal injury, as well as in the recovery process in critically ill patients.

Histomorphometric analysis with a proposed tissue lesion index in ischemia-reperfusion induced gastric mucosa damage.

Damage to the gastrointestinal mucosa caused by ischemia - reperfusion is a significant clinical problem associated with various physiopathological conditions. Our group has conducted various studies in patients in critical conditions and in animal models to identify early damage to the gastric mucosa under ischemia using impedance spectroscopy. It is important to perform a quantitative histopathological analysis which can be linked to changes in impedance of the gastric mucosa under conditions of ischemia and I/R. AIM: To propose a tissue lesion index which considers pathological alterations inherent to the inflammatory process and cell damage which may be directly related to changes in impedance under conditions of ischemia and I/R. METHODS: The animals were randomly distributed into 4 groups: control, ischemia (30 min), and I/R (30 and 60 min). Qualitative histopathological analysis was performed; the vascular area, glandular lumen area, the number of damaged cells, and the depth of the erosion were also quantified to obtain a scale to propose a tissue lesion index (TLI). RESULTS: Under ischemic conditions, histopathological analysis showed edema and necrosis in epithelial cells, and vascular congestion. In I/R (30 and 60 min) conditions, areas of epithelial erosion were generated. Damage was classified based on the TLI. A TLI threshold of 3 showed a predictive value of tissue lesion. CONCLUSION: The proposed gastric lesion index allows us to objectively quantify and classify damage to the gastric mucosa produced by I/R.

Evaluation of HIF-1α and iNOS in ischemia/reperfusion gastric model: bioimpedance, histological and immunohistochemical analyses.

Gastrointestinal ischemia/reperfusion (I/R) generates pathological alterations that could lead to death. Early ischemic damage markers could be used to guide therapy and improve outcomes. AIM: To relate hypoxia-inducible factor 1α (HIF-1α) activation and inducible nitric oxide synthase (iNOS) expression to gastric impedance changes due to I/R damage. METHODS: Experimental animals were randomly distributed into 3 groups: control, ischemia (30 min) and I/R (60 min). Gastric ischemia was generated by celiac artery clamping for 30 min, and then blood flow was restored for 60 min. Impedance spectra and biopsies of the glandular portion were obtained for histological and immunohistochemical analyses. Immunodetection of both HIF-1α and iNOS was performed. RESULTS: Under ischemia and I/R conditions, there was an increase (p<0.05) in the impedance parameters. Histologically, under ischemic conditions, edema and necrosis were observed in epithelium and significant vascular congestion. In I/R condition, alterations of the glandular and luminal integrity were found, which generated areas of epithelial erosion. Immunohistochemical analysis of HIF-1α revealed an increase (p<0.01) in the number of immunoreactive cells in the ischemia (35.7±13.9) and I/R (119.9±18.8) conditions compared to the control (0.8±1.2). Immunodetection of iNOS showed an increase (p<0.01) in the number of cells expressing iNOS under the ischemia (5.4±2.9) and I/R conditions (27.4±11.3) was observed compared to the control (0.4±0.8). CONCLUSION: Early changes in impedance in response to I/R is related to histopathological changes, the nuclear stabilization and translocation of HIF-1α as well as expression of iNOS.