Recombinant Silk Hydrogel as a Novel Dermal Filler Component: Preclinical Safety and Efficacy Studies of a New Class of Tissue Fillers.

BACKGROUND: Hyaluronic acid-based tissue fillers are commonly utilized in reconstructive surgery as well as for aesthetic augmentation. A new type of recombinant silk-based tissue filler might pose a beneficial alternative for surgeons and patients. OBJECTIVES: The aim of this study was to compare injectability, reshaping, tolerability, and postimplantation behavior of dermal filler preparations containing recombinant silk hydrogel with a commercially available hyaluronic acid filler in 2 different animal models. METHODS: Recombinant silk hydrogel as standalone preparation or as a mixture with commercial stabilized hyaluronic acid was tested in rodent and porcine animal models. The preparations were analyzed in detail and administered subdermally followed by clinical, volumetric, and histological monitoring of the subdermal depots over several months. RESULTS: Applicability, dosing, and tissue distribution of the filler preparations were facilitated in the presence of silk hydrogel. No clinical complications attributable to tissue filler application were recorded. State-of-the art methods, such as high-performance magnetic resonance imaging, were applied successfully to monitor the volumetric development of the filler depots in live animals. CONCLUSIONS: The preclinical data demonstrate the basic suitability of recombinant silk hydrogel as safe and convenient tissue filler ingredient. Due to its shear thinning properties, recombinant silk hydrogel has the potential for less painful application, comfortable aesthetic reshaping immediately after administration, and negligible postoperative discomfort.

New model in diabetic mice to evaluate the effects of insulin therapy on biofilm development in wounds.

Objective: Diabetic patients suffer more frequently from biofilm-associated infections than normoglycemic patients. Well described in the literature is a relationship between elevated blood glucose levels in patients and the occurrence of biofilm-associated wound infections. Nevertheless, the underlying pathophysiological pathways leading to this increased infection vulnerability and its effects on biofilm development still need to be elucidated. We developed in our laboratory a model to allow the investigation of a biofilm-associated wound infection in diabetic mice under controlled insulin treatment. Methods: A dorsal skinfold chamber was used on 16 weeks old BKS.Cg-Dock7m +/+ Leprdb/J mice and a wound within the observation field of the dorsal skinfold chamber was created. These wounds were infected with Staphylococcus aureus ATCC 49230 (106 cells/mL). Simultaneously, we implanted implants for sustained insulin release into the ventral subcutaneous tissue (N=5 mice). Mice of the control group (N=5) were treated with sham implants. Serum glucose levels were registered before intervention and daily after the operation. Densitometrical analysis of the wound size was performed at day 0, 3, and 6 after intervention. Mice were sacrificed on day 6 and wound tissue was submitted to fluorescence in situ hybridization (FISH) and colony forming unit (CFU) analysis in addition to immunohistochemical staining to observe wound healing. Experiments were carried out in accordance with the National Institute of Health Guidelines for the Care and Use of Laboratory Animals (protocol number 05/19). Results: The insulin implants were able to reduce blood glucose levels in the mice. Hence, the diabetic mice in the intervention group were normoglycemic after the implantation. The combination with the dorsal skinfold chamber allowed for continuous, in vivo measurements of the infection development. Implantation of the insulin implant and the dorsal skinfold chamber was a tolerable condition for the diabetic mice. We succeeded to realize reproducible biofilm infections in the animals. Discussion: We developed a novel model to assess interactions between blood glucose level and S. aureus-induced biofilm-associated wound infections. The combination of the dorsal skinfold chamber model with a sustained insulin treatment has not been described so far. It allows a broad field of glucose and insulin dependent studies of infection.

A new in vivo model using a dorsal skinfold chamber to investigate microcirculation and angiogenesis in diabetic wounds.

INTRODUCTION: Diabetes mellitus describes a dysregulation of glucose metabolism due to improper insulin secretion, reduced insulin efficacy or both. It is a well-known fact that diabetic patients are likely to suffer from impaired wound healing, as diabetes strongly affects tissue angiogenesis. Until now, no satisfying in vivo murine model has been established to analyze the dynamics of angiogenesis during diabetic wound healing. To help understand the pathophysiology of diabetes and its effect on angiogenesis, a novel in vivo murine model was established using the skinfold chamber in mice. MATERIALS AND METHODS: Mutant diabetic mice (db; BKS.Cg-m+/+Lepr (db) /J), wildtype mice (dock7Lepr (db) +/+m) and laboratory BALB/c mice were examined. They were kept in single cages with access to laboratory chow with an 12/12 hour day/night circle. Lesions of the panniculus muscle (Ø 2 mm) were created in the center of the transparent window chamber and the subsequent muscular wound healing was then observed for a period of 22 days. Important analytic parameters included vessel diameter, red blood cell velocity, vascular permeability, and leakage of muscle capillaries and post capillary venules. The key parameters were functional capillary density (FCD) and angiogenesis positive area (APA). RESULTS: We established a model which allows high resolution in vivo imaging of functional angiogenesis in diabetic wounds. As expected, db mice showed impaired wound closure (day 22) compared to wounds of BALB/c or WT mice (day 15). FCD was lower in diabetic mice compared to WT and BALB/c during the entire observation period. The dynamics of angiogenesis also decreased in db mice, as reflected by the lowest APA levels. Significant variations in the skin buildup were observed, with the greatest skin depth in db mice. Furthermore, in db mice, the dermis:subcutaneous ratio was highly shifted towards the subcutaneous layers as opposed to WT or BALB/c mice. CONCLUSION: Using this new in vivo model of the skinfold chamber, it was possible to analyze and quantify microangiopathical changes which are essential for a better understanding of the pathophysiology of disturbed wound healing. Research in microcirculation is important to display perfusion in wounds versus healthy tissue. Using our model, we were able to compare wound healing in diabetic and healthy mice. We were also able to objectively analyze perfusion in wound edges and compare microcirculatory parameters. This model may be well suited to augment different therapeutic options.