Mitigation of Fibrosis after Myocardial Infarction in Rats by Using a Porcine Cholecyst Extracellular Matrix

Fibrosis that occurs after nonfatal myocardial infarction (MI) is an irreversible reparative cardiac tissue remodeling process characterized by progressive deposition of highly cross-linked type I collagen. No currently available therapeutic strategy prevents or reverses MI-associated fibrotic scarring of myocardium. In this study, we used an epicardial graft prepared of porcine cholecystic extracellular matrix to treat experimental nonfatal MI in rats. Graft-assisted healing was characterized by reduced fibrosis, with scanty deposition of type I collagen. Histologically, the tissue response was associated with a favorable regenerative reaction predominated by CD4-positive helper T lymphocytes, enhanced angiogenesis, and infiltration of proliferating cells. These observations indicate that porcine cholecystic extracellular matrix delayed the fibrotic reaction and support its use as a potential biomaterial for mitigating fibrosis after MI. Delaying the progression of cardiac tissue remodeling may widen the therapeutic window for management of scarring after MI.

Large animal models of thermal injury

Burn injury results in a triad of inter-related adaptive responses: a systemic inflammatory response, a stress response, and a consequent hypermetabolic state which supports the former two. These pathological responses extend beyond the site of injury to affect distant organs and influence long-term outcomes in the patient. Animal models have proven valuable in advancing our understanding of mechanisms underlying the multifactorial manifestations of burn injury. While rodent models have been unprecedented in providing insights into signaling pathways, metabolic responses, protein turnover, cellular and molecular changes; small animal models do not replicate hypermetabolism, hyperinflammation, and wound healing after a burn injury as seen in humans. Herein, we provide a concise review of preferred large animal models utilized to understand burn pathophysiology based on organ systems and associated dysfunction. Additionally, we present a detailed protocol of contact burn injury in the Yorkshire pig model with a focus on preoperative care, anesthesia, analgesia, wound excision and grafting, dressing application, and frequency of dressing changes.

Intra-Operative Bioprinting of Hard, Soft, and Hard/Soft Composite Tissues for Craniomaxillofacial Reconstruction

Reconstruction of complex craniomaxillofacial (CMF) defects is challenging due to the highly organized layering of multiple tissue types. Such compartmentalization necessitates the precise and effective use of cells and other biologics to recapitulate the native tissue anatomy. In this study, intra-operative bioprinting (IOB) of different CMF tissues, including bone, skin, and composite (hard/soft) tissues, is demonstrated directly on rats in a surgical setting. A novel extrudable osteogenic hard tissue ink is introduced, which induced substantial bone regeneration, with ≈80% bone coverage area of calvarial defects in 6 weeks. Using droplet-based bioprinting, the soft tissue ink accelerated the reconstruction of full-thickness skin defects and facilitated up to 60% wound closure in 6 days. Most importantly, the use of a hybrid IOB approach is unveiled to reconstitute hard/soft composite tissues in a stratified arrangement with controlled spatial bioink deposition conforming the shape of a new composite defect model, which resulted in ≈80% skin wound closure in 10 days and 50% bone coverage area at Week 6. The presented approach will be absolutely unique in the clinical realm of CMF defects and will have a significant impact on translating bioprinting technologies into the clinic in the future.

A cholecystic extracellular matrix-based hybrid hydrogel for skeletal muscle tissue engineering

Tailoring the properties of extracellular matrix (ECM) based hydrogels by conjugating with synthetic polymers is an emerging method for designing hybridhydrogels for a wide range of tissue engineering applications. In this study, poly(ethylene glycol) diacrylate (PEGDA), a synthetic polymer at variable concentrations (ranging from 0.2 to 2% wt/vol) was conjugated with porcine cholecyst derived ECM (C-ECM) (1% wt/vol) and prepared a biosynthetic hydrogel having enhanced physico-mechanical properties, as required for skeletal muscle tissue engineering. The C-ECM was functionalized with acrylate groups using activated N-hydroxysuccinimide ester-based chemistry and then conjugated with PEGDA via free-radical polymerization in presence of ammonium persulfate and ascorbic acid. The physicochemical characteristics of the hydrogels were evaluated by Fourier transform infrared spectroscopy and environmental scanning electron microscopy. Further, the hydrogel properties were studied by evaluating rheology, swelling, gelation time, percentage gel fraction, in vitro degradation, and mechanical strength. Biocompatibility of the gel formulations were assessed using the C2C12 skeletal myoblast cells. The hydrogel formulations containing 0.2 and 0.5% wt/vol of PEGDA were non-cytotoxic and found suitable for growth and proliferation of skeletal myoblasts. The study demonstrated a method for modulating the properties of ECM hydrogels through conjugation with bio-inert polymers for skeletal muscle tissue engineering applications.

An Immunopathological Evaluation of the Porcine Cholecyst Matrix as a Muscle Repair Graft in a Male Rat Abdominal Wall Defect Model

With the increasing use of animal-based biomaterials for regenerative medical applications, the need for their safety assessment is paramount. A porcine cholecyst-derived scaffold (CDS), intended as a muscle repair graft, prepared by a nondetergent/enzymatic method was engrafted in a rat abdominal wall defect model. Host tissue–scaffold interface samples were collected 2, 8, and 16 weeks postimplantation and evaluated by histopathology, immunohistochemistry, and electron microscopy. The nature of the tissue reaction was compared with those induced by a jejunum-derived scaffold (JDS) prepared by the same method and a commercial-grade small intestinal submucosa (CSIS) scaffold. A study of the immunopathological response in major lymphoid tissues and immunophenotyping for M1 and M2 macrophages was performed at the host tissue–scaffold interface. Further, “irritancy scores” for CDS and JDS were determined using CSIS as the reference material. Both CDS and JDS appeared to be potential biomaterials for muscle grafts, but the former stimulated a skeletal muscle tissue remodeling response predominated by M2 macrophages. The data support the notion that biomaterials with similar biocompatibility, based on local tissue response on implantation, may cause differential immunogenicity. Additionally, CDS compared to JDS and CSIS was found to be less immunotoxic.

Micropatterning of reagent-free, high energy crosslinked gelatin hydrogels for bioapplications

Hydrogels are crosslinked polymeric gels of great interest in the field of tissue engineering, particularly as biocompatible cell or drug carriers. Reagent-free electron irradiated gelatin is simple to manufacture, inexpensive and biocompatible. Here, the potential to micropattern gelatin hydrogel surfaces during electron irradiation crosslinking was demonstrated as a promising microfabrication technique to produce thermally stable structures on highly relevant length scales for bioapplications. In the present work, grooves of 3.75 to 170 µm width and several hundred nanometers depth were transferred onto gelatin hydrogels during electron irradiation and characterized by 3D confocal microscopy after exposure to ambient and physiological conditions. The survival and influence of these microstructures on cellular growth was further characterized using NIH 3T3 fibroblasts. Topographical modifications produced surface structures on which the cultured fibroblasts attached and responded by adapting their morphologies. This developed technique allows for simple and effective structuring of gelatin and opens up new possibilities for irradiation crosslinked hydrogels in biomedical applications in which cell attachment and contact guidance are favored. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 320-330, 2018.