Isaac Wamala

Tough adhesives for diverse wet surfaces

Sticky even when wet Tissue adhesives are used as an alternative to stitches or staples and can be less damaging to the healthy tissues. But they can suffer from low biocompatibility and poor matching of the mechanical properties with the tissues. Li et al. combined an adhesive surface with a flexible matrix to develop an adhesive that has the right level of stick but moves with the surrounding tissues. The adhesive is effective in the presence of blood and thus might work during wound repair. Science, this issue p. 378 Tough adhesives stick to wet surfaces and show compatibility with blood exposure and dynamic movements. Adhesion to wet and dynamic surfaces, including biological tissues, is important in many fields but has proven to be extremely challenging. Existing adhesives are cytotoxic, adhere weakly to tissues, or cannot be used in wet environments. We report a bioinspired design for adhesives consisting of two layers: an adhesive surface and a dissipative matrix. The former adheres to the substrate by electrostatic interactions, covalent bonds, and physical interpenetration. The latter amplifies energy dissipation through hysteresis. The two layers synergistically lead to higher adhesion energies on wet surfaces as compared with those of existing adhesives. Adhesion occurs within minutes, independent of blood exposure and compatible with in vivo dynamic movements. This family of adhesives may be useful in many areas of application, including tissue adhesives, wound dressings, and tissue repair.

Soft robotic sleeve supports heart function

A soft robotic sleeve modeled on the structure of the human heart assists cardiovascular function in an ex vivo and in vivo porcine model of heart failure. Robots have a change of heart Ventricular assist devices help failing hearts function by pumping blood but require monitoring and anticoagulant therapy to prevent blood clot formation. Roche et al. created a soft robotic device with material properties similar to those of native heart tissue that sits snugly around the heart and provides ventricular assistance without ever contacting blood. The robotic sleeve uses compressed air to power artificial silicone muscles that compress and twist, mimicking the movements of the normal human heart. The authors show that the artificial muscles could be selectively activated to twist, compress, or simultaneously perform both actions on one side or both sides of the heart. The device increased cardiac ejection volume in vitro and when implanted in adult pigs during drug-induced cardiac arrest. There is much interest in form-fitting, low-modulus, implantable devices or soft robots that can mimic or assist in complex biological functions such as the contraction of heart muscle. We present a soft robotic sleeve that is implanted around the heart and actively compresses and twists to act as a cardiac ventricular assist device. The sleeve does not contact blood, obviating the need for anticoagulation therapy or blood thinners, and reduces complications with current ventricular assist devices, such as clotting and infection. Our approach used a biologically inspired design to orient individual contracting elements or actuators in a layered helical and circumferential fashion, mimicking the orientation of the outer two muscle layers of the mammalian heart. The resulting implantable soft robot mimicked the form and function of the native heart, with a stiffness value of the same order of magnitude as that of the heart tissue. We demonstrated feasibility of this soft sleeve device for supporting heart function in a porcine model of acute heart failure. The soft robotic sleeve can be customized to patient-specific needs and may have the potential to act as a bridge to transplant for patients with heart failure.

Up to 9-day survival and control of thrombocytopenia following alpha1,3-galactosyl transferase knockout swine liver xenotransplantation in baboons.

Kim K, Schuetz C, Elias N, Veillette GR, Wamala I, Varma M, Smith RN, Robson SC, Cosimi AB, Sachs DH, Hertl M. Up to 9‐day survival and control of thrombocytopenia following GalT‐KO swine liver xenotransplantation in baboons. Xenotransplantation 2012; 19: 256–264..

High Incidence of Xenogenic Bone Marrow Engraftment in Pig-to-Baboon Intra-Bone Bone Marrow Transplantation

Previous attempts of α‐1,3‐galactocyltransferase knockout (GalTKO) pig bone marrow (BM) transplantation (Tx) into baboons have demonstrated a loss of macro‐chimerism within 24 h in most cases. In order to achieve improved engraftment with persistence of peripheral chimerism, we have developed a new strategy of intra‐bone BM (IBBM) Tx. Six baboons received GalTKO BM cells, with one‐half of the cells transplanted into the bilateral tibiae directly and the remaining cells injected intravenously (IBBM/BM‐Tx) with a conditioning immunosuppressive regimen. In order to assess immune responses induced by the combined IBBM/BM‐Tx, three recipients received donor SLA‐matched GalTKO kidneys in the peri‐operative period of IBBM/BM‐Tx (Group 1), and the others received kidneys 2 months after IBBM/BM‐Tx (Group 2). Peripheral macro‐chimerism was continuously detectable for up to 13 days (mean 7.7 days; range 3–13) post‐IBBM/BM‐Tx and in three animals, macro‐chimerism reappeared at days 10, 14 and 21. Pig CFUs, indicating porcine progenitor cell engraftment, were detected in the host BM in four of six recipients on days 14, 15, 19 and 28. In addition, anti‐pig unresponsiveness was observed by in vitro assays. GalTKO/pCMV‐kidneys survived for extended periods (47 and 60 days). This strategy may provide a potent adjunct for inducing xenogeneic tolerance through BM‐Tx.

Increased transfusion-free survival following auxiliary pig liver xenotransplantation.

Pig to baboon liver xenotransplantation typically results in severe thrombocytopenia and coagulation disturbances, culminating in death from hemorrhage within 9 days, in spite of continuous transfusions. We studied the contribution of anticoagulant production and clotting pathway deficiencies to fatal bleeding in baboon recipients of porcine livers.

Myocardial rescue with autologous mitochondrial transplantation in a porcine model of ischemia/reperfusion

Objective: To demonstrate the clinical efficacy of autologous mitochondrial transplantation in preparation for translation to human application using an in vivo swine model. Methods: A left mini‐thoracotomy was performed on Yorkshire pigs. The pectoralis major was dissected, and skeletal muscle tissue was removed and used for the isolation of autologous mitochondria. The heart was subjected to regional ischemia (RI) by temporarily snaring the circumflex artery. After 24 minutes of RI, hearts received 8 × 0.1 mL injections of vehicle (vehicle‐only group; n = 6) or vehicle containing mitochondria (mitochondria group; n = 6) into the area at risk (AAR), and the snare was released. The thoracotomy was closed, and the pigs were allowed to recover for 4 weeks. Results: Levels of creatine kinase‐MB isoenzyme and cardiac troponin I were significantly increased (P = .006) in the vehicle‐only group compared with the mitochondria group. Immune, inflammatory, and cytokine activation markers showed no significant difference between groups. There was no significant between‐group difference in the AAR (P = .48), but infarct size was significantly greater in the vehicle group (P = .004). Echocardiography showed no significant differences in global function. Histochemistry and transmission electron microscopy revealed damaged heart tissue in the vehicle group that was not apparent in the mitochondria group. T2‐weighted magnetic resonance imaging and histology demonstrated that the injected mitochondria were present for 4 weeks. Conclusions: Autologous mitochondrial transplantation provides a novel technique to significantly enhance myocardial cell viability following ischemia and reperfusion in the clinically relevant swine model.

MECHANICAL ASSIST DEVICE

Cardiac assist devices are the most complicated mechanical/electrical systems placed in human beings. They have fascinated heart specialists, the public, and the press for many years. On the positive side, they are awe‐inspiring examples of sophisticated technology. They provide hope that with technology, determination, and money, the result can be similar to the quest to land men on the moon and return them safely. The journey to mechanical support has advanced a long way this decade. Today we routinely implant life‐saving portable devices powered by small batteries that allow an acceptable quality of life for most patients and extend the life for many patients awaiting heart transplantation. Some patients even have recovery of their own heart function so that the device can be removed, and they may never need a transplant.

Recombinant anti-monkey CD3 immunotoxin depletes peripheral lymph node T lymphocytes more effectively than rabbit anti-thymocyte globulin in naïve baboons

T cell depletion is an important procedure for both experimental and therapeutic immune modulation. Rabbit anti-thymocyte globulin (ATG), which is a commonly used T cell depletion antibody in clinical organ and cell transplantation protocols, is effective in temporarily depleting peripheral blood T lymphocytes but only moderately effective in depleting peripheral lymph node T cells which comprise the majority of T lymphocytes. A recombinant anti-CD3 immunotoxin, A-dmDT390-scfbDb (C207), has been developed and shown in an initial study to retain the lymph node depleting properties of conjugated CD3 immunotoxin. This agent could potentially be used synergistically with or as a replacement for rabbit ATG in preclinical primate models of transplantation. We directly compared the peripheral blood and lymph node depleting abilities of this recombinant anti-CD3 immunotoxin and rabbit ATG in naïve animals at clinically tolerated doses. Baboons were treated with a full course of either rabbit ATG (n=2) or CD3 immunotoxin (n=3). Peripheral blood and lymph node T lymphocytes were measured before and following treatment. Peripheral blood CD3+ cells fell below 100cells/μL in every animal. In the two animals receiving ATG, CD3+ cells represented 53% and 68% of lymph node cells two days following a full course of rabbit ATG. In contrast, CD3+ cells represented 3%, 5%, and 38% in lymph nodes following a full course of CD3-IT. Thus, recombinant anti-monkey CD3 immunotoxin showed improved peripheral lymph node T lymphocyte depletion to rabbit ATG and spared other immune cells.

Soft robotic ventricular assist device with septal bracing for therapy of heart failure

A soft robotic device assists blood flow in isolated left or right heart failure by applying rhythmic loading to either ventricle. Previous soft robotic ventricular assist devices have generally targeted biventricular heart failure and have not engaged the interventricular septum that plays a critical role in blood ejection from the ventricle. We propose implantable soft robotic devices to augment cardiac function in isolated left or right heart failure by applying rhythmic loading to either ventricle. Our devices anchor to the interventricular septum and apply forces to the free wall of the ventricle to cause approximation of the septum and free wall in systole and assist with recoil in diastole. Physiological sensing of the native hemodynamics enables organ-in-the-loop control of these robotic implants for fully autonomous augmentation of heart function. The devices are implanted on the beating heart under echocardiography guidance. We demonstrate the concept on both the right and the left ventricles through in vivo studies in a porcine model. Different heart failure models were used to demonstrate device function across a spectrum of hemodynamic conditions associated with right and left heart failure. These acute in vivo studies demonstrate recovery of blood flow and pressure from the baseline heart failure conditions. Significant reductions in diastolic ventricle pressure were also observed, demonstrating improved filling of the ventricles during diastole, which enables sustainable cardiac output.

Increased levels of anti-non-Gal IgG following pig-to-baboon bone marrow transplantation correlate with failure of engraftment

The development of genetically modified pigs, which lack the expression of alpha 1‐3 galactosyl transferase, (GalT‐KO pigs) has facilitated the xenogeneic transplantation of porcine organs and tissues into primates by avoiding hyperacute rejection due to pre‐existing antibodies against the Gal epitope. However, antibodies against other antigens (anti‐non‐Gal antibodies), are found at varying levels in the pre‐transplant sera of most primates. We have previously found that baboons with high levels of pre‐transplant anti‐non‐Gal IgG, conditioned with a non‐myeloablative conditioning regimen, failed to engraft following pig‐to‐baboon bone marrow transplantation (Xenotransplantation, 17, 2010 and 300). Two baboons with low levels of pre‐transplant anti‐non‐Gal IgG, conditioned with the same regimen, showed porcine bone marrow progenitors at 28 days following transplantation, suggesting engraftment. These baboons also showed evidence of donor‐specific hyporesponsiveness. This observation led us to investigate the hypothesis that selecting for baboon recipients with low pre‐transplant anti‐non‐Gal IgG levels might improve engraftment levels following GalT‐KO pig‐to‐baboon bone marrow transplantation.