Engineering Biodegradable and Biocompatible Bio-ionic Liquid Conjugated Hydrogels with Tunable Conductivity and Mechanical Properties

Conventional methods to engineer electroconductive hydrogels (ECHs) through the incorporation of conductive nanomaterials and polymers exhibit major technical limitations. These are mainly associated with the cytotoxicity, as well as poor solubility, processability, and biodegradability of their components. Here, we describe the engineering of a new class of ECHs through the functionalization of non-conductive polymers with a conductive choline-based bio-ionic liquid (Bio-IL). Bio-IL conjugated hydrogels exhibited a wide range of highly tunable physical properties, remarkable in vitro and in vivo biocompatibility, and high electrical conductivity without the need for additional conductive components. The engineered hydrogels could support the growth and function of primary cardiomyocytes in both two dimentinal (2D) and three dimensional (3D) cultures in vitro. Furthermore, they were shown to be efficiently biodegraded and possess low immunogenicity when implanted subcutaneously in rats. Taken together, our results suggest that Bio-IL conjugated hydrogels could be implemented and readily tailored to different biomedical and tissue engineering applications

Kalbin Elektriksel Aktivitesinin 3 Boyutlu Transmembran Potansiyel Dağılımları Cinsinden Girişimsiz Olarak Görüntülenmesi

TÜBİTAK EEEAG Proje01.04.2015Vücut yüzeyi potansiyel (VYP) ölçümlerinden kalpteki elektriksel kaynakların kestirilmesine ters elektrokardiografi (EKG) problemi denir. Bu yöntem, ölümcül de olabilecek kalp hastalıklarının teşhisinde ve tedavi planlamasında hekimlere yol gösterme potansiyeline sahiptir. Ancak, bu problem kötü konumlanmış bir problemdir ve ölçümlerdeki az miktarda gürültü bile sınırsız çözümler bulunmasına yol açmaktadır. Bunun üstesinden gelebilmek için literatürde, başta Tikhonov düzenlileştirmesi olmak üzere çeşitli düzenlileştirme yöntemleri uygulanmıştır. Ancak uygulanan her yöntem farklı durumlarda test edilmiştir; henüz hangi yöntemin en iyi yöntem olduğu konusunda fikir birliği sağlanamamıştır. Son zamanlarda, üç boyutlu miyokart dokusunda da detaylı bilgi verebildiği için, transmembran potansiyelleri (TMP) cinsinden ters EKG çözümleri popülerleşmiştir. Ancak henüz bu alanda az sayıda çalışma vardır ve özellikle farklı kalp aritmilerinde farklı yöntemlerin nasıl performans sergileyeceği bilinmemektedir. Bu projede temel amaç, bu açığı kapatmak, farklı elektriksel dağılımlar için literatürdeki belli başlı yöntemlerle ters EKG problemini çözmektir. Bu projede, kapsamlı bir çalışmayla, önerilen yöntemlerin performansları aynı test verisiyle ve aynı kriterler kullanılarak objektif bir şekilde karşılaştırılabilmiştir. Ayrıca farklı aritmiler için TMP benzetimleri ve buna bağlı VYPler elde edildiği için, yöntemlerin bu farklı aritmiler karşısında nasıl bir performans sergilediği de araştırılmıştır. Öncelikle Aliev-Panfilov yöntemiyle farklı kalp aktiviteleri için TMP benzetimleri yapılmış, ardından ileri EKG problemi çözülerek bu dağılımlardan VYP dağılımları bulunmuştur. Bu dağılımlar ters EKG çözümlerinde kullanılmıştır. Uygulanan beş değişik ters EKG çözüm yönteminden her durumda en başarılı yöntemin Bayesian MAP olduğu gözlenmiştir. TTLS, LTTLS ve LSQR yöntemlerinin de uyarım noktalarını ve dalga önünü bulmakta çok kötü performans sergilemediği görülmüştür. Bu proje kapsamında iki ayrı dalda daha literatüre katkı sağlanmıştır. Bunlardan ilki, fiber yönelimlerinin TMP dağılımlarına etkilerinin incelenmesidir. Başka bir kalpten aktarılan fiber yönelimini kullanmanın izotropik varsayım kullanmaktan daha doğru sonuçlar verdiği gözlenmiştir. İkinci katkı da, TMP dağılımları cinsinden FEM yöntemi ile ileri problem çözümünün doğrulamasıdır. Uygun ağ sıklığına ulaşıldığında sayısal çözümün analitik çözüme yakınsadığı gösterilmiştir.Inverse electrocardiography is the estimation of cardiac electrical sources from body surface potential (BSP) measurements. Inverse solutions can guide the physicians for diagnosis and treatment planning of lethal heart diseases. However, inverse problem is ill-posed and even small perturbations in the measurements yield unbounded errors in the solutions. To overcome this difficulty, many regularization approaches have been proposed in literature. However, these methods have been applied and tested under varying conditions in different studies; there is no consensus among researchers on the method with the best performance. Lately, solutions in terms of transmembrane potentials (TMP) have become popular, since they provide information about the electrical activity of the three dimensional myocardium. There are few studies in this area and it is still an open question how different methods will perform under different arrythmia conditions. The main goal in this project is to solve the inverse problem in terms of TMPs, using different approaches but under the same (and diverse) cardiac conditions. First, we obtained TMP distributions for various cardiac electrical activity assumptions using Aliev-Panfilov model. Then we solved the forward ECG problem to obtain the corresponding BSPs, which were later used in the inverse problem solutions. Among the five inverse approaches, Bayesian MAP estimation had the best performance under all conditions. TTLS, LTTLS and LSQR were also successful in finding the initial stimulation points and recovering the wavefront. We made contributions in two more areas in this project. The first one is our study of fiber orientation effects on TMP distributions. We found that even using fiber orientations from a different heart is much better than using the isotropic assumption. The second one is the analytical verification of the FEM based forward problem; with an appropriate mesh size, we showed that the numerical solution converges to the analytical solution

ENGINEERING ELECTROCONDUCTIVE AND ADHESIVE HYRDOGELS FOR BIOMEDICAL APPLICATIONS

Bioadhesives, such as tissue sealants, hemostatic agents, and tissue sealants have gained increasing popularity for addressing wound management for traumatic and surgical injuries. This new generation of adhesive demonstrates significant advantages over traditional suturing and stapling techniques that can lead to infection, leakage of bodily fluid and gas, as well as secondary damage to tissues. Bioadhesives can be most broadly classified based on internal or external administration. While bioadhesives designed for external use are most widely used for topical application, such as wound closure, internal bioadhesives are surgically implanted and, therefore, require biocompatibility and strong adhesive ability to wet tissues. Further, hydrogel-based bioadhesives may be designed with nanoparticles or biopolymers that impart specific functionality, such as conductive or hemostatic properties. Scaffolds designed with conductive biomaterials have been extensively investigated in the field of tissue engineering based on their ability to support the function of excitable cell types, such as cardiomyocytes and neurons. Bioadhesives have also been designed to promote hemostasis for applications such as surgical sealants. In first two sections of this project, we aimed to develop conductive bioadhesives for cardiac tissue repair by combining highly biocompatible gelatin methacryloyl (GelMA), with an electrically conductive choline-based bio ionic liquid (Bio-IL). Here, we chemically modified gelatin to form photocrosslinkable hydrogels in the presence of visible or UV light, depending on the photoinitiator used. Conductive hydrogels were fabricated with varying concentrations of GelMA and Bio-IL, which resulted in scaffolds with high biocompatibility, as well as tunable electrical conductivity, and mechanical strength. We then demonstrated the ability of Bio-IL conjugated hydrogels to transduce physicochemical stimuli and modulate the growth of primary CMs in both 2D and 3D cultures in vitro. In addition, we demonstrated that the engineered hydrogels were highly biodegradable and biocompatible in vitro, and that they did not elicit inflammatory responses when implanted in vivo. Our following project investigated the development of cardiopatches using electrospun GelMA conjugated with Bio-IL. The resulting cardiopatches demonstrated tunable conductive and mechanical properties by optimizing the concentration of GelMA and Bio-IL used during synthesis. GelMA/Bio-IL cardiopatches exhibited excellent adhesiveness to cardiac tissues, and biocompatibility both in vitro and in vivo. CMs and CFs seeded on the surface of cardiopatches demonstrated excellent cell attachment and proliferation, and the scaffold supported the expression of gap junction proteins indicating the cells ability to function synchronously. Taken together, these conductive bioadhesives demonstrated excellent potential to be readily tailored to cardiac tissue regenerative therapies. Lastly, our group developed a hemostatic surgical sealant with robust mechanical properties based on the biopolymers GelMA and elastin-like polypeptide (ELP). These adhesive hydrogels were rendered hemostatic by the incorporation of the synthetic clay Laponite (LA) and were rapidly photocrosslinked in the presence of UV radiation using the photoinitiator Irgacure 2959. We demonstrated the highly tunable mechanical and adhesive properties of these nanocomposite hydrogels by varying the concentrations of GelMA and ELP. Likewise, we demonstrated the excellent hemostatic performance of these scaffolds both in vitro and in vivo by varying the concentration of LA. Our nanocomposite GelMA/ELP/LA hydrogels also showed remarkable biocompatibility both in vitro and in vivo and did not elicit an inflammatory response when implanted subcutaneously