Yeni nesil mekanik aort kapakçığı geliştirilmesi:polimer kaplamaların mekanik dayanımve yüzey özelliklerine etkisi
Development of a next-generation mechanical aortic heart valve: Effects of polymer coatings on mechanical strength and surface properties
- Tez No: 996295
- Danışmanlar: DOÇ. DR. SERBÜLENT TÜRK, DOÇ. DR. HAMİD ASADİ
- Tez Türü: Yüksek Lisans
- Konular: Biyomühendislik, Bioengineering
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 2026
- Dil: Türkçe
- Üniversite: Sakarya Üniversitesi
- Enstitü: Fen Bilimleri Enstitüsü
- Ana Bilim Dalı: Biyomedikal Ana Bilim Dalı
- Bilim Dalı: Biyomedikal Mühendisliği Bilim Dalı
- Sayfa Sayısı: Belirtilmemiş.
Özet
Kardiyovasküler hastalıklar dünya genelinde en yüksek mortalite oranına sahip sağlık sorunları arasında yer almakta olup, kapak fonksiyon bozuklukları kalbin hemodinamik performansını doğrudan etkilemektedir. Mevcut mekanik aort kalp kapakçıkları dayanıklı olmalarına rağmen yüksek kesme gerilmeleri, pıhtı oluşumu, biyolojik uyumsuzluk ve ömür boyu antikoagülasyon gereksinimi gibi dezavantajlara sahiptir. Bu nedenle hem geometrik yapısı optimize edilmiş hem de yüzey biyouyumluluğu artırılmış yeni tasarımlara ihtiyaç duyulmaktadır. Bu çalışmada amaç, mekanik aort kalp kapakçıklarının akış dinamiğini, yüzey etkileşimini ve uzun dönem performansını iyileştirebilecek bir tasarım geliştirmek ve bu tasarımda kullanılan polimer kaplamaların mekanik, kimyasal ve biyolojik etkilerini kapsamlı biçimde değerlendirmektir. Çalışmada öncelikle yaprakçık kalınlığı, iç çap, dış çap ve menteşe geometrisi literatürde belirtilen fizyolojik gereklilikler dikkate alınarak optimize edilmiştir. Akış kanallarının yuvarlatılmış kenarlarla yeniden şekillendirilmesiyle, yüksek gerilme bölgelerinde yük dağılımının daha dengeli hale getirilmesi ve buna bağlı olarak hemoliz riskinin azaltılması hedeflenmiştir. Elde edilen tasarım yüksek çözünürlüklü 3D baskı yöntemiyle aligner reçineden üretilmiş ve prototip, sol-jel temelli yöntemle dört farklı polimer kaplama; PEG, PVA/Kitosan, PVA/Kitosan/PEG ve PEG/PU ile modifiye edilmiştir. Bu kaplamaların yüzey morfolojileri, kimyasal yapıları, hidrofiliklik düzeyleri, partikül stabiliteleri, kristal-amorf faz oranları ve mekanik davranışları çeşitli karakterizasyon yöntemleriyle incelenmiştir. FESEM analizleri, kaplamasız yüzeydeki düzensizliklerin kaplamalar ile önemli ölçüde azaltıldığını göstermiştir. EDS ve FTIR analizleri, kaplamaların yüzeye başarıyla bağlandığını ve fonksiyonel grup çeşitliliğinin yüzey etkileşimlerini güçlendirdiğini ortaya koymuştur. Temas açısı ölçümleri, tüm kaplamaların hidrofilikliği artırdığını göstermiş; en düşük temas açısı PVA/Kitosan kaplamasında elde edilmiştir. Zeta potansiyeli ve partikül boyutu analizleri, özellikle PVA/Kitosan/PEG çözeltisinin göreceli olarak daha dengeli ve kontrollü bir yapıya sahip olduğunu göstermektedir. XRD bulguları kaplamaların kristalin ve amorf faz dengesini ortaya koyarak mekanik dayanım potansiyellerinin değerlendirilmesine katkı sağlamıştır. Çekme testleri, kaplamaların Young modülünde hafif bir düşüş olsa da malzemenin elastik karakterinin korunduğunu göstermiştir. Antibakteriyel testlerde ise PVA/Kitosan/PEG kaplaması inhibisyon bölgesini oluşturarak biyolojik güvenlik açısından en güçlü performansı sergilemiştir. Tüm sonuçlar bir arada değerlendirildiğinde, geliştirilen mekanik aort kapakçığı tasarımının geometrik olarak optimize edildiği, polimer kaplamalarla biyouyumluluğunun güçlendirildiği ve özellikle hibrit PVA/Kitosan/PEG kaplamasının mekanik, kimyasal ve biyolojik açıdan en başarılı seçenek olduğu görülmüştür.
Özet (Çeviri)
Valvular heart disease (VHD) is a growing global health problem affecting both industrialized and developing countries, primarily as a result of congenital abnormalities and the progressive aging of the population. Heart valve replacement procedures constitute one of the most frequently performed cardiovascular interventions worldwide. Prosthetic heart valves are generally classified into two main categories: mechanical and bioprosthetic valves. Mechanical heart valves remain a cornerstone in the management of severe valve dysfunction due to their superior durability and long-term structural stability. In contrast, bioprosthetic valves offer a reduced risk of thrombosis, thereby minimizing the requirement for lifelong anticoagulation therapy; however, they are inherently limited by structural valve degeneration, which typically occurs within 10–15 years following implantation. Despite their extensive clinical application, both mechanical and bioprosthetic valve types are associated with complications such as patient discomfort, anticoagulant-related bleeding risks, immüne mediated calcification, and progressive structural degradation. Contemporary mechanical valve designs, in particular, continue to face challenges related to thrombogenicity, surface induced blood damage, and non-physiological flow patterns. Considering the increasing prevalence of severe VHD in developing countries and the aging demographics of developed nations, there is a critical need to develop innovative mechanical heart valve designs that improve hemodynamic performance while ensuring long-term biocompatibility. Within this context, the present study focuses on the development of a bileaflet mechanical aortic heart valve by integrating optimized geometric features with biofunctional polymer-based surface modifications. Instead of treating mechanical reliability and surface compatibility as separate design problems, both aspects were considered simultaneously within a holistic framework. The valve geometry was redesigned by taking into account leaflet thickness, inner and outer diameters, and hinge morphology in accordance with physiological and clinical requirements reported in the literature. A leaflet thickness of 0.65 mm was selected as a compromise between sufficient structural rigidity and minimal obstruction to blood flow, while the inner and outer diameters were determined as 21.2 mm and 25 mm, respectively, to enhance the effective orifice area without compromising mechanical stability. Particular emphasis was placed on the hinge region, which is recognized as one of the most critical zones in bileaflet mechanical valves with respect to thrombosis and hemolysis. To address these issues, the hinge geometry was modified by introducing smoothly rounded edges and controlled flow channels, aiming to distribute stresses more homogeneously and to enable continuous low-velocity blood flow through the hinge gap. This configuration was expected to minimize stagnation regions and reduce shear stress concentrations that contribute to blood damage. Following the completion of the geometric design, the optimized valve geometry was fabricated using a high-resolution 3D printing technique with aligner resin, enabling accurate reproduction of complex micro-scale features. After fabrication, the valve surfaces were functionalized using a sol–gel-based coating method with four different polymer formulations, namely PEG, PEG/Chitosan, PVA/Chitosan/PEG, and PEG/PU. These polymer systems were selected due to their well documented biocompatibility, hydrophilicity, and potential to improve blood surface interactions by reducing protein adsorption and bacterial adhesion. In order to further improve the surface characteristics and overall functional performance of the mechanical aortic heart valve, several polymer systems were synthesized and applied to the valve surface using the sol–gel-based surface modification technique. The coatings were designed to enhance biocompatibility at the blood contacting interface while maintaining adequate mechanical resistance. Accordingly, PEG based structures were prepared due to their hydrophilic nature and low protein adsorption capability, PVA/Chitosan blends were developed to provide mechanical stability and film-forming ability, PVA/Chitosan/PEG hybrid systems were synthesized to combine the advantages of both systems, and PEG/PU copolymers were formulated to improve the balance between elasticity and mechanical durability. Each polymer system was tailored to contribute to improved wettability, optimized elasticity, enhanced cellular interaction, and reduced hemolysis potential on the valve surface. The synthesized coating materials were subsequently incorporated into the mechanical characterization and material modeling process in order to quantitatively evaluate the effect of the coatings on the structural behavior of the valve material. The sol–gel technique was used for surface deposition, and the Young's modulus values were obtained from tensile tests presented in the previous section. The calculated elastic parameters for each coating type were transferred into a reference table to quantitatively describe the mechanical behavior of the materials. The densities of the samples were determined using the Archimedes method and were found to vary only slightly depending on the coating composition, which was attributed to the thin nature of the coating layers. The tensile test results demonstrated that the application of polymer coatings had a noticeable effect on the elastic modulus of the samples; however, this effect was not at a level that would compromise the mechanical integrity of the material. The Young's modulus of the uncoated sample was measured as 102.163 N/mm², whereas the coated samples exhibited values ranging between 88 and 92 N/mm². In this respect, it is important to note that native aortic valve tissue displays a distinct anisotropic biomechanical behavior, with elastic modulus values of approximately 4 MPa in the radial direction and 15 MPa in the circumferential direction depending on collagen fiber orientation, whereas commonly used mechanical heart valve materials such as pyrolytic carbon and titanium alloys exhibit extremely high stiffness values compared to native tissue. Titanium alloys typically have elastic moduli in the range of 80–140 GPa, while isotropic pyrolytic carbon exhibits elastic moduli of approximately 28–32 GPa. In the present study, the Young's modulus values of the developed prototype samples were within the range of 88–102 MPa, indicating that the material provides higher structural resistance than native valve tissue while remaining significantly more flexible than conventional mechanical valve materials. This behavior suggests that the developed system offers an advantageous intermediate stiffness profile. FESEM analyses showed that the surface irregularities observed on the uncoated samples were significantly reduced after the application of polymer coatings. EDS and FTIR analyses confirmed the successful bonding of the coatings to the surface and demonstrated that the diversity of functional groups enhanced surface interactions. In parallel with mechanical characterization, surface wettability was evaluated by contact angle measurements using a computer-based image analysis approach. The experimental setup consisted of a fixed camera, a laboratory elevator for precise sample positioning, and a pipetting mechanism for controlled droplet deposition. The water droplet placed on the sample surface was recorded at a constant angle, and the captured images were processed digitally to calculate the contact angle. Smaller contact angles indicate hydrophilic surfaces with higher liquid affinity, whereas larger angles correspond to hydrophobic behavior. The uncoated CRS resin surface exhibited a contact angle of 57.48°, indicating a moderately hydrophobic character. In comparison, the PEG-coated surface showed a reduced contact angle of 51.43°, confirming improved hydrophilicity. The PVA/Chitosan coated surface exhibited a significantly lower contact angle of 36.19°, demonstrating a strong hydrophilic behavior. The PVA/Chitosan/PEG hybrid coating provided a stable hydrophilic surface with a contact angle of 43.23°, while the PEG/PU coating exhibited a value of 37.56°, indicating enhanced wettability together with preserved mechanical stability due to the polyurethane component. These findings clearly demonstrate that the applied polymer coatings significantly improved the surface wettability of the mechanical aortic heart valve.In addition to wettability, the stability and particle size distribution of the coating solutions were evaluated using zeta potential and dynamic light scattering analyses. Among the tested formulations, the PVA/Chitosan/PEG hybrid system showed the most uniform particle size distribution and the highest stability, indicating a more controlled and homogeneous coating behavior. X-ray diffraction analyses further revealed that all coatings were predominantly amorphous, characterized by broad diffraction halos. Such amorphous polymer networks are advantageous for cardiovascular implants as they provide improved flexibility and resistance to fatigue under cyclic loading conditions. Finally, the biological performance of the coated surfaces was evaluated through antibacterial inhibition zone tests. The PVA/Chitosan/PEG hybrid coating exhibited the most pronounced antibacterial effect, forming a clear inhibition zone around the sample, whereas the uncoated control surface showed dense bacterial colonization. PEG-coated and PEG/PU-coated samples exhibited limited bacterial growth without distinct inhibition zones, indicating that PEG alone reduces bacterial adhesion but does not provide strong antibacterial activity. The PVA/Chitosan-coated surface demonstrated moderate bacterial suppression; however, the inhibition zone was less pronounced than that of the hybrid system. These results indicate that the synergistic interaction between chitosan and PEG provides enhanced antibacterial activity while maintaining surface stability. In conclusion, this study presents a novel bileaflet mechanical aortic heart valve that combines geometric optimization with polymer-based surface functionalization. The redesigned hinge geometry and optimized dimensional parameters resulted in improved surface morphology, enhanced hydrophilicity, preserved mechanical integrity, and superior antibacterial behavior. Among the evaluated coatings, the PVA/Chitosan/PEG hybrid formulation emerged as the most promising candidate. The findings show that combining structural design with surface biofunctionalization is an effective approach to overcome the limitations of conventional mechanical heart valves and to develop safer cardiovascular implants. In addition, this strategy offers a flexible framework that can be adapted to different materials and clinical needs, supporting future translation into practical applications.
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