Ultrasona duyarlı hidrojellerin sentezi ve ilaç salım davranışlarının incelenmesi
Synthesis of ultrasensitive hydrogels and investigation of drug release behavior
Yazar: ŞULE BALCI
Danışman: PROF. DR. CUMA BİNDAL
Sakarya Üniversitesi / Fen Bilimleri Enstitüsü / Biyomedikal Mühendisliği Ana Bilim Dalı
Derece: Yüksek Lisans, 2023
Konu: Biyomühendislik = Bioengineering

Özet:
İlaç taşıyıcı sistemler, tıpta ve sağlık hizmetlerinde ilaçların vücuttaki etkilerini kontrol etmek için kullanılan bir teknolojidir, çünkü doksorubisin (DOX) gibi ilaçların normal dokular üzerindeki çoklu olumsuz yan etkileri vardır ve serbest ilaç tedavisinde kullanımını sınırlamaktadır. İlaç salımını kontrol etmek için tipik ilaç verme sistemleri, polimer bozunmasına ve pasif difüzyona dayanır ancak gerektiğinde ilaç salım hızını geçici olarak kontrol etme yeteneğine sahip değillerdir. Bu yüzden kontrollü salım sistemleri kullanılarak ilaç daha verimli ve güvenli hale getirilebilmektedir. Son yıllarda sağlık alanında kendinden kontrollü bir şekilde ve çevresel faktörlerin etkisi altında sıvıyı serbest bırakabilen hidrojeller büyük ilgi görmektedir. Hidrojellere yüklenen ilacın, ilaç salım hızını geçici olarak kontrol etmek için kullanılan fiziksel enerjilerden biri ultrasondur (US). Enkapsülasyon ile normal dokular üzerindeki olumsuz etkiler önlenebilir ve US kullanılarak ilaç hedefleme ile sorunlu bölgeye ilaç verilmesi sağlanabilir. Bu çalışmada, Polivinil alkol (PVA), Melamin (M) ve Tannik asit (TA) malzemeleri kullanılarak donma-çözülme yöntemiyle US'a duyarlı hidrojeller sentezlenmiş ve US etkisinin ilaç salım davranışlarını nasıl etkilediği araştırılmıştır. Hidrojel sentezlenirken farklı oranlarda (%5, %10, %15) TA ekleyerek enkapsülasyon verimi ve kontrollü ilaç salımı geliştirmek için yeni bir yaklaşım önerilmektedir. Ağırlıkça %35 PVA bazlı hidrojellere önce ağırlıkça %1,5 M ilave edilmiş daha sonra ağırlıkça TA ilave edilerek sentezlenmiştir. TA ilave edilerek hazırlanmış PVA/M hidrojelleri, donma-çözülme yöntemiyle oda sıcaklığında (22°C) en az 6 saat erime ve -20°C'de 30 dk donma işlemi yapılarak sentezlenmiş ve bu donma çözülme döngüsü dört defa tekrarlanmıştır. Dondurma-çözülme işlemi, iyi mukavemetli hidrojeller oluşturduğu ve uygulaması kolay bir yöntem olduğu için tercih edilmiştir. Hazırlanan hidrojeller şişme oranı, fourier transform infrared (FTIR) analizi, taramalı elektron mikroskobu-enerji dağılım spektroskopisi (SEM-EDS) analizi, x-ışını difraksiyon (XRD) analizi, temas açısı ve yüzey gerilimi(enerjisi) ile karakterize edilmiştir. XRD, SEM-EDS analizleriyle PVA'nın kristal yapısını değiştirmediği ve homojen bir morfolojiye sahip olduğu görülmüştür. TA oranı arttıkça FTIR analizinde beklendiği gibi hidrojellerin daha hidrofobik hale geldiği şişme testinde su absorplama kapasitesinin %73'ten %63'e düşmesi, yüzey enerjisinin azalması ve temas açısının ortalama değeri 10,15'ten 62,27'ye artması ile doğrulanmıştır. PVA/M/TA hidrojellerine doksorubisin-hidroklorür (DOX-HCI) yüklenmiştir. İlaç salım deneyleri 15,30,45 ve 60 dk sürelerle oda sıcaklığında (22 °C) US varlığında 40 kHz ultrasonik banyoda ve US olmadan gerçekleştirilmiştir. Salınan ilaç miktarı spektrofotometrik yöntem ile tayin edilmiştir. DOX yüklü hidrojellerin deiyonize su içerisinde bulunduğu ortamda salım gerçekleştirilmiştir. Sentezlenen tüm hidrojellerde, US'la tetiklenen numunelerin, tetiklenmemiş numunelere göre yaklaşık 2 kat kadar fazla ilaç salımı gerçekleştirdiği görülmüştür. TA oranı arttıkça ilaç salımı yaklaşık 1.5 kata kadar düşmüş ve enkapsülasyon etkinliği ise %50 oranında artmıştır. US süresi arttıkça ilaç salımı ortalama 3,7 kat arttı. Kontrollü ilaç salım kinetiğinin belirlenmesi için Korsmeyer-Peppas, birinci derece ve sıfırıncı derece kinetik modellemeleri kullanılmıştır. PVA/M/TA hidrojellerin kinetik modelleme içinde Korsmeyer-Peppas kinetik modellemeyle daha uyumlu olduğu ve Fickian olmayan difüzyon gösterdiği belirlenmiştir. Ultrason etkisi ile süper durum II taşınım mekanizması gösterdiği görülmüştür. Çalışmada, elde edilen bulgulara göre TA 'nın ilaç salımını azalttığı halde US 'un ilaç salımı ve kinetiği üzerinde önemli bir etkiye sahip olduğu ve salımı belirgin derecede artırdığı tespit edilmiştir. Tüm analizler değerlendirildiğinde kontrollü ilaç salımında hidrojellerin yapısının ve US gibi fiziksel etkilerin etkili olduğu anlaşılmıştır.

Abstract:
Drug delivery systems are a technology used in medicine and healthcare to control the effects of drugs in the body, as drugs such as doxorubicin (DOX) have numerous undesirable side effects on normal tissues, limiting their use in free drug therapy. Typical drug delivery systems to control drug release rely on polymer degradation and passive diffusion but do not have the ability to temporarily control the rate of release when needed. Controlled release systems can therefore be used to make drug delivery more efficient and safer.
In recent years, hydrogels that can release liquid in a self-controlled manner under the influence of environmental factors have attracted great interest in the healthcare field. Hydrogels that can release drugs by self-control and under the influence of environmental factors are of interest in the health field. Hydrogels are very similar to living tissues. Thanks to the high water absorption ability of hydrogels, they show high biocompatibility. Therefore, they are often preferred in drug delivery systems. Hydrogels are three-dimensional network structures formed by crosslinking polymers with a large number of hydrophilic groups. Despite the many advantages of hydrogel-based delivery systems, they limit the ability of a hydrophilic hydrogel to retain a hydrophobic drug, i.e., to load the drug onto the hydrogel. Hydrogels used in controlled drug release are hydrophilic, and hydrophilic drugs released often have undesirable release kinetics and times. Reducing the solvent properties and increasing the hydrophobic properties in the design of hydrogels has contributed to overcoming these problems. The design, synthesis, and characterization of hydrogel materials can improve their poor properties by enhancing their properties. The degree of swelling of hydrogels is adjustable, and they respond differently to different physical conditions. Thanks to the porous structure of hydrogels, a smart hydrogel that responds to stimuli can change its responses by changing the ambient conditions (pH, temperature, solution concentration, solvent type, type of solvent, UV radiation, electric field strength, magnetic field strength, etc.). The hydrogel can enhance the release of the drug by physical stimuli at rates determined by the diffusion parameter.
One of the physical stimuli used to temporarily control the rate of release of the drug contained in hydrogels is ultrasound (US). US is an easy technique to use and is harmless when used correctly. For example, the magnetic field is inconvenient for people with pacemakers, but the use of US is harmless. The physiological effects of US application to stimulus-sensitive hydrogels can be grouped into thermal (hyperthermia) and mechanical (non-thermal) effects. In the thermal effect, heat energy is released as US energy is absorbed by the tissue. The amount of heat generated varies depending on the absorption capacity of the tissue, duration of application, dose, and method of application. The thermal effect can cause disruption of the cell membrane and increased permeability of blood vessels. High intensity focused ultrasound (HIFU) can be used to induce the thermal effect. HIFU can lead to a rapid local temperature rise and cause unpredictable and irreversible damage. In non-thermal impacts, acoustic energy is transferred to mechanical energy in the form of oscillation and force. The non-thermal effect can also be divided into stable and unstable cavitation. Unstable cavitation is characterized by rapid growth and collapse of microbubbles, while stable cavitation is characterized by continuous oscillation of microbubbles. The sustained release of microbubbles creates velocities that cause shear stresses that affect the release of the encapsulated drug in the fluid. Stable cavitation is thought to break down the cross-links of the hydrogel, and this breakdown increases the size of the pores in the hydrogel, temporarily altering its characteristic diffusion properties and enhancing drug release.
Negative effects on normal tissue can be prevented by encapsulation, and the drug can be targeted to the problem area by using US. In this study, US-sensitive hydrogels were synthesized using polyvinyl alcohol (PVA), melamine (M), and tannic acid by freeze-thaw method and investigated how the effect of US affects the drug release behavior. A new approach is proposed to improve the encapsulation efficiency and controlled drug release by adding TA at different rates (5%, 10%, 15%) during the synthesis of the hydrogel. It was synthesized by adding 1.5 wt% M to 35 wt% PVA-based hydrogels followed by addition of TA. The PVA/M hydrogels prepared by adding TA were synthesized by freeze-thaw method by melting at room temperature (22°C) for at least 6 hours and freezing at -20°C for 30 minutes. This freeze-thaw cycle was repeated four times. The freeze-thaw process is a type of physical crosslinking method that uses the crystallization process of precursor solutions and hydrogen bonding interactions between polymer chains to produce hydrogels. The freeze-thaw method was preferred because it forms hydrogels with good strength and is an easy-to-use method.
The prepared hydrogels were characterized by swelling analysis, Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), X-ray diffraction (XRD), contact angle, and surface tension (energy) measurement.
The functional groups of the hydrogel were characterized by FTIR analysis. FTIR analysis supports that TA binds with the hydroxyl groups of PVA, reducing the density of hydroxyl groups and increasing the hydrophobic properties of the compound.
In the SEM results, it is thought that the decrease in aggregation with increasing TA ratio, a more homogeneous distribution, and a partially smooth texture are due to the increase in hydrogen bond density. The presence and distribution of carbon, oxygen and nitrogen signals in the hydrogel structure were confirmed by determining the EDS map.
The absence of a large difference in the measured peak density of the hydrogels in XRD analysis indicates that the TA molecules did not change the crystal structure of PVA.In the swelling test of the hydrogel, as the TA ratio increased, the hydrogel chains were bound together, restricting the penetration of water molecules into the hydrogel. Thus, the water absorption capacity decreased from 73% to 63%.
The average value of the contact angle increased from 10.15° to 62.27°. This indicates that as the TA ratio increased, hydrogen bonding with the -OH groups of PVA, the main component of the hydrogel, decreased the polarity of the hydrogel and increased its hydrophobic property. By determining the contact angle, the surface energy was calculated according to the equations in Van Oss Acid-Base, Fowkes, Wu, and Equation of State methods with the help of a software program. As the contact angle increased, hydrophobic properties increased and surface energies decreased. FTIR analysis confirmed these results.
For drug loading, hydrogels were immersed in 100 mL of 200 ppm DOX-HCl solution at 22 °C for three days and shaken at 200 rpm. Drug release analysis was performed both in the presence of ultrasound (US) and without US, using a 40 kHz ultrasonic bath and at room conditions (22°C). Drug release from DOX-loaded hydrogels was performed in tubes containing 5 mL of deionized water. Samples were taken from the tubes at 15-minute intervals to determine the amount of DOX released. The drug concentration in each sample taken was measured at 480 nm and pooled to be 15-30-45-60. Each sample was tested three times at specified intervals. In order to keep the liquid volume in the tube constant, after the samples were taken, all the remaining volume in the tubes was poured out and filled again with 5 ml of deionized water.
The amount of drug released was determined by spectrophotometric method. It was measured at 480 nm using a UV-Vis spectrophotometer. Release was carried out in the presence of DOX-loaded hydrogels in deionized water.
The release was carried out in the presence of DOX-loaded hydrogels in deionized water. In all synthesized hydrogels, it was observed that US-triggered samples released approximately two times more drug than untriggered samples. As the TA ratio increased, the drug release decreased approximately 1.5 times, and the encapsulation efficiency increased by 50%. As the duration of the US increased, the drug release increased by an average of 3.7 times.
Korsmeyer-Peppas, first-order, and zero-order kinetic models were used to determine the kinetics of controlled drug release. It was found that PVA/M/ TA/DOX hydrogels were more compatible with the Korsmeyer-Peppas model in kinetic modeling and showed non-Fickian diffusion. It was observed that it showed a super-state II transport mechanism with the effect of ultrasound.
In the study, it was found that TA decreased drug release, while US had a significant effect on drug release and kinetics and significantly increased release. Evaluation of all analyses showed that it was understood that the structure of hydrogels and physical effects such as US were effective in controlled drug release.