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Makale / Article

Şekil hafızalı polimerlerlerin en ümit vadedici oldu-                  Applications where shape memory polymers are most
ğu uygulamalar biyomedikal mühendislik alanından-                      promising are in the field of biomedical engineering.
dır. ŞHP’ler, bozunabilir ve fonksiyonel kardiyovaskü-                 Shape memory polymers are degradable and materi-
ler implantlar ve diğer iyileştirici uygulamalar için ge-              als of developed for functional cardiovascular implants
liÅŸtirilen materyaller umut verici olarak kabul edilmiÅŸtir             and other curative applications have been considered
(Jung ve ark., 2010a, Karp ve Langer 2007). Geçtiğimiz                 promising. (Jung at al, 2010a, Karp and Langer 2007). A
yıllarda yoğun araştırma yapılan bir stent en çekici mik-              stent that has been intensively researched over the past
ro cihazlardan biridir (Şekil 6’da çalışma prensibi gös-               few years is one of the most attractive micro devices
terilmektedir) (Yakacki ve ark., 2007). Bozunabilir ŞHP                (The working principle is shown in Figure 6) (Yakacki
stentlerinin avantajı kaldırma işlemi için herhangi bir                et al., 2007). The advantage of degradable SMP stents
takip iÅŸlemi gerektirmemesidir (Chen ve ark., 2007a).                  is that they do not require any follow-up for removal.
Bu tür ŞHP’lerden yapılan ameliyat ipliklerinin daha                   (Chen et al., 2007a). Surgical threads made from such
sonrasında kaldırılması gerekmemektedir (Lendlein ve                   shape memory polymers do not have to be removed
Langer 2002). Kontrollü ilaç salınımı için hem biyolo-                 later. (Lendlein and Langer 2002). Both biodegradable
jik olarak bozunabilir hem de bozunmayan ŞHP’ler kul-                  and non-degrading SMPs were used for controlled drug
lanılmıştır (Wache ve ark. 2003, Chen ve ark. 2009b,                   release. (Wache et al.. 2003, Chen ve ark. 2009b, Wis-
Wischke ve ark. 2009, Zhang ve ark. 2010). Günümüz-                    chke et al. 2009, Zhang et al. 2010).
de ŞHP’ler endovasküler trombektomi cihazlarında                       Today, biodegradable and non-degradable SMPs have
(Wilson ve ark., 2007a), aktif mikroakışkan rezervuar-                 been used for controlled drug release in various medi-
larda (Gall ve ark. 2004), oküler implantlarda (Song ve                cal applications (Wache et al., 2003, Chen et al., 2009b,
ark. 2010) ve kendiliğinden yerleşen nöronal elektrot-                 Wischke et al., 2009, Zhang et al., 2010). For exam-
larda (Sharp ve ark. 2006) kullanılmaktadır.                           ple, ocular implants (Song et al., 2010), endovascular
                                                                       thrombectomy devices (Wilson et al., 2007a), sponta-
     Şekil 6. Şekil hafızalı stentler. Yıldız şeklinde deforme edilen  neously placed neuronal electrodes (Sharp et al., 2006)
           stentler uygun koşullarda eski haline dönmektedir.          and active microfluidic reservoirs (Gall et al., 2004) are
                                                                       simply produced from SMPs.
Figure 6. Medical stends produced from SHPs: the stents deformed       3. Shape Memory Polyurethanes
  like star shaped and then recovery process when expoesed to an       Polyurethanes are known to form from long lin-
                                   proper stimulus.                    ear chains of two interconnected types of segments
                                                                       (Figure 7). The flexibility varies with the ratio of soft
3. Şekil Hafızalı Poliüretanlar                                        segments (typically diisocyanate-bonded low melting
Poliüretanların, birbirine bağlı iki tip segmentten olu-               point polyether or polyester segments), elastic and
ÅŸan uzun doÄŸrusal zincirlerden meydana geldiÄŸi bilin-                  relatively hard segments (typically a diisocyanate with
mektedir (Şekil 7). Esneklik, yumuşak bölümler (tipik                  a small molecule glycol chain extender to the resulting
                                                                       diuretic bridges). When the diisocyanate/polyol or soft
                                                                       segment/hard segment ratios is adjusted, the desired
                                                                       elastic properties polymers such as crystallization tem-
                                                                       perature range and melting point can be easily adjust-
                                                                       ed. The soft segments of polyurethanes can be used as
                                                                       transition parts for shape memory effect.
                                                                       A number of shape memory polyurethanes have been
                                                                       developed up to daylight (Chen et al., 2010). Poly-
                                                                       urethane foams with shape memory are manufactured
                                                                       using different techniques and their structure is clari-
                                                                       fied (Chung and Park 2010) to increase the printing
                                                                       ratios (hence the shape recovery after printing) and
                                                                       reduce the density. Because physical aging is impor-
                                                                       tant for medical practice, many research groups are

12 Ocak / January - Şubat / February 2017
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