Hap takviyesinin UHMWPE matrisli kompozitlerinin mikroyapısal ve mekanik özelliklerine etkisinin incelenmesi
Investigation  of the effect of hydroxyapatite supplement on the microstructural and mechanical properties of the UHMWPE matrix composites
Yazar: MERVE SEDA ZOR
Danışman: DOÇ. DR. GÖZDE FATMA ÇELEBİ EFE
Sakarya Uygulamalı Bilimler Üniversitesi / Lisansüstü Eğitim Enstitüsü / İmalat Mühendisliği Ana Bilim Dalı
Derece: Yüksek Lisans, 2023
Konu: Metalurji Mühendisliği = Metallurgical Engineering

Özet:
Günümüzde kullanım alanı ve önemi oldukça artan biyomalzemeler, vücut sıvısıyla temas halinde olup; insan vücudunda hasar görmüş canlı doku veya organların görevini üstlenmektedir. Biyomalzemeler için elastiklik modülü, sertlik, mukavemet, kırılma tokluğu gibi mekanik özellikler çok önemlidir. İdeal bir implant malzemesinden alerji ve hassasiyete sebep olmaması, kanserojen özellik göstermemesi, sterilize edilebilir olması, istenilen şekli alabilmesi ve vücut içinde bozulmadan sürekliliğini koruması beklenir. Vücudun büyük bir ağırlığını taşıyan kalça ekleminde çeşitli sebeplerle meydana gelen hasarlar için de kalça implantları kullanılmaktadır. Günlük yaşamda merdiven çıkma yürüme gibi hareketlere maruz kalan kalça implantlarından yüksek aşınma direnci ve mekanik özellikler beklenmektedir. 
Bu çalışmada, kalça protezlerinde cup ve/veya liner malzemesi olarak kullanılan UHMWPE (ultra yüksek molekül ağırlıklı polietilen) matriks, HAp (hidroksiapat) ile takviye edilerek UHMWPE-HAp kompozitleri üretilmiştir. İdeal bir kalça implantı için yetersiz sertlik ve aşınma dayanımına sahip UHMWPE matriks içerisine kemik onarımında oldukça popüler olan HAp partikülleri ilave edilerek; UHMWPE'in aşınma dayanımı ve kullanım ömrünün arttırılması hedeflenmiştir. UHMWPE-ağ.%0.5, %1, %2 ve %4 HAp bileşimlerdeki tozlar, mekanik aktivasyon yöntemiyle bilyalı değirmende 1\10 bilya oranında, 400 rpm hızında 3 saat boyunca karıştırılmıştır. Mekanik aktivasyon sonrası darbeyle yassılaşan ve homojen karışmış UHMWPE-HAp toz karışımları sıcak presleme ile 200°C'de 50 dakika sıcak şekillendirilmiştir. Elde edilen kompozitlerin mikroyapısal ve mekanik özellikleri saf UHMWPE numune ile karşılaştırılarak sonuçlar ortaya konmuştur. 
Sonuç olarak, üretilen kompozitlerin mikroyapı incelemelerinde HAp tanelerinin UHMWPE içerisinde homojen dağıldığı gözlenmiştir. XRD grafiklerinde UHMWPE'e ait karakteristik pikler literatür ile uyumlu şekilde 21.440, 23.900, 36.239 2θ açılarında tespit edilmiştir. UHMWPE'e ait karakteristik piklerle birlikte HAP'e ait pikler de gözlenmiştir. Ayrıca tüm kompozitlerin sertlik ve aşınma davranışının iyileştiği, en yüksek değerlere sahip UHMWPE-ağ%4 HAp kompozitinin saf UHMWPE'e kıyasla sertlik değerinin %118, aşınma oranının %81 arttığı ve sürtünme katsayısının da %65 azaldığı tespit edilmiştir. UHMWPE-ağ.%4 kompoziti 8 gün boyunca 37 °C'deki SBF çözeltisi içerisinde bekletildikten sonra yapılan ın vitro deneyinde apatit yapının varlığı tespit edilmiştir. DSC eğrilerinden HAp takviyesiyle ergime sıcaklığı ve kristalinitenin arttığı hesaplanmıştır. 

Anahtar Kelimeler: Biyomalzeme, Kalça protezi, UHMWPE-HAp kompozit, Sertlik, Aşınma oranı

Abstract:
Nowadays, biomaterials, whose usage area and importance have increased considerably, are in contact with body fluid and assume the function of damaged living tissues or organs in the human body. Biomaterials improve the quality of life of the person by fulfilling the function of the missing limb. They are exposed to body fluid in the body continuously or under load for a certain period of time. For this reason, the most important feature expected from biomaterials is that they do not cause allergic reactions and are biocompatible. Biocompatibility can be defined as the pH value of the prosthesis to be implanted into the body being compatible with the place where it is used and responding appropriately to the body. In addition to this feature, it is desired to be non-toxic and non-carcinogenic and to have mechanical properties such as appropriate elasticity modulus, friction coefficient, corrosion resistance, hardness and strength. When selecting biomaterials, the place of use in the body, the age of the patient, and the expectation of physical activity should be taken into consideration.
The most used and loaded joint in the human body is the hip joint.  The wear that occurs as a result of the loads on the joints degenerates the joint. Today, hip prosthesis is needed with the prolongation of human life. Total hip prosthesis are implants suitable for the body structure that replace the hip joint. The most common damage to these implants is wear due to time and friction. It is aimed to improve the mechanical properties of this material to eliminate wear problems. Total hip replacement is frequently used for hip fractures and degenerated hip joints. In this way, the patient's joint pain is reduced and daily physical activity is restored.
The hip joint prosthesis consists of four parts: acetabular socket, liner, femoral head and femoral stem. Among these parts, the acetabular socket and liner parts are the most exposed to load. With the wear caused by this load, diseases such as bone loss, joint loosening, fracture, dislocation occur in the implant parts and these diseases cause osteolysis and loosening and shorten the life of the implant. In order to prolong the implant life, it is expected to have a design that allows the ball and the socket to move freely with each other and to be resistant to friction, wear and corrosion. 
The aim of this study was to improve the properties of acetabular socket and liner parts used in total hip replacement implants. UHMWPE is a low-cost, easy-to-process thermoplastic with good mechanical properties; with its long chains, it has strong intermolecular interaction and efficient load transfer, thus emerging as a matrix material that will form a tough and high impact strength, robust skeletal structure. Hydroxyapatite is a highly bioactive material with structural and chemical properties close to human bone. Due to the superior properties of these materials, UHMWPE-HAP composite pair was selected as hip prosthesis liner material. In this study, it was aimed to improve implant instability and loosening problems with composite samples produced by adding hydroxyapatite into the UHMWPE matrix. UHMWPE-0.5, 1, 2, and 4wt% HAp composites were produced and characterized microstructurally and mechanically. 
In the studies, UHMWPE was used as the matrix material and HAp with a size of 200 nm was used as the reinforcement material obtained from Sigma-Aldrich. A better bonding between the polymer grains, which shrink, break and flatten due to the effect of friction and impact in the ball mill, and HAp, which is the reinforcing element, is provided. With this process, both pre-shredding and homogeneous distribution is achieved. In the experimental study, HAp powder was added to UHMWPE powder as reinforcement material at 0,5, 1, 2 and 4 wt%. In order to mechanically activate the prepared powder mixtures, they were mixed in a ball mill with a ball ratio of 1\10 at a speed of 400 rpm for 3 hours. The products in the ball mill were filtered through a sieve to separate the balls and mixture powders. After rotation, impact flattened and homogeneously mixed UHMWPE and HAp blend powder is obtained. UHMWPE and HAp powder mixtures mechanically mixed in the ball mill were subjected to hot pressing at 200 °C for 50 minutes with 1 ton load and UHMWPE-HAp composites were produced. After the hot pressing process, 3 cm in diameter, transparent and white specimens were obtained.
In the microstructure examinations, it was observed that the interfacial interaction of the matrix material UHMWPE and the reinforcing element HAp was good, HAp particles were well bonded to the matrix material and homogeneously distributed in the matrix. In the SEM-EDS spot analysis results of UHMWPE-HAp composites, O, P and Ca were detected in the content of the particles seen in white color.
When XRD spectrum results were analyzed, characteristic peaks of UHMWPE were detected at 21,440, 23,900, 36,239 2θ angles in accordance with the literature. In addition, characteristic peaks belonging to HAp were also detected; HAp peak intensities increased with the increase in HAp. As a matter of fact, the maximum HAp net. is 4%; since this ratio is below the detection limit of the X-ray device, the peak intensities are less pronounced. With the addition of 4% HAp, a slight decrease was observed in the intensity of the 100 peak of UHMWPE. 
While the lowest value in hardness tests was pure UHMWPE; the hardness values of the composites increased by 22%, 25,1%, 70,7%, 118% in proportion to the amount of HAp added. 
In the wear analysis, while the highest rate was found in pure UHMWPE; with the addition of 0.5%, 1%, 2% and 4% by weight of HAp, wear rates decreased by 10%, 35%, 75% and 81%, respectively. According to these results, it can be said that as the amount of reinforcement material HAp added into UHMWPE increases, the wear rate decreases and the wear resistance increases. While the coefficient of friction value of pure UHMWPE was 0.17, the coefficient of friction value was found to be 0.13, 0.09, 0.08 and 0.06 with the addition of 0,5%, 1%, 2%, 4% HAp by weight, respectively. The coefficient of friction of pure UHMWPE decreased by 24%, 47%, 53% and 65%, respectively.
After 8 days of soaking in SBF solution at 37 °C, SEM images revealed the presence of white spherical grains in the microstructure. From the analysis result, it is seen that these large and small grains are Ca concentrated. Considering the concentration of Ca and P elements, this structure is predicted to be apatite.
When we look at the endothermic peaks in this study, the melting temperatures we obtained are 138 °C for pure UHMWPE and 139 °C, 140 °C, 146 °C and 150 °C for UHMWPE-0,5, 1, 2, and 4wt% HAp composites, respectively. A right shift, broadening and some increase in the melting temperature were observed with HAp reinforcement. The highest melting temperature belongs to UHMWPE-4wt % HAp composite with 8.7% increase and it can be said that HAp reinforcement increases the melting temperature.
The endothermic peaks in this study, the melting temperatures we obtained are 138 °C for pure UHMWPE and 139 °C, 140 °C, 146 °C and 150 °C for UHMWPE-ag.% 0,5, 1, 2 and 4 HAp composites, respectively. When the crystallinity amounts of pure UHMWPE and composites were examined, an increase in crystallinity was determined with the increase in HAp amount. The highest shot belongs to UHMWPE-4% HAp composite.

Keywords: Bio metarial, Hip replacement, UHMWPE-HAp Composite, Hardness, Wear rate