Microstructure and mechanical property of 3D printing biomaterial poly (lactic acid) scaffold apply in biomedical

ABSTRACT:

This research surveyed how 3D-printing nozzle moving speeds and temperatures affect the scaffold template structure and mechanical compressive strength, thereby determing parameters for making polymeric materials biological scaffold from poly-(lactic acid) (PLA). A three-dimensional (3D) bio-polymer micro-structured scaffold of PLA was fabricated by 3D-printing technology and it formed a network of PLA fiber with the average dimension sizes of 360-440 micron. Molecular weight and thermoplastic properties were investigated by GPC (Gel Permeation Chromatography) and DSC (Differential Scanning Calorimetry) methods. Morphology and porosity of the scaffold were examined by using a scanning electron microscopy (SEM). Mechanical compressive strength properties of the scaffold were tested in 3 dimensional axis with the maximum measured value of 21 Mpa. Scaffolding structural materials are applied in tissue transplantation with mechanical properties and the structure conforming to biological standards.

Keywords: Poly-(lactic acid), scaffold, biomaterials, 3D printing.

 1. INTRODUCTION

In recent years, various approaches based on tissue engineering principles have been explored to regenerate other functional tissues that are relevant to maxillofacial tissue regeneration. In tissue engineering, scaffolds are critical to provide structure for cell infiltration and proliferation, space for extracellular matrix generation and remodeling, biochemical cues to direct cell behavior, and physical connections for injured tissue. When making scaffolds, design of the architecture on the macro, micro, and nano level is important for structural, nutrient transport , and cell-matrix interaction conditions ^[1-3]. The macro architecture is the overall shape of the device which can be complex (e.g. patient and organ specificity, anatomical features). The microarchitecture reflects the tissue architecture (e.g. pore size, shape , porosity , spatial distribution, and pore interconnection). The nano architecture is surface modification (e.g. biomolecule attachment for cell adhesion, proliferation, and differentiation). ^[4,5] The ability to design and fabricate complex, 3D biomedical devices is critical in tissue engineering. Applications for 3D biomedical devices are restoration of 3D anatomic defects, the reconstruction of complex organs with intricate 3D microarchitecture (e.g. liver, lymphoid organs), and scaffolds for stem cell differentiation. (Fig.1)

Fig.1: Parameters to calculate the surface roughness in AM systems ^[10]

While industrial 3D printers have reached extremely high resolution in the past few years, the advancements in machine capability have not translated to the use with biomaterials. Industrial 3D printers can now reach extremely small build layers such as 16 μm layer thickness for SLA (Polyjet , Stratasys), 178 μm layer thickness for FDM (Fortus 900mc , Stratasys), 80 μm layer thickness for SLS (sPro 230HS , 3D Systems) and 75 μm resolution for SLA (3D Systems) ^[6-8]. This research focuses on advanced 3D Printing technologies that are being used to fabricate tissue engineering scaffolds, with emphasis on their ability of these manufacturing technologies to pattern sample as microstructure and mechanical properties. As seen in Fig. 1, the layered structure of the scaffolding materials has an effect on the thickness and layer cohesion, which is the strength of the product.

2. MATERIALS AND METHODS

Fig.2: Pattern design structure (above)- FD, FG, LG, ST:

distance between filaments and plastic layers- ΦRW: filament diameter;

Axis direction in compressive strength test

PLA used was Normal Filament PLA 302HK 1.75MM/3.0MM from Hangzhou Zhuopu New Materials Technology Co., Ltd. Thermal properties of the material used was tested by means of DSC 204 F1 Phoenix NETZSCH, Germany; thereby identified PLA 3D printing material (original raw material) has Tg ~ 40 °C, Tm ~ 139 ^oC.

PLA materials were tested with GPC POLYMERLAB - Model: PL-GPC 50 to determine molecular weight and dispersion of macromolecular materials. Rapid prototyping MARKERBOT equipment is manufactured at the Department of Mechanical Engineering. The study factors affected to the plastic filaments structure designs (Fig. 2); moving speed of nozzle; temperature of nozzle (Table 1). Porous three dimensional scaffolds of PLA were  developed by laying down the microfilaments directionally layer-by-layer using an 3D-printing Fused Deposition Modelling (FDM). The loading direction, strain rate directly influenced the mechanical properties of the scaffolds ^[9].

Table 1: Nozzle moving speed 40 - 80 mm/s at constant temperature

210 ^oC (left); Temperature of nozzles in range of 180 ÷ 220 ^oC (right)

 3. RESULTS AND DISCUSSION

Analyzing the structure obtained from the imaging methods (optical, SEM)  (Fig. 3), the PLA scaffold pattern is fabricated in an outer shape and internal structure similar to that of the original computerized design (Fig. 2). The horizontal cross-sectional view of the z-axis in Fig. 3, the plastic yarn is distributed in position and size uniformly, while the hole spacing between the structural fibers is guaranteed geometrically, although not maintained completedly on all these hole shapes. The polymer material has an initial molecular weight of 111k and a multiple dispersion of 6.7. The large molecular weight makes the product rugged, while the high dispersion helps to increase the flexibility between macromolecules suitable for thermoplastic forming methods without the need of existing molds.

Measuring the fiber diameter size and calculate the cavity density with Image-J software, as shown in Fig. 4 as part of the experiment to change the speed of the nozzle movement. The results show that the efficiency of the nozzle boosting has improved the reduction in fiber diameter, thereby increasing the porosity of the scaffold. As the sample temperature increases, the sample tends to accumulate, so it expands more after cooling, resulting in an increase in the diameter of the filaments, which reduces internal spaces and also reduces porosity. Processing temperature in the range of 200 - 210 ^oC with fiber diameter of about 360 microns. Meanwhile, if increasing the speed of the nozzle, the yarn diameter tends to decrease in size due to being stretched by the force of the nozzle - plastic yarn. The result at 60 mm/s for a yarn size of 387 microns reaches the minimum value. (Fig.3)

Fig.3: SEM image of the sample S10.5 at 5KV x30 (above),

and GPC spectrum of PLA material (below)

Compressive strength in Fig. 5 with the X/Y-axis represents elasticity/plasticity of PLA resin composition porous hollow structure. While the Z-axis durability after elastic deformation through the pore structure of the material will be thickened and converted to compressed solid so compressive strength will continue to rise, here only get the maximum value linear elastic region. With X-direction, the sample reaches the maximum value 60 mm/s worth 21 MPa, outside this region, stress values decreased markedly. According to the Y-axis, the sample reach the maximum value in the range of 40-50 mm/s with the measured value is 11-12 MPa, then subside. At Z-axis, stresses are stability in range of 70-80 mm/s measured from 17-18 MPa, and peaked at 2 of this border, the periphery tends to decrease. Performance under all 3 methods of measurement samples in range of 40-60 mm/s with X-Y axis, and 70-80 with Z-axis. (Fig.4)

Fig.4:. Filament diameter (micrometre) depends on nozzle temperature

180 - 220 ^oC and nozzle moving speeds 40 - 80 mm/s

4. CONCLUSIONS

Fused deposition modeling method (FDM) is built into a process for making thermoplastic polymeric biomaterials Poly-(lactic acid). Using the observation method in determining the micro-structure of the macroporous and interconnecting scaffold structure samples.  Processing temperatures are from 180-210 ^oC, injection moving speeds 40-80 mm/s. Compressive strength according to 3-axis X-Y-Z are maximum value at 21; 17.5; 11.7 Mpa, respectively. We have determined the scaffold filaments sizes and sample mechanical strength according to fabrication parameters of nozzle temperature and velocity, serving the purpose of prototyping to meet biological material outputs for cell transplantation according to ISO-10995. Biological scaffold samples with interconnect pore structure and good mechanical properties for applications in biomedical and tissue engineering. (Fig.5)

Fig.5: The mechanical stress (Mpa) in the 3-axis of the samples at 210°C and nozzle moving speeds 40 - 80 mm/s.

ACKNOWLEDGMENT:

This work was financially supported by Ho Chi Minh City University of Technology and Vietnam National University - Ho Chi Minh through the Science and Technology Funds granted for T-PTN-2018-60 projects.

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 VI CẤU TRÚC VÀ TÍNH CHẤT CƠ LÍ CỦA VẬT LIỆU SCAFFOLD

SINH HỌC POLY(LACTIC ACID) IN 3D ỨNG DỤNG TRONG Y SINH

ThS. NGUYỄN THÁI HÒA⁽¹⁾⁽²⁾ , TRẦN HUỲNH HOÀNG TRỌNG⁽¹⁾,

TẠ QUANG DUY⁽¹⁾, PGS. TS. HÙYNH ĐẠI PHÚ ⁽¹⁾⁽³⁾

¹ Khoa Công nghệ Vật liệu, Trường Đại học Bách khoa, 

Đại học Quốc gia Tp.HCM.

² Phòng thí nghiệm Trọng điểm ĐHQG Công nghệ Vật liệu, Trường Đại học Bách khoa, 

Đại học Quốc gia Tp.HCM.

³ Trung tâm Nghiên cứu Vật liệu Polymer, Trường Đại học Bách khoa

Đại học Quốc gia Tp.HCM.

TÓM TẮT:

Nghiên cứu tiến hành khảo sát kĩ thuật in 3D với các thông số gia công vận tốc và nhiệt độ đầu phun ảnh hưởng đến cấu trúc và tính chất cơ học của khung giàn giáo scaffold. Qua đó xác định các thông số chế tạo vật liệu sinh học cấu trúc scaffold từ vật liệu polymer Poly(lactic acid) PLA. Sản phẩm khung cấu trúc 3 chiều vi cấu trúc scaffold từ vật liệu sinh học polymer PLA đã được chế tạo bằng kĩ thuật in 3D để tạo thành một mạng lưới sợi đan xen có kích thước trung bình từ 360-440 micromet. Khối lượng phân tử Mw và tính chất nhiệt dẻo của vật liệu được xác định bằng các phương pháp sắc kí gel GPC và phân tích nhiệt vi sai DSC. Hình thái học và mật độ xốp của cấu trúc giàn giáo được kiểm tra với kính hiển vi điện tử quét (SEM). Tính chất cơ học độ bền nén được thử nghiệm theo 3 phương với giá trị đo được tối đa là 21 Mpa. Vật liệu cấu trúc giàn giáo được ứng dụng trong việc cấy ghép mô với các tính chất cơ học và cấu trúc tương thích các tiêu chuẩn sinh học.

Keywords: poly-(lactic acid), khung giàn giáo (scaffold), vật liệu sinh học, in 3D.