Design and Development of Bioactive Scaffold for the Repair of Bone Fracture by 3D Printing

Design and Development of Bioactive Scaffold for the Repair of Bone Fracture by 3D Printing

Dr. Girish K B, Gangadhara J V, Pavan S R, Chandan Kumar A R

Department of Mechanical Engineering

Adichunchanagiri University, BGS Institute of Technology, BG Nagara.

AbstractBone defects caused by trauma or disease pose significant challenges in orthopaedictreatment, with traditional

grafts limited by donor site morbidity and availability. This study develops 3D-printed scaffolds using a novel polylactic acid-calcium composite filament, termed Simubone, to enhance bone regeneration. Scaffolds were designed via computer-aided design, fabricated using fused deposition modeling 3D printing, and tested for mechanical properties at infill density of 40 percent, 50 percent, and 80 percent. Tensile testing showed peak strength at 50 percent infill with 2.49 megapascals for the triangle pattern, while impact testing indicated optimal energy absorption at 80 percent infill with 1.79 kilojoules per meter for the octo-gram pattern. Compression tests revealed higher resistance at 80 percent infill with 43.34 megapascals. Auxetic structures improved flexibility and crack resistance. The calcium reinforcement enhances osteoconductivity, making Simubone a promising material for bone repair. Future work includes biocompatibility testing and clinical validation to translate this technology into orthopaedic applications.

KeywordsBone Tissue Engineering, 3D Printing, Polylactic Acid-Calcium Composite, Scaffolds.

1. INTRODUCTION

   Bone defects resulting from trauma, degenerative diseases, or surgical interventions pose significant challenges in orthopaedic treatment. Traditional bone grafting methods, such as auto grafts and allografts, are limited by donor site morbidity, immune rejection, and supply constraints.

   Auto grafts, considered the gold standard, require dual surgeries, increasing patient morbidity, while allografts carry risks of disease transmission and immune responses. These limitations necessitate engineered alternatives that can mimic the structural and biological properties of native bone, offering patient-specific solutions with minimal complications.

   Fig 1 Three main categories of bone grafts namely autograft taken from the patients body itself, allograft taken from another body of the same species, and xenograft taken from another body of a different species.

   Additive manufacturing, specifically three-dimensional printing, has emerged as a transformative approach in bone tissue engineering. It enables the fabrication of scaffolds with tailored porosity, geometry, and mechanical properties, addressing the shortcomings of conventional grafts. This study introduces a novel polylactic acid-calcium composite filament, termed Simubone, which integrates calcium fillers to replicate bones mineral composition. Unlike standard polylactic acid, Simubone enhances osteoconductivity and mechanical strength, making it a promising material for bone repair scaffolds. The incorporation of auxetic structures further improves flexibility and load distribution, mimicking the hierarchical architecture of bone.

   The objectives of this study are to: (1) design three- dimensional-printed scaffolds using computer-aided design based on bone defect models, (2) fabricate scaffolds via fused deposition modelling with varying infill density, (3) evaluate mechanical properties through tensile, compression, and impact testing, and (4) assess the potential of Simubone scaffolds for bone regeneration.

2. LITERATURE SURVEY

   The development of effective solutions for bone defect repair has been a focal point in orthopaedic research, driven by the limitations of traditional bone grafting methods. Auto grafts, while osteoinductive and osteoconductive, are hindered by donor site morbidity and limited availability [1]. Allografts, conversely, pose risks of immune rejection and disease transmission, necessitating alternatives that can replicate bones structural and biological properties [2]. Recent advancements in bone tissue engineering have focused on biomimetic scaffolds to address these challenges, with additive manufacturing emerging as a promising approach. Three-dimensional (3D) printing, particularly fused deposition modeling (FDM), enables the fabrication of patient-specific scaffolds with controlled porosity and geometry. Hollister [3] highlighted the importance of scaffold architecture, noting that porosity levels of 6090% and pore sizes of 100500 micrometers are critical for cell infiltration and nutrient diffusion. However, achieving mechanical

   properties comparable to native bone (e.g., 212 megapascals for trabecular bone) remains a challenge [4]. Polylactic acid (PLA) is widely used in 3D-printed scaffolds due to its biodegradability and ease of processing, but its limited bioactivity restricts its efficacy in bone regeneration [5].

   To enhance scaffold performance, researchers have explored composite materials incorporating bioactive fillers. Bose et al.

   [6] demonstrated that calcium-based additives, such as hydroxyapatite, improve osteoconductivity by mimicking bones mineral composition, though challenges in uniform dispersion persist. Auxetic structures, characterized by a negative Poissons ratio, have also gained attention for their ability to enhance flexibility and load distribution. Rosetti et al. [7] reported that auxetic scaffolds reduce stress shielding, improving long-term integration with host tissue. Despite these advances, few studies have combined calcium- reinforced composites with auxetic designs in FDM-printed scaffolds, particularly for optimizing both mechanical and biological properties.

   Current literature underscores the need for scaffolds that balance mechanical strength, biocompatibility, and manufacturability. While PLA-based composites show promise, their mechanical performance often falls short of cortical bone requirements, and biocompatibility testing remains limited [8]. Additionally, the scalability of 3D printing for clinical applications is underexplored, with most studies focusing on prototype development rather than translational outcomes. This study addresses these gaps by developing a novel PLA-calcium composite filament (Simubone) for FDM-printed scaffolds, incorporating auxetic structures to enhance mechanical and biological performance, and evaluating their suitability for bone defect repair through comprehensive mechanical testing.

3. METHODOLOGY

   1. Materials The scaffold material is a novel polylactic acid- calcium composite filament, termed Simubone, with a diameter of 1.75 millimetres. Simubone was selected for its biocompatibility and ability to mimic bones mineral content, combining the biodegradability of polylactic acid with calcium fillers to enhance osteoconductivity and mechanical strength. This addresses the limitations of standard polylactic acid, which lacks sufficient bioactivity for bone repair applications.

      Fig:2,3,4, Bone design using Autodesk Fusion

   2. Scaffold Design

      Fig:3

      Fig:4

      Scaffolds were designed using AutoCAD software, based on bone defect models derived from computed tomography or magnetic resonance imaging scans. The designs incorporated auxetic structures with a negative Poissons ratio to improve flexibility and load distribution under mechanical stress. Porosity was maintained at 70 to 90 percent, with pore sizes ranging from 100 to 500 micrometers, to facilitate cell infiltration and ntrient flow. The models were exported in STL format for three-dimensional printing.

   3. Fabrication Scaffolds were fabricated using fused deposition modeling on a three-dimensional printer. Printing parameters included a nozzle temperature of 200 to 220 degrees Celsius, a bed temperature of 60 to 70 degrees Celsius, a layer height of 0.2 millimeters, and infill density of

      40 percent, 50 percent, and 80 percent. Two infill patterns, triangle and octo-gram, were tested to evaluate their impact on mechanical properties. Post-processing steps included support removal, cleaning with isopropyl alcohol, and sterilization via ultraviolet treatment to ensure biocompatibility.

      Fig:5 Fused deposition modeling process for Simubone scaffolds, illustrating layer-by-layer deposition of the polylactic acid-calcium filament.

      Fig:6 Printing Process

      Fig:7 3D printing machine with model

   4. Mechanical Testing Mechanical properties were evaluated according to ASTM standards. Tensile tests, per ASTM D638, used Type I specimens measuring 165 millimeters by 13 millimeters by 3.2 millimeters, with a loading rate of 4 millimeters per minute. Impact tests, per ASTM D256, used Izod specimens measuring 63.5 millimeters by 12.7 millimeters by 3.2 millimeters. Compression tests used cubic

   specimens of 2.5 centimeters by 2.5 centimeters by 2.5 centimeters. Tests were conducted for each infill pattern and density, with three specimens per group to ensure statistical reliability.

4. RESULTS AND DISCUSSION

   1. Tensile Strength

      Fig:8 Tensile Specimen

      Tensile tests were conducted to evaluate the influence of infill density and pattern on the mechanical performance of Simubone scaffolds. Results are summarized in Table I. The triangle infill pattern at 50 percent infill achieved the highest tensile strength of 2.49 megapascals, with a percent elongation of 1.93. The octo-gram pattern peaked at 50 percent infill with 2.24 megapascals and 1.12 percent elongation. At 80 percent infill, both patterns exhibited reduced strength, likely due to internal stress concentrations caused by denser filament packing.

   2. Impact Strength

      Fig:9 Impact test Specimen

      Impact tests assessed the energy absorption capacity of the scaffolds,

      The octo-gram pattern at 80 percent infill demonstrated the highest impact strength of 1.79 kilojoules per meter, absorbing 0.89 joules of energy. The triangle pattern at 80 percent infill followed closely with 1.63 kilojoules per meter. Lower infill density resulted in reduced energy absorption, indicating that denser scaffolds better withstand sudden impacts.

      Materials	Infill pattern	Infill density	Tensile strength MPa	% of Elongation
      PLA- Calcium	Triangle	40%	1.9023	1.0214%
      PLA- Calcium	Triangle	50%	2.4921	1.9262%
      PLA- Calcium	Triangle	80%	2.3012	0.99%
      PLA- Calcium	Octo- gram	40%	1.7562	0.92%
      PLA- Calcium	Octo- gram	50%	2.2439	1.12%
      PLA- Calcium	Octo- gram	80%	1.9431	0.94%

   3. Compression Strength

      Fig:10 Compression test Specimen

      Compression tests evaluated the scaffolds resistance to compressive forces. At 80 percent fill, the triangle pattern exhibited the highest

      compressive strength of 43.34 megapascals, with a 2.36 percent reduction in length. The octo-gram pattern at 80 percent infill achieved 37.41 megapascals. Lower infill density samples showed greater deformation, suggesting that higher infill density enhances structural integrity under compressive loads.

      Fig:11 Process and finished 3D model

      Table I Tensile Testing Results for Simubone Scaffolds

      Materials	Infill pattern	Infill density	Energy absorption in J	Impact strength J/mm2
      PLA- Calcium	Triangle	40%	0.2144	0.7157
      PLA- Calcium	Triangle	50%	0.4914	0.9928
      PLA- Calcium	Triangle	80%	0.8057	1.6278
      PLA- Calcium	Octo- gram	40%	0.2054	0.6823
      PLA- Calcium	Octo- gram	50%	0.5364	1.1829
      PLA- Calcium	Octo- gram	80%	0.8946	1.7914

      Table II Impact Testing Results for Simubone Scaffolds

      Materials	Infill pattern	Infill density	Compr ession strength MPa	% of Reduction in Length
      PLA- Calcium	Triangle	40%	29.32	2.78%
      PLA- Calcium	Triangle	50%	35.91	2.49%
      PLA- Calcium	Triangle	80%	43.34	2.36%
      PLA- Calcium	Octo- gram	40%	27.61	3.17%
      PLA- Calcium	Octo- gram	50%	32.85	2.70%
      PLA- Calcium	Octo- gram	80%	37.41	2.58%

      Table III Compressive Strength Testing Results for Simubone Scaffolds

      Fig. 12 Tensile Strength of Simubone Scaffolds Across Infill Densities for Triangle and Octo-gram Patterns

      Fig:13 Compressive Strength of Simubone Scaffolds Across Infill Densities for Triangle and Octo-gram Patterns

      Fig:14 Compressive Strength of Simubone Scaffolds Across Infill Densities for Triangle and Octo-gram Patterns

   4. Discussion

   The mechanical testing results indicate that Simubone scaffolds with 50 to 80 percent infill density balance strength and flexibility, making them suitable for trabecular bone applications, which typically exhibit compressive strengths of 2 to 12 megapascals. The incorporation of auxetic structures enhanced crack resistance and load distribution, aligning with studies on biomimetic scaffold designs. Compared to standard polylactic acid, which has a tensile strength of 2.5 to 3.5 megapascals, Simubones calcium reinforcement maintains comparable mechanical performance while improving Osteoconductivity, as the calcium fillers mimic bones mineral phase. The scaffolds porosity of 70 to 90 percent and pore sizes of 100 to 500 micrometres support nutrient flow and cell infiltration, critical for bone regeneration. However, the lack of biocompatibility testing limits conclusions about in vivo performance. Future work should include cell viability assays and vascularization studies to validate Simubones clinical potential.

5. CONCLUSION

   This study developed and evaluated three-dimensional (3D)- printed saffolds using a novel polylactic acid-calcium composite filament, termed Simubone, for bone defect repair. Mechanical testing demonstrated that scaffolds with 50 percent infill density achieved optimal tensile strength of 2.49 megapascals for the triangle infill pattern, while 80 percent infill scaffolds exhibited superior impact strength of 1.79 kilojoules per meter for the octo-gram pattern and compressive strength of 43.34 megapascals for the triangle pattern. These properties align with the mechanical requirements of trabecular bone, which typically ranges from

   2 to 12 megapascals in compressive strength [4]. The incorporation of auxetic structures enhanced flexibility and crack resistance, improving load distribution under mechanical stress [7].

   The Simubone filaments calcium reinforcement significantly enhances osteoconductivity compared to standard polylactic acid, addressing a critical limitation in bone tissue engineering scaffolds [6]. With porosity levels of 70 to 90 percent and pore sizes of 100 to 500 micrometres, the scaffolds support nutrient flow and cell infiltration, essential for bone regeneration. However, the absence of biocompatibility testing limits current conclusions about in vivo performance. Future work will focus on conducting cell viability assays, vascularization studies, and in vivo trials to validate Simubone clinical applicability. Additionally, optimizing printing parameters to reduce fabrication time and exploring scalability for clinical production are critical next steps.

   This work advances personalized orthopaedic solutions by demonstrating the feasibility of 3D-printed Simubone scaffolds for bone repair, offering a promising alternative to traditional grafting methods. By addressing mechanical and biological requirements, Simubone scaffolds pave the way for translational research in bone tissue engineering.

6. ACKNOWLEDGEMENTS

   We express our sincere gratitude to the New Age Innovative Network (NAIN), supported by the Department of Science and Technology, Government of Karnataka, for their invaluable encouragement and resources, which significantly contributed to the successful completion of this work.

7. REFERENCES

1. A. R. Amini, C. T. Laurencin, and S. P. Nukavarapu, Bone tissue engineering: recent advances and challenges, Crit. Rev. Biomed. Eng., vol. 40, no. 5, pp. 363408, 2012.

2. R. S. Taichman, Blood and bone: two tissues whose fates are intertwined to create the hematopoietic stem-cell niche, Blood, vol. 105, no. 7, pp. 26312639, 2005.

3. S. J. Hollister, Porous scaffold design for tissue engineering, Nat. Mater., vol. 4, no. 7, pp. 518524, 2005.

4. J. Y. Rho, T. Y. Tsui, and G. M. Pharr, Mechanical properties and the hierarchical structure of bone, Med. Eng. Phys., vol. 20, no. 2, pp. 92 102, 1998.

5. S. Bose, M. Roy, and A. Bandyopadhyay, Bone tissue engineering using 3D printing, Mater. Today, vol. 16, no. 12, pp. 496504, 2013.

6. S. Bose, S. Vahabzadeh, and A. Bandyopadhyay, Calcium phosphate ceramic systems in growth factor and drug delivery for bone tissue engineering: a review, Acta Biomater., vol. 8, no. 4, pp. 14011421, 2012.

7. L. Rosetti, L. Kock, and L. M. Vergani, Scaffolds for bone tissue engineering: state of the art and new perspectives, Mater. Sci. Eng. C, vol. 78, pp. 12461262, 2017.

8. J. R. Jones, Review of bioactive glass: from Hench to hybrids, Acta Biomater., vol. 9, no. 1, pp. 44574486, 2013.