The proper choice of a material system for bioresorbable synthetic bone graft substitutes imposes strict requirements for mechanical properties, bioactivity, biocompatibility, and osteoconductivity. This study aims to characterize the effect of in-mold annealing on the properties of nanocomposite systems based on asymmetric poly(l-lactide) (PLLA)/Poly(d-lactide) (PDLA) blends at 5 wt.% PDLA loading, which was incorporated with nano-hydroxyapatite (HA) at various concentrations (1, 5, 10, 15 wt.%). Samples were melt-blended and injection molded into "cold" mold (50 °C) and hot mold (100 °C). The results showed that the tensile modulus, crystallinity, and thermal-resistance were enhanced with increasing content of HA and blending with 5 wt.% of PDLA. In-mold annealing further improved the properties mentioned above by achieving a higher degree of crystallinity. In-mold annealed PLLA/5PDLA/15HA samples showed an increase of crystallinity by ~59%, tensile modulus by ~28%, and VST by ~44% when compared to neat hot molded PLLA. On the other hand, the % elongation values at break as well as tensile strength of the PLLA and asymmetric nanocomposites were lowered with increasing HA content and in-mold annealing. Moreover, in-mold annealing of asymmetric blends and related nanocomposites caused the embrittlement of material systems. Impact toughness, when compared to neat cold molded PLLA, was improved by ~44% with in-mold annealing of PLLA/1HA. Furthermore, fracture morphology revealed fine dispersion and distribution of HA at 1 wt.% concentration. On the other hand, HA at a high concentration of 15 wt.% show agglomerates that worked as stress concentrators during impact loading.

Department of Engineering Technology Faculty of Mechanical Engineering Technical University of Liberec Studenstka 2 461 17 Liberec Czech Republic

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Nagalakshmaiah M., Afrin S., Malladi R.P., Elkoun S., Robert M., Ansari M.A., Svedberg A., Karim Z. Green Composites for Automotive Applications. Woodhead Publishing; Sawston, UK: 2019. Biocomposites: Present trends and challenges for the future; pp. 197–215.

Ganapini W. Bioplastics: A Case Study of Bioeconomy in Italy. Edizioni Ambiente; Milan, Italy: 2014.

Watkins E., Schweitzer J.-P. Think 2030. Brussels: Institute for European Environmental Policy (IEEP) IEEP; Brussels, Belgium: 2018. Moving towards a circular economy for plastics in the EU by 2030.

Masutani K., Kimura Y. Synthesis, Structure and Properties of Poly(Lactic Acid) Springer; Cham, Switzerland: 2017. Present situation and future perspectives of poly (lactic acid) pp. 1–25.

Fiorentino G., Ripa M., Ulgiati S. Chemicals from Biomass: Technological versus Environmental Feasibility. A Review. Biofuel. Bioprod. Biorefin. 2017;11:195–214. doi: 10.1002/bbb.1729. DOI

Groot W., Van Krieken J., Sliekersl O., De Vos S. POLY (LACTIC ACID): Synthesis, Structures, Properties, Processing, and Applications. Volume 1. Wiley; Hoboken, NJ, USA: 2010. Production and Purification of Lactic Acid and Lactide; pp. 1–18.

Lim L.-T., Auras R., Rubino M. Processing Technologies for Poly(Lactic Acid) Prog. Polym. Sci. 2008;33:820–852. doi: 10.1016/j.progpolymsci.2008.05.004. DOI

Reddy M.M., Vivekanandhan S., Misra M., Bhatia S.K., Mohanty A.K. Biobased Plastics and Bionanocomposites: Current Status and Future Opportunities. Prog. Polym. Sci. 2013;38:1653–1689. doi: 10.1016/j.progpolymsci.2013.05.006. DOI

Tsuji H. Poly(Lactic Acid) Stereocomplexes: A Decade of Progress. Adv. Drug Deliv. Rev. 2016;107:97–135. doi: 10.1016/j.addr.2016.04.017. PubMed DOI

Na B., Zhu J., Lv R., Ju Y., Tian R., Chen B. Stereocomplex Formation in Enantiomeric Polylactides by Melting Recrystallization of Homocrystals: Crystallization Kinetics and Crystal Morphology. Macromolecules. 2014;47:347–352. doi: 10.1021/ma402405c. DOI

Tan B.H., Muiruri J.K., Li Z., He C. Recent Progress in Using Stereocomplexation for Enhancement of Thermal and Mechanical Property of Polylactide. ACS Sustain. Chem. Eng. 2016;4:5370–5391. doi: 10.1021/acssuschemeng.6b01713. DOI

Ikada Y., Jamshidi K., Tsuji H., Hyon S.H. Stereocomplex Formation between Enantiomeric Poly (Lactides) Macromolecules. 1987;20:904–906. doi: 10.1021/ma00170a034. DOI

Tsuji H., Ikada Y. Stereocomplex Formation between Enantiomeric Poly(Lactic Acid) s. XI. Mechanical Properties and Morphology of Solution-Cast Films. Polymer. 1999;40:6699–6708. doi: 10.1016/S0032-3861(99)00004-X. DOI

Tsuji H. Poly (Lactide) Stereocomplexes: Formation, Structure, Properties, Degradation, and Applications. Macromol. Biosci. 2005;5:569–597. doi: 10.1002/mabi.200500062. PubMed DOI

Yin H.-Y., Wei X.-F., Bao R.-Y., Dong Q.-X., Liu Z.-Y., Yang W., Xie B.-H., Yang M.-B. Enantiomeric Poly(d-lactide) with a Higher Melting Point Served as a Significant Nucleating Agent for Poly (l-Lactide) CrystEngComm. 2015;17:4334–4342. doi: 10.1039/C5CE00645G. DOI

Luo F., Fortenberry A., Ren J., Qiang Z. Recent Progress in Enhancing Poly(Lactic Acid) Stereocomplex Formation for Material Property Improvement. Front. Chem. 2020;8:688. doi: 10.3389/fchem.2020.00688. PubMed DOI PMC

Yamane H., Sasai K., Takano M., Takahashi M. Poly (d-Lactic Acid) as a Rheological Modifier of Poly (l-Lactic Acid): Shear and Biaxial Extensional Flow Behavior. J. Rheol. 2004;48:599–609. doi: 10.1122/1.1687736. DOI

Inkinen S., Stolt M., Södergård A. Effect of Blending Ratio and Oligomer Structure on the Thermal Transitions of Stereocomplexes Consisting of Ad-lactic Acid Oligomer and Poly (l-lactide) Polym. Adv. Technol. 2011;22:1658–1664. doi: 10.1002/pat.1654. DOI

Shi X., Jing Z., Zhang G. Influence of PLA Stereocomplex Crystals and Thermal Treatment Temperature on the Rheology and Crystallization Behavior of Asymmetric Poly(l-lactide)/Poly(d-lactide) Blends. J. Polym. Res. 2018;25:71. doi: 10.1007/s10965-018-1467-9. DOI

Wei X.-F., Bao R.-Y., Cao Z.-Q., Yang W., Xie B.-H., Yang M.-B. Stereocomplex Crystallite Network in Asymmetric PLLA/PDLA Blends: Formation, Structure, and Confining Effect on the Crystallization Rate of Homocrystallites. Macromolecules. 2014;47:1439–1448. doi: 10.1021/ma402653a. DOI

Wang J., Lv R., Wang B., Na B., Liu H. Direct Observation of a Stereocomplex Crystallite Network in the Asymmetric Polylactide Enantiomeric Blends. Polymer. 2018;143:52–57. doi: 10.1016/j.polymer.2018.04.012. DOI

Rasal R.M., Janorkar A.V., Hirt D.E. Poly(Lactic Acid) Modifications. Prog. Polym. Sci. 2010;35:338–356. doi: 10.1016/j.progpolymsci.2009.12.003. DOI

Yang S., Leong K.-F., Du Z., Chua C.-K. The Design of Scaffolds for Use in Tissue Engineering. Part I. Traditional Factors. Tissue Eng. 2001;7:679–689. doi: 10.1089/107632701753337645. PubMed DOI

Nazhat S., Kellomäki M., Törmälä P., Tanner K., Bonfield W. Dynamic Mechanical Characterization of Biodegradable Composites of Hydroxyapatite and Polylactides. J. Biomed. Mater. Res. 2001;58:335–343. doi: 10.1002/jbm.1026. PubMed DOI

Teo W., Liao S., Chan C., Ramakrishna S. Fabrication and Characterization of Hierarchically Organized Nanoparticle-Reinforced Nanofibrous Composite Scaffolds. Acta Biomater. 2011;7:193–202. doi: 10.1016/j.actbio.2010.07.041. PubMed DOI

Hanemann T., Szabó D.V. Polymer-Nanoparticle Composites: From Synthesis to Modern Applications. Materials. 2010;3:3468–3517. doi: 10.3390/ma3063468. DOI

Hasnain M.S., Ahmad S.A., Chaudhary N., Hoda M.N., Nayak A.K. 1-Biodegradable polymer matrix nanocomposites for bone tissue engineering. In: Inamuddin, Asiri A.M., Mohammad A., editors. Applications of Nanocomposite Materials in Orthopedics. Woodhead Publishing; Sawston, UK: 2019. pp. 1–37. (Woodhead Publishing Series in Biomaterials).

Bharadwaz A., Jayasuriya A.C. Recent Trends in the Application of Widely Used Natural and Synthetic Polymer Nanocomposites in Bone Tissue Regeneration. Mater. Sci. Eng. C Mater. Biol. Appl. 2020;110:110698. doi: 10.1016/j.msec.2020.110698. PubMed DOI PMC

Seunarine K., Gadegaard N., Tormen M., Meredith D., Riehle M., Wilkinson C. 3D Polymer Scaffolds for Tissue Engineering. Nanomedicine. 2006;1:281–296. doi: 10.2217/17435889.1.3.281. PubMed DOI

Ishii S., Tamura J., Furukawa T., Nakamura T., Matsusue Y., Shikinami Y., Okuno M. Long-Term Study of High-Strength Hydroxyapatite/Poly(l-lactide) Composite Rods for the Internal Fixation of Bone Fractures: A 2–4-Year Follow-up Study in Rabbits. J. Biomed. Mater. Res. B App. Biomater. 2003;66B:539–547. doi: 10.1002/jbm.b.10027. PubMed DOI

Lin P.-L., Fang H.-W., Tseng T., Lee W.-H. Effects of Hydroxyapatite Dosage on Mechanical and Biological Behaviors of Polylactic Acid Composite Materials. ASC Mater. Lett. 2007;61:3009–3013. doi: 10.1016/j.matlet.2006.10.064. DOI

Salerno A., Fernández-Gutiérrez M., del Barrio J.S.R., Pascual C.D. Macroporous and Nanometre Scale Fibrous PLA and PLA–HA Composite Scaffolds Fabricated by a Bio Safe Strategy. RSC Adv. 2014;4:61491–61502. doi: 10.1039/C4RA07732F. DOI

Akindoyo J.O., Beg M.D., Ghazali S., Alam A., Heim H.P., Feldmann M. Synergized Poly(Lactic Acid)–Hydroxyapatite Composites: Biocompatibility Study. J. Appl. Polym. Sci. 2019;136:47400. doi: 10.1002/app.47400. DOI

Šupová M. Problem of Hydroxyapatite Dispersion in Polymer Matrices: A Review. J. Mater. Sci. Mater. Med. 2009;20:1201–1213. doi: 10.1007/s10856-009-3696-2. PubMed DOI

Akindoyo J.O., Beg M.D., Ghazali S., Heim H.P., Feldmann M. Effects of Surface Modification on Dispersion, Mechanical, Thermal and Dynamic Mechanical Properties of Injection Molded PLA-Hydroxyapatite Composites. Compos. Part A Appl. Sci. Manuf. 2017;103:96–105. doi: 10.1016/j.compositesa.2017.09.013. DOI

Akindoyo J.O., Beg M.D., Ghazali S., Heim H.P., Feldmann M. Impact Modified PLA-Hydroxyapatite Composites–Thermo-Mechanical Properties. Compos. Part A Appl. Sci. Manuf. 2018;107:326–333. doi: 10.1016/j.compositesa.2018.01.017. DOI

Hong Z., Qiu X., Sun J., Deng M., Chen X., Jing X. Grafting Polymerization of l-Lactide on the Surface of Hydroxyapatite Nano-Crystals. Polymer. 2004;45:6699–6706. doi: 10.1016/j.polymer.2004.07.036. DOI

Hong Z., Zhang P., He C., Qiu X., Liu A., Chen L., Chen X., Jing X. Nano-Composite of Poly(l-lactide) and Surface Grafted Hydroxyapatite: Mechanical Properties and Biocompatibility. Biomaterials. 2005;26:6296–6304. doi: 10.1016/j.biomaterials.2005.04.018. PubMed DOI

Ko H.-S., Lee S., Lee D., Jho J.Y. Mechanical Properties and Bioactivity of Poly(Lactic Acid) Composites Containing Poly(Glycolic Acid) Fiber and Hydroxyapatite Particles. Nanomaterials. 2021;11:249. doi: 10.3390/nano11010249. PubMed DOI PMC

Shuai C., Yu L., Yang W., Peng S., Zhong Y., Feng P. Phosphonic Acid Coupling Agent Modification of HAP Nanoparticles: Interfacial Effects in PLLA/HAP Bone Scaffold. Polymers. 2020;12:199. doi: 10.3390/polym12010199. PubMed DOI PMC

Ferri J., Jordá J., Montanes N., Fenollar O., Balart R. Manufacturing and Characterization of Poly(Lactic Acid) Composites with Hydroxyapatite. J. Thermoplast. Compos. Mater. 2018;31:865–881. doi: 10.1177/0892705717729014. DOI

Henton D.E., Gruber P., Lunt J., Randall J. Natural Fibers, Biopolymers, and Biocomposites. 1st ed. Volume 16. CRC Press; Boca Raton, FL, USA: 2005. Polylactic Acid Technology; pp. 527–577.

Sarasua J.-R., Prud’Homme R.E., Wisniewski M., Le Borgne A., Spassky N. Crystallization and Melting Behavior of Polylactides. Macromolecules. 1998;31:3895–3905. doi: 10.1021/ma971545p. DOI

Sarasua J., Arraiza A.L., Balerdi P., Maiza I. Crystallization and Thermal Behaviour of Optically Pure Polylactides and Their Blends. J. Mater. Sci. 2005;40:1855–1862. doi: 10.1007/s10853-005-1204-8. DOI

Zhou S., Zheng X., Yu X., Wang J., Weng J., Li X., Feng B., Yin M. Hydrogen Bonding Interaction of Poly(d,l-lactide)/Hydroxyapatite Nanocomposites. Chem. Mater. 2007;19:247–253. doi: 10.1021/cm0619398. DOI

Lv T., Li J., Huang S., Wen H., Li H., Chen J., Jiang S. Synergistic Effects of Chain Dynamics and Enantiomeric Interaction on the Crystallization in PDLA/PLLA Mixtures. Polymer. 2021;222:123648. doi: 10.1016/j.polymer.2021.123648. DOI

Vadori R., Mohanty A.K., Misra M. The Effect of Mold Temperature on the Performance of Injection Molded Poly(Lactic Acid)-Based Bioplastic: The Effect of Mold Temperature on the Performance of Injection Molded Poly(Lactic Acid)-Based Bioplastic. Macromol. Mater. Eng. 2013;298:981–990. doi: 10.1002/mame.201200274. DOI

Kawamoto N., Sakai A., Horikoshi T., Urushihara T., Tobita E. Physical and Mechanical Properties of Poly (l-lactic Acid) Nucleated by Dibenzoylhydrazide Compound. J. Appl. Polym. Sci. 2007;103:244–250. doi: 10.1002/app.25185. DOI

Tang Z., Zhang C., Liu X., Zhu J. The Crystallization Behavior and Mechanical Properties of Polylactic Acid in the Presence of a Crystal Nucleating Agent. J. Appl. Polym. Sci. 2012;125:1108–1115. doi: 10.1002/app.34799. DOI

Kramer E.J., Berger L.L. Crazing in Polymers Vol. 2. Springer; Cham, Switzerland: 1990. Fundamental processes of craze growth and fracture; pp. 1–68.

Renouf-Glauser A.C., Rose J., Farrar D.F., Cameron R.E. The Effect of Crystallinity on the Deformation Mechanism and Bulk Mechanical Properties of PLLA. Biomaterials. 2005;26:5771–5782. doi: 10.1016/j.biomaterials.2005.03.002. PubMed DOI

Park S.D., Todo M., Arakawa K., Koganemaru M. Effect of Crystallinity and Loading-Rate on Mode I Fracture Behavior of Poly(Lactic Acid) Polymer. 2006;47:1357–1363. doi: 10.1016/j.polymer.2005.12.046. DOI

Way J., Atkinson J., Nutting J. The Effect of Spherulite Size on the Fracture Morphology of Polypropylene. J. Mater. Sci. 1974;9:293–299. doi: 10.1007/BF00550954. DOI

Andrews E. Microfibrillar Textures in Polymer Fibers. J. Polym. Sci. Part A-2 Polym. Phys. 1966;4:668–672. doi: 10.1002/pol.1966.160040413. DOI

Graham I., Marshall G., Williams J. The Fracture Mechanics of Crazes. Springer; Cham, Switzerland: 1973. pp. 261–272.

The Injection Molding of Biodegradable Polydioxanone-A Study of the Dependence of the Structural and Mechanical Properties on Thermal Processing Conditions