טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentArtoum Rakovsky
SubjectBioinspired Calcium Phosphte-Polylactide Nanocomposites
and Scaffolds with Controlled Pore Architecture
for Bone Tissue Regeneration
DepartmentDepartment of Materials Science and Engineering
Supervisors Full Professor Rabkin Eugen
Dr. Gotman Irena
Full Professor Gutmanas Elazar
Full Thesis textFull thesis text - English Version


Abstract

Bioresorbable calcium phosphate (CaP)-polymer composites are increasingly considered as implant materials for bone healing. Yet, the high polymer content (? 70 vol.%) of typical literature reported composites limits the strength of these materials making them unsuitable for load-bearing application. CaP-polymer nanocomposites with high ceramic (low polymer) contents, homogeneous phase distribution and improved interfacial bonding are expected to possess significantly higher mechanical properties.

In the present work, Ca-deficient hydroxyapatitie (CDHA) and β-tricalcium phosphate (β-TCP) based nanocomposites with low contents (20 to 40 vol.%) of polylactic acid (PLA) were developed. Bulk, dense specimens were prepared by high pressure consolidation of powders (cold sintering), and their mechanical behavior tested, in the as-produced state and after immersion in a solution mimicking body fluid. To improve the microstructure homogeneity and strength, surface modification of CaP powder or, alternatively, high energy attrition milling of CaP-polymer blends were used. Macroporous scaffolds with pore size suitable for bone ingrowth were fabricated using our modified particulate leaching method and the effect of several processing parameters on the scaffold strength and permeability was investigated.

Surface modification of CDHA with hexamethylene diisocaynate (HDI) resulted in the density and strength enhancement of CDHA-PLA nanocomposites. The compressive strength varied from ~170 to ~300 MPa, the higher values corresponding to higher PLA and HDI contents. Attrition milling of powders prior to cold sintering allowed us to achieve even higher densities and strengths: 250 to 420 MPa in compression and 45 to 65 MPa in bending. The dependence of strength on PLA content was reversed: higher CaP contents yielded higher strengths. CaP-PLA nanocomposites with the coarser ceramic component (β-TCP, ~150 nm) were more ductile and exhibited better water stability compared to the corresponding materials based on very fine (~15 nm) CDHA particles.

The proposed modification of the particulate leaching method consisted in using precompacted powder granules instead of the loose powder and resulted in a ~103 increase in water permeability of the produced 50% porous β-TCP-PLA scaffolds. Scaffolds fabricated from large (300-420 µm) β-TCP-PLA granules using large (300-420 µm) porogen particles exhibited a good combination of properties, especially when high pressure consolidation was performed at the elevated temperature of 120°C. The strength (~5 MPa) and permeability (~1.2•10-6 cm2) of these scaffolds was in the range of the trabecular bone making them attractive candidates materials for bone graft substitutes.