Oriented Polylactic Acid Bone Screw Crystallinity
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Solution Overview
Problem
Existing bone screws made from polylactic acid with D-lactic acid and trimethylene carbonate have poor mechanical properties and short degradation times, leading to insufficient healing time for fractures due to their amorphous structure.
Innovation Solution
A high-strength absorbable internal fixation bone screw made from oriented polylactic acid with poly(L-lactic acid), processed through billet formation, orientation strengthening, and quenching, achieving a crystallinity of 45% to 85% and bending strength of 200 MPa to 450 MPa, using methods like plastic injection molding, forging, and extrusion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a bone screw is made from racemic poly(D-lactic acid) with an amorphous structure, then the material is fully degradable and biocompatible, but the bone screw has poor mechanical properties and short degradation time
Solution Approach 1:
The patent changes the key parameter of crystallinity from low (amorphous) to high (45%-85%) by using poly(L-lactic acid) instead of racemic poly(D-lactic acid). This parameter change fundamentally transforms the material properties, enabling the bone screw to achieve both high mechanical strength (200-450 MPa bending strength) and controlled degradation time (2-4 years) while maintaining biocompatibility.
Solution Approach 2:
The patent uses oriented polylactic acid as a composite material system that combines poly(L-lactic acid) base material with specific molecular orientation and crystalline structure. This composite approach creates a material that simultaneously achieves high strength, controlled degradation, and biocompatibility, resolving the contradiction between mechanical properties and degradation characteristics.
2Loss of substance
If a bone screw is made from racemic poly(D-lactic acid) with an amorphous structure, then the material is fully degradable, but the degradation time is too short to provide sufficient healing time for bone fracture
Solution Approach 1:
The patent changes the crystallinity parameter to 45%-85% and uses poly(L-lactic acid) with specific optical rotation of -155° to -160°, which fundamentally alters the degradation kinetics. The high crystalline structure slows down hydrolysis rates, extending degradation time from months to 2-4 years, providing sufficient healing time while maintaining complete biodegradability.
3Strength
If orientation strengthening and quenching processes are applied to increase crystallinity to 45%-85%, then the bending strength increases to 200-450 MPa, but the manufacturing process becomes more complex
Solution Approach 1:
The patent applies orientation strengthening and quenching as preliminary actions during the manufacturing process to establish the desired crystalline structure and molecular orientation before final machining. By performing these strengthening operations on the billet before cutting and threading, the process achieves high strength (200-450 MPa) while maintaining manufacturing efficiency and avoiding complex post-processing steps.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The bone screw provides sufficient mechanical support during healing, gradually losing strength after 18-36 weeks, ensuring complete biological reabsorption in 2-4 years, thus ensuring adequate healing time and reducing osteoporosis risk.
Implementation Method 1
the crystallinity of the section is 45% to 85%
Implementation Method 2
the oriented polylactic acid section is made of the poly(L-lactic acid) through the processes of making a billet, orientation strengthening and quenching in order
Data Source
AI summary
A high-strength absorbable internal fixation bone screw for a fracture. The bone screw is made of a degradable oriented polylactic acid section. A raw material for the oriented polylactic acid section is a poly(L-lactic acid). The specific optical rotation of the poly(L-lactic acid) is −155° to −160°. The section is made of the poly(L-lactic acid) through the processes of making a billet, orientation strengthening and quenching in order. The method for making the billet is plastic injection molding. The method for orientation strengthening is forging and pressing or extrusion. The section is turned, finely milled, or directly molded into the bone screw. The bone screw has high strength and a low rate of mechanical strength loss, ensures mechanical support during bone healing and sufficient healing time for an injured bone, has good biocompatibility, and can be degraded and absorbed.