- Additive manufacturing can be used to produce bioresorbable implants and scaffolds for bone repair from polymers and metals. - Metals such as magnesium and iron-manganese alloys have mechanical properties similar to bone but their degradation rates need to be optimized. - Alloying elements like calcium and magnesium can accelerate the corrosion of iron-manganese alloys printed using additive manufacturing. - In vitro tests of printed iron-manganese scaffolds showed good cell attachment and proliferation, suggesting their potential for bone regeneration applications. - Further studies involving in vivo testing and innovative implant designs tailored for 3D printing are needed to develop effective bioresorbable metal implants.

1. Additive Manufacturing
Of Bioresorbable Scaffolds
R3D@TRI-C
September 9, 2016
Howard A. Kuhn PhD FASM
Adjunct Professor, University of Pittsburgh
Technical Advisor, America Makes

2. Selective transformation of material
having primitive form
(liquid, powder, wire, sheet)
Additive Manufacturing
Additive
Manufacturing
Machine
solid 3D form prescribed
by a CAD solid model
into a
0
CAD solid model

3. Major Applications
of Additive Manufacturing
Aerospace
Tooling
Biomedical

4. Biomedical Applications
Surgery Planning Models
Splints
Exoskeleton Components
Prostheses
Limbs
Hearing Aids
Dental Aligners
Implants (Replacement Therapy)
Bioresorbable implants (Regenerative Therapy)
Functional Tissue Generation (Organ Replacement)
Taking advantage of additive manufacturing/3DPrinting capabilities
for production of patient specific parts:

5. Windpipe Splint
produced by Selective Laser Sintering
of a Bioresorbable Polymer
Polycaprolactone
Splints degrade after they’ve
done their job

6. How about
bioresorbable
materials for
bone repair?
Windpipe Splint
produced by Selective Laser Sintering
of a Bioresorbable Polymer
Polycaprolactone
Splints degrade after they’ve
done their job

7. Bioresorbable Materials for
Bone Tissue Repair
• Bioresorbable polymer and ceramic alternatives to
permanent metal implants or bone grafts
• Advantages
– No side effect from long term use
– No secondary surgery
– Potential for multi-functional treatments
• Limitations
– Low mechanical properties [1]
– Acidic degradation products (polymers) [1]
– Slow degradation (biocomposites, ceramics, and some polymers)
[1,2]
1. J.C. Middleton, A.J. Tipton / Biomaterials 21 (2000) 2335}2346
2. Arthroscopy: The Journal of Arthroscopic and Related Surgery, Vol 22, No 9 (September), 2006: pp 993-999

8. Bioresorbable Materials for
Bone Tissue Repair
• Bioresorbable polymer and ceramic alternatives to
permanent metal implants or bone grafts
• Advantages
– No side effect from long term use
– No secondary surgery
– Potential for multi-functional treatments
• Limitations
– Low mechanical properties [1]
– Acidic degradation products (polymers) [1]
– Slow degradation (biocomposites, ceramics, and some polymers)
[1,2]
How about Bioresorbable Metals ?

9. Bioresorbable Magnesium alloys
Properties Natural
Bone
Magnesium
alloys
Titanium
alloys
Stainless steel PLGA/PLLA
Density (g/cm3) 1.8–2.1 1.74–2.0 4.4–4.5 7.9–8.1 ~1.3
Elastic modulus (GPa) 14 - 17 41–45 110–117 189–205 7-0.2
Comp, yield strength (MPa) 130–180 250-1000 758–1117 170–310 NA
Tensile yield strength (MPa) 104-120 100-300 700-900 221-1213 27-1
But, pure Mg resorbs too quickly
Through Density Functional Modeling,
alloy additions to extend resorption of
pure Mg were developed and patented
Properties of Mg alloys closer to those of bone than other implant materials

10. Bioresorbable Mg Alloy Examples
Bone plates and screws
ACL screw
AV fistula stent
1mm
1mm
Nerve guide
Craniofacial (TMJ) screw
Tracheal stent

11. Mg Ti
Mg degradation does not inhibit
fracture healing
In vivo Tests
Mg enhances bone growth

12. ERC-RMB Devices Implanted in Animal Models
Orthopedic plates and screws
AV fistula Stents
Trachea stent
Kirschner wire Just after
implantation
14 weeks after
implantation

13. ERC-RMB Devices Implanted in Animal Models
What about
Additive Manufacturing
of Bioresorbable Metals?

14. Conforming bone plates could be produced by
additive manufacturing
with properties matched to localized stresses

15. Image
acquisition of
bone defect
site
Image post-
processing
and analysis
3D CAD model of
bone graft
generated
Implant 3D
printed from
biodegradable
metal
Customized biodegradable bone graft substitute by 3DPrinting
Sterilized bone
graft substitute is
implanted into
defect site
Image credit: Synthes CMF Patient Specific Implants
Benefits:
• Avoids need for bone grafting
• Matching complex 3D anatomical defects reduces
operating room time ($56 per minute)
• Eliminates secondary surgery ($58,000 per
operation)
: Biodegradable Metallic Bone Scaffolds

16. Binder-jet 3D printed prototype scaffolds using
pure Mg powder (particle size < 50 μm)
But sintering the scaffolds proved to be difficult

17. Additive Manufacturing of Mg
BJ 3DP
• Pros: Easily printed
• Cons: Difficult to sinter
SLM/EBM
• Pros: No sintering
• Cons: Low vapor
pressure, melting point
Further research is necessary
to achieve 3D printing of
stable Mg-based alloys

18. Bioresorbable Fe-Mn alloys
Material Yield
strength
(MPa)
Ultimate
strength
(MPa)
Elongation
(%)
Young’s
modulus
(GPa)
Fe-30Mn
3DP
106 ± 8 115 ± 1 0.73 ± 0.15 32 ± 5
Natural
bone
104-121 86-151 1-3 14-17

19. Bioresorbable Fe-Mn alloys
Material Yield
strength
(MPa)
Ultimate
strength
(MPa)
Elongation
(%)
Young’s
modulus
(GPa)
Fe-30Mn
3DP
106 ± 8 115 ± 1 0.73 ± 0.15 32 ± 5
Natural
bone
104-121 86-151 1-3 14-17
But Fe-Mn alloys take too long to resorb

20. ThermoCalc determination of suitable alloying elements
to accelerate resorption of Fe-Mn

21. Material
Corrosion potential, Ecorr
[V)
Corrosion current density, icorr
[µA cm-2]
Fe-Mn -0.72±0.04 1.00±0.06
Fe-Mn-1Ca -0.71±0.02 2.12±0.92
Fe-Mn-2Ca -0.66±0.02 6.36±1.75
Fe-Mn-1Mg -0.65±0.02 5.89±0.80
Fe-Mn-2Mg -0.64±0.03 9.16±1.25
~10-fold increase in
corrosion rate of 3DP Fe-Mn
compared to pure iron
(0.73 to 0.065 mmpy)

22. Cytotoxicity testing of 3DP Fe-Mn alloys
• Live/dead cell viability assay of the cytotoxicity of 3DP Fe-based alloys
• Pure Fe exhibited no live cells on the surface
• Fe-Mn-1Ca exhibited most live cells (green)

23. Fe-Mn
3DPrinting of Fe-Mn alloys
Fe-Mn-1Ca
3D printing
& Sintering
20µm20µm
• ExOne’s RX1 BJ printer was used for this study
• Sintered at 1200 ºC, 3 hours
20µm20µm

24. Fe-30Mn 3DPrinted/Sintered parts
Bone cells seeded
onto scaffolds
In Vitro results
prototype
scaffolds with
1 mm and
500 µm
square pores
miniature
femur before
and after
tumble
finishing

25. •High cell attachment
•Cells infiltrated into pores
Chou et al., Acta Biomater. 2013
In-vitro testing of 3DPrinted Fe-30Mn alloys

26. Technical feasibility
Goat mandible model
2. CT Scan
Goat mandible CT Scan STL file 3DP mandible
BJ/Sintering SLM - Renishaw

27. Next Steps
In-Vivo Testing
Innovative Design
(for 3DPrinting)
of Bone Implants

28. To Your Good Health
Acknowledgements:
Drs. Daeho Hong, Da-Tren Chou, Abhijit Roy, Prashant Kumta