Determining Material Specifications for A Biocompatible Implantable Mechanism to

Enhance Grasping

Omar SheikhDepartment of Chemical, Biological, and

Environmental EngineeringCollege of Engineering; Honors College

Oregon State UniversityMay 26, 2015

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Definitions

Determining Material Specifications• Selecting Materials

Biocompatible Implantable Mechanism• Safety of device

Modifying Force Transmission Inside the Body

• Device will split forces to make grasp less forceful

• Takes advantage of biomechanics

To Enhance Grasping• Aim to improve hand grasping

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My Timeline in the RHCS Lab

• Joined RHCS Lab in April 2013• Interest in medical devices

• First used Open Sim Software• Realized that I was more

interested in biomaterials• Difficulty with software

• Changed roles within RHCS Lab to focus on biocompatible materials

• Looked at safety of device in body

2013

2014

2015

Graduation

• Completed research in May 2015

3

Research Questions

1. What are all the different materials useful for implants that attach soft tissues to other soft tissues and/or bone?

2. What materials should be used for the proposed pulley, lever, and tendon network forearm implants if the goal is site-specific biocompatibility as defined above?

• Essentially: pick safe and appropriate materials

3. Following implantation, how should postoperative care be performed to prevent both tendon adhesions and muscle damage while helping the patient adapt to their new grasp?

• This device is intended to improve patient quality of life

4

Tendon Transfer Surgery

• Surgical procedure– Transfers tendon(s) from a dysfunctional

muscle to a functioning (donor) muscle to restore joint function

• Conventional procedure sutures the tendon to the muscle– Forceful grasp that makes holding objects

difficult• Image on right

– Postoperative care• Must be complete or lose gains from

surgery

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Proposed Device Types

• Lever has same needs as pulley

• Use plastic tendon network to transmit force• Needs screws to stay taut

Device 3: Tendon Network

Device 2: Lever

• Pulley system rerouting tendons

Device 1: Pulley

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Proposed Devices

• Shared Components

– Anti-adhesion coating

• Improve device efficacy

– Cabling to connect tendon to device

– Encapsulating bag filled with hyaluronic acid

• Device will move inside the body

– Must be safe and biocompatible

Device Components

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Device Needs and Goals

• Grasp is critical to major life activities– Definition of disability– Solutions improve patient life quality

• Current tendon transfer procedures do not improve grasp substantially enough– May have adhesions form (Allan 2011)

• Reduce range of motion

– This implant fulfills this need

• Device empowers patients– Improve life quality – Gives patient satisfaction

The goal of this device to improve postoperative grasp after tendon transfer surgery

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Initial Testing

Initial designs included:

• Cadaver testing

– Pulley design

– Basis for OpenSim model

– Biomechanical testing

• OpenSim testing

– Biomechanicalsimulation

– Ignore biocompatibility

– Simple model (only ECRL)

– Show that finger flexion improveso Force production and

o Range of motion (degrees)

Concerns: Biocompatibility

• When a device is implanted, proteins/cells attach to the surface, a fibrous capsule forms around it, and inflammation occurs (Ratner and Bryant 2004)

– Reflects poor biocompatibility and lowers device efficacy

– Improper response

• Biocompatible materials requires:

– Site specific and safe for situation

– Appropriate for implant needs (adapted from Ratner et. al 2007)

– Consider tissue healing 10

Concerns: Skin, Tendon, Muscle Healing

Why is this important?

– Device could cause harm to patients

– Healing can be fibrotic or regenerative

Tendon Muscle Skin

Bear large forces Exert mechanical action Undergoes reconstruction post injury

Immune system aids healing

Immune system involvement

Immune system involvement

Hyaluronic acid modulates healing

Release creatinine kinase when damaged

Use silicone gel sheets to limit damage

(Voleti et. al 2012) (Shin et. al 2014) (Ogawa 2011)

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Concerns: Aspects for Materials

• Metals release ions into body (Bianco et. al 1996)– Could be toxic

– Measure in serum and urine

• Release of wear particles from polymer/metal is toxic (Bracco et. al 2011)– Harm bone/other tissues

• Ceramic materials can be brittle– But biocompatible (Warashima et. al 2003)

– Use in device is generally questionable

• Device durability – Device should not release possibly toxic particles

– Device should be durable

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Concerns: Other Factors

Bacterial Infection Importance of Mechanical Environment

Toxicology PostoperativeCare

Spurred by deviceimplantation

Cells convert physical forces into chemical signaling

Many implant materials dangerous in a raw form

Tissue healing important to consider

Poor biocompatibility can harm immune cells

Mechanical environment critical

Helps distinguish unsafe materials from safe ones

Biocompatibility seeks to enhance this care

(Biomaterials Associated Infection)

(Stamenovic and Ingber 2009)

(Wright and Welbourn 2002)

(Killian et. al 2012)

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Data Collection of Materials And Methods

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Search Terms

Biomaterials

Stent

Joint Implants and Biomaterials

Total knee replacement

Total joint replacement

Biocompatibility

Foreign Body Response

Prosthetic

Data Collection of Materials And Methods (Cont.)

Exclusion Criteria Rationale

Drug-eluting devices are excluded, including drug-eluting stents

This literature survey aims to specify materials for a device lacking bioactivity and achieves its goals mainly through mechanical action not chemical action.

External devices are excluded. An external device does not have the proper mechanical or chemical environment to model the forearm device.

Exclude devices relying solely upon cement (bone or teeth).

Using cement to hold a device in place or together constitutes a very different set of mechanical requirements than are present in this device,

Exclude implants that are exposed to obvious fluid flow (especially blood-contacting implants such as stents, catheters, and prosthetic heart valves).

The environment with high fluid flow represents the wrong mechanical environment because a shear component due to fluid flow is introduced (Yoganathan et. al 2004), which is quite different from the environment in which the device will be implanted.

Exclude implants that are just implantation of a material (i.e. performed solely for the sake of an experiment).

These implants are typically only performed for the sake of assessing material biocompatibility but do not necessarily capture the mechanical environment.

Exclude devices using sutures as the main linkage. Implants that rely primarily on sutures are typically connections between soft tissue, which represents a different physiological setting.

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Selected Implants

Types of Implants Connections Materials Used

MCP and IP Prostheses(Goldner and Urbaniak 1973)

Stems (cemented with PMMA) Silicone implant, UHWMPE

Breast Implant (Puskas and Chen, 2004)

S.A./Tissue Ingrowth Silicone; silicone rubber bag is filled with silicone gel and backed with polyester mesh to encourage tissue ingrowth

Total Knee Replacement(Illalov et. al 2013; Biomaterials Science; Jacobs et. al 2005)

(cementless) use pegs, screws, and stems UHMWPE, Porous Tantalum (cementless)

Total Hip Replacement (Hulbert and Megremis 1996; Shanhbag et. al 1993; Biomaterials Science)

Ti-6Al-4V stems UHMWPE (acetabular surface) and Cobalt alloy (femoral head) or Ti-6Al-4V (femoral head)

Total (Intervertebral) Disk Arthroplasty (Biomaterials science)

Ti-6Al-4V screws (1) Co-Cr (endplates), UHMWPE (core); (2) Stainless Steel, Co alloy (endplates);(3) Cobalt alloy (ball-and-socket joints),

Cobalt alloy (spring between joints)Zygomatic Implants (Prithviraj et. al 2014)

Commercially Pure Ti screws N/A

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Material Specifications

Device Component Material Device

Pulley UHMWPE-Vitamin E Pulley

Cabling Kevlar Pulley, Lever, Tendon Network

Screws Ti6Al4V Tendon Network

Device Coating Poly(ethylene oxide) Pulley, Lever, Tendon Network

Lever UHMWPE-Vitamin E Lever

Tendon Network Silastic Tendon Network

Bag Silicone Pulley, Lever, Tendon Network

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Alternative Specifications

Device Component Material Rationale

Pulley Acetals, PEEK Biocompatible; has orthopedic uses

Cabling Nylon Used in Sutures

Screws Tantalum Biocompatible; has orthopedic uses

Device Coating Phosphorylcholine, Pluronics

Effective at anti-adhesion

Lever Acetals, PEEK Biocompatible; has orthopedic uses

Tendon Network Silastic’ Medical Grade Slicone

Biocompatible and has orthopedic uses

Bag Dacron, PET, Gore-Tex Biocompatible, many kinds of uses

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Postoperative Care

• Questions to consider:– Tissue healing

• Device biocompatibility and motion

• Device force transmission

– Device goals

• Muscle control is complex

– Redundant system

• Therapeutic exercises (Bowers and Lasardi 2007)

– Minimize movement dysfunction

– Avoid stressing tissues

• Avoid tendon shortening and adhesions

• Avoid pain

– Own experience with physical therapy

– Retain/improve range of motion 19

Postoperative Care (Cont.)

• Encourage patient healing and grasping

– Need appropriate mechanical loading to encourage healing (Killian et. al 2012)

– Passive motion over cast immobilization

• Active motion may be difficult

– Need to monitor device and progressively increase length of sessions

– Measure muscle strength: (Shin et. al 2014)

• Electromyogram– Electrical flow after muscular contraction

• Muscle grading scheme– Rating 1-5

– Track tendon healing and assess potential damage

• Ultrasound/MRI

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Postoperative Care (Cont.)

• Utilize a splint to allow for movement but provide stretch

• Should be beneficial for patient

• Personally relevant

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Survey Limitations

• Assumed that more widelyused is better

• Ignored article year,age of implant,and culture of researchers

• Limited by what’s out there

• All three have a significant impact on the materials chosen– Is a slightly weak but completely safe material okay? – Or, must it be absolutely strong at the potential cost of

biocompatibility?

– Should the device be “bio-inactive” materials?• Material specifications

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Lessons Learned

• Survey procedures– Important to look past orthopedic devices despite

biomechanical needs– Learn about cool materials like PEEK and acetals– Culture may play a role in how materials are chosen

• Surveying can be enhanced– Look more at pacemakers, IUDs, neural prostheses

May help understanding of biocompatibility– Ex: Nexplanon

• Contraceptive device• Only example of a forearm actual implant

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Future Work

• Model device heating up

– Model heat transfer

– Find way to cool

• Model predictions about device motion

– Damaging to body?

• Proof-of-concept biocompatibility tests on prototype

– Simple experiments outside of body

– Do immune cells attach?

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Another Approach

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Biomimetics replicates body biochemistry

Challenges:- Biochemistry

complex- Must consider

spatial arrangement

Concluding Remarks

• Another way to think about it• “Going Out On A Limb About Regrowing An

Arm” (Ratner 2013)– Regenerative healing to regrow arm– Ultimate goal of our device

• Regain use of arm

• Grasping is the most critical arm function– Want to return use of arm to patient– Ultimately want integration of device with body

• Improve efficacy and keep safety• Encourage device support from FDA

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Selected References

1. Allan, Christopher H. “Repair of Acute Digital Flexor Tendon Disruptions.” “Operative Techniques in Orthopedic Surgery.” Ed. Sam W. Wiesel. Philadelphia: Lippincott Williams & Wilkins, 2011. Print.

2. Bianco, P.D., P. Ducheyne, and J.M. Cuckler. “Local accumulation of titanium released from a titanium implant in the absence of wear.” Journal of Biomedical Materials Research 31.2 (1996): 227-234. Print.

3. Bowers, Donna M., and Michelle M. Lusardi. “Motor Learning and Motor Control in Orthotic and Prosthetic Rehabilitation.” Orthotics and Prosthetics in Rehabilitation Second Edition. Eds. Michelle M. Lusardi and Caroline C. Nielsen. St. Louis, Missouri: Saunders Elsevier, 2007. 93-108. Print.

4. Bracco, Pierangiola and Ebru Oral. “Vitamin E-stabilized UHMWPE for Total Joint Implants.” Clin Orthop Relat Res 469(2011): 2286-2293. Print.

5. Bryers, James D. and Buddy D. Ratner. “Bioinspired Implant Materials Befuddle Bacteria.” ASM News 70.5(2004): 232-237. Print.

6. Killian, Megan L., Leonardo Cavinatto, Leesa M. Galaltz, and Stavros Thomopoulos. “The role of mechanobiology in tendon healing.” Journal of Shoulder and Elbow Surgery 21 (2012): 228-237.

7. Ogawa, Rei. “Mechanobiology of scarring.” Wound Repair and Regeneration (2011) 19: S2-S9. Print. 8. Biomaterials Associated Infection: Immunological Aspects and Antimicrobial Strategies. Eds. T. Fintan Moriarty, Sebastian A.J.

Zaat, and Henk J. Busscher. New York: Springer, 2013. Print.9. Ratner, Buddy D. “A paradigm shift: biomaterials that heal.” Polymer International 56 (2007):1183-1185. Print.10. Ratner, Buddy D. “Going out on a limb about regrowing an arm.” Journal of Materials Science – Materials in Medicine 24.11

(2013): 2645-2649. Print. 11. Biomaterials Science: An Introduction to Materials in Medicine. Eds. Ratner, Hoffman, Schoen, and Lemons. Academic Press,

2004. 12. Shin, Emily H., Edward J. Caterson, Wesley M. Jackson, and Leon J. Nesti. “Quality of healing: Defining, quantifying, and

enhancing skeletal muscle healing.” Wound Repair and Regeneration 22 (2014): 18-24. Print.13. Stamenovic, Dimitrije and Donald Ingber. “Tensegrity-guided self assembly: from molecules to living cells.” Soft Matter 5.6

(2009). Print. 14. Tseng, Po-Yuan, Shyam S. Rele, Xue-Long Sun, and Elliot L. Chaikof. “Membrane-mimetic films containing thrombomodulin and

heparin inhibit tissue factor-induced thrombin generation in a flow model.” Biomaterials 27 (2006): 2637-2650. Print.15. Warashima, Hideki, Shinji Sakano, Shinji Kitamura, Ken-Ichi Yamauchi, Jin Yamaguchi, Naoki Ishiguro, and Yukiharu Hasegawa.

“Biological reaction to alumina, zirconia, titanium, and polyethylene particles implanted onto murine calvaria.” Biomaterials 24 (2003): 3655-3661. Print.

16. Wright, David A. and Pamela Welbourn. Environmental Toxicology. Cambridge: Cambridge University Press, 2002. Pgs 249-348.Print.

17. Voleti, Pramod B., M.R. Buckley, and L.J. Soslowsky. “Tendon Healing: Repair and Regeneration.” Annu Rev Biomed Eng 14 (2012):47-71. Print.

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Questions?

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