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BIOMATERIALS USED IN THE EAR

(50 Marks — RGUHS Standard Answer)

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INTRODUCTION

• Tympanic membrane reconstruction (tympanoplasty grafts)
• Ossicular chain reconstruction (OCR)
• Mastoid and canal wall obliteration
• Cochlear implantation
• Bone-anchored hearing aids (BAHA)
• External ear canal reconstruction
• Middle ear and inner ear drug delivery systems

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IDEAL PROPERTIES OF A BIOMATERIAL (For Exam)

Mnemonic: "BIO-CAMPS"

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CLASSIFICATION OF BIOMATERIALS IN THE EAR

┌─────────────────────────────────────────────────────────┐
│              BIOMATERIALS USED IN THE EAR               │
└───────────────────────┬─────────────────────────────────┘
                        │
        ┌───────────────┴──────────────┐
        │                              │
  ┌─────▼──────┐                ┌──────▼──────┐
  │  BIOLOGICAL│                │  SYNTHETIC  │
  │  (Autograft│                │  (Alloplastic│
  │  Allograft)│                │  Materials)  │
  └─────┬──────┘                └──────┬──────┘
        │                              │
  ┌─────▼──────────────┐    ┌──────────▼──────────────┐
  │ • Temporalis fascia│    │ • Metals (Titanium,      │
  │ • Perichondrium    │    │   Stainless steel,       │
  │ • Cartilage        │    │   Gold, Platinum)        │
  │ • Fat              │    │ • Ceramics (Hydroxyapatite│
  │ • Vein graft       │    │   Bioglass, Alumina)     │
  │ • Dura mater       │    │ • Polymers (Silastic,    │
  │ • Homograft ossicles│   │   PTFE, Teflon,          │
  │ • Tympanic membrane│    │   Polyethylene, PMMA)    │
  └────────────────────┘    │ • Composites             │
                            │ • Bioabsorbable materials│
                            └─────────────────────────┘

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PART I: TYMPANIC MEMBRANE (TM) RECONSTRUCTION

A. Autografts

1. Temporalis Fascia

• Most commonly used graft material worldwide (Dhingra, p. 312)
• Harvested from the temporalis muscle above the root of zygoma
• Advantages: Readily available, excellent take rate, minimal donor site morbidity, acoustically favorable
• Disadvantages: Can be thin, requires drying before use to prevent curling (Cummings, p. 2062)
• Success rate: 85–95% (Scott Brown)

2. Perichondrium

• Harvested from tragal or conchal cartilage
• More resistant to retraction than fascia
• Used when eustachian tube dysfunction is suspected
• Perichondrium-cartilage island graft — highly favored in RGUHS-level practice

3. Cartilage (Tragal/Conchal)

• Provides structural support especially in retraction pockets, adhesive otitis
• Island cartilage graft technique (Eavey technique): cartilage + perichondrium in one
• Cartilage tympanoplasty — superior outcomes in revision cases
• Thickness: 0.5 mm (ideal) — thicker cartilage may reduce sound transmission by 5–10 dB (Dornhoffer, 2006)

4. Fat Graft

• Used for myringoplasty of small central perforations (< 3 mm)
• Harvested from ear lobe or post-auricular region
• Fat plug myringoplasty — office procedure under LA (Mitchell, 1997)

5. Vein Graft

• Historical interest; used for small perforations
• Replaced by fascia and perichondrium in modern practice

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B. Allografts (Homografts)

1. Homograft Tympanic Membrane / Ossicles

• Obtained from cadavers, preserved in glutaraldehyde
• Used when autografts unavailable
• Risk: prion transmission — largely abandoned (Scott Brown)
• Now replaced by alloplastic materials

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FLOWCHART: GRAFT SELECTION IN TYMPANOPLASTY

           START: Tympanoplasty Planned
                        │
           ┌────────────▼────────────┐
           │ Size of perforation?    │
           └────────────┬────────────┘
                        │
          ┌─────────────┼──────────────┐
          │             │              │
      Small (<5mm)   Medium        Large / Subtotal
          │           (5-10mm)     / Revision
          │             │              │
      Fat plug      Temporalis     Cartilage-
      Myringoplasty   fascia       perichondrium
                                   island graft
                        │
          ┌─────────────▼──────────┐
          │ Eustachian tube       │
          │ dysfunction?          │
          └─────────────┬──────────┘
                       Yes ──► Cartilage graft
                        │
                       No ──► Temporalis fascia

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PART II: OSSICULAR CHAIN RECONSTRUCTION (OCR)

Classification of Ossicular Prostheses

┌──────────────────────────────────────────────────────┐
│         OSSICULAR PROSTHESES CLASSIFICATION          │
├──────────────────────────────┬───────────────────────┤
│  PORP                        │  TORP                 │
│  (Partial Ossicular          │  (Total Ossicular     │
│  Replacement Prosthesis)     │  Replacement          │
│                              │  Prosthesis)          │
├──────────────────────────────┼───────────────────────┤
│ Malleus/Stapes present       │ Only stapes           │
│ Connects incus/malleus to    │ footplate present     │
│ stapes head                  │ Connects TM to        │
│                              │ footplate directly    │
├──────────────────────────────┴───────────────────────┤
│            MATERIALS USED                            │
│  • Autologous ossicle (Gold standard)                │
│  • Cortical bone / cartilage (autologous)            │
│  • Hydroxyapatite (ceramic)                          │
│  • Titanium (metal)                                  │
│  • Plastipore / Proplast (Polyethylene)              │
│  • Bioglass                                          │
│  • Teflon-wire prosthesis                            │
└──────────────────────────────────────────────────────┘

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A. Biological Materials for OCR

1. Autologous Incus / Ossicle

• Gold standard for OCR (Dhingra, Zakir Hussain)
• Reshaped and repositioned
• Excellent biocompatibility, no rejection
• Best acoustic coupling
• Limitation: Not available if destroyed by disease

2. Cortical Bone (Mastoid)

• Carved from mastoid cortex
• Readily available during mastoid surgery
• Drawback: Resorption over time

3. Cartilage (Tragal)

• Carved and used as an interposition graft
• Excellent biocompatibility
• More resistant to extrusion than alloplastic materials

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B. Alloplastic/Synthetic Materials for OCR

1. Hydroxyapatite (HA)

• Chemical formula: Ca₁₀(PO₄)₆(OH)₂
• Most widely used synthetic OCR material
• Advantages:
  • Excellent biocompatibility (chemically similar to bone mineral)
  • Osteoconductive and osseointegrative
  • Low extrusion rate (~5%)
  • Available as PORP and TORP (Applebaum, 1988)
• Disadvantage: Brittle, difficult to trim intraoperatively
• Examples: Ceravital, Bioceram HA prostheses

2. Titanium

• Currently most preferred alloplastic material (Stupp, Dalchow, 2000s)
• Properties:
  • MRI compatible
  • Excellent tensile strength
  • Low mass → superior acoustic transfer
  • Corrosion resistant
  • Long-term stability
• Types: Kurz titanium PORP/TORP, Vario system
• Mass advantage over HA: Better high-frequency transmission
• Extrusion rate: ~3–5% (low)
• Current recommendation: Titanium PORP/TORP = prosthesis of choice in most modern ENT centers

3. Bioglass (Bioactive Glass)

• Composition: SiO₂-Na₂O-CaO-P₂O₅
• Bonds directly to bone without fibrous interface
• Drawback: Brittle, poor machinability
• Historical use: S53P4 Bioglass (Merwin, 1986)

4. Plastipore (High Density Polyethylene – HDPE)

• Porous polyethylene
• Tissue ingrowth into pores
• Higher extrusion rate than HA (~10–12%)
• Still used in some centers (Cummings)

5. Proplast (Teflon-Carbon Composite)

• Largely abandoned due to high extrusion and tissue reaction rates

6. Teflon (PTFE) Piston – for Stapedectomy/Stapedotomy

• Material of choice for stapes surgery
• Teflon wire-loop piston — most widely used (Cummings, p. 2100)
• Advantages:
  • Inert, flexible, easy to crimp
  • Low mass, excellent acoustic properties
  • MRI compatible
• Alternatives: Gold piston, Titanium piston, Nitinol (shape-memory alloy) piston

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COMPARATIVE TABLE: OCR PROSTHESIS MATERIALS

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PART III: MASTOID OBLITERATION MATERIALS

1. Bone Pâté / Bone Dust

• Autologous mastoid bone collected during drilling
• Best biocompatibility, slow resorption

2. Hydroxyapatite Cement

• Injectable/moldable
• ProOsteon, BoneSource — commercially available HA cements
• Sets in situ, osseoconductive

3. Calcium Phosphate Cement

• Similar to HA, biodegradable variant available

4. Silicone (Silastic)

• Used for canal wall reconstruction temporarily
• Creates epithelial lining
• Silastic sheeting placed in middle ear to prevent adhesions post-tympanoplasty (Dhingra p. 315)

5. Bioabsorbable Materials

• Gelfoam (Absorbable gelatin sponge): Used to support graft during tympanoplasty healing
• Surgicel (Oxidized cellulose): Hemostasis and graft support
• Merocel (Polyvinyl alcohol): Ear canal packing
• Hyaluronic acid: Middle ear adhesion prevention

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PART IV: COCHLEAR IMPLANT MATERIALS

┌─────────────────────────────────────────────────────────┐
│              COCHLEAR IMPLANT — COMPONENTS              │
│              AND BIOMATERIALS USED                      │
├─────────────────────────────────────────────────────────┤
│ EXTERNAL COMPONENTS:                                    │
│  • Microphone housing — Medical-grade ABS plastic       │
│  • Speech processor — Polycarbonate casing             │
│  • Transmitter coil — Silicone rubber + copper coil     │
├─────────────────────────────────────────────────────────┤
│ INTERNAL COMPONENTS:                                    │
│  • Receiver-stimulator housing — TITANIUM (hermetic     │
│    titanium casing — inert, MRI-compatible)             │
│  • Magnet — Samarium-cobalt or neodymium                │
│  • Electrode array — PLATINUM-IRIDIUM electrodes        │
│    embedded in SILICONE carrier                         │
│  • Lead wire — Platinum-iridium alloy                   │
│  • Cochlear seal — Silicone, Dacron mesh                │
└─────────────────────────────────────────────────────────┘

Key Materials in Cochlear Implants:

• Titanium: Receiver-stimulator housing — biocompatible, hermetic, MRI conditional (1.5T)
• Platinum-iridium alloy: Electrodes — excellent biocompatibility, charge injection capacity, corrosion resistant
• Silicone elastomer: Electrode carrier — soft, flexible, allows atraumatic insertion
• Dacron mesh: Anchor/sealing at cochleostomy site

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PART V: BONE-ANCHORED HEARING AID (BAHA)

Materials Used:

• Titanium implant (fixture): Osseointegrates into mastoid bone — BAHA concept originated by Brånemark (1977)
• Titanium abutment: Percutaneous connection piece
• Sound processor housing: Polycarbonate/acrylic
• Mechanism: Osseointegration of titanium — direct bone conduction

Osseointegration (Brånemark Principle):

Titanium implant inserted → Surface TiO₂ layer
       → Protein adsorption → Osteoblast adhesion
       → New bone deposition → Direct bone-implant contact
       = OSSEOINTEGRATION (3–6 months)

Modern BAHA systems:

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PART VI: EXTERNAL EAR RECONSTRUCTION

Auricular Prostheses:

• Silicone elastomer — most commonly used for auricular prostheses (microtia, post-auriculectomy)
• Porous polyethylene (Medpor/Stryker): Alloplastic auricular framework
  • Tissue ingrowth into pores → stable, permanent
  • Used in Nagata technique modification for microtia repair
• Rib cartilage autograft: Still gold standard for auricular reconstruction (Brent technique, Nagata technique)

Ear Canal:

• Split-thickness skin graft (STSG): After canalplasty or meatoplasty
• Silastic stents: Maintain canal patency post-surgery

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PART VII: MIDDLE EAR DRUG DELIVERY — RECENT ADVANCES

Biomaterial-based Drug Delivery Systems:

1. Hydrogels (hyaluronic acid, chitosan) — Intratympanic steroid delivery
2. Polylactic acid (PLA) microspheres — Sustained release gentamicin for Meniere's disease
3. PLGA (Poly lactic-co-glycolic acid) nanoparticles — Controlled release into inner ear
4. Round window membrane permeation enhancers — Chitosan, poloxamer gels
5. Fibrin sealant (Tisseel): Secures grafts, delivers growth factors

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PART VIII: RECENT ADVANCES IN EAR BIOMATERIALS (RGUHS Important)

1. Bioabsorbable Ossicular Prostheses

• PLGA-based prostheses — degrade as autologous tissue replaces them
• Reduces long-term extrusion rates

2. Tissue Engineering of Tympanic Membrane

• Scaffold: Electrospun PLGA/collagen nanofibers
• Seeded with fibroblasts and keratinocytes
• Early clinical trials showing promising results (Mao et al., 2014; van der Toom et al., 2020)

3. 3D-Printed Ear Prostheses

• Polyurethane / silicone 3D-printed auricular frameworks
• Patient-specific, precise fit
• Titanium 3D-printed anchors for BAHA

4. Smart Biomaterials

• Shape-memory alloys (Nitinol): Piston for stapedotomy that self-crimps at body temperature
• Piezoelectric materials (PZT, PVDF): Used in implantable middle ear hearing devices (Vibrant Soundbridge)

5. Bioactive Surface Coatings

• Titanium with HA coating: Improves osseointegration rate for BAHA fixtures
• Antimicrobial coatings (silver nanoparticles, chlorhexidine): Reduce implant-associated infection

6. Vibrant Soundbridge (Middle Ear Implant)

• Floating Mass Transducer (FMT): Titanium titanium housing with electromagnetic coil
• Attached to ossicular chain or round window
• Silicone-coated titanium components

7. Totally Implantable Hearing Devices

• Envoy Esteem: All components implanted; utilizes piezoelectric sensors made from PZT ceramics

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COMPREHENSIVE FLOWCHART: BIOMATERIAL SELECTION IN EAR SURGERY

         OTOLOGICAL SURGERY PLANNED
                    │
    ┌───────────────┼───────────────┐
    │               │               │
  EXTERNAL       MIDDLE EAR      INNER EAR
    EAR               │               │
    │          ┌──────┴──────┐    Cochlear
Auricular      │             │    Implant
Reconstruction TM Repair   OCR    → Ti housing
    │              │          │    → Pt-Ir electrodes
Autologous     Temporalis  Autologous → Silicone carrier
Rib Cartilage  fascia/    Incus (1st)
(1st choice)   Perichondrium/   │
    │          Cartilage (1st) No incus?
Alloplastic:       │              │
Medpor/HDPE   Perforation  ┌─────┴──────┐
Silicone      size?    PORP          TORP
prosthesis       │    (stapes      (stapes
              Small   head intact) footplate only)
              →Fat plug    │              │
              Medium    Ti PORP      Ti TORP
              →Fascia   or HA PORP   or HA TORP
              Large/    (Ti preferred)  (Ti preferred)
              Revision
              →Cartilage
              island graft

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COMPLICATIONS OF BIOMATERIALS IN THE EAR

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SUMMARY TABLE: ALL BIOMATERIALS IN THE EAR

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IMPORTANT SHORT NOTES FOR EXAM

"Gold standard for OCR" → Autologous incus reshaping "Most common TM graft" → Temporalis fascia "Best alloplastic for OCR today" → Titanium PORP/TORP "Stapes piston material" → Teflon (PTFE) — Shea, 1958 "BAHA implant material" → Titanium (Brånemark osseointegration) "Cochlear implant electrodes" → Platinum-iridium in silicone "Least extrusion rate alloplastic" → Titanium < HA < HDPE

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REFERENCES

1. Dhingra PL, Dhingra S. Diseases of Ear Nose and Throat & Head and Neck Surgery. 7th ed. Elsevier; 2018. pp. 305–325.
2. Scott-Brown WG (Gleeson M, ed.). Scott-Brown's Otorhinolaryngology, Head and Neck Surgery. 8th ed. CRC Press; 2018. Vol 3, Ch. 236.
3. Cummings CW et al. Cummings Otolaryngology Head and Neck Surgery. 6th ed. Saunders Elsevier; 2015. Ch. 141, 163.
4. Stell PM, Maran AGD. Head and Neck Surgery. 4th ed. Butterworth-Heinemann; 2000. pp. 437–445.
5. Hazarika P et al. Textbook of Ear, Nose and Throat Diseases. 13th ed. CBS Publishers; 2019. pp. 560–580.
6. Zakir Hussain. Handbook of ENT for Undergraduate Students. Current edition. pp. 214–230.
7. Dornhoffer JL. Cartilage tympanoplasty: indication, techniques and outcomes in a 1000-case experience. Otolaryngol Head Neck Surg. 2003;128:223–234.
8. Stupp CH et al. Titanium as an ossicular replacement material: results after 336 operations. Am J Otol. 1996;17(1):41–45.
9. Mao N et al. Tissue engineering of the tympanic membrane. Front Bioeng Biotechnol. 2020;8:236.
10. Staecker H et al. Drug delivery to the inner ear using PLGA nanoparticles. Otol Neurotol. 2010;31(6):915–919.

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Total Word Count: ~3,500 words | RGUHS 50-mark standard | Covers all major textbooks cited in the question