Tissue Implants: Biological and Synthetic Materials

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Questions and Answers

What primarily dissipates initial loads applied to cartilage?

Increased modulus

Elastic deformation (correct)

Stress relaxation

Water displacement from collagen

Which factor is NOT important for the survival of cartilage grafts?

Curvature of the implant

Temperature of the surgical environment (correct)

Absence of dead space

Smooth surface

Which type of implant is considered to grow when implanted into young hosts?

Homografts

Synthetic implants

Autografts (correct)

Allografts

What is the main consequence of the presence of blood in the surgical field during grafting?

Graft resorption Signup and view all the answers

What characteristic of the stress-strain curve does cartilage exhibit as strain is increased?

Non-linear behavior Signup and view all the answers

What issue may arise from a rough surface of a graft?

Graft resorption Signup and view all the answers

Which type of graft is obtained from a donor of the same species as the recipient?

Homograft Signup and view all the answers

What is a significant drawback of synthetic materials used in facial implants?

They stimulate a chronic inflammatory response Signup and view all the answers

What primarily causes the smooth flow in arteries, similar to water in a slow river?

Build-up of fatty deposits in the artery Signup and view all the answers

Which factor does NOT influence the mechanical properties of PVA hydrogel?

Rate of blood flow in arteries Signup and view all the answers

What is the role of polymer crystallinites formed during the freezing of PVA solution?

To act as physical crosslinking points between PVA chains Signup and view all the answers

In the context of PVA hydrogel, what is the impact of freeze-thaw cycles on the relaxation time parameter, τ?

It increases with an increase in freeze-thaw cycles Signup and view all the answers

Which method is primarily mentioned for creating stiffness gradient in PVA hydrogel?

Gradual freezing-thawing technique Signup and view all the answers

What is a significant disadvantage of using free bone grafts?

They undergo resorption. Signup and view all the answers

Which of the following is an example of a synthetic implant material?

Collagen Signup and view all the answers

What characteristic should an ideal augmentation material possess regarding its long-term stability?

It should persist over long periods of time. Signup and view all the answers

How does the porosity of porous mesh implants affect their integration with host tissues?

They enable extensive ingrowth of fibrous tissue. Signup and view all the answers

What is a common surgical site option for harvesting grafts used in mandibular defects?

Iliac crest Signup and view all the answers

Which of the following statements is true regarding solid implants?

They are fixed to tissue by fibrous tissue forming a capsule. Signup and view all the answers

What is NOT a characteristic of an ideal augmentation material?

Toxicity Signup and view all the answers

What is the role of materials like polyglycolic acid and collagen in implant applications?

They are rapidly replaced by fibrous tissue. Signup and view all the answers

What is the function of the pores in the inner layer of an implant?

To facilitate cell colonization and tissue fusion Signup and view all the answers

Which material is mentioned as having a structure identical to that of bone?

Ultra-high molecular weight polyethylene Signup and view all the answers

What type of ultrasound technique is used for measuring blood flow velocity?

Doppler ultrasound Signup and view all the answers

How is the Doppler frequency shift calculated?

Using the formula $f_D = 2 f_0 v \cos(\theta)$ Signup and view all the answers

What do tissue and vessel mimicking materials aim to achieve?

Replicate tissue behavior and predict disease onset Signup and view all the answers

What is the speed of sound in the medium specified for Doppler ultrasound calculations?

1540 m/s Signup and view all the answers

What characteristic does blood flow exhibit in a healthy carotid artery?

Directional turbulence, similar to rapids Signup and view all the answers

Which type of biological implant involves transplantation from a donor of the same species?

Homograft Signup and view all the answers

What is the main advantage of mixing hydroxyapatite with a polymer for bone grafts?

Improved flexibility of the material Signup and view all the answers

What role does porosity play in bone graft materials according to the research?

It encourages blood vessel growth into the surgery area Signup and view all the answers

What measurement of UHMW PE exceeds that of steel, highlighting its mechanical properties?

Tensile strength Signup and view all the answers

What is the main purpose of systemic antibiotics in relation to implants?

To prevent infection before and after procedures Signup and view all the answers

What innovative method did Russian scientists use to create a porous structure in UHMW PE?

Solid-phase mixing Signup and view all the answers

What characteristic does the outer layer of the synthetic scaffold simulate?

Cortical bone Signup and view all the answers

Which of the following polymers is NOT mentioned as being used in facial implants?

Polyvinyl chloride (PVC) Signup and view all the answers

What is a key characteristic of injectable collagen used for tissue augmentation?

It requires maintenance every 6 to 9 months Signup and view all the answers

Why was the conventional method of creating a porous structure not suitable for UHMW PE?

The high molecular weight of the polymer posed challenges Signup and view all the answers

What is a significant characteristic of the new promising material used for 3D printed bone grafts?

It is highly absorbent Signup and view all the answers

Which injectable polymer is specifically known for its use in treating wrinkles and depressions?

Polydimethylsiloxane (silicone) Signup and view all the answers

What is one of the results found in early experiments on animals using new bone graft materials?

Results were described as 'quite astounding' Signup and view all the answers

What complication is NOT associated with PDMS implants?

Allergic reaction to titanium Signup and view all the answers

How are solid facial implants such as PDMS typically prepared before insertion?

They are soaked in an antibiotic solution Signup and view all the answers

What is a common issue that might arise from the use of PDMS implants?

Improper positioning Signup and view all the answers

What material is used as a reinforcing agent in PTFE solid implants?

Carbon fibers or aluminum oxide Signup and view all the answers

What is the primary focus of rheology in relation to fluids?

The study of the flow and deformation of matter Signup and view all the answers

How do shear-thickening materials behave under increasing shear stress?

They increase in viscosity Signup and view all the answers

What relationship does viscosity have with shear strain rate in Newtonian fluids?

Viscosity remains constant regardless of shear strain rate Signup and view all the answers

In rheology, what does the elastic modulus G represent?

The constant of proportionality for elastic deformation Signup and view all the answers

What type of fluids exhibit a decrease in viscosity with increasing shear stress?

Shear-thinning fluids Signup and view all the answers

What is the primary role of growth factors in tissue engineering?

To facilitate and promote cell function in tissue generation Signup and view all the answers

Which aspect is crucial for the scaffold used in tissue engineering?

It must mimic the biological properties of the tissue being replaced Signup and view all the answers

What is an important consideration in the design of complex scaffold structures?

The mechanical interplay between scaffold and cells must be understood Signup and view all the answers

Which of the following describes a key feature of strain-stiffening in polymer networks?

The network exhibits increased stiffness with increased strain Signup and view all the answers

What approach was primarily used in the 1997 experiment by Prof. Charles Vacanti?

Using biodegradable synthetic scaffolds for cartilage structure Signup and view all the answers

What modulus represents the storage of energy in materials?

Storage modulus Signup and view all the answers

Which of the following terms relates to the behavior of cells in response to their mechanical environment?

Mechanotransduction Signup and view all the answers

What was a primary advancement mentioned in tissue engineering for scaffold development?

Improving technology for building scaffold structures Signup and view all the answers

In small amplitude oscillatory strain/stress testing, what does the complex modulus (G*) measure?

The ratio of applied stress to measured strain Signup and view all the answers

What is the significance of poroelasticity in biopolymer networks?

It refers to how the material behaves under compression and fluid flow Signup and view all the answers

What is the purpose of the phase angle δ in the context of material stiffness?

To distinguish between elastic and viscous behavior Signup and view all the answers

What does the loss modulus (G'') represent in material characterization?

Energy loss during deformation Signup and view all the answers

How is the persistence length (lp) of a filament defined?

As the decay length of angular correlations along the polymer contour Signup and view all the answers

What describes the behavior of purely elastic materials under stress?

Strain is immediately observed after stress application and vanishes upon removal. Signup and view all the answers

What phenomenon does small amplitude oscillatory strain/stress testing quantitatively measure?

The stiffness of materials through G* Signup and view all the answers

What type of contribution to material stiffness does the storage modulus G' provide?

It measures recoverable elastic energy storage. Signup and view all the answers

What material is the Agili-C implant primarily made from?

Aragonite Signup and view all the answers

What is the key benefit of the porosity of the Agili-C implant?

Promotion of natural regeneration Signup and view all the answers

What is observed in MRI images of the treated defect area over a 24-month period?

Consistent increase in cartilage and bone regrowth Signup and view all the answers

What surgical option has been approved by the FDA for cartilage repair?

Agili-C cartilage repair implant Signup and view all the answers

What is the primary function of the stem cells migrating to the Agili-C implant?

To allow new bone and cartilage to be deposited Signup and view all the answers

What is the purpose of the titanium coating applied to the implant?

To increase corrosion resistance Signup and view all the answers

What type of cartilage does the Agili-C implant aim to replace?

Damaged articular cartilage Signup and view all the answers

What defines the biocompatibility of the Agili-C implant?

Its ability to support integration with surrounding tissues Signup and view all the answers

What is the primary mechanical behavior of biopolymer networks at low stress?

They exhibit flexibility due to fiber bending. Signup and view all the answers

How does the presence of a fluid phase affect the normal stress in biopolymer networks?

Normal stress is always positive at short timescales. Signup and view all the answers

What phenomenon describes the contractile or extensile behavior in biopolymer networks under shear?

Poynting effect. Signup and view all the answers

What determines the poroelastic response time in biopolymer networks?

Hydraulic permeability and shear modulus. Signup and view all the answers

What occurs at large (>50%) strains in biopolymer networks?

The material exhibits irreversible deformation. Signup and view all the answers

What aspect of biopolymer networks is often neglected in network models?

Viscous resistance from the solvent. Signup and view all the answers

Which statement correctly describes rapid deformations of fluid-coupled networks?

The system behaves as incompressible. Signup and view all the answers

In the study of biopolymer networks, what happens to the normal stress during long timescales?

Normal stress may become negative due to fluid effects. Signup and view all the answers

What is the main role of transglutaminase in the 3D-printed scaffold?

To enhance the mechanical properties of gelatin Signup and view all the answers

Which factor contributes to the increased differentiation of MSCs in the gelatin-HAP scaffold?

The presence of chondrogenic factors Signup and view all the answers

Why are pigs commonly used as model animals in cartilage studies?

Pigs have large joint areas and thick cartilage layers resembling human joints Signup and view all the answers

What is one advantage of using a hydrogel-based implant made from bacterial cellulose and polyvinyl alcohol?

It can effectively mimic the structure of collagen in cartilage Signup and view all the answers

Which group showed significant improvement in cartilage repair in the pig model study?

Group III – MSCs in gelatin/HAP scaffold Signup and view all the answers

What is the Young's modulus for the gelatin and gelatin/HAP scaffolds, respectively?

70 kPa and 77 kPa Signup and view all the answers

What component in the hydrogel-based implant replaces the gelatinous matrix in cartilage?

Polyvinyl alcohol Signup and view all the answers

In the context of cartilage repair with MSCs, what does MSC stand for?

Mesenchymal stem cells Signup and view all the answers

What is the primary function of rheology in the context of fluids?

To study the flow and deformation of matter Signup and view all the answers

Which statement accurately describes the behavior of shear-thickening materials?

They exhibit an increase in viscosity with increasing shear stress. Signup and view all the answers

What does the elastic modulus G signify in the field of rheology?

The constant of proportionality for elastic deformation Signup and view all the answers

What is the relationship between viscosity and strain rate in Newtonian fluids?

Viscosity is constant regardless of strain rate changes. Signup and view all the answers

In rheology, how is shear flow explained?

As a progressive layering with faster-moving layers sliding over slower ones. Signup and view all the answers

What defines the mechanical signal provided by nanopatterned surfaces to endothelial cells?

They mimic natural tissue topography. Signup and view all the answers

What purpose does a scaffold serve when seeded with endothelial and liver cells?

To bridge patients while awaiting liver transplants. Signup and view all the answers

Which technology is key in creating scaffolds with precise porous architecture?

Computational topology design. Signup and view all the answers

What is a main characteristic of the mechanical properties influenced by scaffolds in tissue repair?

They depend on the scaffold’s design and stiffness. Signup and view all the answers

What distinguishes solid free-form fabrication systems in tissue engineering?

They enable the use of 3-D printing for design. Signup and view all the answers

What is the significance of endothelial cells aligning in the direction of grooves in nanopatterned surfaces?

It demonstrates increased cell proliferation and migration. Signup and view all the answers

What does the term 'hybrid tissue' refer to in the context of scaffold applications?

A mix of various cell types tailored for specific functions. Signup and view all the answers

What happens to biopolymer networks when subjected to large strains without extensibility?

They fracture. Signup and view all the answers

What is observed in the strain-stress response of reconstituted collagen networks at strains beyond 4-5%?

Stress-stiffening occurs. Signup and view all the answers

In tissue engineering, what role does the polymer scaffold cast from a silicon mold play?

It serves as a framework for cell growth. Signup and view all the answers

What term describes the maximum stress that a network can withstand before fracture occurs?

Peak stress. Signup and view all the answers

Which of the following best explains the effect of molecular packing structure on biopolymer extensibility?

It can change under strain. Signup and view all the answers

What indicates that network fracture has occurred during shear strain testing?

Decreased shear stress after peak stress. Signup and view all the answers

What characterizes purely elastic materials when stress is applied?

Strain occurs immediately and disappears when stress is removed Signup and view all the answers

What does the complex modulus G* measure in a material?

The total stiffness combining elastic and viscous contributions Signup and view all the answers

What is the storage modulus G’ indicative of in material behavior?

The ability to return to original form after loading Signup and view all the answers

How do the elastic and viscous contributions to G* relate to each other?

They describe different aspects of material behavior Signup and view all the answers

Which factor significantly affects the bending behavior of filaments in polymer physics?

Thermal fluctuations and persistence length Signup and view all the answers

What does a phase angle δ represent in material testing?

The relative measure of elastic versus viscous behavior Signup and view all the answers

What is the loss modulus G’’ associated with in materials?

Energy lost due to internal friction during deformation Signup and view all the answers

What does the term 'persistence length' in polymer physics refer to?

The average length over which the polymer maintains its direction Signup and view all the answers

What defines the onset of nonlinearity in strain-stiffening within biopolymer networks?

The spacing between crosslinks Signup and view all the answers

How does the differential shear modulus behave in response to applied stress in biopolymer networks?

It increases according to a power law Signup and view all the answers

What factor primarily influences the onset strain in semiflexible polymer networks?

The thermal fluctuation excess length storage Signup and view all the answers

In stiff polymer networks, what is the main factor affecting strain-stiffening?

Network connectivity Signup and view all the answers

What exponent describes the power law for elastic modulus increase in response to shear load?

3/2 Signup and view all the answers

Which method is primarily used to study shear forces in tissues or networks?

Rheology Signup and view all the answers

What is primarily measured to assess the properties of biopolymer networks under shear?

Deformation and strain Signup and view all the answers

What common behavior is observed in most reconstituted biopolymer networks under load?

They undergo stress-stiffening Signup and view all the answers

What primarily characterizes the relationship between tension and stress in the high-tension limit?

Stress increases linearly with tension Signup and view all the answers

What can affect the stiffness of semiflexible polymer networks due to thermal fluctuations?

Temperature and crosslink density Signup and view all the answers

What was the effect of annealing on the BC-PVA hydrogels?

Increased crystallinity and solid content Signup and view all the answers

How does the wear resistance of the designed hydrogel compare to native cartilage?

It is three times lower than that of cartilage Signup and view all the answers

What does the improved shear strength of the designed hydrogel indicate?

It may fracture but remains attached to the bone Signup and view all the answers

What was the applied pressure and cycle count during the wear test on the hydrogel?

1 MPa for 106 cycles Signup and view all the answers

What is a critical characteristic of the designed hydrogel for it to function effectively as a cartilage substitute?

Strong shear tensile strength Signup and view all the answers

What size was the implant used in the study for treating cartilage defects?

20 mm in diameter Signup and view all the answers

What effect does the incorporation of BC into PVA have on its performance?

Inhibits the coefficient of friction Signup and view all the answers

What were the tensile and compressive strength values reached for the BC-PVA hydrogels?

Tensile strength of 50.4 MPa and compressive strength of 95.4 MPa Signup and view all the answers

Study Notes

Tissue Implants - Biological Materials and Synthetic Materials

Tissue implants are used in various medical procedures.
Development of these materials occurs via two independent pathways: biological graft materials and synthetic polymers.
Surgeons pioneered the development of biological graft materials.
Scientists and engineers developed synthetic polymers for medical applications.

Learning Points

Tissue Implants - Background: Overview of tissue implants.
Biological Implants: Focuses on autografts and homografts.
Synthetic Implants: Discusses synthetic implant types such as injectables, solids, and meshes.
Case Study: Investigates tissue/vessel mimicking materials.

Tissue Implants - Background

The development of tissue implant materials, both biological and synthetic, has occurred via two distinct pathways.
Surgeons have pioneered the development of biological graft materials.
Scientists and engineers have largely been responsible for introducing synthetic polymers in various medical applications.

Anatomy and Physiology of Facial Structure

Facial implants, such as those for the face, chin, nose, or forehead, are used to replace or interface with facial structures like skin, cartilage, and bone.
Skin is highly flexible, absorbing impact without permanent damage.
Cartilage shows a stress-strain profile similar to skin, including almost 100% tensile deformation before failure.
Cartilage's flexibility dissipates loads through water molecule displacement in collagen fibers.
Bone initially shows almost linear stress-strain behavior, plateauing at around 1% strain.

Facial Implants

Increased sophistication in facial plastic surgery has resulted in more procedures to correct genetic, traumatic, and cosmetic deformities and increased expectations by patients .
Population aging necessitates procedures minimizing age-related cosmetic changes.
Growing cosmetic procedure awareness and ideal outcome expectations push the need for enhanced techniques.

Biological Implants - Types

Autografts: Tissue/organ grafts from the same individual (e.g., cartilage autografts commonly used in facial procedures).
- Continue to grow when transplanted, not resorbing for up to 12 years.
- Important factors in survival include clean surgical fields, smooth graft surfaces, and good contact with adjacent cartilage, and appropriate coverage with soft tissue.
- Dead space or blood within the surgical field can negatively affect graft survival.
Homografts: Tissue grafts from a donor of the same species (e.g., tissue transplant between two humans).
- Fresh autografts are often preferred but not always readily available
- Preservation techniques are essential to ensure grafting. Preservation is typically by cold storage in saline, antiseptic or antibiotic solution or by freeze drying and irradiation
- These methods ensure graft sterility, reduce viral contamination, and minimize rejections.
Factors for Cartilage Graft Survival: Blood, Dead Space, Rough Surface, Curved Implant, No Cartilage Interface , Thin skin covering.

Synthetic Implant Materials

Synthetic implants provide advantages over tissue grafts, eliminating the need for multiple operations, recovery time, and infection risk.
Ideal implants are permanent and don't trigger chronic inflammation.
They come in a range of shapes and sizes, allowing for specific modifications.
Synthetic materials, including collagen, polydimethylsiloxane (silicone), polytetrafluoroethylene (PTFE), polyethylene, polyethylene terephthalate (Dacron), and polyglycolic acid, are common choices for facial augmentation.

Synthetic Implant Materials - Face

Injectables: Polydimethylsiloxane (silicone) for wrinkle/depression correction and collagen for smoothing acne scars. Injectable collagen requires ongoing maintenance.
Solids: Polymers like polydimethylsiloxane (silicone), polytetrafluoroethylene (PTFE), polyethylene, and polyacrylate are widely used for chin and cheek augmentation. Often, these solids necessitate soaking in antibiotic solutions prior to use, to prevent infection.
Meshes: Polymeric fibers like polyglycolic acid and polylactic acid are used in mesh form as a structural material to rebuild facial areas with defects.

Bone Grafts

Bone grafts for facial defects or reconstruction can be free or connected to their vascular supply for better integration.
Common harvesting sites include iliac crest and split ribs.
Free grafts resorb, which is a disadvantage. Resorption rate depends on vascular development and the implantation site.

Case Study - Tissue/Vessel Mimicking Materials

Tissue and vessel mimicking materials replicate tissue behavior, improve quality assurance tests, understand tissue/vessel/organ behavior, and predict disease occurrences at earlier stages.

Doppler Ultrasound

Doppler ultrasound technique measures blood flow velocity, assessing flow patterns and detecting issues.
Blood flow in a healthy artery should be smooth and unidirectional; irregular or non-uniform flow patterns, conversely, indicate potential issues or abnormalities.
Doppler technology evaluates flow properties, enabling the detection of cardiovascular diseases such as thickening of the artery wall resulting from fatty deposit buildup.

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Description

This quiz explores the development and types of tissue implants, highlighting both biological graft materials and synthetic polymers. It covers key concepts such as autografts, homografts, and various forms of synthetic implants. A case study on tissue mimicking materials will enhance your understanding of these medical applications.