Infection, Tumorigenesis and Calcification of Biomaterials - Chapter 14

Why are implants vulnerable to infection?

They provide surfaces for bacteria to attach, form biofilms, and persist.

What are the main implant infection categories and pathogens?

Categories: superficial immediate, deep immediate, and late. Pathogens: S. aureus, S. epidermidis, P. aeruginosa, and Candida.

What are the stages of implant infection?

Attachment, adhesion, biofilm growth, and dispersion.

How do Gram-positive and Gram-negative envelopes differ?

Gram-positive: one membrane and thick peptidoglycan. Gram-negative: two membranes, thin peptidoglycan, and outer-membrane LPS.

How does a biofilm differ from a capsule?

A biofilm matrix surrounds a bacterial community; a capsule coats one bacterium.

Why are biofilms difficult to clear?

Their matrix protects bacteria, and slow or dormant cells tolerate antibiotics.

What are bacterial persisters?

Bacteria that survive treatment in a tolerant state without inherited antibiotic resistance.

Which surface properties affect bacterial attachment?

Charge, hydrophobicity, chemistry, roughness, steric repulsion, and adsorbed proteins.

How does surrounding fluid affect bacterial adhesion?

Adsorbed proteins provide binding sites; ions alter charge interactions. Adhesins recognize proteins such as fibronectin.

What is the race for the surface?

Competition between host cells and bacteria to colonize an implant.

How can implant infection be prevented?

Compatible sterilization, attachment-resistant surfaces, and appropriate local antimicrobials.

Does sterilization remove endotoxin?

Not necessarily. LPS can remain after bacteria die; the LAL assay detects endotoxin.

How are bacterial hydrophobicity and charge measured?

Hydrophobicity: MATH and HIC. Charge-related behavior: electrophoretic mobility and EIC.

What does a bacterial adhesion assay show?

How many bacteria remain attached after washing; reduced attachment does not prove killing.

What does a zone of inhibition assay show?

Growth inhibition around a material on agar. Zone size depends on activity, release, and diffusion; it does not prove killing.

Which infection models are used?

Shunts model flowing blood; small animals screen treatments; larger animals accommodate complete devices. Assess recovered bacteria and tissue histology.

What conditions matter in bacterial testing?

Protein composition, flow, strain, exposure, washing, and controls. Match the assay to attachment, inhibition, or killing.

How do tumorigenesis, genotoxicity, and mutagenesis differ?

Tumorigenesis: tumor development. Genotoxicity: genetic damage. Mutagenesis: DNA sequence changes. Genetic damage alone does not prove cancer.

How do neoplasia, neoplasm, benign, and malignant differ?

Neoplasia: persistent uncontrolled proliferation. Neoplasm: resulting growth. Benign: noninvasive, without metastasis. Malignant: invasive and may metastasize.

What is a carcinogen?

A cancer-causing agent or stimulus, such as certain chemicals, viruses, or UV light.

What are the stages of tumorigenesis?

Initiation: cellular changes. Latency: no obvious tumor. Promotion: expansion of altered cells and tumor growth.

How do chemical and foreign body carcinogenesis differ?

Chemical: carcinogenic substances leach from material. Foreign body: implant-associated tumors without known chemical carcinogenic activity; the mechanism is incompletely understood.

How might inflammation contribute to cancer?

Reactive oxygen and nitrogen species can damage DNA. Persistent changes may contribute to tumors, but cancer is not inevitable.

What tumor-related concerns apply to nanoparticles and cell-containing implants?

Nanoparticles may disrupt DNA repair or increase reactive species. Implanted cells, especially pluripotent cells, may grow uncontrollably.

How do genotoxicity screens and tumor studies differ?

Screens detect potential genetic hazards; in vivo histopathology evaluates tumor formation. Neither alone excludes all long-term risks.

What matters in an in vivo tumor study?

Relevant species, implant geometry, site, duration, comparable controls, and tissue histopathology.

What do the main genotoxicity assays measure?

Unscheduled DNA synthesis: repair activity. Ames: mutations. Chromosomal aberration testing: chromosome damage.

How does the Ames test work?

Count mutations that let histidine-requiring bacteria grow without histidine; compare controls with and without metabolic activation.

How does chromosomal aberration testing work?

Expose mammalian cells and examine metaphase chromosomes for structural abnormalities compared with controls.

What is pathologic calcification, and why is it harmful?

Unwanted calcium-containing mineral deposits that can stiffen, embrittle, obstruct, or crack implants.

What promotes calcification?

Membrane remnants nucleate deposits; collagen supports crystal growth. Fixation chemistry, mineral metabolism, and loading affect risk.

How can calcification be reduced?

Remove cellular remnants, modify fixation or processing, and use inhibitors while preserving function and compatibility.

How do calcification models differ?

In vitro: controlled conditions. Subcutaneous: convenient screening. Intended site: more realistic loading and fluid exposure.

Why can EDTA distort calcification results?

It binds calcium, suppressing the mineral deposition being measured.

How is calcification stained and quantified?

Alizarin Red stains calcium deposits red; calibrated assays quantify calcium, often per tissue mass.

How do radiography and micro-CT assess mineral?

Radiography shows radiopaque deposits in 2D; micro-CT shows 3D distribution and mineralized volume.