Tissue Engineering of the Anterior Cruciate Ligament: The Viscoelastic Behavior and Cell Viability of a Novel Braid–Twist Scaffold

http://www.ncbi.nlm.nih.gov/pubmed/19723437

• OVERVIEW OF STUDY- "In this study we tested novel braid–
  twist scaffolds, as well as braided scaffolds, twisted fiber scaffolds and aligned fiber scaffolds, for use as ACL replacements composed of poly(L-lactic acid) fibers. Scaffolds were examined using stress relaxation tests, cell viability assays and scanning electron microscopy."
• WHAT IS AN AUTOGRAFT AND WHAT IS AN ALLOGRAFT- "Autografts utilize tissue from the patient and allograft materials are obtained from a cadaver."
• FUNCTION WHAT ACL DOES- "The ACL is a viscoelastic tissue with a time-dependant and load history dependant response to applied forces [10]. This is typically manifested as creep, a change in sample length at a constant stress, or stress relaxation, a decrease in
  stress at a constant length. The viscoelastic response of the tissue is typically studied
  with creep or relaxation tests at one load or strain level [10]. This behavior is
  caused by the arrangement of the collagen fibers in the ligament, interactions between
  collagen and other macromolecules in the matrix (such as proteoglycans),
  and removal of water from the matrix with applied force."
• THEIR TECHNIQUE- "Our scaffold technique (the braid–
  twist) is designed to mimic the biomechanical properties and structure of the natural
  ligament while providing an environment conducive for cell and tissue growth."
• PARAMETERS- "Structural parameters such as braiding and twisting angle were varied in order to optimize
  scaffold behavior. Differences in cellular proliferation between these braid–twist
  and braided scaffolds were also measured."
• THEIR TYPES OF SCAFFOLD- "Braiding and twisting angles were varied for each type of scaffold, yielding a total of 15 types of scaffolds for testing
  (6 twisted scaffolds, 3 braided scaffolds and 6 braid–twist scaffolds)."
• USE OF MATH MODELS 2.3 MODELING OF MECHANICAL DATA- "The mechanical behavior of the different braid–twist scaffolds were modeled with
  a linear viscoelastic model and a quasi-linear viscoelastic (QLV) model. The linear
  viscoelastic model was a series of Maxwell models, a combination of a spring and
  a dashpot. The equation for the stress at time, t , for a Maxwell model is given in
  equation (1):
  σ(t) = σ0e−t/τ , (1)
  where the stress is noted by σ and the relaxation time is τ . After placing three
  Maxwell models in series, the equation for the stress in this system at time t is
  given by equation (2):
  σ(t) = Xσ0e−t/τx + Yσ0e−t/τy +Zσ0e−t/τz , (2)
  where X, Y and Z are the contributions of the yarns, fiber bundles and fibers. The
  relaxation times of these parts are τx , τy and τz.
  The constants X, Y and Z were the same for each combination of braiding and
  twisting angle with four and six turns per inch."
• RABBIT ACLS- "Primary patella tendon (PT) fibroblasts from female New Zealand
  white rabbits were harvested and cultured as reported earlier"
• PROMISE OF REGENERATION OF LIGAMENTS- "In vivo studies with this 3-D braided tissue-engineered ligament (TEL) display
  the tremendous promise of this scaffold toward the functional replacement
  and regeneration of ligaments [22]."
• WHY USE 3-D BRAIDING- "The fibers in the 3-D braiding technique all reinforce
  one another, thus increasing scaffold strength; 3-D braiding also creates a network
  of interconnected pores to aid in tissue infiltration and cell migration."
  
• WHY USE BIOMATERIAL-" PLLA is a
  degradable polymer which allows load to gradually shift from the implant to the
  neoligament over time."
• GROWTH OF ECM IN FIGURE 9- "growth of extracellular
  matrix material on both types of scaffolds over a 28-day period"
• HOW TO IMPROVE- "Future work will focus on optimizing the stress relaxation behavior,
  investigating braid–twist scaffold porosity and optimizing the mathematical models."