Biomedical Engineering Reference
In-Depth Information
choice for GTR technique. Polylactide-based polymers indicated sufficient mechanical properties
and adjustable biodegradation rates. By controlling their chemical compositions, the membranes can
maintain for a period long enough to achieve tissue regeneration before membrane disintegration
[13,27]
. However, the polylactide-based membranes are inherently hydrophobic and exhibit poor cell
affinity; surrounding soft tissue inflammation often took place in clinical trails when this kind of GTR
membranes were used, which was due to acidic degradation products
[20,28,29]
. Considering these
problems, to find an ideal barrier membrane material is still the key to promote GTR technique.
Composite GTR membranes developed from osteoconductive calcium phosphate ceramics
and biodegradable polymers have been highlighted in recent years. As early as in 1995, Jansen had
mixed hydroxyapatite (HA) grains with a segmented copolymer consisting of poly(ethylene glycol
terephthalate) and poly(butylene terephthalate) (PEG/PBT, Polyactive
®
) to prepare biodegradable
GTR membranes and demonstrated their biocompatibility with tissues
[30]
. Their histological find-
ings in rabbit demonstrated that this kind of HA-polymer composite membrane could maintain its
integrity for 10-month period. The polymer appeared to be completely resorbed in about 4-6 months,
while the inorganic component, HA, appeared to begin to be resorbed after the tenth month
[31]
.
Lee et al.
[32]
had used molded porous PLA and PLA/β-tricalcium phosphate (β-TCP) compos-
ites with platelet-derived growth factor to guided bone regeneration (GBR). Kikuchi et al.
[33,34]
developed membranes composed of β-TCP and poly L-lactide, poly (L-lactide-
co
-e-caprolactone) or
poly (L-lactide-
co
-glycolide-
co
-e-caprolactone) and reported their applications for periodontal tissue
regeneration and GBR. More recently, novel GTR membranes, which contained mineralized nano-
HA collagen/polyester (PLA or PLGA), have been biomimetically fabricated by the precipitation
and casting procedures
[35-37]
. β-TCP or HA/chitosan composite membranes were also investigated
as candidates for potential bioresorbable barrier membranes
[38,39]
. These composite membranes
exhibited excellent biocompatibility, biodegradability, and mechanical properties.
10.2.3
Layer-Designed Membranes for GTR
The design of GTR membranes attempts to meet the criteria acting as a barrier to deflect the gingi-
val tissue away from the root surface and creates a protected space over the defect. In treating bone
defects and alveolar ridge augmentation, the GTR membranes should allow the migration of regen-
erative bone cells into the defect, in addition to exclude the epithelium and connective tissue growing
into the defect. It is hard to balance all these needs including biocompatibility, cell-occlusiveness,
space-making, tissue integration, osteoconductivity, and clinical manageability by a single layer
without gradual changes in structure and composition. Functional graded materials provided us one
new concept for GTR membrane design with graded component and graded structure. Commercially
available GTR membranes such as Bio-Gide (collagen type I and III; Geistlich Biomaterials,
Wolhusen, Switzerland) and Guidor (PLLA; Guidor AB, Huddinge, Sweden) employed a two-layer
design
[40-43]
.
Milella et al.
[44]
prepared a bilamellar membrane constituted of an asymmetric poly(L-lactic
acid) (PLLA) membrane with an alginate film, in which, the alginate film contained β-TCP to accel-
erate osteogenesis. The PLLA membrane functioned to both support the alginate film and separate
the soft tissue and was less rougher than alginate film, which was used in contact with the bone
defect. Park et al.
[45]
had synthesized a kind of PLGA-grafted hyaluronic acid copolymer and used
it with PLGA to fabricate by-layered films with a nonporous PLGA top layer and a porous hyaluronic
