Resorbable continuous-fibre reinforced polymers for osteosynthesis

In-patient versus in vitro degradation of P(L/DL)LA and PLGA

To assess and compare degradation rates, poly(70L-lactide-co-30DL-lactide) [P(L/DL)LA] and poly(85L-lactide-co-15-glycolide) (PLGA) copolymer degradation were studied in patients (maxillofacial region) and in vitro. Five patients of a total of 20 with 85:15 PLGA osteosyntheses, and 15 of a total of 60 with 70:30 P(L/DL)LA osteosyntheses, (10 females and 10 males, 26-55 years; mean, 33 years) underwent explantations after 3, 6, 9, 12, 18, and 24 months. Identical resorbables immersed in physiological buffer solution at 37 degrees C were compared at identical intervals. P(L/DL)LA's initial average molecular weight of 45,000 decreased to 25,000 in patients (and to 21,000 in vitro) after 6 months, and to 8000 in patients after 18 months. PLGA's average molecular weight decreased from 44,600 to 22,000 after 3 months in patients and in vitro, and to 11,000 in patients and 1300 in vitro at 6 months. In-patient and in vitro glass-transition temperatures decreased from approximately 60 degrees C to 50 degrees C over 18 months. Crystallinity in explants was < or = 4% in P(L/DL)LA throughout testing, and 16% and 30% in PLGA at 6 and 12 months, respectively. Both copolymers decomposed reliably in patients: 85:15 PLGA within 12 months and 70:30 P(L/DL)LA within 24 months on average (p < 0.005), leaving only extremely small granules that powder upon finger touch. In vitro rates were significantly faster (p < 0.005). Crystallinity associated with foreign-body reactions was minor and did not inhibit decomposition.

Recent Developments in Ring Opening Polymerization of Lactones for Biomedical Applications

Aliphatic polyesters prepared by ring-opening polymerization of lactones are now used worldwide as bioresorbable devices in surgery (orthopaedic devices, sutures, stents, tissue engineering, and adhesion barriers) and in pharmacology (control drug delivery). This review presents the various methods of the synthesis of polyesters and tailoring the properties by proper control of molecular weight, composition, and architecture so as to meet the stringent requirements of devices in the medical field. The effect of structure on properties and degradation has been discussed. The applications of these polymers in the biomedical field are described in detail.

Effect of filler content on mechanical and dynamic mechanical properties of particulate biphasic calcium phosphate--polylactide composites

A bioabsorbable self-reinforced polylactide/biphasic calcium phosphate (BCP) composite is being developed for fracture fixation plates. One manufacturing route is to produce preimpregnated sheets by pulling polylactide (PLA) fibres through a suspension of BCP filler in a PLA solution and compression moulding the prepreg to the desired shape. To aid understanding of the process, interactions between the matrix and filler were investigated. Composite films containing 0-0.25 volume fraction filler, produced by solvent casting, were analysed using SEM, tensile testing and dynamic mechanical analysis (DMA). Homogeneous films could be made, although some particle agglomeration was seen at higher filler volume fractions. As the filler content increased, the failure strain decreased due to a reduction in the amount of ductile polymer present and the ultimate tensile strength (UTS) decreased because of agglomeration and void formation at higher filler content. The matrix glass transition temperature increased due to polymer chain adsorption and immobilization onto the BCP particles. Complex damping mechanisms, such as particle-particle agglomeration, may exist at the higher BCP volume fractions.

Biologically and chemically optimized composites of carbonated apatite and polyglycolide as bone substitution materials

We report on the development and characterization of a new composite material consisting of amorphous carbonated apatite, Ca(5)(PO(4), CO(3))(3)(OH), and microstructured poly(hydroxyacetic acid), polyglycolide (PGA). This material is able to keep the pH of a surrounding solution within the physiological range (7.2-7.6). This was achieved by chemical fine-tuning of the counterplay between the acidic degradation of the polyester and the basic dissolution of calcium phosphate. Microporous samples with pore sizes of <1 microm and compact samples were prepared. The biological behavior was assayed in vitro by long-term osteoblast culture. Morphological and biochemical analyses of cell differentiation revealed excellent biocompatibility, leading to cell attachment, collagen and osteocalcin expression, and mineral deposition. This material could be of use as a biodegradable bone substitution material and as a scaffold for tissue engineering.