Biobased plastics and bionanocomposites: Current status and future opportunities

The mechanical properties of biodegradable polymers and composites proposed for use in internal fixation (in place of stainless steel) are crucial to the performance of devices made from them for support of healing bone. To assess the reported range of properties and degradation rates. we searched and reviewed papers and abstracts published in English from 1980 through 1988. Mechanical property data were found for poly(lactic acid), poly (glycolic acid), poly(ϵ-caprolactone), polydioxanone, poly(ortho ester), poly(ethylene oxide), and/or their copolymers. Reports of composites based on several of these materials, reinforced with nondegradable and degradable fibers, were also found. The largest group of studies involved poly(lactic acid). Mechanical test methods varied widely, and studies of the degradation of mechanical properties were performed under a variety of conditions, mostly in vitro rather than in vivo.

Compared to annealed stainless steel, unreinforced biodegradable polymers were initially up to 36% as strong in tension and 54% in bending, but only about 3% as stiff in either test mode. With fiber reinforcement, reported highest initial strengths exceeded that of stainless steel. Stiffness reached 62% of stainless steel wiht nondegradable carbon fibers, 15% with degradable inorganic fibers, but only 5% with degradable polymeric fibers.

The slowest-degrading unreinforced biodegradable polymers were poly(L-lactic acid) and poly(ortho ester). Biodegradable composites with carbon or inorganic fibers generally lost strength rapidly, with a slower loss of stiffness, suggesting the difficulty of fiber-matrix coupling in these system. The strength of composites reinforced wiht (lower modulus) degradable polymeric fibers decreased more slowly.

Low implant stiffness might be expected to allow too much bone motion for satisfactory healing. However, unreinforced or degradable polymeric fiber reinforced materials have been used successfully clinically. The key has been careful selection of applications, plus use of designs and fixation methods distinctly different from those appropriate for stainless steel devices.

Mechanical properties of biodegradable polymers and composites proposed for internal fixation of bone

Researchers have recently focused on the advancement of new materials from biorenewable and sustainable sources because of great concerns about the environment, waste accumulation and destruction, and the inevitable depletion of fossil resources. Biorenewable materials have been extensively used as a matrix or reinforcement in many applications. In the development of innovative methods and materials, composites offer important advantages because of their excellent properties such as ease of fabrication, higher mechanical properties, high thermal stability, and many more. Especially, nanocomposites (obtained by using biorenewable sources) have significant advantages when compared to conventional composites. Nanocomposites have been utilized in many applications including food, biomedical, electroanalysis, energy storage, wastewater treatment, automotive, etc. This comprehensive review provides chemistry, structures, advanced applications, and recent developments about nanocomposites obtained from biorenewable sources.

/pdf/chemistry-structures-and-advanced-applications-of-1e0y79sgtf.pdf

Chemistry, Structures, and Advanced Applications of Nanocomposites from Biorenewable Resources.

Eighty-two patients with 105 metacarpal and/or phalangeal fractures stabilized with plates were retrospectively reviewed to assess complications and outcomes. Despite stable fixation and early mobilization, major complications were encountered in 36% of fractures, especially with phalangeal and open fractures. Complications included stiffness, nonunion plate prominence, infection, and tendon rupture. Forty-eight of 63 (76%) metacarpal fractures and 44 of 66 (67%) closed fractures had a final range of motion greater than 220 o ; however, only 4 of 37 (11%) phalangeal fractures and 8 of 34 (24%) open fractures achieved this outcome. Despite technical advances in plate design and instrumentation, including lower-profile titanium plates, complications occur commonly with metacarpal and phalangeal fractures, leadig to a high incidence of unsatisfactory results. We do not condemn plate fixation, and attribute many of our unsatisfactory results to the frequent use of plates in open and phalangeal fractures.

Complications and range of motion following plate fixation of metacarpal and phalangeal fractures

Surgical applications of biodegradable polymers in human tissues

Nine types of internal fixation techniques were tested in 4-point bending using a pig metacarpal model for phalangeal fractures. Levels of bending rigidity and bending moments at failure were determined, and the modes of failure are described. Plate and screw fixation afforded the greatest rigidity, and epiphyseal fractures occurred, leaving intact the test section. Flexible wire loop fixation failed by wire cutting into bone when a square knot was used. Twisted wire unraveled when placed in tension. Depending on the fracture type and the wire placement, Kirschner wires failed either by slipping in the bone, twisting in the bone cortex, or bending at the bone cortex interface. Rigidity varied widely depending on the way in which the wires were employed.

A phalangeal fracture model—Quantitative analysis of rigidity and failure

Transverse divisions of the mid-shaft of freshly frozen pig metacarpals were fixed with Kirschner wires of two sizes and using four different configurations. Compared to the usual cross-pin fixation using wires of 0.889 mm, four wires (0.712 mm) eccentrically placed and with their ends hooked provided a 300% improvement in bending rigidity and 170% in bending movement.

Mechanical analysis of Kirschner wire fixation in a phalangeal model

Development of new methods for phalangeal fracture fixation.

SUMMARY The importance of lacerations of the hand resides in both their direction in relation to flexion creases and their potential for injury to the vital functional structures within the hand and the digit. If the lacerations are thought of in these terms and examination is made with an attempt to determine what functional loss has occurred, the need for reconstructive surgery may be lessened. Reconstructive surgery frequently is required when primary surgery is either neglected or inexpertly performed.

James B. Massengill

Papers

A phalangeal fracture model—Quantitative analysis of rigidity and failure

Mechanical analysis of Kirschner wire fixation in a phalangeal model

Development of new methods for phalangeal fracture fixation.

Pitfalls in management of fingertip injuries and hand lacerations.