Experimental Study On Human Hair Keratin Polyactic Acid (HHK-PLA) Composite Rods For Internal Fixation

Bioabsorbable internal fixation devices have become a focus of many researchers in the past 30 years because of their incomparable advantages to metal materials in orthopaedic operations. However, they can only be used for internal fixation of non weight-bearing bones as their low initial mechanical quality and rapid early period degradation, which originate from their material and technical characteristics. In this study, we summarized foreign and domestic data and produced a new kind of internal fixation rods (HHK-PLA rods), which is made of polyactic acid (PLA) and human hair keratin (HHK). Then, we performed corresponding tests and observation to obtain more evidences for further study and clinical applications. Objective:1. Mechanical intensity tests were performed on the HHK-PLA rods, including the shearing force and the tri-points bending force, and then shearing strength, bending strength and elastic modulus were calculated.2. To obtain the data of degradation of the HHK-PLA rods in vivo.3. To observe the biocompatibility of the HHK-PLA rods. Methods:1. A material testing machine (MTS 858 Bionix Material Testing System, MTS, Minneapolis, MN) was introduced to test 20 HHK-PLA rods.2. 36 HHK-PLA rods were randomly transplanted into the hypodermis around the vertebra of 18 SD rats, two rods for each rat, and were taken out 1, 2, 4, 8, 12, 16, 20, 24 and 28 weeks after the operations respectively. And then, weight reduction of each rod was tested to be an indicator of the HHK-PLA rod degradation in vivo. At the same time, the constitution changes of the rods were also observed under the scanningconstitution changes of the rods were also observed under the scanningelectron microscope (SEM). 3. The tissue peripheral to the HHK-PLA rod was cut off and made intotissue sections to observe the inflammatory reaction, which can indicatethe biocompatibility of the HHK-PLA rod. Results:1. The HHK-PLA rod processed an outstanding initial mechanical quality, with 241MPa in shearing strength, 358MPa in bending strength and 13GPa in elastic modulus.2. The degradation procedure of the HHK-PLA rods in vivo was very satisfying as it degraded slowly in the earlier period and went out fast in the anaphase.3. 1 to 2 weeks after the transplantation, transparent fibrous tissue encapsulation and connective tissue proliferation were seen around the HHK-PLA rods, with the appearance of capillary telangiectasia and hyperemia and macrophage, plasmacyte, neutrophilic granulocyte, fibroblast and monocyte infiltration. The inflammatory reaction died off gradually after 8 weeks and by the end of 12 weeks after the transplantation, there were almost no foreign body reaction and inflammatory cell infiltration seen.Conclusions:1. The HHK-PLA rods can fully gratify the demands of internal fixation of limb bones.2. The characteristic degradation behavior of the HHK-PLA rods was very advantageous to the healing of the fracture because, when in the earlier period, they can produce powerful fixation effects as they degraded little and, while in the anaphase, the rods broke down gradually as the bone itself could already take the place.3. The HHK-PLA rods presented a satisfying biocompatibility. In the early period, the reaction was foreign body reaction and, after 12 weeks, no abnormality was seen.