Abstract
Novel calcium phosphate cements containing a mixture of four amino acids, glycine, proline, hydroxyproline and either lysine or arginine (CAL, CAK) were characterized and used for treatment of artificial osteochondral defects in knee. It was hypothesized that an enhanced concentration of extracellular collagen amino acids (in complex mixture), in connection with bone cement in defect sites, would support the healing of osteochondral defects with successful formation of hyaline cartilage and subchondral bone. Calcium phosphate cement mixtures were prepared by in situ reaction in a planetary ball mill at aseptic conditions and characterized. It was verified that about 30–60% of amino acids remained adsorbed on hydroxyapatite particles in cements and the addition of amino acids caused around 60% reduction in compressive strength and refinement of hydroxyapatite particles in their microstructure. The significant over-expression of osteogenic genes after the culture of osteoblasts was demonstrated in the cement extracts containing lysine and compared with other cements. The cement pastes were inserted into artificial osteochondral defects in the medial femoral condyle of pigs and, after 3 months post-surgery, tissues were analyzed macroscopically, histologically, immunohistochemically using MRI and X-ray methods. Analysis clearly showed the excellent healing process of artificial osteochondral defects in pigs after treatment with CAL and CAK cements without any inflammation, as well as formation of subchondral bone and hyaline cartilage morphologically and structurally identical to the original tissues. Good integration of the hyaline neocartilage with the surrounding tissue, as well as perfect interconnection between the neocartilage and new subchondral bone tissue, was demonstrated. Tissues were stable after 12 months’ healing.
Highlights
Degeneration and damage to cartilage, or even subchondral bone, due to primary, as well as secondary, factors are a significant social problem;e.g., osteoarthritis (OA) affects about 40 million people in Europe and about 10–13%of adults 60 years of age or older in the US [1,2]
The XRD analysis verified the presence of pure tetracalcium phosphate phase (JCPDS25-1137) and the formation of fine monetite phase (with reflections from (020), (−220) and (−112) monetite planes (JCPDS09-0080) at 2θ equal 26.51◦ and 30.21◦ ) during reaction milling
The formation of HAP verified the chemical analysis of cements after 7 days setting in simulated body fluid (SBF), where the Ca/P ratio was close to 1.65 ± 0.02
Summary
Degeneration and damage to cartilage, or even subchondral bone, due to primary (mainly genetic, in the absence of a predisposing trauma or disease), as well as secondary, factors (e.g., metabolic, inflammatory, post-traumatic) are a significant social problem;e.g., osteoarthritis (OA) affects about 40 million people in Europe and about 10–13%of adults 60 years of age or older in the US [1,2]. The biomechanical and biochemical relationships between articular cartilage and subchondral bone play an important role in the development of osteoarthritis. Several surgical procedures are applied to treat articular cartilage and subchondral defects, depending on the degree of their damage [4,5,6]. Due to the low number of active chondrocytes in the cartilage, direct seeding of autologously harvested mesenchymal stem cells or chondrocytes, on developed polymeric porous scaffolds, complicates and makes a more expensive surgical procedure [8,9,10,11,12]. The problem of the widespread use of biopolymers for the treatment of osteochondral defects is the insufficient coverage of both the mechanical properties and the characteristic zonal structure of hyaline cartilage
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