To the Editor:
Today’s social demographic is changing, with the proportion of people older than 65 years in Australia projected to increase from 12% to 21% by 2031 (1). As a result, it is predicted that the number of fractures suffered annually by Australians will also increase (2). It has been established that 15% of fractures result in non-union and require surgical intervention. The treatment of fracture non-unions is therefore clearly set to become an increasingly important issue from both a public health and an individual perspective. For this reason, there has recently been increasing focus on bone implants and the development of improved methodologies.
Recent articles have discussed/examined the possibility of using a biodegradable implant in a load bearing application (3,4). However the principles behind the development of these implants need to be addressed because without in-depth focus and analysis on potential vascularisation of these implants, regardless of their possible osteoinductive properties, these novel/biomimetic scaffolds are bound to fail. As such, the ideal implant has remained an elusive entity.
Wintermantel and Mayer (5) developed criteria to describe the ideal implant, which include biocompatibility, bioactivity, native bone growth and angiogenesis., Biocompatibility is the chemical, biological and physical suitability of an implant to the host tissue, and is enhanced when it resembles the tissue it is replacing (6,7). Bioactivity occurs when healthy progenitor cells can ultimately replace lost or damaged tissue, thus allowing cell and vessel in-growth (8,9,10). Native bone growth is required in order for an implant to be considered as a suitable alternative to current grafting techniques and angiogenesis is necessary for bone metabolism, nutrient delivery and therefore bone regeneration.
Biomimetic scaffolding holds promise for the future as an ideal implant material. It has been suggested that composite materials offer greater potential of surface biocompatibility than the homogenous monolithic materials (11). However, to date, no graft alternative has been found to combine all of the aforementioned aspects.
There are currently many composite materials at the forefront of bone implant options for load bearing applications. Many of which fulfill components of the criteria set out by Wintermantel and Mayer (5). Some are true homogenous nano-scaffolds that resembles Hodge Petruska’s model of bone (12) while others are composites made at certain percentage ratios with calcium phosphate crystals.
For load bearing applicability and eventual use as an arthroplasty device, vessel in-growth is essential. For an implant to be replaced by native tissue and consequently fail due to avascular necrosis is pointless. As stated above, if an implant prevents vascularisation or angiogenesis from taking place, bone regeneration will consequently fail.
The authors did not receive any outside funding or grants in support of their research for or preparation of this work. Neither they nor a member of their immediate families received payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity. No commercial entity paid or directed, or agreed to pay or direct, any benefits to any research fund, foundation, division, center, clinical practice, or other charitable or nonprofit organization with which the authors, or a member of their immediate families, are affiliated or associated.
References
1. Williamson OD. Measuring the success of joint replacement surgery. Med J Aust. 1999;179;229-30.
2. Sanders KM, Nicholson GC, Ugoni AM, Pasco JA, Seeman E, Kotowicz MA. Health burden of hip and other fractures in Australia beyond 2000. Projections based on the Geelong Osteoporosis Study. Med J Aust. 1999;170;467-70.
3. Cool SM, Kenny B, Wu A, Nurcombe V, Trau M, Cassady AI, Grřndahl L. Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) composite biomaterials for bone tissue regeneration: in vitro performance assessed by osteoblast proliferation, osteoclast adhesion and resorption, and macrophage proinflammatory response. J Biomed Mater Res A. 2007;82;599-610.
4. Bostman OM. Absorbable implants for the fixation of fractures. J Bone Joint Surg Am. 1991;73:148-153.
5. Wintermantel E, Mayer J. Anisotropic biomaterials strategies and developments for bone implantation. In: Wise DL, editor. Encyclopedic Handbook of Biomaterials and Bioengineering. New York: CRC; 1995. p 3-42.
6. Wintermantel E, Ha SW. Biokompatible Werkstoffe und Bauweisen: Implantate fur Medizen und Umwelt. Berlin: Springer; 1998. p 1-36.
7. Hellman KB, Picciolo GL, Fox CF. Prospects for application of biotechnology-derived biomaterials. J Cell Biochem. 1994;56;210-24.
8. Shea LD, Wang D, Franceschi RT, Mooney DJ. Engineered bone development from a pre-osteoblast cell line on three-dimensional scaffolds. Tissue Eng. 2000;6;605-17.
9. Ishaug-Riley SL, Crane-Kruger GM, Yaszemski MJ, Mikos AG. Three-dimensional culture of rat calvarial osteoblasts in porous biodegradable polymers. Biomaterials. 1998;19:1405-12.
10. Lutton C, Read J, Trau M. Nanostructured biomaterials: a novel approach to artificial bone implants. Aust J Chem. 2001;54:621-23.
11. Peter SJ, Kim P, Yasko AW, Yaszemski MJ, Mikos AG. Crosslinking characteristics of an injectable poly(propylene fumarate)/beta-tricalcium phosphate paste and mechanical properties of the crosslinked composite for use as a biodegradable bone cement. J Biomed Mater Res. 1999;44:314-21.
12. Rho JY, Kuhn-Spearin L, Zioupos P. Mechanical properties and the hierarchical structure of bone. Med Eng Phys. 1998;20:92-102.
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