Resorbable tricalcium phosphates

Morris L.M. and Bajpai P.K. 1989. Development of a resorbable tricalcium phosphate (TCP) amine antibiotic composite. Mat. Res. Soc. Symp. 110 293-300. 

Other Ceramic Calcium Phosphate Materials. Other ceramic calcium phosphate materials for repairing bony defect iaclude p-tricalcium phosphate (P-TCP) [7758-87-4], P-Ca2(PO, and biphasic calcium phosphate (BCP) ceramics which consist of both P-TCP and HA. Unlike ceramic HA, P-TCP resorbs ia the tissue (293). The in vivo dissolution of BCP ceramic implants was shown (296) to iacrease with increasing P-TCP/HA ratio ia the implants. Both P-TCP and BCP can lead to new bone growth to various extents depending on the appHcations and the type of materials used (293,296). 

Calcium phosphate, also called tricalcium phosphate (TCP), serves as a model for a whole group of calcium phosphates which end with hydroxyapatite (HA). Another name for these materials, which resemble the mineral part of the bone chemically seen, is resorbable ceramics. 

Regrettably, no biomaterial is known to date that is both mechanically stable and sufficiently osseoinductive classic bioceramics such as alumina or stabilised zirconia are strong but bioinert, osseoconductive hydroxyapatite is mechanically weak and essentially non-resorbable, whereas the even weaker osseoconductive tricalcium phosphate is resorbable (Figure 3.9). 

Although Plaster of Paris was used inl892asabone substitute [Peltier, 1961], the concept of using synthetic resorbable ceramics as bone substitutes was introduced in 1969 [Hentrich et al., 1969 Graves et al., 1972]. Resorbable ceramics, as the name implies, degrade upon implantation in the host. The resorbed material is replaced by endogenous tissues. The rate of degradation varies from material to material. Almost all bioresorbable ceramics except Biocoral and Plaster of Paris (calcium sulfate dihydrate) are variations of calcium phosphate (Table 39.8). Examples of resorbable ceramics are aluminum calcium phosphate, coralline. Plaster of Paris, hydroxyapatite, and tricalcium phosphate (Table 39.8). 

Metsger S., Driskell T.D., and Paulsrud J.R. 1982. Tricalcium phosphate ceramic — A resorbable bone implant review and current status. JADA105 1035-1038. 

Bioceramics are used in the human body. The response of these materials varies from nearly inert to bioactive to resorbable. Nearly inert bioceramics include alumina (AI2O3) and zirconia (Zr02). Bioactive ceramics include hydroxyapatite and some special glass and glass-ceramic formulations. Tricalcium phosphate is an example of a resorbable bioceramic it dissolves in the body. Three issues will determine future progress ... 

If a nearly inert material is implanted into the body it initiates a protective response that leads to encapsulation by a nonadherent fibrous coating about 1 i.m thick. Over time this leads to complete isolation of the implant. A similar response occurs when metals and polymers are implanted. In the case of bioactive ceramics a bond forms across the implant-tissue interface that mimics the bodies natural repair process. Bioactive ceramics such as HA can be used in bulk form or as part of a composite or as a coating. Resorbable bioceramics, such as tricalcium phosphate (TCP), actually dissolve in the body and are replaced by the surrounding tissue. It is an important requirement, of course, that the... 

In recent years, attention has been paid to biphasic ceramics which are aimed at securing an optimum balance between the more stable hydroxyapatite, and the more soluble and better bonding P-tricalcium phosphate which is bio-resorbable [26]. 

Based on observed tissue response, synthetic bone-graft substitutes can be classified into inert (e.g., alumina, zirconia), bioactive (e.g., hydroxyapatite, bioactive glass), and resorbable substitutes (e.g., tricalcium phosphate, calcium sulfate). Of these, resorbable bone-graft substitutes are preferred for bone defect filling because they can be replaced by new natural bone after implantation, p-tricalcium phosphate (Ca3(PO )2, p-TCP) is one of the most widely used bone substitute material, due to its faster dissolution characteristics. Preparation of magnesium-substituted tricalcium phosphate ((Ca, Mg)3(PO )2, p-TCMP) has been reported by precipitation or hydrolysis method in solution. These results indicate that the presence of Mg stabilizes the p-TCP structure (LeGeros et al., 2004). The incorporation of Mg also increases the transition temperature from p-TCP to a-TCP and decreases the solubility of p-TCP (Elliott, 1994 Ando, 1958). 

Tricalcium phosphate (TCP) has a Ca P ratio of 1.5, similar to the amorphous biologic precursors of bone [5]. It can be prepared by sintering Ca deficient apatite (Ca P ratio 1.5). TCP is a polymorph ceramic and exhibits two phases (a- and -whitlockite), known as a- and (S-TCP. Variation in sintering temperature and humidity determine, which phase is being formed a-TCP occurs at dry heat >1300°C and subsequent quenching in water [4]. Solubility and resorbability of both forms is much higher compared to HA. However, a-TCP is unstable in water and reacts to produce HA. a-TCP is used mainly as a compound... 

Biomaterials which are used to repair the body need to last as long as the patient does. At present this is not the case and some people may face several hip replacement operations, for example, each time there being less bone material (or less healthy bone material) for incorporation of devices. The current life expectancy of such replacements is on the order of 10 years at present. This needs to be doubled on tripled in the future. None of the materials described above is able to address the problem of tissue alteration with age and disease. The skeletal system has the capacity to repair itself, this ability diminishing with age and disease state of the material. The ideal solution to the problem is to use biomaterials to augment the body s own reparative process. Certain of the resorbable implants such as tricalcium phosphate and some bioactive glasses are based on this concept. Problems which exist with the development of resorbable materials are (a) the products of resorption must be compatible with cellular metabolic processes and (b) the rate of resorption must also be matched by the capacities of the body to process and transport the products of this process. In addition, as the material is resorbed and new material formed, the properties of both phases will alter and compatibility must be maintained at all times. This is difficult to achieve. 

Biodegradable or resorbable As the name implies, the ceramic dissolves with time and are gradually replaced by the natural tissues. A very thin or non-existent interfacial thickness is the final results. This type of bioceramics would be the ideals, since only remain in the body while their function is necessary and disappear as the tissue regenerates. Their greater disadvantage is that their mechanical strength diminishes during the reabsorption process. One of the few bioceramics that fulfil partially these requirements is the tricalcium phosphate (TCP). 

Dense and resorbable bioceramics The implant is replaced slowly by the bone. Belong to this group the tricalcium phosphate (TCP) and other phosphates as well as the calcium sulphate (CaS04V2H20 = plaster of Paris). 

Synthetic Ceramics Hydroxyapatite, tricalcium phosphate, bioactive glass, and calcinm silicate Resorbed materials, presenting conductive, and inductive properties Bachar et al. (2013), Tampieri et al. (2014), and Vimalnath et al. (2015)... 

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