preferred embodiments of the present invention includes ( but not limited to ) the following : 1 . a prosthetic bone implant comprising a cortical portion having two opposite sides , and a cancellous portion integrally disposed in said cortical portion and being exposed through said two opposite sides , wherein said cortical portion comprises a hardened calcium phosphate cement has a porosity of less than 40 % in volume , and said cancellous portion comprises a porous hardened calcium phosphate cement having a porosity greater than 20 % in volume , and greater than that of said cortical portion . 2 . the implant according to item 1 , wherein the cortical portion is in the form of a hollow disk , and the cancellous portion is in the form of a column surrounded by the hollow disk . 3 . the implant according to item 2 further comprising a transitional portion between said column and said hollow disk surrounding said central cylinder , which has properties range from those of said cancellous portion to said cortical portion . 4 . the implant according to item 1 , wherein the cortical portion is in the form of a disk having one or more longitudinal through holes , and the cancellous portion is in the form of one or more columns surrounded by said one or more longitudinal through holes . 5 . the implant according to item 1 , wherein said hardened calcium phosphate cement of said cortical portion comprises an apatitic phase as a major phase giving rise to broadened characteristic x - ray diffraction peaks in comparison with a high - temperature sintered apatitic phase . 6 . the implant according to item 5 , wherein said broadened characteristic the x - ray diffraction peaks are at 2 - theta values of 25 – 27 ° and 30 – 35 °. 7 . the implant according to item 1 , wherein said hardened calcium phosphate cement of said cortical portion is prepared without a high temperature sintering . 8 . the implant according to item 1 , wherein said hardened calcium phosphate cement of said cortical portion comprises an apatitic phase as a major phase having a ca / p molar ratio of 1 . 5 – 2 . 0 . 9 . the implant according to item 1 , wherein said hardened calcium phosphate cement of said cancellous portion comprises an apatitic phase as a major phase giving rise to broadened characteristic x - ray diffraction peaks in comparison with a high - temperature sintered apatitic phase . 10 . the implant according to item 9 , wherein said broadened characteristic the x - ray diffraction peaks are at 2 - theta values of 25 – 27 ° and 30 – 35 °. 11 . the implant according to item 1 , wherein said hardened calcium phosphate cement of said cancellous portion is prepared without a high temperature sintering . 12 . the implant according to item 1 , wherein said hardened calcium phosphate cement of said cancellous portion comprises an apatitic phase as a major phase having a ca / p molar ratio of 1 . 5 – 2 . 0 . 13 . the implant according to item 1 , wherein said cortical portion comprises 10 – 90 % in volume of said implant . 14 . the implant according to item 1 , wherein said cortical portion has a porosity of less than 30 % in volume . 15 . the implant according to item 1 , wherein said cancellous portion has a porosity greater than 40 – 90 % in volume . 16 . a method for preparing a prosthetic bone implant comprising a cortical portion having two opposite sides , and a cancellous portion integrally disposed in said cortical portion and being exposed through said two opposite sides , said method comprises the following steps : a ) preparing a first paste comprising a first calcium phosphate cement and a first setting liquid ; b ) preparing a second paste comprising a second calcium phosphate cement , a pore - forming powder and a second setting liquid ; c ) i ) preparing a shaped article in a mold having two or more cells separated by one more partition walls comprising introducing said first paste and said second paste into said two or more cells separately , and removing said one or more partition walls from said mold , so that said second paste in the form of a single column or two or more isolated columns is integrally disposed in the first paste in said mold ; or ii ) preparing a shaped article comprising introducing one of said first paste and said second paste into a first mold to form an intermediate in said first mold , placing said intermediate into a second mold after a hardening reaction thereof undergoes at least partially , and introducing another one of said first paste ad said second paste into said second mold , so that said second paste as a single column or as two or more isolated columns is integrally disposed in the first paste in said second mold ; d ) immersing the resulting shaped article from step c ) in an immersing liquid for a first period of time so that said pore - forming powder is dissolved in the immersing liquid , creating pores in said single column or said two or more isolated columns ; and e ) removing the immersed shaped article from said immersing liquid . 18 . the method according to item 16 , wherein said pore - forming powder is selected from the group consisting of licl , kcl , nacl , mgcl 2 , cacl 2 , naio 3 , ki , na 3 po 4 , k 3 po 4 , na 2 co 3 , amino acid - sodium salt , amino acid - potassium salt , glucose , polysaccharide , fatty acid - sodium salt , fatty acid - potassium salt , potassium bitartrate ( khc 4 h 4 o 6 ), potassium carbonate , potassium gluconate ( kc 6 h 11 o 7 ), potassium - sodium tartrate ( knac 4 h 4 o 6 . 4h 2 o ), potassium sulfate ( k 2 so 4 ), sodium sulfate , and sodium lactate . 19 . the method according to item 16 , wherein said first calcium phosphate cement comprises at least one ca source and at least one p source , or at least one calcium phosphate source ; and said second calcium phosphate cement comprises at least one ca source and at least one p source , or at least one calcium phosphate source . 20 . the method according to item 19 , wherein said first calcium phosphate cement comprises at least one calcium phosphate source , and said second calcium phosphate cement comprises at least one calcium phosphate source . 21 . the method according to item 20 , wherein said calcium phosphate source is selected from the group consisting of alpha - tricalcium phosphate ( α - tcp ), beta - tricalcium phosphate ( β - tcp ), tetracalcium phosphate ( ttcp ), monocalcium phosphate monohydrate ( mcpm ), monocalcium phosphate anhydrous ( mcpa ), dicalcium phosphate dihydrate ( dcpd ), dicalcium phosphate anhydrous ( dcpa ), octacalcium phosphate ( ocp ), calcium dihydrogen phosphate , calcium dihydrogen phosphate hydrate , acid calcium pyrophosphate , anhydrous calcium hydrogen phosphate , calcium hydrogen phosphate hydrate , calcium pyrophosphate , calcium triphosphate , calcium phosphate tribasic , calcium polyphosphate , calcium metaphosphate , anhydrous tricalcium phosphate , tricalcium phosphate hydrate , and amorphous calcium phosphate . 22 . the method according to item 21 , wherein said first calcium phosphate cement and said second calcium phosphate cement are identical . 23 . the method according to item 22 , wherein said first calcium phosphate cement and said second calcium phosphate cement are tetracalcium phosphate . 24 . the method according to item 16 , wherein the first setting liquid and the second setting liquid independently are an acidic solution , a basic solution , or a substantially pure water . 25 . the method according to item 24 , wherein said acidic solution is selected from the group consisting of nitric acid ( hno 3 ), hydrochloric acid ( hcl ), phosphoric acid ( h 3 po 4 ), carbonic acid ( h 2 co 3 ), sodium dihydrogen phosphate ( nah 2 po 4 ), sodium dihydrogen phosphate monohydrate ( nah 2 po 4 . h 2 o ), sodium dihydrogen phosphate dihydrate , sodium dihydrogen phosphate dehydrate , potassium dihydrogen phosphate ( kh 2 po 4 ), ammonium dihydrogen . phosphate ( nh 4 h 2 po 4 ), malic acid , acetic acid , lactic acid , citric acid , malonic acid , succinic acid , glutaric acid , tartaric acid , oxalic acid and their mixture . 26 . the method according to item 22 , wherein said basic solution is selected from the group consisting of ammonia , ammonium hydroxide , alkali metal hydroxide , alkali earth hydroxide , disodium hydrogen phosphate ( na 2 hpo 4 ), disodium hydrogen phosphate dodecahydrate , disodium hydrogen phosphate heptahydrate , sodium phosphate dodecahydrate ( na 3 po 4 . 12h 2 o ), dipotassium hydrogen phosphate ( k 2 hpo 4 ), potassium hydrogen phosphate trihydrate ( k 2 hpo 4 . 3h 2 o ), potassium phosphate tribasic ( k 3 po 4 ), diammonium hydrogen phosphate (( nh 4 ) 2 hpo 4 ), ammonium phosphate trihydrate (( nh 4 ) 3 po 4 . 3h 2 o ), sodium hydrogen carbonate ( nahco 3 ), sodium carbonate na 2 co 3 , and their mixture . 27 . the method according to item 16 , wherein step c - i ) further comprises allowing said first paste and said second paste undergoing a hardening reaction in said mold . 28 . the method according to item 16 , wherein step c - i ) further comprises pressurizing said first paste and said second paste in said mold after removing said one or more partition walls from said mold to remove a portion of liquid from said first paste and said second paste , so that a liquid / powder ratio of said first paste and of said second paste decreases ; and allowing said first paste and second paste undergoing a hardening reaction in said mold . 29 . the method according to item 16 , wherein step c - ii ) further comprises allowing said intermediate undergoing a hardening reaction in said first mold , and allowing said another one of said first paste and said second paste undergoing a hardening reaction in said second mold . 30 . the method according to item 16 , wherein step c - ii ) further comprises pressurizing said one of said first paste and said second paste in said first mold to remove a portion of liquid therefrom before the hardening reaction of said intermediate is completed ; allowing said intermediate undergoing a hardening reaction in said first mold ; pressuring said another one of said first paste and said second paste in said second mold , so that a liquid / powder ratio of said another one of said first paste and of said second paste decreases ; and allowing said another one of said first paste and second paste undergoing a hardening reaction in said second mold . 31 . the method according to item 28 , wherein said pressuring is about 1 to 500 mpa . 32 . the method according to item 30 , wherein said pressuring is about 1 to 500 mpa . 33 . the method according to item 16 , wherein the immersing liquid is an acidic aqueous solution , a basic aqueous solution , a physiological solution , an organic solvent , or a substantially pure water . 34 . the method according to item 33 , wherein the immersing liquid comprises at least one of ca and p sources . 35 . the method according to item 33 , wherein the immersing liquid is a hanks &# 39 ; solution , a hcl aqueous solution or an aqueous solution of ( nh 4 ) 2 hpo 4 . 36 . the method according to item 16 , wherein the immersing in step d ) is carried out for a period longer than 10 minutes . 37 . the method according to item 16 , wherein the immersing in step d ) is carried out for a period longer than 1 day . 38 . the method according to item 16 , wherein the immersing in step d ) is carried out at a temperature of about 10 and 90 ° c . 39 . the method according to item 38 , wherein the immersing in step d ) is carried out at room temperature . 40 . the method according item 17 further comprising cleaning said immersed shaped article before said drying ; and heating the resulting dried shaped article at a temperature between 50 and 500 ° c . four different designs of prosthetic bone implants constructed according to the present invention are shown in fig1 a to 1 d . in fig1 a , the prosthetic bone implant of the present invention has a dense cortical portion d 1 in the tubular form and a porous cancellous portion p 1 formed in the central through hole of the tubular cortical portion d 1 . both the dense cortical portion d 1 and the porous cancellous portion p 1 are made of a hardened calcium phosphate cement having an apatitic phase as a major phase . in fig1 b , the prosthetic bone implant of the present invention has a dense cortical portion d 1 in the tubular form ; a cylindrical porous cancellous portion p 1 in the center of the tubular cortical portion d 1 ; and an annular transitional portion p 2 connecting the tubular cortical portion d 1 and the cylindrical cancellous portion p 1 . the transitional portion p 2 is made of a hardened calcium phosphate cement having an apatitic phase as a major phase , and a porosity gradient increasing from the lower porosity of the cylindrical cancellous portion p 1 to the higher porosity of the tubular cortical portion d 1 , which maybe formed in - situ during molding of two different two different cpc pastes , one of them having an additional pore - forming powder for forming the cylindrical cancellous portion p 1 , and another one being a regular cpc powder for forming the dense cortical portion d 1 . the porous cancellous portion p 1 may be in the forms of isolated columns surrounded by the dense cortical portion d 1 as shown in fig1 c and 1 d . other designs are also possible in addition to those shown in fig1 a to 1 d . a suitable method for preparing the prosthetic bone implant of the present invention includes placing a tubular partition wall 10 in a hollow cylindrical mold 20 , as shown in fig2 a ; pouring a first paste comprising a calcium phosphate cement and a setting liquid in the annular cell and a second paste comprising the calcium phosphate cement , a pore - forming powder and the setting liquid in the central cell , as shown in fig2 b ; removing the partition wall and pressing the cpc pastes before hardening , as shown in fig2 c , wherein a portion of the setting liquid is removed from the gap between the mold 20 and the press 30 and / or holes ( not shown in the drawing ) provided on the press 30 . the cpc paste will undergo a hardening reaction to convert into apatitic phase . the hardened disk is removed from the mold and is subjected to surface finishing to expose the central portion hardened from the second paste , as shown in fig2 d , followed by immersing in a bath of an immersing liquid as shown in fig2 e , where the pore - forming powder is dissolved in the immersing liquid while the hardened cpc thereof gaining compressive strength . the immersing may last from 10 minutes to several days . the composite disk so formed is washed with water after being removed from the bath , and dried and heated in an oven to obtain the prosthetic bone implant as shown in fig2 f . the heating is conducted at a temperature between 50 and 500 ° c . for a period of several hours to several days , which enhance the compressive strength of the cortical portion of the prosthetic bone implant . an alternative method for preparing the prosthetic bone implant of the present invention from the same raw materials includes pouring the second paste in a first mold , pressing the second paste to remove a portion of the setting liquid from the second paste before the hardening reaction is completed , so that the liquid / powder ratio in the second paste decreases , and allowing the hardening reaction undergo in the mold for a period of time , e . g . 15 minutes starting from the mixing of the cpc powder , the pore - forming powder and the setting liquid , to obtain a cylindrical block having a diameter of 7 mm . then , the cylindrical block is removed from the first mold , and placed in the center of a second mold having a diameter of 10 mm . the first paste is poured into the annular space in the second mold , and a press having a dimension corresponding to the annular shape is used to pressure the first paste to remove a portion of the setting liquid from the first paste before the hardening reaction is completed , so that the liquid / powder ratio in the first paste decreases . again , the first paste will undergo a hardening reaction to convert into apatitic phase . the , hardened cylinder having a diameter of 10 mm is removed from the second mold , followed by immersing in an immersing liquid , where the pore - forming powder contained in the second paste is dissolved in the immersing liquid while the hardened cpc thereof gaining compressive strength , to obtain the prosthetic bone implant of the present invention , as shown in fig3 a and 3 b . it is apparently to people skilled in the art that the prosthetic bone implant shown in fig3 a and 3 b can also be prepared by changing the sequence of the molding of the first paste and the second paste with modifications to the second mold used in this alternative method . the following examples are intended to demonstrate the invention more fully without acting as a limitation upon its scope , since numerous modifications and variations will be apparent to those skilled in this art . a ca 4 ( po 4 ) 2 o ( ttcp ) powder was prepared by mixing ca 2 p 2 o 7 powder with caco 3 powder uniformly in ethanol for 24 hours followed by heating to dry . the mixing ratio of ca 2 p 2 o 7 powder to caco 3 powder was 1 : 1 . 27 ( weight ratio ) and the powder mixture was heated to 1400 ° c . to allow two powders to react to form ttcp . the resulting ttcp powder from preparative example 1 was sieved and blended with dried cahpo 4 ( dcpa ) powder in a ball mill for 12 hours . the blending ratio of the ttcp powder to the dcpa powder was 1 : 1 ( molar ratio ) to obtain the conventional cpc powder . particles of this c - cpc powder have no whisker on the surfaces thereof . the ttcp powder prepared according to the method of preparative example 1 was sieved and blended with dried cahpo 4 ( dcpa ) powder in a ball mill for 12 hours . the blending ratio of the ttcp powder to the dcpa powder was 1 : 1 ( molar ratio ). the resultant powder mixture was added to a 25 mm diluted solution of phosphate to obtain a powder / solution mixture having a concentration of 3 g powder mixture per 1 ml solution while stirring . the resulting powder / solution mixture was formed into pellets , and the pellets were heated in an oven at 50 ° c . for 10 minutes . the pellets were then uniformly ground in a mechanical mill for 20 minutes to obtain the non - dispersive ttcp / dcpa - based cpc powder ( nd - cpc ). the particles of this nd - cpc powder have whisker on the surfaces thereof . to a setting solution of 1m phosphoric acid solution ( ph = 5 . 89 ) the nd - cpc powder from preparative example 3 was added in a liquid / powder ratio ( l / p ratio ) of 0 . 4 , i . e . 4 ml liquid / 10 g powder , while stirring . the resulting paste was filled into a cylindrical steel mold having a length of 12 mm and a diameter of 6 mm , and was compressed with a gradually increased pressure until a maximum pressure was reached . the maximum pressure was maintained for one minute , and then the compressed cpc block was removed from the mold . at the 15 th minute following the mixing of the liquid and powder , the compressed cpc block was immersed in a hanks &# 39 ; solution for 1 day , 4 days , and 16 days . each test group of the three different periods of immersion time has five specimens , the compressive strength of which was measured by using a ags - 500d mechanical tester ( shimadzu co ., ltd ., kyoto , japan ) immediately following the removal thereof from the hanks &# 39 ; solution without drying . the cpc paste in the mold was compressed with a maximum pressure of 166 . 6 mpa , and in the course of the compression the compression speeds were about 5 mm / min during 0 ˜ 104 . 1 mpa ; 3 mm / min during 104 . 1 ˜ 138 . 8 mpa ; 1 mm / min during 138 . 8 ˜ 159 . 6 mpa : and 0 . 5 mm / min during 159 . 6 ˜ 166 . 6 mpa . the measured wet specimen compressive strength is listed table 1 . * this value was measured before the compressed cpc blocks were immersed in the hanks &# 39 ; solution , and it was substantially the same for the compressed cpc blocks not immersed in the hanks &# 39 ; solution measured a few days after the preparation . it can seen from table 1 that the compressive strength of the compressed cpc blocks is increased remarkably after one - day immersion in comparison with the non - immersed block , and declines a little for a longer immersion time . the procedures of example 1 were repeated by using the c - cpc powder prepared in preparative example 2 and the nd - cpc powder prepared in preparative example 3 . the maximum pressure used to compress the cpc paste in the mold in this example was 156 . 2 mpa . the results for one - day immersion time are listed in table 2 . it can be seen from table 2 that the compressive strength , 62 . 3 mpa , of the immersed compressed cpc block prepared from the conventional cpc powder ( no whisker ) is about 1 . 7 times of that ( 37 . 3 mpa ) of the non - immersed compressed cpc block in table 1 , and the compressive strength , 138 . 0 mpa , of the immersed compressed cpc block prepared from the non - dispersive cpc powder ( with whisker ) is about 3 . 7 times of that of the non - immersed compressed cpc block in table 1 ca 4 ( po 4 ) 2 o ( ttcp ) powder as synthesized in preparative example 1 was sieved with a # 325 mesh . the sieved powder has an average particle size of about 10 μm . to the ttcp powder hcl aqueous solution ( ph = 0 . 8 ) was added according to the ratio of 1 g ttcp / 13 ml solution . the ttcp powder was immersed in the hcl aqueous solution for 12 hours , filtered rapidly and washed with deionized water , and filtered rapidly with a vacuum pump again . the resulting powder cake was dried in an oven at 50 ° c . the dried powder was divided into halves , ground for 20 minutes and 120 minutes separately , and combined to obtain the non - dispersive ttcp - based cpc powder , the particles of which have whisker on the surfaces thereof . a setting solution of diammonium hydrogen phosphate was prepared by dissolving 20 g of diammonium hydrogen phosphate , ( nh 4 ) 2 hpo 4 , in 40 ml deionized water . the procedures in example 1 were used to obtain the wet specimen compressive strength for one - day immersion time , wherein the maximum pressure to compress the cpc paste in the mold was 156 . 2 mpa . the results are shown in table 3 . the procedures of example 1 were repeated except that the maximum pressure used to compress the cpc paste in the mold was changed from 166 . 6 mpa to the values listed in table 4 . the period of immersion was one day . the results are listed in table 4 . the data in table 4 indicate that the compressive strength of the cpc block increases as the pressure used to compress the cpc paste in the mold increases . effect of reducing liquid / powder ratio during compression of the cpc paste in the mold on compressive strength of nd - cpc block the procedures of example 1 were repeated except that the maximum pressure used to compress the cpc paste in the mold was changed from 166 . 6 mpa to the values listed in table 5 . the liquid leaked from the mold during compression was measured , and the liquid / powder ratio was re - calculated as shown in table 5 . the period of immersion was one day . the results are listed in table 5 . the procedures of example 1 were repeated . the period of immersion was one day . the cpc blocks after removing from the hanks &# 39 ; solution were subjected to post - heat treatments : 1 ) 50 ° c . for one day ; and 2 ) 400 ° c . for two hours with a heating rate of 10 ° c . per minute . the results are listed in table 6 . to a setting solution of 1m phosphoric acid solution ( ph = 5 . 89 ) the nd - cpc powder from preparative example 3 was added in a liquid / powder ratio ( l / p ratio ) of 0 . 4 , i . e . 4 ml liquid / 10 g powder , while stirring . kcl powder in a predetermined amount was mixed to the resulting mixture by stirring intensively . the resulting paste was filled into a cylindrical steel mold having a length of 12 mm and a diameter of 6 mm , and was compressed with a gradually increased pressure until a maximum pressure of 3 . 5 mpa was reached . the maximum pressure was maintained for one minute , and then the compressed cpc block was removed from the mold . at the 15 th minute following the mixing of the liquid and powders , the compressed cpc block was immersed in a deionized water at 37 ° c . for 4 days , 8 days , and 16 days . the compressive strength of the specimens of the three different periods of immersion time was measured by using a ags - 500d mechanical tester ( shimadzu co ., ltd ., kyoto , japan ) after the specimens were dry . the measured dry specimen compressive strength is listed table 7 . the procedures of example 7 were repeated by using sugar , ki , c 17 h 33 coona and c 13 h 27 cooh instead of kcl . the immersion time was 14 days in deionized water . in the cases where the c 17 h 33 coona and c 13 h 27 cooh were used , the cpc blocks were further immersed in ethanol for additional four days . the conditions and the results are listed in table 8 . it can be seen from table 8 that various powders which are soluble in water can be used in the preparation of a porous cpc block according to the method of the present invention . to a setting solution of 1m phosphoric acid solution ( ph = 5 . 89 ) the nd - cpc powder from preparative example 3 was added in a liquid / powder ratio ( l / p ratio ) of 0 . 4 , i . e . 4 ml liquid / 10 g powder , while stirring . kcl powder in a ratio of kcl powder / cpc by volume of 2 was mixed to the resulting mixture by stirring intensively . the resulting paste was filled into a cylindrical steel mold having a length of 12 mm and a diameter of 7 mm , and was compressed with a gradually increased pressure until a maximum pressure of 3 . 5 mpa was reached . the maximum pressure was maintained for one minute , and then the compressed cpc block was removed from the mold at the 15 th minute following the mixing of the liquid and powders . the resulting cylinder having a diameter of 7 mm was placed in another cylindrical steel mold having a diameter of 10 mm . to a setting solution of 1m phosphoric acid solution ( ph = 5 . 89 ) the nd - cpc powder from preparative example 3 was added in a liquid / powder ratio ( l / p ratio ) of 0 . 4 , i . e . 4 ml liquid / 10 g powder , while stirring . the resulting paste was filled into the gap between said cylinder and said another mold , and was compressed with a gradually increased pressure until a maximum pressure of 50 mpa was reached . the maximum pressure was maintained for one minute . at the 15 th minute following the mixing of the liquid and nd - cpc powder , the cpc / kcl composite block was immersed in a deionized water at 37 ° c . for 4 days . kcl powder was dissolved in the deionized water , and a dual - functional cpc block having a porous cpc cylinder surround by a dense cpc annular block was obtained . the compressive strength of the specimen was measured by using a ags - 500d mechanical tester ( shimadzu co ., ltd ., kyoto , japan ) after the specimens were dry . the measured dry specimen compressive strength is 68 . 8 mpa . the porosities of the porous cpc cylinder and the dense cpc annular block were measured by archimedes &# 39 ; method , and calculated as in astm c830 , after the dual - functional cpc block was broken intentionally , and the results are 74 % and 30 %, respectively . x - ray diffraction pattern of the powder obtained by grinding the dual - functional cpc block shows broadened characteristic x - ray diffraction peaks of apatite at 2θ = 25 – 27 ° and 2θ = 20 – 35 ° with a scanning range of 2θ of 20 – 40 ° and a scanning rate of 1 °/ min . the results indicate that the powder is a mixture of apatite and ttcp with apatite as a major portion .
the present invention discloses a prosthetic bone implant made of a hardened calcium phosphate cement having an apatitic phase as a major phase , which includes a dense cortical portion bearing the majority of load and a porous cancellous portion allowing a rapid blood / body fluid penetration and tissue ingrowth .