Simultaneously improving fabrication accuracy and interfacial bonding strength of multi-material projection stereolithography by multi-step exposure

Figures & data

Figure 1. (a) Multi-material PSL process. (b) A two-step example of multi-step exposure method for multi-material PSL process.

Figure 2. Flow chart of the multi-step exposure method.

Figure 3. Multi-step exposure in layer n. (a) Calculation of interfacial areas. (b) Multi-step exposure.

Figure 4. Working curve of TMPTA resin and PEGDA resin. N = 8. Error bars represent standard deviation.

Table 1. Effect of total exposure time on cure depth and overcure on PEGDA and TMPTA resin.

Total exposure time [s]	8	11	14
PEGDA cure depth [μm]	123	135	144
PEGDA overcure [μm]	23	35	44
TMPTA cure depth [μm]	117	134	147
TMPTA overcure [μm]	17	34	47

Figure 5. A) Different types of tensile specimens. PE stands for PEGDA resin specimen, TM stands for TMPTA resin specimen, PT stands for specimen with PEGDA-TMPTA interface (PEGDA was printed first), TP stands for specimen with TMPTA-PEGDA interface (TMPTA was printed first), PP stands for specimen with weakened PEGDA-PEGDA interface (went through material-exchange process), TT stands for specimen with weakened TMPTA-TMPTA interface. b) Effect of interface exposure time on tensile strength of PT and TP specimens. c) effect of interface exposure time on tensile strength of PP specimens. d) effect of interface exposure time on tensile strength of TT specimens. For (a), (b), (c), and (d): N = 5. Error bars represent standard deviation.

Table 2. Additional exposure time used for multi-step exposure.

Interface type	PT	TP	PP	TT
Interface exposure time [s]	14	8	14	11
Additional exposure time [s]	6	0	6	3

Figure 6. Comparison of vertical accuracy between single-step exposure and multi-step exposure method. Scale bars represented 200 μm.

Table 3. Fabricated height and error of single-step and multi-step exposure method.

Channel type		Single-step exposure			Multi-step exposure
	Designed height [μm]	100	200	300	100	200	300
In PEGDA	Fabricated height [μm]	– ^a)	119	255	–	181	294
	Error [μm]	–	−81	−45	–	−19	−6
In TMPTA	Fabricated height [μm]	–	–	258	–	174	298
	Error [μm]	–	–	−42	–	−26	−2
At PT interface	Fabricated height [μm]	33	176	275	122	213	309
	Error [μm]	−67	−24	−25	+22	+13	+9
At TP interface	Fabricated height [μm]	–	157	276	–	199	302
	Error [μm]	–	−43	−24	–	−1	+2

^a)Channel was blocked.

Figure 7. Comparison of lateral fabrication accuracy between single-step exposure and multi-step exposure method. a) microfluidic channels fabricated within TMPTA resin. b) microfluidic channels fabricated within PEGDA resin. Scale bars represented 200 μm.

Table 4. Fabricated width and error of single-step and multi-step exposure method.

Channel type	Exposure method	Designed width [μm]	110	120	130	140	150	160	170	180	190	200
Within TMPTA	Single-step	Fabricated width [μm]	– ^a)	–	–	–	97	122	116	149	175	187
		Error [μm]	–	–	–	–	−53	−38	−54	−31	−15	−13
	Multi-step	Fabricated width [μm]	–	86	111	130	150	173	178	189	200	206
		Error [μm]	–	−34	−19	−10	0	+13	+8	+9	+10	+6
Within PEGDA	Single-step	Fabricated width [μm]	–	–	68	82	116	122	141	162	182	196
		Error [μm]	–	–	−62	−58	−34	−38	−29	−18	−8	−4
	Multi-step	Fabricated width [μm]	99	102	128	129	148	171	178	198	207	207
		Error [μm]	−11	−18	−2	−11	−2	+11	+8	+18	+17	+7

^a)Channel was blocked.